Knowledge Base Report on 

Emergency Core Cooling 

Sump Performance in 

Operating Light Water 

Reactors

Office of Nuclear Regulatory Research

NUREG/CR-7172

ANL-10/38
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Knowledge Base Report on 

Emergency Core Cooling 

Sump Performance in 

Operating Light Water 

Reactors

Manuscript Completed: April 2013

Date Published: January 2014

Prepared by:

K. Natesan, A. Moisseytsev, C. Bahn, and D. R. Diercks

Argonne National Laboratory

9700 S. Cass Avenue

Argonne, IL 60439

C. Shaffer

ARES Corporation

851 University Blvd., SE, Ste 100

Albuquerque, NM 87106

John Burke, NRC Project Manager

NRC Job Code N6954

Office of Nuclear Regulatory Research

NUREG/CR-7172

ANL-10/38

iii

ABSTRACT

This report describes the current status of the knowledge base regarding the performance of 

long-term core and containment cooling in operating light water reactors. The report discusses 

the substantial knowledge that has been amassed as a result of the research on clogging issues 

related to the suction strainers in boiling water reactors (BWRs) and the sump strainers in 

pressurized water reactors (PWRs). These issues concern the potential insulation and other 

debris generated in the event of a postulated loss-of-coolant accident within the containment of 

a light water reactor and the subsequent transport to and accumulation on the recirculation 

strainers. This debris accumulation could potentially challenge the plant’s capability to provide 

adequate long-term cooling water to the pumps in the emergency core cooling and in the 

containment spray systems.

The report briefly discusses the historical background on the sump performance issue and 

presents the NRC regulatory considerations, with emphasis on guidance provided by NRC to 

the licensees during recent years. The report presents the current state-of-the-art resolution 

methodology for understanding the strainer blockage phenomena and processes that have 

evolved over the years. In particular, the report discusses the details of plant-by-plant licensee 

responses to the NRC Bulletin 2003-01 and the NRC Generic Letter 2004-02. The licensee 

responses were collected in several areas such as strainer characteristics, physical and plant 

modifications, head loss testing procedures, head loss test information, net positive suction 

head data, debris generation, debris characteristics, coating debris, chemical effects, 

downstream effects, etc. as well as assessment of net positive suction head requirements and 

availability.

The report is designed to serve as a source of updated information from the previous reports 

(Rao et al. 2001, NUREG/CR-6808) on all aspects of issues concerning the emergency core 

cooling sump performance in both BWRs and PWRs. 

v

FOREWORD

In the event of a loss-of-coolant accident (LOCA) within the containment of a light-water reactor 

(LWR), piping thermal insulation and other materials in the vicinity of the break will be dislodged 

by the pipe break and the ensuing steam/water-jet impingement. A portion of this fragmented 

and dislodged insulation and other materials, such paint chips, paint particulates, latent dirt and 

dust, suspression pool sludge, chemical corrosion products and concrete dust, will be 

transported to the containment floor by the steam/water flows induced by the break and by the 

containment sprays. Some of this debris will eventually be transported to and accumulate on the 

emergency core cooling system (ECCS) pump suction strainers. Debris accumulation on the 

strainers could challenge the plant's capability to provide adequate, long-term cooling water to 

the ECCS and to the containment spray system (CSS) pumps. 

As a result of the research on the boiling water reactor (BWR) and pressurized water reactor 

(PWR) suction strainer clogging issues, a substantial base of knowledge has been amassed 

that covers all aspects of the issues, from the generation of debris to the head loss associated 

with a debris bed on a strainer or screen. This report describes the different analytical and 

experimental approaches that have been used to assess the various aspects of sump and 

strainer blockage and identifies the strengths, limitations, important parameters, and plant 

features and the appropriateness of the different approaches. The report also discusses 

significant U.S. Nuclear Regulatory Commission regulatory actions regarding resolution of the

suction and sump strainer debris issue. In essence, the report is designed to serve as a 

reference for plant-specific analyses with regard to whether the sump or strainer would perform 

its function without preventing the operation of the ECCS pumps.

This report is an update of the previous ECCS debris clogging knowledge base document, 

NUREG/CR-6808, “Knowledge Base for the Effect of Debris on Pressurized Water Reactor 

Emergency Core Cooling Sump Performance,” published in Feburary 2003. The most notable 

additions to this report are related to the research performed for PWRs in response to Generic 

Letter 2004-02 in the technical areas of chemical effects, protective coatings, latent debris, 

downstream effects, and strainer head loss testing.

It is noted that this report does not address the risk-informed approach that is mentioned in 

SECY 12-0093 because it is still being evaluated. Nor does it address suction strainer debris 

clogging concerns for new reactor designs such as the AP 1000 or the Advanced Boiling Water 

Reactor (ABWR).

vii

TABLE OF CONTENTS

ABSTRACT................................................................................................................................iii

FOREWORD ..............................................................................................................................v

TABLE OF CONTENTS............................................................................................................ vii

LIST OF FIGURES .................................................................................................................. xiii

LIST OF TABLES.................................................................................................................... xvii

EXECUTIVE SUMMARY ......................................................................................................... xix

ACKNOWLEDGMENTS........................................................................................................... xxi

ACRONYMS...........................................................................................................................xxiii

UNITS CONVERSION TABLE...............................................................................................xxvii

1 INTRODUCTION............................................................................................................... 1-1

2 DESCRIPTION OF THE SAFETY CONCERN .................................................................. 2-1

3 DISCOVERY OF SUMP PERFORMANCE ISSUE............................................................ 3-1

3.1 Sump Performance Issues ......................................................................................... 3-1

3.2 Events Rendering a System Inoperable ..................................................................... 3-5

3.3 LOCA Debris Generation Events................................................................................ 3-7

3.4 Events Involving Debris Found in Containment .......................................................... 3-8

3.5 Inadequate Maintenance Leading to Potential Sources of Debris............................. 3-10

3.6 Sump Strainer Inadequacies .................................................................................... 3-11

3.7 Assessment of Plant Vulnerability ............................................................................ 3-14

3.7.1 BWRs ............................................................................................................ 3-14

3.7.2 PWRs ............................................................................................................ 3-15

3.8 Other PWR Plant Design Features That Influence Accident Progression ................. 3-21

3.8.1 Plant Features ............................................................................................... 3-21

3.8.2 Debris Accumulation ...................................................................................... 3-23

3.8.3 Debris Head Loss .......................................................................................... 3-25

4 REGULATORY CONSIDERATIONS................................................................................. 4-1

4.1 Code of Federal Regulations...................................................................................... 4-1

4.2 Regulatory Guidance.................................................................................................. 4-3

4.3 Generic Safety Issue-191........................................................................................... 4-4

4.4 NRC Bulletin 2003-01................................................................................................. 4-8

4.5 NRC Generic Letter (GL) 2004-02.............................................................................. 4-9

4.6 NRC Guidance on Strainer Head Loss and Vortexing .............................................. 4-11

4.7 NRC Guidance on Coatings Evaluation.................................................................... 4-12
viii

4.8 NRC Guidance on Evaluations of Plant-Specific Chemical Effects For PWRs.......... 4-13

5 STATE-OF-THE-ART RESOLUTION METHODOLOGY................................................... 5-1

5.1 System Pumps........................................................................................................... 5-3

5.2 Pipe Break Characterization....................................................................................... 5-4

5.3 Debris Generation/Zone of Influence.......................................................................... 5-4

5.3.1 Applicable Phenomena .................................................................................... 5-5

5.3.2 Break Jet Dispersion Analytical Models ........................................................... 5-9

5.3.2.1 Blast Wave Dispersion Models ......................................................... 5-9

5.3.2.2 Established Jet Dispersion Models................................................... 5-9

5.3.3 Debris Generation Testing Considerations..................................................... 5-11

5.3.3.1 Established Prototypical RCS Conditions ....................................... 5-11

5.3.3.2 Test Jet Scaling Considerations ..................................................... 5-12

5.3.3.3 Target Scaling, Construction, and Positioning Considerations........ 5-15

5.3.3.4 Instrumentation .............................................................................. 5-17

5.3.3.5 Debris Characterization.................................................................. 5-17

5.3.3.6 Comparison of Debris Generation Testing...................................... 5-17

5.3.4 Zone-of-Influence Debris Generation Models................................................. 5-20

5.3.4.1 USI A-43 Conical ZOI Modeling...................................................... 5-21

5.3.4.2 Spherical ZOI Plant Analysis Model ............................................... 5-22

5.3.5 Characteristics of Generated Debris .............................................................. 5-29

5.4 Debris Transport Evaluation..................................................................................... 5-31

5.4.1 Overview........................................................................................................ 5-31

5.4.2 Blowdown/Washdown Debris Transport......................................................... 5-35

5.4.2.1 Blowdown/Washdown Debris-Transport Phenomenology .............. 5-35

5.4.2.2 PWR Blowdown/Washdown Transport........................................... 5-36

5.4.2.3 BWR Blowdown/Washdown Transport........................................... 5-42

5.4.3 Pool Debris Transport and Recirculation........................................................ 5-45

5.4.3.1 PWR Sump Pool Debris Transport ................................................. 5-46

5.4.3.2 BWR Suppression Pool Debris Transport....................................... 5-53

5.4.4 Erosion of Containment Materials and Debris ................................................ 5-55

5.4.4.1 Post-LOCA Damage to Containment Materials .............................. 5-55

5.4.4.2 Erosion of LOCA-Generated Debris ............................................... 5-55

5.4.5 Characteristics of Debris Transported to the Strainer..................................... 5-60

5.5 Coatings and Coatings Debris.................................................................................. 5-61

5.5.1 Introduction.................................................................................................... 5-61
ix

5.5.2 Coating Failures in Operating Nuclear Plants................................................. 5-63

5.5.3 Testing of Qualified Coatings ......................................................................... 5-66

5.5.4 Testing of Unqualified Coatings ..................................................................... 5-68

5.5.5 Coating Debris Generation............................................................................. 5-68

5.5.6 Summary ....................................................................................................... 5-70

5.6 Latent Debris............................................................................................................ 5-70

5.6.1 Introduction.................................................................................................... 5-70

5.6.2 Baseline Approach......................................................................................... 5-71

5.6.2.1 Estimation of Surface Area Inside Containment ............................. 5-71

5.6.2.2 Evaluation of Resident Debris Buildup ........................................... 5-71

5.6.2.3 Surface Area Susceptibility to Debris Accumulation ....................... 5-72

5.6.2.4 Total Quantity and Composition of Debris ...................................... 5-73

5.7 Debris Accumulation, Head Loss, and Vortex Evaluation ......................................... 5-73

5.7.1 Overview........................................................................................................ 5-73

5.7.2 Role of Prototype Head Loss Testing in GSI-191 Resolution ......................... 5-79

5.7.2.1 Trends in Replacement Strainer Design......................................... 5-79

5.7.2.2 Inputs and Outputs of Prototypical Head Loss Testing................... 5-80

5.7.2.3 Uncertainties and Conservatism in Head Loss Testing .................. 5-83

5.7.3 Strainer Test Module Scaling ......................................................................... 5-84

5.7.3.1 Strainer Vendor Scaling Approaches ............................................. 5-84

5.7.3.2 Theoretical Considerations............................................................. 5-85

5.7.3.3 Test Module Design - Area Ratio-Based Scaling............................ 5-87

5.7.3.4 Test Module Design - Debris Accumulation Pattern ....................... 5-88

5.7.4 Similitude Considerations for Near-Field Debris Transport ........................ 5-91

5.7.4.1 Simulation of Strainer Upstream Hydraulic Conditions ................... 5-92

5.7.4.2 Analytical Verification of Prototypical Hydraulic Conditions ............ 5-93

5.7.4.3 Debris Introduction with Respect to Hydraulic Conditions............... 5-94

5.7.5 Surrogate Debris Similitude ........................................................................... 5-96

5.7.6 Testing Matrix ................................................................................................ 5-98

5.7.6.1 Consideration of Head Loss Testing Input Parameters ................ 5-100

5.7.6.2 Tailoring of Test Matrix to Test Objectives ................................... 5-103

5.7.7 Test Termination.......................................................................................... 5-110

5.7.8 Post-Test Data Scaling and Analysis ........................................................... 5-114

5.7.8.1 Temperature Scaling.................................................................... 5-114

5.7.8.2 Deviations between Test Module and Replacement Strainer ....... 5-115
x

5.7.8.3 Post-Test Debris and Debris Bed Characterization ...................... 5-116

5.7.8.4 Clean Strainer Head Loss ............................................................ 5-116

5.7.9 Qualification Testing of PWR Replacement Strainer Head Loss .................. 5-116

5.7.10 Qualification Testing of BWR Strainer Head Loss ........................................ 5-120

5.8 Debris Head Loss Correlations............................................................................... 5-121

5.8.1 NUREG/CR-6224 Correlation ...................................................................... 5-122

5.8.1.1 NUREG/CR-6224 Correlation and Deaeration Software .............. 5-122

 Package

5.8.1.2 BLOCKAGE 2.5 Code.................................................................. 5-129

5.8.2 NUREG-1862 Correlation ............................................................................ 5-131

5.9 Chemical Effects .................................................................................................... 5-136

5.9.1 Introduction.................................................................................................. 5-136

5.9.2 Integrated Chemical Effects Test ................................................................. 5-138

5.9.2.1 Test Conditions............................................................................ 5-138

5.9.2.2 Overall Results............................................................................. 5-141

5.9.2.3 Solution Chemistry....................................................................... 5-142

5.9.2.4 Precipitation ................................................................................. 5-144

5.9.2.5 Passivation of Aluminum in ICET Solutions.................................. 5-145

5.9.2.6 Summary and Discussion............................................................. 5-146

5.9.3 ICET Aluminum Chemistry........................................................................... 5-147

5.9.3.1 Bench-Scale Experiments............................................................ 5-147

5.9.3.2 Summary of Important Results..................................................... 5-147

5.9.3.3 Summary and Discussion............................................................. 5-149

5.9.4 ANL Head Loss Testing ............................................................................... 5-150

5.9.4.1 Overview...................................................................................... 5-150

5.9.4.2 Solution Chemistry....................................................................... 5-151

5.9.4.3 Precipitation ................................................................................. 5-152

5.9.4.4 Head Loss in ICET Environments ................................................ 5-155

5.9.4.5 Relationship of ICET to Plant Environments................................. 5-159

5.9.4.6 Comments and Observations....................................................... 5-159

5.9.5 Thermodynamic Modeling............................................................................ 5-161

5.9.5.1 Thermodynamic Simulation Studies ............................................. 5-161

5.9.5.2 Commercial Simulation Codes ..................................................... 5-161

5.9.6 Peer Review of Chemical Effects Studies .................................................... 5-162

5.9.6.1 Integrated Chemical Effect Tests ................................................. 5-162
xi

5.9.6.2 ANL Head Loss Testing ............................................................... 5-164

5.9.6.3 Thermodynamic Modeling............................................................ 5-165

5.9.7 Industry Approach to Evaluate Chemical Effects.......................................... 5-166

5.9.7.1 Overview...................................................................................... 5-166

5.9.7.2 Summary of Important Results..................................................... 5-166

5.9.7.3 WCAP-16530 Follow-on Study..................................................... 5-170

5.9.7.4 Description of Technical Letter Report on WCAP-16530-NP........ 5-173

5.9.7.5 Description of Technical Letter Report on WCAP-16530-NP ....... 5-174

5.9.7.6 Description of Technical Letter Report on AlOOH and SAS ........ 5-178

5.9.7.7 Description of Technical Letter Report on AlOOH Stability........... 5-180

5.9.7.8 Description of WCAP-16785-NP and WCAP-16530-NP .............. 5-182

5.9.7.9 Aluminum Chemistry and Aluminum Corrosion Products ............. 5-184

5.9.7.10 Long-Term Al Solubility Test ....................................................... 5-187

5.9.7.11 Aluminum Solubility Curve........................................................... 5-188

5.9.7.12 Alternative Buffers....................................................................... 5-192

5.9.7.13 Additional Issues on Chemical Effects ........................................ 5-195

5.9.8 Summary and Completeness Assessment................................................... 5-197

5.10 Downstream Effects ............................................................................................. 5-197

5.10.1 Ex-Vessel Debris Effects.............................................................................. 5-198

5.10.2 In-Vessel Debris Effects............................................................................... 5-199

5.11 Vendor Head Loss Test Programs........................................................................ 5-201

5.11.1 Strainer Debris Head Loss Testing by PWR Vendors .................................. 5-201

5.11.2 Strainer Debris Head Loss Testing by BWR Vendors .................................. 5-218

6 BWR INDUSTRY RESPONSE.......................................................................................... 6-1

6.1 NRC Bulletin 1995-02................................................................................................. 6-2

6.2 NRC Bulletin 1996-03................................................................................................. 6-3

7 PWR INDUSTRY RESPONSE.......................................................................................... 7-1

7.1 NRC BULLETIN 2003-01 ........................................................................................... 7-1

7.1.1 Introduction.....................................................................................................................7-1

7.1.2 NRC Bulletin 2003-01 Database.................................................................................7-3

7.1.3 NRC Bulletin 2003-01 Database Results ..................................................................7-4

7.2 NRC Generic Letter 2004-02...................................................................................... 7-6

7.2.1 Introduction.....................................................................................................................7-6

7.2.2 Generic Letter 2004-02 Database ..............................................................................7-7

7.2.3 Generic Letter 2004-02 Database Results................................................................7-9
xii

8 SUMMARY........................................................................................................................ 8-1

9 REFERENCES.................................................................................................................. 9-1

9.1 NRC Documents Cited............................................................................................... 9-1

9.2 Other Documents Cited.............................................................................................. 9-6

Appendix A. NRC BULLETIN 2003-01 AND GENERIC LETTER 2004-02 DATABASES......A-1
xiii

LIST OF FIGURES

Figure 3.7-1. Sump-Strainer Schematics...........................................................................3-16

Figure 3.7-2. PWR LLOCA Accident Progression in Large Dry Containment ....................3-20

Figure 3.8-1. Head Losses vs. Fiber Volume for Fixed Quantities of Particulate ...............3-27

Figure 4.8-1. Chemical Effect Evaluation Process Flow Diagram......................................4-15

Figure 5.3-1. Air-Jet Testing Destruction Data...................................................................5-14

Figure 5.3-2. Radial Pressure Profiles at Selected Axial Distances ...................................5-16

Figure 5.3-3. Saturation Pressures for Debris Generation Testing ....................................5-20

Figure 5.3-4. Schematic of Conical Jet Model ...................................................................5-21

Figure 5.3-5. Schematic Diagram of Spherical-Equivalent Jet Model ................................5-23

Figure 5.4-1. Chart for Sump Pool Debris Transport .........................................................5-34

Figure 5.4-2. Example of a Section of a Debris Transport Chart .......................................5-39

Figure 5.4-3. Schematic Diagram of Debris-Washdown Processes...................................5-40

Figure 5.4-4. Capture of Small Debris by Grating..............................................................5-44

Figure 5.4-5. Example CFD Sump Pool Flow Velocity Pattern ..........................................5-51

Figure 5.4-6. Debris Stalled in a Slow-Flowing Region of the Simulated Annulus..............5-52

Figure 5.4-7. Typical Accumulation of Fine Fibrous Debris ...............................................5-56

Figure 5.5-1. ASTM Standards Relevant to NPP Service Level I, II, and III 

Protective Coatings......................................................................................5-62

Figure 5.7-1. Schematic Diagram of Processes Used to Qualify Replacement 

Strainers ......................................................................................................5-80

Figure 5.7-2. Schematic Diagram of Modules Connected End-to-End with 

Common Central Flow Plenum ....................................................................5-90

Figure 5.7-3. Schematic Diagram of Array of Modules Connected to Common 

In-Floor Plenum ...........................................................................................5-90

Figure 5.7-4. Analytical Debris Concentration as a Function of Pool Turnovers ..............5-113

Figure 5.7-5. Non-Porous Thin-Bed on PCI Replacement Strainer..................................5-117

Figure 5.7-6. Thin-bed on CCI Pocket Strainer Design....................................................5-118

Figure 5.8-1. Performance Comparison of Original and Revised Correlations.................5-127

Figure 5.9-1. Head Loss versus Materials Concentration ................................................5-137

Figure 5.9-2. Ratio of Measured Head Loss With and Without Chemical Precipitates

as a Function of Metal Ion Concentration...................................................5-138

Figure 5.9-3. Measured pH During ICETs .......................................................................5-143

Figure 5.9-4. Measured Aluminum Concentrations in Tests 1 and 5 ...............................5-143

Figure 5.9-5. Measured Calcium Concentrations in Tests 1-5 ........................................5-144

Figure 5.9-6. Measured Silicon Concentration in Tests 1-5. ............................................5-144
xiv

Figure 5.9-7. TEM Micrographs of Day-15 and Day-30 Filtered Test Samples 

from ICET 1 Solution..................................................................................5-148

Figure 5.9-8. Particle Size Distribution for Test 1 Solution at Room Temperature 

after 4-Month Aging....................................................................................5-149

Figure 5.9-9. Particle Size Distributions for Aluminum/Boron Metal Dissolution 

Surrogate Solution at 60°C after 8 hr .........................................................5-149

Figure 5.9-10. Schematic Diagram of ANL Test Loop .......................................................5-151

Figure 5.9-11. Bed Approach Velocities and Differential Pressures across the 

Strainer as a Function of Time for several ICETs .......................................5-156

Figure 5.9-12. Bed Approach Velocity and Differential Pressure across the 

Strainer as a Function of Time for Test ICET-3-18 .....................................5-157

Figure 5.9-13. Bed Approach Velocities and Differential Pressures for ICET-3-8 and -9 ...5-157

Figure 5.9-14. Pressure and Velocity History in Test ICET-1-1-B2....................................5-159

Figure 5.9-15. Comparison of Total Mass Released during Dissolution Testing 

by Element.................................................................................................5-167

Figure 5.9-16. Comparison of Total Mass Released from the Tested Materials ................5-168

Figure 5.9-17. Aluminum Concentrations with Time Estimated by 

WCAP-16530-NP Chemical Model in Comparison with Actual 

Measured Concentrations in ICET 1 ..........................................................5-169

Figure 5.9-18. Measured Al Concentration in the Supernate after 22 Days from 

the 80, 100, and 120°F Precipitation Kinetics Tests, 134-day 

Extrapolated Values, and Predicted Solubility ............................................5-177

Figure 5.9-19. Pressure and Temperature History during Head Loss Test ICET-5-2-B2 ...5-178

Figure 5.9-20. Pressure Drop and Strainer Approach Velocity vs. Time in a Loop 

Test using the WCAP16530-NP Aluminum Hydroxide Surrogates .............5-179

Figure 5.9-21. Pressure Drop Across the NUKON Bed and Approach Velocity 

as a Function of Time for a Vertical-Loop Head Loss Test with Tap 

Water at Initial pH=9.0 ...............................................................................5-181

Figure 5.9-22. Pressure Drop and Loop Water Temperature vs. Time in a Loop Test 

using 6061 Al Plates with 2500 ppm B, Initial pH=9.35 Solution, 

and Temperature of 80°F ...........................................................................5-186

Figure 5.9-23. Pressure Drop across the Strainer and Temperature vs. Time in 

1100 Al Loop Test......................................................................................5-186

Figure 5.9-24. Typical Solution Temperature History for the 30-day Al Solubility Tests.....5-188

Figure 5.9-25. Al Stability Map in the pH + p[Al]T vs. Temperature Domain for 

Solutions Containing Boron........................................................................5-189

Figure 5.9-26. Al Solubility Curves as Functions of pH and Temperature 

without Considering Test Data from Al Corrosion Loop Tests ....................5-191

Figure 5.9-27. Al Solubility Curves as a Function of pH and Temperature 

with Consideration of Test Data from Al Corrosion Loop Tests ..................5-192
xv

Figure 5.11-1. Photo of Atomic Energy of Canada Limited Large Scale Test Module........5-203

Figure 5.11-2. Example Plant General Electric Strainer Design ........................................5-205

Figure 5.11-3. Photograph of General Electric Prototype Test Module..............................5-205

Figure 5.11-4. Photograph of General Electric Prepared Fibrous Debris...........................5-206

Figure 5.11-5. H. B. Robinson Strainer .............................................................................5-210

Figure 5.11-6. Isometric View of Alion Test Tank with Prototype Strainer .........................5-210

Figure 5.11-7. Schematic of Individual Pocket and Small Test Strainer Module ................5-212

Figure 5.11-8. Photograph of Installed Plant Strainer........................................................5-212

Figure 5.11-9. Illustration of the Multifunctional Head Loss Test Rig .................................5-213

Figure 5.11-10. Illustration of the Multifunctional Head Loss Test Rig .................................5-213

Figure 5.11-11. Isometric View of a Typical GE BWR Replacement Strainer ......................5-221

Figure 5.11-12. Schematic of the General Electric Test Facility ..........................................5-222

Figure 5.11-13. Performance Contacting Incorporated Stacked Disk Strainer 

Being Installed at Pilgrim Nuclear Power Plant...........................................5-223

Figure 5.11-14. Core Tube Used in the PCI Stacked Disk Strainers ...................................5-223

Figure 5.11-15. Individual Enercon Mark III Strainer Module...............................................5-224

Figure 5.11-16. Illustration of Installed Enercon Mark III Strainer ........................................5-225

Figure 6.1-1. NRC Bulletin 95-02 Responses on Last Suppression Pool Cleaning..............6-2

Figure 7.1-1. Action Type by ICM/COA Categories.............................................................7-5

Figure 7.2-1. Total Strainer Screen Area...........................................................................7-10

xvii

LIST OF TABLES

Table 3.1-1. BWR Strainer Blockage Issue Timeline.............................................................3-2

Table 3.2-1. Events Rendering a System Inoperable............................................................3-6

Table 3.3-1. Events with LOCA-Generated Insulation Debris................................................3-8

Table 3.4-1. Events with Debris Found Inside Containment..................................................3-8

Table 3.5-1. Events of Inadequate Maintenance, Potentially Leading to Sources 

of Debris .........................................................................................................3-11

Table 3.6-1. Events With Inadequacies Found in Suction Strainers ....................................3-12

Table 3.7-1. PWR LLOCA Sequences ................................................................................3-18

Table 3.8-1. Minimum Strainer Approach Velocity for Debris to be Hydraulically “Lifted” 

onto a Sump Strainer......................................................................................3-24

Table 5.3-1. Selected PWR RCS Hydraulic Conditions.........................................................5-6

Table 5.3-2. Selected BWR RCS Hydraulic Conditions.........................................................5-6

Table 5.3-3. Test Program Comparison ..............................................................................5-19

Table 5.3-4. Damage Pressures and Corresponding Volume-Equivalent Spherical 

ZOI Radii ........................................................................................................5-26

Table 5.3-5. Debris-Size Categories and Their Capture and Retention Properties..............5-30

Table 5.4-1. Small Debris Capture Fractions ......................................................................5-44

Table 5.5-1. Summary of Selected Coating Failures in U.S. Nuclear Power Plant 

Containments as Reported in NRC Communications......................................5-64

Table 5.7-1. Number of Tank Turnovers to Reach Steady State.......................................5-112

Table 5.8-1. Deficiencies Identified in Formulation of NUREG/CR-6224 Correlation.........5-125

Table 5.9-1. Material Quantity/Sump Water Volume Ratios for ICETs ..............................5-139

Table 5.9-2. Physical Parameters for ICETs .....................................................................5-140

Table 5.9-3. Chemical Parameters for ICETs....................................................................5-140

Table 5.9-4. Test Series Parameters ................................................................................5-140

Table 5.9-5. Conditions for Head Loss Tests in ICET-3 Environment................................5-153

Table 5.9-6. Summary of ICET-1 Head Loss Tests with NaOH and STB..........................5-154

Table 5.9-7. Containment Material Classification Summary ..............................................5-167

Table 5.9-8. Indication of Precipitate Formation as either a Cloudy Suspension or 

a Flocculent in Test Solutions on Cooling from 200 to 80°F ..........................5-188

Table 5.9-9. Summary of Characteristics of Candidate ECCS Buffering Agents ...............5-194

Table 6.2-1. Summary of Strainer Modifications Made in Response to NRC 

Bulletin 96-03....................................................................................................6-5

Table 7.1-1. Interim Compensatory Measures (ICM) and Their Categories...........................7-2

Table 7.1-2. Candidate Operator Actions and Their Categories ............................................7-2

xix

EXECUTIVE SUMMARY

The containment sump (also known as the emergency or recirculation sump) and emergency 

core cooling system (ECCS) strainers are parts of safety systems in both boiling water and 

pressurized water reactors (BWRs and PWRs). Every nuclear power plant in the United States 

is required by the Code of Federal Regulations (10 CFR 50.46) to have an ECCS that is

capable of mitigating design basis accidents. 

The containment emergency sump or suppression pool collects reactor coolant leakage and 

chemically inactive or reactive spray solutions after a loss-of-coolant accident (LOCA). The 

sump serves as the water source to support long-term recirculation for residual heat removal,

emergency core cooling, and containment pressure control and atmosphere cleanup. This 

water source, the related pump inlets, and the piping between the source and inlets are 

important safety components. In the event of a LOCA within the containment of a light water 

reactor, piping thermal insulation and other materials in the vicinity of the break will be dislodged 

by the pipe break and steam/water-jet impingement. A fraction of this fragmented and 

dislodged insulation and other materials, such as paint chips, paint particulates, and concrete 

dust, will be transported to the containment floor by the steam/water flows induced by the break 

and by the containment sprays. Some of this debris eventually will be transported to and 

accumulate on the recirculation-sump suction strainers in PWR containments or on the pumpsuction strainers in BWR containments. Debris accumulation on the suction strainers could 

challenge the plant’s capability to provide adequate, long-term cooling water to the ECCS and 

the containment spray system (CSS) pumps and may compromise the containment cooling. 

The Generic Safety Issue (GSI)-191 (“Assessment of Debris Accumulation on PWR Sump 

Performance”) was established to determine if the transport and accumulation of debris in a 

containment following a LOCA would impede the operation of the ECCS in operating PWRs. 

Assessing the risk of the ECCS and CSS pumps at domestic PWRs experiencing a debrisinduced loss of the net positive suction head (NPSH) margin during sump recirculation was the 

primary objective of the NRC's technical assessment of GSI-191. 

 

This report describes the current status of the knowledge base on emergency core cooling 

sump performance in operating light water reactors. The compiled database information for 

various plants covers a period up to March 4, 2011. The compiled database also includes the 

Watts Bar-2 reactor, which is planned to be operational in the near future. The report discusses 

the substantial knowledge that has been developed as a result of the research on debris 

clogging issues for BWR suction strainers and PWR sump strainers. The report provides brief 

background information (Sections 1 through 4) regarding the clogging issues. This background 

information includes a historical overview of the resolution of the BWR issue with a lead-in to the 

PWR issue, a description of the safety concern relative to PWR reactors, the criteria for 

evaluating sump failure, descriptions of postulated accidents, descriptions of relevant plant 

features that influence accident progression, and a discussion of the regulatory considerations. 

Section 5 of the report presents the current state-of-the-art resolution methodology for 

understanding the strainer blockage phenomena and processes that have evolved over the 

years. This section incorporates our current understanding of many of the actions/processes 

that can have an impact on the available NPSH margin in the ECCS. The section presents 

details on pipe break characterization, debris generation and zone of influence, debris transport 
xx

evaluation, coatings and coating debris, latent debris, debris accumulation and head loss, debris 

head loss correlations, chemical effects on head loss, and downstream effects. The section 

also includes a description of the test programs conducted by several vendors in support of 

BWRs and PWRs. 

Section 6 is a summary of the industry response of BWR licensees and the closure of NRC 

Bulletin 1996-03, based on the utility resolution guidance (URG) for ECCS suction strainer 

blockage and NRC audits of four plant sites. In 2001 Los Alamos National Laboratory published 

a report summarizing the efforts of the NRC, the NRC’s contractors, and industry to resolve the 

BWR ECCS strainer clogging issue (LA-UR-01-1595). 

Section 7 discusses in detail the plant-by-plant PWR licensee responses to the NRC Bulletin 

2003-01 and the NRC Generic Letter 2004-02 (GL-04-02). The licensee responses to the initial 

generic letter and the responses to the requests for information were collected in several areas 

such as strainer characteristics, physical and plant modifications, head loss testing procedures, 

head loss test information for full debris-load beds and thin beds, net positive suction head data, 

debris generation, debris characteristics, coating debris, chemical effects, downstream effects, 

etc. as well as assessment of net positive suction head requirements and availability. The 

collected information has been incorporated in the Appendix A, in a user-friendly interface 

based on Microsoft Access, with a capability to select various criteria to filter the information, 

carry out search/sort of the data, and assess phenomenon-specific or plant-specific information. 
xxi

ACKNOWLEDGMENTS

The U.S. Nuclear Regulatory Commission (NRC) Office of Nuclear Regulatory Research (RES) 

sponsored this work. Mr. John Burke is the Technical Monitor for this project. He provided 

technical direction and actively participated in all aspects of the project, including access to 

necessary proprietary and other documents to accomplish the goals of the project. The authors 

would also like to acknowledge S. J. Smith, R. E. Architzel, R. Torres and J. Lehning of the NRC 

for their assistance in providing up-to-date information on several nuclear power plants.

xxiii

ACRONYMS

ABB ABB Atom/Combustion Engineering

ACRS Advisory Committee on Reactor Safeguards

AECL Atomic Energy of Canada Limited

AES Atomic Emission Spectroscopy

AJIT Air-Jet Impact Testing

ANL Argonne National Laboratory

ANS American Nuclear Society

ANSI American National Standards Institute

ARL Alden Research Laboratory

ASTM American Society for Testing and Materials

BS Building Spray

BWR Boiling Water Reactor

BWROG Boiling Water Reactor Owners’ Group

CCI Control Components, Inc.

CDA Containment Depressurization Actuation

CEQ Containment Pressure Equalization

CHRS Containment Heat Removal Systems

CNWRA Center for Nuclear Waste Regulatory Analysis

COA Candidate Operator Actions

CS Containment Spray

CSNI Committee on the Safety of Nuclear Installations

CSS Containment Spray System

DBA Design Basis Accident

DB-LOCA Design-Basis Loss-of-Coolant Accident

DDTS Drywell Debris Transport Study

DEGB Double-Ended Guillotine Break

DGM Debris Generation Model

ECCS Emergency Core Cooling System

EPRI Electric Power Research Institute

ESF Engineered Safeguard Feature

FME Foreign Material Exclusion

FSAR Final Safety Analysis Report

GDC General Design Criteria

GE General Electric Nuclear Energy

GEH General Electric-Hitachi

GGNS Grand Gulf Nuclear Station

GL Generic Letter

GSI Generic Safety Issue

HELB High Energy Line Break

HL Head Loss

HPSI High-Pressure Safety Injection

ICET Integrated Chemical Effects Test

ICM Interim Compensatory Measures

ICP Inductively Coupled Plasma

LANL Los Alamos National Laboratory
xxiv

LBB Leak-Before-Break

LBLOCA Large-Break Loss-of-Coolant-Accident

L/D Distance Divided by Pipe-Break Diameter

LER Licensee Event Report

LDFG Low-Density Fiberglass

LOCA Loss-of-Coolant Accident

LLOCA Large Loss-of-Coolant Accident

LPCI Low-Pressure Coolant Injection

LPCS Low-Pressure Core Spray

LPSI Low-Pressure Safety Injection

LTR Licensing Topical Report

LWR Light Water Reactor

MLOCA Medium Loss-of-Coolant Accident

MSL Main Steam Line

MSLB Main-Steam-Line Break

NDE Non Destructive Evaluation

NEA Nuclear Energy Agency

NEDO New Energy and Industrial Technology Organization 

NEI Nuclear Energy Institute

NMR Nuclear Magnetic Resonance

NPSH Net Positive Suction Head

NPSHA Available Net Positive Suction Head

NPSHR Required Net Positive Suction Head

NRC Nuclear Regulatory Commission

NSSS Nuclear Steam Supply System

OECD Organization for Economic Cooperation and Development

OEM Original Equipment Manufacturer

OPG Ontario Power Generation

PCI Performance Contracting Inc.

PIRT Phenomena Identification and Ranking Table

PNNL Pacific Northwest National Laboratory

PRT Pressure Relief Tank

PVC Polyvinyl Chloride

PWR Pressurized Water Reactor

PWROG Pressurized Water Reactor Owners Group

RB Reactor Building

RBES Reactor Building Emergency Sump

RCDT Reactor Coolant Drain Tank

RCP Reactor Coolant Pump

RCS Reactor Coolant System

RFI Request for Information

RFO Refueling Outage

RG Regulatory Guide

RHR Residual Heat Removal

RLB Recirculation-Line Break

RMI Reflective Metal Insulation

RMT Recirculation Mode Transfer

RPV Reactor Pressure Vessel
xxv

RSS Reactor Spray System

RWST Refueling Water Storage Tank

SAS Sodium Aluminum Silicate

SBLOCA Small-Break Loss-of-Coolant Accident

SE Safety Evaluation

SAT Spray Additive Tank

SEM Scanning Electron Microscopy

SER Safety Evaluation Report

SG Steam Generator

SI Safety Injection

SLOCA Small Loss-of-Coolant Accident

SNL Sandia National Laboratories

SONGS San Onofre Nuclear Generation Station

SRP Standard Review Plan

SRTC Savannah River Technology Center

SRV Safety Relief Valve

SS Stainless Steel

SSC System, Structure, and Component

STB Sodium Tetraborate

STPP Sodium Tripolyphosphate

TEM Transmission Electron Microscopy

TLR Technical Letter Report

TPI Transco Products, Inc.

TSP Trisodium Phosphate

UNM University of New Mexico

URG Utility Resolution Guidance

USI Unreviewed Safety Issue

WSRC Westinghouse Savannah River Company

XRD X-ray Diffraction

ZOI Zone of Influence

xxvii

UNITS CONVERSION TABLE

Convert from Convert to Multiply by

Length

in. m 0.02540

mil* m 2.540 x 10-5

ft m 0.3048

Area

in.2 m2 6.452 x 10-4

ft2 m2 0.09290

Volume

ft3 m3 0.02832

gal m3 0.003785

gpm m3/s 6.308 x 10-5

Pressure

psi Pa 6895

Mass

lbm** kg 0.4536

Density

lbm/ft3 kg/m3 16.02

Velocity

ft/s m/s 0.3048

Temperature

°F*** °C 0.5556

* mil = one-thousandth of an inch

** lbm is often simply given as lb

*** Subtract 32 before multiplying

1-1

1 INTRODUCTION

This report describes the current status of the knowledge base regarding the performance of 

long-term core and containment cooling in operating light water reactors. The report discusses 

the substantial knowledge that has been amassed as a result of the research on clogging issues 

related to the suction strainers in boiling water reactors (BWRs) and the sump strainers in 

pressurized water reactors (PWRs). The containment sump (also known as the emergency or 

recirculation sump in PWRs and suppression pool in BWRs) and emergency core cooling 

system (ECCS) strainers are parts of a safety system in both reactor types. Every nuclear 

power plant in the United States is required by the Code of Federal Regulations (10 CFR 50.46) 

to have an ECCS that is capable of mitigating a design basis accident. The ECCS is one of 

several safety systems required by the Nuclear Regulatory Commission (NRC).

The containment sump collects reactor coolant and containment spray solutions after a loss-ofcoolant accident (LOCA). The sump serves as the water source to support long-term 

recirculation for residual heat removal, emergency core cooling, and containment cooling and 

atmosphere cleanup. This water source, the related pump inlets, and the piping between the

source and inlets are important safety components. 

The performance of ECCS strainers in currently operating BWRs and PWRs was recognized 

decades ago as an important regulatory and safety issue. The primary concern is the potential 

for debris generated by a jet of high-pressure coolant during a LOCA to clog the strainer and 

obstruct core cooling. The issue was considered resolved for both reactor types a decade or 

more ago. But additional evaluation and testing indicated in the late 1990s that the issue should 

be re-evaluated for PWRs. The re-evaluation led the licensees to significantly increase the 

strainer sizes and to make other plant-specific modifications. A complex test and evaluation 

program was undertaken to verify that the larger strainers adequately meet the design 

requirements. 

This report does not include new plants licensed to 10 CFR 52 which governs the issuance of 

early site permits, standard design certifications, combined licenses, etc. and may have different 

design considerations for the ECCS.

This report supplements the previous knowledge base report (NUREG/CR-6808). Research for 

PWRs to address Generic Letter 2004-02 (GL 04-02) has resulted in an enhanced knowledge 

base, which has led to additional questions regarding BWR strainer performance. Even though 

the BWR strainers are comparable in size to the replacement PWR strainers, the NRC staff and 

the BWR Owners Group are currently evaluating what, if any, additional changes are needed in 

BWRs to ensure adequate strainer performance.

2-1

2 DESCRIPTION OF THE SAFETY CONCERN 

To function properly, the ECCS pumps require adequate available net positive suction head 

(NPSH). Inadequate NPSH could result in cavitation and subsequent failure to deliver the 

amount of water needed for cooling during a design basis accident. The available NPSH is a 

function of the static head of water above the pump inlet, the pressure of the atmosphere above 

the sump water surface, friction losses in the pump suction piping and strainer, and the 

temperature of the water at the pump inlet.

In the event of a LOCA or a high-energy pipe break within the containment of a BWR or a PWR, 

piping thermal insulation and other materials in the vicinity of the break can be dislodged 

because of the break and the ensuing steam/water-jet impingement. The area near the break 

where insulation debris is generated is called the zone of influence (ZOI). Some portion of the 

debris would likely be transported across the drywell, past and/or through structures such as 

gratings, and through the downcomer vents to the suppression pool in BWRs and may be 

transported to the containment floor by the steam/water flows induced by the break and by the 

containment sprays in PWRs. Some of this debris will eventually be transported to and 

accumulate on the recirculation-sump suction strainers in PWR containments or the pump 

suction strainer in BWR containments. Debris accumulation on the pump strainers could 

challenge the plant’s capability to provide adequate, long-term cooling water to the ECCS and to 

the containment spray system (CSS) pumps. 

The debris that accumulates on the sump strainer can form a bed that can increase the 

differential pressure across the sump. Head loss across the debris bed may reduce the NPSH 

available to the ECCS or containment spray pumps such that the pumps will not operate 

properly. 

The purpose of the debris strainers installed on the pump suction lines is to minimize the 

amount of debris entering the ECCS and CSS suction lines. Debris can block openings or 

damage components in the systems served by these pumps. However, excessive head loss 

due to debris accumulation on containment sump strainers can prevent or impede the flow of 

water into the core or containment (via containment spray).

3-1

3 DISCOVERY OF SUMP PERFORMANCE ISSUE

The NRC first published regulatory guidance on the performance of PWR containment sumps 

and BWR suction strainers in 1974 with the issuance of revision 0 of Regulatory Guide (RG) 

1.82, “Sumps for Emergency Core Cooling and Containment Spray Systems.” The BWR 

suction strainers perform the same function as PWR containment sump strainers. 

Because of internal questions by the NRC staff, the NRC first sponsored research to study the 

accumulation of debris on PWR containment sump strainers and BWR suction strainers in the 

late 1970s (approximately 1979). With the information and engineering tools available in the 

late 1970s and early 1980s, the NRC concluded that its regulatory guidance needed to be 

revised and issued revision 1 of RG 1.82 (1985). As documented in Generic Letter-85-22, 

“Potential for Loss of Post-LOCA Recirculation Capability Due to Insulation Debris Blockage,” 

the NRC concluded that no additional regulatory action was warranted for operating nuclear 

power plants, but that new nuclear power plants would need to satisfy the guidance in the 

revised RG 1.82, and that operating nuclear power plants should consider the guidance in the 

revised RG 1.82 when making plant modifications, namely, to change thermal insulation to 

something like reflective metal insulation (RMI), which is less likely to cause blockage. 

From a historical perspective, in January 1979 the NRC originally declared sump-strainer 

blockage to be an Unresolved Safety Issue (USI A-43, “Containment Emergency Sump 

Performance”) and subsequently published the concerns identified in the USI in the report 

NUREG-0510, “Identification of Unresolved Safety Issues Relating to Nuclear Power Plants.” 

USI A-43 dealt with concerns regarding the availability of adequate long-term recirculation 

cooling water following a LOCA. This cooling water should be sufficiently free of debris so that 

pump performance is not impaired and long-term recirculation flow capability is not degraded. 

However, the importance of particulate matter in debris beds was not recognized during USI A43, and the issue was closed without realizing that particulate debris had a large effect on head 

loss. 

3.1 Sump Performance Issues 

The NRC has sponsored research to quantify sump performance and to look more deeply into 

the strainer blockage issue in general. Substantial experimental and analytical research was 

conducted to support the resolution of USI A-43, and USI A-43 was declared resolved in 1985. 

Subsequent to the closure of USI A-43, several discovery events regarding ECCS strainer and 

foreign material (e.g. corrosion products, dirt , etc.) prompted a review of the strainer blockage 

issue. The NRC-sponsored research had the objectives of estimating possible shortcomings of 

existing suction strainer designs in U.S. BWR plants and evaluating the actions taken by the 

nuclear power industry to ensure availability of long-term recirculation of cooling water in BWR 

plants. The historical overview of USI A-43 Resolution, including an overview of subsequent 

BWR strainer clogging and pump failure events, an overview of NRC research and regulatory 

actions, and the BWR issue resolution, was discussed in an earlier report (Rao et al., 2001). 

That report included the key technical findings of NRC research supporting the resolution of the 

BWR strainer blockage issue along with a summary of the actions taken by the nuclear power 

industry to ensure availability of long-term recirculation of cooling water in BWR plants. It has 

served as a source of information on the strainer blockage issue, summarizing the key aspects 

of the issue and identifying the most important documents. In particular, the report provided the 

following: 
3-2

• An overview of the BWR strainer blockage issue and its resolution.

• A summary of the NRC-sponsored research performed to gain an understanding and 

insight into the BWR strainer blockage issue.

• A summary of the NRC review of applicable research sponsored by the U.S. industry 

and by international organizations.

• Details on the NRC review of the Boiling Water Reactor Owners Group (BWROG) issue 

resolution guidance to the industry.

• A summary of the implementation of industry resolutions of the strainer clogging issue 

and the NRC’s review of individual plant strainer solutions.

The chronology of the BWR strainer blockage issue and its resolution is illustrated in the 

timeline presented in Table 3.1-1, and each of these events is discussed below.

Table 3.1-1. BWR Strainer Blockage Issue Timeline

Date Event

January 1979 NRC declared “Containment Emergency Sump Performance” an 

Unresolved Safety Issue (USI A-43) and published the issue’s concerns 

in NUREG-0510, “Identification of Unresolved Safety Issues Relating to 

Nuclear Power Plants.”

October 1985 NRC published regulatory analysis results related to resolving USI A-43 

in NUREG-0869, “USI A-43 Regulatory Analysis.”

October 1985 NRC published technical findings of research related to resolving USI A43 in NUREG-0897, “Containment Emergency Sump Performance.”

October 1985 NRC declared USI A-43 resolved with resolution presented to 

Commission in SECY-85-349, “Resolution of Unresolved Safety Issue A43, Containment Emergency Sump Performance.”

November 1985 NRC Issued Regulatory Guide 1.82, Revision 1, “Water Sources for 

Long-Term Recirculation Cooling Following a Loss-of-Coolant Accident.”

December 1985 NRC issued GL-85-22, “Potential for Loss of Post-LOCA Recirculation 

Capability Due to Insulation Debris Blockage,” outlining safety concerns 

and recommendations to all holders of operating licenses.

May 1992 First strainer clogging event occurred at Perry Nuclear Plant.

July 1992 Strainer blockage incident occurred at Barsebäck Unit 2 in Sweden.

March 1993 Second strainer clogging event occurred at Perry Nuclear Plant.

May 1993 NRC issued Bulletin 93-02, “Debris Plugging of Emergency Core Cooling 

Suction Strainers,” to all holders of operating licenses for nuclear power 

plants. Licensees were requested to identify and remove sources of 

fibrous air filters and temporary fibrous material in primary containment 

not designed to withstand a LOCA.

September 

1993

NRC initiated detailed study of a reference BWR4 Mark I plant.

January 1994 Organization for Economic Cooperation and Development (OECD) 

conference held in Stockholm, Sweden, to exchange information and 

experience and provide feedback of actions taken to the international 

community.
3-3

February 1994 NRC Issued Supplement 1 to Bulletin 93-02, “Debris Plugging of 

Emergency Core Cooling Suction Strainers,” requesting licensees to take 

further interim actions (e.g., implementing operating procedures and 

conducting training and briefings).

August 1994 NRC published results of reference plant study as draft for comment in 

NUREG/CR-6224, “Parametric Study of the Potential for BWR ECCS 

Strainer Blockage Due to LOCA Generated Debris.” 

September 

1995

Strainer blockage event occurred at Limerick.

October 1995 NRC published final results of reference plant study (NUREG/CR-6224).

October 1995 NRC issued Bulletin 95-02, “Unexpected Clogging of a Residual Heat 

Removal (RHR) Pump Strainer While Operating in Suppression Pool 

Cooling Mode,” to all operating BWR licenses. This bulletin requested 

actions be taken by licensees to ensure that unacceptable buildup of 

debris that could clog strainers does not occur during normal operation. 

February 1996 International Knowledge Base prepared by USNRC for OECD, CSNI 

PWG 1 was published in NEA/CSNI/R (95) 11, “Knowledge Base for 

Emergency Core Cooling System Recirculation Reliability.” 

May 1996 NRC issued Revision 2 of RG 1.82, “Water Sources for Long-Term 

Recirculation Cooling Following a Loss-of-Coolant Accident.” Revision 2 

altered the debris blockage evaluation guidance for BWRs because 

operational events, analyses, and research work after the issuance of 

Revision 1 indicated that the previous guidance was not comprehensive 

enough.

May 1996 NRC issued Bulletin 96-03, “Potential Plugging of Emergency Core 

Cooling Suction Strainers by Debris in Boiling-Water Reactors,” to all 

holders of BWR operating licenses. Licensees were requested to 

implement appropriate measures to ensure the capability of the ECCS to 

perform its safety function following a LOCA. 

September 

1996

NRC initiated a drywell debris transport study (DDTS) to investigate 

debris transport in BWR drywells using a bounding analysis approach.

November 1996 The BWROG submitted their utility resolution guidance (URG) in NEDO32686, Rev. 0, “Utility Resolution Guidance for ECCS Suction Strainer 

Blockage,” to NRC for review and approval.

December 1996 The NRC strainer blockage head loss analysis code, BLOCKAGE, was 

completed and the code manuals published as NUREG/CR-6370, 

"BLOCKAGE 2.5 User’s Manual," and NUREG/CR-6371, "BLOCKAGE 

2.5 Reference Manual."

June 1997 The NRC reviewed submittals regarding Edwin I. Hatch Nuclear Plant, 

Units 1 and 2, response to NRC Bulletin 96-03. The findings were 

documented in a letter from N. B. Lee to H. L. Sumner, “Safety 

Evaluation Related to NRC Bulletin 96-03, ‘Potential Plugging of 

Emergency Core Cooling Suction Strainers by Debris in Boiling Water 

Reactors,’ - Edwin I. Hatch Nuclear Plant, Units 1 and 2 (TAC Nos. 

M96148 and M96149).”

August 1997 NRC draft results of the DDTS in NUREG/CR-6369, “Drywell Debris 

Transport Study.” 

October 1997 NRC issued GL-97-04, “Assurance of Sufficient Net Positive Suction 

Head for Emergency Core Cooling and Containment Heat Removal 

Pumps,” to all holders of operating licenses for nuclear power plants 
3-4

requesting current information regarding their net positive suction head 

(NPSH) analyses. 

October 1997 The NRC technically reviewed submittals regarding Hope Creek 

Generating Station response to NRC Bulletin 96-03. These findings were 

documented in a letter from D. H. Jaffe to L. Eliason, “Safety Evaluation 

for Hope Creek Generating Station – NRC Bulletin 96-03 (TAC No. 

M96150).”

July 1998 NRC issued GL-98-04, “Potential for Degradation of the Emergency Core 

Cooling System and the Containment Spray System After Loss-ofCoolant Accident Because of Construction and Protective Coating 

Deficiencies and Foreign Material in Containment,” to all holders of 

operating licenses for nuclear power plants alerting addresses of 

continuing strainer blockage concerns and requested information under 

10 CFR 50.54(f) to evaluate the addresses’ programs for ensuring that 

Service Level 1 protective coatings inside containment do not detach 

from their substrate during a design-basis LOCA and interfere with the 

operation of the ECCS and safety-related CSS. 

August 1998 NRC issued Safety Evaluation Report (SER) regarding BWROG URG as 

Docket No. PROJ0691, “Safety Evaluation by the Office of Nuclear 

Reactor Regulation Related to NRC Bulletin 96-03 Boiling Water Reactor 

Owners Group Topical Report NEDO-32686, ‘Utility Resolution Guidance 

for ECCS Suction Strainer Blockage,” (NRC-SER-1988).

February 1999 NRC review of GE report NEDC-32721-P (ML081840175) for BWR 

stacked disc strainer.

September 

1999

NRC published final results of DDTS (NUREG/CR-6369).

January 1999 NRC Audit of Limerick NRC Bulletin 96-03/95-02 Resolution.

March 1999 NRC Audit of Dresden NRC Bulletin 96-03/95-02 Resolution.

August 1999 NRC Audit of Grand Gulf NRC Bulletin 96-03/95-02 Resolution.

October 1999 NRC Audit of Duane Arnold NRC Bulletin 96-03/95-02 Resolution.

April 2000 NRC technically reviewed the licensee submittals regarding Brunswick 

Steam Electric Plant, Units 1 and 2, response to NRC Bulletin 96-03. 

The findings were documented in LA-UR-00-2574, “Technical Review of 

Licensee Submittals Regarding Brunswick Steam Electric Plant, Units 1 

and 2 Response to US NRC Bulletin 96-03, ‘Potential Plugging of ECCS 

Strainers by Debris in Boiling Water Reactors’.”

October 2000 The NRC issued Amendment 185 to Facility Operating License No. 

DPR-35 for the Pilgrim Nuclear Power Station that changed the plant’s 

licensing basis involving the use of containment overpressure to ensure 

sufficient NPSH for ECCS pumps following a LOCA. This issuance was 

stated in a letter from A. B. Wang to M. Bellamy, “Pilgrim Nuclear Power 

Station – Issuance of Amendment Re: Use of Containment Overpressure 

(TAC No. MA7295).”

March 2001 A report entitled, “BWR ECCS Strainer Blockage Issue: Summary of 

Research and Resolution Actions” LA-UR-01-1595, prepared by Los 

Alamos National Laboratory for the USNRC (Rao et al., 2001).

After the closure of USI A-43, several discovery events regarding the ECCS strainer and foreign 

material prompted a review of the strainer blockage issue for BWRs. Operational events that 
3-5

have occurred at both BWR and PWR plants pertaining to the issue of sump-strainer or suctionstrainer blockage are briefly reviewed below. These events are described in the general order 

of their relative severity, starting with operational events that have rendered systems inoperable 

with regard to their ability to complete their safety mission. Two of these events resulted from 

the generation of insulation debris by jet flow from a LOCA caused by the unintentional opening 

of safety relief valves (SRVs). Other events have resulted in accumulation of sufficient 

operational debris to effectively block a strainer or to plug a valve. Some event reports simply 

noted debris found in the containment, as well as inadequate maintenance that would likely 

cause potential sources of debris within the containment. Related event reports identified 

inadequacies in a sump strainer where debris potentially could bypass the strainer and enter the 

respective system.

Subsequent to the assessment of sump performance in BWRs, NRC concentrated on the sumpstrainer clogging issues pertaining to PWRs. In the event of a LOCA within the containment of a 

PWR, piping thermal insulation and other materials in the vicinity of the break will be dislodged 

by break-jet impingement. A fraction of this fragmented and dislodged insulation and other 

materials such as paint chips, paint particulates, and concrete dust will be transported to the 

containment floor by the steam/water flows induced by the break and the containment sprays. 

Some of this debris eventually will be transported to and accumulate on the recirculation sump 

suction strainers. Debris accumulation on the sump strainer may challenge the sump’s 

capability to provide adequate, long-term cooling water to the ECCS and the containment spray 

(CS) pumps. 

Examination of plant drawings, preliminary analyses, and test results suggested that a 

prominent mechanism for recirculation sump failure involves pressure drop across the sump 

strainer induced by debris accumulation. However, sump-strainer failure through other 

mechanisms is also considered possible for some configurations. Three failure modes were 

considered as part of the study:

• Loss of the NPSH margin caused by excess pressure drop across the strainer resulting 

from debris buildup. This concern applies to all plant units having sump strainers that are 

completely submerged in the containment pool.

• Loss of the static head necessary to drive recirculation flow through a strainer because of 

excess pressure drop across the strainer resulting from debris buildup. This concern 

applies to all plant units having sump strainers that are not completely submerged or have 

vents that communicate with the containment atmosphere above the water level of the 

containment pool.

• Blockage of water-flow paths may (a) cause retention of water in some regions of the 

containment or (b) prevent adequate water flow through partially-blocked openings and 

result in lower water levels in the sump and thus a lower NPSH margin than estimated by 

the licensees.

3.2 Events Rendering a System Inoperable

In operating BWRs and PWRs, events have resulted in systems being declared inoperable; that 

is, the ability of that system to perform its safety-related mission was in considerable doubt. 

These events include the accumulation of debris on a strainer, excessive head loss caused by a 

strainer, and events in which debris entered a system and thereby adversely affected the 
3-6

operability of a component of that system. These events, which occurred at BWR and PWR 

plants within the U.S., are summarized in Table 3.2-1.

Table 3.2-1. Events Rendering a System Inoperable

Year

Plant

(Type)

Event

Initiator Debris Consequence Reference

1988 Grand Gulf

(BWR Mark 

III)

Inspection Plastic wrap 

and other 

debris.

Clogged RHR strainers. IN-93-34

1989 Grand Gulf

(BWR Mark 

III)

Inspection Plastic wrap 

and other 

debris.

Debris could potentially 

block ECCS strainers 

during LOCA.

IN-93-34

1989 Trojan

(PWR Dry)

Inspection Numerous 

debris items 

found in the 

sump. Sections 

of strainer 

missing, 

damaged, or 

did not agree 

with drawings. 

Welding rod 

jammed in RHR 

pump impeller.

Debris blocked one 

pump and could 

potentially have blocked 

other ECCS strainers 

during LOCA.

IN-89-77

1992 H. B. 

Robinson

(PWR Dry)

Surveillance 

testing of 

safety 

injection 

pumps 

during Mode 

4 hot 

shutdown 

operations

Small piece of 

plastic blocked 

in-line orifice. 

Plastic used in 

a modification 

of RHR system.

Pumps rendered 

inoperable and loss of 

recirculation flow.

IN-92-85

1992 Perry 

(BWR Mark 

III)

Inspection Operational 

debris and a 

coating of fine 

dirt. Water 

samples 

showed fibrous 

material and 

corrosion 

products.

Clogged and deformed 

strainers.

IN-93-02

IN-93-34

1992 Point Beach

Unit 2

(PWR Dry)

Quarterly 

test of 

containment 

spray pumps

Foam rubber 

plug.

Debris blocked pump 

impeller suction. One 

train of safety injection 

(SI) piping rendered 

inoperable in 

recirculation mode.

IN-92-85

1993 Perry Several Glass fibers Clogged and deformed IN-93-02
3-7

Year

Plant

(Type)

Event

Initiator Debris Consequence Reference

(BWR Mark 

III)

SRVs were 

manually 

lifted and 

RHR used 

for 

suppression 

pool cooling.

(from temporary 

cooling filters), 

corrosion 

products, dirt, 

and misc. 

debris.

strainers IN-93-34

1994 Palisades

(PWR Dry)

Inspection Plastic material. High-pressure safety 

injection (HPSI) and CS 

system pumps declared 

inoperable.

IN-95-06

1994 Quad Cities 

Unit 1

(BWR Mark 

I)

Postmaintenance 

test

Plastic bag and 

other 

miscellaneous 

operational 

debris.

Plugged valve on RHR 

torus cooling system. 

Pump fouled by metallic 

debris wrapped around 

a vane.

IN-94-57

1995 Limerick

Unit 1

(BWR Mark 

II)

Unexpected 

opening of 

SRV at 

100% power

Polymeric fibers 

and sludge.

RHR Loop A suction 

strainer (suppression 

pool cooling mode) 

covered by thin mat of 

fibers and sludge. Loop 

B to a lesser extent. 

Cavitation indicated on 

Loop A.

IN-95-47

NRC 

Bulletin-95-

02

3.3 LOCA Debris Generation Events

The two LOCA events that generated insulation debris both involved the unintentional opening 

of SRVs; these occurred at:

• German reactor Gundremmingen-1 (KRB-1) in 1977, where the 14 SRVs of the primary 

circuit opened during a transient and 

• Barsebäck-2 nuclear power plant on July 28, 1992, during a reactor restart procedure after 

the annual refueling outage. 

Both of these reactors were BWRs with similarities to U.S. reactors. Details on these events are 

shown in Table 3.3-1.
3-8

Table 3.3-1. Events with LOCA-Generated Insulation Debris

Year

Plant

(Type)

Event

Initiator Debris Consequence Reference

1977 Gundremmingen 

Unit 1

(BWR)

Unintentional 

opening of 

14 SRVs

Fiberglass 

insulation 

debris.

Potential clogging of 

recirculation 

strainers.

NEA/CSNI/R 

(95) 11

1992 Barsebäck Unit 

2

(BWR)

Unintentional 

opening of 

SRV

Metaljacketed 

mineral wool 

insulation 

debris.

Clogged two of five 

spray-system 

suction strainers 

with loss of 

containment sprays 

at 1 hour.

NEA/CSNI/R 

(95) 11

IN-92-71

IN-93-02 

(S1)

3.4 Events Involving Debris Found in Containment

In operating BWR and PWR plants, events have occurred in which debris was found inside the 

containment that had the potential to impair the operability of a safety system. Details on these 

events are listed in Table 3.4-1.

Table 3.4-1. Events with Debris Found Inside Containment

Year

Plant

(Type)

Event

Initiator Debris Consequence Reference

1975 Haddam 

Neck

(PWR Dry)

Inspection Six 55-gal drums of 

sludge with varying 

amounts of other 

debris removed from 

ECCS sump.

Debris potentially 

could block ECCS 

strainers during a 

LOCA.

GL-98-04

1988 Surry Units 

1 and 2

(PWR Sub)

Inspection Construction 

materials and debris 

found in the sump, in 

cone strainer of 

recirculation spray 

system, and in 

recirculation pumps.

Materials could 

have rendered 

system inoperable.

GL-98-04

IN-89-77

1989 Diablo 

Canyon 

Units 1 and 

2

(PWR Dry)

Inspection Debris found in 

sumps.

Debris could 

potentially block 

ECCS strainers 

during LOCA.

GL-98-04

IN-89-77

1990 McGuire 

Unit 1

(PWR Ice)

Inspection Loose material 

discovered in upper 

containment.

Material not likely to 

have made ECCS 

inoperable but 

debris could 

contribute to 

potential ECCS 

strainer blockage.

GL-98-04

1993 North Anna

(PWR Sub)

Steam 

Generator 

Most of the 

unqualified silicon 

Paint fragments 

potentially could 

IN-93-34
3-9

Year

Plant

(Type)

Event

Initiator Debris Consequence Reference

Replacement aluminum paint had 

come loose from the 

steam generator (SG) 

and pressurizer and 

was supported only 

by insulation 

jacketing.

reach sump during a 

LOCA.

1993 Spanish 

Plant

(PWR)

Inspection Unspecified debris 

(believed to have 

been there since 

commissioning), dirty 

sump water, and flow 

blockage.

ECCS lines taking 

suction from the 

sumps were partially 

blocked.

IN-96-10

1994 Browns 

Ferry Unit 2

(BWR Mark 

I)

Inspection Cloth-like material. Partial strainer 

blockage, potential 

for 25% blockage.

IN-95-06

1994 LaSalle 

Unit 1

(BWR Mark 

II)

Inspection Assortment of 

operational debris and 

sludge.

Potentially 

contribute to strainer 

blockage.

IN-94-57

1994 River Bend

(BWR Mark 

III)

Inspection Miscellaneous 

operational debris and 

sediments. Plastic 

bag removed from 

RHR suction strainer.

Potentially 

contribute to strainer 

blockage.

IN-94-57

1996 Haddam 

Neck

(PWR Dry)

Outage 

Maintenance

Five 55-gal drums of 

sludge with varying 

amounts of other 

debris removed from 

ECCS sump.

Debris could 

potentially block 

ECCS strainers 

during a LOCA.

GL-98-04

1996 LaSalle 

Unit 2

(BWR Mark 

II)

Outage 

suppression 

pool 

cleaning.

Miscellaneous 

operational debris and 

sludge.

Suppression pool 

debris could 

potentially block

ECCS strainers 

during a LOCA.

IN-96-59

1996 Millstone 

Unit 3

(PWR Sub)

Inspection Pieces of Arcor 

protective coating and 

mussel shell 

fragments. 

Construction debris 

found in recirculation 

spray system suction 

lines.

Potential failure of 

recirculation spray 

heat exchangers to 

perform specified 

safety function 

because of debris.

GL-98-04

IN-97-13

1996 Nine Mile 

Point Unit 2

(BWR Mark 

II)

Inspection Miscellaneous 

operational debris, 

including foam rubber, 

plastic bags, Tygon 

Suppression pool 

debris potentially 

could block ECCS 

strainers during a 

IN-96-59
3-10

Year

Plant

(Type)

Event

Initiator Debris Consequence Reference

tubing, and hard hats. LOCA.

1996 Vogtle Unit 

2

(PWR Dry)

Inspection Loose debris 

identified inside 

containment.

Debris could 

potentially block 

ECCS strainers 

during LOCA.

GL-98-04

1996 Zion Unit 2

(PWR Dry)

Inspection Extensive failure of 

protective coatings. 

Unqualified coatings 

identified. 

Miscellaneous debris 

found throughout 

containment.

Debris could 

potentially block 

ECCS strainers 

during LOCA.

IN-97-13

Calvert 

Cliffs Units 

1 and 2

(PWR Dry)

Inspection Unit 2 sump 

contained 11.3 kg (25 

lb) of dirt, weld slag, 

pebbles, etc. Unit 1 

had less than 1 lb 

debris.

Debris could 

contribute to 

potential ECCS 

strainer blockage.

GL-98-04

D. C. Cook 

Units 1 and 

2

(PWR Ice)

Inspection Fibrous material 

found in containment.

Debris potentially 

could block ECCS 

strainers during 

LOCA.

GL-98-04

3.5 Inadequate Maintenance Leading to Potential Sources of Debris

In operating BWR and PWR plants, events have occurred in which inadequate maintenance 

conditions within containments could potentially result in significant debris. Details on these 

events are listed in Table 3.5-1. In general, these events involved unqualified protective 

coatings and materials.
3-11

Table 3.5-1. Events of Inadequate Maintenance, Potentially Leading to Sources of Debris

Year

Plant

(Type)

Event

Initiator Debris Consequence Reference

1984 North Anna

Units 1 and 2

(PWR Sub)

Inspection Unqualified 

coatings 

identified.

Debris could 

potentially block 

ECCS strainers during 

LOCA.

GL-98-04

1988 Susquehanna

Unit 2

(BWR Mark II)

Inspection Extensive 

delamination of 

aluminum-foil 

jacketing 

fiberglass 

insulation.

Debris could 

potentially block 

ECCS strainers during 

LOCA.

IN-88-28

1993 Sequoyah

Units 1 and 2

(PWR Ice)

Inspection Unqualified 

coatings 

identified.

Debris could 

potentially block 

ECCS strainers during 

LOCA.

GL-98-04

IN-97-13

1994 Browns Ferry 

Units 1, 2, & 3

(BWR Mark I)

Inspection Unqualified 

coatings 

identified.

Debris could 

contribute to potential 

ECCS strainer 

blockage.

GL-98-04

1995 Indian Point

Unit 2

(PWR Dry)

Inspection Failure of 

protective 

coatings. 

Unqualified 

coatings 

identified.

Debris could 

potentially block 

ECCS strainers during 

LOCA.

IN-97-13

GL-98-04

1997 Clinton

(BWR Mark III)

Inspection Unqualified 

coatings 

identified.

Debris could 

potentially block 

ECCS strainers during 

LOCA.

GL-98-04

1997 Millstone Unit 1

(BWR Mark I)

Inspection Unqualified 

coatings 

identified.

Debris could 

potentially block 

ECCS strainers during 

LOCA.

GL-98-04

IN-88-28

1997 Sequoyah Units 

1

(PWR Ice)

Inspection Oil cloth 

introduced into 

containment.

Potential to block one 

or both refueling 

drains.

GL-98-04

3.6 Sump Strainer Inadequacies

In operating BWR and PWR plants, events have occurred in which defects in the integrity of the 

strainers were found. These defects could have caused a potential failure to adequately filter 

the ECCS water source that could result in degradation and eventual loss of ECCS function as 

a result of damaged pumps or clogged flow pathways. Details on these events are given in 

Table 3.6-1.
3-12

Table 3.6-1. Events with Inadequacies Found in Suction Strainers

Year

Plant

(Type)

Event 

Initiator

Strainer

Condition Consequence Reference

1988 Millstone

Unit 1

(BWR Mark I)

Safety 

Analysis

Existing suction 

strainers too small

when criteria of 

RG 1.82, Rev. 1 

applied.

Potential strainer 

blockage due to 

accumulation of 

debris.

GL-98-04

1990 Three Mile 

Island Unit 1

(PWR Dry)

Inspection Modification of 

sump access 

hatches left holes 

in top of sump 

strainer cage.

Potential debris 

bypass of the 

sump strainers 

and subsequent 

potential damage 

to pumps or 

clogged spray 

nozzles.

GL-98-04

1993 Arkansas 

Nuclear One

Unit 1

(PWR Dry)

Inspection Several breaches 

found in sump 

strainers.

Potential debris 

bypass of sump 

strainers and 

subsequent 

potential 

degradation or 

even loss of 

ECCS function.

IN-89-77 Sup. 1

1993 Arkansas 

Nuclear One

Unit 2

(PWR Dry)

Inspection Seven holes 

found in masonry 

grout below 

strainer assembly 

of ECCS sump.

Potential debris 

bypass of sump 

strainers and 

subsequent 

potential 

degradation of 

both trains of 

HPSI and 

containment 

spray.

GL-98-04

IN-89-77 Sup. 1

1993 San Onofre

Units 1 and 2

Inspection Irregular annular 

gap surrounding 

low-temperature 

over-pressure 

discharge line 

penetrating 

horizontal steel 

cover plate.

Potential debris 

bypass of the 

sump strainers 

and subsequent 

potential 

degradation or 

even loss of 

ECCS function.

GL-98-04

1993 Vermont 

Yankee

(BWR Mark I)

Safety 

Analysis

Low-pressure 

core spray 

(LPCS) suction 

strainers smaller 

than assumed in 

NPSH 

calculations. 

Potential loss of 

NPSH margin on 

LPCS during 

accident 

conditions.

GL-98-04
3-13

Year

Plant

(Type)

Event 

Initiator

Strainer

Condition Consequence Reference

Existing NPSH 

calculations 

invalid.

1994 South Texas

Units 1 and 2

(PWR Dry)

Inspection Sump-strainer 

openings from 

initial construction 

discovered.

Potential debris 

bypass of sump 

strainers and 

potential 

degradation of 

ECCS function.

GL-98-04

1996 Watts Bar

Unit 1

(PWR Ice)

Inspection Containment 

sump trashstrainer door 

found open with 

plant in Mode 4 

and ECCS 

required to be 

operable.

Potential 

impairment of 

sump strainer 

function.

GL-98-04

1996 Millstone

Unit 2

(PWR Dry)

Inspection Containment 

sump strainers 

incorrectly 

constructed.

Debris larger than 

analyzed could 

pass through 

strainers.

GL-98-04

The regulatory analysis results and the technical findings of research related to resolving USI A43 were reported in NUREG-0869 and NUREG-0897, respectively.

The NRC findings documented in NUREG-0897 Revision 1 were:

• Formation of an air-core vortex that would result in unacceptable levels of air ingestion that 

potentially could severely degrade pump performance was a concern. This was more 

applicable to PWRs but was still relevant to BWRs. Hydraulic tests showed that the 

potential for air ingestion was less severe than previously hypothesized. In addition, under 

normal flow conditions and in the absence of cavitation effects, pump performance was only 

slightly degraded when air ingestion was less than 2%.

• Effects of LOCA-generated insulation debris on RHR recirculation requirements depend on: 

1. types and quantities of insulation, 

2. potential of a high-pressure break to severely damage large quantities of insulation, 

3. transport of debris to the sump strainer, 

4. blockage potential of the transported debris, and 

5. impact on available NPSH. 

• The effects of debris blockage on the NPSH margin should be dealt with on a plant-specific 

basis. Insulation debris transport tests showed that severely damaged or fragmented 

insulation was readily transported at relatively low velocities (0.2 to 0.5 ft/s). Therefore, the 

level of damage near the postulated break location became a dominant consideration. The 
3-14

level of damage to insulation was correlated with distance between the insulation and the 

break, in terms of L/D (distance divided by the pipe-break diameter). Data showed that jet 

load pressures would inflict severe damage to insulation within 3 L/Ds, and substantial 

damage would occur in the 3- to 5-L/D range with damage occurring out to about 7 L/D. 

• The types and quantities of debris small enough to pass through strainers or suction 

strainers and reach the pump impeller should not impair long-term hydraulic performance. 

However, in pumps with mechanical shaft seals, debris could cause clogging or excessive 

wear, leading to increased seal leakage. However, catastrophic failure of a shaft seal as a 

result of debris ingestion was considered unlikely. If the seal did fail, pump leakage would 

be restricted.

• Nineteen nuclear power plants were surveyed in 1982 to identify the insulation types used, 

the quantities and distribution of insulation, the methods of attachment, the components 

and piping insulated, the variability of plant layouts, and the sump designs and locations. 

The types of insulation found were categorized into two major groups: reflective metallic 

insulation (RMI) and fibrous insulations.

The regulatory analysis documented in NUREG-0869 did not support a generic backfit action 

because plant-specific design features and post-LOCA recirculation flow requirements govern 

debris blockage effects. As a result, the analysis conclusion was that the issue should be 

resolved on a plant-specific basis. The staff recommended that RG 1.82, Revision 1, be used 

as guidance for the evaluation (10 CFR 50.59) of plant modifications involving replacement 

and/or modification of thermal insulation installed on the piping and components of the primary 

coolant system. 

3.7 Assessment of Plant Vulnerability

3.7.1 BWRs

On July 28, 1992, a spurious opening of a safety valve at Barsebick Unit 2, a Swedish BWR, 

resulted in clogging of two ECCS pump suction strainers leading to loss of both containment 

sprays within one hour after the accident. The release of steam dislodged mineral wool 

insulation, pieces of which were subsequently transported by steam and water into the 

suppression pool located at the bottom of the containment. Instances of clogging of ECCS 

pump suction strainers have also occurred at U.S. plants, including two instances that occurred 

at the Perry Nuclear plant, which is a BWR/6 with Mark III containment. The instances at Perry 

suggested that filtering of small particles, e.g., suppression pool sludge, by the fibrous debris 

bed will result in increased pressure drop across the strainers. Given these precursor events, 

NRC staff initiated analyses to estimate potential for loss of NPSH of the ECCS pumps in a 

BWR due to clogging of suction strainers by a combination of fibrous and particulate debris. 

A BWR/4 with a Mark I containment was selected as the reference plant for the study. The 

analysis methodology ,as documented in NUREG/CR-6224, has two components: probabilistic 

and deterministic. Based on historical evidence and piping failure analyses, this study 

concluded that pipe breaks in reactor cooling systems would most likely occur at the weld 

locations, and that weld break frequency is strongly dependent on the type of weld and 

operating environment. As a result, the number, type and location of each weld in the drywell of 

the reference plant subjected to high pressure during normal operation were identified. For 

each weld type, a weld break frequency was obtained based on data extracted from a LLNL 
3-15

BWR pipe break study described in NUREG/CR-4792 taking into consideration the effects of 

enhanced inspections.

A transient strainer blockage model was developed to estimate the impact of a break for each of 

the identified welds at the reference plant. Important components of this model included: 1. A 

reference plant specific LOCA debris generation model (DGM) developed to estimate the 

quantity of insulation debris generated by postulated DEGB at that weld and the size distribution 

of the debris. A three region spherical DGM was developed to account for the lower operating 

pressure of BWRs and the layout of BWR drywells. 2. A reference plant-specific transient

drywell transport model was developed to estimate the fraction of the fibrous and particulate 

debris reaching the suppression pool as a result of transport by blowdown and washdown. 3. A 

suppression pool model was developed to estimate the type and volume of fibrous and 

particulate debris reaching the strainer as a function of time. The model accounts for (a) resuspension of sludge contained at the bottom of the suppression pool, (b) gravitational 

sedimentation (or settling) of the particulate and fibrous debris, and (c) continued deposition on 

the strainer. 4. A head loss model was developed to estimate the pressure drop across the 

strainer due to debris bed buildup. The key components described above were integrated into a 

single strainer blockage model which was used to evaluate whether or not a pipe break at each 

of the welds located in the primary system piping of the reference plant resulted in a head loss 

larger than the available ECCS NPSH margin. Those welds that resulted in loss of NPSH 

margin were summed to obtain an estimate of the overall frequency for the loss of NPSH for the 

reference plant. The pipe break frequency estimates for a DEGB postulated to occur on piping 

systems analyzed ranged from 3.2 x 10-06 to 1. 2 x 10-04 and the overall pipe break frequency 

was estimated to be of 1.59 x 10-04. Almost all postulated DEGBs resulted in unacceptable 

strainer blockage leading to the loss of NPSH margin for the ECCS pumps. The estimates of 

the frequency for loss of NPSH margin attributable to the piping systems studied were 

essentially the same as the pipe break frequency estimates. 

3.7.2 PWRs

To address plant vulnerability to debris accumulation on the sump strainer in PWRs, the NRC 

and industry groups compiled much of the information that is necessary to effectively judge the 

vulnerability of ECCSs during recirculation following specific accidents (large LOCA [LLOCA], 

medium LOCA [MLOCA], and small LOCA [SLOCA]) and to draw insights regarding the 

potential severity of the problem for classes of reactors with similar design features 

(subatmospheric containments, ice condenser containments, etc.). The study performed 

"representative" parametric analyses to address the following safety questions for each plant to 

the extent possible (NUREG/CR-6762):

If a LOCA of a given break size occurs, would the amount and type of debris generated from 

containment insulation and other sources of debris cause significant buildup on the ECCS 

recirculation sump? If so, would such blockage be of sufficient magnitude to challenge the 

ECCS function either by reducing the available head, NPSHA, below the required head, 

NPSHR, or by reducing flow through the sump strainer below the ECCS pump flow 

demand?

It was concluded that a firm determination of the vulnerability of any individual plant would 

require a plant-specific evaluation. It was reported that such an evaluation might have to 

incorporate plant features such as:

• physical layouts of primary and auxiliary piping in the containment, 
3-16

• possible locations of the postulated breaks and the likely ECCS response to these 

breaks, 

• locations, types, and quantities of insulation used on each piping system and equipment 

component, 

• physical layouts of intervening structures that may inhibit debris transport, 

• a physical description of the sump geometry and its location in containment, 

• the time until switchover to recirculation, and

• and the required flow rates through the sump. 

Because plant-specific analysis for the 69 operating PWRs is complex, a parametric study was 

used to examine the range of possible conditions present at these plants and to incorporate 

variations such as insulation type in proportion to its occurrence in the population so that the 

plausibility of sump blockage could be assessed. Approximations of individual plant features 

were used in the parametric analysis, and individual cases were developed to represent specific 

plants in the industry. Even though the best information available was used for each unit, it was 

recognized that these cases do not describe conditions at any single plant in great detail. 

Therefore, the individual entries for each unit were referred to as "cases" or as "parametric 

cases" rather than as "plant analysis" so that it would be understood that the individual cases do 

not provide a complete perspective of sump blockage risk at the corresponding plants. 

The sump failure criterion applicable to each plant was determined primarily by sump 

submergence. Figure 3.7-1 illustrates the two basic sump configurations of fully and partially 

submerged strainers. Although only vertical sump configurations were considered, the same 

designations are applicable for inclined strainer designs. The key distinction between the fully 

and partially submerged configurations is that partially submerged strainers allow equal 

pressure above both the pit and the pool, which are potentially separated by a debris bed. Fully 

submerged strainers have a complete seal of water between the pump inlet and the 

containment atmosphere along all water paths through the sump strainer. The effect of this 

difference in evaluation of the sump failure criterion is described below. 

(a) Fully submerged strainer configuration 

showing water from pump inlet to containment 

atmosphere.

(b) Partially submerged strainer configuration 

showing containment atmosphere over both 

the external pool and the internal sump pit with 

water on lower portion of strainer.

Figure 3.7-1. Sump-Strainer Schematics
3-17

For fully submerged sump strainers (see Figure 3.7-1a), failure is likely to occur because of 

cavitation within the pump housing when head loss caused by debris accumulation exceeds the 

NPSH margin (NPSHM). For this set of plants (in which sump strainers are fully submerged at 

the time of switchover), the onset of cavitation is determined by comparing the plant NPSHM, as 

reported by plants responding to GL-97-04 with the strainer head loss (∆HS) calculated in the 

parametric study. Therefore, for this case, the sump failure criterion is assumed to be reached 

when ∆HS ≥ NPSHM.

For the partially submerged sump strainers (see Figure 3.7-1b), failure can occur in one of two 

ways: pump cavitation as explained above or due to head loss caused by insufficient water 

entering the sump due to debris buildup. This flow imbalance occurs when water infiltration 

through a debris bed on the strainer can no longer satisfy the volumetric demands of the pump. 

Because the pit and the pool are at equal atmospheric overpressure, the only force available to 

move water through a debris bed is the static pressure head in the pool. Numeric simulations 

confirm that an effective head loss across a debris bed approximately equal to half of the 

submerged screen height is sufficient to prevent adequate water flow. For all partially 

submerged sump strainers, the sump failure criterion is assumed to be met when 

∆HS ≥ NPSHM or ∆HS ≥ 1/2 of submerged screen height.

After switchover to ECCS recirculation, some plants can change their sump configuration from 

partially submerged to fully submerged. This can occur for a number of reasons, including 

accumulation of containment spray water, continued melting of ice-condenser reservoirs, and 

continued addition of refueling water storage tank (RWST) inventory to the containment pool. 

As the pool depth changes during recirculation, the "wetted area" (or submerged area) of the 

sump strainers can also change. The wetted area of the strainer determines the average 

approach velocity of water that may carry debris. It may be that the conditions for transport are 

enhanced due to the velocities present during washdown and early pool fill, but the most 

significant transport from the head loss perspective may be the fine debris that may transport 

over a longer period of time. Larger debris may stay at the base of the strainer while fine debris 

may collect over the entire strainer and result in high head losses. Because information about 

time-dependent pool depths was difficult to obtain, only the pool depth at the time of switchover 

to the ECCS was used in the parametric evaluations.

Calculations were made for the LLOCA events in large dry and ice condenser containments in 

PWRs. The simulations were used to develop a generic description of LLOCA accident 

progression in a PWR, both in terms of the system’s response and its implications on debris 

generation and transport. Table 3.7-1 provides a general chronology of events for a PWR 

LLOCA sequence. Because plant designs vary, the descriptions are not accurate for every 

plant. Figure 3.7-2 summarizes key findings to supplement the tabulated results.
3-18

Table 3.7-1. PWR LLOCA Sequences

(from NUREG/CR-6762, Vol 1 Table 2-4)

Time after 

LOCA (s)

Accum. 

(SI Tanks) HPSI LPSI CS Com

0-1 Reactor scram. Initially high containment pressure. Followed by low pressure in pressurizer. Deb

begins due to initial pressure wave, followed by jet impingement. Blowdown flow rate is large; flow 

mostly saturated water. Quality <0.05. Saturated jet-models are appropriate. Sandia National Labo

(SNL)/American National Standards Institute (ANSI) models suggest wider jets, but static pressures 

with distance.

2 Initiation signal Initiation signal Initiation signal Initiation signa

pressurizer pre

containment 

pressure/temp

5 Accumulator 

injection begins

Pumps start to inject 

into vessel 

Pumps start (pressure of 

reactor coolant system 

greater than pump dead 

head)

Pumps start 

and sprays on

In a cold-leg b

bypass is caus

current injectio

downcomer. H

does not have 

10 Blowdown flow rate decreases steadily from ≈20,000 lb/s to 5000 lb/s. Cold-leg pressure falls cons

1000 psia. At the same time, effluent quality increases from 0.1 to 0.5 (especially that from steam g

the break). Flow at the break is vapor continuum with water droplets suspended in it. Saturated wa

models are appropriate. At these conditions, SNL/ANSI models show that jet expansion induces hi

from break location.

25 End of bypass; highpressure safety 

injection (HPSI)

25-30 Break velocity reaches a maximum > 1000 ft/s. Quality in excess of 0.6. Steam flow at less than 5

energetic blowdown is probably complete. However, blowdown continues as residual steam contin

35 Accumulators 

empty

LPSI ramps to design 

flow.

40 Blowdown is terminated, and therefore debris generation is mostly complete. Blowdown pressure a

psi. Debris would be distributed throughout the containment. Pool is somewhat turbulent.

55-200 Reflood and quenching of fuel rods (Tmax about 1036oF). In the cold-leg break, quenching occurs 

150 s. In hot-leg break, quenching occurs between 45 and 60 s (Tmax about 950oF). 
3-19

200-1200 Debris added to lower containment pool by spray washdown drainage and break washdown. Cont

keeps filling. Heavy debris may settle down.

1200 Low-level indication in RWST received by operator. Operator prepares to turn on ECCS in sump re

1500 Switch suction to 

sump

Switch suction to sump Terminate or to 

sump

Many plants ha

fan coolers for 

cooling.

1500-18000 Debris may be brought to the sump strainer. Buildup of debris on sump strainer may cause excess

general, containment sprays may be terminated in large dry containments at the 2-h mark.

>36000 Switch to hot-leg 

recirculation.

Switch to hot-leg 

recirculation
3-20

Figure 3.7-2. PWR LLOCA Accident Progression in Large Dry Containment (Figure 2-2 NUREG
3-21

3.8 Other PWR Plant Design Features That Influence Accident Progression

Other plant design features (beyond those previously discussed) may influence the debrisrelated accident progression. For example, many plants have heat exchangers installed directly 

in the core-cooling recirculation flow paths to ensure that the water is cooled before it is returned 

to the core. However, in some plants, the core cooling recirculation systems do not have 

dedicated heat exchangers and instead make indirect use of heat exchangers from other 

systems (e.g., CSS) to ensure that heat is removed from the reactor coolant. Examples of 

plants where core cooling makes indirect use of heat exchangers from CSS include those with 

subatmospheric containments and some Combustion Engineering (CE) plants. For these types 

of plants, successful core cooling during recirculation may require (a) direct sump flow from the 

core cooling system and (b) sump recirculation cooling from the CSS. 

3.8.1 Plant Features

Some general conclusions regarding important plant features that influence accident outcome 

are listed below. The primary source for this information is the PWR plant survey published in 

2002 (NUREG/CR-6762) and is presented from an historical perspective of the issues 

addressed by the NRC and the industry and may not represent the current status of operating 

PWRs(i.e, post-GSI-191). See Appendix A for data on PWR suction strainers installed in 

response to GL 04-02.

Sump Design and Configurations

• The ECCS and/or CSS pumps in nearly one-third of the PWR plants surveyed have an 

NPSH margin of less than 2 ft of water, and another one-third have an NPSH margin 

between 2 and 4 ft of water. In general, PWR sumps have low NPSH margins compared 

with the potential head loss effects of debris accumulation on the sump strainer. This 

assessment was based on the information available prior to the modification made in 

response to NRC Generic Letter 2004-02 (GL-04-02).

• PWR sump designs vary significantly, ranging from horizontal strainers located below the 

floor elevation to vertical strainers located on pedestals. The sump-strainer surface areas 

vary significantly from unit to unit and some plants employ curb-like features to prevent 

heavier debris from accumulating on the sump strainer, while others do not have noticeable 

curbs. 

In some PWR units, the sump strainer would not be completely submerged when ECCS 

recirculation starts. However, these strainers are fully submerged relatively quickly. The mode 

of failure is strongly influenced by sump submergence. 

Sources and Locations of Debris

• U.S. PWRs employ a variety of types of insulation and modes of encapsulation, ranging 

from non-encapsulated fiberglass to fully encapsulated stainless steel RMI. A significant 

majority of PWRs have fiberglass and calcium-silicate insulation in the containment, either 

on primary piping or on supporting systems.1

 The types of fibrous insulation varied 

 

1 About 40 PWR units have in excess of 10% of the plant insulation in the form of fiberglass and another 5–10% in 

the form of calcium-silicate. A typical plant has approximately 7500 ft3 of insulation on the primary pipes and 

supporting systems pipes that are in close proximity to the primary pipes.
3-22

significantly, but most are in the form of generic low-density fiberglass (LDFG) and mineral 

wool. 

• Given that (a) very small quantities of fibrous insulation would be necessary to induce large 

pressure drops across the sump strainers and (b) many plants have comparatively large 

inventories of fibrous insulation, plant-specific analyses are necessary before the 

recirculation sumps of any particular plant can be declared safe with respect to strainer 

blockage.

• Additional sources of debris in the PWR containments include cement dust and dirt (either 

present in the containment a priori or generated by a LOCA), particulate insulations used on 

the fire barriers (e.g., marinite), failed containment coatings, and precipitates (of zinc and 

aluminum precipitation by-products).2

 Estimates for this type of debris range from 100 to 

several thousand pounds; either of these quantities of particulate debris could result in very 

large head losses when combined with fibrous material.

Containment Features Affecting Debris Transport

• Set points for the CSS typically are defined based on LLOCA and equipment qualification 

considerations. Consequently, sprays may not (automatically) actuate during SLOCAs3

because of their lower peak containment pressures. Actuation of the CS plays an important 

role in the transport of debris to the sump, and at the same time, it affects the timing of 

potential sump failure.4

• A number of features in nuclear power plant containments would significantly affect the 

transport of insulation debris. These features include the containment’s engineered safety 

features and associated plant operating procedures. Perhaps the most significant 

containment feature is the containment pressure-suppression system.

• In a PWR plant, the relatively large free volume functions to keep pressure from becoming 

excessive thus, the large free volume is essentially a pressure-suppression system. The 

containment sprays also help keep pressure from becoming excessive. Containment size 

was reduced in ice-condenser plants because of their banks of ice, which would condense 

steam effectively,. 

• The most significant difference between PWR and BWR containments with respect to 

debris transport is the pressure-suppression system, and its location relative to the 

postulated break. In BWR containments, the break effluences would flow down and 

through the suppression pool via downcomer vents (i.e., toward the ECCS suction 

strainers). In PWR containments, the break effluences would tend to flow generally up 

 

2 PWR design basis accidents evaluate the potential for precipitation of aluminum and zinc when they are subjected 

to high-pH, hot, borated water because these chemical reactions generate H2. 3 Fan cooler response to LOCAs also plays a vital role in determining spray actuation following SLOCA. These 

concerns are not applicable to LLOCAs or MLOCAs, where automatic actuation of sprays is expected in every plant. 

Some plants such as Fort Calhoun uses water management and do not have sprays automatic actuate for any size 

LOCA.

4 The drainage of the spray water from the upper reaches of the containment down to the containment sump could 

transport substantial quantities of debris to the sump that otherwise would likely remain where deposited following the 

RCS depressurization (i.e., the containment sprays would substantially increase the fraction of debris transported to 

the sump strainers over the fraction that would be transported without spray operation).
3-23

toward the large free volume of the containment dome (i.e., away from the ECCS sump 

strainers). For example, in ice-condenser containments, the containment is designed to 

direct the break flows through the ice banks, which exit into the dome. These flows also 

would carry debris into these regions. This means that for PWR plants, substantial 

quantities of debris would be propelled away from the lower regions of the containment and 

toward the higher regions of the containment. If it were not for the containment sprays 

washing the debris down toward the recirculation sump, some portion of the debris carried 

aloft likely would remain in the higher reaches of the containment.

• The flow propelling debris upward in the containment could be channeled through relatively 

narrow passageways in some containment designs, such as an ice condenser bank, where 

substantial portions of the debris entrained within the flow likely would be deposited initially 

within the channel. Such an effect could potentially be analyzed to determining the debris 

quantity that would not likely be subsequently transported downward to the sump if there 

are no sprays to wash off the debris. 

• After the airborne debris is dispersed throughout the containment, the washdown of that 

debris to the recirculation sump would be determined primarily by the design of the CSS, 

including the drainage of the sprayed water. First, the spray droplets would tend to sweep 

any remaining airborne debris out of the containment atmosphere, and then the falling 

droplets would wash debris off surfaces (structures, equipment, walls, floors, etc.). As the 

drainage water works its way downward, the entrained debris would move along with the 

flow. However, not all debris would be washed off the surfaces and the containment sprays 

may not flow over substantial areas within the containment.

• Containments are generally designed to readily drain the spray water to the sump in order 

to minimize water holdup and maximize sump water levels. However, the refueling pools 

could hold up substantial quantities of water if the pool drains are not open or are blocked 

by debris. Thus, the design of the refueling pools, including the pool drainage system, can 

be an important containment feature with regard to debris inventory in the sump.

3.8.2 Debris Accumulation

Debris generated by a LOCA will have an adverse effect on recirculation sump performance if 

this matter either (a) covers the sump strainer in sufficient quantity and over a sufficient surface 

area to impede flow or, (b) accumulates at critical locations for the flow of recirculation water 

such that the debris diverts water away from the sump.5

 After debris is transported to a location 

of concern, it must accumulate in sufficient quantity and in a configuration that impedes flow. 

The principal location of concern for debris accumulation is the surface of a recirculation sump 

strainer. The physical configuration of the sump strainer, as well as its position and orientation 

in the pool of water that it services, varies among U.S. PWRs. Additional locations of concern 

are those in which the flow path for recirculating water passes through a narrow passageway or 

restriction in cross-sectional area. If debris were to accumulate at these locations (because of 

the presence of a trash rack or a similar feature), water might be diverted away from the sump, 

thereby reducing the sump water level and associated hydraulic head.

 

5

The knowledge associated with debris accumulation also applies to strainers in the upper containment levels (e.g., 

refueling pool drain strainers), but the potential blockage of such strainers usually is treated as part of debris 

transport from the upper levels down to the sump pool.
3-24

Historically, the sump strainer has been the principal location of concern for debris 

accumulation. For fully submerged strainers, excessive accumulation of debris can cause the 

head loss across the debris bed to reduce the available NPSH to ECCS or containment spray 

pumps. For partially submerged strainers, excessive debris accumulation can reduce the static 

head necessary to drive recirculation flow through the strainer. Details on parameters such as 

local flow field, local geometry, degree of submergence, and debris characteristics are 

discussed in NUREG/CR-6808, Section 6. 

Several experiments have been performed to evaluate the hydrodynamic conditions required to 

move debris of various types from their position of arrival on the containment floor to the 

recirculation sump. The BWROG and various ECCS recirculation suction strainer vendors 

performed experiments to characterize the accumulation and head loss associated with LOCAgenerated debris for replacement strainer designs. Based on several experiments, the flow 

conditions required for debris to deposit on the upper portions of a vertical strainer were inferred 

from measurements made of the velocity required to “lift” debris over a 2- or 6-in. curb. The socalled “lifting” velocities for fiber fragments, moderate-size pieces of fiber matting, and RMI foils 

are listed in Table 3.8-1. These values were reported to be generally consistent with earlier 

measurements of the flip-up velocity. That is, debris can be lifted over a 6-in. curb (or up onto a 

vertical strainer) at relatively low velocities (i.e., less than 0.3 ft/s), if the flow field in the pool of 

water is turbulent. In laminar flow fields, the “lift” velocity increases only slightly for fiber 

fragments. Stainless steel RMI debris was observed to remain near the base of the strainer at 

velocities greater than 1 ft/s when the flow stream was laminar.

Table 3.8-1. Minimum Strainer Approach Velocity for Debris to “Flip Up” or be 

Hydraulically “Lifted” onto a Sump Strainer (Source: Table 6-1 in NUREG/CR-6808)

DATA SOURCE

Velocity (ft/s)

Intact Fiber 

Pillows *

Fiber

Fragments * 

#

Shredded

Fiber *

Intact RMI 

Cassettes

SS RMI 

foils

NRC 

(1983)=NUREG 

2982

1.1–2.4 0.5–0.7

(turbulent)

0.2

(turbulent) — —

NRC (1984)

=NUREG 3616 — — — > 1.0 1.8–2.0 **

Bremen 

Polytech. (1995) 0.9–1.3 0.7–1.1(laminar)

0.9–1.2

(laminar)

Tested by 

flipping on 

strainer not 

observed

1.9 **

NRC (2001) = 

NUREG 6772 —

0.30–0.47 

(laminar)

0.25–0.39 

(turbulent)

0.28–0.34 

(laminar)

0.25–0.30 

(turbulent)

—

No lift 

(laminar)

0.30 

(turbulent)

*Fibrous material varied among tests, but included fiberglass and mineral wool.

**Although stainless steel (SS) foil fragments were observed to “lift” and flip onto the vertical 

strainer at these velocities, the debris mass remained primarily near the bottom of the 

strainer. Brocard reports maximum flow blockage in such cases was 60-70% of the strainer 

area (NUREG/CR-3616).

#Fragment size typically 4 x 4-in.pieces of fiber matting.
3-25

A limitation of the studies listed in Table 3.8-1 is that none of them involved a sufficiently large 

quantity of debris fragments to allow an accumulation pattern that would result at water 

velocities above the “lifting” threshold. Experiments conducted at the University of New Mexico 

examined debris bed patterns on a vertical strainer for moderate- and small-size debris 

fragments of fiber, RMI foils, and calcium-silicate. Three specific observations were made from 

these tests:

• Shredded fiber and disintegrated calcium silicate developed a near-uniform debris bed at 

velocities exceeding approximately 0.5 ft/s, when the strainer was fully submerged. 

• Crumpled stainless-steel RMI foils (~2 in. in size) accumulated in a bottom-skewed pattern 

at velocities less than 1 ft/s. Individual foils that arrived at the base of the strainer “climbed” 

on top of foils that arrived earlier and gradually formed a debris bed that was triangular in 

cross-section.

• Very small particles of calcium silicate and suspended fibers collected on the strainer in a 

uniform pattern at velocities as low as 0.2 ft/s. A significant fraction of larger calcium 

silicate debris (e.g., clumps of particulate and binding fiber) either settled to the floor of the 

flume before reaching the strainer or collected as a mass near the base of the strainer at 

velocities as high as 0.9 ft/s.

3.8.3 Debris Head Loss

Information related to estimating the pressure drop (or head loss) across the ECCS strainer or 

sump strainer as a result of debris buildup was addressed in a knowledge base report published 

in 1996 by the Committee on the Safety of Nuclear Installations (CSNI), specifically Section 4 of 

that report, entitled “Strainer Pressure Drop.” NUREG/CR-6808 discussed the head loss data 

and technical developments achieved subsequent to the CSNI report. Two major uncertainties 

identified in the CSNI document are:

A proven, accurate, and repeatable methodology for predicting the head loss caused by mixed 

beds is not yet fully developed. Although the NRC methodology performs well for flat strainers, 

its application to specialty strainers has not been established.

Various test methodologies, setup designs, and test debris preparations may contribute 

significantly to pressure drop. No systematic evaluation has been performed to analyze the 

desirability of each test methodology relative to that of other methods.

Head loss across the debris bed depends to a great extent on the debris bed constituents and 

their morphology. Debris beds of importance can be divided broadly into the following groups: 

(a) fibrous debris beds, (b) mixed fibrous and particulate debris beds, (c) beds formed by 

fragments of RMI, and (d) mixed RMI and fibrous/particulate debris beds. We discuss the first 

two groups below.

Fibrous Beds

In the case of fibrous beds, the flow to a strainer would deposit the fibrous shreds on the 

strainer surfaces such that the fibers generally lay across the strainer penetrations and the 

subsequent drag caused by the fibers would create a pressure differential across the bed of 

debris. As the pressure drop across the fibrous beds increases, such beds have been observed 

to compress, leading to progressively higher head losses. Furthermore, it has been observed 

that compressed beds do not completely regain their original state when the water flow is 
3-26

terminated. Head loss across a debris bed increases linearly with velocity in the viscous region 

and increases with the square of the velocity in the turbulent region.

The head loss across the strainer depends on the quantity of the fibrous debris trapped on the 

strainer surface. A convenient measure for this quantity is the debris bed thickness based on 

the as-fabricated density of the insulation, i.e., defined as the mass of fibrous debris per unit of 

strainer area divided by the as-fabricated density. This thickness has been generally referred to 

as the “theoretical” thickness. Typically, head loss varies linearly with bed thickness for beds 

that are uniform or nearly uniform. Deviation from this linear behavior has been seen where 

debris has accumulated in a non-uniform manner on the strainer surface; specifically, such 

behavior has been observed at lower bed thicknesses, where clumps of fibrous debris have 

deposited non-uniformly on the strainer surface. The non-uniformity also may lead to lower 

filtration efficiencies for entrapment of non-fibrous debris passing through the strainer. As a 

result, pressure drop for non-uniform beds would be lower than that predicted by extrapolating 

the data obtained for uniform beds. This is mentioned as an important issue in the evaluation of 

specialized strainers designed to collect debris in a non-uniform manner (e.g., a star strainer).

Size distribution of the fibrous debris is another factor that significantly influences head loss. 

Fibrous debris reaching the strainer may range in size from individual fibers to shreds or clumps 

to large pieces of torn blankets. Considerable attention was given to studying the head loss 

characteristics of finer debris, which is much more likely to be transported to the strainer surface 

and form more uniform and compact beds, thereby offering more resistance to flow than nonuniform or loose beds. Additional factors that influence head loss include fibrous material type 

(e.g., mineral wool vs. fiberglass) and water temperature. Typically, higher water temperatures 

result in lower pressure drops that are caused primarily by corresponding decreases in viscosity 

of the water. Analyses have successfully handled this effect by simply accounting for the 

temperature dependency of viscosity in the respective head loss correlations. Similarly, the 

differences in materials can typically be handled by accounting for differences in the material 

properties of the insulation and the individual fibers. 

Mixed Particulate and Fiber Beds

A mixture of fibrous material and particulates such as corrosion products, paint chips, organic 

sludge, concrete dust, and fragments of non-fibrous insulation (such as calcium silicate) are 

generally termed “mixed bed” or “debris bed.” Attempts have been made to characterize the 

characteristics of the debris (e.g., size distributions) and to use appropriate material to simulate 

LOCA-generated debris in experiments and the appropriate characteristics in analyses. 

Experiments have shown that the addition of particulate debris would increase the pressure 

drop substantially. The data demonstrated that the head loss could increase by a factor of 100 

as the particle-to-fiber mass ratio increases from zero to about 20.

The experiments also established that for a fixed amount of particulate debris, pressure 

differentials across the bed are significantly higher for smaller, rather than larger, quantities of 

fibrous material if amount of particulate debris in the bed is maintained at a constant value. This 

effect, which often is referred to as the “thin-bed effect,” has been studied extensively. Closer 

examination of the bed morphology reveals that thin beds closely resemble granular beds 

(rather than fibrous beds) and that higher head loss is a direct result of bed morphology. This 

effect is illustrated in Figure 3.8-1, which shows head losses vs. fiber volume for fixed quantities 

of particulate, as predicted using the head loss correlation in NUREG/CR-6224. In Figure 3.8-1, 

the thin-bed peaks reflect the higher head losses associated with the thin layer fiber supporting 

a granular bed of particulates. Even if a plant has large quantities of fibers that could lead to 
3-27

potentially thick mixed beds of debris, the initial bed formation would begin with a thin layer of 

fibers that could cause a thin bed head loss relatively early into the accident.

Figure 3.8-1. Head Losses vs. Fiber Volume for Fixed Quantities of 

Particulate (predictions assumed LDFG insulation debris, dirt particulate, 

200°F, 100 ft2 of strainer area, and 5000 GPM flow)

In the prior PWR knowledge-base report (NUREG/CR-6808), details are presented on various 

analytical and experimental approaches used to assess the various aspects of sump blockage 

and to identify the strengths, limitations, important parameters, plant features, and the propriety 

of the different approaches. That report also discussed significant NRC regulatory actions 

regarding resolution of the issue. In essence, the report was designed to serve as a reference 

for plant-specific analyses with regard to whether the sump would perform its function without 

preventing the operation of the ECCS pumps. In particular, the report provided the following: 

• A description of the safety concerns pertaining to PWRs

• A description of the major phenomena associated with the potential for strainer failure and a 

summary of research and experiment s conducted to date

• An evaluation of the research conducted for the various phenomena associated with 

strainer blockage

• Criteria for evaluating sump failure

• Descriptions of postulated PWR accidents

• Relevant plant features that influence accident progression, and

0

5

10

15

20

25

30

1 10 100 1000

Fiber Volume (ft3)

Head Loss (ft)

300 lbm

200 lbm

100 lbm

50 lbm

0 lbm
3-28

• Regulatory considerations.

Due to lessons learned in the 1990s during the assessment of BWR suction strainers and 

oversight of BWR plant-specific evaluations and modifications, NRC sponsored a new research 

effort to study the accumulation of debris on PWR containment sump strainers. The 2001 

parametric study, “GSI-191 Technical Assessment: Parametric Evaluations for Pressurized 

Water Reactor Recirculation Sump Performance” (NUREG-6762, Volume 1), concluded that 

recirculation sump clogging is a credible concern for the population of domestic PWRs. 

However, as a result of limitations with respect to plant-specific data and other modeling 

uncertainties, the parametric study did not definitively identify whether or not particular PWR 

plants are vulnerable to sump clogging when phenomena associated with debris blockage are 

modeled mechanistically. 

The NRC implemented a plan to have all PWR licensees (i) perform a plant-specific evaluation 

for the potential for head loss across the containment sump strainer because of the 

accumulation of debris on the containment sump strainer and (ii) evaluate effects of the debris 

that might pass through the sump strainers. To provide additional assurance regarding the 

continued operation of PWRs, the NRC asked the licensees of PWRs to implement 

compensatory measures at least until plant specific evaluations were completed. This was 

done through the issuance of NRC Bulletin 2003-01, “Potential Impact of Debris Blockage on 

Emergency Sump Recirculation at Pressurized-Water Reactors.” 

In November 2003, the NRC issued Revision 3 of RG 1.82, “Water Sources for Long-Term 

Recirculation Cooling Following a Loss-of-Coolant Accident,” to include guidance on the effects 

of debris on PWR sump screens. Revision 3 also incorporated guidance on the net positive 

suction head of the ECCS and containment heat removal pumps.

In September 2004, NRC issued a Generic Letter 2004-02, “Potential Impact of Debris Blockage 

on Emergency Recirculation During Design Basis Accidents at Pressurized Water Reactors.” 

This Generic Letter requested all holders of operating licenses for PWRs to perform an 

evaluation of the ECCS and CSS recirculation functions in light of the information provided in 

the Generic Letter and, if appropriate, take additional actions to ensure system function. 

Additionally, the addressees were requested to submit the information specified in the letter to 

the NRC. This request was based on the potential susceptibility of PWR recirculation sump 

strainers to debris blockage during design basis accidents and on the potential for additional 

adverse effects due to debris blockage of flowpaths necessary for ECCS and CSS recirculation 

and containment drainage. 
4-1

4 REGULATORY CONSIDERATIONS

Federal regulations are established to govern design and operational aspects of nuclear power 

reactors that affect the safety of those plants. These regulations are codified in the U.S. Code 

of Federal Regulations (CFR). Title 10 of the CFR deals with energy, and Part 50 of Title 10 

consists of regulations promulgated by the NRC to provide for the licensing of production and 

utilization facilities. The NRC publishes Regulatory Guidance (RG) documents for the nuclear 

power industry on compliance with the regulations. 

4.1 Code of Federal Regulations

This section describes the regulations that apply to the strainer blockage issue. Title 10 of the 

CFR provides the authority to the NRC to regulate nuclear power plants. Section 50.46, 

“Acceptance Criteria for Emergency Core Cooling Systems for Light-Water Nuclear Power 

Reactors,” of 10 CFR requires that licensees of a boiling or pressurized water reactor design 

their ECCS systems to meet five criteria. Specifically the rule provides acceptance criteria for 

peak cladding temperature, maximum cladding oxidation, maximum hydrogen generation, 

coolable core geometry, and long-term cooling. 

The long-term cooling criteria states “After any calculated successful initial operation of the 

ECCS, the calculated core temperature shall be maintained at an acceptably low value and 

decay heat shall be removed for the extended period of time required by the long-lived 

radioactivity remaining in the core.” Licensees are required to demonstrate this capability while 

assuming the most conservative (worst) single failure. The capability of the ECCS pumps to 

fulfill the criteria of limiting the peak cladding temperature and to provide long-term cooling over 

the duration of the postulated accident could be seriously compromised by a loss of adequate 

NPSH and the resulting cavitation. Because excessive buildup of debris on ECCS pump 

strainers may result in a common-cause failure of the ECCS, thereby preventing the ECCS from 

providing long-term cooling after a LOCA, Section 50.46 clearly applies to the strainer blockage 

issue. Licensees must demonstrate that their respective plants are in compliance with the 

regulations.

General Design Criteria (GDC) 35, 36, and 37 (Appendix A to 10 CFR Part 50) require 

appropriate design, inspectability, and testability of the ECCS. Note that the GDC establish 

minimum requirements for the principal design criteria for water-cooled nuclear power plants 

similar in design to plants for which the NRC has issued construction permits. The GDC are 

also considered to be generally applicable to other types of nuclear power units and are 

intended to provide guidance in establishing the principal design criteria for such other units. 

Specifically, these criteria state the following:

Criterion 35 -- Emergency core cooling. A system to provide abundant emergency core cooling 

shall be provided. The system safety function shall be to transfer heat from the reactor core 

following any loss of reactor coolant at a rate such that (1) fuel and clad damage that could 

interfere with continued effective core cooling is prevented, and (2) clad metal-water reaction is 

limited to negligible amounts. Suitable redundancy in components and features, and suitable 

interconnections, leak detection, isolation, and containment capabilities shall be provided to 

assure that for onsite electric power system operation (assuming offsite power is not available) 

and for offsite electric power system operation (assuming onsite power is not available) the 

system safety function can be accomplished, assuming a single failure. 
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Criterion 36 -- Inspection of emergency core cooling system. The emergency core cooling 

system shall be designed to permit appropriate periodic inspection of important components, 

such as spray rings in the reactor pressure vessel, water injection nozzles, and piping, to assure 

the integrity and capability of the system.

Criterion 37 -- Testing of emergency core cooling system. The emergency core cooling system 

shall be designed to permit appropriate periodic pressure and functional testing to assure (1) the 

structural and leak-tight integrity of its components, (2) the operability and performance of the 

active components of the system, and (3) the operability of the system as a whole and, under 

conditions as close to design as practical, the performance of the full operational sequence that 

brings the system into operation, including operation of applicable portions of the protection 

system, the transfer between normal and emergency power sources, and the operation of the 

associated cooling water system. 

Section 50.65 of 10 CFR Part 50, “Requirements for Monitoring the Effectiveness of 

Maintenance at Nuclear Power Plants,” (referred to hereinafter as the maintenance rule) 

provides the requirements for monitoring and maintenance of plant structures, systems, and

components (SSCs). The maintenance rule requires the licensee of a nuclear power plant to 

monitor the performance or condition of SSCs in a manner sufficient to provide reasonable 

assurance that the SSCs are capable of fulfilling their intended functions. When the 

performance or condition of an SSC does not meet its established goals, appropriate actions 

are required to be taken. Based on the criteria in the rule, the maintenance rule includes in its 

scope PWR and BWR ECCS suction strainers, all safety-related SSCs, and those non-safetyrelated SSCs that fall into the following categories:

(1) Those that are relied upon to mitigate accidents or transients or are used in plant 

emergency operating procedures,

(2) Those whose failure could prevent safety-related SSCs from fulfilling their safety-related 

function, and

(3) Those whose failure could cause a reactor scram or an actuation of a safety-related 

system.

Protective coatings are also covered by the maintenance rule to the extent that coating activities 

can affect operability of safety-related equipment, e.g., suction strainers or safety-related 

components subject to corrosion. On the basis of the guidelines in the rule, the maintenance 

rule requires that licensees monitor the effectiveness of maintenance for these protective 

coatings. The staff also considers the requirements of 10 CFR Part 50, Appendix B, “Quality 

Assurance Criteria for Nuclear Power Plants and Fuel Reprocessing Plants,” to be applicable to 

safety-related containment coatings. Criterion IX of Appendix B, "Control of Special Processes," 

is especially relevant requiring that "Measures shall be established to assure that special 

processes are controlled and accomplished by qualified personnel using qualified procedures in 

accordance with applicable codes, standards, specifications, criteria, and other special 

requirements."

Appendix K of 10 CFR Part 50, “ECCS Evaluation Models,” establishes requirements for 

analytical determinations that impact aspects of the strainer blockage issue. These analytical 

requirements include the following: (1) fission-product decay heat generation rate (impacts the 

calculated containment pool temperature), (2) break flow characteristics and discharge model 

(impacts the estimated amounts of debris), (3) post-blowdown phenomena and heat removal by 

the ECCS, and (4) required ECCS model documentation. Appendix K also specifies that single 
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failures be considered and that containment pressure be used for evaluating cooling 

effectiveness.

4.2 Regulatory Guidance

This section provides a description of regulatory guidance that applies to the strainer blockage 

issue. The NRC provides regulatory guidance on ensuring adequate long-term recirculation 

cooling following a LOCA in RG 1.82, “Water Sources for Long-Term Recirculation Cooling 

Following a Loss-of-Coolant Accident.” The guide describes acceptable methods for 

implementing applicable GDC requirements with respect to the sumps and suppression pools 

functioning as water sources for emergency core cooling, containment heat removal, and 

containment atmosphere cleanup. Guidelines for evaluating availability of the sump and 

suppression pool for long-term recirculation cooling following a LOCA are included in the RG.

Revisions 1 and 2 of RG 1.82 were issued in November 1985 and May 1996, respectively. 

Revision 1 reflected the staff’s technical findings, related to USI A-43, that were reported in 

NUREG-0897. A key aspect of the revision was the staff’s recognition that the 50% strainer 

blockage criteria of Revision 0 did not adequately address the potential for strainer blockage 

and was inconsistent with the technical findings developed for the resolution of USI A-43. It was 

assumed in Revision 0 that the minimum NPSH margin could be computed by assuming that 

50% of the strainer area was blocked by debris. GL-85-22 recommended use of Revision 1 of 

RG 1.82 for changeout and/or modifications of thermal insulation installed on primary coolant 

system piping and components. Revision 2 altered the strainer blockage guidance for BWRs 

because operational events, analyses, and research following Revision 1 indicated that the 

previous guidance was not comprehensive enough to adequately evaluate a BWR plant’s 

susceptibility to the detrimental effects caused by debris blockage of the suction strainers. 

Revision 2 of RG 1.82 addressed operational debris, as well as debris generated by a 

postulated LOCA. Specifically, this revision stated that all potential debris sources should be 

evaluated, including, but not limited to, insulation materials (e.g., fibrous, ceramic, and metallic), 

filters, corrosion material, foreign materials, and paints/coatings. Operational debris included 

corrosion products, (such as BWR suppression pool sludge), and foreign materials (although 

foreign material exclusion [FME] procedures were not specifically introduced into Revision 2). 

This revision also noted that debris could be generated and transported by the washdown 

process, as well as by the blowdown process. Other important aspects of Revision 2 included: 

the use of debris interceptors (i.e., suction strainers) in BWR designs to protect pump inlets and 

NPSH margins; the design of passive and/or active strainers; instrumentation, in-service 

inspections; suppression pool cleanliness; the evaluation of alternate water sources, analytical 

methods for debris generation, transport, and strainer blockage head loss, and the need for 

appropriate supporting test data. Revision 2 references provide further detailed technical 

guidance for the evaluation of potential strainer clogging.

Revision 2 of RG 1.82 cited RG 1.1, “Net Positive Suction Head for Emergency Core Cooling 

and Containment Heat Removal System Pumps,” for specific conditions to be used in 

determining the available NPSH for ECCS pumps in a BWR plant’s licensing basis RG 1.1 

considered the potential for degraded pump performance for ECCS and containment heat 

removal, which could be caused by a number of factors, including inadequate NPSH. If the 

available NPSH to a pump is insufficient, cavitation of the pumped fluid can occur, thereby 

significantly reducing the capability of the system to accomplish its safety functions. The proper 

performance of ECCS and containment heat removal systems should be independent of 

calculated increases in containment pressure caused by postulated LOCAs in order to ensure 
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reliable operation under a variety of postulated accident conditions. The NRC’s regulatory 

position is that the ECCS and containment heat removal systems should be designed with an 

adequate NPSH margin, assuming the maximum expected temperatures of the pumped fluids 

and no increase in containment pressure from that present before postulated LOCAs.

Revision 1 of RG 1.54, "Quality Assurance Requirements for Protective Coatings Applied to 

Water-Cooled Nuclear Power Plants," in July 2000 provided guidance regarding compliance 

with quality assurance requirements related to protective coating systems applied to ferritic 

steel, aluminum, stainless steel, zinc-coated (galvanized) steel, and masonry surfaces. The 

revision endorsed industry developed codes, standards, and guides. The American Society for 

Testing Materials (ASTM) standards cited in the regulatory position of Revision 1 for the 

selection, qualification, application, and maintenance of protective coatings in nuclear power 

plants were reviewed by the NRC staff and found acceptable. NRC issued Revision 2 of RG 

1.54 in October 2010 to update the guidance to the latest ASTM documents..

4.3 Generic Safety Issue-191

The Generic Safety Issue (GSI)-191 study, “PWR Sump Blockage,” was established to 

determine if the transport and accumulation of debris in a containment following a LOCA would 

impede the operation of the ECCS in operating PWRs. The primary objective of the GSI-191 

study was to assess the likelihood of debris induced failures of ECCS and CSS pumps at 

domestic PWRs. The technical assessment culminated in a parametric study that 

mechanistically treated phenomena associated with debris blockage. The study used analytical 

models of domestic PWRs generated with a combination of generic and plant-specific data. 

As documented in Volume 1 of NUREG/CR-6762, “GSI-191 Technical Assessment: Parametric 

Evaluations for Pressurized Water Reactor Recirculation Sump Performance,” the GSI-191 

parametric study concludes that recirculation sump clogging is a credible concern for the 

population of domestic PWRs. However, as a result of limitations with respect to plant-specific 

data and other modeling uncertainties, the parametric study does not definitively identify 

whether particular PWR plants are vulnerable to sump clogging. 

The methodology employed by the GSI-191 parametric study is based on the substantial body 

of test data and analysis documented in technical reports generated during the GSI-191 

research program and earlier technical reports generated by the NRC and industry during the 

resolution of the BWR strainer clogging issue and USI A-43. The following pertinent technical 

reports, which cover debris generation, transport, accumulation, and head loss, are incorporated 

by reference into the GSI-191 parametric study:

NUREG/CR-6770, “GSI-191: Thermal-Hydraulic Response of PWR Reactor Coolant 

System and Containments to Selected Accident Sequences,” dated August 2002. 

NUREG/CR-6762, Vol. 3, “GSI-191 Technical Assessment: Development of Debris 

Generation Quantities in Support of the Parametric Evaluation,” dated August 2002.

NUREG/CR-6762, Vol. 4, “GSI-191 Technical Assessment: Development of Debris 

Transport Fractions in Support of the Parametric Evaluation,” dated August 2002. 

NUREG/CR-6224, “Parametric Study of the Potential for BWR ECCS Strainer Blockage 

Due to LOCA Generated Debris,” dated October 1995.
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In addition to demonstrating the potential for debris to clog containment recirculation sumps, 

operational experience and the NRC’s technical assessment of GSI-191 have identified three 

integrally related modes by which post-accident debris blockage could adversely affect the 

sump strainer’s design function of intercepting debris that could impede or prevent the operation 

of the ECCS and CSS in the recirculation mode.

First, as a result of the 50% blockage assumption (in RG Revision 0), PWR sump strainers were 

typically designed with the assumption that relatively small structural loadings would result from

the differential pressure associated with debris blockage. Consequently, PWR sump strainers 

may not be capable of accommodating the substantial structural loadings that would occur due 

to debris beds that may cover essentially the entire strainer surface. Inadequate structural 

reinforcement of a sump strainer may result in its deformation, damage, or failure, which could 

allow large quantities of debris to be ingested into the ECCS and CSS piping, pumps, and other 

components, potentially leading to their clogging and failure. The ECCS strainer plugging and 

deformation events that occurred at Perry Unit 1 are further described in 

• Information Notice (IN) 93-34, “Potential for Loss of Emergency Cooling Function Due to a 

Combination of Operational and Post-LOCA Debris in Containment,” dated April 26, 1993 

and

• Licensee Event Report (LER) 50-440/93-011, “Excessive Strainer Differential Pressure 

Across the RHR [Residual Heat Removal] Suction Strainer Could Have Compromised Long 

Term Cooling During Post-LOCA Operation,” submitted May 19, 1993. 

These documents were cited for the credibility of this concern for strainers that have not been 

designed with adequate reinforcement.

Second, in some PWR containments, the flowpaths by which containment spray or break flows 

return to the recirculation sump may include “chokepoints” at which the flow path becomes so 

constricted that it could become blocked with debris following a high-energy line break (HELB). 

For example, chokepoints may include drains for pools, cavities, or isolated containment 

compartments, and other constricted drainage paths between physically separated containment 

elevations. As a result of debris blockage at certain chokepoints, substantial amounts of water 

required for adequate recirculation could be held up or diverted into containment volumes that 

do not drain to the recirculation sump. The holdup or diversion of water assumed to be 

available to support sump recirculation could result in an available NPSH for ECCS and CSS 

pumps that is lower than the analyzed value, thereby reducing assurance that recirculation 

would function successfully. A reduction in available NPSH directly affects sump strainer design 

because the NPSH margin of the ECCS and CSS pumps should be conservatively calculated in 

order to determine the required surface area of sump strainers when debris loadings are 

considered. Significant holdup of inventory could also result in the lack of full submergence for 

some strainers. The NRC’s GSI-191 research identified the holdup or diversion of recirculation 

sump inventory as an important and potentially credible concern, and a number of LERs 

associated with this concern have further confirmed both its credibility and potential significance. 

These LERs include:

LER 50-369/90-012, “Loose Material Was Located in Upper Containment During Unit 

Operation Because of an Inappropriate Action,” McGuire Unit 1, submitted August 30, 

1990.

LER 50-266/97-006, “Potential Refueling Cavity Drain Failure Could Affect Accident 

Mitigation,” Point Beach Unit 1, submitted February 19, 1997.
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LER 50-455/97-001, “Unit 2 Containment Drain System Clogged Due to Debris,” Byron 

Unit 2, submitted April 17, 1997.

LER 50-269/97-010, “Inadequate Analysis of ECCS Sump Inventory Due to Inadequate 

Design Analysis,” Oconee Unit 1, submitted January 8, 1998.

LER 50-315/98-017, “Debris Recovered from Ice Condenser Represents Unanalyzed 

Condition,” D.C. Cook Unit 1, submitted July 1, 1998.

Third, debris blockage at flow restrictions within the ECCS recirculation flowpaths downstream 

of the sump strainer is of potential concern for PWRs. For this mode of debris blockage to 

occur, pieces of debris would need to have dimensions that would allow them to pass through 

the sump strainer’s intended openings, or through strainer defects such as gaps or breaches. 

This debris could then become lodged at downstream flow restrictions such as pump internals, 

HPSI throttle valves, fuel assemblies, or containment spray nozzles. In particular, conditions 

conducive to downstream debris blockage may be present at PWRs with strainer defects, and at 

PWRs where the dimension of the sump strainer’s openings is not the most restrictive point in 

the ECCS and CSS recirculation flowpaths. Downstream debris blockage at restrictions in the 

ECCS flow path could impede or prevent the recirculation of coolant to the reactor core, thereby 

leading to inadequate core cooling. Similarly, downstream debris blockage at restrictions in the 

CSS flow path could impede or prevent CSS recirculation, thereby leading to inadequate 

containment heat removal. 

Three additional items increased the urgency of the NRC staff’s efforts to ensure that PWR 

licensees were aware of and had appropriately responded to the above concerns about the 

potential for debris blockage. These were:

1 LER submitted by the licensee for Davis-Besse Unit 1 that declared the recirculation 

sump inoperable (LER 50-346/02-005-01) 

2 subsequent LER submitted by the Davis-Besse licensee that declared the high-pressure 

injection (HPI) pumps inoperable (LER 50-346/02-002-00)

3 NRC-sponsored risk study concerning operator actions to mitigate sump clogging (Kern 

and Thomas, 2003). 

In February 2003, Los Alamos National Laboratory published the NRC-sponsored technical 

report LA-UR-02-7562 entitled, “The Impact of Recovery From Debris-Induced Loss of ECCS 

Recirculation on PWR Core Damage Frequency” (Kern and Thomas, 2003). The report 

analyzes the potential risk benefit of operator actions to recover from sump clogging events 

using a generic probabilistic model to demonstrate that the potential increase in risk due to 

sump clogging could be reduced by approximately one order of magnitude if PWR licensees 

have appropriate mitigation measures in place. 

In response to these items associated with the potential post-accident debris blockage concerns 

identified in NRC Bulletin 03-01, the NRC requested that individual PWR licensees submit 

information on an expedited basis to document that they have either (1) analyzed the ECCS and 

CSS recirculation functions with respect to the identified post-accident debris blockage effects, 

taking into account the recent research findings and determined that compliance exists with all 

applicable regulatory requirements, or (2) implemented appropriate interim compensatory 
4-7

measures to reduce the risk which may be associated with potentially degraded or nonconforming ECCS and CSS recirculation functions while evaluations to determine compliance 

proceeded. 

To assist in determining whether the ECCS and CSS recirculation functions are in compliance 

with existing applicable regulatory requirements, addressees were directed to use the guidance 

in Draft Regulatory Guide 1107 (DG-1107), “Water Sources for Long-Term Recirculation 

Cooling Following a Loss-of-Coolant Accident,” dated February 2003. The NRC also published 

a technical report entitled NUREG/CR-6808, “Knowledge Base for the Effect of Debris on 

Pressurized Water Reactor Emergency Core Cooling Sump Performance,” dated February 

2003, which is designed to serve as a reference for plant-specific analyses with regard to 

whether a sump would perform its function without preventing the operation of the ECCS and 

CSS pumps. 

Conditions at various PWRs were expected to vary with respect to susceptibility to post-accident 

debris blockage, and various options may have been available to addressees for preventing or 

mitigating the effects of debris blockage. For these reasons, addressees that were unable to 

confirm compliance with all existing regulatory requirements within 60 days were asked to 

consider a range of possible interim compensatory measures and to implement those that they 

deemed appropriate, based upon the specific conditions associated with their plants. As stated 

above, the risk benefit of certain interim compensatory measures was demonstrated by the 

NRC-sponsored technical report LA-UR-02-7562 (Kern and Thomas, 2003). Addressees 

electing to implement interim compensatory measures in response to this bulletin were asked to 

ensure that the interim measures are implemented as soon as practical. 

A parametric evaluation was performed as part of the GSI-191 study to demonstrate the 

potential for recirculation-sump clogging for operating PWRs. Each of the 69 domestic PWRs 

was modeled in the evaluation using a mixture of generic and plant-specific data. The minimum 

amount of debris accumulation on the sump strainer that was needed to exceed the required 

NPSH margin for the ECCS and CSS pumps was determined for each of the 69 representative 

models. GSI-191 PWR research activities, as well as existing BWR research results, were used 

to support the development of these models and the input to these models. The evaluation 

considered small, medium, and large LOCAs and used both favorable and unfavorable 

assumptions, relative to the plant, for a number of parameters. The results of the parametric 

evaluation formed the technical basis for making the determination that sump blockage was a 

credible concern. 

However, the parametric evaluation had a number of limitations. The most notable were 

attributed to the extremely limited plant-specific data available to the study. The need for more 

accurate plant-specific assessments of the adequacy of the recirculation function of the ECCS 

and CSS for each operating PWR was indicated clearly. The Nuclear Energy Institute (NEI) 

also recognized this need and conducted a program to develop evaluation guidance for the 

industry. NEI issued a report (NEI, 2004) to provide licensees with guidance for evaluating the 

post-accident performance of the containment sump screen for a PWR. The report presented 

an approach called, “Baseline Evaluation Method,” for evaluating the generation and transport 

of debris to the sump screen, and the resulting head loss across the sump screen. Section 1 of 

the report contains an introduction to the PWR strainer debris issue, including a historical review 

describing the steps that led to the current understanding. Section 2 is a high-level summary of 

the overall process considerations that need to be addressed during the evaluation process, 

while Section 3 describes a Baseline Evaluation Method that may be applied to all PWR’s and 

provides sample calculation using the Baseline Evaluation Method. In Section 5, refinements in 
4-8

administrative control and design are discussed. Section 6 provides a guidance on a riskinformed evaluation. Section 7 provides guidance for additional design considerations.The 

document did not address the implementation and/or licensing of any design or operational 

changes resulting from the use of the evaluation methodology. 

The NRC staff has performed a safety evaluation of the NEI guidance report (SE NEI-04-07, 

ML043280007, 2004) and found portions of the proposed guidance to be acceptable. For the 

areas that were found to be inadequate, the staff stipulated conditions and limitations for use of 

the NEI report, including alternative guidance which supplemented the guidance in the NEI 

submission. It was concluded that the resultant combination of the NEI submission and staff 

safety evaluation provided an acceptable overall guidance methodology for the plant-specific 

evaluation of ECCS or CSS sump performance with specific attention given to the potential for 

debris accumulation that could impede or prevent the ECCS or CSS from performing its 

intended safety functions. Methods for calculating strainer head loss due to debris 

accumulation on the strainer or on downstream components was not within the scope of this 

guidance. 

4.4 NRC Bulletin 2003-01

The NRC issued Bulletin 2003-01 to:

(1) Inform addressees of the results of NRC-sponsored research identifying the potential 

susceptibility of PWR recirculation sump strainers to debris blockage in the event of a HELB 

requiring recirculation operation of the ECCS or CSS.

(2) Inform addressees of the potential for additional adverse effects due to debris blockage of 

flowpaths necessary for ECCS and CSS recirculation and containment drainage.

(3) Request that, in light of these potentially adverse effects, addressees confirm their 

compliance with 10 CFR 50.46(b)(5) and other existing applicable regulatory requirements, or 

describe any compensatory measures implemented to reduce the potential risk due to postaccident debris blockage as evaluations to determine compliance proceed.

(4) Require addressees to provide the NRC a written response in accordance with 10 CFR 

50.54(f).

All addressees were requested to provide a response within 60 days that contains the 

information in either Option 1 or Option 2: 

Option 1: State that the ECCS and CSS recirculation functions have been analyzed with respect 

to the potentially adverse post-accident debris blockage effects identified in this bulletin, taking 

into account the recent research findings described in the Discussion Section, and that they are 

in compliance with all existing applicable regulatory requirements.

Option 2: Describe any interim compensatory measures that have been implemented or that will 

be implemented to reduce the risk that may be associated with potentially degraded or 

nonconforming ECCS and CSS recirculation functions, until an evaluation to determine 

compliance is complete. If any of the interim compensatory measures listed in the Discussion 

Section will not be implemented, provide a justification. Additionally, for any planned interim 

measures that will not be in place before the response to this bulletin, submit an implementation 
4-9

schedule and provide the basis for concluding that their implementation is not practical until a 

later date.

The NRC justified the information request on the basis of research and analysis suggesting that 

(1) most PWR licensees’ current safety analyses do not adequately address the potential for the 

failure of the ECCS and CSS recirculation functions as a result of debris blockage, and (2) the 

ECCS and CSS recirculation functions at a significant number of operating PWRs could become 

degraded as a result of the potential effects of debris blockage identified in this bulletin. An 

ECCS that is incapable of providing long-term reactor core cooling through recirculation 

operation would be in violation of 10 CFR 50.46. A CSS that is incapable of functioning in the 

recirculation mode may not comply with GDC 38 and 41 or with other plant-specific licensing 

requirements or safety analyses. Furthermore, to address the risk that may be associated with 

potentially degraded or nonconforming ECCS and CSS recirculation functions, NRC required 

addressees that are unable to confirm regulatory compliance to implement compensatory 

measures until a determination can be made. 

4.5 NRC Generic Letter (GL) 2004-02

The NRC issued GL-2004-02 to:

(1) Request that addressees perform an evaluation of the ECCS and CSS recirculation 

functions in light of the information provided in the letter and, if appropriate, take additional 

actions to ensure system function. Additionally, addressees were requested to submit the 

information specified in this letter to the NRC. This request was based on the potential 

susceptibility of PWR recirculation sump strainers to debris blockage and on the potential for 

additional adverse effects due to debris blockage of flowpaths necessary for ECCS and CSS 

recirculation and containment drainage.

(2) Require addressees to provide the NRC a written response in accordance with 10 CFR 

50.54(f).

To assist in determining, on a plant-specific basis, the impact on sump strainer performance and 

other related effects of extended post-accident operation with debris-laden fluids, addressees 

were permitted to use the guidance in RG 1.82, Revision 3, “Water Sources for Long-Term 

Recirculation Cooling Following a Loss-of-Coolant Accident,” dated November 2003.

The timeframes for addressee responses in this generic letter were selected to allow (1) 

adequate time to perform an analysis, (2) proper design and installation of any identified 

modifications, (3) adequate time to obtain NRC approval, as necessary, for any licensing basis 

changes, (4) adequate time to obtain NRC approval, as necessary, for any exemption requests, 

and (5) closure of the generic issue in accordance with the published schedule. 

The NRC requested all addressees to take the following actions: Using an NRC-approved 

methodology, perform an evaluation of the potential for adverse effects of post-accident debris 

blockage on ECCS and CSS recirculation. All postulated accidents should be considered for 

which the recirculation of these systems is required. Alternative methodologies were also 

allowed, but were subject to additional NRC review.

Further, NRC requested all addressees to provide the following information within 90 days:
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(a) A description of the methodology that is or will be used to analyze the ECCS and CSS 

recirculation functions considering the potential for post-accident debris blockage. Also, specify 

the completion date for the analysis that will be performed.

(b) A statement of whether a containment walkdown will be performed in support of the analysis. 

Also, justification if no containment walkdown will be performed. If a containment walkdown is 

planned, provide the methodology to be used and the planned completion date.

In addition, NRC requested the licensees to provide the following information no later than 

September 1, 2005:

(a) Confirmation that the ECCS and CSS recirculation functions are or will be in compliance with 

the applicable regulatory requirements. Also, the configuration of the plant that will exist once 

all required modifications have been made and the licensing basis has been updated to reflect 

the results of the analysis. 

(b) A general description of and implementation schedule for corrective actions, including any 

plant modification that the licensee identified while responding to this generic letter. 

(c) A description of the methodology that was used to perform the analysis. 

(d) The following information was requested:

(i) The minimum available NPSH margin for the ECCS and CSS pumps with an unblocked 

sump strainer.

(ii) The submerged area of the sump strainer under the current design and a statement as to 

whether the strainer is fully or partially submerged at the time of the switchover to sump 

recirculation.

(iii) The maximum head loss postulated from debris accumulation on the sump strainer, and a 

description of the primary types of debris that result in this head loss. Debris created by the 

post-LOCA containment environment (thermal and chemical) and CSS washdown were to be 

considered in the analyses. Examples of this type of debris are disbonded coatings in the form 

of chips and particulates and chemical precipitants caused by chemical reactions in the pool.

(iv) The basis for concluding that the inventory required to ensure adequate recirculation would 

not be held up or diverted by debris blockage at chokepoints in the containment.

(v) The basis for concluding that adequate core or containment cooling would result considering 

debris blockage at flow restrictions in the ECCS and CSS flow paths downstream of the sump 

strainer. Also, an evaluation of the adequacy of the sump strainer’s design openings and the 

basis for concluding that adverse gaps or breaches are not present in the strainer.

(vi) Verification that close-tolerance subcomponents in pumps, valves, and other ECCS and 

CSS components are not susceptible to plugging or excessive wear due to extended postaccident operation with debris-laden fluids.

(vii) Verification that the strength of any trash rack is adequate to protect the strainers from 

missiles and other large debris. Also, verification that the trash racks and sump strainers are 

capable of withstanding the loads imposed by expanding jets, missiles, the accumulation of 
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debris, and pressure differentials caused by post-LOCA blockage under predicted flow 

conditions.

(viii) A description of any active approach selected (e.g., backflushing, powered strainers) in lieu 

of or in addition to a passive approach.

(e) A description and schedule for any changes to the plant licensing bases resulting from 

actions taken in response to the generic letter. Also, any licensing actions or exemption 

requests needed to support changes to the plant-licensing basis.

(f) A description of existing or planned programmatic controls that ensure that potential sources 

of debris in the containment (e.g., insulation, signs, coatings, and foreign materials) will be 

assessed for potential adverse effects recirculation. 

4.6 NRC Guidance on Strainer Head Loss and Vortexing

The Guidance Report, Pressurized Water Reactor Sump Performance Evaluation Methodology 

(NEI-04-07), was developed by Westinghouse and Alion Science and Technology under the 

sponsorship of the Westinghouse and Babcock & Wilcox Owners Groups and under the 

technical guidance of the NEI PWR Sump Performance Task Force. The methodology in the 

document provided basic guidance on approaches and various methods for evaluating sump 

performance but recognized that the best strategy for each plant could involve a combination of 

methods since PWRs vary greatly in containment size, floor layout, sump configuration, 

insulation types and location, and post-LOCA operational requirements. The Baseline 

Evaluation Method, and the guidance to perform the Baseline Evaluation Method, provided a 

conservative approach for evaluating the generation and transport of debris to the sump screen, 

and the resulting head loss across the sump screen.

The NRC staff evaluated each area of the Guidance Report, concluded that the guidance 

proposed by NEI, as approved in accordance with the NRC Safety Evaluation of NEI-04-07 

(ML04328007), provided an acceptable evaluation methodology and established the necessary 

basis and provided the realistic conservatism for an acceptable PWR guidance document. 

However, the staff questioned aspects of the baseline that are clearly not conservative, while 

other aspects are conservative. The subject aspects were identified at the appropriate locations 

in the SE Report (ML04328007). NRC further stipulated that acceptance of the baseline 

evaluation requires that the approach results in an evaluation that, overall, is realistically 

conservative.

At the time that the NEI guidance report and staff SE were issued, methodologies for performing 

strainer head loss tests had not been developed to the point that consistent results could be 

attained. Strainer test vendors used different test methods and made different assumptions 

when developing test procedures. To establish appropriate staff review criteria for head loss 

testing, the NRC staff developed review guidance and documented the staff’s positions for the 

areas important to the topic in “NRC Staff Review Guidance Regarding Generic Letter 2004-02 

Closure in the Area of Strainer Head Loss and Vortexing” (ML080230038) in March 2008. The 

important aspects of strainer evaluations discussed in this guidance are presented in some 

detail in Section 5 of this document. 

The staff recognized that because the procedures for integrated prototypical head loss testing 

were still being developed by the industry the document could be revised to reflect new 

information. While the NRC staff intended to use this guidance in its review, licensees were 
4-12

allowed to use this guidance in their strainer evaluations. Licensees were also allowed to use 

alternative approaches to resolve sump performance issues as long as the approach was 

adequately justified and complied with the NRC’s regulations. 

4.7 NRC Guidance on Coatings Evaluation

In March 2008, NRC staff provided guidance on the information needed for a supplemental 

response to GL-04-02 in the review area of protective coatings. In April 2010, NRC provided a 

supplement to this guidance document (ML080230462). The document described acceptable 

technical assumptions based on research conducted by the NRC and industry. Both the NRC 

and the industry conducted numerous testing efforts to address technical uncertainties in areas 

such as zone of influence (ZOI), coating debris characteristics, unqualified coating performance, 

and assessment of qualified coatings. Licensees were given an option to provide an 

interpretation of the test data from the industry test reports that differed from the NRC staff 

perspective and to supply adequate technical justification in the supplemental response to 

support the licensee’s interpretation. 

The NRC requested information in the following areas to support closure of GL-04-02 in the 

area of protective coatings:

1. A summary of type(s) of coating systems used in containment, (e.g., Carboline CZ 11 

Inorganic zinc primer and Ameron 90 epoxy finish coat). If licensees are taking credit for a 

reduction of unqualified coating debris based on the Original Equipment Manufacturers 

(OEM) coatings testing program of the Electric Power Research Institute, an accurate 

estimate of the quantities of each coating type and its substrate may be necessary.

2. Description of the assessment program for the containment coating condition. This 

description should include the frequency, extent, and method of coating assessment. It 

should also discuss qualification of personnel. A description of how degraded coatings are 

reported, tracked, remediated, and/or scheduled for future remediation is also needed. 

Licensees were allowed to reference the EPRI coatings adhesion-testing program as 

confirmation of the validity of their coatings assessment program (EPRI, 2007a). 

3. Description and bases for assumptions about coatings debris generation. Based on the 

NRC generic safety evaluation (SE, ML043280007), the licensees were to use a coatings 

ZOI spherical-equivalent as determined by plant-specific analysis based on experimental 

data that correlate to plant materials over the range of temperatures and pressures of 

concern, or 10D (10 pipe diameters). In addition, the NRC generic SE recommended that 

licensees assume 100% failure of unqualified coatings.

4. Description of which debris characteristics were assumed, i.e., chips, particulate, size 

distribution, and bases for the assumptions. The NRC generic SE addresses two scenarios 

for formation of a fiber bed on the sump strainer surface. For a thin-bed case, the SE states 

that all coating debris should be treated as particulate and assumes 100% transport to the 

sump strainer. For the case in which no thin bed is formed, the SE states that the coating 

debris should be sized on the basis of plant-specific analyses for debris generated from 

within the ZOI and from outside the ZOI, or that a default chip size equivalent to the area of 

the sump strainer openings should be used.

5. Description and bases for assumptions made in analysis of post-LOCA paint debris 

transport. If less than 100% of the coating debris generated is analyzed to arrive at the 
4-13

strainer surface, the basis for settlement of the debris should be assessed. That basis may 

be computational fluid dynamics (CFD) analysis, plant-specific transport testing, NRCsponsored coating chip transport testing (NUREG/CR-6916), or some combination of these. 

If coatings debris is assumed to settle, a detailed description of the debris characteristics is 

needed and should include the assumed chip or particle size and the basis for that 

assumption.

6. Discussion of testing regarding suction strainer head loss testing performed as it relates to 

both qualified and unqualified coatings and type and basis for the surrogate material used to 

simulate coatings debris. Licensees were asked to address the type of surrogate material 

used, the size range of surrogate coatings debris, and the density of the surrogate debris, 

compare the surrogate debris characteristics to the actual coatings debris characteristics, 

and establish that the choice of surrogates conservatively represents the coating debris that 

is expected in a LOCA and the characteristics of the coatings debris assumed in the 

mechanistic analysis.

4.8 NRC Guidance on Evaluations of Plant-Specific Chemical Effects For PWRs

In March 2008, the NRC provided guidance on the important technical issues to be considered 

when reviewing plant-specific chemical effect evaluations of individual licensees in response to 

GSI-191, “Assessment of Debris Accumulation on PWR Sump Performance.” The NRC also 

provided guidance to licensees on the content of the chemical effects portion of their final 

supplemental responses to GL-04-02. The fundamental issue requiring assessment was 

whether the plant-specific evaluations appropriately address the chemical effects that can occur 

following a postulated LOCA (NRC, 2008c, ML080380214).

In the PWR post-LOCA environment, several challenges are created to material integrity based 

on temperature, chemical reactions, and effects from sprayed and pooled water. During a 

LOCA, materials in the ZOI of the break can become debris that may be transported to the 

sump area, where spray solution, spilled reactor coolant, and borated water from other safety 

injection sources are accumulating. The combination of spray chemicals, insulation, corroding 

metals, and submerged materials can create a potential condition for the formation of chemical 

substances that may impede the flow of water through the sump strainers or that may affect 

downstream components in the emergency core cooling or reactor coolant systems.

Evaluations of plant-specific chemical effects should use a conservative analytical approach. In 

general, areas considered include:

• Break selection and location

• Debris generation

• Latent debris

• Debris transport

• Chemical interactions ahead of the sump strainer

• Prolonged interaction (chemical) with recirculating liquid while materials are impinged on 

the sump strainer

• Potential of debris to decompose and generate suspended particulates in the liquid 

flowing over the debris

• Head loss

• Potential chemical effects on components downstream of the sump strainer
4-14

The flow diagram in Figure 4.8-1 provides a logical sequence that outlines the paths of various 

plant-specific approaches to chemical effect evaluations. The diamonds represent decision 

points for testing that needs to be performed. These decision points lead to options used in 

vendor testing. The description for the diamond identifies the options that may be selected. 

The evaluation process flow path chosen by the licensee can affect the relevant technical issues 

to be addressed as part of the plant-specific evaluation. These topics are further described in 

the sections that follow. 
4-15

Figure 4.8-1. Chemical Effect Evaluation Process Flow Diagram
4-16

Debris Characteristics

Plants should follow the NEI guidance report (NEI, 2007) supplemented by the NRC safety 

evaluation (NRC-SER-2004), to determine plant-specific debris characteristics. An alternative 

approach may be used with justification and NRC concurrence. Consistent with the safety 

evaluation, the licensee testing should simulate the debris from the break location that produces 

the maximum head loss.

Plants that are able to demonstrate sufficient bare strainer area may use a more simplified 

chemical effect evaluation because chemical precipitates are expected to pass through a bare 

strainer. The methodology used to determine sufficient clean strainer area should demonstrate 

that sufficient bare strainer area will remain available to support the design basis flow rate to the 

reactor core, considering all break locations within the uncertainties of debris generation and 

transport.

Debris Bed Formation

Licensees should follow the NEI guidance report (NEI, 2004) supplemented by the NRC safety 

evaluation (NRC-SER-2004), to determine the bed characteristics of plant-specific debris. 

Alternative approaches are acceptable if justified. Licensees should discuss why the debris 

from the break location selected for plant-specific head loss testing with chemical precipitate 

yields the realistic head loss for the plant condition.

Plant-Specific Materials and Buffers

To assess potential chemical effects, licensees should identify the specific materials in their 

containment building that may react with the post-accident containment environment. Plant 

materials should identify metallic and non-metallic items in the containment building, including 

insulation types, concrete, and coatings. Other considerations should include plant systems in 

containment that may contain chemicals (e.g., reactor coolant pump oil, corrosion prevention 

chemicals in thermal barrier system, air handling system, drying materials such as molecular 

sieves, etc.). The materials inventory evaluation includes overall mass, location in the 

containment, and potential for being sprayed or immersed following a LOCA.

Approach to Determine Chemical Source Term

This is the first decision point in determining the method to be selected for plant-specific testing. 

The strainer vendor selected by the licensee decides upon the basic approach to determine the 

chemical source term. These require single chemical-effect tests that are later combined via a 

specific algorithm or integrated chemical effect tests (ICETs) in which a plant-specific mixture of 

materials is tested in a representative post-LOCA environment to identify the specific chemical 

effects that will be observed in the plant. The evaluation should consider the chemical form of 

each of these materials and the potential for interaction with the environment during the LOCA 

and the subsequent ECCS mission time.

Separate Effects Decision

The methods to assess the plant-specific chemical effects are based on single-variable test 

measurements in WCAP-16530 (Lane et al., 2006) or on single-effects bench testing developed 

by the strainer vendors (e.g., Atomic Energy of Canada Ltd.). Input of plant parameters (e.g., 

sump temperature, pH, and containment spray durations) into the WCAP-16530 spreadsheet 
4-17

should be in a manner that results in a conservative amount of precipitate formation. In other 

words, plant parameter input selection will not be biased so as to lower the predicted amount of 

precipitate beyond that justified.

Precipitate Generation

Two basic methods of precipitate generation have been used in strainer head loss tests. Each 

of these methods has advantages and drawbacks. In the first method, chemicals are injected 

into the flowing stream of the test flume. Both solutions initially contain no precipitates, and the 

combination of the two causes a reaction leading to precipitation from a homogeneous solution. 

The second method creates a surrogate precipitate in a separate mixing tank, and the 

precipitate is then injected into the flowing system to simulate the transport of precipitated 

material to the sump strainer area. This leads to precipitation from a heterogeneous solution. 

The time-dependency effect of injection of the precipitate into the loop should be understood in 

terms of the amount of chemical that transforms into precipitate and the timing of precipitation 

relative to test termination.

Debris Transport

Debris transport represents another decision point in the flow chart. Plant-specific analysis 

determines the amount of debris that is generated and transported to the sump strainer. Test 

vendors have selected two basic debris transport approaches. These include the attempt to 

credit settlement of debris away from the strainer surface, i.e., “near-field” settlement, and the 

use of agitation or other means to keep debris suspended so that essentially all debris analyzed 

as reaching the strainer in the plant reaches the strainer in head loss testing.

Integrated Head-Loss Testing

For tests with near-field settlement credit in which settling of chemical precipitates occur, it is 

critical that the precipitate used in these tests settle no more rapidly than would be expected in 

the projected plant environment. For tests without near-field settlement credit, the surrogate 

chemical debris should be kept suspended in solution until it is able to deposit on the test 

strainer’s surface. Low-flow areas of test tanks and flumes should be agitated mechanically or 

hydraulically so that the debris does not settle out before reaching the strainer surface.

Test Termination Criteria

All measurement objectives that determine test termination should be stated before 

commencement of the test. Factors that should be considered in these measurement 

objectives are:

1 Has all the material that will yield an effect had the opportunity to get into solution?

2 Do the test termination criteria represent a point in time where formation of further 

significant impediments to flow will not occur?

3 For precipitates formed by chemical injection into the test loop, measurement of the test 

solutions at various times in the event sequence is needed to show that the precipitation 

is completed before test termination.
4-18

4 Have the overall chemical effects stopped or slowed to the point that any further 

changes will be insignificant?

Data Analysis

When evaluating head loss test results, licensees should consider items such as settlement of 

debris and precipitates, presence of debris bed boreholes, test repeatability, and pressure drop 

across the bed as a function of time.
5-1

5 STATE-OF-THE-ART RESOLUTION METHODOLOGY

An evaluation of recirculation strainer issues began with the declaration of USI A-43 in 1979. 

Issuance of USI A-43 was based on the safety concerns associated with potential ingestion of 

air and debris into either PWR sump screens or BWR pump suction intake strainers, and the 

potential blockage of these strainers. The overall blockage issue has continued beyond the 

closure of USI A-43, through resolution of the BWR blockage issue and the GSI-191 PWR 

blockage issue, and finally with the ongoing BWR reassessment based on recent PWR-related 

research. Disparities between PWRs and BWRs were identified in NUREG/CR-7011. The 

techniques and guidance associated with evaluation of the issue have evolved over a 

considerable period, with research efforts being based on the state of the methodology of the 

time. An understanding of this evolutionary process is needed to fully understand and apply the 

accumulated base of knowledge.

Revision 0 of RG 1.82 included a 50% strainer blockage criterion that was recognized as 

technically inconsistent with the findings related to the resolution of USI A-43, as documented in 

NUREGs-0869 and 0897. The general idea of the 50% blockage criterion is that debris would 

cover no more than 50% of the screen surface area, leaving the remaining area unobstructed. 

We now know that the flow velocities approaching the large passive replacement strainers now 

installed in PWR containments are generally too slow to entrain larger debris that has a higher 

probability of settling. As such, the more likely debris accumulation would consist of small 

groups of fibers and particles that tend to remain suspended in water with moderate flow 

turbulence. Such fine debris is not significantly influenced by gravitational pull and, therefore, 

tends to accumulate more or less equally on surfaces of any orientation. Further, this type of 

debris accumulates on all screen surfaces, leaving no strainer screen area free and clear of 

debris. The NRC staff has repeatedly observed this accumulation behavior during visits to 

vendor test sites (e.g., a trip report to the Alden Research Laboratory by S. Smith dated 

4/30/2008 in document ML 080920398 discussed this behavior with distinctive photos included). 

These debris accumulation realities are very different from the accumulation process assumed 

before initiation of the debris blockage concerns. Similarly, debris accumulation on BWR 

suppression pool recirculation strainers would result in debris accumulation on all strainer 

surfaces, leaving no area completely uncovered. However, unique to BWRs, the initial vigorous 

downcomer discharge into the suppression pool immediately following a LOCA causes 

substantial pool turbulence capable of maintaining larger debris in suspension until the pool 

turbulence dissipates. 

Investigation of the strainer blockage phenomena and processes has continued to evolve over a 

period of approximately 30 years. Early head loss testing, as presented in NUREG/CR-2982, 

published in 1983, was based on fiberglass insulation debris prepared as either as-fabricated 

pieces or hand-torn shreds. Neither preparation technique resulted in a significant contribution 

from suspendable fines. In addition to a non-prototypical preparation of the test debris, early 

head loss testing failed to recognize the importance of particulates so that head loss testing was 

based on fibrous debris alone resulting in an underassessment of potential head losses. The 

preparation of fibrous debris in head loss testing has evolved from using pieces of as-fabricated 

insulation and hand-torn shreds during the resolution of USI A-43, to machine-shredded 

insulation used during the BWR resolution, to the special attention paid to preparing adequate 

suspendable fines during the GSI-191 resolution. In addition, flow velocities through the strainer 

surfaces slowed considerably from the 0.1 to 3 ft/s associated with the early PWR strainers to 

the typical velocity of about 0.005 ft/s for the large replacement PWR strainers (velocities based 

on total screen area). Velocities also slowed through the replacement BWR strainers with 

respect to the initial strainer installations. State-of-the-art head loss testing requires the 
5-2

prototypical or conservative representation of suspended fibrous and particulate fines that can 

accumulate as a relatively thin layer with a much lower porosity than that of fibrous debris alone. 

A thin layer of debris with a relatively high particulate to fiber ratio resulting in a significant head 

loss has been referred to as a thin-bed debris bed.

The potential sources for particulate debris were not fully recognized in the early evaluations of 

strainer blockage; for example, coating particulates generated by the impact of the 

depressurizing jet were not realistically considered until the GSI-191 PWR resolution. The BWR 

resolution considered coating debris only as paint chips (NUREG/CR-6224). Calcium silicate 

insulation debris was treated in the early assessments (NUREG/CR-2982) as insoluble and 

buoyant (NUREG-0897). We now know that LOCA-generated calcium silicate insulation debris 

can include a substantial quantity of relatively fine particulates and that a relatively small 

quantity of such calcium silicate fines can cause significant strainer head losses when combined 

with fibrous debris. The potential effects of calcium silicate were not recognized during the 

original BWR resolution. Further, it was found that calcium silicate debris from calcium silicate 

insulation manufactured by different processes (e.g., press shaping or molding shaping) could 

have different characteristics. For BWRs, iron-oxide corrosion products in the suppression pool 

can be a dominant type of particulate debris in terms of quantity.

Implementation of large passive replacement strainers in PWRs and BWRs changed the focus 

of the debris transport analyses due to the resulting lower strainer approach velocities. With 

PWR strainer perimeter approach velocities of less than about 0.1 ft/s (based on the perimeter 

area of the overall strainer rather than the total surface area), even the fibrous shreds that have 

settled onto the sump pool floor are not likely to become sufficiently re-entrained to leave the 

floor and accumulate on the strainer. The RMI debris will typically have settled to the PWR pool 

floor and will remain there with the possible exception of a few floating pieces of crumpled 

debris having retained trapped pockets of air. Similarly, the bulk of the coating paint chips will 

reside on the pool floor. Again, it is the suspendable fines that are most important in strainer 

head loss testing. With BWR recirculation strainers, vent downcomer discharge due to RCS 

depressurization could churn the suppression pool so that larger debris can accumulate on the 

strainer screen areas before the turbulence dissipates.

The significance of the impact of particulate penetration of the recirculation strainer screens was 

underestimated in the early debris evaluations. The report NUREG-0897, published in 1985, 

found that ingestion of small particulates did not appear to pose a pumping problem for the postLOCA circulating pumps, and that catastrophic failure of shaft seals was unlikely. This issue 

was reconsidered in the resolution of GSI-191 under the important subject of downstream 

effects, which was not evaluated during the BWR resolution. Prior to GSI-191 the effects of 

chemical interactions and chemical precipitates on strainer blockage had not been evaluated 

realistically. 

The evolution of debris generation modeling began with the assumption of conical jets from the 

two completely separated restrained ends of broken piping striking containment structures and 

other piping (NUREG/CR-2791). A USI A-43 plant-specific probabilistic study (NUREG/CR3394) which evaluated a large number of potential weld breaks, needed a more efficient method 

of calculating debris generation than considering all the potential orientations of the cone model 

for each of the weld breaks. A three-region hemispherical model was adopted to simulate 

projected zones-of-destruction (ZOI), i.e., regions of space where insulation is postulated to 

become damaged into debris. A hemisphere was projected from the end of each broken pipe 

extending first to a radius of 3 times the diameter of the broken pipe (Region 1), then onto 5 

times the diameter (Region 2), and then onto 7 times the diameter (Region 3). Within each 
5-3

radial region (to 3, then 3 to 5, and then 5 to 7 diameters), a specified fraction of insulation 

contained therein was assumed destroyed into debris that could reach the strainer and affect 

head loss, leaving the remainder of the insulation intact. The degree of destruction was 

generally assumed to lessen with distance from the break. The fractions of insulation assumed 

destroyed have been referred to as the destruction fractions. Beyond a radius of 7 diameters, 

the insulation was assumed to remain undamaged. The NRC BWR reference plant study 

(NUREG/CR-6224) that supported the BWR resolution adopted this probabilistic model but 

extended it to a full sphere to consider both ends of a double-ended guillotine break (DEGB) 

simultaneously. The spherical model was adapted for the GSI-191 evaluation as well, except 

for the specifically selected destruction regions. Here, the outer radius of the ZOI sphere was 

specified as an outer threshold for destruction, and the overall debris size distribution was 

based on experimental data. In addition to practical convenience, the rationale for the use of 

the spherical ZOI model is that it accounts for jet reflections, jet interference, and pipe whip 

assuming the insulation is located relatively uniformly throughout containment. Because the 

spherical approach is the primary model in use, it is considered state-of-the-art; however users 

should remain aware of the possibilities of a directed jet striking either an unusually dense 

source of insulation or a significant source of problematic insulation that the spherical model 

does not include within its boundary. 

5.1 System Pumps

The ECCS and containment heat removal system (CHS) are to be designed so that sufficient 

available NPSH is provided to the system pumps, with no increases in containment pressure 

from that present before the postulated LOCA. The ECCS and CSS pumps are normally 

centrifugal pumps. For a centrifugal pump to operate properly, there should be adequate 

margin between the available and the required NPSH. Failure to provide and maintain 

adequate NPSH for the ECCS and CSS pumps could cause cavitation and subsequent failure 

to deliver the amount of water assumed in design-basis LOCA safety analyses. Because the 

safety of a nuclear power plant depends on the performance of the pumps in the ECCS and the 

containment heat removal system, it is important to maintain an adequate margin between the 

available and required NPSH under all potential conditions. The NRC guidance on this issue 

appears in RG 1.82, GL-97-04, NEI 04-07 (NEI, 2004), and NRC-SER-2004.

The definition of NPSHM from RG 1.82 is the difference between the NPSHA and NPSHR. The 

NPSHA is the total suction head of liquid absolute, determined at the first-stage impeller datum, 

less the absolute vapor pressure of the liquid. The NPSHR, as defined in Hydraulic Institute 

standards, is the amount of suction head, over vapor pressure, required to prevent more than a 

3% loss in total head of the first stage of the pump (due to factors such as cavitation and the 

release of dissolved gas) at a specific capacity.

In general, the NPSHA is computed as the difference between the containment atmosphere 

pressure and the vapor pressure of the sump water at its assumed temperature, plus the height 

of water from the surface of the containment pool to the pump inlet centerline, minus the 

hydraulic losses for the suction piping (not including the head loss contribution from the sump 

strainer and debris bed, which are accounted for separately).

• A conservative assumption that the containment pressure equals the vapor pressure of the 

sump water ensures that credit is not taken for the containment pressurization above the 

vapor pressure during the transient. For PWR subatmospheric containments, after 
5-4

termination of the injection phase, NPSH analyses should include conservative predictions 

of the containment atmospheric pressure and sump water temperature as a function of 

time.

• Because high water temperatures reduce available NPSH, the decay and residual heat 

produced after accident initiation should be included in the determination of water 

temperature. This calculation should include the uncertainty in the determination of the 

decay heat (the uncertainty in decay heat is typically included at the 2 sigma level). The 

residual heat should be calculated with margin. 

• Calculation of available NPSH should minimize the height of water above the pump suction 

and strainer surfaces. The calculated height of water should not consider quantities of 

water that do not contribute to the sump/pool (e.g., atmospheric steam, pooled water on 

floors and in refueling canals, spray droplets and other falling water, and the volume of 

empty system piping). 

• Calculating pipe and fitting resistance and nominal strainer resistance without blockage by 

debris should be done in a recognized, defensible method or determined from applicable 

experimental data. The clean strainer head loss (i.e., the friction head loss caused by the 

passage of flow through the strainer and any associated connecting pipes and plenums) 

should be calculated with consideration of the potential worst-case distribution of flow 

through the strainer under debris loading conditions. In general, the staff considers equal 

flow through all strainer surfaces to be a realistic condition. For strainers that are not 

uniform flow design the majority of the flow enters the clean strainer close to the pump 

suction thus reducing the clean strainer head loss. As debris is deposited on the strainer it 

is likely that a relatively uniform flow distribution will occur.

• Available NPSH should be calculated as a function of time until it is clear that the available 

NPSH will not further decrease. 

5.2 Pipe Break Characterization

The objective of the break selection process is to identify the most challenging break location 

and size that results in debris generation that produces a conservative head loss across the 

sump strainer considering plant specific conditions. All aspects of the accident scenario are to 

be considered for each postulated break location, including debris generation, debris transport, 

latent debris, coating debris, chemical effects, upstream and downstream effects of debris 

accumulation, and sump strainer head loss. 

5.3 Debris Generation/Zone of Influence

The debris potentially capable of being transported to the recirculation strainers includes: latent 

debris already in containment at the time of the LOCA break; debris directly generated by the 

impact of the break effluent onto piping and structures; and debris created by post-LOCA 

environmental effects. This section addresses the generation of debris as a result of the impact 

of break effluent onto insulation and fire barrier materials. 

The generation of coating debris has been treated separately from that of other potential debris 

sources. Qualified coatings that are not directly affected by the break effluents are assumed to 

remain intact in the post-LOCA environment and therefore not form debris. 
5-5

Alternately, unqualified coatings are conservatively assumed to fail, thereby forming some type 

of debris. All coatings located within the break’s ZOI are assumed to fail, resulting in debris.

The aspects of debris generation discussed herein include (1) the applicable blast and jet 

erosion phenomena associated with debris generation, (2) the analytical modeling of blast wave 

dispersion and the dispersion of an established jet, (3) the scaling considerations important to 

the realistic or conservative performance of debris generation testing, (4) the analytical models 

that have been used to assess the ZOI and the bounding quantities of debris and the application 

of those models, and (5) the assessment of debris size distributions and associated 

characteristics.

5.3.1 Applicable Phenomena

The rupture of a PWR or BWR high-energy high-pressure pipe in a PWR or BWR would result 

in compression waves and jets of coolant that project from the piping due to the high system 

pressure, until that pressure dissipates. Debris is generated as the compression waves and jets 

impact surrounding insulation, coatings, surfaces, and other materials within the ZOI. The 

spherical volume of space affected by this impact (the ZOI) are modeled to define and 

characterize the debris generated (ML043090005, 2004). The proper development of such a 

model requires a reasonable understanding of the applicable phenomena involved. The 

discussion of these phenomena leads off and focuses on PWR breaks followed by BWR 

specific considerations. The PWR systems operate at higher pressure than the BWR systems, 

but the BWR main steam lines (MSL) breaks would create essentially single-phase steam jets 

whereas all PWR breaks of significance would release a two-phase jet. The typical hydraulic 

conditions of each reactor type are briefly discussed.

The hydraulic conditions of a postulated depressurization jet would depend on the hydraulic 

conditions upstream of the break and the size of the break. To put the initial RCS conditions 

into perspective, selected RCS hydraulic temperatures taken from NUREG/CR-5640 are shown 

in Table 5.3-1 for seven PWR plants and Table 5.3-2 for five BWR plants. The typical PWR 

operating pressure is 2250 psia with the corresponding saturation temperature of 652.7°F. 

Table 5.3-1 shows the approximate degrees of subcooling associated with the cold and hot 

sides of the RCS. The points to note are (1) the degree of subcooling depends on the location 

of the postulated break, (2) there is substantially less subcooling associated with the larger hot 

legs than with the smaller and colder cold legs, and (3) the degree of subcooling depends on 

the specific plant, as well as the specific RCS design. Further, the least subcooling would 

presumably be associated with piping lines connected to the pressurizer. Debris generation 

analysis and testing should be based either on a conservative position or on the plant-specific 

and break-specific initial hydraulic conditions and break sizes. For a specific pipe, the 

temperature of the fluid flowing within it indicates the energy transported within it. Engineering 

intuition would seem to indicate that the higher the energy density, the greater the destruction 

potential following a break, whereas some steady-state fully-established jet models indicate that 

more subcooling, to a point, results in higher stagnation jet pressures due to the increased mass 

flux out of a critically choked break. When considering the high energy density consideration, 

the potential non-plant-specific conservative position would be to analyze and test while 

assuming saturated water at 2250 psia. The NRC staff has adopted the position that the cold 

leg break conditions will produce the controlling destruction pressures.

The typical BWR operating pressure is 1015 to 1040 psia, and the corresponding saturation 

temperature is 546 to 549°F. Table 5.3-2 shows the typical BWR RCS temperatures for the 

reactor vessel steam dome, the core inlet, and the feedwater. A single-phase break in a MSL 
5-6

pipe would be more destructive than a break in a two-phase break in either a recirculation pipe 

or a feedwater pipe of the same diameter. The BWR resolutions focused on MSL breaks but 

considers breaks in all locations required by the approved guidcance.

Table 5.3-1. Selected PWR RCS Hydraulic Conditions*

Plant

RCS 

Design

Saturation 

Temperature 

at Operating 

Pressure (°F)

Vessel Temperatures RCS Subcooling

Inlet

(°F)

Outlet

(°F)

Cold 

Leg

(°F)

Hot 

Leg

(°F)

Ginna W 2-Loop 653 552 634 101 19

H. B. Robinson W 3-Loop 546 642 107 11

South Texas 1&2 W 4-Loop 560 629 93 24

San Onofre 2&3 CE 2-Loop 553 611 100 42

Palo Verde 1,2&3 CE 2-Loop 564 621 88 32

TMI-1 B&W 649 555 602 94 47

Davis-Besse B&W 555 608 94 41

*Note that the temperatures and pressures are subject to change due to plant modifications and 

power uprates.

Table 5.3-2. Selected BWR RCS Hydraulic Conditions*

Plant

Reactor 

Type

Nominal 

Dome 

Pressure 

(psia)

Saturation 

Temperature 

(°F)

Approximate 

Core Inlet 

Temperature 

(°F)

Feedwater 

Temperature 

(°F)

Oyster Creek BWR/2 1035 549 525 312

Monticello BWR/3 1015 546 529 376

Peach Bottom BWR/4 1020 547 533 376

La Salle BWR/5 1020 547 533 420

Grand Gulf BWR/6 1040 549 533 420

*Note that the temperatures and pressures are subject to change due to plant modifications and 

power uprates.

A large break in a PWR RCS pipe at 2250 psia or a BWR RCS pipe at 1015 psia would be a 

rather violent event within the immediate proximity of the break. The generation of debris 

following a LOCA is caused by the effects of an initial compression wave emerging from the 

pipe rupture and subsequently by erosion associated with the jet impingement. Since the 

relative destructiveness of the initial compression wave to that of erosion of an established jet 

flow has not been experimentally determined, both should be properly accounted for in debris 

generation testing.

The RCS pressure boundary separates high-pressure, high-temperature water from the 

surrounding environment that is essentially quiescent at atmospheric pressure. If a section of 

the pressure boundary in a PWR were instantaneously removed, the high-pressure hightemperature water nearest the break would flash to a high-quality wet steam very quickly and a 

large amount of energy would be deposited into a small localized volume. For BWR MSL 

breaks, the effluent would be single-phase steam. A powerful compressive wave would 

propagate outwards from the break as the energy of this flashed steam performed work against 
5-7

a quiescent atmosphere. The power or amplitude of the compression wave would depend on 

the area of the break and the temperature of the water.

The PWR RCS coolant is subcooled prior to a break due to the 2250 psia system 

pressurization. When this subcooled RCS coolant is released through the break, it becomes a 

superheated fluid. This superheated fluid will then evaporate vigorously as the fluid rapidly 

depressurizes The vapor pressure of the superheated liquid at the point of release drives the 

gas dynamics of the vapor release.

A Battelle-Columbus report (Scott et al., 1996) discussed the role of sonic velocities in the 

formation of a shock wave. The report described the shock wave as a more damaging type of a 

compression wave, due to increased rate of pressure change as the wave interacts with the 

target. The sonic velocities of interest are, first, that of the surrounding air and, second, that of 

the two-phase mixture. The sonic velocity of the air limits the speed of the expanding twophase mixture. The sonic velocities in a two-phase mixture can be much slower than either of 

the associated single-phase velocities, but two-phase sonic data (e.g., Städtke, 2006) show that 

sonic velocity for two-phase high-void fraction wet steam exceeds that of the surrounding air. If 

water initially at 620°F and 2250 psia, for example, were adiabatically expanded to atmospheric 

pressure, the void fraction would be 99.93%, where the mixture sonic velocity would certainly 

exceed that of air. An additional uncertainty is the effect of the two-phase slip factor, which 

could result in the liquid component slipping behind the vapor component.

The NRC staff position is that a significant blast wave is not likely to form during a hypothetical 

LOCA where the fluid upstream of the break location is sub-cooled, and if a blast wave did 

occur, the forces exhibited by the subsequent jet blowdown would probably cause most of the 

damage. Further, the staff determined that the two-phase debris generation testing performed 

is representative of conditions expected during LOCAs and that the staff accepts damage 

predictions based on established-jet destruction pressures as an adequate metric rather than 

predictions due to shock wave metrics. That is, the two-phase jet testing included the effects of 

any shock wave that would occur during a LOCA. 

After the initial propagation of a shock or compression wave, an expanding jet develops as the 

RCS depressurizes. The shape of an expanding jet depends on what the geometry of the break 

is (e.g., circumferential vs. longitudinal), and whether or not pipe separation occurs. 

Immediately downstream of a subcooled water break, the choked-flow liquid jet core extends 

from the pipe under the same stagnation conditions as the RCS. A cone shaped jet would be 

assumed for a break at one end of a DEGB. Outside the jet’s core the fluid undergoes a 

continued free isentropic expansion to a condition referred to as an asymptotic condition with 

the fluid reaching supersonic velocities. Additional expansion occurs as the jet interacts with the 

surrounding environment. Whenever the supersonic flows encounter a structure such as piping 

insulation, a stationary shock wave is established immediately upstream of the structure 

because the flow velocity at the front stagnation point should be subsonic. This standing shock 

wave should not be confused with the potential shock wave propagating outward from the break 

immediately following the breach. Whereas the propogating shock wave would impact a 

structure at sonic speeds with a singular impact, the developed jet would continue to flow 

around the structure with the potential of eroding that structure. 

During the NRC-sponsored air jet debris generation/transport testing conducted for the DDTS 

(NUREG/CR-6369), the air-jet-impacted targets were videotaped and those tapes clearly 

showed essentially instantaneous target destruction. The initial wave striking the target in the 

single-phase air-jet testing could have been a shock wave, however regarding the initial wave 
5-8

following a two-phase break, the staff deems it likely that that wave would be a simple 

compression wave rather than a shock wave. In the single-phase air-jet testing, the initial shock 

wave was decidedly more destructive than the subsequent erosion of the expanded jet. 

Definitive controlled experiments have not been conducted that would conclusively determine 

the presence or lack of a shock wave or whether the initial wave or the subsequent jet erosion 

would be the more destructive following a two-phase break. The Battelle-Columbus report 

(Scott et al., 1996) discussed building damage that followed a weld failure test that was an 

illustration of blast damage. Here, a pressure wave in the building caused the end of the 

building roof to separate from the roof trusses. The damage was attributed to a pressure wave 

being focused in a corner, which was approximately 65 ft from the crack location. In addition, a 

1⁄4-inch thick blast plate located 10 ft from the crack was significantly bent. In addition, the 

Heisdampfreaktor tests (NEA/CSNI/R(95)11) demonstrated high dynamic loadings within the 

vicinity of the break.

In addition, CFD analytical results from a Sandia study that used the CSQ code (NUREG/CR2913) to examine the steady-state expansion of a two-phase jet (based on saturation conditions 

for stagnation pressures varying between 30 and 100 bars) demonstrated that: (1) the steadystate jet centerline target pressure was reduced to about 2% of the test initial pressure within 

about 5 L/Ds from the nozzle and (2) the extension of the water core from the break is limited to 

about 2 L/D from the nozzle for a PWR hot leg break and about 3 L/D for cold leg breaks. The 

steady state jet centerline pressure reduction mentioned above, is an asymptotic curve. Even at 

20L/D it is still near 2%. It is also noted that 2% of 2250 psi is 45 psi which is large enough 

pressure to damage some insulation types. While this analytical information suggests that the 

destructiveness of a relatively steady-state expanding test jet is limited to within about 5 L/D 

from the nozzle, the Ontario Power Generation tests (OPG, 2001) performed with 1450 psia 

saturated water showed that destruction occurred at significantly greater distances than 5 L/D. 

For OPG Test 15, where the target was placed 20 L/D from the nozzle, considerable damage 

was done to the target (22% of the calcium silicate became debris). 

It is evident that steady-state jet expansion does not explain the BWROG results. However, it 

should be noted that these are single-phase air-jet test results and not two-phase test results.

The BWROG argued against a blast wave in Volume 4 of the URG based on the time required 

for piping components to separate. This volume included an embedded technical evaluation 

report on this subject, which was prepared by General Electric (GE) Nuclear Energy (Moody 

and Green, 1996). Two independent technical reviews were performed on the BWROGsponsored GE technical evaluation that argued against the potential to form blast waves 

following a DEGB. Battelle-Columbus (Scott et al., 1996) conducted the first technical review 

and Wilfred Baker Engineering, Inc. (non-public) performed the second review. The technical 

review findings stated that the GE report did not substantiate the BWROG’s position that a blast 

wave capable of damaging insulation will not be generated following a DEGB, and that the 

model used in the GE study was overly simplistic and nonconservative. The review determined 

that the GE criteria for production of a blast wave based on the ratio of the rupture opening time 

to the acoustic propagation time lacked foundation, so that the validity of the approach was 

questionable. The Battelle-Columbus review also pointed out that a compression wave can 

form even if the pipe halves only partially separate. Therefore, the debris generation analysis 

has treated a DEGB as an instantaneous rupture, and debris generation testing resorted to 

testing the break flow from a scaled-down section of piping associated with one side of the 

DEGB.

The debris generation testing for the BWR resolution was performed using single-phase air jets 

to simulate a single-phase steam jet emanating from a MSL break. The air jets were produced 
5-9

using a 1000 psig rupture disk attached to a large source of compressed air. The primary 

differences between the test air jet and the postulated MSL line break are the thermodynamic 

behaviors of differing gases and the diameters of the pipes. A CFD analysis performed for the 

BWROG indicated that the air and steam would generate similar jets from the standpoint of 

steady-state jet expansion. Analysis was not performed to verify the air/steam similarities for 

the initial compression or blast wave emanating from the break. The NRC current staff position 

is that the steady state stagnation pressures measured during destruction testing provided an 

adequate metric to determine destruction thresholds for different debris, when tested under 

conditions similar to those in the plant.

5.3.2 Break Jet Dispersion Analytical Models

5.3.2.1 Blast Wave Dispersion Models

When a blast wave is generated at a point source, if unobstructed, that wave would propagate 

spherically outward. The original wave would likely become fragmented due to reflection and 

diffractions by the structures and some of those fragments could merge once again. Blast wave 

analysis is done using complex numerical computer codes.

No method was developed for scaling the potential blast wave destructiveness from the debris 

generation test data based on the relatively small size of the test nozzle up to a postulated 

LBLOCA. Rather, scaling has been based on a steady-state jet expansion model in which the 

volume within a conical jet isobar was used to calculate the zones of destruction. If the primary 

cause of insulation destruction is the result of a shockwave or pressure wave rather than the 

sustained erosion of an expanded jet, then there is the concern that the steady-state expanded 

jet method of scaling is neither physically representative nor realistic. 

5.3.2.2 Established Jet Dispersion Models

The typical jet dispersion model for a postulated high-energy line break accident is based on the 

idealized case of a DEGB, in which high-temperature, high-pressure reactor coolant is ejected 

(from both sides of the broken pipe) and may impinge on structures, equipment, piping, 

insulation, and coatings in the vicinity of the break. The degree of damage induced by the break 

jets is specific to the materials and structures involved, but the size and shape of the expanding 

jets and the forces imparted to surrounding objects depend on the thermodynamic conditions of 

the reactor coolant. Destruction models based on jet dispersion maximize the volume of the 

damage zone (ZOI) by conservatively considering free expansion of the break jet to ambient 

conditions with no perturbation, reflection, or truncation by adjacent structures. Jet volumes 

within an isobar at which damage to a given material may occur are defined by empirical 

correlations of local jet pressure. The material damage pressure is based on material behavior 

during testing. The volume within the isobar can then be integrated over the free-jet conditions 

and remapped into convenient geometries, such as spheres, disks, or cones. These shapes 

can approximate the shape of the damage zone by assuming the effects of reflection in a 

congested space without crediting the associated shadowing, jet disruption, and energy 

dissipation.

The analytical methods used to evaluate the expansion of a LOCA jet have included CFD 

codes, the ANSI/ANS-58-2-1988 standard (ANSI, 1988), and a few other smaller-scale efforts. 

The CFD analyses included a two-phase jet load study conducted at SNL (NUREG/CR-2913) 

and the BWROG steam jet analysis with the NPARC code reported in the URG, Vol. 3. The 

ANSI/ANS-58-2-1988 standard, applicable to a steady state or perhaps a quasi-steady-state jet, 
5-10

has been accepted for determining the volumes within a specific pressure isobar and calculating 

an equivalently sized sphere to be used as the ZOI. 

The jet model in the ANSI/ANS-58-2-1988 standard subdivides the expanding jet into three 

regions. Region 1 contains the core region, where it is assumed that liquid extrudes from the 

pipe under the same stagnation conditions as the upstream reservoir. Region 2 represents a 

region of continued isentropic expansion. Region 3 represents a region of significant mixing 

with the environment, where the jet boundary is assumed to expand at a fixed 10-degree half 

angle. Despite the apparent complexity of the equation set needed to evaluate the ANSI jet 

model, it is based on relatively few thermodynamic assumptions and limited comparisons with 

experimental observation. Key geometry features that are determined by the thermodynamic 

conditions of the break include the length of the core region, the distance to the asymptotic 

plane between Regions 2 and 3, and the radii of the jet envelope at the transition planes 

between regions. At the asymptotic plane, the centerline static pressure is assumed to 

approach the absolute ambient pressure outside the jet. Due to the standard’s built-in 

assumptions and decision steps in its application, the calculational results can differ among 

analysts. The NRC evaluation and accepted application of the standard is found in Appendix I 

of the safety evaluation (NRC-SER-2004).

The Advisory Committee on Reactor Safeguards (ACRS) reviewed the ANSI model and noted 

several inconsistencies and errors in the models described in the standard, which were provided 

to the NRC in a letter dated October 18, 2004 (Bonaca, 2004; Wallis, 2004). The ACRS review 

concluded that there were several problematic areas with the methods in the standard regarding 

the model’s ability to simulate supersonic jet flow, the unrealistic representation of the physics, 

the inappropriate use of one-dimensional assumptions for an asymptotic plane, the assumption 

of a non-physical asymptotic plane, the evaluation of the density at this fictional asymptotic 

plane as if the fluid were at rest (whereas in reality it is flowing at a high Mach number), and the 

user manipulation of the model assumptions. In the SE, the staff agreed with the ACRS 

comments on the ANSI/ANS model and observed that additional model inaccuracies, such as 

unrealistically large isobars calculated for lower stagnation pressures, are noted in Appendix I of 

NRC-SER-2004. Notwithstanding these technical points, the staff considers the standard 

acceptable for use in determining the ZOI to be used for modeling debris generation during 

DBAs. This determination is based in large part on the method that is used to approximate the 

debris generation resulting from postulated breaks. To account for jet reflections, shadowing 

effects, directionally changing discharge from a whipping pipe, and the difficulty of assessing all 

potential orientations of breaks, the GR proposes using a spherical volume equivalent to a 

volume determined using the ANSI/ANS model using the demonstrated destruction pressure of 

debris sources. This volume translation conservatively ignores the energy that would be lost in 

multiple reflections and in the generation of debris. The SE stated that the precision that could 

be gained by the development of a more accurate method to determine the characteristics of a 

freely expanding jet is more than offset by conservatism in using an equivalent-volume 

approach for determining ZOIs.

The NRC staff accepted that the ANSI/ANS 58.2-1988 standard provides a suitable basis for 

computing spatial volumes inside a damage zone defined by a jet impingement pressure isobar. 

Specific application recommendations accepted by the staff for generic implementation of the 

model and calculation of isobar volumes for conversion to alternate models included:

1 The mass flux from the postulated break was determined using the Henry Fauske 

model, as recommended in the standard, for subcooled water blowdown through 

nozzles, based on a homogeneous, non-equilibrium flow process without considering 
5-11

irreversible losses (irreversible losses refer to internal pipe and pipe component friction 

losses between the upstream reservoir and the location of the break). However, 

licensees using this technique should refer to confirmatory Appendix I to NRC-SER-2004 

for guidance.

2 The initial and steady-state thrust forces were calculated on the basis of guidance in 

Appendix B to the standard, with reservoir conditions postulated. However, only the 

steady-state thrust coefficient should be used in this calculation as a conservative 

bound.

3 The jet outer boundary and regions were mapped using the guidance in Section 1.1 of 

Appendix C for a circumferential break with full separation.

4 A spectrum of isobars was mapped using the guidance in Appendix D to the standard.

5 The volume encompassed by the various isobars was calculated using a trapezoidal 

approximation to the integral with results doubled to represent a DEGB.

6 The radius of an equivalent sphere was calculated to encompass the same volume as 

twice the volume of a single freely expanding jet.

7 Insulation damage pressures can only be interpreted with a full understanding of the test 

conditions under which they were experimentally measured. The computed jet 

conditions will not match the experimental test conditions; therefore, care should be 

taken to ensure that equivalent damage effects are considered.

5.3.3 Debris Generation Testing Considerations

Small-scale debris generation testing is conducted to determine the jet centerline stagnation 

pressures needed to cause threshold damage to various kinds of insulation blankets and 

cassettes and to determine the debris size characteristics corresponding to degrees of 

destruction. It is important that these debris generation test results should be conservative for 

both bounding quantities and debris size with respect to the postulated breaks for the full-sized 

plant. The validity of the small-scale debris generation testing depends on establishment of test 

conditions prototypical of the plant RCS and on a conservative scaling of (1) the test jet with 

respect to a full-sized jet, and (2) the test target with respect to the full-sized plant blanket or 

cassettes. It also depends on the positioning of the target within the test jet to allow the entire 

test target to be prototypically impacted by the test jet. The tests need to be properly 

instrumented to gain the data needed to accomplish the scaling. The test debris should be 

processed to obtain debris size characteristics.

5.3.3.1 Established Prototypical RCS Conditions

Small-scale debris generation testing should be conducted at test conditions either prototypical 

or conservative with respect to the plant RCS conditions. Prototypical conditions are 

established by the plant-specific RCS pressures and temperatures. Regarding jet pressures on 

target for an established two-phase jet, analyses using, for example, the HEM choked flow 

model and the ANSI/ANS 58.2-1988 standard (both steady-state models) demonstrated higher 

stagnation pressures on target to be associated with colder breaks, primarily due to the higher 

choked break flow associated with the higher density water of colder water. Regarding the 

destructive capability of the initial compression wave impacting a target, the conservative 
5-12

position is less clear, the affect of the higher energy density associated with the hot leg relative 

to a cold leg on the destructive capability of a compression wave can only be reliably assessed 

experimentally (steady-state models do not apply to a very dynamic compression wave). After 

considerable review, the staff has concluded that the established jet would be more destructive 

that the initial compression wave; therefore resolution analyses focused on the established jet, 

as conservatively analyzed using the ANSI/ANS 58.2-1988 standard.

During an experiment, the water temperature directly upstream of the rupture disk should be 

properly maintained, as must the bulk tank temperature. Rupture disks have typically been 

used to initiate debris generation testing in an attempt to simulate instantaneousness because 

the alternative of using fast-opening valves has been perceived as much too slow to properly 

simulate a LOCA break. It is crucial that the test procedures ensure that the water temperature 

directly upstream of the rupture disk be maintained within a few degrees of the test 

specification, as should the bulk tank temperature.

Regarding debris generation testing practices, such matters as the piping resistance associated 

with the piping components between the tank of water and the nozzle exit could affect the jet or 

compression wave properties. It is important that resistance to flow upstream of the rupture disk 

does not restrict the flow so that choked flow will not occur at any upstream location. Any piping 

downstream of the disk should be minimized, so that the break flow is not significantly altered by 

the downstream piping. Note that for a postulated LOCA, there is no piping flow resistance 

immediately downstream of the break. Because the piping and fittings between the test tank 

and the nozzle will affect the nozzle discharge flow with respect to that of a LOCA, the actual 

break flow conditions can differ substantially from the conditions predicted by the application of 

a choked flow model without evaluating the effect of the piping. Therefore, jet dispersion 

analysis of the test jet using ANSI/ANS-58.2-1988 (ANSI, 1998) should determine the actual 

test nozzle exit conditions and test rate of flow using a computer code like RELAP, which 

models the choked flow at the limiting flow location and the subsonic flow elsewhere in the 

piping. The jet blowdown is transient, rather than steady state, and the flow in the piping will 

transition from an initial single phase flow to two-phase flow further transitioning through the 

various two-phase flow regimes. Test measurements designed to determine rates of flow must 

consider the two-phase aspects of the flow.

5.3.3.2 Test Jet Scaling Considerations

The size of a DEGB on the RCS piping of a typical PWR ranges from about 27 in. for some cold 

leg pipes to 42 in. for some hot leg piping, depending on the plant design. Conducting full-scale 

debris generation testing is expensive and impractical. However, it is not clear how large a test 

nozzle should be for the test results to be considered sufficiently prototypical of the full-sized 

postulated break. The typical test nozzle diameter for currently accepted scaled destruction 

testing has ranged from about 2.8 to 4 in. Test nozzle diameter has also been related to test 

duration (i.e., a smaller diameter allows the jet to continue longer for a given volume of water 

reservoir), albeit in a more limited spatial range. The use of a relatively small nozzle may 

provide realistic results (for locations on the target where the stagnation pressure is fully 

realized) if the primary mechanism for debris generation was erosion (where duration would be 

important), but the validity of using a relatively small jet size is less clear when considering the 

instantaneous destruction caused by a forces that would be applied over the full area of the 

insulation system. These forces could include pressure from the jet impingement or potentially 

from a compression wave. Generally speaking, a larger test nozzle would provide more realistic 

the test results than a smaller test nozzle.
5-13

Whether the diameter of a test jet can be considered large enough depends on the destruction 

mechanics of the target. If, for example, the target is a coating of paint where the destruction 

mechanics are localized, then prototypical results can be obtained with a relatively small nozzle 

and target coupon because the jet centerline conditions are the most important variables. But 

when destruction of a target depends on the failure of more than one jacketing latch or bands on 

a piece of pipe insulation, then an entire prototypical section of the jacketing may have to be 

subjected to near-prototypical pressures associated with destruction; otherwise, the test 

insulation jacketing might remain intact due to latches located outside the main jet flow. The 

stagnation pressure associated with a test jet peaks near the jet centerline and generally

decreases with the radial distance from that centerline.

For a given test nozzle diameter, it is likely that there is a minimum nozzle-to-target distance 

that can be accepted as prototypical, although the minimum distance may be difficult to define 

for some conditions. The closer a target is placed to the test nozzle, the larger the test nozzle 

needs to be for the test data to be considered prototypical. The staff’s position, agreed to with 

the PWROG, for jacketed banded targets, is that the jet profile will be measured at the distance 

from the nozzle that the target will be placed. The profile is to be relatively flat over the full 

diameter of the pipe and also over two times the band spacing. If a banding strap fails or moves 

significantly during the test the area of flat profile would have to be larger to ensure that the 

components are stressed adequately to determine if a failure would occur. Between jacketed 

targets and coatings targets are unjacketed blankets. These should be subjected to a jet profile 

adequate to stress the blanket material, seams, and straps such that the potential failure modes 

are explored. 

The quality of the debris generation test data depends on the diameter of the test nozzle with 

respect to the target characteristic dimensions, as well as the jet centerline stagnation pressures 

(and the impact of the initial pressure wave) and perhaps the prototypicality of the target 

installation on the piping. For example, if the target insulation is held onto the pipe more 

aggressively than it would be in the plant it may have more damage than if it is allowed to blow 

off the pipe and out of the jet influence. Also some types of insulation may be damaged to a 

greater degree if they are blown off and strike a solid object. This is illustrated by Figure 5.3-1 

(Figure II-2 of NRC-SER-2004 with a reduced set of data), which shows the destruction of 

unjacketed LDFG relative to the jet centerline stagnation pressure and which compares

BWROG air jet test data for a 3-in.-diameter nozzle.
5-14

Figure 5.3-1. Air-Jet Testing Destruction Data (BWROG 3-in. Nozzle)

The data point shown in Figure 5.3-1 that shows 7% destruction for the 3-in. nozzle at about 20 

psig and another data point not shown in the figure where 25% destruction occurred at a 

pressure of 190 psig demonstrate that targets mounted too closely to the jet nozzle were

probably too close to generate valid test data. The jet likely completely pulverized the center of 

the test blanket but left the ends relatively intact. That is, the ends of the target extended 

beyond the effective reach of the jet. The data for these two test data points should have been 

interpreted as complete destruction, but the BWROG interpreted the data to mean that as the 

target was placed ever closer to the jet nozzle, the level of destruction actually decreased (refer 

to Figures G.1 and G.3 in NRC-SER-1998). 

The SE-accepted 2D ZOI for Transco RMI was based on BWROG 3-in. nozzle testing in which 

the cassettes were placed too close to the nozzle for the test data to be prototypical. Because 

RMI debris is relatively benign with respect to causing significant strainer head losses, this 

testing issue had not been a concern to the staff. However, several licensees that use Transcoencapsulated non-RMI insulation have assumed a 2D ZOI for these insulation materials (e.g., 

Microtherm) based on the SE-approved 2D ZOI for similarly jacketed RMI. Some of the 

BWROG-tested Transco RMI cassettes were disassembled at relatively low pressures (e.g., 

Test 21-1), thereby exposing the RMI foils without generating significant quantities of small RMI 

debris. However, if problematic insulation materials were exposed to the sump pool, the 2D ZOI 

could become an issue. The BWROG tested a Transco SS-encapsulated cassette containing 

lead and Min-K insulation. Following Test 27-3, the atmosphere was noticeably thick with a fine 

particulate attributed to the Min-K insulation. This Min-K particulate was generated even though 

the dented and deformed steel cassette was still mounted on the pipe (as shown in an NRCSER-1998 post-test photo). The test jet centerline pressure was approximately 42 psig 

(approximately 4D). The same discussion may also apply to the SE-approved 2.4D ZOI for 

NUKON® secured with Sure-Hold® bands, although few, if any PWRs have this NUKON®

system installed. In addition, the OPG testing did not actually determine the threshold pressure 

for a jet to cause damage to calcium silicate insulation, although this difference appears to be 

due to how OPG intended to apply their data. The technical basis for nozzle size should ensure 
5-15

that the test jet is large enough to prototypically engulf the target with respect to the target’s 

characteristic damage dimension.

5.3.3.3 Target Scaling, Construction, and Positioning Considerations

The scaling, construction, and positioning of a test insulation target should be considered with 

respect to the size of the test jet compared to a full-sized LOCA. The important test target 

characteristics depend on the target’s failure mechanism. That failure mechanism suggests a 

dimension associated with the primary failure mechanism, as well as the target’s physical 

dimension, referred to herein as the target’s “characteristic damage dimension.” This dimension 

probably depends more on the effective failure mechanism than on the physical dimension. 

There may be more than one potential failure mechanism for any insulation system. For 

coatings, the failure mechanism is the localized strength of the coating; therefore the test 

coupon would not need to be overly large, nor would the test jet need to be. Conversely, for a 

36-in.-long stainless steel jacket held in place by three mechanical latches evenly spaced along 

the target, where the failure mechanism for this jacket involves the failure of all three latches, 

the characteristic damage dimension could be the target length. A jet that effectively impacted 

the center latch but not the other two latches would be less likely to cause jacket failure than a 

more prototypical jet that would effectively impact all three latches. Under some conditions, the 

center latch could fail but the jacketing would remain held in place by the outer latches so that 

the jacketing continues to protect the enclosed insulation material. In the prototypical RCS 

LOCA, the jet would have been much larger so that all three latches would be stressed to a 

similar degree, causing insulation failure under that condition. In addition, the mode of jacket 

failure varies with jacket design. Failure of the latches or banding may be the primary mode of 

jacket failure. In other situations where the bands could remain relatively intact, the failure 

mechanism could be tearing of the sheet metal between the bands, thereby exposing the 

underlying insulation material. This failure mechanism was seen, for instance, by OPG in the 

testing of aluminum-jacketed calcium silicate with stainless steel bands (OPG, 2001).

As the target is placed ever closer to the jet nozzle, the pressure becomes more focused toward 

the center. Conversely, further away from the nozzle, the distribution would tend to flatten out. 

Four radial pressure profiles calculated with the ANSI/ANS-58-2-1988 standard are compared in 

Figure 5.3-2. These profiles illustrate how jet pressures become more focused toward the 

target center as the target is mounted closer to the jet nozzle. If the test jet radial profile is too 

skewed relative to the target characteristic failure dimension, then the jet nozzle is too small for 

that axial positioning down range from the nozzle.

The linearity of these distributions is likely related to the standard assumption in ANSI/ANS-58-

2-1988 that the jet was assumed to expand at the half angle of 10° after the jet became fully 

expanded asymptotically. Physically, the distribution could be non-linear. The calculated 

pressures in the ANSI/ANS-58-2-1988 standard have uncertainties that would only increase 

with the distance from the break plane.

Another potential jet size concern is how the jet flows around the test target and thus affects the 

stresses at jacketing seams. If a full-sized LOCA jet were to impact a prototypically sized 

insulated pipe, the flow at the jet center would be essentially two-dimensional, with half the flow 

passing above the pipe and half the flow passing below the pipe. When a jet impacts a solid 

plate (or a solid wall) perpendicularly, the jet is redirected in a full 360° circle. The flow direction 

associated with a small jet impacting a full-sized piping target would be somewhere between 

these two considerations, with part of the deflected flow re-orienting more along the target axis; 

this situation, for example, could reduce the stresses on a jacket seam oriented 45° off center. 
5-16

Because target diameter can strongly affect the jet flow patterns, diameter is a characteristic 

dimension associated with insulation damage and could, for jet size scaling purposes, become 

the limiting characteristic damage dimension relative to the corresponding axially oriented 

dimensions, such as the spacing between the bands.

Figure 5.3-2. Radial Pressure Profiles at Selected Axial Distances

Determining the threshold pressure for destruction has involved selective placement of the 

target further and further from the jet nozzle until a certain distance is reached whereby the 

target does not sustain significant damage. The pressure at that distance then becomes the 

threshold destruction pressure for the target.

When adapting data from debris generation tests to plant-specific conditions other than the 

conditions of the test, users should take into account both the test conditions and the relative 

strengths of the test targets. The jacketing and banding systems of the insulation system being 

evaluated should be at least as structurally strong as the tested jacketing and banding systems 

to ensure that the test data are applicable to the plant installation. Differences in designs of 

jacketing and banding systems for piping and other components such as steam generators, 

pressurizers, and reactor coolant pumps should be considered. The jet size should be 

adequately scaled to the plant condition, and the limiting orientation of the break jet impacting 

the insulation should be considered. Additionally, the base insulation materials used in the 

adopting plant should be as strong as the materials used in testing. For example, two very 

different manufacturing processes have been used to produce calcium silicate. One of the 

processes results in a product that readily dissolves in water, while the other type dissolves 

relatively slowly. It stands to reason that these two types of calcium silicate insulation may also 

behave differently in debris generation testing.

Radial Pressure Distributions

2250 psia, 100F Subcooled, & 3.5 inch Nozzle

0

20

40

60

80

100

120

140

160

180

200

0 10 20 30 40 50 60 70 80

Radial Distance From Jet Center Line (inch)

Pressure (psig)

10.2 inch (2.9 L/D)

20.0 inch (5.7 L/D)

43.8 inch (12.5 L/D)

67.8 inch (19.4 L/D)

Axial Distance from Nozzle
5-17

5.3.3.4 Instrumentation 

Test instrumentation is needed to control the test environment and to characterize the resultant 

jet, making it possible to correlate insulation destruction with test conditions and to scale test 

results to plant conditions. The staff has not established guidance regarding test 

instrumentation. Test instrumentation should be included to measure the water temperature 

and pressure in the bulk reservoir, the piping between the reservoir and the nozzle, and/or 

immediately upstream of the rupture disk. In addition, the mass flow rate should be measured 

during the blowdown. Test instrumentation could be included to measure jet parameters 

downstream of the nozzle. Measurements should include jet stagnation pressures, static 

pressures, temperatures, and the dynamic pressures associated with any compression wave. 

Data recorders should be used to measure test results from before the test initiation to test 

completion. Rapid response instrumentation is required to accurately measure the jet during 

blowdown. Destruction tests cannot be instrumented to the same degree as tests that do not 

include targets. It is unlikely that parameters of the jet can be measured during target tests. 

However, the parameters upstream of the nozzle can be measured and compared to 

instrumented tests conducted under similar conditions to verify that the mass flow rates, system 

pressures, and fluid temperatures are similar between the tests. 

5.3.3.5 Debris Characterization

Analysis of debris transport and behavior in a debris bed requires specification of the debris size 

distribution for each type of insulation affected by the LOCA jet. The size distributions should be 

realistic or conservatively biased toward finer debris since finer debris transport more easily and 

result in greater strainer head loss. For these reasons, a debris generation test program should 

include a procedure for collecting post-test insulation debris and characterizing that debris.

5.3.3.6 Comparison of Debris Generation Testing

Test protocols for the debris generation test programs have varied considerably, and insights 

can be gained by comparing these test protocols and their test results. A general pattern of test 

results based on the test conditions and protocols might be expected. The test programs 

include: (1) air jet testing conducted at the Colorado Engineering Experiment Station, Inc. 

(CEESI) by the BWROG (NRC-SER-1998); (2) NRC-sponsored air jet testing for the DDTS 

(NUREG/CR-6369); (3) OPG two-phase testing (OPG, 2001); (4) prototypically sized HDR 

(Heisdampfreaktor) experiments in Germany (NUREG-0897, NEA/CSNI/R(95)11); and (5) highpressure water jet fibrous insulation pillow testing conducted by SNL (NUREG/CR-3170). 

BWROG Air Jet Testing 

The BWROG debris generation testing was conducted at the CEESI, where a high-pressure jet 

of air was focused on an insulation target (NRC-SER-1998). Air pressurized to 1110 psig in a 

large tank was piped to a nominal 3-inch-diameter test nozzle through a control valve assembly. 

When the control valves were opened, air pressure built up behind a single rupture disk 

designed to burst at a pressure of 1000 psig. Targets of various insulation types and jacketing 

were placed at various distances from the jet with the objective of determining the minimum 

threshold pressures for generating insulation debris. The BWROG placed a differential 

pressure transducer in a target-mounting pipe to measure the actual jet pressure at specific 

distances from the jet nozzle to benchmark a CFD model used to define jet stagnation 

pressures at any targeted distance so that target damage could be correlated to the jet 

stagnation pressure. A 20 L/D pressure measurement confirmed the results of the CFD 
5-18

predictions inside 20 L/D and other more distance measurements were used to interpolate 

pressures between 20 and 117 L/D.

NRC-Sponsored Air Jet Testing

The NRC-sponsored air jet testing for the DDTS was conducted at CEESI using the same basic 

equipment as in the BWROG testing (NUREG/CR-6369). Initial testing used a nominal 3-in. jet 

nozzle, but after an initial exploratory testing phase, the 3-in nozzle was replaced with a 4-in. 

nozzle to enhance the destruction of the insulation blankets. The objective of these tests was to 

study the transport behavior of LDFG debris as the debris passed through or impacted a 

prototypical representation of BWR drywell congestion of structural obstacles such as gratings. 

An array of pitot tubes was used to measure the downstream flow velocities in an axial and 

radial configuration for comparison with a CFD flow simulation used to estimate stagnation 

pressures. The targets were LDFG blankets mounted on a test pipe and generally placed to 

maximize blanket destruction, thereby generating the greatest potential density of debris 

transiting the chamber test obstructions. At 30 L/D (distance from jet nozzle divided by nozzle 

diameter), the fraction of the debris small enough to pass through the test gratings was typically 

greater than 90% of the original insulation material. At 10 L/D and 20 L/D, the target was too 

close to the jet to be completely engulfed by it so that substantial insulation at the target ends 

became debris too large to pass through the first grating. A video camera focused directly on 

the test target showed that destruction was essentially instantaneous and did not appear to be 

due to erosion. 

OPG Debris Generation Testing

Ontario Power Generation conducted debris generation testing to support its programs. The 

NRC staff reached an agreement in which a test report for aluminum-clad calcium silicate 

insulation (OPG, 2001) was made available for staff review. A dual rupture disk assembly 

attached to a 2.87-in. diameter test nozzle was used to release water pressurized to 10 MPa 

(1450 psia) and heated to saturation. Piping heaters were installed to maintain the initial test 

conditions within the piping before initiating the test. Because the OPG did not measure test 

pressures downstream of the jet nozzle, the NRC staff calculated the pressures associated with 

insulation destruction by using the jet model in the ANSI/ANS-58.2-1988 standard. Target 

placement at the greatest test distance from the nozzle (20 L/D) was used to estimate the 

threshold damage pressure for calcium silicate insulation; however, the target at this position 

still sustained substantial damage. In addition, for at least some of the trials, the target may 

have been too close to the jet for the jet to impact the entire target with a prototypical pressure.

HDR Debris Generation Testing

The HDR experiments were conducted in Germany and used an out-of-production prototype 

BWR reactor vessel that had been refitted as a testing facility for blowdown testing 

(NEA/CSNI/R(11)). The initial conditions were typically water at 11 MPa (1595 psig) and 

saturation temperature. Significant damage was noted in the vicinity of the break which seemed 

to be caused by the dynamic pressure wave that occurred at rupture, as well as by the forces of 

the outflowing jet. The HDR deflection plate was placed in front of the nozzle at a distance of 

about 3.3 L/D, such that the jet first struck this plate before reflecting and hitting the insulation 

materials. Test observations that illustrate the destructive capability of the jet include: (1) 

conventional fibrous insulation (mineral wool reinforced with wire mesh and jacketed with 

galvanized carbon steel sheet) was blown away as soon as the cover was damaged, and 

material located within a radius of 3 to 5 m from the break nozzle (about 6.7 to 11.1 L/D) was 
5-19

dislodged; (2) unjacketed NUKON® or NUKON® covered with metal mesh located within 9 L/D 

was totally destroyed, and more than 90% of the insulation was reduced to fine fibers; 

(3) metal-jacketed wool insulation within 7 L/D was damaged, with up to 50% of the wool 

reduced to fine fibers; and (4) inspection revealed that concrete spallation had occurred, which 

was attributed to thermal shock.

SNL Water Jet Debris Generation Testing

In 1983, the NRC sponsored testing conducted by SNL designed to assess the susceptibility of 

fibrous insulation pillows to debris formation under impingement by break-flow jets (NUREG/CR3170). Three types of fibrous insulation pillows were tested by using liquid jets with an objective 

to determine the stagnation pressure required for damage to the cover fabrics and for failure of 

the insulation pillows through insulation material release. A 300-ft-head (130 psi) centrifugal 

pump supplied low-temperature water to a 2-inch nozzle that directed the flow vertically 

downward toward an insulation pillow. The procedure was to expose the pillow to the jet flow 

for 5 min at a set pressure, which was incrementally increased in 5-psi steps until insulation 

material was released from the pillow. Because the pressure loadings on the insulation pillows 

were at steady state, the pressures needed to fail the pillow protective covers were substantially 

higher than those typical of dynamic loadings such as in the air jet testing.

The above four test programs are compared in Table 5.3-3. Because each test program had 

relatively independent test objectives, none of the tests involved the same insulation and 

jacketing systems and the same specified test conditions so that the test results could be 

directly compared to ascertain, for example, the effects of air jet testing vs. two-phase jet 

testing. This comparison leaves unanswered the question of whether an air jet is more 

destructive than a two-phase jet. The video from the air jet testing showed that in many cases 

the blanket destruction was virtually instantaneous. This supports the concept that the primary 

mode of blanket destruction is the initial dynamic effect from the jet. Further, LDFG blankets 

were damaged at a distance corresponding to a stagnation pressure of 6 psig in the dynamic air 

jet testing; substantially lower pressure than the minimum steady-state pressure of about 35 

psig was required to rip the canvas covers in the SNL water jet tests, i.e. dynamic vs. static 

pressure loadings.

Table 5.3-3. Test Program Comparison

Test Program

Nozzle

(in.) Initial Conditions

Target Position / 

Stagnation Pressure Damage Description

Air Jet 3 Air at 1110 psig 20 L/D

20 psig

SS jacket removed, and 

NUKON® destroyed with 

46.3% small fines and 

53.7% large pieces

50 L/D

12 psig

SS jacket removed, and 

NUKON® damaged with 

11.9% small fines and 

29% large pieces

4 Air at 1110 psig 30 L/D

19 psig

Unjacketed LDFG totally 

destroyed

OPG 2.87 Saturated water at 

1435 psig

20 L/D

24 psig

Substantial damage to Al 

clad calcium silicate

HDR 17.72 Saturated water at 

1595 psig

9D (deflected once),

unknown pressure

Unjacketed LDFG totally 

destroyed

SNL Water Jet 2 130 psi pump head Damage occurred at 

> 35 psig

Covers ripped with onset 

of debris generation
5-20

Experimental data is lacking to definitively determine the relative destructiveness of the initial 

pressure wave impacting a target (whether the wave is a simple compression wave or a shock 

wave) to the subsequent pressures associated with a fully expanded jet. While the steady-state 

HEM choked flow model combined with the steady-state ANSI/ANS-58-2-1988 standard jet 

expansion model predicts greater stagnation pressures for the cold leg break over that of a hot 

leg break, primarily due a greater mass flow rate associated with the higher density cold leg 

break, the relative destructiveness of the initial pressure wave is not determined by these 

models, nor is the relative destructiveness of the wave to that of the established jet. At break 

initiation, the system pressure at the break water/atmospheric interface dropped off rapidly to 

the saturation pressure where the water flashes to steam. The saturation pressures for the 

HDR and OPG debris generation tests are compared in Figure 5.3-3 (solid circles) to 

prototypical saturation pressures for PWR hot and cold leg piping (dashed boxes). The typical 

PWR operating pressure of 2250 psia is also noted. The saturation pressures for the hot leg 

generally range from about 1500 to 1800 psia, and those for the cold leg range from about 980 

to 1120 psia. The HDR saturation pressure of 1595 psia was within the general PWR hot leg 

range but the OPG saturation pressure of 1435 psia was significantly lower than that of the 

typical PWR hot leg saturation pressures. Flashing following a 620°F hot leg break would be 

associated with a saturation pressure of about 1800 psia. Additional study would be required to 

understand the magnitude of difference between pressure waves that would occur at saturation 

pressures corresponding to cold and hot leg breaks.

Figure 5.3-3. Saturation Pressures for Debris Generation Testing

5.3.4 Zone-of-Influence Debris Generation Models

The shape of the jet formation immediately after a break would be transient and complex. The 

flow from the two broken pipe ends would interact, and the broken ends would move (i.e., pipe 

whip) within the limits of the pipe restraints, with those limits depending on the number and 

location of restraints and structures near the break. Simulation of pipe motions would require 

modeling of the structures and the jet thrusts. The jets would be affected by containment 

obstructions including other piping, vessels, pumps, walls, and gratings. Further, the number of 

potential pipe break locations for evaluation is large even if the break locations were limited to 

welds. A detailed evaluation of even one break scenario could be resource-intensive. 

800

1000

1200

1400

1600

1800

2000

2200

2400

520 540 560 580 600 620 640

Temperature (F)

Pressure (psia)

Saturation Pressure Curve

HDR Test Pressure

OPG Test Pressure

Hot Legs

Cold Legs

Typical PWR Operating Pressure 2250 psia

At Rupture System 

Pressure Drops 

Rapidly 

Towards Saturation

Approximate 

Homogeneous 

Nucleation 

Temperature

577°F
5-21

A simplified evaluation model was clearly needed to evaluate potential debris quantities so that 

limited resources could be used to achieve the goals of conservatively calculating a bounding 

quantity for each type of insulation debris in each break scenario.

5.3.4.1 USI A-43 Conical ZOI Modeling

A conical jet model, illustrated in Figure 5.3-4, was used in 1982 during the USI A-43 evaluation 

(NUREG/CR-2791). The conical model assumed a DEGB with complete pipe separation but 

essentially located at a point source. The conical model was not implemented during the GSI191 resolution but was not disallowed by the NRC staff. If a licensee chose the conical model, 

that licensee would have had to justify the conservative use of the model, which likely would 

have proven difficult for a large number of potential breaks, and required evaluation of the pipe 

whip effects. Implementation of this model did not account for jet reflections from a structure.

Figure 5.3-4. Schematic of Conical Jet Model
5-22

5.3.4.2 Spherical ZOI Plant Analysis Model

A simple volume-equivalent model was initiated for a probabilistic study in 1983 in which a large 

number of breaks needed to be readily evaluated (NUREG/CR-3394). The model is illustrated 

as a hemisphere in Figure 5.3-5 for one end of a fully separated DEGB. Subsequently, a full 

sphere was used to simulate both the ends of DEGB. The concept of the sphere is that the 

volume within the sphere is equivalent to the conical jet volumes associated with both pipe-end 

jets. The figure shows three hemispherical zones of destruction (L/Ds of 3, 5, and 7) where the 

probabilistic study postulated the damage percentages for the insulation located within each of 

these zones; those damage percentages were used to calculate quantities of debris generated 

for the break. The report NUREG/CR-3394 did not provide validation of the spherical model. 

Rather, the justification was apparently the need of the probabilistic study to quantify a large 

number of breaks and the spherical ZOI model met that need. In retrospect, the probabilistic 

study would have provided somewhat relative debris generation probabilities with the general 

idea that perhaps once a grouping worst case breaks were identified, and then refined analyses 

could be performed for this subset of breaks to determine bounding debris estimates.

The spherical concept was again used in a BWR strainer blockage volunteer plant analysis 

study (NUREG/CR-6224) where the concept was extended from a hemisphere to a full sphere 

to evaluate the discharge from both ends of a double ended pipe break simultaneously. In this 

study, the sphere was systematically applied to all RCS pipe locations where a weld existed. 

The use of the spherical model was subsequently adopted for the BWR strainer blockage 

resolution methodology.

The spherical model was again adopted for the GSI-191 resolution. The diameter defined the 

ZOI within which insulation damage was assumed to occur. The ZOI was based on a damage 

pressure defined as the threshold for the insulation material. The damage threshold and the 

severity of damage within the ZOI was either based on experimental data or conservatively 

specified. 

RG 1.82, Revision 4 does not specifically recommend the shape of ZOI used in the debris 

generation analyses. Rather, RG 1.82, Revision 4 states that the size and shape of the ZOI 

should be consistent with experiments performed for specific debris sources and should extend 

until the pressure wave impulse and jet pressures decrease below the experimentally 

determined damage pressures appropriate for the debris source. Further, Rather, RG 1.82, 

Revision 4 states that if the evaluation uses simplified ZOI models, such as the spherical ZOI 

models, licensees should apply sufficient conservatism to account for simplifications and 

uncertainties in the model. The NRC staff’s acceptance of the spherical ZOI model is based on 

the URG’s adoption of the use of the spherical model as the best means to account for the 

impact of drywell congestion, drywell structural interactions, and the dynamic effects of pipe 

separation. The staff acceptance of the spherical model for the GSI-191 resolution appears in 

the staff safety evaluation report, “Safety Evaluation by the Office of Nuclear Reactor Regulation 

Related to NRC Generic Letter 2004-02, Nuclear Energy Institute Guidance Report, NEI 04-07, 

Pressurized Water Reactor Sump Performance Evaluation Methodology,” on the industry 2004 

resolution guidance document, NEI 04-07. The staff agreed that the spherical zone is a 

practical convenience that accounts for multiple jet reflections and mutual interference of jets 

from opposing sides of a guillotine break, as well as the pipe whip, and that the staff concurs 

with the use of a spherical ZOI as a practical approximation for jet impingement damage zones.

The spherical model is applied by determining the volume of the isobar within a freely 

expanding jet that corresponds to the destruction pressure for a specific material. 
5-23

The destruction pressure for the material of interest is determined on the basis of experimental 

data. If the jet stagnation pressure exceeds this pressure, damage to the insulation can be 

expected. The volume of a pressure isobar within the freely expanding jet which corresponds to 

the destruction pressure for the material is then calculated, typically using the ANSI/ANS-58-2-

1988 standard (ANSI, 1988). This volume is then doubled to simultaneously account for jets 

from both ends of a DEGB and then converted to an equivalent spherical volume for each 

specific insulation-system type.

Figure 5.3-5. Schematic Diagram of Spherical-Equivalent Jet Model 

(SG = steam generator, RCP = reactor coolant pump, 

RPV = reactor pressure vessel, HL = hot leg)

The dynamics of an expanding jet have been correlated to the diameter of the pipe break to 

facilitate the analysis of post-LOCA debris generation in reactor containments. Using this 

relationship destruction pressure test data for various target materials taken with small-diameter 

nozzles have been correlated with the larger-diameter plant piping breaks. The jet expansion 

model in the ANSI/ANS-58-2-1988 standard (ANSI, 1988) is also correlated to the break 

diameter. Since the equivalent spherical ZOI model is based on the ANSI standard, it also 

correlated to the break pipe diameter. The terminology associated with the dispersing jet and 

with the corresponding spherical model is similar and can be confusing. In relation to an actual 

jet, the jet centerline pressures and associated destruction are typically correlated to the number 

of L/Ds, where L represents the axial distance from the jet nozzle to the point in question and D 

represents the nozzle diameter. For example, if the test target was physically placed 20 in. in 

front of a 4-in. diameter test nozzle, then that target was placed 5 L/D downstream of the 

nozzle. With respect to the spherical ZOI model, the radius of the sphere is specified in a

number of pipe diameters. For example, a 5D specification refers to a spherical ZOI radius that 

is five times that of the pipe diameter, whereas a 5 L/D specification refers to an axial position 

inside a prototypical jet that is five times the test nozzle diameter downstream from the test 

nozzle. These two very different specifications are related only when the volumes within isobar 
5-24

pressures of a test jet are related to the equivalent spherical volumes. These two specifications 

have sometimes been misreported and perhaps misunderstood. Herein, “L/D” refers to a test 

jet and “D” refers to a spherical ZOI.

Basis for Model 

For unobstructed flow, the equivalent spherical model preserves the pressure isobar volumes 

associated with jet dispersion as predicted by the ANSI/ANS-58-2-1988 standard or an alternate 

model. The spherical zone is a practical convenience that accounts for multiple jet reflections 

and mutual interference of jets from opposing sides of a guillotine break, as well as pipe whip. It 

is important to note that when the spherical volume is computed using an acceptable 

approximation for unimpeded free-jet expansion, the actual energy loss involved in multiple 

reflections is conservatively neglected to maximize the size of the ZOI. The staff concurs with 

the use of a spherical ZOI as a practical approximation for jet impingement damage zones. 

Extensive damage due to a redirected jet was demonstrated in the HDR tests, although 

destructive energies would decrease with each deflection. The spherical ZOI has not been 

validated with respect to pressure wave effects, where unobstructed wave propagation likely 

differs from that of an expanding jet, and wave dispersions, reflections, diffractions, merging, 

and focusing were not evaluated.

The spherical ZOI model has the inherent assumption of a uniform distribution of insulation 

within the break compartment, that is, the piping and insulation around the break reasonably 

well represents that of the break compartment. The model might give non-conservative results 

in a situation where the conical jet could impact the substantial quantities of insulation on a 

steam generator, for example, but the spherical model does not reach from the break to the 

steam generator. Nonetheless, insulation quantities tend to collocate with the concentration of 

probabilistic break locations. This issue is a greater concern for the insulation types that require 

higher destruction pressures, and hence smaller ZOIs. Many of the lower destruction pressures 

result in ZOIs so large that the ZOI nearly encompasses the entire break compartment and all 

such insulation within the compartment is predicted to become debris. In other words, the 

uncertainty associated with this inherent assumption is greater for a smaller ZOI. In certain 

cases, an important insulation type, such as calcium silicate (known to cause high strainer head 

losses), is located rather sporadically at locations where bulkier insulations do not fit well. As 

noted in RG 1.82, Revision 4, the spherical model may or may not conservatively encompass 

such insulation. It is up to the analyst to ensure that these conditions are conservatively treated.

The staff allowed the truncation of the spherical ZOI whenever the ZOI intersects a robust 

barrier, such as a wall structure or large piece of equipment. The spherical ZOI should be 

centered at the location of the break, and where the sphere extends beyond robust barriers, 

such as walls, or encompasses large components, such as tanks and steam generators, the 

extended volume can be truncatedThe shadowed surfaces of components should be included in 

this analysis and not truncated, because debris generation tests clearly demonstrate damage to 

shadowed surfaces of components. Licensees electing the conical jet model (direct 

impingement model refinement) should retain the volume for conservatism.

In some cases it may be necessary to resize a truncated ZOI. If a truncated ZOI is resized to 

retain the original jet isobar volume, the resized ZOI radius would increase from that of the untruncated ZOI. Although jet reflections off of the robust barrier would dissipate energy, the 

reflection would not remove all of the reflected jet’s energy. The impact of the truncation process 

depends on the extent of the truncation. The truncation could shave off a small sector of the 

sphere or could reduce a sphere to a near hemisphere (a break next to a wall), and even more 

severe truncations are possible. For example, for a nozzle break inside the annular gap 
5-25

between the reactor vessel and the shield wall, truncation of the ZOI would reduce the original 

ZOI to a small fraction of the original volume, but this is clearly unreasonable. In this situation, 

the annulus would channel the break flow, extending the region of destruction well beyond the 

original ZOI radius from the break location. Sound judgment should be used when determining 

whether to resize the ZOI after truncation. 

A different ZOI size can be used for each material based on its specific destruction pressure, or 

alternatively, the largest ZOI based on the least robust material, could be applied to all 

containment materials.

Accepted ZOIs for Insulations, Fire Barriers, etc.

Table 5.3-4 presents the material-specific destruction pressures for both BWRs and PWRs that 

were accepted by the NRC staff as documented in the respective utility guidance staff 

evaluation reports [NRC-SER-1998 for BWRs and NRC-SER-2004 for PWRs]. Destruction 

pressures were obtained from small-scale debris generation tests and volumes were obtained 

by using the ANSI/ANS-58.2-1988 standard; these data were used to determine the pressure 

isobars corresponding to each destruction pressure. The isobar volume calculated for one pipe 

end is doubled to account for both pipe ends. A different ZOI size can be used for each 

material-specific destruction pressure for each potential debris source in the vicinity of a break.

With one exception, all the destruction pressures in Table 5.3-4 were obtained from the air jet 

debris generation testing conducted during the course of the BWR resolution. Some pressures 

were adjusted downwards from the original utility recommendations by the staff to account for 

uncertainties, such as interpretation of the data and the conservative application of air jet test 

data to a two-phase depressurization flow. During the BWR resolution, it was recognized that a 

main steam line break would generate substantially greater volumes of debris than would a 

recirculation pipe break because the steam line break was not only live steam, it was at a higher 

temperature than a low-quality two-phase recirculation pipe break. A CFD evaluation 

demonstrated that compressed air at 1000 psig would be considered a reasonable 

approximation of a live steam at a BWR operating pressure of about 1015 to 1040 psig. The 

CEESI test facility had the capability of compressing air to 1110 psig and could deliver air to a 

test nozzle at 1000 psig. Hence, it was decided that the CEESI test facility could generate data 

compatible with a BWR steam line break. Targets of various insulation types and jacketing 

were placed at various distances from the jet with the objective of determining the minimum 

threshold pressures for generating insulation debris. These thresholds became the evaluation’s 

destruction pressures.

A PWR hot leg break would result in a two-phase steam/water jet at a higher pressure than a 

BWR steam line break. The saturation pressures in the PWR hot leg can reach about 1800 

psia. Lacking debris generation test data specific to PWR two-phase break, the staff 

conservatively reduced some destruction pressures from those accepted for BWRs due to the 

associated uncertainties. For example, the destruction pressure for K-wool, shown in Table 5.3-

4, was reduced 40% from 40 psig down to 24 psig. The staff’s evaluation of the ANSI standard 

isobars [NRC-SER-2004] associated with the PWR destruction pressures resulted in the ZOI 

radii are also shown in Table 5.3-4 to provide visualization of the impact of the destruction 

pressures on ZOI size.

The reduction of the Cal-Sil destruction pressure from 150 psig down to 24 psig was based on 

the OPG two-phase test data (OPG, 2001) where calcium silicate with aluminum cladding and 

stainless steel bands was tested. The destruction pressure of 24 psig was based on the OPG 
5-26

test that was located farthest from the nozzle, i.e., 20 L/D. There were two non-conservative 

factors associated with this 20 L/D test. First, substantial damage occurred to the target (22% 

of the target was reduced to debris); therefore the actual threshold for the onset of destruction 

was not experimentally achieved. Second, the OPG test pressure of 1450 psia was less than 

the typical PWR operating pressure. Regardless the staff, after careful review, chooses to 

accept the 24 psig as the calcium silicate destruction pressure and considers it conservative for 

the application.

Table 5.3-4. Damage Pressures and Corresponding Volume-Equivalent Spherical ZOI 

Radii

Insulation Type

Destruction 

Pressures for 

BWRs (psig)a

Destruction 

Pressures for 

PWRs (psig)

PWR 

ZOI Radius/

Break Diameter

Transco RMI Darchem DARMET 190 114 2.0

Jacketed NUKON® with Sure-Hold®

bands Mirror® with Sure-Hold® 

bands

150 90 2.4

K-wool 40 24 5.4

Cal-Sil (Al cladding, SS bands) 150 24 5.45

Temp-Mat with stainless steel wire 

retainer

17 10.2 11.7

Unjacketed NUKON®, Jacketed 

NUKON® with standard bands 

Knaupf

10 6 17.0

Koolphen-K 6 3.6 22.9

Min-K/Mirror® with standard bands 4 2.4 28.6 a

The destruction pressures for Cal-Sil and Min-K for BWRs are from NUREG/CR-6762, Vol. 3.

Debris generation tests and studies have confirmed that insulation products having outer 

casings, jackets, or other similar mechanical barriers resistant to jet impingement yield smaller 

quantities of debris than do less robust systems. Various studies have also demonstrated 

dependence between the orientation of the jacketing seam relative to the jet and the amount of 

debris generation. This finding suggests that the integrity of the jacket during impingement is an 

important feature for minimizing debris generation. Russell reports (OPG, 2001), for example, 

that double-jacketing of an insulation product with a second overcladding of stainless steel 

having a rotated opposing seam was effective in minimizing the distance between the jet and 

target before the onset of damage occurred.

Estimating Size Distributions

The debris transport analysis requires the realistic or conservative specification of a size 

distribution for each type of debris. Finer debris is transported much more readily than coarser 

debris. The first step in specifying debris size distribution is characterizing debris categories 

with respect to the transport properties of the various debris sizes. The following discussion 

(taken from SE Appendix II of NRC-SER-2004) pertains to debris formed from fibrous insulation 

blankets and serves as a good example of debris size categorization.

The debris generation analysis assumed some damage to all insulation within the break-region 

ZOI such that all of the insulation within the ZOI is assumed to be debris. The damage could 
5-27

range from slight (e.g., insulation erosion occurring through a rip in the blanket cover), which 

leaves the blanket attached to its piping, to the total destruction of a blanket with its insulation 

reduced to small or very fine debris. Fibrous debris was categorized into one of four categories 

based on transport properties so that the transport of each type of debris could be analyzed 

independently. Table 5.3-5 shows these categories and their properties. The two smaller and 

two larger categories differed primarily with regard to whether the debris was likely to pass 

through a grating typical of those found in nuclear power plants. Thus, fines and small pieces 

pass through gratings but large and intact pieces do not. The fines and small pieces are much 

more transportable than the large debris. The fines were then distinguished from the small 

pieces because the fines would tend to remain in suspension in a sump or suppression pool, 

even under relatively quiescent conditions, whereas the small pieces would tend to sink. 

Furthermore, the fines tended to transport more like an aerosol in the containment-air/steam 

flows and were slower to settle than the small pieces when airflow turbulence decreased. The 

CEESI tests (NUREG/CR-6369) illustrated that when an LDFG blanket was completely 

destroyed, 15 to 25% of the insulation was in the form of very fine debris (i.e., debris too fine to 

collect readily by hand). The distinguishing difference between the large and intact debris was 

whether the blanket covering still protected the fibrous insulation. Fibrous insulation without a 

cover may erode further due to containment sprays, spray drainage, or exposure within a sump 

or suppression pool, whereas a covered blanket is not likely to undergo further erosion.

Debris-transport analysis has used volumes of fibrous debris interchangeably with mass on the 

basis that the density is that of the undamaged (as-fabricated) insulation. Certainly, the density 

would be altered by the destruction of the insulation and by water saturation of the debris. 

Estimation of debris-size distribution should be based on experimental data, but when such data 

are not available, it is conservative to assume that all of the ZOI debris would be reduced to 

highly transportable suspendable fines.

The volume of debris generated within a ZOI depends on (1) the size of the ZOI defined by the 

spherical ZOI radius, (2) the concentration of a particular insulation within the ZOI. Plantspecific information (i.e., the volume of a particular insulation within the ZOI divided by the 

volume of the ZOI) determines the insulation average concentration within a ZOI. Integration of 

experimental data on debris generation is required in order to determine the fraction of the ZOI 

insulation that is damaged into a particular debris-size classification. The integration is 

represented by the following equation:

( ( )) ∫ = ZOI r

d jet

ZOI

ZOI f P r r dr

r

F

0

2

3

3

where,

FZOI = fraction of the ZOI insulation type i that is damaged into a particular debris size 

classification

fd = fraction of debris damaged into a particular debris size as a function of the jet pressure 

Pjet, which is a function of the spherical radius, r, within the ZOI, and

rZOI = outer radius of the ZOI.

Implicit in this integration is the assumption that the insulation is uniformly distributed within the 

ZOI, which may not be realistic. Because the functional information needed for this integration 

is not available in an equation form simple enough for a formal integration to proceed, the 

following simplification is used.
5-28

where

f fines = fraction of debris damaged into a particular debris size as a function of the jet 

pressure Pjet at a radius of rj

The spherical ZOI is first subdivided into numerous spherical shells (j), which could, but not 

necessarily, correspond to specific pressure isobars. The same integration would be performed 

for each debris size classification, e.g., fines, small, large, and intact debris size categories. 

The precision of the integration increases with the number of subdivisions. In a spreadsheet, jet 

pressures are listed in increasing values, and then the spherical radii are determined, followed 

by the damage fractions evaluated at each rj. For the intervals, the average damage across the 

interval and the volume of the interval are determined. Multiplying the average interval damage 

by the interval volume, then summing, and dividing by the total ZOI volume, yields the debris 

fraction for the ZOI.

A review of the air jet testing debris generation data, both the BWROG air-jet impact testing 

(AJIT) data (NRC-SER-1998) and the DDTS data (NUREG/CR-6369) indicated that NUKON®, 

Transco Products Inc., and Knauf fiberglass insulation underwent similar damage. These types 

of insulation have approximately the same as-manufactured density (approximately 2.4 lb/ft3), 

and their recommended minimum pressures for destruction are usually taken to be the same 

pressure. Therefore, these and similar insulations have been grouped together as LDFG 

insulation. The fractions for the small fines (small and fine categories together) from the AJIT 

debris generation test data as a function of the jet centerline pressure for these three types of 

LDFG insulation are plotted in Figure II-2 of Appendix II in NRC-SER-2004 (from which Figure 

5.3-1 was generated). The data represented by a curve drawn though the data correlate the 

damage as a function of jet pressure, which subsequently can be used to integrate the damage 

over the ZOI. The DDTS test data in Figure 5.3-1 used a 4-in. nozzle, whereas the BWROG 

test data used a 3-in. nozzle. For LDFG, any jet pressures greater than 17 psi have been 

observed to destroy a significant portion the blanket into small fine debris.

At the NRC-SER-2004 damage pressure of 6 psi for NUKON insulation, the integration of the 

curve in Figure 5.3.1 resulted in 22% of the ZOI debris being either small pieces or suspendable 

fines. The baseline methodology assumes that all of this debris transports to the strainer. 

Plants that perform evaluations that are more realistic than the baseline method may need to 

subdivide the baseline small-fine-debris class into fines and small-piece debris. In the refined 

analysis the fines (e.g., individual fibers) remain suspended in the pool, and the small-piece 

debris sinks to the pool floor and may or may not transport to the sump screen. In the debris 

generation tests conducted during the DDTS, 15 to 25% of the debris from a completely 

disintegrated fiberglass blanket was classified as non-recoverable because the debris either 

exited the test chamber through a fine-mesh catch screen or was otherwise too small for hand 

collection. Therefore, it would be reasonable to assume that 25% of the small fine debris is in 

the form of individual fibers, and that the other 75% is in the form of small-piece debris. 

The focus of the debris size categorization should be on conservatively estimating the 

suspendable fines. The rather large PWR replacement strainers typically resulted in sump 

pools that flowed so slowly that only the suspendable debris would tend to be transported to the 
5-29

strainers. However, debris accumulation on BWRS strainers may differ somewhat from the 

PWRs strainer in that the BWRs located in a suppression pool would be subjected to a period of 

higher turbulence associated with RCS depressurization and some BWR have relatively smaller 

strainers.

5.3.5 Characteristics of Generated Debris

The debris generation evaluation must characterize the debris and estimate the bounding 

quantities of the debris. The most important characteristic is size distribution, which has been 

discussed above with respect to both debris generation testing and analytical determination of 

debris size distribution within the spherical ZOI model. Debris size can affect buoyancy and the 

tendency for the debris to be affected by turbulence in the pool. Some debris would readily sink 

in a pool of water, very fine debris would remain suspended in solution, and some debris could 

even float on the surface. Debris size strongly affects the transport of debris, its accumulation 

on a strainer, and how it affects head loss when deposited in a debris bed. Whether or not a 

piece of settled debris would move with the flow of water across the floor of the pool depends on 

the size of the debris. The uniformity of accumulation on a strainer also depends upon the size 

of the debris.

In addition to debris size, density is important. Specifically, both the bulk density of the piece of 

debris and the density of the material itself. For example, the bulk density of fibrous debris 

includes the free space between the fibers that is filled with air. The material density is the 

density of the fiberglass forming the fibers. The densities, the fiber diameters, and the spacing 

between the fibers affect how readily water can replace the air once a piece of fibrous debris 

becomes submerged in water, thus affecting its buoyancy. Staff evaluation of the debris density 

values and their concerns on the use of the density data are discussed in SE of NEI 04-07 

(ML043280007). 

The rate at which individual fibers can erode or break away from a bulk piece of debris is 

important. The erosion process is typically treated in the transport analysis. Erosion or 

disintegration of larger debris into smaller pieces increases debris transport; especially 

important is the generation of individual fibers or fine particulates, which would effectively 

remain suspended.
5-30

Size Description Airborne Behavior Waterborne Behavior Debris-Capture 

Mechanisms

Requirem

Retention

Fines Individual fibers 

or small groups 

of fibers.

Readily moves with 

airflows and slow to settle 

out of air, even after 

completion of blowdown.

Easily remains suspended 

in water, even relatively 

quiescent water.

Inertial impaction

Diffusiophoresis

Diffusion

Gravitational settling

Spray washout

Should be 

that is not 

to CSs or 

Natural-ci

transport 

into a spra

quiescent 

flow throu

possible.

Small 

Pieces

Pieces of debris 

that easily pass 

through gratings.

Readily moves with 

depressurization airflows 

and tends to settle out 

when airflows slow.

Readily sinks in hot water, 

then transports along the 

floor when flow velocities 

and pool turbulence are 

sufficient. Subject to 

subsequent erosion by flow 

water and by turbulent pool 

agitation.

Inertial impaction

Gravitational settling

Spray washout

Should be 

that is not 

to high ra

substantia

Retention 

reactor ca

subseque

Large 

Pieces

Pieces of debris 

that do not easily 

pass through 

gratings.

Transports with dynamic 

depressurization flows but 

generally is stopped by 

gratings.

Readily sinks in hot water 

and can transport along the 

floor at faster flow velocities. 

Subject to subsequent 

erosion by flow water and by 

turbulent pool agitation.

Trapped by structures 

(e.g., gratings)

Gravitational settling

Should be 

structure 

drainage 

are not su

object. S

erosion.

Intact Damaged but 

relatively intact 

pillows.

Transports with dynamic 

depressurization flows, 

stopped by a grating, or 

may even remain attached 

to its piping.

Readily sinks in hot water 

and can transport along the 

floor at faster flow velocities. 

Assumed to remain encased 

in its cover, thus, it is not 

subject to significant 

subsequent erosion by 

water and by turbulent pool 

agitation.

Trapped by structures 

(e.g., gratings)

Gravitational settling 

Not detached from 

piping

Should be 

structure 

drainage 

are not su

object. In

would not 

encaseme

Table 5.3-5. Fibrous Debris-Size Categories and Their Capture and Retention Proper
5-31

5.4 Debris Transport Evaluation

5.4.1 Overview

The debris generation methodology is used for estimating bounding quantities of debris that 

could result from dislodged piping thermal insulation, fire barrier materials, coatings, and other 

materials in the vicinity of the break. Subsequently, the debris would be chaotically propelled by 

the jet effects as the primary system coolant is blown down and pressurizes the containment. 

RCS depressurization flow would dynamically propel debris, which could, due to inertial forces, 

impact structures causing the debris to stick onto those structures. Larger debris could be 

captured by structures, such as gratings, and wherever depressurization flow slowed, the debris 

could settle due to gravity. Because the containment pressurization results in air and vapor flow 

into all containment free space, fine debris would be propelled toward the space. At the end of 

the primary system depressurization, debris would be dispersed into both the upper and lower 

containments, where debris would be both inertially captured onto surfaces of all orientations 

and gravitationally settled onto compartment floors and equipment. These transport processes 

are referred to as the “blowdown transport.” For PWRs, some debris would reside on the sump 

pool floor before the sump pool is established. For BWRs, some debris would reside on the 

drywell floor and within the suppression pool.

This LOCA-generated debris, along with the preexisting containment latent debris, would then 

be subject to subsequent transport by the drainage of the break overflow, the containment 

sprays, and any condensate flow. These transport processes are referred to as the “washdown 

transport.” For PWRs, debris that is either initially deposited onto the sump pool floor or washed 

down from the upper containment to the sump pool would subsequently undergo transport 

within the sump pool, first as the sump pool fills before the recirculation pumps start, and then 

within the established sump pool. For BWRs, the debris is either deposited within the 

suppression pool by the depressurization flows through vent downcomers or subsequently by 

the break, spray, and condensate drainage flows. For BWRs, the blowdown and chugging 

associated with RCS depressurization has a large influence on transport (and erosion) within 

the suppression pool. Additionally the ECCS recirculation starts immediately in BWRs, while in

PWRs there is a significant delay. This delay may allow significant debris to settle and prevent 

its transport. Within the BWR suppression pool or PWR sump pool, debris transport would be 

governed by various physical processes, including the settling of debris in pools in which 

turbulence levels may vary significantly, tumbling/sliding of settled debris along the pool floor, 

re-entrainment of settled debris, lifting of debris over structural impediments, retention of debris 

on strainers of various orientations, and further destruction of debris as a result of pool flow 

dynamics, thermal effects, and chemical effects. Some types of debris residing within a pool 

can be further degraded by pool flow dynamics (e.g., individual fibers can detach from fibrous 

shreds). Some portion of the debris within the pool would subsequently be transported to and 

accumulated on the recirculation suction strainers. 

The blowdown/washdown processes also have the potential to generate additional debris due to 

the interactions of flows, elevated temperatures, and moisture with various otherwise 

undamaged materials within the containment. These include, but are not limited to, such 

materials as unjacketed insulations, unqualified coatings, and labels. For example, a deluge of 

spray drainage over unjacketed/uncovered fibrous insulation could erode transportable fibers 

from that insulation. The primary concern has been the generation of coating debris from 

unqualified coatings, but all potential sources should be considered.
5-32

Long-term recirculation cooling must operate according to the range of possible accident 

scenarios. A comprehensive debris transport study should consider an appropriate selection of 

these scenarios, as well as all engineered safety features and plant-operating procedures. The 

maximum debris transport to the strainer likely will be determined by a small subset of accident 

scenarios, but this scenario subset should be determined systematically. Many important debris 

transport parameters will be dependent on the accident scenarios. These parameters include 

the timing of specific phases of the accident (i.e., blowdown, injection, and recirculation phases) 

and pumping flow rates. The blowdown phase refers to primary-system depressurization. The 

injection phase corresponds to ECCS injection into the primary system from an external source, 

a process that subsequently establishes the PWR sump pool. The recirculation phase refers to 

long-term ECCS recirculation. 

The physical processes of all these transport phases are so varied and complex that detailed 

analysis is difficult at best and is typically considered to be too complex to pursue, except in 

areas where debris characteristics ans conditions affecting transport can be predicted with more 

confidence. Because the primary analytical objective is the realistic or conservative estimation

of the maximum quantity of debris that can reach the strainer by type and size category, the 

more difficult-to-analyze processes can be conservatively bounded, while processes more 

amenable to analysis can be more realistically yet conservatively estimated. An analytical 

approach was developed during the BWR Drywall Debris Transport Study (DDTS) referred to as 

the “logic chart” approach (NUREG/CR-6369). It uses event-tree models to decompose the 

complex overall process into many smaller steps; some of which may be solved analytically or 

estimated based on data obtained from small-scale experiments. In quantifying such a chart, 

conservatively estimated fractions are used for steps where data or analysis is not available and 

more realistic fractions are used for the steps where data or analysis is available. The 

multiplication of step fractions throughout the logic chart results in a final distribution of the 

debris that is conservative with respect to debris accumulation on the strainer. An example 

logic chart is shown in Figure 5.4-1.

The transport of each debris type and size category should be considered separately because 

each has unique transport characteristics. The important transport characteristics are whether 

the debris is buoyant, prone to settling, or likely to be transported as relatively uniformly 

dispersed suspended debris. A four-category size classification for fibrous debris, shown in 

Table 5.3-5, was developed during a reference plant study (Appendix VI in NRC-SER-2004), 

which addressed the associated key aspects of fibrous debris transport. The four-category 

system was recommended (NRC-SER-2004) for licensee use in the GSI-191 resolutions. The 

size categories are (1) fines that remain suspended, (2) small-piece debris that is transported 

along the pool floor, (3) large-piece debris with the insulation exposed to potential erosion, and 

(4) large debris with the insulation still protected by a covering, thereby preventing further 

erosion.

The level of detail employed in a transport evaluation depends on resources and resolution 

tolerance to conservatism. The simplest analysis uses the conservative assumption of 

complete transport and accumulation onto the strainer, but this oversimplification is typically 

unacceptable. A more detailed evaluation could involve analysis such as CFD simulations to 

predict flow metrics of a PWR sump pool, combined with debris (type and size specific) 

empirical transport data, to determine whether transport would occur. 
5-33

Alternately small-scale plant-specific experiments could be conducted to gain understanding of 

the transport processes. The remaining subsections discuss (1) blowdown/washdown debris 

transport, (2) sump or suppression pool transport, and (3) erosion of containment materials and 

further degradation of debris. The final subsection discusses the importance of characterizing 

the size distribution of the debris estimated to arrive at the recirculation strainers (i.e., 

characteristics that affect debris accumulation). 
5-34

Figure 5.4-1. Chart for Sump Pool Debris Transport
5-35

5.4.2 Blowdown/Washdown Debris Transport

This section discusses the blowdown and washdown transport methodology that provides an 

estimate for the transport of debris from its points of origin to the sump or suppression pool. 

The transport analysis consists of two components: blowdown debris transport, where the 

effluences from a high-energy pipe break would destroy insulation near the break and then 

transport that debris throughout the containment, and washdown debris transport due primarily 

to operation of the containment sprays. Along the debris-transport pathways, substantial 

quantities of debris would come into contact with containment structures and equipment, where 

that debris could be retained, thereby preventing or delaying further transport. The 

blowdown/washdown debris-transport analysis provides the source term for the subsequent 

recirculation transport (i.e., within PWR sump pool or a BWR suppression pool. Different types 

of insulation would havd different capture mechanisms. For example, RMI and fibrous debris 

would be captured by significantly different mechanisms during blowdown. The methodology 

would also consider particulate types of insulation (e.g., calcium silicate) where the primary 

difference might be in the erosion process. Further detailed guidance includes (1) a detailed 

blowdown/washdown transport analysis performed for a PWR reference plant that had a 

Westinghouse reactor and large-dry containment (Appendix VI in NRC-SER-2004) and (2) the 

DDTS (NUREG/CR-6369).

5.4.2.1 Blowdown/Washdown Debris-Transport Phenomenology

A spectrum of physical processes and thermal-hydraulic phenomena govern the transport of 

debris within containment. The physical processes range from the transport/deposition physics 

of aerosols to the dynamic impaction of larger pieces of debris onto containment surfaces. The 

design of a particular containment would influence the flow dispersions and thereby affect debris 

transport and deposition. Because of the energetic blowdown flows following a LOCA, 

insulation destruction and subsequent debris transport are rather chaotic. For example, a piece 

of debris could be deposited directly near the sump strainer or it could take a much more 

tortuous path, first going to the dome and then being washed back down to the sump by the 

sprays. Alternately, a piece of debris could be trapped in any number of locations. Aspects of 

the blowdown/washdown portion of the debris transport analysis include characterization of the 

break, design and configuration of the plant, generation of debris by the break flows, and both 

air- and water-borne debris dynamics.

Many features in nuclear plant containments significantly affect the transport of insulation 

debris. As the RCS depressurizes, the break effluents will flow towards the suppression pool in 

BWRs and towards the containment dome in PWRs. Structures such as gratings located in the 

paths of the dominant flows likely would capture substantial quantities of debris. For PWRs, the 

lower compartment geometry - such as the open floor areas, ledges, structures, and other 

obstacles - defines the shape and depth of the sump pool area and is important in determining 

the potential for airborne debris to deposit directly onto the sump floor. Furthermore, the relative 

locations of the sump, LOCA break, and drainage paths from the upper regions to the sump 

pool are important in determining the distribution of debris deposition onto the sump floor during 

blowdown and washdown. For BWRs, the geometry of drywell floor and entrances into the vent 

downcomers influence the transport of debris into the suppression pool.

Transport of debris is strongly dependent on the characteristics of the debris that has formed. 

These characteristics include the types of debris (insulation type, coatings, dust, etc.) and the 

size distribution and form of the debris. Each type of debris has its own set of physical 

properties, such as density, specific surface area, buoyancy (including dry, wet, or partially wet), 
5-36

and settling velocity in water. Pooled water can form within the upper containment regions, e.g., 

the drywell floor in a BWR or a refueling pool in a PWR. These pools can affect the transport of 

debris during the washdown phase. The size and form of the debris, in turn, depends on the 

method of debris formation (e.g., jet impingement, erosion, aging, and latent). The size and 

form of the debris affect transport of the debris to the sump or suppression pool. For example, 

fibrous debris may consist of individual fibers or large sections of an insulation blanket and all 

sizes between these two extremes.

Debris transport is affected by a full spectrum of physical processes, including particle 

deposition and re-suspension for airborne transport and both settling and re-suspension within 

calm and turbulent water pools for both buoyant and non-buoyant debris. The dominant debriscapture mechanism in a rapidly moving flow likely would be inertial capture; however, in slower 

flows, the dominant process likely would be gravitational settling. Much of the debris deposited 

onto structures likely would be washed off by the containment sprays or possibly even by 

condensate drainage. Other debris on structures could be subject to erosion. Relatively 

complete discussion of the range of transport phenomena is found in the BWR and PWR PIRT 

panel reports (BWR-PIRT, PWR-PIRT). The BWR DDTS and the PWR SE on NEI 04-07, 

Appendix VI, provide analysis processes that focus on the phenomena determined to most 

govern the transport processes.

5.4.2.2 PWR Blowdown/Washdown Transport

PWR Blowdown Containment Dispersion

Following a break, primary system depressurization effluents flow toward the upper containment 

dome in a PWR. For large dry and subatmospheric containments, the steam generator 

compartments are designed to direct the flows directly into the upper containment. For ice 

condenser containments, the flows are directed into the ice condenser banks, which exit into the 

upper containment. Debris generated by a LOCA would be carried by these flows until either 

the debris was captured by or deposited onto a structure, or the debris gravitationally settled 

onto equipment and floors. The dominant deposition mechanism for larger airborne debris 

ejected from a steam generator compartment into the upper containment dome would be 

gravitational settling. For very fine particulate, containment spray fallout may become the 

dominant mechanism. The reference plant blowdown transport analysis presented in Appendix 

VI of staff SE on the NEI guidance document, NEI 04-07 (SE NEI-04-07, 2004) provides further 

guidance for conducting a detailed debris dispersion analysis.

The source of insulation debris is the region immediately surrounding the LOCA break, which is 

typically contained within a steam generator compartment. This region would be subject to the 

most violent of the containment flows where the primary debris capture mechanism would be 

inertial capture.1 For these reasons, the transport of debris within the region of the pipe break 

should be solved separately from that of the rest of the containment. 

The first step in determining the dispersal of debris from near the break is to determine the 

distribution of the break flow from the region, specifically, the fractions of the flow directed to the 

dome vs. other locations. 
5-37

In the Appendix VI analysis of NRC-SER-2004, the containment thermal-hydraulics code, 

MELCOR, was used to determine the flow distribution within and out of the steam generator 

compartment in which the break occurs for a large dry PWR containment.6

The LOCA-generated debris not captured within the region of the break would be carried away 

from the break region by the break flows. The primary capture mechanism near the break 

would be inertial capture or entrapment by a structure such as a grating. The break-region flow 

that occurred immediately after the initiation of the break would be much too energitic to allow 

debris simply to settle to the floor of the region. 

The inertial capture of fine and small debris occurs when a flowpath changes directions, such as 

flowpaths through doorways from a steam generator compartment into the sump-level annular 

space. These flowpaths often have at least one 90° bend, and because the structural surfaces 

are wetted by steam condensation and the liquid blowdown from the break, a portion of this 

debris could stick to the impacted surfaces. Debris-transport experiments conducted at CEESI 

(NUREG/CR-6369) demonstrated an average capture fraction of 17% for fine debris and small 

debris that make a 90° bend at a wetted surface. The flow in any of the flowpaths could 

encounter bends as the break effluents interacted with various equipment and walls. 

The platform gratings within the break region steam generator compartment would capture 

substantial debris, even if the gratings do not extend across the entire compartment.7

 The 

CEESI debris-transport tests demonstrated that an average of 28% of the fine and small debris 

was captured when the airflow passed through the first wetted grating that it encountered, and 

that an average of 24% was captured at the second grating. The large and intact debris would, 

by definition, be trapped completely by a grating. In addition, equipment such as beams and 

pipes were shown to capture fine and small debris. In the CEESI tests, the structural 

congestion of a typical BWR drywell was simulated using gratings, beams, and piping. Air jet 

generated fibrous debris was driven through this structural simulation to determine realistic 

capture fractions that could be applied to containment analysis. An average of 9% of the debris 

passing through the entire test section was captured.

To evaluate the transport and capture within the break region, the evaluation should be 

separated into many smaller problems that are amenable to resolution. The Appendix VI NRCSER-2004 analysis accomplished this separation using a logic-chart approach similar to that in 

Figure 5.4-1, but based on the structural details of the break region compartment. The headers 

across the top of the chart alternated among volume capture, flow split, and junction capture as 

the debris transport process progressed through the nodalization scheme. The nodalization 

scheme was constructed to place the gratings at junction boundaries. Chart header questions 

 

6

Most of the break effluent would be directed upward toward the large upper containment volume. 

Effluents venting into lower-level compartments by way of open access doorways would flow at much 

lower mass flow rates than those flowing to the upper containment. The MELCOR calculations predicted 

reference plant characteristic flow velocities within the break region steam generator compartment that 

ranged from approximately 25 to 200 m/s (80 to 660 ft/s) for a large break LOCA. Such large break flow 

velocities are capable of propelling even intact insulation blankets upwards into the upper containment. 

Inertial debris deposition is dependent on the flow velocities transporting the debris, debris properties, 

surface properties, and flow direction changes.

7

If a steam generator compartment grating at a level above the break is continuous across the entire 

compartment, then large piece debris may be effectively prevented from being ejected into the upper 

containment. If there is no grating or only partial gratings, large piece debris can be propelled into the 

upper containment and fall into the refueling pool, which is a concern for the upstream effects evaluation. 
5-38

asked (1) how much debris would be captured in a specific volume, (2) what is the debris 

transport distribution at a flow split, and (3) how much debris would be captured at a flow 

junction between two volumes? This analytical approach is rather detailed; therefore the 

interested reader is directed to the detailed example presented in Appendix VI of staff SE on the 

NEI guidance report, NEI 04-07 (SE NEI-04-07, 2004) for a more detailed discussion. The 

results were based on estimates of inertial capture on structures within a sub-volume region and 

at grating at specific junctions, and the airflow distributions at junction flow splits. For fine and 

small-piece debris, it is reasonable to assume that the debris split is approximated by the flow 

split. For large and intact-piece debris, the debris split may differ substantially from the flow 

split, depending on the geometry. The break region chart is used to track the progress of small 

debris from the pipe break until the debris is assumed to be captured or is transported beyond 

the compartment. Each application of this methodology should develop a plant specific chart.

Outside the break region compartment, debris dispersion and capture throughout the 

containment could also be handled by such detailed modeling, but the effort would be highly 

resource-intensive. Figure 5.4-2 shows an example of a small section of a potentially very large 

logic chart. This figure is an illustration of the number of decisions possible in a detailed 

transport analysis. In this chart, the regions are designated as Region j and Region j+1 

indicating that total number of regions for which the containment is subdivided is determined by 

the depth of the analysis and could be a substantial number. A simpler method was used in the 

reference plant study. The method was based first on dispersion of the debris by free volume 

and then by surface orientation within specific free-volume regions. First the free volume of 

each specific volume region was divided by total containment free volume, then these fractions 

were multiplied with the debris quantity of each debris type and size category to arrive at 

distributions for dispersing the debris among the volume regions. Then, in a similar manner, 

areas fractions were used to distribute the debris among the surfaces within each volume 

region. Dispersion distributions were based on actual volumes and areas and then adjusted 

with weighting factors based on engineering judgment. Obviously, the debris would 

preferentially settle to the floor surfaces, hence the weighting factors were adjusted to make 

most of the debris deposit onto the floors; however some of the fines would stick to vertical 

surfaces. 
5-39

Figure 5.4-2. Example of a Section of a Debris Transport Chart

PWR Containment Spray and Condensate Drainage Washdown

Debris that is deposited throughout the containment subsequently would be subject to potential 

washdown by the containment sprays and by drainage of the spray water to the sump pool and 

(to a lesser extent) by drainage of condensate. Debris on surfaces that would be hit directly by 

the sprays would be much more likely to be transported with the flow of water than would debris 

on a surface that is merely wetted by condensation. The transport of debris entrained in spray 

water drainage is not as easy to characterize. If the drainage flows were substantial and rapidly 

flowing, the debris likely would be transported with the water. However, at some locations, the 

drainage flow could slow enough for the debris to remain in place. That is, the force that the 

water exerts on a piece of debris depends on both the localized velocity of the water flow and on 

the projected contact surface area. When the water depth is shallow, then only a portion of the 

piece of debris (depending on the size of the debris) may be in contact with the water and the 

water would simply flow around the piece. With smaller amount of water, a sheeting effect can 

be effective at moving the debris. As drainage water drops from one level to another, as it 

would through the floor drains, strairwells, or by falling over floor edges, the impact of the water 

on the next lower level could cause splashing sufficiently to transport debris beyond the main 

flow of the drainage, thereby essentially capturing the debris a second time. In addition, the 

flow of water could erode the debris further, generating more fine debris. These considerations 
5-40

should be factored into the analysis. The washdown processes are illustrated schematically in 

Figure 5.4-3.

Figure 5.4-3. Schematic Diagram of Debris-Washdown Processes

The drainage of spray water from the location of the spray heads down to the sump pool is 

evaluated to provide insights for the transport analysis, such as identifying areas that would not 

be affected by the sprays, the water drainage pathways, likely flowpaths for drainage water to 

the sump pool, and locations where drainage water would fall from one level to the next. A key 

result of the washdown analysis is an estimation of how much debris is washed to the sump 

pool via each of the main drainage pathways (based on the assumption of the debris being 

uniformly mixed with the flows entering the pool). This information is typically needed for the 

evaluation of sump pool debris transport.

The spray and condensate drainage analysis can contribute to the upstream effects analysis, 

which addresses the potential holdup of drainage water in the upper containment to the extent 

that the holdup can adversely affect the sump pool water level, which in turn, can affect strainer 

submergence, vortexing, and the recirculation pump NPSH. The blockage of any water 

drainage could result in water holdup, but the primary locations of concern are the refueling pool 

drains because the refueling pool represents a substantial potential volume of water. An 

adequate understanding of the water drainage from the upper containment to the sump pool is 

needed to ascertain potential locations for water holdup, as well as debris washdown transport.

Certain types of insulation debris could potentially continue to erode to smaller debris during 

containment washdown. Experiments conducted in support of the DDTS analysis (NUREG/CR6369) demonstrated that fibrous insulation debris could be eroded further by the flow of water. 

The primary concern of the DDTS analysis was LDFG debris that was deposited directly below 

the pipe break and, therefore, was inundated by the break overflow. Debris erosion in this case 

was substantial (i.e., ≈9%/h at full flow). Debris erosion due to the impact of the sprays and 
5-41

spray drainage flows was certainly possible but was found to be much less significant. The 

DDTS concluded that <1% of the LDFG was eroded due to the direct impact of the containment 

sprays. However, the debris caught within cascading flows of accumulated spray drainage 

could be subjected to more forceful erosion than the direct spray droplets. However, in many 

situations falling water flows could simply push the debris aside. Debris erosion due to 

condensation and condensate flow was neglected. Insulation debris still within its cloth cover 

was not expected to erode further. For RMI debris, erosion was not a consideration. For 

microporous insulations such as calcium silicate or Min-K, the degree of potential washdown 

erosion has not been determined, and the outcome could vary substantially with the type of 

insulation and even by the insulation’s manufacture process (e.g., one vendor’s calcium silicate 

readily dissolves while another’s does not). The key PWR debris erosion process during 

washdown would be the erosion of debris impacted directly by the sprays and possibly debris 

layered on any gratings located below the break overflow. The erosion of debris on the sump 

pool floor would typically be evaluated under the sump pool transport processes, and most of 

the debris located directly below the break likely would be pushed away from the break area 

and be considered in the sump pool transport evaluation. 

Because the result of the erosion process is additional very fine and easily transportable debris, 

the process should be evaluated. All erosion products should be assumed to transport to the 

sump pool. Further, this debris would also likely remain suspended in the sump pool until 

filtered from the flow at the sump strainers. Therefore, even a small amount of erosion could 

contribute to strainer blockage.

To estimate the volume of debris that was eroded, the volume of small and large debris that was 

impacted by the sprays should be estimated first. In the reference plant study, 1% of the smalland large-piece debris that was directly impacted by the sprays was considered to have eroded 

on the basis of the DDTS conclusion that erosion by sprays was <1%. Note that the 1% value 

was based on small-scale tests where the spray flow rates were scaled to the volunteer BWR 

plant. If the spray flow rate was increased, the erosion rate could possibly increase; however 

the 1% erosion represented a conservative conclusion for a minor rate of erosion. Even if the 

spray-driven rate of erosion was increased, its contribution to the overall erosion within 

containment would likely remain relatively minor compared to the recirculation pool erosion. 

Note that erosion does not apply to fine debris because it is already considered to be individual 

pieces incapapble of being eroded, and does not apply to intact debris because the canvas 

cover would likely protect the enclosed insulation.

Retention of debris on surfaces during washdown needs to be estimated for the debris 

(postulated to be deposited) on each surface (i.e., the fraction of debris that remains on each 

surface). The estimates would be based on a combination of experimental data and 

engineering judgment. Generic assumptions used in the reference plant study included:

• For surfaces that would be washed only by condensate drainage, nearly all deposited fine 

and small debris likely would remain there. The study assumed 1% of the fibrous debris 

would be washed away (99% retention on the surface) in a realistic central estimate, and 

10% for an upper-bound estimate.

• For surfaces that were hit directly by sprays, the DDTS assumed 50% and 100% of small 

fibrous debris was washed away for the central- and upper-bound estimates respectively. 

Large and intact debris was assumed not be washed down to the sump pool (complete 

retention). 
5-42

• For surfaces that were not sprayed directly but subsequently drain accumulated spray 

water, such as floors close to spray areas, the retention fractions are much less clear. 

These fractions likely would vary with location and drainage flow rates and, therefore, 

should be location specific, with more retention for small pieces than for fine debris.

• All erosion products are assumed to completely wash to the sump pool. 

The overall blowdown/washdown transport fraction is the total quantity of debris entering the 

sump pool divided by the total volume of insulation generated within the ZOI.

In conclusion, the reference plant study in Appendix VI of NRC-SER-2004 developed a 

methodology that considered both transport phenomenology and plant features, and that 

divided the overall complex transport problem into many smaller problems that either are 

amenable to solution by combining experimental data with analysis or able to be judged 

conservatively based on the existing debris transport knowledge. The reference plant 

methodology resulted in predicted transport fractions that were conservative. The conservatism 

in the transport decisions is related to the availability of applicable data. Without data, the 

results should be conservatively hedged toward transporting the debris to the sump pool. The 

results also depended upon the analytical objective (i.e., bounding versus realistic results). 

Plant-specific analyses must consider a range of break locations. In performing 

blowdown/washdown analyses, it is important that (1) the debris-transport model correctly 

estimates the size and type of debris to match the characteristics of the debris-transport 

behavior, (2) the break region and the break region exits are analyzed in substantial detail 

because a significant portion of the debris capture may occur there, (3) the containment spray 

drainage patterns should be determined to support the washdown analysis, to determine where 

the debris would enter the sump pool, and to determine how the spray drainage would affect 

sump pool turbulence, and (4) the spray-drainage pathways, where potential debris blockage 

might occur, should be identified. The complexity of plant-specific methodologies could vary 

significantly from one plant to the next. 

In general, for the fine LOCA-generated debris, it is likely that realistic analysis will show that a 

high percentage of the fines would be transported to the sump pool via the spray drainage 

flows. The fines retained in the upper containment would be the fines blown into areas not 

impacted by the containment sprays or the spray drainage. Transport fractions tend to 

decrease as the debris size increases. Realistically speaking, RMI might be expected to 

transport less readily than fibrous debris because it is more dense. During the resolution of 

GSI-191, the licensees typically chose to make highly conservative blowdown/washdown 

assumptions rather than perform the detailed analyses outlined herein. This conservative 

approach was not unreasonable, considering that the majority of the fines blown into the upper 

containment would be predicted to wash down to the sump pool, and that the majority of the 

larger debris residing in or entering the sump pool would typically settle in the sump pool rather 

than accumulate on the strainer.

5.4.2.3 BWR Blowdown/Washdown Transport

BWR Blowdown Containment Dispersion

The physical processes governing BWR blowdown dispersion are basically the same as the 

processes described in Section 5.4.2.2 for PWRs. Blowdown within a BWR containment results 

in primary system depressurization with flows through the downcomer vents to the suppression 

pool. Debris generated by a LOCA would be carried by these flows, with portions of the debris 
5-43

being captured along the way by deposition onto structures or by gravitationally settling onto 

equipment and floors. The blowdown dispersion within a BWR drywell was studied in the DDTS 

(NUREG/CR-6369).

The BWR containments differ from PWR containments in both size and design. The BWR 

suppression pools allow the BWR containment volumes to be significantly smaller than the 

PWR containments. The break discharge from a BWR primary system would cause flows

toward the vent downcomers leading to the suppression pool. Gratings rather than solid floors 

typically separate the elevation levels in BWR drywells. A break above a continuous grating 

would trap the larger debris. Debris trapped on a grating directly below the break overflow 

would be subjected to substantial erosion. In addition to the break flows, the containment 

sprays would transport debris. Depressurization flows entering a vent downcomer may undergo 

turns, resulting in inertial debris capture at the vent entrances or debris may fallout onto the 

drywell floor. A pool of water would form on the drywell floor with its depth governed by the 

elevation of the entrances into the vent downcomers. The transport of debris in the drywell floor 

pool could be evaluated similarly to PWR sump pool transport. A CFD code was used in the 

DDTS to simulate the drywell floor pool for each of the BWR Mark I, II, and III designs. Debris 

transport within a BWR suppression pool is unique to BWRs and is discussed in Section 5.4.3.2.

The DDTS employed the logic-chart approach to decompose the overall transport process into 

individual steps, similar to the evaluation process described in the preceding section for PWRs. 

Typically, these charts treat each debris type and size category, and each break scenario 

separately. The analyst can choose the level of detail based on the application requirements 

and the information available.

A system level code, e.g., MELCOR, can be used to estimate containment conditions, flow 

dispersions, rates of flow, flow composition, condensation rates, etc. This information is useful 

when applying engineering judgment to transport models. The dominant debris capture 

mechanisms considered were inertial capture from fast moving flows and gravitational settling 

once flows slowed down.

Inertial capture of flow-driven fibrous debris was studied in the DDTS. The CEESI facility air jets 

were used to destroy fibrous insulation blankets and then to carry the debris downstream 

through a series of structural obstacles based on prototypical BWR containment congestion. 

The tests demonstrated the ability of structural components to capture debris. The average 

overall transport fraction for small debris in the CEESI tests was 33% of the total debris 

generated (i.e. ≈2/3 of the generated debris was captured, primarily by inertial impaction) within 

the test facility. Gratings were found to be the most effective debris catcher. Photographs of 

test debris capture on a grating were shown in Figure 5.3-2. Figure 5.4-4 shows a plot of the 

available debris capture data on a specific test grating, where the capture efficiency is plotted 

versus the debris loading approaching the grating. The capture efficiency did not seem to 

depend significantly upon the debris loading but did depend upon surface wetness. MELCOR 

analyses showed that steam condensation onto containment surfaces would happen relatively 

rapidly. The average fractions of small debris captured by each test structure component are 

shown in Table 5.4-1. The first continuous test grating stopped almost all of the larger debris 

but the capture fraction for that grating was not obtained due to the failure of the test mister 

system to adequately wet the continuous grating (i.e., this grating illustrated dry behavior). The 

subsequent two gratings in the test were successfully wetted and it was found that second of 

these two wetted gratings captured less efficiently than the first wetted grating (downstream of 

the first grating that failed to become wetted). This makes sense because the debris that had 

passed through the first wetted grating was smaller and more likely to pass through subsequent 
5-44

gratings. The 90-degree bend between two test chambers captured debris. The bend was 

maintained wet by a mister. About 17% of the debris entering the second auxiliary chamber 

was trapped on the chamber wall as a direct result of the bend. The pipes and I-beams 

captured a lesser, but still substantial amount. 

Figure 5.4-4. Capture of Small Debris by Grating

Table 5.4-1. Small Debris Capture Fractions

Structure Type Debris Capture

I-Beams and Pipes (Prototypical Assembly) 9%

Gratings

 V-Shaped Grating

 Split Grating

28%

24%

90o Bend in Flow 17%

Following the blowdown process, the containment sprays and/or condensate drainage would 

wash debris from surfaces and down into the drywell pool with overflow into the vent 

downcomers. Debris on surfaces hit directly by the sprays would be much more likely to 

transport with the flow of water than would debris on a surface that is merely wetted by 

condensation. 

The washdown process in BWRs differs from that in PWRs, since elevations within the drywell 

of BWRs are, typically, separated by gratings rather than concrete floors. In PWRs, water 

would often flow across a floor to a floor drain but in BWRs the sprays pass through a grating 

from one level down to the next level. The DDTS included a small-scale experiment where 

debris was placed on top of a prototypical section of grating and then exposed to water spray. 

The purpose of the experiment was to study the erosion of the fibrous debris at various flow 

rates and to determine the ability of debris to remain on the grating. These tests are described 

in Volume 2 of NUREG/CR-6369. These tests demonstrated that nearly all of captured fibrous 

debris generally smaller than the grating openings would be washed through the grating, and 

that larger debris remaining trapped on top of the gratings would erode into finer debris, with the 
5-45

erosion fraction dependent upon flow rate. The debris directly under a simulated full break flow 

eroded at approximately 9%/hr. Debris erosion due to the impact of the sprays and spray 

drainage flows was found to be much less significant. The DDTS concluded that <1% of the 

LDFG was eroded due to the containment sprays. The spray experiments were carried out for 

30 min, which was estimated to be the maximum credible time spray would be operated 

following a LOCA in a BWR. Further, the <1% result was based on tests with debris large 

enough to not be washed down through the support grating, thereby distinguishing erosion from 

the washdown transport fraction that was typically associated the fines and small piece debris. 

Debris erosion occurring because of condensation and condensate flow was neglected. 

Insulation within it cloth cover was not expected to erode further. These tests did not evaluate

the erosion of microporous insulation debris.

The DDTS studied the turbulence levels within a drywell pool for each of the BWR Mark I, II, 

and III containment designs using a CFD code (Volume 3 of NUREG/CR-6369). The turbulence 

levels were correlated with debris settling by using the same CFD code to simulate flume tests 

that studied debris settling within a pool. That is, if the turbulence levels as predicted with this 

code were sufficiently high to keep debris from settling within the test flume, then the debris 

would not likely settle within the drywell pool at similar or higher turbulence levels. The 

turbulence levels were studied for scenario conditions where the drywell pool received full 

break-water overflow and for conditions where the break steamed so that the pool was driven by 

condensate and/or spray drainage. Under full flow the debris was predicted to likely transport 

into vent downcomers, but under more quiescent conditions, the debris was found more likely to

remain in the drywell pool.

5.4.3 Pool Debris Transport and Recirculation

The blowdown/washdown analysis provides a debris source term for the evaluation of the debris 

transport to the PWR sump pool or the BWR suppression pool, which in turn, provides an 

estimate for debris accumulation on the strainer. The source term should include the quantities 

of debris by type and size classification and the locations where the debris enters the sump or 

the suppression pool. In addition, the blowdown analysis would provide an estimate for the 

quantities of debris deposited directly on the sump pool floor or in the suppression pool. The 

pool debris transport analysis estimates the quantities of debris by type and size classification 

postulated to accumulate on the recirculation strainers.

Re-suspension, the opposite of settling, is the phenomena by which debris or sediment located 

at the bottom of the suppression pool is picked up from the bottom and transported upwards. 

Re-suspension is possible when turbulence levels and/or recirculation velocities in the boundary 

layer are capable of providing sufficient upward drag on the debris to overcome gravitational 

forces. Analytically, the re-suspension mass flux can be calculated as a product of the sediment 

mass and a re-suspension coefficient that is a function of the sediment particle size and shape, 

the pool velocity profiles, and the pool turbulence levels. The re-suspension coefficient would 

transition from a value of one, associated with complete re-suspension during the initial highly 

turbulent blowdown phase, to zero or near zero during the post blowdown recirculation phase, 

which is relatively quiescent. In between one and zero, the coefficient would be governed by a 

time-dependent decay in the rate of re-suspension. This analytical technique was described in 

the BWR ECCS strainer blockage parametric study [NUREG/CR-6224] and implemented into 

the wetwell transport model of the BLOCKAGE 2.5 code (NUREG/CR-6371). Appropriate 

values for the re-suspension coefficient should be obtained from experimental studies where 

possible. Otherwise, conservative assumptions, based on achieving a conservative head loss 

result, are required.
5-46

Settling of debris within the suppression pool, reduces the debris available for accumulation on 

the strainers. The rates of debris sedimentation, also referred to as the “settling velocities,” are 

a function of the debris characteristics of density, shape, and size, and the suppression pool 

dynamics of turbulence levels and flow velocity profiles. Analytical estimates of settling 

velocities are unreliable, even in still water, for complex undefined shapes characteristic of 

typical debris. The effects of pool turbulence on settling velocities are also difficult to predict 

analytically.

5.4.3.1 PWR Sump Pool Debris Transport

The sump pool debris transport evaluation considers two relatively distinct phases. The first 

phase involves the transport of debris as the sump pool fills, before activation of the 

recirculation pumps. The second phase examines the transport of debris within the established 

sump pool with the recirculation pumps operating. The further erosion of debris within the sump 

pool is considered to be a relatively long-term process and is, therefore, evaluated in the second 

phase rather than the first. 

The information requirements for the sump pool transport analyses include the geometric shape

of the pool including objects within the pool, the locations and rates of flows entering the pool, 

the location of and flow through the recirculation strainer, and the debris source terms from the 

blowdown/washdown analyses. The physical description includes any debris interceptors 

designed to preclude or reduce debris transport. The typical debris interceptor is a curb-like 

device designed to inhibit debris from moving across the sump pool floor, at least until sufficient 

debris piles up behind the interceptor to form a ramp that allows additional debris to slide over 

the top. Another type of interceptor is a grating or perforated plate across a flow pathway that 

traps debris at that pathway; once blocked by debris, the interceptor effectively reroutes flow 

over the interceptor or through a more torturous pathway to the recirculation strainer. 

Sump Pool Formation Debris Transport

The PWR sump would begin to fill with water immediately after the LOCA break due to both 

RCS blowdown effluents and the drainage of the containment sprays. Filling of the pool

continues until a relatively steady water level is achieved. Analytically, the sump pool formation 

period is generally assumed to range from break initiation to ECCS switchover to the 

recirculation mode. The analysis of transport after switchover is described in the sump pool 

recirculation debris transport section. The primary driving force for moving debris during pool 

formation, especially for the large debris, is sheeting flow as the initial water from the break 

spreads across the sump floor. This behavior was observed during the integrated debris 

transport tests (NUREG/CR-6773) in which debris, initially deposited on the floor, was observed 

to be pushed along with the wave front. These observations demonstrated that sheet-flow 

driven debris can be transported a considerable distance, even to the other side of the sump 

pool, and that once in motion, a piece of debris can readily gain enough momentum to carry it 

past openings where water would otherwise flow, such as a doorway from the primary sump 

area into an interior space such as the reactor cavity. Once the water depth becomes sufficient, 

drag forces of the water flow on the debris becomes substantially less dynamic than the original 

sheeting flow such that further debris movement is significantly decreased, especially for larger 

debris. Individual fibers continue to move as suspended debris in the water flow.

Substantial quantities of debris may be initially deposited on the floor of the compartment where 

the LOCA break occurred (e.g., a steam generator compartment), and the subsequent break 

compartment sheeting flow could transport substantial portions of that debris from the break 
5-47

compartment into other sump locations (e.g., the annular sump pool area via personnel access 

doorways). As the sump pool fills, water containing debris will flow into spaces located below 

the sump pool floor, such as the reactor cavity. However, in some situations, the pathway is 

sufficiently tortuous that larger debris would not transport in the space. When one of these 

spaces becomes completely filled and relatively quiescent, that space is referred to as an 

inactive pool or inactive volume. Once debris enters an inactive pool, that debris may be 

considered as permanently trapped there unless there is subsequent sufficient flow to once 

again entrain the debris. Once large-piece debris enters an inactive pool region, it is likely to 

remain there. The situation is less clear with respect to fine suspended matter because even 

natural circulation could allow the suspended matter to escape.

The debris entering the sump pool during the pool fill transport period would include debris 

initially deposited in the sump pool during blowdown and any debris washed back down into the 

sump pool by the containment sprays during this period. The sump formation period would 

likely be relatively short compared to the time it would take for the majority of washdown to 

occur; therefore most of the washdown debris would typically be expected to transport into the 

sump pool during the recirculation transport phase. While larger debris may be moved around 

during pool fill, such debris would likely remain on the pool floor, unless buoyant. Such debris 

would not accumulate on the strainer prior to switchover to recirculation and after switchover the 

strainer approach velocities would typically be too slow to lift the large debris from the floor and 

onto the strainer. Fine suspended matter would likely become relatively uniformly mixed within 

the pool, with the possible exception of the inactive pool regions.

 

The quantity of fine debris trapped within inactive pools has been estimated by multiplying the 

total quantity of fine debris estimated to be in the sump pool as a result of blowdown transport8

by the ratio of the inactive pool volume to the total sump pool volume. Due to the associated 

uncertainties, the NRC staff limited the fraction of debris moving into inactive pools to a 

maximum of 15% of the blowdown source, unless analysis demonstrates otherwise. Regarding 

the distribution of the larger debris on the sump pool floor following pool fill, it is not conservative 

to assume that all such sump pool debris is uniformly distributed across the containment floor as 

settled debris. If it can be shown that debris of a specific size category would be settled debris, 

and that the subsequent sump pool velocities and turbulence were insufficient to cause such 

debris to accumulate on the strainers (i.e., entrainment), then the issue of debris distribution is 

of no consequence. Otherwise, an analysis with conservative assumptions will be required to

determine the initial distribution of debris before switching to recirculation mode. For example, it 

could be conservatively assumed that the pool fill relocated all such debris near the recirculation 

strainers. A more detailed analysis could be used to relax the conservatism.

Sump Pool Recirculation Debris Transport

This phase in the debris transport evaluation estimates the quantities of debris, by type and size 

classification, that would arrive at the recirculation strainer for potential accumulation. The 

source debris includes the debris already in the sump pool when the recirculation pumps start 

 

8

Because the transport of debris by the washdown processes are time-dependent, washdown debris will 

enter the sump pool both before and after the pool has filled and the recirculation pumps have started. 

Analytical capabilities have not been sufficiently developed to determine how much washdown debris 

enters before and how much enters after the pool has filled. Therefore, the only reasonable conservative 

assumption is that only the debris deposited in the sump pool area by blowdown processes can be 

transported into inactive pool volumes.
5-48

and the debris subsequently entering the pool due to washdown processes. The typical 

recirculation transport analysis estimates the overall potential quantities of debris transported, 

i.e., the transport processes are sufficiently complex that time-dependent analyses are not 

practical. However, if the only debris with the potential for accumulation on the strainers 

consisted of suspended matter such that settling and other forms of deposition could be 

neglected, and the time frame for the washdown processes was reasonably short compared to 

that for the recirculation processes, a first-order estimate of time dependency could be made

based on a uniform concentration within the pool.

The three main types of debris that are considered to exhibit prototypical behavior for 

recirculation sump pool transport are: (1) suspended debris, (2) buoyant debris, and (3) settled 

debris. Suspended matter typically consists of fine debris (i.e., basically individual fibers and 

fine particulates). Although these fine debris types will settle in still or relatively calm water, the 

settling process can take substantially more time than the typical sump pool turnover times. For 

example, NRC staff has observed test tank water during vendor head loss testing that was 

completely obscured by fine suspended particulates, and after standing stagnant overnight, was 

still completely obscured the next day. In another example, chemical-effect precipitates (ICET 

Test 1) collected in a bucket took about three days to settle to the bottom of the bucket. An 

actual plant sump pool is not calm due to the continuous entrance of break overflow and 

containment spray drainage into the sump pool. This drainage added to the recirculation flow, 

especially at channels through passageways induces turbulence. In the absence of analysis 

that shows otherwise, it is conservative and reasonable to assume complete transport of the 

suspended fines to the strainer. 

Debris that remains buoyant will float on the surface of the pool and, therefore, may tend to drift 

toward the strainer. Examples of buoyant debris are types of closed cell foam insulations where 

water penetration is unlikely. Typically, such debris would not be a strainer blockage problem 

because the typical strainer would be submerged. Hence, the buoyant debris is typically 

dismissed from further consideration. The exception, of course, would be the partially 

submerged strainer where the accumulation of the buoyant debris against the strainer could 

contribute to the potential blockage problem.

Settled debris may or may not transport to the strainer. The settled debris of greatest concern is 

typically shreds of fibrous debris. Dry fibrous debris will initially float because most of its volume 

is free space filled with air. But over time, water will infiltrate the fibers, and eventually the 

debris will sink to the pool floor, whether it is a small shred or a complete intact pillow 

(NUREG/CR-2982). The rate of water infiltration is highly dependent on the temperature of the 

water (surface tension effect). Whereas cold water can take hours to days to infiltrate fibrous 

insulation, hot water can saturate shreds of fibrous debris rather rapidly. If large-piece fibrous 

debris (or an intact pillow) remains buoyant for a sufficient time, it could float over the top of the 

recirculation strainer and then sink onto the strainer. However, the probability of this behavior 

resulting in significant blockage to the strainer is relatively small, i.e., the large piece would 

either simply lie across the top of the strainer or fall to the floor beside the strainer.

Once fibrous debris has settled to the sump pool floor, its mode of transport would be to either 

slide or roll along the floor toward the strainer. The debris could also be resuspended if it 

transports to an area of higher flow or turbulence. Floor transported debris would be subject to 

entrapment by obstacles such as curbs and debris interceptors. Small-scale testing has been 

conducted to measure the necessary velocities to cause the movement of various kinds of 

settled debris (e.g., NUREG/CR-6772).
5-49

For a given type and size of debris, a certain flow velocity is needed to move the piece of debris 

along the floor. A greater velocity would be needed to cause the debris to become sufficiently 

entrained to lift over an obstacle. If a piece of debris were to arrive at a strainer located above 

the sump floor, it may take a greater velocity to lift the piece onto the strainer resulting in 

accumulation. Further, for debris on a vertical strainer surface, a minimum velocity may be 

required to keep the debris attached to the strainer. Turbulence affects minimum transport 

velocities. Most separate-effects testing was conducted with uniform low-turbulent flows, and 

some testing has been conducted with turbulence induced. A flow assessment can estimate 

whether or not the flows approaching a strainer are sufficiently fast or turbulent to transport floor 

debris from the floor and onto the strainer. Some strainer configurations have a strainer 

recessed into a pit below the sump pool floor where the floor transported debris could simply fall 

into the pit and onto the strainer. Limited vendor-performed head loss testing in conjunction 

with debris transport to the strainer in facilities designed to replicate plant strainer approach 

velocities have shown a tendency for the heavier RMI debris and the typical paint chips to settle 

within the flume rather than accumulate on the test strainer, i.e., the flume test velocities were 

less than the debris transport velocities for debris that has settled to the flume floor. This 

vendor testing was plant-specific and therefore not generally applicable to all plants, however 

the noted trend would apply to a significant number of plants. There are exceptions to generic 

transport metrics. For example, a piece of RMI debris with an entrapped air bubble or a paint 

chip that floats may transport to the strainer. In addition, in vendor head loss testing, some 

fibrous insulation shreds remained buoyant and floated over top of the test strainer most likely 

due to air entrapment.9 The final important aspect of floor debris transport is that some types of 

debris (e.g., fibrous and particulate insulation debris) are subject to erosion, resulting in 

additional suspendable fines that would likely be completely transported to the strainer. The 

erosion process is discussed in Section 5.4.4.

Determination of the transport fractions for floor-transportable debris requires an assessment of 

sump pool flow velocities and patterns, together with flow turbulence. The best method for this 

hydraulic assessment is the application of a computational fluid dynamics (CFD) code to the 

plant-specific sump pool. An example CFD application is the CFD study performed for 

reference plant, which is found in the Appendix III of NRC-SER-2004.

After a suitable CFD code is selected, a three-dimensional geometric model of the sump pool is 

developed. Models should include an appropriately detailed calculational mesh. The geometric 

model should be sufficiently detailed to include significant structures located within the sump 

pool and such details as stairwells and flow passageways. The height of the model should 

extend from the bottom of the pool to the maximum anticipated depth of water. Note that some 

CFD codes support the importation of CAD models. The locations and flow rates of water 

sources to the sump pool, including effluents from the LOCA break and containment spray 

drainage, are simulated. There should be sufficient detail to reasonably capture the locations of 

the incoming water to model its influence on flow and turbulence. The water drawn from the 

pool via the recirculation pump is simulated.

Analysts have typically focused on simulating the steady-state flows of a fully established pool 

but some have simulated the pool fill-up transient. A simulation typically requires appropriate 

 

9

Vendor head loss testing was typically conducted with colder water that may not easily saturate fibrous 

debris. The usual test procedure would include a step were the fibrous debris was pre-saturated before 

introduction into the test tank typically using heated water. The floating fibrous debris noted during 

vendor testing was likely due to incomplete saturation.
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boundary condition assumptions for surfaces, and inlet and outlet flows. Steady-state 

conditions must satisfy conservation of water mass within the pool; for example, the simulation 

might use a specified flow rate for mass inflow but then use a pressure boundary condition that 

allows the code to adjust the pressure at the bottom of the sump to balance the mass flow 

entering and exiting the pool without introducing numerical instabilities. Many CFD codes have 

user options for selecting numerical models for solving incompressible flow (Navier-Stokes 

equations), as well as for simulating turbulent kinetic energy and the dissipation of the 

turbulence. CFD codes that include features that model phenomena in sump pools should be 

selected. For example, codes should model specific sump pool flow behavior like turbulence 

dissipation of swirling flows. CFD codes require the analyst to specify appropriate initial 

conditions to initiate a simulation and to specify the numerical convergence criteria for the 

acceptance of a solution.

The CFD results are typically two-dimensional figures showing either the velocity flow patterns 

or the patterns of flow turbulence at particular levels within the pool. An example of a flow 

velocity pattern is shown in Figure 5.4-5 (Figure III-36 in NRC-SER-2004). The scale on the 

right side of the figure shows the color codes used for the pool velocities. Referring to Figure 

5.4-5, shreds of LDFG debris located in the yellow or red zones (i.e. velocities greater than 

about 0.06 m/s (0.2 ft/s)) would most likely move with the flows, and the shreds located in the 

blue zones (i.e., velocities less than about 0.03 m/s (0.1 ft/s)) would likely remain at those 

locations, but the movement of the shreds located with the green zones is less certain. In 

addition, CFD results can include streamline plots that would indicate how fine suspended 

debris moves within the pool. 

The scenarios that need to be simulated likely include both SBLOCAs and LBLOCAs and the 

various break locations, e.g., alternate steam generator compartments. Both the pumping flow 

rate and the pool depth can vary with the size of the break. Activation of the containment 

sprays is dependent on containment pressurization, which in turn, depends upon the size of 

break. In addition, the debris source term under evaluation may depend upon the size of the 

break, as well as break location.
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Figure 5.4-5. Example CFD Sump Pool Flow Velocity Pattern

With the pool hydraulics simulated, debris transport should be estimated by using the velocity 

and turbulence patterns and an assessment of the initial debris location in the sump pool. 

Unfortunately, no debris transport model has been developed in which a straightforward 

application of a computer code could be used to calculate the transport. The primary method in 

use involves the application of engineering judgment of the CFD results to estimate transport 

fractions. As such, it can be useful to establish CFD plot contours corresponding to threshold 

transport velocities that determine whether specific floor-settled debris would likely be 

transported. 

Refer to the logic chart for the debris-transport model shown in Figure 5.4-1, as an example of 

transport assessment. This figure includes steps for debris transport during pool fill-up and 

during the recirculation phase for which the analyst could implement transport fractions based 

on analysis, experimental data, or conservative engineering judgment. During the evaluation of 

the fill-up phase, the chart shows that debris was either transported to the sump strainer, away 

from the sump strainer, or into an inactive pool. The debris transported to the strainer was 

added to the debris that was determined to be deposited at the strainer by the 

blowdown/washdown processes and the debris in the inactive pool was assumed to remain in 

the inactive pool. The fraction of debris predicted to be transported away from the strainer by 

the pool fill processes and that did not enter an inactive pool region would then be subjected to 

the recirculation transport processes. For material remaining in the active pool, the debris is 

either transported to the strainer or is predicted to stall in the pool, where it may then be subject 

to further erosion.

Pool velocity and turbulence characteristics determine the areas of the pool where debris may 

be entrapped. Flow streamlines can be used to determine whether debris entering the pool at a 

discrete location would likely pass through a potential entrapment location. During the
5-52

integrated debris transport tests (NUREG/CR-6773), shreds of water-saturated fibrous debris 

were observed to accumulate in relatively quiescent locations within the simulated sump pool. 

Figure 5.4-6 is a photo showing debris stalled within a slow-flowing region from a one-tenth 

scale simulation of a plant sump annulus. Most of these shreds tended to remain in these 

locations for the relatively short duration of these tests. However, close observation showed an 

occasional shred exiting the low-flow area and was re-entraining in the surrounding flows. If 

such a shred subsequently encountered another quiescent location, it was likely to become 

stalled again. For a shred to be transported all the way to the strainer, a continuous transport 

pathway was needed where the flow velocities generally exceeded the minimum velocity 

required to keep the piece moving. This behavior suggests a method of estimating the fraction 

of debris transported along the floor within the sump pool.

CFD analyses can provide realistic descriptions of the flow conditions at floor level. By 

designating velocity contours based on experimentally measured thresholds for movement of 

the settled debris, the locations for debris entrapment become clearly indicated. By overlaying 

the CFD plots with the estimates for conservative debris placement at the start of pump 

recirculation and the locations where washdown debris enters the pool from above, a graphical 

integration can be performed to arrive at transport fraction estimates. Debris predicted to be 

located in a region of flow moving slower than the threshold for debris movement would be 

considered as not being transported. The transport fraction is obtained by summing these 

quantities and subtracting it from the total debris load to calculate the quantities transported, 

then dividing the obtained value by the original source terms. The actual calculation method 

could, for example, subdivide the pool floor into a fine mesh grid with each grid space 

independently assessed, the results of which are then combined.

Figure 5.4-6. Debris Stalled in a Slow-Flowing Region of the Simulated Annulus

(Figure 6-3 in NUREG/CR-6773)
5-53

In addition to velocity contours, the streamline plots provide reasonable connecting pathways 

whereby a piece of debris would likely travel from its original location in the pool to the 

recirculation sumps. If a transport pathway passes through a slower portion of the pool, then 

debris moving along that pathway could stall and not be transported to the recirculation sump. 

Otherwise, transport to the strainer is more likely. 

Effects of pool turbulence are more difficult to quantify. The transport results based on flow 

velocities may need to be adjusted by also overlaying the CFD-calculated turbulence level plots 

with the velocity plots. For example, turbulence levels may be relatively high near a location 

with a source of water plummeting into the pool. If high turbulence coincides with a flow velocity 

slower than the threshold transport velocity, it is prudent and conservative to assume that debris 

would be transported from that location. As noted above, stalled debris has been observed to 

resume movement, a behavior attributed to localized pulsations of turbulence that suddenly 

peaked at the position of that piece of debris. Although this behavior cannot be reasonably 

quantified, transport estimates should be modified to consider these effects because turbulence 

is capable of moving debris when bulk flow will not or keeping debris suspended to move with 

the flow at any velocity. One method of accounting for turbulence effects might be to decrease 

the threshold velocities for transport. In addition, a certain amount of engineering judgment may 

be required to arrive at a reasonable solution.

5.4.3.2 BWR Suppression Pool Debris Transport

During a postulated LOCA in a BWR, the suppression pool would be affected by the clearing of 

the vent downcomers of water as the drywell pressures rapidly increase. The suppression pool 

level will swell due to the vent clearing which will also induce significant turbulence in the pool. 

Debris transport within a suppression pool was studied and documented in NUREG/CR-6224. 

Steam and non-condensable gases from the drywell would be discharged into the pool. Initial 

large-scale turbulence would lead to re-suspension of a large fraction of any accumulated 

suppression pool sludge. Near the end of the drywell blowdown phase, oscillatory steam 

condensation could result in a chugging oscillation in the downcomers. Experimental data 

suggest that amplitude, frequency, and duration of the condensation oscillations are primarily 

functions of the mass flow rate, concentration of the non-condensables in the mass flow, 

downcomer submergence, suppression pool temperature, and break size. Pool turbulence

would retard debris settling, and the high intensity turbulence would persist for the first 

approximately 50-100 sec for a LBOCA. After the pool turbulence dissipates, the pool would 

enter a longer term low-energy phase with recirculation flow patterns governed by the 

recirculation of water draining into the pool from the drywell and the recirculation pump draw. 

Debris located within the suppression pool would include suppression pool sludge and any other 

debris originally in the pool, and debris transported into the wetwell from the drywell both during 

the dynamic RCS depressurization phase and the post-depressurization recirculation phase.

The dynamics of the suppression pool turbulence provides a time-dependent behavior that 

would affect the accumulation of debris on the recirculation strainers. In addition, the 

recirculation flows may be throttled back according to operating procedures, which can also 

affect debris accumulation. BWR recirculation pumps start almost immediately following a 

LOCA and would therefore be operating during the initial period of high turbulence, which could 

cause larger debris, maintained in suspension by the high turbulence, to accumulate. Once the 

turbulence had dissipated, the larger debris would tend to settle to the bottom of the 

suppression pool rather than accumulate on the strainers. Then during the quiescent phase, 

debris accumulation would be due primarily to the suspendable fines. Suppression pool 

dynamics would vary among the Mark I, II, and III containment design.
5-54

The NRC-sponsored tests to study the settling rates for fibrous insulation debris and BWR 

suppression pool sludge in BWRs are described in NUREG/CR-6368. Settling velocities were 

found to depend upon the characteristics of the test debris. The test debris was based on the 

characteristics of debris expected to transport into the suppression pool. The fibrous insulation 

debris was prepared by passing fibrous insulation cut into large pieces through a leaf shredder. 

A sludge simulant was prepared using a mixture of iron oxide powders designed to match a 

BWROG characterization of suppression pool sludge. During the high-energy phase which 

lasts about 50 sec for a LLOCA and about 10 min for a MLOCA, these tests demonstrated that 

the turbulence would suspend all of the sludge initially contained at the bottom of the 

suppression pool and would keep both the sludge and the fibrous debris in suspension 

throughout the high energy phase. The turbulence would also further disintegrate the fibrous 

debris. After the high-energy phase, the residual turbulence in the pool is expected to decay to 

relatively quiescent conditions, allowing for sedimentation of the suspended debris. Note that 

these NRC sponsored tests did not include a simulation of the turbulence associated with the 

steady state operation of the recirculation flows Turbulence could maintain the finer debris in 

suspension. In the NRC experiments, the suppression pool was initially brought to a fully mixed 

condition by simulated chugging. After about 10 min the chugging was terminated, and the 

turbulence in the suppression pool was allowed to decay naturally. Visual observations 

revealed that soon after the termination of chugging, the debris began to settle to the pool floor. 

Water samples were drawn from five locations in the suppression pool at pre-determined 

intervals to measure debris concentrations. The debris concentrations were then used to 

estimate settling rates for each species, i.e. fibrous debris and particulate sludge. More than 

60% of the total debris by mass exhibited settling velocities of less than 1 mm/sec, suggesting 

the that fibrous debris would require considerable time to settle in the suppression pool. The 

NRC experiments demonstrated that, on average, the sludge particles settle faster than the 

fibrous shreds. With the test particulate ranging from about 6 to 100 μm in diameter, about 

30% by mass exhibit settling velocities in excess of 10 mm/sec, about 60% in excess of 2 mm, 

and the remaining approximately 10% of the sludge particles have settling velocities below 0.1 

mm/sec. The median particle settling velocity was about 3 mm/sec. 

Those applying the NRC-sponsored debris settling test results should consider that significant 

differences existed between the scaled test facility and the referenced plant suppression pool. 

The test facility mechanically simulated the condensation oscillations rather than the actual 

condensation. The mechanically induced turbulence was an approximation of a realistic 

postulated accident scenario. In addition, the tests did not include a simulation of the flow 

turbulence associated with the steady state operation of the recirculation flows. The sludge test 

debris had a larger size distribution than the BWROG-recommended distribution. The test 

results were judged to be characteristic of the types of behavior that could be expected within a 

suppression pool. When using the test results to predict plant behavior, the differences 

discussed above should be considered. Settling velocities would certainly be affected by these 

characteristics.

The NRC developed the BLOCKAGE 2.5 code (NUREG/CR-6370 and -6371) as a tool to 

evaluate licensee compliance regarding the design of suction strainers for ECCS pumps in 

BWRs as required by NRC Bulletin 96-03. This code includes scoping-level models for drywell 

debris generation and transport to the suppression pool (which are inferior to the latest PWR 

generation and transport models), a state-of-the-art suppression pool transport model, a strainer 

head loss model, and a probabilistic model that calculates a full range of postulated breaks to 

determine an overall plant probability of strainer blockage. The processes affecting debris 

accumulation are all time-dependent. These include drywell debris transport into the 

suppression pool, the re-suspension coefficient, the turbulence dissipation rate, the water 
5-55

temperature, and the pump flow rates. The code subdivides the size distribution into many 

groups, with each group having a group-specific settling velocity and head loss characteristics. 

The rate of debris accumulation on each active strainer is based on the time-dependent 

concentration of debris and the pump rate of flow. The calculations for strainer head loss are 

based on the head loss correlation in NUREG/CR-6224.

The conservative approach to modeling suppression pool transport with respect to maximum 

debris accumulation on the strainer was to assume complete re-suspension of debris and 

preclude sedimentation. Therefore all debris that is initially within, or later enters the wetwell,

would be assumed to accumulate on the strainer or strainers. The NRC position in RG 1.82, 

Revision 3, and Section 2.3.2.4 is that credit should not be taken for debris settling until LOCAinduced turbulence in the suppression pool has ceased. However, the maximum head loss may 

not occur with the maximum quantity of debris, but may be associated with a debris bed

composed of a smaller amount of fiber. Having less fiber can result in the particulate debris 

collecting in a smaller volume creating a denser debris bed. 

5.4.4 Erosion of Containment Materials and Debris

The post-LOCA containment environment can potentially damage containment materials or 

further degrade LOCA-generated debris. The damage to containment materials could generate 

additional debris, and the degradation of existing debris could generate transportable fines from 

less transportable larger debris. Although, the erosion could be considered a debris-generation 

issue, it is addressed in the transport section because the assessment of such damage requires 

knowledge of the containment environment, such as locations of water pools, water flow

patterns and the rates of flow.

5.4.4.1 Post-LOCA Damage to Containment Materials

The possibility of containment materials that were previously damaged by the LOCA being 

further degraded by the post-LOCA environment of containment sprays and flowing water 

should be considered. One degradation mechanism would be water flowing over such materials 

as insulation and fire barriers that were not protected by a cover or jacketing, such that the 

water could erode a surface, resulting in production of fine fibers or fine particles. Evaluation of 

this issue has typically not resulted in the prediction of the generation of significant additional 

insulation or fire barrier debris.

A key concern is the failure of coatings, other than those damaged directly by the break jet. 

Qualified coatings are expected to survive the post-LOCA environment because they are 

designed to withstand post-LOCA environmental conditions. Conversely, non-qualified coatings 

consisting of either degraded qualified coatings or coatings lacking qualification certification 

should be conservatively assumed to form debris, either as particulate or as paint chips. The 

coatings assessment is addressed separately under the coatings in Section 5.5.

5.4.4.2 Erosion of LOCA-Generated Debris

The subject of further erosion of LOCA-generated debris with respect to washdown debris 

transport was discussed in Sections 5.4.2.2 and 5.4.2.3. There, the postulated drivers for the 

erosion were the break overflow, the containment sprays, and/or spray and condensate 

drainage. The primary driver for erosion, however, is immersion in a pool of water, with water 

flowing over and around the debris. The types of debris of primary concern for erosion are 

fibrous debris and microporous particulate insulation debris.
5-56

Erosion of Fibrous Debris

Individual fibers will erode from larger non-transportable fibrous debris residing within a pool,

then become readily transportable. This behavior was observed in the NRC-sponsored 

integrated debris transport tests (NUREG/CR-6773), which were designed to simulate the sump 

pool of a typical PWR plant. During four longer-term tests (3 to 5 hr durations), debris that 

accumulated on the simulated sump screen was collected every 30 min. Fine fibrous debris 

continued to accumulate on the test screen throughout these tests; the fineness of the eroded 

fiber is evidenced by the uniformity of the accumulation, which is illustrated in the test photo 

shown in Figure 5.4-7. The shreds (small clumps of fiber) typically accumulated in a heap at the 

bottom of the test screen. Sources of this fine fibrous debris included the initial fine fiber in the 

debris batches introduced into the test, as well as the eroded fibers. However, the initially 

suspended fibers would have been removed relatively early in the test, after a few turnovers of 

the tank volume. Therefore, the continued accumulation at a somewhat sustainable rate was 

concluded to have been primarily that of eroded fibers.

It was also apparent that the level of pool turbulence affected the rate of erosion, i.e., an 

increase in turbulence increased the rate of erosion. One test was conducted with a pool depth 

of 9 in. rather than the usual 16 in. but at the same volumetric rate of flow and the erosion rate 

was greater in the shallower pool. The water in the shallower pool flowed significantly faster 

with a corresponding greater turbulence than the deeper pool. In fact, the accumulation was 

about eight times more rapid for the shallow pool test. 

Figure 5.4-7. Typical Accumulation of Fine Fibrous Debris

(Figure 6-7 in NUREG/CR-6773)

This test data for debris erosion in a sump pool strongly indicate a sustainable rate of erosion 

that is affected by the relative turbulence in the pool. Although these longer-term tests ran for 

several hours, they were of shorter duration than those of the LOCA long-term recirculation 

tests, which ran for up to 30 days. If it is assumed that the erosion rate remains constant 

beyond the measured erosion rate until the end of the mission time, a conservative fraction for 

the quantity of debris eroded can be calculated. The following extrapolation equation takes into 

account the steadily decreasing mass of debris in the pool:
5-57

Based on the erosion rate of 0.3% of the current tank debris per hour, associated with the 16-in. 

pool tests and extrapolating to 30 days (720 hr), the analysis indicates that nearly 90% of the 

initial debris mass would become eroded. This conclusion is based on a constant erosion rate, 

which is unlikely to be realisitc in practice. 

While the application of this 90% value, which was approved by the NRC staff in their safety 

evaluation of NEI GR 2004-07, to the overall transport results would be conservative, it may not 

be realistic. The calculation had substantial sources of uncertainty, including: (1) the integrated 

debris transport tests lasted only 3 to 5 hr, (2) flow turbulence would depend on plant-specific 

geometry and flow rates, and (3) the tests did not study large-piece debris (note that fibrous 

debris still enclosed within a protective cover is not likely to erode). The greatest uncertainties

associated with the 90% value are the questions of whether the erosion rate declines with time, 

and whether the erosion rate measured for small shreds applies to large pieces of relatively 

intact insulation. It was expected that this 90% value could be reduced with better or more 

extensive erosion rate data. 

Several vendors have conducted independent testing to justify reducing the erosion rate. One 

such test program, reviewed by the NRC staff, was sponsored by the licensee for the Salem 

plant, which conducted plant-specific erosion testing for Nukon® and Kaowool fibrous debris 

(NRC, 2008f). The licensee placed samples of insulation of various sizes within wire mesh 

baskets that were, in turn, placed within a linear flume. A turbulence suppressor and a flow 

straightener were used to condition the flow upstream of the sample baskets. Flume velocity 

was specified to approximately match a CFD-predicted maximum recirculation velocity for the 

post-LOCA sump pool. A nominal (average) flume velocity of 0.72 ft/s was used for the testing 

(greater than the velocities found in 98% of the containment pool). Note that this test velocity is 

much higher than the typical tumbling velocity for small pieces making the results conservative 

for debris lying on the floor unretained by some object, such as a debris interceptor. Debris 

samples were placed in the flume for a specific time period; removed, dried, and weighed, and 

then generally placed in the flume again later for one or more additional erosion test intervals 

(the intervals provided time-dependent information). The differences between the initial masses 

and the post-test masses were attributed to erosion. The Salem licensee extrapolated the 

measured erosion percentages for small and large pieces of NUKON® and Kaowool® debris 

from the test durations out to the 30-day test period, which resulted in a 30-day erosion estimate 

of 30% for NUKON® and 10% for Kaowool®. These numbers were conservatively increased to 

40% for NUKON® and 15% for Kaowool® in its debris transport calculation. Although the NRC 

staff noted technical concerns with the test procedure and methodology, these results were 

considered acceptable for Salem based on compensating conservatisms in the Salem debris 

transport conclusion.

• The review of the Salem erosion testing provided points of guidance that should be 

observed whenever such erosion testing is conducted. These points include:

• The conduct of such erosion testing should ensure that the velocity and turbulence test 

conditions are prototypical or conservative with respect to the plant sump pool. Due to the 

turbulence associated with the often chaotic and multidirectional variations in prototypical 

flow conditions, a bounding flow velocity may not by itself guarantee the prototypicality of 

the turbulence.

( ) Hours

eroded F =1 − 1− Rate
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• Preparation of debris samples should render debris prototypically representative of LOCAgenerated insulation debris. For example, destroying insulation with a shredder would 

produce debris more prototypical of a LOCA than simply cutting insulation into pieces.

• The size distribution of the debris samples should be representative of or conservative with 

respect to predicted debris size distributions. It is conservative to hedge test samples to the 

smaller size because smaller pieces have a higher surface-to-volume ratio than larger 

pieces, which tends to increase the erosion rate.

• Placement and grouping density within the test basket should be prototypical of the plant 

sump pool, in that the grouping should not shield individual debris pieces from turbulence in 

a non-prototypical manner.

• If the measured erosion rates depend upon the size of the debris, then the overall erosion 

of the LOCA-generated debris necessarily would involve an integration of the rates with the 

predicted debris size distribution.

• Erosion test data are specific to the type of fibrous debris tested. There is no guidance 

regarding the adaption of erosion data for one type of fibrous insulation to another type of 

insulation.

Alion Science and Technology also conducted erosion testing on fibrous debris (ML101540221). 

Alion exposed submerged small pieces of Nukon low-density fiberglass insulation to water flows 

representative of a PWR containment sump pool following a LOCA. The test report concluded 

that a cumulative erosion percentage of 10% over a 30-day period following a LOCA is justified. 

The staff reviewed the Alion testing and considers the test recommendation of not less than 

10% erosion over a 30-day period appropriate. It was concluded that it would be acceptable for 

PWR licensees to reference the Alion proprietary erosion test report for Nukon low-density 

fiberglass in their responses to Generic Letter 2004-02 if it was shown that the testing was 

applicable to their plant condition. Prior to application of the Alion proprietary erosion test 

results to their plant, PWR licensees should verify that the test conditions (e.g., velocity and 

turbulence levels, debris material properties) are applicable to their plant-specific conditions. 

The Alion testing demonstrated that the previous NRC assessment of 90% erosion based on 

extrapolating a few hours of test data out to 30-days was overly conservative for PWRs (similar 

data have not been developed for BWRs).

Regarding BWRs, the turbulence that would occur in the suppression pool during the highenergy depressurization phase would further disintegrate fibrous debris including the generation 

of individual fibers (NUREG/CR-6224). Such fragmentation behavior was observed in scaled 

suppression pool tests investigating debris sedimentation of LOCA-generated debris and 

sludge, but a method was not developed for quantifying the fragmentation (NUREG/CR-6368).

In the erosion of LOCA-generated debris, it is likely that destruction of the insulation leaves 

fibers rather loosely attached, so that moderate turbulence working these fibers back and forth 

will cause the fibers to detach. Testing during the DDTS (NUREG/CR-6369) showed that fibers 

will also erode from undamaged insulation, but that more turbulent energy is required to sustain 

erosion. Therefore, it is reasonable to expect that the rate of erosion for LOCA-generated 

debris would taper off with exposure time. As the more loosely attached fibers have been 

detached the increasing total eroded mass is expected to approach an asymptotic limit. As 

such, it may be possible and reasonable to extrapolate test results that demonstrate a taperingoff effect from shorter test durations out to a 30-day test period. 
5-59

Erosion of Microporous Insulation Debris

Microporous insulation debris (e.g., calcium silicate, Min-K, and Microtherm) subject to postLOCA environmental conditions can erode into fine particulates that could contribute to strainer 

head losses. During NRC-sponsored separate-effects testing, one type of calcium silicate 

(obtained from Performance Contracting, Inc.) was tested for its dissolution behavior in water 

(NUREG/CR-6772). In these tests, pieces of debris that had been created by shattering this 

calcium silicate insulation were dropped into water at both ambient and 80°C. The water was 

quiescent or was stirred to induce turbulence. Within 20 minutes in the stirred 80°C water, 

about 75% of the material became suspendable fines due to the disintegration process. This 

process was found to increase with temperature and turbulence.

Similar vendor conducted tests were reviewed by the NRC staff during the Indian Point audit 

(NRC, 2008e). This licensee sponsored the dissolution testing of two pieces of calcium silicate 

(identified as asbestos-bearing) that had been removed from the Indian Point Unit 2 

containment. These two pieces were tested in 200°F (93.3°C) water for 2 hr with stirring added 

for 30 min. The data indicated that the erosion was very minor, after which the licensee 

assumed that all such pieces of calcium silicate debris would not further erode. However, the 

NRC staff concluded that the testing duration was too short to ascertain whether the 

disintegration that would occur over a 30-day period could be significant (e.g., 0.05% for 2 hr 

extrapolates to 18% in 30 days). The licensee’s vendor noted another vendor dissolution test in 

which about 5% erosion occurred in 2 weeks for a type of calcium silicate similar to that found in 

the Indian Point containments. This information suggests that significant erosion would likely 

occur in 30 days.

The Indian Point vendor testing had substantially different results from the NRC-sponsored 

tests. During the onsite Indian Point audit, a calcium silicate insulation expert was consulted to 

help discern why the two sets of test results were so different. The primary reason for the 

behavior difference was attributed to the manufacturing process of the calcium silicate insulation 

i.e., either a press-shaping process or a molding-shaping process. The Indian Point asbestos 

insulation was manufactured by the press-shaping process, which is resistant to water erosion, 

whereas the calcium silicate used in the NRC-sponsored testing was manufactured by the 

molding-shaping process, which is apparently highly susceptible to water erosion.

The erosion rate depends on the type and manufacture of the calcium silicate, and it is apparent 

that at least some erosion would occur for any calcium silicate insulation. The same conclusion 

should be assumed for Min-K and Microtherm unless adequate research is conducted to 

support a different conclusion. When erosion tests are conducted, the tests should last for a 

sufficiently length of time to adequately determine the rate of erosion. The lower the rate of 

erosion, the longer the test duration needed to accurately determine the erosion rate. Even a 

low rate could be important over the long-term post-LOCA mission time of the containment 

sump. The conditions to which the test debris are subected should be prototypical (or 

conservative) with respect to the plant sump pool. In addition, steps should be taken to ensure 

that the samples are properly dried before weighing to ensure accuracy. Because the 

measured mass differences during the testing can range from hundredths to tenths of a gram, 

small variations in the quantity of water adhering to the samples at the time of weighing could 

easily influence differential mass measurements. 
5-60

5.4.5 Characteristics of Debris Transported to the Strainer

The characteristics of the debris arriving at the strainer will differ from those of the as-generated 

debris. In particular, larger and heavier debris would likely not reach the strainer. The typical 

debris arriving at a PWR large passive strainer installed above the sump pool floor will likely 

consist primarily of suspended fines. Head loss evaluations, whether analytical or experimental, 

should be based on the debris expected to arrive at the strainer rather than on the as-generated 

debris, in particular the debris size distributions. For BWRs, the debris arriving at the strainer 

would be affected by the RCS depressurization induced turbulence in the suppression pool. 

Early on, the suppression pool turbulence would keep some larger debris in suspension and 

available for accumulation. Later in the event the suspended debris in the suppression pool 

would become finer as the larger debris settled. Characterizing the size distributions of debris 

arriving at the strainer would be at least somewhat time dependent, and therefore difficult to 

assess. Therefore BWR evaluations should maintain adequate conservatism to account for the 

unknowns. For PWRs, the typical debris arriving at a large passive strainer installed above the 

sump pool floor will likely consist primarily of suspended fines.

The strainer debris transport evaluation must conservatively interface with the head loss 

evaluation, i.e., the debris quantities (and properties) predicted to arrive at the strainer should 

match up with the debris quantities (and properties) used to initiate the head loss evaluation. 

The correlation between the head loss evaluation and transport evaluation should be based on 

head loss, rather than simply debris quantities. That is, smaller quantities of very fine debris 

can cause substantially higher head loss than larger quantities of bulkier debris. Different

approaches are suitable provided that the transport and the head loss evaluations are 

compatible. If the transport analysis is to evaluate the debris approaching the strainer but not 

actually reaching the strainer, then the head loss testing would need to conservatively simulate 

the near field transport. If the transport analysis is to evaluate the debris actually accumulating 

on the strainer, then the head loss testing would not need to simulate the near field transport. 

For example, a PWR evaluation may assess the transport of floor transportable debris to the 

base of the a strainer positioned above the sump floor. If the transport evaluation demonstrated 

that the floor transported debris could be lifted from the floor and onto the strainer the head loss 

evaluation should consider that debris. However, the head loss evaluation should also be 

conducted for a debris load that does not include that debris in order to determine which 

condition results in a larger head loss. The more conservative value should be used in the plant 

evaluation because of the uncertainties associated with predicting debris transport. Specifically, 

some vendor head loss testing used agitation to force debris to accumulate on a strainer, to 

achieve a goal of conservative transport. The agitation may have resulted in some debris 

collecting on the stainer that would not have accumulated under prototypical conditions. The

forced accumulation can preclude the formation of a worse case head loss debris bed (i.e., bed

formed with fine tightly packed debris). Under these conditions a non-conservative

assessments of the head loss can be made. The ‘common interface’ between the transport 

evaluation and the head loss evaluation is very important.
5-61

5.5 Coatings and Coatings Debris

5.5.1 Introduction

Painted industrial coatings are applied to a large number of systems, structures, and 

components housed in the containment of both PWRs and BWRs to protect the surfaces from 

corrosion, to facilitate decontamination, and to provide for wear protection during plant operation 

and maintenance activities. These coatings are of several types (primer, sealer, topcoat, 

surfacer, etc.) and encompass a great variety of chemical formulations. These chemical 

formulations commonly used include alkyd, vinyl toluene modified alkyd, epoxy, urethane, 

acrylic, styrenated acrylic, basic zinc carbonate, and inorganic zinc-rich materials. It has been 

estimated that a medium-sized PWR containment has approximately 650,000 ft2 of coated 

surfaces inside (NUREG/CR-6808). In a survey of conducted by EPRI, it was reported that 6% 

of the more than 11 million square feet of nuclear Service Level I coatings inside containments

(represented by the survey) have shown signs of degradation (EPRI, 2006).

The NRC issued Revision 2 of RG 1.54, "Quality Assurance Requirements for Protective 

Coatings Applied to Water-Cooled Nuclear Power Plants," in October 2010 to provide updated 

guidance regarding compliance with quality assurance requirements for protective coatings 

applied to ferritic steel, aluminum, stainless steel, zinc-coated (galvanized) steel, and masonry 

surfaces. This guide encourages industry to develop codes, standards, and guidance that can 

be endorsed by the NRC and carried out by industry. The principal industrial standard cited in 

RG 1.54 is ASTM D 5144-08 (ASTM, 2008a). This top-level standard, in turn, incorporates by 

reference a number of other ASTM standards applicable to nuclear power plant coatings, as 

illustrated in Fig. 5.5-1.

Service Level I, II, and III coatings are defined in Revision 2 of RG 1.54 as follows:

a. Service Level I coatings are used in areas inside the reactor containment where coating 

failure could adversely affect the operation of postaccident fluid systems and thereby 

impair safe shutdown.

b. Service Level II coatings are used in areas where coating failure could impair, but not 

prevent, normal operating performance. The functions of Service Level II coatings are to 

provide corrosion protection and enhance decontamination in those areas outside the 

reactor containment that are subject to radiation exposure and radionuclide 

contamination. Service Level II coatings are not safety related.

c. Service Level III coatings are used in areas outside the reactor containment where 

failure could adversely affect the safety function of a safety-related SSC. 

With noted exceptions related to quality assurance standards and the definitions of Service 

Levels I, II, and III coatings, the ASTM standards cited in the Revision 2 of RG 1.54 for the 

selection, qualification, application, and maintenance of protective coatings in nuclear power 

plants have been reviewed by the NRC staff and found acceptable.
5-62

Figure 5.5-1. ASTM Standards Relevant to NPP Service Level I, II, and III Protective Coatings (NRC 
5-63

For nuclear applications, the NRC has categorized those coatings that meet the requirements of 

ASTM D5144-08 as qualified coatings. Qualified coatings are expected to adhere to their 

substrates during a design-basis LOCA (DB-LOCA), unless directly impacted by the break jet, 

except for coatings that have received extensive irradiation (>109 rad) (ANSI, 1972). Coatings 

that do not meet the requirements of ASTM D5144 are classified as unqualified coatings. The 

NRC currently holds the position that 100% of design basis accident (DBA) unqualified coatings 

in reactor containments will fail (disbond from their substrate) during a LOCA and thus be 

available for transport to the ECCS sump.

A substantial quantity of unqualified coatings may be present in nuclear plant containments, and 

their presence represents a potentially significant contribution to ECCS sump clogging in the 

event of a LOCA. In addition, qualified coatings may also fail under conditions described above 

or because of improper application or maintenance, and the resulting debris from these coatings 

can also potentially contribute to sump clogging. The testing and failure of both qualified and 

unqualified coatings and the nature of the debris generated are summarized here.

5.5.2 Coating Failures in Operating Nuclear Plants

The Electric Power Research Institute (EPRI) has sponsored a research program designed to 

gain an understanding of the degradation of nuclear Service Level 1 coatings and to evaluate 

the effects of aging on the qualified coatings used inside containment. As a part of that 

program, EPRI report 1013465 documents the results of a survey of the U.S. nuclear industry to 

gather data regarding qualified coating degradation and failure inside reactor containment. This 

survey reported that the generic coatings systems with the highest percentage of area with 

signs of degradation involved modified phenolic epoxy coatings. Coating application issues 

(inadequate surface preparation, improper thickness of the applied coating, or insufficienct

curing) were the most commonly reported causes of degradation. The most frequently reported 

visual evidence of coating degradation was delamination, followed by blistering, cracking, and 

flaking. Finally, the report concluded that aging is not a major degradation mechanism. 

The related EPRI report (2007b) describes coating failures in industrial applications and 

compares them with coating degradation and failures in nuclear primary containments. The 

report compares industrial exposure environments with nuclear primary containment operating 

environments, presents case histories of industrial failures of coating systems that are similar to 

those used in nuclear primary containments, and discusses the relevance of industrial case 

histories to the nuclear coatings degradation described in EPRI report (2006). 

As indicated in the two EPRI reports cited above, a significant number of coating failures in 

nuclear containments have occurred over the years. However, these two reports do not identify 

the specific nuclear plants that have experienced such failures. Summaries of some of the 

more significant failures reported in NRC communications are given in Table 5.5-1. It can be 

seen that these failures involve both qualified and unqualified coatings and that failures have 

occurred in both PWRs and BWRs. Where the cause of failure has been identified, it is most 

commonly attributed to the use of unqualified coatings and/or improper coating application.
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Table 5.5-1. Summary of Selected Coating Failures in U.S. Nuclear Power Plant 

Containments as Reported in NRC Communications

Plant Description of Failure Referenc

e

North Anna 

1 (PWR), 

March 1993

During steam-generator replacement, it was discovered that most 

of the unqualified silicon aluminum paint covering the SGs had 

come loose from the exterior surfaces and was being supported 

only by the insulation jacketing. Paint pieces ranged in size from 

dust particles to sheets 0.61 m (2 ft) wide. This same paint on the 

pressurizer was also loose. The quantity of this coating in 

containment was estimated at 1,087 m2 (11,700 ft2).

IN-93-34

Indian Point 

2 (PWR),

March 1995

An inspection found that paint was peeling from the containment 

floor. The factors contributing to the delamination of the paint 

were: (1) the paint thickness exceeded the manufacturer’s 

specifications by up to twice the allowed thickness; (2) there was 

excessive paint shrinkage caused by use of too much paint 

thinner; (3) the surface had not been cleaned and prepared 

properly before the paint was applied; and (4) appropriate 

inspection and documentation requirements were not 

implemented.

IN-97-13

Millstone 3

(BWR)

July 1996

About 20 pieces of Arcor were found in the Train-A recirculation 

spray heat exchangers. Arcor is an epoxy coating material that 

was applied to the inside surfaces of the service water system 

piping. The Arcor chips were apparently swept into the 

recirculation spray heat exchanger channel during testing. The 

licensee also found 40 to 50 mussel shell fragments in the heat

exchangers. The Arcor chips and mussel fragments were 

relatively small (on the order of 1 in.2). The licensee determined 

that the debris could have prevented the heat exchangers from 

performing their specified safety function. In addition, construction

debris was discovered in all four containment recirculation spray 

system (RSS) suction lines, and gaps were found in the RSS sump 

cover plates.

IN-97-13

GL-98-04

Zion 

2(PWR),

November 

1996

Inspections found that 40 to 50% of the concrete floor coatings 

showed extensive failure as a result of mechanical damage and 

wear, and that about 5% of the coating associated with the 

concrete wall and liner plate was degraded. Unqualified coatings 

had been applied to various surfaces, including instrument racks, 

struts, charcoal filter housings, valve bodies, and piping. Although 

adhesion tests showed acceptable adhesion strength in most of 

the locations tested, one test conducted on an unqualified coating 

system did not satisfy the acceptance criteria. Documentation was 

not found for over-coating (i.e., touch-up work) that had been 

applied to many of the liner plates and concrete wall surfaces.

IN-97-13
5-65

Clinton

(BWR),

July 1997

A significant quantity of degraded protective coating was removed 

from the containment because of substantial degradation in the 

wetwell and some degradation in the drywell. Because of the 

indeterminate condition of these degraded coatings, reasonable 

assurance could not be given that the coatings would not disbond 

from their substrates enough to clog the ECCS suction strainers 

during accident conditions.

GL-98-04

Braidwood 

2(PWR),

April 1999

During a refueling outage, the NRC resident inspector noticed a 

significant amount of paint peeling off the containment wall outside 

of the missile shield. This qualified coating system consisted of an 

inorganic zinc primer and an epoxy phenolic topcoat. The topcoat 

was coming off of the primer, with part of the primer adhering to 

the topcoat. The licensee's preliminary root cause for the 

degradation is that the primer was applied too thickly and is failing 

cohesively. Many of the paint chips were several inches square. 

Similar peeling was noted during the last several refueling outages. 

The peeling was initially observed in an area classified as outside 

of the ZOI for material blockage of the sump. However, there is a 

concern that the larger paint chips may block flow paths to the 

sump strainers.

NRCSECY99-127

Vermont 

Yankee 

1(BWR),

October 

2001

Carboline Carbozine CX-11SG paint primer was applied to the 

drywell shell (inner wall) to the floor joint as part of a qualified seal 

design. The purpose of this seal is to provide a moisture barrier to 

mitigate water entering the shell to concrete interface. In 

preparation for and during subsequent applications of the primer, 

significant gelling/premature set-up of the paint was exhibited. 

Within 24 hr of the paint application, the paint began to lift and 

blister. The failure was most likely due to a moisture problem 

during manufacture.

NRCEvent 

Notificati

on 

Report 

(ENR)

38408

Dresden 2 

(BWR)

Nov. 2001

An inservice inspection identified an area of missing coating and 

primer encircling the drywell shell adjacent to the basement floor. 

The area was 5-10 cm (2-4 inches) wide. In this area, the base 

metal of the drywell shell was found corroded. However, based on 

ultrasonic and visual examinations, the degraded area was found 

to be within the corrosion allowance for the drywell shell. The shell 

coating was repaired in this area to prevent further degradation.

IN 2004-

09

Sequoyah 2 

(PWR)

May 2002

During an inspection, the NRC identified areas of the steel 

containment vessel (SCV) with degraded coatings and rust. One of 

the floor drains was clogged in the annulus area (1.5 m [5 feet] 

wide) between the SCV and the reinforced concrete shield 

building. Localized water ponding at the clogged drain had come 

in contact with a section of the SCV, causing deterioration of the 

SCV coatings and rusting of the SCV.

IN 2004-

09
5-66

Oconee 1, 

2, 3

(PWR),

2003-2004

During the Unit 1 refueling outage in Fall 2003, the inspectors 

discovered what appeared to be a significant amount of Service 

Level 1 coatings that were severely blistered, delaminated, peeling 

and falling off of the reactor building (RB) dome and liner, polar

crane, and sprinkler grid support assembly. Similar degraded 

coating conditions were discovered by the inspectors during the 

Unit 2 EOC20 refueling outage and the Unit 3 forced outage 

following its February 26, 2004, reactor trip. 

NRCONS 

2004

5.5.3 Testing of Qualified Coatings

The Savannah River Technology Center (SRTC) has conducted an extensive experimental 

program on the potential for degradation and failure of qualified protective coatings applied to 

exposed surfaces within primary containment of nuclear power plants. The results of this 

program are summarized in a series of technical reports: WSRC-TR-2000-00079, WSRC-TR2000-00340, WSRC-TR-2001-00067, and WSRC-TR-2001-00163 (Dupont et al., 2000a, 2000b, 

2001a, and 2001b). Dupont et al. (2000b) describe results obtained for an epoxy-polyamide 

primer and topcoat (Amercoat® 370 over Amercoat® 370) applied to a steel substrate. The 

experimental approach involved a combination of (1) measuring critical coating materials 

properties at conditions representative of a post-LOCA period, (2) developing a predictive 

coating system failure model, (3) subjecting such coating systems to DBA conditions, (4) 

comparing model and test results to judge predictive capability, (5) documenting the degree of 

failure, and (6) characterizing the failed coating debris, for integration into the PWR sump 

blockage research program (GSI-191).

The research results reported in this report resulted in the following conclusions:

1 Properly applied qualified coatings systems can be expected to exhibit adequate 

adhesion strength to a steel substrate following exposure to simulated DBA conditions.

2 Selected samples artificially aged by exposure to gamma radiation to a cumulative dose 

of 109 rad in accordance with ASTM D-4082-95 (ASTM, 1995d), exhibited some nearsurface degradation. This degradation appeared as a consequence of coating oxidation 

resulting from irradiation and temperature effects and would be expected to vary with 

oxygen availability and permeability in a particular coating system.

As part of the investigation, an Ameron Coatings System 5 epoxy and modified polyamide 

resins coating system (Amercoat® 370 over Amercoat® 370) was evaluated. A properly 

applied coating exhibited only blistering without detachment when subjected to a simulated 

LOCA, but it was projected that this coating system (if there were coating flaws that had 

entrapped moisture) could fail during the rapid containment cool down introduced by activation 

of containment spray systems.

In a second follow-on report (Dupont et al., 2000a), the same investigators describe the results 

of tests conducted on an epoxy-phenolic topcoat (Phenoline 305) over an epoxy 

(Starglaze -90 (ASTM, 1996e). 2011S ) a pplie d to concrete in a ccor 

This coating system, which was designated Coating System 2, is representative of coatings 

applied to concrete within PWR containments in the early to mid-1970s. Selected samples were 

again artificially aged by exposure to gamma radiation in accordance with ASTM D-4082-95 

(ASTM, 1995d). In addition, both unaged and aged samples were exposed to DBA conditions 

specified in the ASTM D3911-95 (ASTM, 1995g) steam temperature profile for PWR 
5-67

containments, as well as other relevant DBA conditions, including a “pulse” steam temperature 

profile and a high temperature (up to 200°F) water immersion. This investigation resulted in the 

following conclusions:

1 Properly applied coatings that contain only minor defects and that have not been 

subjected to irradiation of 109 rad can be expected to remain fully adhered and intact on 

a concrete substrate following exposure to simulated DBA conditions.

2 Non-bonded embedded defects(or intentiontionally induced defect),greater than 

approximately 3.2 mm (1/8 in.) in diameter, are subject to cracking and failure during 

DBA exposure.

3 Properly applied coatings that have been subjected to irradiation of 109 rad exhibited 

profound blistering, leading to disbondment of a near-surface coating layer (0.025-0.05 

mm [1-2 mils] of the 0.25-mm [10-mils] thickness) when exposed to elevated 

temperatures and moisture associated with DBA conditions. This failure of the coating 

produced a coating debris source term.

In the third stage of this research program (Dupont et al., 2001b) the same investigators tested 

an epoxy-phenolic topcoat (Phenoline 305) over an inorganic zinc primer (Carbozinc 11), which 

is representative of a coating system that was applied to steel substrates within PWR 

containment in the early to mid-1970s. The experimental approach was similar to that 

described above (Dupont et al., 2000a) and the following conclusions were reached:

1 Properly applied coatings that have not been subjected to irradiation of 109 rad, can be 

expected to remain fully adhered and intact on a steel substrate, following exposure to 

all simulated DBA LOCA conditions. In addition, no minor cracking in defect-free regions 

of the coating and regions near embedded defects was observed. This finding is in 

contrast to previous test results on a concrete system (Dupont et al., 2001b) and is 

predicted by the deformation modeling.

2 2. Properly applied coatings that have been subjected to irradiation of 109 rad exhibited 

profound blistering, leading to disbondment of a near-surface coating layer (0.025-0.05 

mm [1-2 mils] of the 0.25-mm [10-mils] thickness) when exposed to elevated 

temperatures and moisture levels within the range of DBA conditions. This behavior is 

similar to that of the epoxy-phenolic topcoat/epoxy surfacer system described above and 

again produced a coating debris source term.

Finally, qualified coating specimensfrom the containment of four nuclear stations were 

evaluated for coating degradation and failure. These specimens included coating chips that had 

become disbonded during normal plant operation and intact coating specimens that were 

sectioned from steel components in the containment. These specimens were evaluated by 

several characterization techniques in the as-received (service-experienced) condition, and after 

irradiation-aging and simulated DBA-LOCA conditions to provide structural and chemical 

information.

The as-received coating chip specimens were found to have failed within the inorganic zinc 

(IOZ) layer. A non-uniform distribution of the ethyl silicate binder was observed that most likely 

caused poor adhesion within the IOZ. The failure was attributed to improper application, rather 

than in-service environmental degradation. The coating chips had a topcoat layer and a layer of 

IOZ. Exposure of the two-layer chip to simulated DBA-LOCA conditions resulted in extreme 
5-68

curling of the initially flat chip, apparently because of differential expansion/contraction between 

the two layers of the chip.

The intact coating specimens that were sectioned from plates and handrails from two plants 

were tested in the as-received condition. The coatings were found to be sound and strongly 

adhered following exposure to simulated DBA-LOCA conditions. The as-received condition of 

these materials represented 10-20 years of normal operational service. The intact coating 

specimens were also tested following irradiation aging to 109 rad (at 106 rad/hr and 120°F). 

Severe blistering and the formation of particulate debris occurred when these specimens were 

exposed to simulated DBA-LOCA conditions. This behavior is similar to that observed in

coatings on laboratory specimens but the damage was more severe in the plant specimens.

A series of adhesion tests was conducted under EPRI sponsorship on existing qualified Service 

Level 1 coatings at four nuclear plants, namely, the San Onofre Nuclear Generation Station 

(SONGS) Unit 3, Waterford Unit 3, McGuire Unit 1, and Oconee Unit 2 (EPRI, 2007). The 

coatings tested included zinc-rich and epoxy primers, epoxy surfacers, and epoxy and phenolic 

topcoats applied to sound and degraded steel and concrete. The tests were conducted in 

accordance with (1) dry film thickness testing as stated in ASTM D4138-00 (ASTM, 2000) 

and/or ASTM D6132-04 (ASTM, 2004) as appropriate, (2) adhesion testing according to ASTM 

D4541-02 (ASTM, 2002), and (3) knife adhesion testing according to ASTM D6677-01 (ASTM, 

2001). In all cases, coatings that exhibited no visual anomalies (flaking, peeling, chipping, 

blistering, etc.) continued to exhibit system pull-off adhesion at or in excess of the originally 

specified in the ASTM D5144 minimum value of 200 psi, even though the coatings had been in 

place for approximately 20-35 years.

5.5.4 Testing of Unqualified Coatings

Design basis accident testing has been performed on selected unqualified OEM coatings under 

EPRI sponsorship. The test samples consisted of 37 components of the sort typically found in 

PWR containments, all with the OEM-applied coatings. The NRC Staff Review Guidance 

Regarding Generic Letter 2004-02 Closure in the Area of Coatings Evaluation [ADAMS 

Accession No. ML080230462] issued in March 2008, noted that five of the 37 coatings in the 

EPRI tests showed greater than 80% failure, with some as high as 99% failure. These coatings 

included alkyds, moisture-cured urethane, and inorganic zinc-rich coatings. The Review 

Guidance document concludes that licensees would not be able to demonstrate, based on this 

report alone, that their coatings would not fail at these high rates and therefore would not be 

able to take credit for a reduced amount of unqualified coating debris. For specific coatings, the 

licensee might be able to justify a lower failure rate, based upon the EPRI data for that coating 

or upon results from plant- and coating-specific testing.

5.5.5 Coating Debris Generation

The amount of coating debris generated in a LOCA event depends upon the failure 

characteristics of the coating as well as the size of the region (i.e., the zone of influence or ZOI) 

over which coating failure is expected for a given accident scenario. The amount of this debris 

that actually reaches the ECCS sump further depends upon the transport characteristics of that 

debris under the accident conditions in question. These two points will be briefly considered 

here.

As noted above, the NRC issued the document “NRC Staff Review Guidance Regarding 

Generic Letter 2004-02 Closure in the Area of Coatings Evaluation” [ADAMS Accession No. 
5-69

ML080230462] in March 2008. The purpose of this document is to provide guidance to NRR 

staff on what information is needed in a licensee’s response to GL 2004-02 in the review area of 

protective coatings. In addition, the document provides guidance to licensees in preparing their 

supplemental responses to GL 2004-02 with respect to coatings. Six broad categories of 

information are described as sufficient to support closure of the aspects of the generic letter, as 

follows:

1 Summary of the type(s) of coating systems used in containment.

2 Description of the containment coating condition assessment program.

3 Description and the bases for coatings debris generation assumptions. For example, 

description of how the quantity of paint debris was determined based on ZOI size for 

qualified and unqualified coatings.

4 Description of debris characteristics assumed, i.e., chips, particulate, size distribution, 

and bases for the assumptions.

5 Description and bases for assumptions made in post-LOCA paint debris transport 

analyses.

6 Discussion of suction strainer head loss testing performed as it relates to both qualified 

and unqualified coatings and what surrogate material was used to simulate coatings 

debris. Discussion of bases for the choice of surrogates.

Most of these categories deal directly or indirectly with the issues of debris generation and 

transport resulting from coating failure, and category 3 deals directly with the question of ZOI 

size for the coatings in the region impacted by a pipe failure. The NRC-SE-2004 conservatively 

recommends an assumed coatings ZOI spherical equivalent of 10 pipe diameters, or 10D. The 

2008 Review Guidance document described conditions under which the licensee may assume a 

less conservative ZOI of 4D or greater for qualified epoxy coatings and 10D or greater for 

qualified untopcoated inorganic zinc coatings (ML100960495). 

The characteristics of failed coating debris have been examined by the BWROG for selected 

types of coatings and test conditions (Bostelman et al., 1998), as summarized by Shaffer et al. 

in NUREG/CR-6808. Test samples were prepared by first exposing the coating to a minimum 

radiation dose of 109 rad at an average dose rate of 1.65 Mrad/h at the University of 

Massachusetts Lowell Radiation Laboratory. The specimens next were subjected to a series of 

three LOCA tests at the testing department of the Carboline Company to investigate the postLOCA failure mechanisms and the failure timing of the coating systems. Scanning electron 

microscopy was used to perform a detailed examination of pieces of debris. Microhardness 

measurements also were taken and compared for selected coating types. The coating debris 

examined ranged from powder residues to large, slightly curved pieces.

The hydraulic transport characteristics of coatings particulates under LOCA conditions were 

examined in a series of experiments conducted at the Carderock Naval Surface Warfare Center 

in 2006 (NUREG/CR-6916). Five coatings systems, typical of coatings applied to equipment 

and structures located in the containment buildings of PWRs, were tested. The effects of chip 

size, shape, density, thickness, stream velocity, water saturation of the coatings, and thermal 

curing on transportability were examined. Three types of tests were performed, quiescent 

settling tests, transport tumbling-velocity tests, and steady-state velocity tests. In the quiescent 
5-70

settling tests, coating chips were dropped onto the water surface under quiescent conditions. It 

was found that coating chips with a density close to that of water tended to remain on the 

surface indefinitely, and heavier chips tended to sink almost immediately. In the transport 

tumbling-velocity tests, the chips were placed on the flume floor under flowing water conditions. 

These tests demonstrated that all but the lightest chips and curled chips remained in their initial 

position at stream velocities in excess of 0.09 m/s (0.3 ft/s). In the steady-state velocity tests, 

the coating chips were released into the moving stream below the water surface. These tests 

found that, at a uniform water velocity of 0.06 m/s (0.02 ft/s), all but the lightest chips settled to 

the bottom before reaching the end of the flume.

5.5.6 Summary

In the event of a LOCA, the debris generated by failed coatings in the containments of nuclear 

power plants represent a potentially significant source of material available for transport to the 

ECCS sump. Furthermore, operating experience at a number of plants has demonstrated that 

coatings can fail even under normal operating conditions. Accordingly, Revision 2 of RG 1.54, 

"Quality Assurance Requirements for Protective Coatings Applied to Water-Cooled Nuclear 

Power Plants," provides guidance on the use and testing of these coatings. Both qualified and 

unqualified coatings have been extensively tested under simulated DBA conditions, and the 

debris characteristics and transport behavior have also been studied. In March 2008, the NRC 

issued the document “NRC Staff Review Guidance Regarding Generic Letter 2004-02 Closure 

in the Area of Coatings Evaluation,” which provides guidance on what information is needed for 

a licensee’s supplemental response to GL 2004-02 in the review area of protective coatings. 

The document also describes acceptable technical assumptions for those licensee responses 

based on research conducted by the NRC and the industry.

5.6 Latent Debris

5.6.1 Introduction

Dirt, fiber, and other foreign materials that are generally found in nuclear power plant 

containment buildings are referred to as “latent debris.” Consideration should be given to the 

potential for latent debris to gather in containment during plant operation. This debris may 

transport to and affect head loss across the ECCS sump strainers. Therefore, it is necessary to 

determine the types, quantities, and locations of latent debris. Due to variations in containment 

design and size, latent debris sources should be evaluated on a plant-specific basis. It is 

unlikely that foreign materials exclusion (FME) programs can entirely eliminate sources of latent

debris within containment. Reasonably conservative estimates for latent debris need to be 

included in the overall debris source term unless plant-specific walkdowns verify lower values. 

Plant-specific walkdown results can be used to determine a conservative amount of dust and 

dirt to be included in the debris source term. Walkdowns will not be able to directly measure the 

entire amount of latent debris. However, it is possible to quantify the amount of debris with 

additional steps. The following activities are recommended to quantify the amount of latent 

debris inside containment and are described in greater detail in sections below:

• Calculate the horizontal and vertical surface areas inside the containment. This calculation 

will determine the total area with the potential for accumulation of debris.

• Evaluate the resident debris buildup on representative surface areas within containment. 

Generally, samples of debris are taken at several locations. 
5-71

• Define the debris characteristics. This information will be used in subsequent steps of the 

sump performance evaluation.

• Calculate the total quantity and composition of debris. This information will also be used in 

subsequent steps of the sump performance evaluation, such as evaluation of the transport 

of latent debris to the sump strainer and the resulting head loss. Detailed guidance is 

provided below for accomplishing the recommended activities for quantification of the 

amount of latent debris.

5.6.2 Baseline Approach

Latent debris is considered a contributor to head loss across the sump strainer and should be 

evaluated accordingly. Information is provided in the NRC staff SE on the NEI guidance report 

(SE NEI-04-07) to evaluate the quantity of latent debris with sufficient rigor to eliminate 

excessive conservatism. Note that in many cases, the contribution to head loss by latent debris 

will be small in comparison to that caused by debris from other sources, such as insulation 

materials. In these cases, latent debris will not determine the course of action for mitigating 

ECCS sump strainer issues. However, for cases where there is little fibrous debris generated 

by the LOCA jet, latent debris may have a significant effect on the head loss evaluation. If other 

debris sources create amounts of transportable debris much greater than that expected from 

latent debris a detailed latent debris evaluation should not be required. The impact on the 

results of the sump performance evaluation as a whole should be considered before performing 

a rigorous analysis of latent debris loading. 

5.6.2.1 Estimation of Surface Area Inside Containment

Estimates are made of the horizontal and vertical surface areas. Vertical surfaces such as walls 

and sides of equipment are considered, although a significant amount of debris does not 

typically collect on vertical surfaces in the absence of factors that promote adhesion of solids to 

the surface. The list of items that should be included in the surface area calculation (floor area, 

walls, cable trays, major ductwork, control rod drive mechanism coolers, tops of reactor coolant 

pumps, and equipment, such as valve operators, air handlers, etc.) provides a starting point for 

licensees to consider for major inputs. The five steps provided for surface-area calculations (flat 

surface considerations, round surface area considerations, vertical surface area considerations, 

thorough calculation of surface areas in containment, and use of estimated dimensions when 

exact dimensions are unavailable) are considered informative.

5.6.2.2 Evaluation of Resident Debris Buildup

Although sampling of surfaces inside the containment at a number of plants indicated that the 

maximum mass of latent debris inside containment is likely less than 200 pounds for PWRs, a 

survey of each plant’s containment is recommended, with the objective of determining the 

quantity of latent debris. Surveying the containment for latent debris ensures that higher-thanaverage debris loads are accounted for and will allow plants to take advantage of smaller latent 

debris loading if lower quantities are present. Note that it is recommended to perform periodic 

surveys (as part of outage efforts) to validate that there has been no significant change in the

latent debris load inside the containment, especially if latent debris can contribute significantly to 

the head loss evaluation. The required rigor of these surveys is dependent on the effectiveness 

of the licensee’s FME and housekeeping programs with respect to containment cleanliness. If 

the licensee has rigorous programs in place to control the cleanliness of containment and 

documents the condition of containment after an outage, it is adequate to perform inspections 
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and limited sampling of surfaces. If the cleanliness of containment is not controlled through 

rigorous programs, or if the programs in place do not address all areas of containment, it is 

necessary to perform more comprehensive surveys.

The NRC staff guidance report (SE NEI-04-07) does not recommend direct measurement of 

latent debris thickness because (1) masses can be measured much more accurately than 

thickness, (2) comparison of dirt layers to reference thickness standards is subjective and prone 

to error because of heterogeneous small objects that may reside on the surface and because of 

non-uniform dust thickness across a surface like piping, and (3) in situ estimates of thickness do 

not characterize size distributions, particulate-to-fiber mass ratios, or densities that are needed 

to define hydraulic head-loss properties. These problems can be avoided by measuring total 

masses within a known surface area and then partitioning the fiber and particulate mass 

fractions either by physical measurement or by generic assumptions. 

5.6.2.3 Surface Area Susceptibility to Debris Accumulation

Not all areas are susceptible to accumulation of debris. For example, housekeeping activities at 

some plants may involve cleaning floors with special wipes, vacuum cleaners, or other methods. 

In these cases, the areas that are within the scope of the cleaning program could have 

essentially no debris accumulation, whereas inaccessible areas of the same surface could have 

an accumulation of debris. A single debris layer thickness would not accurately represent the 

entire surface.

It is appropriate to conservatively assume that the entire surface area is susceptible to debris 

accumulation. If it is unreasonable to use this assumption, then in addition to determining the 

total horizontal surface area inside containment, licensees must determine the fraction of the 

surface area of each component and surface that is susceptible to debris accumulation. To 

make this determination, evaluate the fraction of the surface area susceptible to debris 

accumulation on a component-by-component or surface-by-surface basis. The following 

guidance was recommended:

1 Assume that 100% of the surface area is susceptible to debris accumulation in 

inaccessible areas as well as in accessible areas that are not thoroughly cleaned and 

documented as clean per plant procedures before restart (e.g., cable trays, junction 

boxes, and valve operators), and floors with gratings positioned on flat surfaces.

2 Evaluate the fractional area susceptible to debris accumulation on smooth floor areas 

and on other surfaces cleaned per plant procedures before restart on a case-by-case 

basis. Considerations include the method of cleaning (e.g., pressure washing vs. 

vacuuming) and accessibility of areas. Because of wide variations in containment 

design and effectiveness of housekeeping and FME programs, evaluations should be 

performed on a plant-specific basis. For all cases in which the area susceptible to debris 

accumulation is reduced, a conservatively large fractional area susceptible to 

accumulation should be determined, and bases should be provided for the fractions 

used. The following guidance was given:

• Calculate the total surface area of the surface being considered.

• Calculate the area of the surface that is clean. Use simplifying assumptions that will result 

in a conservatively small clean area.
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• Calculate the ratio of potentially dirty area to the total area.

5.6.2.4 Total Quantity and Composition of Debris

The final step in determining the quantity of latent debris inside the containment is to compute 

the total quantity of latent debris. Use the following guidance when performing the final 

calculations:

1 Perform calculations on an area-by-area basis, which will facilitate adequate 

representation of the debris densities and characteristics in the various areas inside the 

containment.

2 Compute the total quantity of debris for each area by multiplying the total surface area 

susceptible to debris accumulation by the debris layer thickness for the area of 

containment being considered.

3 Include quantities of other types of latent debris such as tape, equipment tags, and 

stickers.

4 Categorize and catalog the results for input to the debris transport analysis.

5.7 Debris Accumulation, Head Loss, and Vortex Evaluation

5.7.1 Overview

ECCS recirculation strainers are designed to prevent debris from entering the ECCS and CSS 

and causing damage to the pumps and other downstream components. However, debris 

accumulating on the strainers can cause head loss that, if sufficient, could result in pump 

degradation or failure by cavitation, air entrainment, or flow starvation. Air ingested into the 

strainer due to lack of full submergence or due to a vortex formation can result in similar pump 

issues. The pool water contains non-condensible gasses. The pressure decrease due to the 

water flow through the debris bed can cause deaeration-generated bubbles. In addition, when 

the water temperature is sufficiently close to the saturation temperature, flashing can occur 

within the debris bed or the strainer due to pressure decreases associated with flow induced 

head losses. These concerns are discussed in this section. Small debris penetrating the 

strainer may reduce flow to the core, cause equipment damage, or have other effects on 

downstream components. These potentials are evaluated in the section covering downstream 

effects. 

The head loss and vortex evaluation requires assessment of the associated time-dependent 

variables that affect important phenomena associated with pump and strainer performance. 

Pump flow rates, water temperature, containment pressure, and sump or suppression pool 

water level, debris generation and transport, and the potential for chemical precipitation are key 

factors that should be included. Key aspects of the strainer design should be specified, 

including strainer area, surface geometry, and screen mesh or hole size. Debris generation and 

transport to the strainer should be assessed to provide the quantities of debris by debris type 

predicted to arrive at the strainer and the size distributions for each type of debris. Guidance 

requires that strainers be designed to accommodate the most problematic debris load. The 

most problematic debris combination may not be the greatest quantity of debris, but may be 

caused by a thin debris bed or some combination of debris types. Thin debris beds, or thin 

beds are created when a relatively small amount of fiber collects on a strainer with a significant 
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amount of particulate debris. The particulate debris is concentrated in a small volume resulting 

in a dense bed that may be relatively highly resistant to flow. In a thicker bed, the particulate 

may be distributed among a larger volume of fiber resulting in a lower head loss. Several debris 

generation and transport scenarios may have to be considered to identify the most problematic 

debris combination for any particular strainer. All of this information is required to ensure that 

strainer qualification head loss testing results in a realistic or conservative design basis head 

loss for the plant specific debris load and hydraulic conditions. The head loss evaluation 

provides the design basis head loss and potential air ingestion amounts for the NPSH 

evaluation, and the maximum head loss for the strainer structural evaluation. The head loss 

evaluation may provide a head loss that varies with time or temperature. In general, head loss 

is lowest at the start of recirculation and increases as debris builds a bed on the strainer and 

pool temperature decreases resulting in increased water viscosity. 

The bed porosity and the debris bed surface area through which the water flows are the debris 

bed parameters that most govern head loss. Flow rate though the debris bed and water 

temperature are also important variables. A comparison between pipe flow and the fiber bed

may be useful in understanding debris bed head loss. The debris bed head loss is similar to the 

piping frictional pressure loss. The piping head loss is a function of flow area and the pipe 

surface area, typically specified by using the hydraulic diameter. As the diameter of a circular 

pipe is increased, the cross-sectional area increases, the flow velocity decreases, the surface 

area per unit of flow in contact with the flow decreases, and the pressure drop decreases. The 

shape of the flow channel also affects the pressure drop, e.g., a narrow rectangular conduit of 

the same flow area as a circular pipe would have a greater specific surface area in contact with 

the flow than the circular pipe, resulting in a higher frictional pressure drop. For a debris bed, 

the bed porosity roughly correlates with the hydraulic diameter while the debris bed surface area 

correlates with the pipe flow area. The pressure drop for flow through a debris bed increases 

with reduced porosity and/or a higher specific surface area. In general flow through pipes is 

turbulent. In many cases flow through a debris bed is mostly laminar due to the very small flow 

passages through the bed. 

For a given porosity and surface area, head loss also increases with the thickness of the debris 

bed. This could be interpreted to indicate that a thicker debris bed would always result in higher 

head loss. However, bed porosity is also a function of how the debris accumulates. Debris 

arrival timing and sequencing can result in varying debris bed porosities. A thinner and tighter 

(less porous) bed can cause a higher head loss than a thicker and more porous bed. Of 

specific interest, a uniform thin debris bed formed of fine fiber and particulate debris can cause 

substantially higher head losses than a similar bed formed by larger fibrous shreds given the 

same particulate debris loadings. If a specific amount of particulate debris is distributed 

relatively evenly through fibrous beds of similar characteristics, but varying fiber amounts, 

frequently a bed with less fiber will result in higher head loss. This is because the particulates 

are trapped more closely together resulting in less porosity. It has been observed that up to a 

point debris beds with higher particulate to fiber ratios result in higher head losses. Uniform 

debris beds are generally associated with higher head losses than non-uniform beds containing 

the same amount of debris. 

Other important aspects of debris beds include particulate filtration efficiency and bed structural 

strength. The size of strainer openings can affect the initial filtration efficiency of fibrous debris. 

Because the porosity of a layer of fibrous debris ranges from about 92% to 99%, fine particles 

can pass through the fiber bed while coarser particles are filtered. The fiber bed compresses 

due to increasing head loss. This increases filtration efficiency and reduces the bed porosity. 

As larger particulate is filtered, the overall filtration efficiency of the bed is increased and finer 
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and finer particles are filtered. A typical thin bed of fine hardened particulate may have a 

porosity of about 80%. Coarse sand may have porosity as low as about 40%. 

The slow buildup of a debris bed would first result in an accumulation of fibers, and then larger 

particles, followed by smaller particles until all debris is filtered from the fluid or the particles are 

too small to be filtered. Some of the more problematic materials with respect to head loss are 

microporous insulation (Microtherm, Min-K, and calcium silicate), and chemical-effect 

precipitates. Because these materials can be very small they sometimes pass through the 

debris bed without adding to head loss until filtration of the coarser materials increases the 

bed’s filtration efficiency. This is an example of potential synergistic effects among debris types. 

Another possible synergistic effect could be the structural strength of the bed, specifically for 

thin beds. Some debris beds have been observed to develop flow channels through the bed, 

referred to as “boreholes,” as head loss builds. These boreholes relieve and limit head loss. 

Boreholes through a calcium silicate thin-bed layer can be observed in NUREG/CR-6874, 

Figure 3.18. Whether or not boreholes can develop within a bed of particulates likely depends 

upon the structural strength of the bed, which in turn likely depends upon the composition of the 

bed, such as types of particulate and the fiber composition. Although not observed in testing, it 

is possible that the addition of hardened particulate (such as coating particulates) to the calcium 

silicate (fragile crystallized particulate) beds tested in NUREG/CR-6874 could have affected the 

development of the observed boreholes. 

Structural strength of a debris bed may be limited if there is inadequate fibrous debris present to 

support the bed. The staff has observed head loss tests that formed very thin uniform beds. In 

some cases pressure drop across the debris beds was limited by structural strength. Head loss 

was observed to increase up to a point at which is would suddenly decrease as bore holes 

developed due to the pressure drop. In some cases the head loss would increase and then 

suddenly decrease repeatedly due to bore holes being filled in by debris followed by additional 

bore hole formation. 

The complexities of the debris bed formation and filtration, along with the many variables 

resulting from differences among plants, require that head loss tests be conducted for plant 

strainer qualification. Head loss testing has been conducted in small-scale apparatus and in 

larger-scale tests of plant strainer prototypes. The small-scale tests typically use a closed 

piping loop that sends water though a small flat screen and continuously recirculates the flow 

(e.g., NUREG/CR-6874). The prototype tests use a section of the plant strainer (e.g., for a 

stacked-disk strainer, the prototype would include a short section of the disks or one or more 

modules out of a multi-module strainer) with pumped water recirculation. The advantage of the 

small-scale closed-loop testing is simplicity. Prototype testing includes the geometric 

complexities of the plant strainer. However, when the debris bed is uniform, such that debris 

accumulation does not depend on screen surface orientation, the closed-loop test may provide 

head loss results similar to those of the prototype test. The small closed-loop tests are typically 

used in a separate-effects approach to ascertain debris head loss characteristics for specific 

types of debris. 

Head loss and vortex evaluations use calculations to: (1) design a prototype strainer before 

conducting head loss testing, (2) conduct post-test scaling of test data to alternative conditions 

from the conditions tested, and (3) support testing and evaluation of the test results. 

Calculations may also be performed for other analyses. The available NRC-developed head 

loss correlations include the NUREG/CR-6224 correlation. Three NUREGs were developed in 

support of this correlation. They are NUREG/CR-6224 which developed the correlation, 
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NUREG/CR-6371 which explains the use of the correlation as intended for BWRs, and 

NUREG/CR-6874 which developed parameters to be used in the 6224 correlation to predict the 

effects of calcium silicate on head loss. Another NRC correlation, presented in NUREG-1862, 

was developed in concert with the head loss tests at Pacific Northwest National Laboratory 

(PNNL), discussed in earlier reports (NUREG/CR-6917). The advantage of the NUREG/CR6224 correlation is that it has been programmed into a user-friendly quality checked code and 

has undergone extensive technical review and application. The code is called BLOCKAGE. 

However, the NUREG/CR-6224 head loss correlation is an empirically derived equation that is 

dependent on water properties, flow velocity, and debris properties. The correlation assumes 

that temperature affects only the fluid properties and not the debris properties and 

characteristics. The correlation was developed to calculate single-phase pressure drop, and 

has not been validated and cannot be applied to two-phase flow conditions. The 6224 

correlation was later updated for use by PWRs and the code was rewritten to include a module 

that could predict deaeration of fluid as it passed through the debris bed. Other issues with the 

NUREG/CR-6224 correlation is that it was developed and validated by tests that used a 

relatively small population of debris types, the tests used fibrous shreds instead of fine fibers 

which are more likely to transport, flow rates were relatively high, and thin beds were not 

validated. The newer NUREG-1862 correlation was developed to counter technical criticisms of 

the NUREG/CR-6224 correlation; however, this correlation was not developed into a userfriendly program and is only available through the NUREG-1862 report. It has not been used 

extensively for strainer evaluation. 

Potential vortex formation was analytically correlated to the Froude number (NUREG-0897). 

Because a vortex can draw air from the pool surface to a significant depth below the surface 

and then into a strainer, plants often installed structures designed to physically prevent the 

formation of a vortex.

Prototype head loss testing cannot fully model prototypical plant conditions. For practicality, 

most prototype testing has been conducted at colder water temperatures than postulated 

accident pool temperatures. Subsequent temperature scaling of head loss test data has been 

based primarily on the temperature-dependent viscosities. The temperature-dependent 

viscosity scaling is based on head loss correlations, e.g., the NUREG/CR-6224 correlation, and 

is valid when the velocities through the debris bed are sufficiently slow that the head losses are 

linearly dependent upon the velocity rather than the square of the velocity. In the NUREG/CR6224 correlation, the linear velocity term is proportional to the viscosity, but its velocity-squared 

term is not a function of the viscosity. If boreholes occur during testing it may be nonconservative to correct the measured head loss to a higher temperature because higher 

temperatures results in lower differential pressures. At lower differential pressures, the bore 

holes may not form. Any temperature correction to higher temperatures should be carefully 

reviewed. 

Sometimes, the strainer design differs slightly from the tested prototype design. For example, 

the final design may result in an increase or decrease in strainer area. This would require that 

the effects of changes in debris loadings from the scaled loadings used in the prototype tests be 

reassessed. Because it is impractical to test strainers using plant conditions the use of

analyses to estimate differences in head loss between the actual plant strainer and the tested 

prototype is necessary. The uncertainties associated with these estimates grow as the 

divergence between the actual plant strainer and the prototype strainer increase. Post-test 

calculations to scale head loss test results to the plant conditions should be carefully performed.
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If the strainer is not fully submerged within the sump or suppression pool, the exposed strainer 

surface allows air to be drawn directly into the strainer. In this situation, if the debris bed head 

loss exceeds approximately one-half of the strainer submergence, as measured from the bottom

of the strainer screen area to the pool surface, the water passing through the strainer will be 

inadequate to support the require pump flow rate and air can be sucked directly to the pump. 

For this reason RG 1.82 states that head loss should be limited to a maximum of one-half of the 

strainer submergence. To prevent this type of failure most strainers are designed to be 

completely submerged at the start of recirculation or soon thereafter. Some PWR strainers are 

vented to the containment above the sump water level. These strainers should be evaluated for 

the potential for air ingestion due to inadequate flow through the strainer surfaces as described 

above. 

Even if a strainer is fully covered, air ingestion can still be caused by vortices and deaeration. 

Deaeration may occur as the water pressure decreases as it passes through a debris bed. At 

elevated temperatures flashing may occur. Flashing would likely have a much more detrimental 

effect than deaeration because the volume of gas formed by flashing is potentially much greater 

than that which could be caused by deaeration. During testing with colder water, deaeration 

typically results in a buildup of air immediately downstream of the test strainer, where the 

bubble-rise velocities exceed the pumped flow velocities. A similar air accumulation situation 

could occur within plant strainers. Increasing strainer submergence decreases the potential for 

flashing and deaeration because it increases the pressure on the water at the point that it 

passes through the debris bed. Colder water reduces the probability for flashing because it 

increases subcooling. However, as the water cools, head loss increases. Therefore colder 

water can result in the limiting condition for deaeration. Both flashing and deaeration should be 

evaluated for various conditions to ensure that they will not adversely affect the operation of the 

strainer or the pumps taking suction from the pool. 

In response to NRC Bulletins 95-02 and 96-03, U.S. BWR licensees installed large capacity 

passive replacement strainers with total screen areas ranging from 475 to 6253 ft2 (Elliot, 

2001). The BWR vendors conducted head loss tests on scaled design-specific modules to 

develop an analytical capability to estimate head losses on plant-specific strainers. The testing 

was not plant specific, but was intended to bound conditions that strainers could experience. 

The data from the testing was used to develop correlations that could be used to interpolate a 

plant’s potential head loss based on its specific debris load. The NRC staff reviewed the test 

results from a number of these tests. The NRC staff also reviewed the head loss correlations 

and found them to be acceptable when applied with certain limitations. 

In response to GL-04-02, U.S. PWR licensees installed large capacity passive replacement 

strainers with total screen areas ranging from 769 to 8275 ft2. Vendors conducted prototypical 

head loss testing to qualify the design of new replacement strainers. The NRC staff followed 

the industry’s head loss testing through testing observation trips and plant audits. The NRC 

staff documented their positions in areas relating to head loss testing and evaluation including 

scaling, debris near-field settlement simulation, surrogate debris similitude requirements, test 

procedures, and post-test data processing and extrapolation. The intent of the staff work in this 

area was to establish appropriate evaluation criteria for the staff review of licensee corrective 

action associated with GL-04-02 and future strainer head loss analyses. The staff positions and 

the findings of many NRC and industry test programs provided a basis for writing review 

guidance for evaluations regarding strainer head loss and vortexing. This review guidance was 

issued in March, 2008 and may be found in ADAMS, ML080230038. Because of uncertainties 

regarding the head loss behavior of some debris types the staff determined that strainer head 

loss testing with plant specific debris loads should be conducted under most conditions. 
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The goal of prototypical head loss testing is to determine the strainer potential peak head loss 

that could occur during the postulated LOCA scenario during its mission time, considering the 

plant specific factors that could affect head loss. The mission time is considered to be the time 

from accident initiation to when the flow is permanently and substantially reduced by licensee 

emergency operation procedures (EOPs). In theory, head loss testing should continue until the 

mission time is reached, but practical considerations limit the period of testing. Because of the 

limited test time, peak head loss may be estimated by extrapolating the test head loss results 

from data whose values can be demonstrated to be approaching the final head loss reasonably 

closely. In prototypical head loss testing, the accumulation of debris depends on the filtration of 

the suspended debris within the test tank by the fibrous bed. The filtration, and therefore head 

loss, is dependent on the debris-dependent strainer filtration efficiency and may take some time 

to reach a value that is relatively stable. Assurance is needed that the test termination criteria 

are suitable to determine the potential peak head losses. In addition, there are potential timerelated phenomena can affect debris bed head loss. For example, compression of the debris 

bed or material degradation may occur over time resulting in changes in head loss. 

Prototypical head loss testing usually consists of a scaled strainer module tested in a 

representative fluid flow environment with scaled plant-specific debris loading. The strainer test 

modules are usually scaled-down versions of the plant replacement design or simply single 

modules of a multi-module strainer train. Specifically, the test module strainer surface areas are 

much smaller than the replacement strainers. Assurance is needed that the scaling between 

the test strainer module and the plant replacement strainer has been correctly evaluated and 

that scaling issues do not result in non-conservative test results. The primary scaling 

parameters include the screen area, the dimension of the strainer elements (e.g., disks), the 

level of submergence, the number of strainer elements, the debris amounts, and the local fluid 

flow conditions. These parameters affect the flow velocities approaching the test strainer and 

the velocities through the strainer and debris bed. 

The debris surrogate material should be prepared and introduced into the test loop in a 

conservative or realistic way so that the debris accumulation on the testing module either 

represents the actual debris accumulation or bounds the realistic debris distribution.

The NRC staff positions on various aspects of head loss testing are discussed next. Section 

5.7.2 discusses the role of head loss testing as part of the overall strainer design evaluation 

methodology and the staff’s view regarding the uncertainties involved in head loss testing. 

Section 5.7.3 discusses the scaling of the plant replacement strainer design to the test strainer 

module. Section 5.7.4 discusses the similitude considerations for debris transport and debris 

accumulation on the strainer when a licensee proposes to take credit for near-field settlement. 

Section 5.7.5 discusses the similitude requirements for the surrogate debris. Section 5.7.6 

discusses recommendations for developing conservative procedures for head loss testing. 

Section 5.7.7 discusses the criteria for terminating a head loss test. Section 5.7.8 discusses 

potential scaling of post-test data to actual plant conditions. Section 5.7.9 is a look back 

through the PWR resolution process to identify the governing aspects of head loss testing that 

should be the focus of future strainer qualification testing. The PWR methodology summary 

includes applicable resolution guidance information found in NRC-SER-2004, the supplemental 

March 2008 head loss guidance (NRC, 2008d), and relevant observations from the audit 

process. Additional head loss guidance is found in RG 1.82. Section 5.7.10 is a look back 

through the BWR resolution process. The BWR methodology is based on the BWROG URG 

(NEDO-32686) and the associated SE to the URG (NRC-SER-1998).
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5.7.2 Role of Prototype Head Loss Testing in GSI-191 Resolution 

5.7.2.1 Trends in Replacement Strainer Design

The primary trend in replacement strainer design has been replacement of passive strainers 

with significantly larger complex geometry strainers. The effects of replacing a strainer with a 

large strainer are to (1) distribute the debris over a larger area, resulting in thinner beds of 

debris accumulation, and (2) reduce the water flow velocity through the debris accumulation. 

Both effects reduce head losses through the debris. Vendor designs differ primarily on how 

large screen areas are incorporated into relative small volumes that can be tailored to fit within a 

containment sump or suppression pool. One distinguishing design feature is whether the 

internal strainer flow resistance is structured to enable uniform flow across the strainer surface. 

Most strainers incorporate disks, pockets, or some other geometry that allows the strainer 

surface area to volume ratios to be maximized. 

Given a specific replacement strainer design, head loss depends primarily on the quantities, 

compositions, and distribution of the accumulated debris on the strainer. Some types of debris 

are relatively non-problematic. For example, pieces of crumpled RMI foil debris tends to be very 

porous, and the accumulation of relatively flat overlaying sheets of foils is not realistic at the low 

approach velocities expected with the new strainers. For BWRs, during periods of high 

turbulence RMI may transport more easily to the strainer. Some other types of debris are 

problematic and have caused serious head losses even at very low surface approach velocities. 

These types of debris include microporous insulation and chemical effect precipitates. Typical 

microporous insulation includes calcium silicate, Min-K, and Microtherm.

With the typical PWR screen approach velocity less than 0.01 ft/s, a fiber debris bed, lacking 

added particulate debris, accumulated on the screen would almost certainly be very porous. 

The primary threat to the typical large replacement strainer designs is a thin-bed formation that 

includes substantial quantities of particulate debris (e.g., calcium silicate or coatings) and/or 

precipitates from chemical effects. In addition, a thick bed accumulation of fiber with relatively 

large quantities of these particulates or chemical precipitates can potentially cause high head 

loss, especially if the strainer becomes engulfed with debris to such an extent that a 

circumscribed or transitioning debris bed is formed. A circumscribed bed is formed when the 

strainer is completely covered in debris so that the area through which the water flows is 

significantly reduced. For example the disks of a stacked disk strainer would be completely 

filled with debris. A transitioning bed is one that eliminates some of the surface area by partially 

filling in the complex geometry with debris. 

For BWR strainers, the issue of thin-bed formation is less clear. Based on the BWR audit 

reports for the Limerick Generating Station (ML003684437), Dresden Nuclear Power Station 

(ML010930074), Duane Arnold Energy Center (ML012610017), and Grand Gulf Nuclear Station 

(ML012560213), the screen approach velocities are typically somewhat faster for BWR than for 

PWR strainers. However, the effects of BWR vent downcomer turbulence during primary 

system depressurization on the formation of the debris bed are not well understood. High 

turbulence can keep larger debris in suspension, which could disrupt the formation of a thin bed. 

The timing of the turbulence dissipation relative to the operation of the pumps could be a 

determining factor in whether a thin bed could be formed early in the event. Even if turbulence 

could preclude the formation of a thin bed during blowdown, once the turbulence subsided, the 

debris accumulation could be similar to that of a PWR. Once the heavier debris has settled, the 

fine suspended debris accumulates independent of gravity and, therefore, can accumulate 

uniformly on any strainer geometry. 
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For RMI and/or paint chips to result in high head losses on a large strainer in a PWR, the debris 

would have to be piled on top of and around the strainer in a circumscribed accumulation. For 

this type of accumulation, at typical low approach velocities, the strainer would likely have to be 

located inside a pit below the containment floor level such that the debris falls onto the strainer 

from above. It is unlikely that engulfing quantities of such debris would fall directly into a pit. 

However, the geometry of a strainer pit installation can enhance approach velocities toward the 

pit, resulting in velocities much higher than for strainers installed on the containment floor and 

thereby enhancing near-pit debris transport. Therefore the potential for this type of 

accumulation should be considered on a plant specific basis. 

5.7.2.2 Inputs and Outputs of Prototypical Head Loss Testing

The overall resolution process based on head loss testing of strainer prototypes is represented 

schematically in Figure 5.7-1. This scheme is discussed in this section in order to put the steps 

in perspective before focusing on prototype head loss testing. This process was developed 

during the resolution of GL 2004-02 for PWRs. BWR testing was conducted more generically 

and correlations were developed to allow individual BWR plants to apply the test results to their 

particular conditions. Almost all PWRs conducted plant specific testing. The NRC staff is 

working with the industry to validate that the application of BWR testing to individual plants was 

conducted properly. Some of the areas discussed below may not have been addressed during 

the BWR testing in the 1990s. 

Figure 5.7-1. Schematic Diagram of Processes Used to Qualify Replacement Strainers
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Head loss testing is performed with a reduced section of the licensee’s replacement strainer 

design in a tank of water. The test strainer module is connected to a recirculation loop that 

pumps water from the tank through the test strainer and returns the water to the tank. A 

prototypical load of debris is introduced into the tank where accumulation on the test strainer 

usually results in measurable head loss. A water sampling method may be used to sample the 

flow downstream of the test strainer for subsequent analysis of debris bypassing the strainer. 

Test measurements include differential pressure across the strainer, flow rate, and water 

temperature. The challenge in prototype head loss testing is ensuring that the conditions within 

the test tank are prototypical or conservative with respect to the plant sump pool or suppression 

pool. These conditions include the postulated debris loading, strainer submergence, strainer 

flow velocity (or pump flow), and aspects of the various accident scenarios. Water temperature 

should be considered either in the actual testing or the subsequent analytical application of test 

data to strainer head loss determination. When adding turbulence to the test loop, care should 

be taken to preclude forcing debris to accumulate on the strainer that would not prototypically 

accumulate in an actual plant scenario or preventing debris from accumulating on some 

sections of the strainer. For example, if a shred of fibrous debris is predicted to settle to the 

pool floor and remain there, then the induced turbulence in the test tank should not cause such 

debris to accumulate on the test strainer. This condition is especially true in thin-bed head loss 

tests, where forced accumulation of such shreds can readily preclude the formation of 

conservative thin-bed formation. However, staff guidance has attempted to minimize or ensure 

conservative, the effects of having some debris transport to the strainer non-prototypically. 

Maximum debris accumulation does not always mean maximum head loss, especially for thin 

beds. The test matrix box shown in Figure 5.7-1 illustrates the input logic and information for 

the head loss test.

The NRC guidance on debris generation and transport provides a methodology to determine 

conservative bounds for the maximum quantities of various types of debris that could potentially 

reach the replacement strainers. A replacement strainer should be capable of handling the 

maximum potential debris load and any reasonable combination of lesser quantities as well. 

The strainer should retain acceptable head loss considering any realistic order in which the 

various types of debris could arrive at the strainers. The chaotic nature of debris generation and 

transport following a pipe break, the variety of post-LOCA debris types, and the extensive 

variation of break types and locations make it difficult to determine debris quantities and arrival 

sequences. In general, licensees determine the maximum debris quantities that could be 

produced for various breaks for use in full-load tests but also must conduct thin-bed testing 

based on minimal fiber accumulation and maximum particulate debris terms. For strainer 

testing, these maximum quantities are scaled down to the test strainer module, and either the 

actual plant material or a suitable surrogate is used to create prototypical debris for the head 

loss test.

The licensee specifications, often determined from accident analyses, provide the operating 

conditions for the sump strainer, including pump flow rate, sump pool water temperatures, and 

pool depths. An upstream analysis is conducted to ensure that a blockage of the flow of water 

into the sump or suppression pool cannot cause a reduction in the expected pool depth at the 

strainer after a LOCA. All of this information is used to determine prototypical hydraulic 

conditions for the conduct of the head loss testing. The licensee NPSH analysis determines 

how much debris-induced head loss can be tolerated across the replacement strainer. 

The design of the test facility, in conjunction with the test strainer module, should be such that 

the hydraulic conditions within the test tank are prototypical or conservative with respect to the 

sump or suppression pool and plant strainer. These conditions include the flow velocities that 
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transport debris and the turbulence levels that influence debris suspension and deposition on 

the strainer. The test specifications should be designed to determine the worst-case head loss 

from all the possible types of debris beds that could accumulate given the bounding quantities of 

debris analyzed to arrive at the strainer (i.e., thin-bed versus maximum debris accumulations 

and potentially stratified beds). Staff guidance is that, as a minimum, full-load tests and thin-bed 

tests that incorporate the full particulate load be performed. Testing experience has shown that 

a thin debris bed that includes a problematic particulate, such as calcium silicate, can become 

relatively non-porous, thereby causing very high head losses. Prior to conducting prototype 

testing, vendors used the head loss correlations, such as the NUREG/CR-6224 correlation to 

initially size the plant replacement strainer. Subsequently the prototype strainer was usually 

tested in accordance with the test matrix. The test results either provided the validation of the 

adequacy of the strainer design or demonstrated a need for a redesign.

Post-test evaluations are required in order to validate the head loss results, and apply the 

results to the replacement strainer, Results of head loss tests conducted with colder water are 

often scaled to the plant sump or suppression pool water temperatures. Sometimes scaling to 

an alternative approach velocity is performed. Scaling is discussed in Section 5.7.3 below.

The establishment of prototypical debris settlement within the test tank, referred to as the “nearfield effect” or “near-field settling,” has been problematic in prototype head loss testing. Debris 

accumulation on the test strainer should not be less than the corresponding expected debris 

accumulation on the plant strainer. At the same time, debris expected to settle in the plant 

sump or suppression pool should not be forced to accumulate, especially when conducting thinbed testing. Some strainer vendors have agitated the test pool in an attempt to keep all debris 

in suspension and, therefore, make it much more likely to get all debris to the strainer. Other 

vendors did not agitate the pool, thereby allowing debris to settle. In some cases, agitation 

forced shreds to accumulate non-prototypically, thus precluding formation of a thin bed. It 

should be ensured that agitation does not prevent prototypical debris transport and that debris is 

not prevented from accumulating on the strainer as it would in the plant. The staff guidance for 

head loss testing is structured to reduce the effects of any non-prototypical debris transport 

during testing. For example, the guidance for thin bed tests states that fine debris should be 

added prior to larger debris and that this debris should be added in small batches. In addition, 

the guidance is to allow head loss to stabilize between debris batches. With this methodology, it 

is unlikely that larger debris pieces will disrupt a potential thin bed. 

Sampling of flows downstream of the test strainer is sometimes conducted to determine the 

amounts and types of debris bypassing the strainer. This debris could potentially damage or 

clog components such as pumps, throttling valves, or the reactor core. The downstream debris 

characteristics are used to determine the likelihood that downstream blockage could threaten 

long-term core cooling or adversely affect other components downstream of the strainer. There 

is not a consistent methodology or staff guidance for determination of strainer bypass. 

However, the staff is working with industry to ensure that bypass testing results in realistic or 

conservative quantification of strainer bypass. The staff has noted that sampling of the fluid 

downstream of the strainer may not provide an accurate measure of bypass and that filtering of 

the full flow stream should be employed. 

Some vendors use closed-loop flat-screen testing (rather than prototype testing) to determine 

head loss characteristics for test debris. In a closed loop test, essentially all of the debris 

accumulates on the test screen so the closed loop head loss can be correlated with the debris 

quantities and characteristics. Properly conducted flat screen tests result in very uniform debris 

beds. Based on debris-specific head loss tests, vendors can use a version of the NUREG/CR-
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6224 relationship to correlate the measured head losses with debris quantities by backing out 

effective head loss parameters, such as the particulate specific surface area, so that the plantspecific head loss correlation reproduces the head loss test results. Subsequent application of 

the revised plant specific correlation to replacement strainer design has validity as long as the 

application conditions are close to the closed loop test conditions. Uncertainty occurs in the 

extrapolation to alternate conditions as variations from the closed loop condition occur. One 

approach to the evaluation of replacement strainers could be to use the validated correlation 

with parameters deduced from applicable closed-loop head loss testing to design the 

replacement strainer. A prototype of that strainer would then be tested to ensure the prototype 

functions as intended. Note that while the correlation is a useful developmental tool that 

because there are uncertainties in the applications of correlations to head loss, the staff position 

is that the final validation of the plant strainer should be based on head loss testing conducted

under conditions that match the plant conditions as closely as possible. The staff may accept 

some extrapolations using the 6224 correlation, as long as the tested conditions are relatively 

close to the extrapolated conditions and some conservatism is included in the extrapolation. 

5.7.2.3 Uncertainties and Conservatism in Head Loss Testing

The inputs to prototypical head loss testing can be divided into two categories. The first is plant 

hydraulic conditions, which use the maximum ECCS/CSS flow rate based on the worst-case 

single-failure assumption, the minimum containment sump pool subcooling, and the minimum 

sump level. The second is the debris load on the strainer based on debris generation and 

transport analyses. Rather than attempting to predict time-dependent debris transport, it is 

conservatively assumed that all the debris accumulated during the post-LOCA ECCS mission 

time for a given break location has accumulated on the strainer at the beginning of recirculation. 

The staff has allowed some analyses to credit delayed arrival of debris when evaluated 

conservatively. Additionally, the staff has allowed analyses to credit delayed precipitation of 

chemicals. 

Conservatism has been built into the methodology for developing inputs to the head loss testing. 

In the area of plant hydraulic conditions at the beginning of recirculation, it has been assumed 

by many licensees that all ECCS and CSS pumps would be in operation for an extended period 

of time, up to 30 days. It is conservative to assume maximum flow through the strainer for head 

loss testing. For those plants whose design includes logic that shuts down the low-pressure 

safety injection (LPSI) pumps during switchover from the RWST to the sump, licensees may 

have to consider one LPSI train failure-to-stop, as the single active failure. This assumption 

leads to a conservatively calculated maximum flow rate through the screen. In addition, at the 

beginning of the recirculation phase, the sump or suppression pool subcooling is assumed to be 

at a minimum resulting in minimum NPSH margin. In reality, the NPSH margin increases 

significantly after the heat removal systems have removed significant heat from the reactor 

coolant system and the containment. The NPSH margin usually increases from its minimum 

value before the beginning of recirculation. Evaluations also assume the minimum strainer 

submergence which decreases NSPH margins, decreases flashing margins, and increases the 

potential for deaeration. 

In the area of debris load input to the head loss testing, debris generation and transport are 

conservatively evaluated. The approved methodology conservatively assumes that all of the 

eroded fine fiber is present with other debris to cause head loss at the beginning of recirculation. 

In reality, erosion is a relatively slow process, and therefore the NPSH margin could increase 

significantly before all of the eroded fiber reaches the screen. There is a potential for debris 
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agglomeration during transport to the strainer, thereby enhancing debris settlement, but this 

possibility is not considered in the transport analysis guidance. 

With the key inputs to the head loss testing developed conservatively, the measured head loss 

is also expected to be conservative, as long as the test facility is scaled properly and the testing 

procedures are conservative. Specifically, the thin-bed test procedure should be carefully 

controlled to ensure it is conservatively conducted. Because test results are intended to be 

bounding no analysis has been performed to identify the uncertainty band of the measured head 

loss data. To ensure conservatism, guidance includes direction to design the test facility 

properly, conduct the test following conservative testing procedures, and perform a conservative 

evaluation of the test results. 

5.7.3 Strainer Test Module Scaling

5.7.3.1 Strainer Vendor Scaling Approaches

Ideally, a scaled-down test facility is designed so that the debris transport and head loss 

processes that would occur in a plant following a postulated accident would also occur in a 

similar manner in the test facility. That is, the dimensions of the test facility would all be reduced 

by some common scaling parameter or parameters derived from that of the plant sump or 

suppression pool and replacement strainer based on the dominant processes. If the essence of 

the dominant processes is captured in one or more of the accepted dimensionless parameters, 

then the maintenance of the dimensionless parameters between the plant sump or suppression 

pool and the test facility can become the basis of scaling down the design. If scaling some 

aspects of the test are impractical or the required scaling is not well understood, the test facility 

and methodology should be designed to treat these areas so that realistic or conservative 

results can be expected. 

For prototype head loss testing, several considerations tend to affect the options associated 

with scaling. These include:

• Strainer test vendors will likely construct only one test facility, or a limited number of 

such facilities, that can be modified to represent the various configurations of different 

plants.

• Plant replacement strainers are sometimes designed interactively with head loss testing, 

where the head loss measurements provide data critical to sizing the strainer.

• Strainer designs vary significantly in geometric configuration and size.

• Plant sump or suppression pool geometries, pool depths, and flow conditions vary 

considerably among plants.

• The types and quantities of postulated LOCA-generated debris vary with the plants.

• Head loss tests are generally conducted by using room-temperature or slightly warmer

water rather than water at plant sump or suppression pool temperatures. 

The typical geometrical scaling approach adopted by the nuclear industry is based on the ratio 

of areas between the plant strainer and the test strainer. Based on this principle, a full-size 
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strainer module or a portion of a strainer module is placed in a test loop within which the total 

flow rate is determined by multiplying the total plant sump or suppression pool flow rate by the 

ratio of the surface area for the test module to that of the plant strainer array. In this way, the 

screen surface approach velocity in the test strainer is the same as that in the plant strainers. 

Debris loading for the test is also scaled on the basis of strainer surface area ratio with the 

assumption that debris accumulation is representative or bounding of the actual plant condition. 

In some cases, the debris loading and approach velocities may be based on the ratio of the 

circumscribed areas between the plant and test strainers. In general, this approach could be

taken if the plant strainer can become completely engulfed in debris. However, for this case, an 

additional thin bed test is then run using the strainer surface areas for scaling. 

The design of the flow channel upstream of the testing module or test tank surrounding the 

module varies among strainer vendors. Most test vendors do not scale the upstream flow path. 

Instead, testing procedures involve agitating the test pool so that most of the debris introduced 

into the test loop accumulates on the screen surface. However, for thin-bed testing in an 

agitated tank, the fibrous debris should be prepared prototypically fine to represent plant fibers 

that would not settle in the sump or suppression pool under plant conditions; otherwise, the 

formation of the thin bed is compromised. Some vendors have decided to take credit for nearfield settlement and developed specific approaches to design the upstream flow path of the test 

loop. The design of test facilities that credit the settlement of debris can be problematic 

because it is difficult to evaluate the many complex flow paths in the plant and model them in a 

relatively small test facility. The velocity and turbulence in the test facility should be 

demonstrated to result in realistic or conservative transport with respect to the plant. The 

calculations required to demonstrate adequate transport in the test are complex and have been 

carried out using CFD models of the plant and test facility. 

In addition to the geometrical scaling effort, the strainer vendors proposed various extrapolation 

schemes to address temperature scaling. This scaling is generally based on the ratio of the 

kinematic viscosity of water at the test and postulated plant temperatures. Some caution should 

be applied to temperature scaling to ensure that it is performed validly. 

5.7.3.2 Theoretical Considerations

When scaling a large fluid field to a smaller test loop, dimensionless numbers are normally 

derived from the governing equations or are based on experience with and understanding of the 

dominant physical processes. A dimensionless analysis of the fluid flow associated with head 

loss testing primarily includes the Froude and Reynolds dimensionless parameters.

Reynolds number = ratio of inertial forces to viscous forces

Froude number = ratio of inertial forces to gravity forces

The debris transport and filtration processes that these forces influence include:

• The settling rate of debris within a relatively calm pool of water near the strainer

• The level of turbulence within a pool

• The thickness of the pool floor boundary layer
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• The drag forces on debris residing on the pool floor near the strainer

• The lift forces on a piece of debris if the flow goes over a curb or if debris lifts from the 

floor onto a screen surface

Analysis of particles settling in calm or still water is usually treated by a Stokes Law approach in 

which the terminal settling velocity is inversely proportional to viscosity and directly proportional 

to the water density. Therefore, the relationship contains significant temperature dependence. 

Debris settling involves gravity; therefore, the Froude number is relevant. Because settling is 

also influenced by pool turbulence, which is typically correlated by using the Reynolds number, 

the Reynolds number is also relevant. Once a piece of debris has settled on the pool floor, a 

balance of drag and weight forces determines whether that piece of debris will move along with 

the flow toward the strainer. Flow velocity around the debris piece is affected by the thickness 

of the boundary layer relative to the debris height. Boundary layer models typically use the 

Reynolds number (e.g., to define the transitions between laminar and turbulent regimes). The 

force of drag on a piece of debris depends on the flow velocity, the debris dimensions, and a 

drag coefficient that is typically correlated by using the Reynolds number. Note that the length 

parameter (L) resides in the numerator of the Reynolds number but in the denominator of the 

Froude number, meaning that a decrease in L would decrease the Reynolds number but 

increase the Froude number.

The processes associated with scaling a test facility also have to consider the phenomena that 

generate a head loss across a bed of accumulated debris. The primary hydraulic parameters 

for head loss are the velocity of flow through the debris, and the viscosity of the water, and to a 

lesser extent, the water density. Another hydraulic aspect for head loss testing is thickness, 

compression, morphology, distribution, and porosity of the debris bed. Water temperature 

should be considered and adequately factored into the testing data extrapolation because of its 

effect on viscosity and density, which are inherently involved in the strainer fluid flow hydraulic 

processes.

Debris will settle significantly faster in still hot water than still cold water, which tends to make 

near-field settling in room-temperature head-loss tests somewhat conservative with respect to 

maximizing debris transport. However, as temperatures increase, viscosity will decrease, and 

hence, the Reynolds number will increase, which indicates more turbulence in the hotter sump 

pool than in the head loss test tank. More turbulence tends to keep debris suspended. This 

effect may tend to make room-temperature head-loss tests less conservative. The drag forces 

on floor debris will change somewhat due to an increase in Reynolds number as temperature 

increases. Colder water would enhance drag and increase the chance of debris being 

transported to the strainer. The complexity of the sump pool geometry relative to the head loss 

test tank must also be considered along with the variations in water returning to the sump or 

suppression pool from the break overflow and the containment drains. Staff guidance states 

that justification regarding the extrapolation of the room temperature near-field head loss testing 

should be provided if a credit is sought for near-field settlement. Computational fluid dynamics 

analyses of the sump pool and the test tank may be useful in the comparison of the test and 

predicted plant conditions. 

Because the theoretical considerations associated with strainer head loss testing are complex it 

is frequently conducted in a conservative manner so that sophisticated evaluations are not 

required. Testing that credits debris settlement (near-field settling) requires significantly more 

complex evaluation than testing that attempts to ensure that most debris reaches the strainer 

through agitation. 
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5.7.3.3 Test Module Design - Area Ratio-Based Scaling

Typical designs for plant replacement strainers consist of strainer modules that are either 

interconnected along a common axis or connected to a common outlet plenum. A test strainer 

module typically consists of a single strainer module or a section of a strainer module. The test 

module must realistically or conservatively represent the array of modules or elements in the 

typical plant replacement strainers in both strainer design and prototypical conditions of flow 

approach velocities and debris accumulation. If the modules in a larger array have similar flow 

resistance characteristics, then under clean screen conditions, the modules closest to the pump 

suction will have more flow entering the modules than the modules farther away. Some strainer 

vendors compensate for this flow imbalance by including module-specific internal flow 

resistance that balances out module flows so that the approaching flow velocities tend toward 

uniformity. If the approaching velocities are uniform from one module to another, then under 

many conditions the debris accumulation can be expected to be relatively uniform from one 

module to another. (This expectation does not necessarily hold for pit geometries and may be 

challenged for flow conditions that are strongly influenced by external obstacles in containment.) 

However, if the approaching velocities are not uniform from one module to another, the module 

with the higher approach velocities will preferentially accumulate debris. This kind of debris 

accumulation also tends to shift the incoming flow to the modules farther from the pump suction

as the head loss across the closer modules increases. This can result in sequential debris 

accumulation along the entire array. Other parameters that affect debris accumulation are 

debris distribution in the pool, debris characteristics, pool turbulence caused by flow entering the 

pool or objects in the pool, and distribution of velocities throughout the pool.

Prototype head loss testing procedures have typically specified the test flow rate and test debris 

quantities based on the average conditions for the strainer array. The average plant strainer 

conditions may be more applicable when the strainer has designed in flow controls that ensure 

a uniform approach velocity from one module to another. Whether the average flow rate may 

be applied to the test of a non-uniform velocity replacement strainer depends on the internal 

flow resistance of the strainer relative to the head losses caused by the actual debris 

accumulation. If internal flow resistance is relatively minor with respect to the postulated debrisdriven head losses, then the average strainer conditions may be appropriate. If the internal flow 

resistance is not minor with respect to the postulated debris-driven head losses, then the 

average strainer conditions may not be appropriate or sufficiently conservative. In that case, the 

test should evaluate the postulated strainer conditions that will lead to conservative head loss 

results as opposed to testing with average conditions. Specification of the flow rate for the test 

strainer module may need to be based on a strainer module with an approach velocity greater 

than the average approach velocity for the plant.

The potential for vortex formation increases with the strainer approach velocity. Therefore, in a 

string of modules the strainer module closest to the pump suction intake has the greater 

likelihood of forming a vortex if uniform flow is not part of the strainer design. Therefore, the 

determination of whether a vortex could form should be based on the velocities associated with 

the module closest to the pump suction intake.

In summary, the important criteria for test designs that are based on screen area ratio scaling 

are: (1) the fiber and particulate amount based on the area-ratio scaling is not sufficient to form 

a circumscribed debris bed, and (2) the testing module screen surface approach velocity is 

equal to or higher than the average velocity. In cases where the strainer approach velocity 

varies significantly due to local flow patterns or due to variations in internal strainer head loss, it 

may be necessary to test with a somewhat increased velocity to ensure conservatism.
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5.7.3.4 Test Module Design - Debris Accumulation Pattern

Pressure drop caused by a debris bed depends on the velocity of flow passing through the 

debris. The average velocity depends on the pump flow rate and the strainer area but localized 

velocities may vary due to localized variances in debris composition and localized flow 

resistance variations in the design of the strainer. For replacement strainers of relatively 

complex geometry, such as stacked disk strainers, debris can accumulate differently for very 

fine debris than for coarse debris. The accumulation pattern also depends on the total volume 

of debris that has accumulated and the types of debris present. For very fine debris, such as 

individual fibers or small particles, accumulation will likely be relatively uniform initially because 

this type of debris is typically suspended uniformly in the fluid. Fine debris is not significantly 

affected by the pull of gravity, and therefore, it will seek all screen surfaces through which water 

is flowing, relatively equally, regardless of the surface orientation. For example, for large PWR 

replacement strainers, in which the perimeter approach velocities are typically less than 0.1 

ft/sec and the flow velocities through the screen surfaces are less than about 0.01 ft/sec, the 

debris arriving at the strainer can be characterized as suspended matter. If this fine suspended 

debris (typically fibers and/or particles) were to build up somewhat non-uniformly, the flows 

would be redistributed to follow the path of least resistance, thereby rerouting additional debris 

to locations of less accumulation. In this manner, a uniform thin layer of debris can accumulate 

over the entire screen area. This layer of debris will filter additional fiber and particulates, 

particularly smaller particulates that decrease the porosity of the debris bed and increase head 

loss. Such debris accumulation can lead to the so-called thin-bed effect where a modest layer 

of fibers forms a particulate filter. Subsequent particulate buildup within the bed results in a 

debris bed with porosity similar to a bulk accumulation of that particulate. For a thin uniform 

debris accumulation over the entire screen area, the test strainer approach velocity is 

appropriately determined by dividing the plant volumetric flow by the total plant screen area. 

Vendor prototype testing observed by the NRC staff has focused on this total screen area 

approach velocity, which is correct for thin-bed accumulations.

Suspension of non-buoyant larger debris would depend on the level of pool turbulence. For the 

BWR strainers, debris in the suppression pool would likely be maintained in suspension by the 

primary system depressurization flows of the turbulent vent downcomer until completion of the 

blowdown phase, after which the turbulence would rapidly decay, allowing all but relatively fine 

debris to settle (NUREG/CR-6368). The fine debris that would readily stay in suspension would 

become thoroughly mixed. Pool turbulence could also affect debris accumulation by disturbing 

debris already accumulated. For BWRs, the primary source of turbulence would come from the 

primary system depressurization. For PWRs, the primary source of turbulence would come 

from the drainage from the upper containment in proximity of the strainer.

Some types of debris, specifically coarser debris, can bridge the entrances into the interior gaps 

of the strainer and thereby accumulate on the outer perimeter of the strainer. It is also possible 

that a large volume of debris can fill the interior gaps of the strainer. This type of accumulation 

is referred to as “circumferential accumulation.” Debris that could result in bridging of the gaps 

could include RMI debris, paint chips, or larger pieces of fibrous debris. Consider the case 

where a mixture of RMI, coatings, and miscellaneous debris were to pile up around a strainer to 

such an extent that the strainer was essentially fully engulfed. When the strainer is engulfed by 

debris the correct flow area to use for scaling is the circumscribed or perimeter area of the 

strainer. The correct velocity to use in estimating head loss is the circumscribed velocity 

determined by dividing the volumetric flow by the circumscribed strainer area. Test modules 

can preserve the circumscribed velocity either by using a full-scale module, with the same 
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dimensions as the plant module, or by increasing the test module flow rate to achieve the 

average circumscribed flow.

Even fine suspended debris can accumulate non-uniformly, depending on the strainer design 

and sump layout configuration. Given a stacked disk strainer design, if the flow entering the 

gaps between the disks is fast enough (not typical of the large replacement strainers), it may 

push surface accumulations deeper into the gaps, filling the gaps from inside to the outside. 

Because the transport of debris deeper into the gaps clears the outer disk areas, the head loss 

is maintained relatively low. Non-uniformities can also prevent formation of a thin-bed 

accumulation. The correct test approach velocity for this type of non-uniform accumulation can 

vary from the total screen area velocity to the circumscribed velocity. Therefore, testing may 

have to focus on the two extremes. The simplest test strategy is to use a strainer module that 

has a total area to circumscribed area ratio that matches the plant strainer. This is described 

below. 

For some proposed plant strainer designs, it may be possible to have testing similitude for both 

screen and circumscribed approach velocities simultaneously. Figure 5.7-2 schematically 

shows several modules connected end-to-end. In this figure, the ratio of the screen to 

circumscribed areas for a single module is reasonably close to the same ratio for the entire 

assembly. Therefore, during prototype testing of a single module, it is conceivable that 

similitude for both the total screen and the circumscribed velocities can be simulated 

simultaneously. For other strainer designs, it may not be possible to achieve similitude for both 

velocities simultaneously. Figure 5.7-3 schematically shows modules connected into a common 

plenum with the modules arranged in an array. In this type of arrangement, the center modules 

may only have one (or none if the top surfaces are not perforated) outer surface contributing to 

the circumscribed area. During prototype testing of a single module, the similitude for both the 

screen and the circumscribed velocities can probably not be simulated simultaneously. For 

these strainers, the test matrix may have to include tests in which the respective similitude is 

achieved piecemeal. A simple area-ratio-scaled head loss test may not be conservative. 

Alternately, the test facility could limit the volume around the test module to the minimum 

available for any module in the array by installing walls around the module. This would be a 

conservative method because it would allow a circumscribed bed to form with less debris than 

would be required in the plant. This type of test setup has to ensure that transport to the 

strainer is not non-conservatively affected by the structure surrounding the test strainer. 

For high-fiber and high-particulate plants, the sump or suppression pool configuration plays a 

significant role in the debris accumulation pattern. For example, a design that has the strainer 

installed in a pit below the floor level could be a cluster of strainer modules with the interstitial 

volume higher than the estimated total debris volume. This type of design may experience a 

non-uniformly high debris accumulation at the top of the strainer array or at the entrance of the 

sump pit. Bridging may occur, and a debris bed may form over the top of the strainer at the 

entrance to the sump pit. The potential for this type of accumulation is that large debris may be 

transported by high velocity flow toward the below floor sump as it fills during washdown. In this 

case, high flow velocity could be expected through the debris bed, and the effective 

circumscribed area could be equivalent to the cross-sectional area of the sump pit opening. 

The head loss in this situation would be expected to be significantly higher than that measured 

by a testing module loaded with a scaled average debris load based on area-ratio scaling. For 

this type of configuration, the strainer surface area ratio based scaling practice is likely non-
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Figure 5.7-2. Schematic Diagram of Modules Connected End-to-End with Common 

Central Flow Plenum

Figure 5.7-3. Schematic Diagram of Array of Modules Connected to Common In-Floor 

Plenum

conservative. Designs with this configuration should test at the circumscribed velocity or 

provide justification to demonstrate that the measured head loss using the area-ratio scaling (or 

other approach) is conservative. 

A similar, although likely less significant issue, is the debris accumulation pattern experienced 

by a strainer array mounted in a shallow sump pit. If debris loading is high enough, the debris 

may form a thick circumscribed debris bed, and total head loss may be significantly 

underestimated by head loss testing that uses the area-ratio-based scaling approach.

In summary, the use of area-ratio-based scaling for head loss testing should be justified by 

evaluating the possible debris accumulation patterns. If severe non-uniform debris patterns are 

expected to cause significant circumscribed flow and pressure drop, head loss testing based on 

area-ratio scaling may be non-conservative.
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5.7.4 Similitude Considerations for Near-Field Debris Transport on Strainer 

Accumulation

The concept of near-field debris settling was developed for the PWR sump pools. The debris 

transport within a BWR suppression pool would have considerable differences with respect to 

the debris transport within the typical PWR sump pool. When surrogate debris is introduced into 

a PWR test tank at some distance from the strainer, a substantial portion of that debris may 

settle within the test tank rather than accumulate on the test strainer module. In effect, if settling 

occurs the test combines the effects of debris transport with debris accumulation and head loss. 

Some strainer vendors and licensees considered this phenomenon as a realistic representation 

of the plant and took credit for debris settling during testing. The settling phenomenon is 

referred to as “near-field settling” or the “near-field effect.” Tests that take credit for near-field 

settling should show that this settling is realistic for the strainer as installed in the plant. The 

main concern is that the test may result in unrealistic, non-conservative transport to the strainer. 

Assurance is needed that the near-field debris settling within the test tank is similar to or less 

than the settling that would actually occur within the plant following a postulated LOCA. Due to 

the complexities and uncertainties involved in predicting and creating realistic debris transport 

within a test facility, some conservatism should be applied to tests that credit near-field settling. 

An issue related to near-field settling is the prototypicality of the accumulation of debris on the 

strainer. For example, excessive turbulence in the test tank can drive debris onto the strainer 

non-prototypically or can wash or dislodge previously accumulated debris from the strainer. 

Some debris, particularly larger pieces of fibrous debris, may have the effect of reducing head 

loss by disturbing the uniformity of a thin layer of fine debris. Debris types not predicted to 

reach the strainer should not be forced onto the strainer by non-prototypical flow patterns or 

turbulence. The preparation and introduction of surrogate debris for the test can also affect 

debris transport and debris bed head loss. The design of a test that balances the prevention of 

near-field settling, by using agitation to keep debris in suspension, with prevention of nonprototypical transport is not trivial. However, the effects of non-prototypical transport can be 

limited by careful evaluation of the plant and test conditions and proper debris preparation and 

introduction.

The quantity of debris introduced into the test tank is usually scaled down from the bounding 

quantities determined from replacement strainer debris generation and transport analyses 

based on the area-ratio scaling approach. Because the test tank can, at best, only simulate the 

portion of debris transport relatively close to the plant strainer, the test should define an 

interface between the plant transport analysis and the debris introduction into the tank. The 

interface defines where the analytical evaluation of transport in the plant ends and the transport 

in the test begins. The interface could be a relatively short distance from the strainer perimeter, 

or it could be at the strainer surface. If, for example, the test tank was designed to simulate the 

debris settling and transport in the near field of the strainer, the methodology could require a 

transport analysis to determine the conservative bounding quantities of debris generated and 

subsequently transported to the interface. The method would then scale these quantities down 

to the appropriate test conditions based on the area-ratio approach. The interface-based 

scaling must also consider debris size, because debris such as RMI pieces may completely 

settle out before reaching the near field, but suspended fines would be expected to completely 

transport not only to the near field but also to the strainer. If the interface is specified at the 

strainer itself, then the analytical transport evaluation would be taken from debris generation to 

the strainer surface at which point the test debris amount would be calculated based on arearatio scaling. Again the size distribution of the arriving debris should be determined for test 

specifications. For the typical PWR large replacement strainers, the debris arriving at the 

strainers would be, primarily, suspended fines although there may be exceptions. Consistency 
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between the analytical/experimentally based transport analysis and the debris loads introduced 

into the prototype head loss tests is critical to test validity. 

The near-field debris transport aspect within a BWR suppression pool is more dependent on 

timing than debris distribution. Spatially, the debris would enter the suppression pool at multiple 

locations through the vent downcomers some of which would be nearer a recirculation strainer 

than others. The duration and level of the depressurization flow-driven turbulence in the 

suppression pool depend upon the break size, break location, and plant design. Debris 

transport into the suppression pool is time-dependent. The activation times of the recirculation 

pumps are also scenario and plant dependent. Pumps activated prior to the dissipation of the 

turbulence could draw flows laden with larger and heavier debris than pumps activated after the 

turbulence has dissipated. The presence of turbulence would tend to maximize the quantities of 

debris accumulation, but the lack of turbulence would be more likely to accumulate a thin bed 

consisting of tightly compacted fines from suspended debris.

To ensure that replacement strainers are not undersized, the key aspects of head loss testing 

should be maintained prototypical (or conservative) with respect to the plant strainer and sump 

or suppression pool. The important aspects of the test include debris preparation, debris 

addition sequencing, debris introduction, debris characteristics, and debris transport within the 

test tank. This section addresses the testing aspects associated with the prototypicality of the 

debris transport from its introduction into the test tank until the debris either settles to the tank 

floor or accumulates on the strainer module. These aspects are (1) the methods used to 

achieve the hydraulic conditions within the test tank to achieve the prototypical conditions of the 

plant sump, (2) the analytical verification that prototypical conditions were achieved, and (3) the 

sequence of debris introduction into the test tanks.

5.7.4.1 Simulation of Strainer Upstream Hydraulic Conditions

The test facility for head loss testing consists of a test strainer module mounted in a sizable tank 

full of water. A piping loop with a recirculation pump draws water from the tank through the test 

strainer and then returns the water to the test tank at a location far enough away from the 

strainer to limit the impact of the associated turbulence on strainer debris accumulation. Debris 

introduced into the tank generally moves with the flow toward the strainer. Gravity tends to 

settle the debris and pool turbulence opposes the settling of the finer debris. With water 

continually being recirculated through test loop, the concentration of suspended debris 

decreases as it accumulates on the test strainer, but it may take many pool turnovers before the 

water clears of the finer suspended debris.

Various methods have been used to establish the hydraulic conditions within the tank, including 

flow channeling, water level control, adjustments to flow rate, water injection to cause pool 

turbulence, mechanical agitation, and installation of baffles or other mechanical obstacles to 

influence flow patterns. Some vendors have controlled flow velocities through the test tank by 

using specifically shaped flow channels that cause the water to change velocity as it 

approaches the test strainer to match the predicted plant condition. Paneling has been used to 

simulate plant features in the immediate vicinity of the replacement strainer, such as a nearby 

wall or sump or suppression pool installation. Flow velocity is controlled by the flow rate through 

the recirculation pump. This flow rate is usually established so that the strainer screen 

approach velocity matches that of the replacement strainer design for a specific accident 

scenario.
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Tank water level is typically controlled to establish a prototypical level above the test strainer. 

In some cases, a vendor may implement a time-dependent water level corresponding to water 

buildup in the plant sump or suppression pool. Water-injecting downcomers have been used to 

introduce turbulence into the tank water pool in an attempt to represent the predicted sump or 

suppression pool turbulence or to artificially suspend debris within the pool. The pump, which 

takes suction downstream of the test strainer, discharges back to the test tank. The returning 

water can result in non-prototypical turbulence around the test strainer. Some test setups use 

baffles between the pump discharge and test strainer module to prevent this turbulence from 

disturbing the debris bed non-prototypically.

5.7.4.2 Analytical Verification of Prototypical Hydraulic Conditions

Analysis is needed to facilitate the establishment and verification of prototypical hydraulic 

conditions during head loss testing. For tests that credit near-field settling validation requires 

more than simply matching screen approach velocities. Similitude for debris transport should 

verify the prototypicality of transport velocities and pool turbulence levels for the test apparatus. 

The effects of structures near the replacement strainer that could affect debris transport and/or 

accumulation on the replacement strainer should be considered because such structures can 

create relatively fast-flowing channels approaching the strainer. If these structures are not 

represented in the test tank or otherwise accounted for, debris transport could be underrepresented.

PWR licensees and vendors have used CFD codes to perform comparative flow analysis 

between the plant sump and the prototype tests. The key flow parameters that need to be 

prototypically represented in the tests are flow velocities and pool turbulence. Flow drag that 

could move settled debris across the test tank floor is a direct function of flow velocity. Pool 

turbulence affects the settling and potential resuspension of debris within a pool. Computational 

fluid dynamics codes provide a numerical modeling method of comparing both flow velocities 

and turbulence between the plant sump pool and the test tank. Although uncertainty exists in all 

such analytical evaluations, the CFD tools have proven to simulate reasonably well the key 

features of hydraulic flow. Use of the same CFD code and modeling options to simulate both 

the plant sump with the replacement strainer and the test tank with the prototype strainer should 

provide reasonable comparisons of both three-dimensional flow velocities and pool turbulence. 

The CFD simulations can account for flow channeling in the sump pool due to nearby 

structures. The CFD analyses should account for containment spray drainage flows into the 

plant sump pool and the LOCA break overflow into the pool, both of which could cause 

turbulence within the sump pool. The turbulence can suspend debris that would otherwise 

settle in a calm pool. The CFD analyses could also consider the effects of debris accumulation 

near or on the replacement strainer that could significantly alter subsequent flow patterns. 

Average flow velocities near the replacement strainer or at key sump pool locations can be 

determined from the CFD results. A CFD code could be used to perform similar analyses within 

a BWR suppression pool.

Unfortunately, simplified transport models are limited in capabilities, and the results likely have a 

relatively large uncertainty. These methods are limited, in general, to one-dimensional 

predictions of average flow velocity. Therefore, the best uses for these methods are in 

application to flow channels that are reasonably well defined. These methods cannot predict 

pool turbulence. Use of non-CFD methods will usually require a significant conservatism to 

account for the aspects of the flow stream that are not predicted by the model.
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Simple flow calculations, such as estimating the average strainer approach velocity at the 

perimeter of the strainer, provide a rough characteristic velocity that can be compared to 

separate-effects data for debris transport. This information may be used to demonstrate 

whether settled debris reaching the base of the strainer could subsequently lift off the floor and 

accumulate over the surface of a strainer that is positioned above the sump floor. Further, 

average screen approach velocities can be compared to separate-effects data that measured 

the minimum screen velocity required to hold a piece of debris to a vertical screen surface. 

Such considerations could be used to determine whether heavier debris, such as RMI, could 

effectively accumulate on the strainer. 

An additional complication with modeling of sump pools for strainer tests is the difficulty in either 

modeling an adequate number of flow paths to represent the pool flow toward the strainer or 

combining all of the plant flow paths into a single path for the test. Modeling of the entire area 

surrounding the strainer for a test would require a large test facility and the control of many 

boundary conditions to ensure that the test is an adequate representation of the plant. 

Alternately, analytically combining the sum of the flow paths approaching the strainer into one or 

more flow paths is complex and requires some conservatism to account for uncertainties 

involved in the analysis. 

In summary, testing that takes credit for near-field settlement should realistically or 

conservatively simulate the strainer upstream flow and turbulent conditions. Proper analytical 

evaluation of the similitude between the test tank and the actual plant condition should be 

conducted. The NRC considers CFD codes to be useful tools to assist in the evaluation.

5.7.4.3 Debris Introduction with Respect to Hydraulic Conditions

A critical aspect of conducting prototypical head loss testing is to simulate the accumulation of 

the debris on the strainer if not realistically, then conservatively. Simulation of prototypical 

accumulation requires the debris surrogates, flow velocities, and flow turbulence near the test 

strainers to be recreated prototypically. The finer particulates and individual fibers, which are 

also capable of causing substantial head loss, will typically remain suspended in both sump 

pools and suppression pools. Suspension of fibrous debris is a real issue. Shreds of fibrous 

debris typically become saturated with water in a relatively short time within a pool of heated 

water. Without adequate turbulence the shreds may sink. The potential for the shreds to 

remain in suspension depends on the size of the shred, and the velocity and turbulence of the 

pool. Once on the pool floor, these shreds require adequate flow velocity and/or turbulence to 

again become suspended. A shred arriving at a strainer screen surface may not remain 

attached to a vertical or horizontally downward facing screen surface unless the associated 

velocities are relatively high. 

The method of debris introduction into the test loop upstream of the strainer-testing module can 

significantly alter head loss measurement and debris settlement. Because of the variables and 

unknowns involved in a LOCA scenario it is not possible to identify a single realistic debris 

arrival sequence. Various debris introduction methods define the location, rate, and timing of 

debris introduction, as well as the sequence of the introduction of different types of debris. 

Some vendors typically introduce the debris well away from the test strainer and take credit for 

near-field debris settling. Other vendors introduced debris very close to the strainer to limit 

near-field settling. The advantage of introducing the debris immediately upstream of the strainer 

is that the licensee may be able to avoid analyses to demonstrate whether non-prototypical 

near-field debris settling occurred. However, a potential disadvantage of this approach is that 

the debris accumulation may become skewed, resulting in a nonprototypical accumulation
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compared to that in expected plant conditions. The staff is concerned that a non-prototypical, 

artificially skewed debris accumulation could affect the potential for thin-bed formation or have 

other unintended consequences. Conversely, introduction of debris well away from the strainer 

allows the finer suspended debris to become relatively uniformly distributed within the tank pool 

so that it follows the flow as the fluid seeks the paths of least resistance through the strainer 

debris bed.

Another important aspect of debris introduction is whether to introduce the debris before or after 

starting the recirculation pump. Following a LOCA, some debris would be deposited directly at 

the containment sump or suppression pool level, and some other debris that was initially 

deposited in the upper levels of containment would be washed down to the containment pool 

level by the containment sprays before the switch over to the recirculation mode. After the start 

of recirculation, debris would continue to wash down into the pool. Analytical capabilities are 

not sufficiently developed to accurately estimate the debris distribution in the containment pool 

before the operation of the recirculation pumps or to estimate how much debris would be 

located near the PWR containment sump or within the BWR wetwell. In addition, pool 

turbulence due to the break effluents and containment spray drainage can be substantial. A 

decision on whether debris is introduced before or after starting the test pump should be based 

on ensuring a realistic or conservative test.

If the debris is introduced into the test tank before the pump is started, turbulence modeling that

associated with the LOCA break effluence and containment spray drainage should be present in 

the tank so that the debris does not settle unrealistically in the test tank. It would be nonconservative to introduce the debris into still water before starting the test pump. Further, 

introducing the debris before starting the pump can allow the debris to agglomerate nonprototypically. Agglomeration is of particular concern for the fine normally suspended debris 

such as fibers that erode from settled fibrous insulation over a relatively long period or those 

generated during the initial LOCA blowdown. In addition, vendor test flumes have not been 

designed to readily allow scaling of phenomena associated with transport modes other than flow 

rates. In general, the ratio of debris to water mass is much greater in a test facility than in a 

plant. A similar observation occurs for the amount of debris per floor area. Based on typical 

test scaling ratios, the debris amount added to a test flume before the start of the test pump 

could result in a debris layer on the floor of the test flume that is significantly thicker than that of 

the layer expected in the plant containment. This situation could result in greater agglomeration 

so that less transport will occur when the test pump is started. Similarly, the increased 

concentrations of suspended debris in the water may also tend to increase debris 

agglomeration. For these reasons, absent justification to the contrary, debris introduction before 

pump start has not been considered an acceptable approach for head loss testing.

If debris is introduced into the test tank after starting the pump, it should be shown that the 

introduction sequence is conservative. If less transportable debris is introduced first or mixed 

with fine fiber or particulate, the settled debris may trap the fine fiber and particulates, causing 

non-conservative settlement of fine fiber debris away from the strainer. Mixing fine debris with 

larger debris pieces may also result in non-prototypical debris agglomeration. This practice may 

cause a non-conservative measurement of head loss. Therefore, the staff considers a 

conservative introduction sequence of debris to be that the most transportable debris is 

introduced first and the least transportable introduced last.

The presence of particulate in the test pool affects the accumulation pattern of the fibrous 

debris. The initial accumulation of fibers would occur preferentially near the connection of the 

pump to the strainer because of higher flow velocities at this location. Without flow control
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designed into the strainer, the debris accumulates preferentially on the disk nearest the pump 

connection. Even when the strainer is designed with velocity flow controlling devices [e.g., 

Performance Contracting Inc. (PCI) strainers], the accumulation can preferentially occur near 

the center of the disks rather than evenly over the surface of the disks. As debris accumulates 

at the areas of high flow it causes head loss at the initial locations and flow in these areas 

decreases. The preferential accumulation locations move away from the pump connection until 

the whole strainer has debris accumulation. The accumulation pattern for fibrous debris without 

the presence of particulates can be substantially different from the corresponding patterns with 

particulates present because a fiber bed with particulates causes substantially greater localized 

head losses than a bed of fibrous debris alone. If a limited fibrous debris source term was 

added to a prototype test to determine whether the fiber was sufficient to form a thin bed, but 

the fiber accumulated preferentially at the areas of high flow velocity while leaving other portions 

of the strainer uncovered, it may be concluded that the fiber was not sufficient to form a thin 

bed. Conversely, with particulates available to be filtered by the fibers, the bed could cause 

sufficient localized head losses to shift the accumulation pattern toward initially uncovered 

portions of the strainer before the entire fibrous source is collected on the strainer. This could 

result in complete screen coverage and the formation of a thin bed. As such, the order of debris 

introduction can strongly affect the head loss outcome of the test. The conservative approach in 

head loss testing is to introduce the particulate before the fibrous debris.

In summary, proper debris introduction procedures should take into account that variations in 

the sequence and rate of debris introduction can potentially affect the head loss measurement. 

The introduction approach that is considered most conservative is to introduce the debris slowly 

into the test tank with the pump running and prototypical hydraulic conditions established. 

Particulate debris should be introduced before the fibrous debris, with the exception of the 

chemical precipitate that is predicted to be generated relatively late in the accident scenario. In 

general, the most transportable debris should be added first and the least transportable last. 

Other approaches may also be used if justified.

5.7.5 Surrogate Debris Similitude

For several reasons, test debris that exactly replicates the debris that would be formed in the 

plant following a LOCA cannot be obtained. The material may no longer be commercially 

available, or it may be too hazardous to handle from a practical standpoint. Therefore, 

surrogate materials are often used to simulate the postulated plant debris. Assurance is needed 

that the debris created using the surrogate materials is prototypical of the postulated plant 

debris.

The similitude considerations for the surrogate debris include selection of materials, preparation 

of the surrogate debris, and prevention of non-prototypical agglomeration of the prepared debris 

before and during the debris introduction process. For chemical effect precipitates, in addition 

to preparation of the precipitates, the potential for chemical interactions with other surrogate 

debris, such as coatings debris, should be considered.

For test strainer head losses to be considered representative of the plant strainer, the debris 

used in the test should represent the postulated plant debris prototypically or conservatively. 

Debris generation and transport analyses are used to estimate both the quantities and the 

characteristics of debris expected to arrive at the strainers. For each type of debris, a number 

of characteristics govern the behavior of that debris with regard to transport, accumulation, and 

head loss, and significant uncertainty is typically associated with estimating these 

characteristics (e.g., size distributions). Debris substitutions in testing add to the uncertainty in 
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the head loss results. The important characteristics include debris settling tendencies, filtration, 

and head loss parameters. 

To determine the similitude of surrogate debris, a licensee should first characterize the 

postulated debris as LOCA-generated, post-LOCA-generated, and latent debris. Second, the 

proposed surrogate debris should be characterized and compared to the expected plant debris. 

This comparison should be performed for each characteristic parameter that significantly affects 

strainer head loss to ensure either realism or conservatism. The characteristics include those 

parameters that govern debris transport, accumulation, and head loss. For example, fibers 

introduced into the test to represent latent fibers should not only be of characteristic diameters 

but should effectively be transported as individual fibers. The staff is unaware of any 

reasonable justification for latent fiber to accumulate and transport as clumps. Therefore, it is 

prototypical or conservative to assume individual fibers unless a different approach can be 

justified. If near-field settling is not credited during testing some of the surrogate debris 

characteristics may become less important. 

Surrogates are frequently used to represent coatings debris. In paint chip form, the transport of 

coating debris depends on chip size, thickness, density, and shape. A conservative approach is 

to generate the debris in the form of particulate if chips are proved not transportable. If chips 

are transportable and may be generated during the event, separate or repeat testing may be 

needed to ensure that conservative head loss is measured. Reflective metallic insulation (RMI) 

debris should be manufactured from insulation samples if the manufacturing of replicated debris 

is not feasible.

Testing may require the introduction of chemical precipitates as part of the debris mix. The 

Integrated Chemical Effects Test (ICET) reports (NUREG/CR-6914) and the WCAP-16530 

report form the basis for the types of chemicals and quantities added to the PWR head loss 

tests (NUREG/CR-6914). Methods of introducing chemicals into the test are discussed in the 

staff’s review guidance for chemical effects. For example, chemicals precipitates can be 

introduced already formed or can be allowed to precipitate in the head loss apparatus. 

Additionally, the manner of controlling water pH and temperature should be considered. 

Surrogate debris preparation should first render the material into debris that reasonably 

represents the size distribution determined by the debris generation and transport analyses. 

Once the debris has been generated, debris is typically pre-wetted to remove trapped air. The 

debris is usually added to a relatively large volume of water and mixed well to reduce 

subsequent agglomeration before introducing the debris into the test tank. For some head loss 

testing, fibrous debris is preheated to effectively age new insulation material so that it resembles 

insulation that has been installed at a plant for an extended period of time. This step is 

necessary only if the aging process significantly alters the head loss characteristics of the 

insulation material. Boiling or mixing the prepared fibrous debris in hot water can shorten the 

time required for entrained air to escape. 

Of particular concern is preparation of very fine fibrous debris that would likely remain 

suspended, and therefore almost entirely accumulate on the strainers. Such fine fibers consist 

of a portion of the LOCA-generated fibrous insulation debris, eroded fibers from settled fibrous 

debris, and the latent fibers. In general fine fiber can result in higher head losses than coarser 

fibrous debris. Typically, vendors have used some form of shredded insulation debris to 

represent very fine fibers. This approach resulted in the concern that the debris may not be 

prototypically fine. A representative portion of the fibrous debris should be rendered into very 

fine pieces for maximum debris load testing. For thin bed testing, the finest fibrous debris 
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present in the plant-specific debris size distribution should be used unless another approach is 

justified on a plant-specific basis. For plants that have a very small fibrous debris load, the fine 

fibers may not be adequate to result in a filtering debris bed during testing. The thin-bed testing 

for these plants may add all of the postulated fine fibrous debris, and then add sequentially 

larger debris to determine if a thin bed will form. 

Specification of surrogate fibrous debris should consider filtration characteristics such as bed 

porosity and compressibility. The debris should be prototypical in the transport characteristics 

such as floor tumbling velocities and settling velocities. The specification of surrogate 

particulate and fibrous debris should consider head loss characteristics such as specific surface 

areas, porosity, compressibility, and fiber diameter. The debris surrogate should also consider 

the settling characteristics of the various sizes of debris. Settlement behavior of potential 

chemical surrogate materials should be considered during material selection and preparation 

process.

In summary, surrogate debris materials used in head loss testing should be either the actual 

plant materials or suitable substitutions. Substitutions should be justified by comparing the 

important characteristics of the plant debris sources and the surrogate to ensure that the debris 

preparation creates prototypical or conservative debris characteristics. Tests generally use the 

actual type of insulation installed in the plant for testing but use surrogates for coatings and 

other particulates. Surrogates for coatings include silicon carbide, stone flour, walnut shell flour, 

and tin powder (as a surrogate for zinc coatings). 

5.7.6 Testing Matrix

Once the prototypical hydraulic conditions are established and the surrogate debris material is 

properly selected and prepared, the testing matrix should be developed to ensure control of the 

various testing input conditions and parameter variations that can affect the test results. That is, 

the test matrix include a range of tests that will ensure that a bounding head loss is determined 

for the conditions specific to the plant being evaluated. In principle, all test variables for a 

particular test case should be considered so that the effects of potential variations are 

understood. The important variables are addressed below. The variables should be controlled 

such that either a prototypical or conservative approach can be adequately specified. 

The prototypical matrix for the head loss test should be based on the plant conditions expected 

during the postulated accident scenario. Specifically, the time-dependent ECCS hydraulic 

aspects of pump flow rates, water temperature, containment pressure, and sump or suppression 

pool water level, flow velocities, and pool turbulence. A basic understanding of the operation of 

the ECCS and CSS during the injection and recirculation phases is needed. Some test 

procedures make assumptions or use methodologies that result in conservative conditions so 

that some of these plant variables will not have to be considered carefully in the development of 

the test matrix. 

Recirculation Sump Pool or Suppression Pool Water Level 

The minimum water level of the recirculating pool should be used when testing clean strainer 

head loss and head loss across the debris bed accumulated on the screen. The minimum 

submergence of a completely submerged strainer is needed under both SBLOCA and LBLOCA 

conditions, which may need to be evaluated separately. Water depth above the top of the 

strainer affects the potential formation of vortices. The minimum water level should also be 

used for evaluations related to the strainer and the head losses determined during testing. The 
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static water level affects the NPSH available to the pumps taking suction from the pool. 

Inadequate submergence can lead to flashing in the strainer or air ingestion into the ECCS and 

CSS pumps. The strainer submergence should be sufficient to preclude flashing, which 

depends on the temperature of the water, and the submergence should be adequate to 

preclude vortexing. For partially submerged sump screens, the water level affects the wetted 

screen area, which affects the water approach velocity, the area available for debris collection, 

and head loss. 

Strainer Flow Rate

The conservative approach for determination of strainer flow rate is to assume maximum pump 

flows. The rate of flow through the screen, along with the screen area, determines the velocity 

of flow through the screen and the accumulated debris bed. Under certain conditions, pumps 

might be throttled back to a lesser flow rate. The maximum pump flow assumption removes the 

uncertainty that a lesser flow rate will be exceeded. If a lesser, throttled flow is assumed at 

some time during the scenario mission time, the basis for the lesser flow should be such that the 

throttling can be ensured to actually occur. This lower flow rate may be used during testing to 

measure a head loss for the low flow condition or a low flow head loss may be calculated based 

on test results. In general, the staff does not accept extrapolations to flow rates greater than 

those tested due to potential non-conservatism that could result. In some cases extrapolations 

to slightly higher flow rates have been accepted. 

Recirculation Sump Pool or Suppression Pool Water Temperature

Water temperature is used in the head loss evaluation, the deaeration and flashing evaluation, 

and the NPSH evaluation. Temperature determines the viscosity of the water, which affects 

head loss. A lower water temperature increases the viscosity and, therefore, conservatively 

gives a higher frictional head loss across the debris bed on the strainer screens. The 

temperature dependence for the deaeration evaluation is more complicated because the water 

aeration depends on containment pressure and humidity, as well as the sump temperature and 

further, the quantity of air released within a debris bed depends upon the pressure differential 

across the bed, which in turn depends upon the temperature dependent viscosity. The flashing 

and NPSH evaluations are more conservative when a higher temperature is assumed. A 

conservative calculation would maximize the assumed temperature for the NPSH analysis and 

minimize the assumed temperature for the head loss analysis. The temperature range would be 

that predicted to occur during post-LOCA ECCS operation in recirculation. The maximum 

temperatures are taken from the LOCA analyses that conservatively maximize the temperature. 

The ultimate temperature is generally calculated using a conservatively cold ultimate heat sink 

temperature value. 

An alternative approach is to evaluate these physical processes in a more realistic timedependent fashion. That is, for multiple temperatures along the temperature transient, the head 

loss, deaeration, flashing, and NPSH are evaluated. These evaluations are then combined to 

determine a time-dependent NPSH margin. However, there are two time-dependent 

temperature evaluations, with and without the non-safety-related heat removal systems; 

therefore the appropriate temperature curve should be applied to each evaluation. The flow 

may also vary with time, as well as with the system status, depending on operating procedures. 

The maximum flow allowed by procedures should be used in these evaluations. Although 

debris accumulation is also a time-dependent process, debris transport evaluation capability is 

not sufficient to predict such a time-dependent accumulation; therefore the worst-case debris 

accumulation loads and processes should be assumed throughout the evaluation. There are 
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two exceptions to this rule. First, some obviously conservative short-term delay in debris arrival 

has been accepted. Second, some plants have demonstrated that chemical effects will not 

affect head loss until temperatures are reduced below a plant-specific value due to precipitation 

properties specific to the plant. The time-dependent approach is a valid approach if properly 

evaluated, i.e., provided that (1) the flow rate remains that of the maximum pump flow, (2) the 

debris bed is the worst-case debris accumulation throughout the time-dependent temperature 

transient except as noted above, and (3) the pool temperatures are properly determined.

Containment Pressure

Specification of containment pressure is needed to evaluate the potential for flashing to occur 

within the debris bed and the potential for deaeration of water flowing through the debris bed, as 

well as for the NPSH evaluation. The level of containment pressure needed to preclude debris 

bed flashing depends on the water temperature. The containment pressure is also used in the 

deaeration evaluation. The head loss evaluation is not dependent on the absolute containment 

pressure. In general, containment accident pressure should not be credited for these 

evaluations. The staff has accepted the application of small amounts of containment accident 

pressure to suppress flashing when the amount credited is clearly conservatively bounded by 

LOCA calculations. NPSH calculations should be made crediting containment accident 

pressure only if the plant is licensed to do so. The best method to ensure that flashing will not 

occur is to maintain strainer submergence at a value greater than the head loss across the 

strainer. Having a greater strainer submergence also minimizes the potential for deaeration. 

PWR Sump Pool or BWR Suppression Pool Characteristics

The pool flow velocities and turbulence affect the characteristics of the debris accumulating on 

the strainer. As discussed in the transport methodology section, debris transports as either 

buoyant material suspended in the flow or along the pool floor. The characteristic velocities 

include (1) the velocity through the screen surfaces, which affect debris attachment to the 

strainer, as well as the head loss, (2) the strainer perimeter velocities, which affect potential resuspension of settled debris, and (3) the near-field velocities, which affect debris settling and 

transport within the pool. Buoyant debris may remain on the pool surface without interaction 

with the strainers unless the debris subsequently absorbs sufficient water to lose buoyancy. 

The turbulence level within a pool is influenced by water entering the pool, water pumped out of 

the pool, and water flowing between the points of entrance and exit. For PWRs, the main 

sources of turbulence are the break overflow, the containment spray, and condensate drainage 

from the upper containment. For BWRs, the main source of turbulence is flow passing through 

the vent downcomers, which initially includes the RCS depressurization flow. For both PWRs 

and BWRs some turbulence is created by water flowing in the pools toward the strainers. The 

amount of turbulence generated by these sources is plant specific. Turbulence can keep debris 

in suspension, and if the turbulence is near a strainer, it can affect debris accumulation. 

Information regarding turbulence is needed to either predetermine the types, quantities, and 

size characteristics of debris accumulation on the test strainer or to construct a flowing channel 

within the overall head loss test apparatus that is capable of prototypically recreating the 

postulated near-field debris transport and settling.

5.7.6.1 Consideration of Head Loss Testing Input Parameters

Prototypical head loss testing should test a sufficient number of postulated plant accident 

scenarios and potential debris strainer accumulation scenarios to ensure that the operation of 

the plant replacement strainers cannot be compromised by any combination or quantities of 
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debris from the evaluated break locations. Given the plant post-accident operating parameters, 

including pump flow rates and water temperatures, the replacement strainer should be able to 

support operation of the required systems with the accumulation of the upper bound quantities 

of the various types of debris. In addition, the strainer should accommodate combinations of 

lesser amounts of debris, in any potential variation of time-dependent accumulation. Practical 

considerations for demonstrating this are discussed in the following subsections.

Break Selection for Testing

For each postulated LOCA break, the debris generation and transport analyses determine the 

bounding quantities of debris that could potentially accumulate on the strainer. These bounding 

quantities likely vary both in quantity and composition due to the variations in size and location 

of the postulated breaks. Typically, if a postulated LBLOCA is located near or within the same 

confined compartment as a postulated SBLOCA, then the quantity of debris that would be 

generated by the LBLOCA would bound the SBLOCA debris quantity making it unnecessary to 

consider the SBLOCA in the test matrix. The analysis should show that the potential debris 

compositions are comparable if a break is excluded based on another break’s debris load. 

Typically, LBLOCA scenarios are postulated to occur within SG compartments. Some breaks 

are postulated to occur outside SG compartments where the jets could affect types of insulation 

other than those within the SG compartments. In such cases, it may be necessary to include 

this postulated LOCA debris composition in the test matrix. An example of a LOCA scenario 

that may have a different composition of debris than the typical SG LBLOCA is a break at the 

reactor vessel (RV) nozzles located within the shield wall surrounding the RV such that the RV 

insulation becomes a debris source. 

In summary, the testing matrix should be developed to test a spectrum of break locations if it 

cannot be shown that a single break location can bound the rest of the break locations with 

regard to debris generation and transport. The test matrix may include bounding amounts of 

debris from several breaks to reduce the required number of tests performed. This practice is 

acceptable as long as the licensee can demonstrate that combinations of debris that result in 

limiting head loss are included in the test matrix. This is a common practice used to limit the 

number of head loss tests conducted for each plant. 

Debris Configuration for Testing

The configuration of the debris accumulation on the strainer depends on a number of factors 

including quantities and composition of potential debris, relative timing of the arrival of debris, 

approach velocities and turbulence levels, and design of the strainer. The number of potential 

test scenarios to cover all possibilities is prohibitively large. Therefore, the test matrix should be 

carefully established and based on those debris configurations for which test experience has 

demonstrated the worst-case head losses are likely to occur. In general, the highest head 

losses have occurred in the thin-bed configurations or in fully loaded configurations.

Fully Loaded Case

A fully loaded debris bed configuration is based on the concept that the resultant head loss 

increases as the quantity of debris on the strainer is increased. The thickness of debris that the 

water must flow through is greater for a fully loaded bed than for a thin bed. An important 

consideration of fully loaded configurations is that the debris could completely fill the internal 

spaces between strainer components such as the gaps between disks in a stacked-disk strainer 

arrangement. When these internal spaces are filled, subsequent accumulation will occur 
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around the strainer perimeter. This effect has been referred to as “circumscribed accumulation,” 

in which the effective flow area is substantially less than that of the total strainer screen area. 

The lower-flow area results in increased flow velocity through at least a portion of the debris, 

which can increase head loss. Further, the strainer could be positioned in the plant in a 

closeted situation, for example, in a below-floor PWR sump pit. If the space housing the 

strainer were to fill with debris, then the approaching flow could be forced through debris over a 

relatively small area at the pit entrance; head loss at that point could become substantial. The 

test matrix should consider testing the upper bounding debris quantities and should account for 

any special surrounding geometry situations.

Thin Bed Case

The test matrix should consider situations in which debris quantities smaller than the maximum 

design basis load can cause a higher head loss than would the bounding quantities. An 

example of this condition is the thin-bed configuration, where a limited quantity of fine fibers 

filters and traps a layer of particulate on the strainer screens. With this debris mix, the bed 

porosity effectively corresponds to that of packed particulate, which is substantially less than a 

layer of fibrous debris. The thin-bed term originated because observations have been made in 

which a relatively thin layer of debris resulted in a large head loss. 

For plants with minimal fibrous debris, a single test with the upper-bound fiber quantities may be 

able to test for both the thin bed and the maximum debris load. In this situation, the test matrix 

may consist of a single test per break scenario. The one consideration for plants that cannot 

generate a filtering fibrous bed is that it may be more conservative to add coating debris as 

chips than particulate. For low-fiber plants, in the absence of a plant-specific evaluation on the 

characteristics of coating debris, the licensee may need to test with paint chips to validate that 

head losses are not adversely affected by the chips. It may also be possible for plants to show 

that paint chips will not be transported to their strainers, in which case it would be conservative 

to test with coatings as particulate. If a licensee can demonstrate that the coatings will fail as 

chips and also that the chips will not transport to the strainer they would not need to be included 

in the testing. In general, the staff believes that testing with coatings, as particulate, will yield 

conservative head loss results. Unless there is significant bare screen, the NRC staff will 

accept the treatment of coatings as particulate as conservative. 

Historically, the thin bed has been viewed as about a 1/8-in.-thick bed of fiber, but this 

assessment was not based on realistically suspended fibers and problematic particulates. Head 

loss testing, particularly, in the presence of particulate insulation, such as calcium silicate or 

chemical precipitates, much thinner fibrous beds have resulted in significant head loss. To date 

there has been no experimental or analytical work that has defined a minimum thickness at 

which a filtering debris bed cannot form. The effect of minimal fibrous debris with other plant 

specific debris can only be determined experimentally. Use of fibrous fines (as opposed to 

shreds) for thin bed testing will tend to decrease the bed thickness necessary to generate a 

filtering bed. The size of the screen mesh or the diameter of the strainer holes also affects the 

minimal thickness for thin bed formation. Some strainer modules with non-uniform approach 

velocities may require average bed thicknesses that are somewhat greater than those observed 

on flat plates or uniform flow strainers before a filtering bed covers the entire strainer.

For plants with the potential to generate relatively large quantities of fibrous debris, the test 

matrix should provide confidence that the peak head loss has been conservatively or 

prototypically determined. The preferred approach is to cover the thin-bed and fully loaded 

debris bed cases either in a single test or multiple tests. Even if the plant has enough fiber to 
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form a thick fibrous bed, the accumulation process should pass from zero accumulation to bed 

thicknesses greater than the typical thin-bed thickness incrementally to ensure that the peak 

head loss is determined. During thin-bed testing, the fibrous debris should be added slowly, in 

small batches, so that the flows are allowed to transport the individual fibers and particles into 

the screen areas that have less debris to achieve uniform coverage. Head loss should be 

allowed to stabilize between batches. Once enough fiber has been added to ensure that the 

thin-bed thickness has been exceeded, the remaining fiber may be added somewhat faster but 

prototypical fiber deposition on the bed should be maintained. For high-fiber plants, the testing 

should ascertain the peak potential head losses associated with the thickness of fiber 

supporting the thin bed because the thin-bed head loss can depend on the quantity of 

supporting fiber, which is known to affect the filtration efficiency for the particulate. For highfiber plants, the thin bed test can be performed during an early part of a thicker bed test, or it 

can be performed individually. Complications in performing only a single can test arises when 

chemical debris is added to the test loop or if all of the particulate debris filters onto the fiber 

before all of the fiber is added to the test. Because many potential interactions can occur 

between the chemical and non-chemical debris, a series of tests may need to be performed to 

ensure conservative bounding head loss. 

The depressurization flow-driven turbulence within a BWR suppression pool could make the 

formation of a thin bed more difficult than has been observed in PWR tests. However, it is 

possible that a thin bed could form at some time during the event, especially given the variety of 

break scenarios. Therefore, BWR head loss testing should include tests with procedures 

conducive to forming thin beds. 

In summary, the head-loss testing matrix should provide for high confidence that the testing 

bounds the potential peak head loss considering the plant specific conditions. It should, 

therefore, include both full load and thin-bed testing cases. If a given debris load does not have 

sufficient fiber to form a filtering bed, one full load case may suffice for both. If the fiber load is 

greater than the minimum amount of fiber to form a thin fiber bed, both the thin-bed case and 

the full-load case should be included in the testing matrix unless justification is provided to 

support a different approach. The debris introduction procedure should be designed to allow 

slow debris accumulation on the strainer surface to capture the potential for thin bed formation, 

including the filtration of the particulate debris. The potential for interaction of chemical debris 

with different debris bed thicknesses should be evaluated and tested if necessary.

5.7.6.2 Tailoring of Test Matrix to Test Objectives

Because of the large number of test parameters that can be varied in testing of prototypical 

strainers and the limited number of tests that can be conducted from a practical standpoint, the 

test matrix should be developed to ensure that significant variables are fully covered in the 

testing. The approach to specifying the test matrix will vary from plant to plant, but each set of 

head loss tests has the primary objective of showing strainer performance to be acceptable. 

Some of the test objectives, which if met may allow qualification, include:

• Determining whether sufficient fibrous material can accumulate on the plant replacement 

strainer to effectively filter particulate and chemical precipitates.

• Determining the worst-case head loss for a thin-bed accumulation.

• Determining the worst-case head loss for the maximum debris quantities on the basis of 

the licensee's conservative debris generation and transport analyses. 
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• Validation that vortex formation does not occur under minimum submergence conditions. 

• The test matrix should be designed to achieve the primary specific test objective rather 

than to use a single test to complete all test objectives. The following sections discuss 

basic test procedures that should be considered when tailoring the test matrix.

• Validation of Insufficient Fiber to Filter Particulate

The primary sources of fibrous debris in containment are fibrous insulation, fire barrier materials, 

and latent fiber. Some plants in which the containment insulation is exclusively RMI or nearly so 

may not have enough fibrous debris sources to accumulate a fibrous layer sufficient to 

effectively filter particulates. In this case, the resultant head loss from fibrous and particulate 

debris could be well below the level of concern. However, even if a plant's insulation is 

exclusively RMI, latent fibers will exist in containment in some quantity. Other sources of fibers 

can include the fiber component in particulate insulations such as calcium silicate. If, for 

example, a plant had 100 lbm of latent debris and 15 lbm of that were fibrous, to the fiber could 

theoretically cover 600 ft2 of strainer surface with a 1/8-in. layer of fiber. Fibrous debris loads 

with a nominal thickness much less than 1/8 in. have resulted in significant head loss during 

testing when combined with problematic materials. Therefore, a validation of insufficient fiber to 

fiber particulate can only be experimentally determined using plant specific debris loads and 

conditions. 

NEI Guidance Report 04-07, as accepted by the staff SE, recommended assuming a minimum 

of 1/8-in. fiber as the criterion for potential thin-bed formation. The source of this criterion was 

an observation made in NUREG/CR-6224 that included statements to the effect: "to form a 

uniform debris bed, a thickness larger than 0.125 in. was needed. For a lesser thickness, the 

bed does not have the required structure to bridge the strainer holes and filter the sludge 

particles.” This observation was made from tests that used shredded NUKON® fibrous debris 

with approach velocities typically ranging from 0.2 to 1 ft/s, and screens typically either 

manufactured using 1/8-in. wire mesh screen or perforated plates with 1/8-in. holes. The SE 

noted that this 1/8-in. guideline may not apply for all types of fiber debris. During the NRCsponsored calcium silicate tests (NUREG/CR-6874), a head loss of 14 ft was achieved at 1.4 

ft/s flow with a layer of NUKON® and calcium silicate that was 0.11-in. thick (i.e., slightly less 

than 1/8-in.). The NRC staff has also observed high head losses during vendor testing of 

prototype strainers with calculated fiber bed thicknesses of much less than 1/8 in. These tests 

were conducted at prototypical plant approach velocities and used prototypical plant strainer 

modules, unlike the NUREG/CR-6874 testing described above. A debris bed accumulating from 

suspended individual fibers is formed more uniformly than a bed of shredded (larger) fibrous 

debris, for which the minimum thickness observation was made. High-density fiberglass 

insulations, such as Temp Mat are substantially less porous than NUKON®; therefore, a lesser 

thickness of Temp Mat may be needed to result in filtration compared with NUKON®. Some 

compression of NUKON® seems to be needed to effectively filter calcium silicate (alone, without 

other particulate), while less compression may be needed for Temp Mat or similar higher 

density fibrous sources. The particulate filtration efficiency for a layer of fibrous debris depends 

on the thickness of the fibrous layer, the porosity of the fibrous material, bed compression, 

approach velocity, and particle size distribution, as well as possibly the diameter of the screen 

holes or wire mesh size. Therefore, it is difficult to analytically evaluate whether a fiber bed is 

sufficient to form an effective filter for chemical precipitates and particulate debris. An indicator 

that a filtering bed would likely not occur would be that a significant portion of the strainer area 

remains completely free of fiber after all fibrous debris is added to the test flume and allowed to 

accumulate on the strainer. For this test the fiber should be suspendable fibers allowed to 
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accumulate slowly in the presence of the particulate unless it can be shown that alternate debris 

characteristics or arrival sequences are expected. 

A prototype strainer test designed to experimentally determine whether a fibrous layer could 

form should ensure that a conservative quantity of fibrous debris actually accumulates on the 

strainer. Given the very low screen approach velocities of the PWR replacement strainers, 

accumulation of fibrous debris over the entire strainer surface area would probably occur almost 

entirely due to suspended fibers or very fine shreds. In addition, the presence of particulate in 

the flow affects the uniformity of the fiber accumulation. The primary sources of suspended 

fibers include (1) latent fibers, (2) the fraction of the LOCA-generated fibrous debris that is 

destroyed into individual fibers or very fine shreds, and (3) fibers that erode away from larger 

fibrous debris in the sump pool. Latent fibers should be considered to transport completely as 

suspended fibers because they generally exist as individual or easily separable fibers in 

containmnet. When a fibrous insulation blanket is destroyed, a significant fraction of the debris 

is too fine to collect by hand (NUREG/CR-6369), and this component should be considered to 

transport as suspended debris. When fibers erode from small and large fibrous debris in the 

sump pool, they are transported as suspended debris (Appendix III.3.3.3 of NRC-SER-1998). 

This erosion occurs over hours, if not days, and is enhanced by pool turbulence. In BWR 

suppression pools, the depressurization flow-driven turbulence would further fragment fibrous 

debris resulting in more of the very fine fibers.

The NRC staff have observed tests, in which latent fibers were simulated in the test by using 

shredded NUKON®. The majority of the NUKON® shreds settled to the tank floor, where they 

remained. In these cases, only a portion of the NUKON® was accumulated on the strainer 

surface, and the accumulation of latent debris on the test strainer was considered neither 

realistic nor conservative by the staff. The staff made similar observations when fibrous debris 

classified as fines were added to the tests. The staff reached these conclusions because the 

fibrous debris used in the testing was not prepared to match the size of the debris predicted to 

reach the strainer by the transport calculation. In some cases, the flow was not prototypical or 

conservative with respect to the flow patterns expected in the plant. Test procedures should be 

designed to ensure proper latent and ZOI fiber debris preparation, especially the fine fibers, and 

a prototypical or conservative accumulation on the strainer before concluding that fibrous debris 

is not sufficient to form a filtering layer on the plant replacement strainer. 

The NRC staff also witnessed a number of tests for which the fibrous debris size distribution 

was based on a generic debris preparation procedure. The size distribution of the generated 

debris was not verified to be representative of the size distribution of the debris predicted to 

reach the strainers by the plant-specific debris transport analysis. The staff expectation is that 

test procedures verify that the debris has a size distribution that is prototypical or conservative 

with respect to the plant-specific debris. 

Peak Thin-Bed Debris Head Loss

Once it has been determined that there would be sufficient debris to form a fibrous layer that 

could efficiently filter particulate, the worst-case thin-bed head loss will generally have to be 

experimentally determined. Since all plants have some latent fibers and significant head loss 

have formed with minimum fibers in head loss tests with problematic particulates such as 

calcium silicate or chemical precipitates, a worst case thin-bed head loss test will generally have 

to be performed. . Even if the bounding maximum possible quantity of fiber debris would far 

exceed that needed to form a thin bed, the accumulation process in the testing should attempt 

to develop a thin bed to reflect the possibility that a smaller amount of debris could be 
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generated, transported to the strainer, or that a thin bed could develop as an intermediate 

condition in a full-load case. The head loss in such a scenario can be significant. The limiting 

head loss in the plant can result from any amount of fibrous debris generation and transport, 

from a small amount up to the maximum postulated amount. Therefore, the thin-bed testing 

should cover the full range of potential debris generation in increments small enough to 

determine the limiting head loss for the plant-specific debris.

The following is guidance on testing to determine whether a thin bed will form. Variations from 

this guidance are acceptable as long as there is reasonable assurance that a bounding peak 

head loss for the plant specific conditions has been determined.

1 Analytically estimate conservative quantities of fine suspended fiber that could 

accumulate on the plant replacement strainer and then scale these quantities to the test 

strainer area.

2 Select the fibrous material(s) for head loss testing that have prototypical characteristics 

to the plant debris sources. NUKON® may be used for latent fibers and similar lowdensity fiberglass, but high-density fiberglass should be used for high-density fiberglass, 

mineral wool for mineral wool, etc.

3 Prepare the fine surrogate fibrous materials as fine debris that will tend to remain 

suspended with relatively little pool turbulence. Ensure that the concentration of the 

prepared debris slurry is adequate to prevent non-prototypical agglomeration of the fine 

debris before its addition to the test flume. The NRC staff has identified excessive 

debris agglomeration as a concern, and steps should be taken to avoid the 

agglomeration of fibrous debris associated with batching. The steps include debris 

dilution and slow introduction into the test tank.

4 The pump flow should be established before introducing the test debris, and the rate of 

flow should be scaled to provide similitude for the strainer approach velocity based on 

the total screen area.

5 The total amount of particulate debris should be added before introduction of the fibrous 

debris, with the exception of the later addition of the chemical effect precipitate. The 

particulate debris should be introduced as a wet slurry rather than as a dry powder to 

preclude non-prototypical agglomeration of the particulate.

6 The addition of fibrous debris should occur slowly in incremental batches, with the head 

loss allowed to stabilize between batches to ensure representative accumulation on the 

strainers. The first batch should be sufficiently small that the resultant fiber layer 

thickness is significantly less than the optimal thin-bed fiber thickness, which likely is 

somewhere between 1/8 in. and 5/8 in. This value tends to vary depending on the 

design of the strainer. The initial increments should be no greater than about 1/8-in. 

thickness equivalent per batch and should continue until the stabilized head loss does 

not increase significantly with additional fiber additions. If it appears that head loss is not 

increasing significantly after a batch is added, but it is indeterminate as to whether a thin 

bed has been formed another smaller batch (about 1/16 inch) can be added to validate 

whether or not a thin bed has been attained. If the total available fiber is less than 1/8 

in., the total quantity can be added in the first and only batch. 
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7 When the fiber is added to the test flume, all of the finest fiber in the plant-specific debris 

size distribution should be added to the thin-bed test before larger sizes are added

unless another approach is justified on the basis of plant-specific conditions. If all fine 

fiber is added and the thin bed has not formed, the small pieces should be added next, 

etc., until all debris that the plant-specific analysis shows would be transported to the 

strainer is added, or it can be demonstrated that the thin-bed region has been passed.

 

In summary, there is no realistic minimum fiber bed thickness that can be used as a criterion to 

determine whether a thin bed will form. Testing should be performed to support the 

determination of whether a thin bed can occur on a plant’s strainer considering its specific 

debris load and flow conditions. Thin-beds are especially likely to form in the presence of 

chemical precipitates and particulate type insulations such as calcium silicate. Based on the 

observation of tests conducted with similar debris loads added in various sequences, the NRC 

staff has concluded that the debris introduction sequence has a large impact on thin bed head 

loss. During bed formation, the prompt accumulation of particulate in the interstitial areas of the 

fiber bed appears to create a thinner and more uniform bed. Without the particulate, the fibrous 

debris can preferentially accumulate toward the pump connection to the strainer or even toward 

the strainer central core, resulting in non-conservative non-uniformity. In this case, larger 

quantities of fiber are necessary to create sufficient localized head loss to redistribute debrisladen flow to clean areas of the strainer surface. Adding the fibrous debris before the 

particulate tends to result in the formation of a more porous layer of debris on the strainer 

surface and requires more fibrous debris for complete strainer coverage. Because the 

accumulation of fibrous debris in the absence of particulate debris is not expected to be 

prototypical of plant conditions, the staff expects that licensees will conservatively add the full 

particulate load that could be transported to the strainer before the fiber is added to the test 

unless an alternate debris arrival sequence can be justified. 

The NRC staff has also observed that the preparation of fibrous debris and the near-field pool 

turbulence can have a significant effect on accumulation and resulting head loss. The debris 

should be prepared either prototypically or conservatively, and the near-field transport should be 

either prototypical or conservatively simulated. Agitation intended to enhance debris transport 

to the strainer can have the adverse consequence of forcing debris to accumulate that would 

prototypically settle in the plant pool. Such debris can disrupt the formation of a prototypical thin 

bed, resulting in non-conservative conclusions from head loss testing. For high-fiber loads, thinbed testing should allow such debris to prototypically settle before reaching the strainer so that 

the incremental buildup consists of the suspended fibers. For low-fiber plants, such as all RMI 

plants where the fibrous debris consists primarily of the latent fibers, all of the fiber should be 

introduced as suspended fibers. Agitation may also adversely affect the formation of a bed on 

the strainer by preventing debris from collecting on some areas of the strainer. Turbulence 

should not affect debris bed formation non-prototypically. 

Maximum Debris Loading Head Loss

Debris generation and transport analyses provide conservative or prototypical estimates for the 

maximum quantities of debris that could potentially arrive at the plant recirculation sump or 

suppression pool strainers. Except for thin-bed formation and possibly other bed stratifications, 

the worst-case head loss would generally be associated with the accumulation of maximum 

quantities of debris on the replacement strainers.

The typical large replacement strainer has interior gap volumes. Once these interior spaces are 

filled, the remaining debris must accumulate around the exterior of the strainer, a condition 
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referred to as “circumscribed accumulation.” Depending on strainer design, the head losses 

associated with maximum accumulations may be lower than with thin-bed accumulations. If a 

circumscribed accumulation occurs, then the effective flow area through the bed of debris is 

reduced substantially from that of the total screen area. The velocity of flow increases as area 

decreases. It is the velocity of flow as it passes through the debris, as well as the bed thickness 

and composition, that determines the resultant head loss. The circumscribed area is typically 

the strainer perimeter area. Therefore, the prototypical circumscribed velocity for a replacement 

strainer is the pump recirculation flow rate divided by the strainer perimeter area. If 

circumscribed accumulation occurs, then the recirculation pump flow rate for the test module 

should be scaled to achieve a prototypical circumscribed velocity. Further, the thickness and 

composition of the circumscribed layer should be prototypical of the plant replacement strainer. 

When a replacement strainer is located near a wall or in a small compartment, the walls could 

affect the debris accumulation and/or approach velocity by further reducing the effective flow 

area. Testing conditions should also account for the possibility of a circumscribed bed 

surrounding an array of strainers in that the spacing between the strainer modules may limit the 

volume where debris can collect. For these conditions, the test should simulate nearby 

obstructions so that the debris bed forms prototypically, or should otherwise account for the 

expected accumulation, potentially by adjusting the debris scaling. 

1 The following is guidance on testing to achieve the limiting head loss for a maximum 

debris loading case. Variations are acceptable as long as reasonable assurance is 

provided that peak head loss for the plant specific conditions has been achieved.

2 Determine the maximum quantities of debris of various types predicted to reach the 

strainer. It is recommended to test with the actual materials if possible. Select suitable 

surrogate materials with prototypical characteristics when the actual debris sources 

cannot be used in the head loss testing. The amount predicted to reach the strainer is 

scaled based on the strainer area or the strainer perimeter area as appropriate to 

determine the amount required for testing. 

3 Determine the fraction for each type of fibrous debris that should be simulated as 

individual fibers or very fine shreds (for latent debris, this fraction is one).

4 First prepare the fibrous debris as shreds to simulate LOCA-generated debris. Then 

further refine a fraction of these shreds as fine debris that will tend to remain suspended 

with relatively little pool turbulence, consistent with the calculation of plant-specific debris 

transport. 

5 Prepare each type of particulate debris as wet slurry. Ensure that the debris is dilute 

enough that non-prototypical agglomeration does not occur before or during its addition 

to the test tank.

6 Establish the recirculation pump flow for prototypical flow conditions. If a circumscribed 

accumulation is expected, then scale the pump flow to achieve the circumscribed flow 

velocity of the replacement strainer. If the maximum fiber accumulation is not expected 

to approach a circumscribed accumulation, then scale the pump flow to the full-screen 

area approach velocity of the replacement strainer. Some test strainer modules may be 

designed to achieve both circumscribed and full-screen area approach velocities in the 

same test.
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7 Introduce the debris slowly, with particulate and the most transportable fibers being 

added first until all debris that the plant-specific analysis shows would transport to the 

strainer is added. Chemical-effects precipitates predicted to be generated later in the 

accident scenario would be introduced last.

Potential debris-bed stratification can be explored by introducing some types of debris later in 

the test after other types have reached maximum accumulation. For example, if a specific 

particulate is intended to simulate an unqualified coating that is postulated to fail relatively late in 

the scenario, then this particulate could be added after the early debris accumulation reaches a 

steady-state condition. This could result in a higher concentration of the particulate on the outer 

surface of an existing bed, causing a relatively high head loss.

In summary, maximum-load head loss tests should ensure that the testing properly models the 

circumferential debris accumulation with a correct circumferential approach velocity, if 

applicable. If the full load test and the thin-bed test are to be the same test, then the thin-bed 

test guidance should be followed.

RMI and Coatings Paint Chip Debris Head Loss

Heavier debris such as stainless steel RMI and most paint chips may be transported along the 

floor of the PWR sump pool, depending on the velocity and turbulence in the pool. It is unlikely 

that significant quantities of debris of this type will accumulate on the strainer, with the possible 

exception of low density paint chips. Before this heavier debris can cause blockage problems in 

a large strainer, the debris must first be transported along the sump pool floor to the strainer and 

then accumulate on the strainer. For strainer designs positioned well off the floor, the flow 

velocities would have to be relatively high in order to lift the debris from the floor onto the 

strainer. For stainless steel RMI, testing indicates that the flow velocity would have to be at 

least 1 ft/s to lift a relatively small piece over a 6-in.-high curb. With many current PWR strainer 

installations, flow sufficient to lift such debris off of the floor and onto the strainer is unlikely. For 

this type of debris, complete lack of transport would be a realistic assumption. Exceptions to 

this situation could include strainers recessed below the sump floor where floor transported 

debris simply falls onto the strainer from above, or cases where strainers are located directly 

below sources of debris. In a BWR suppression pool, the depressurization flow-driven 

turbulence would tend to keep the heavier debris, including RMI and coatings chips debris, in 

suspension until the turbulence dissipates. The duration and level of turbulence would depend 

upon the break scenario and plant specific configuration.

If the debris transport analyses or testing clearly demonstrates that such debris will not 

accumulate on the strainer, it may be appropriate to simply omit it from testing so the test can 

focus on the remaining types of debris. On the other hand, if the strainer is recessed below the 

floor (in a pit), head loss testing should consider this type of debris because such debris can 

cover areas of the strainer and provide surfaces for fibrous debris deposition. This fibrous 

debris can then form a filtering bed with a surface area much smaller than the strainer surface 

area. The smaller area would result in a high velocity through the bed and potentially high head 

losses. The large debris should be included in tests for pit installations unless the floor transport 

analyses can clearly demonstrate that such debris cannot reach the strainer in sufficient 

quantity to cause a blockage problem. If the analyses indicate this heavier debris could 

accumulate on or around the strainer test module, then the head loss test should be prototypical 

enough to result in similar debris accumulation. In a situation where significant amounts of large 

debris can accumulate on or near the stainer the prototypical approach velocity for the strainer 

is most likely the circumscribed velocity. 
5-110

The velocity in the test facility may have to be based on the flow velocity through the area of the 

pit opening in the containment floor if it is possible for the pit opening to be bridged with debris. 

If coating chips are light enough to transport as either suspended debris or can be easily moved 

across the floor and subsequently lifted onto the screen, these chips should be tested with the 

strainer prototype module under prototypical flow velocity and turbulence conditions.

In summary, both RMI and coating chips can be excluded from the head loss test if it is

determined that they are not transportable to the strainer surface based on transport tests or 

analyses. However, the coating debris may need to be added into the test in a particulate form 

to conservatively account for unknown coating debris-size distribution. For pit strainer 

installations, strong justification should be supplied if the larger debris is excluded from the test. 

Testing for pit installations should ensure prototypical velocities approaching the strainer, 

prototypical paths for transport of larger debris, and prototypical test geometries that will allow 

simulation of plant debris accumulation. Test velocities should be scaled to be prototypical of 

the plant approach velocities.

5.7.7 Test Termination

The goal of head loss testing is to determine the plant specific peak head loss that could occur 

across a sump strainer during a postulated LOCA scenario over the strainer mission time. The 

mission time is the time from accident initiation to when the flow is permanently reduced by 

licensee EOPs. Ideally, the head loss testing would continue until the mission time is reached, 

but practical considerations may limit the period of testing. Also, conservatism in the testing 

procedure tends to mitigate the need to run a test through the full length of the mission time. 

Under certain conditions, the peak head loss can be estimated by the extrapolation of the test 

head loss results. Extrapolation is possible when the test head loss can be demonstrated to 

have approached the peak head loss value reasonably closely. 

During testing, head loss may approach a steady state relatively soon after the majority of the 

debris has transported to the strainer. Once all debris has settled out or has been deposited on 

the debris bed, the water may appear clear indicating that the majority of fine particulate debris 

has been filtered onto the debris bed. In other situations, the filtration efficiency may be poor 

enough that the water remains cloudy. A final steady state head loss can sometimes require 

many pool turnovers as the filtration process gradually clears the water of finer and finer 

particles until the remaining particulate is too fine to be filtered or all of the particulate is 

removed. In addition, there are time-based phenomena that may result in longer-term head loss 

increases. Test termination and data extrapolation methods should consider this possibility as 

well. Some phenomena that can result in long-term head loss increases are bed compression 

due to differential pressure and physical or chemical degradation of debris bed components 

resulting in reduced bed porosity. 

When pump flows are throttled, as would be typical of plant operating procedures, the head loss 

associated with the debris accumulated at that time will decrease. If testing simulates the flow 

reductions and debris is available to collect on the strainer, the test should continue until all 

debris has accumulated or demonstrated to settle and not be available for transport. In general, 

the approach used in head loss testing of prototype strainers has been to test at the full pump 

flow rate and ensure accumulation of the majority of the debris predicted to reach the strainer. 

This allows test durations to be much shorter than the typical times for throttling back the pumps 

while ensuring conservative results. Some tests have simulated reduced flow rates and delayed 

chemical precipitate arrival when it has been demonstrated that these assumptions are 

conservative for the specific plant condition. 
5-111

In head loss testing that has been observed by NRC staff, criteria have been established to 

determine when the test has achieved a sufficient steady state that the test can be terminated. 

The typical criteria have involved specification of (1) a maximum increase in head loss over a 

minimum time period, and (2) a minimum number of pool turnovers. Typically, a basis for 

specifying the criteria has not been provided but appears to be the result of engineering 

judgment rather than experimental determination. The criteria for head loss increase generally 

assume that an asymptote is being approached and that the rate of increase will continually 

decrease. The staff has observed a number of tests in which head loss was continuing to 

increase at test termination, at a rate that appeared somewhat constant. Based on these 

observations, the staff is concerned that these criteria may not be sufficient to ensure the 

determination of peak head losses. 

The processes that could cause the increase in head loss to continue for hours, if not days, 

include continuing filtration of the very fine particulate, erosion of the fibrous debris that is 

settled on the test tank floor, slow compression of the debris bed, and chemical changes. It is 

known that shredded NUKON®, for example, will continuously give up fibers in a turbulent pool 

for several hours, if not days (Appendix III.3.3.3 in NRC-SER-1998). For example, a longerterm vendor test conducted in 1992 (that tested 2-in of Nukon without particulate at 0.3 ft/sec 

and 9.4 pH) demonstrated that the head loss continued to increase at a somewhat constant rate 

until the test was terminated at 24 hrs (NUREG/CR-6808, Section 7.4.1). The NRC staff has 

reviewed vendor test data, which indicated that substantial overnight increases in head loss 

were likely attributable to achieving nearly complete filtration due to the extended testing period. 

Other vendor data have shown a rate of head loss increase that was approximately constant for 

about 12 days after which the test was terminated while the head loss continuing to increase. 

Although it is not practical to conduct all head loss tests over a long term, the head loss results 

can be more reliable if selected key design basis tests are run for extended periods. Test 

termination criteria should be based on experimental observations rather than on engineering 

judgment. The achievement of steady-state head loss can be affected by test conditions and 

the time required to reach steady state can vary significantly. To illustrate this point, closed-loop 

head loss testing sponsored by the NRC was reviewed to ascertain the trend in how many times 

suspended debris circulated through the test screen before the head loss became effectively 

steady state. The tests that were reviewed included testing of calcium silicate (NUREG/CR6874) and a surrogate for latent particulate debris (NUREG/CR-6877), both with fine Nukon 

fibers forming the underlying bed. Results of this review are reported in Table 5.7-1, which 

shows the number of flow circulations in the closed-loop apparatus, which correspond to pool 

turnovers in the vendor tests. First, all of the debris was introduced into the test loop upstream 

of the strainer screen, and then the pump rate of flow was incrementally increased after head 

loss reached a reasonable stabilization. The table shows the number of circulations needed to 

reach a relative steady state for each incremental increase in the flow. Whereas some vendor 

test criteria specified only a minimum of five pool turnovers for justification for terminating a test, 

the number of turnovers in Table 5.7-1 typically exceeded 10 circulations. Because incremental 

flow-increase No. 7 for Test 6H, conducted with NUKON® fibers and calcium silicate, required 

an excessive 150 circulations before head loss stabilized, some additional clarification is 

provided. This was a thin-bed test in which the nominal fiber thickness (without compression) 

was approximately 0.23 in. For the first six flow rates, the fibers did not effectively filter the fine 

calcium silicate so that bed head loss generally remained under 1 ft, however, in flow increment 

seven, compression of the fiber bed increased enough to substantially increase the bed filtration 

efficiency, resulting in a steadily increasing head loss over a period of about 90 min before head 

loss stabilized at approximately 13 ft. The period of 90 min corresponded to about 150 

circulations of the test fluid volume. Such inefficient filtration behavior illustrates that in some 
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situations, a relative long time is needed for test head losses to stabilize. However, it is possible 

that some of the increase in head loss was a result of time based effects instead of filtration. 

The number of turnovers as well as time under flow can affect debris bed head loss. Test 

termination criteria should be carefully specified.

Table 5.7-1. Number of Tank Turnovers to Reach Steady State

Flow Increase 

Increment

Number of Closed Loop Circulation (Turnovers)

CalSil Test 6B CalSil Test 6H Latent Test 

11

Latent Test 19

1 9.4 4.3 8.0 11.8

2 14.8 7.7 7.8 11.1

3 18.3 8.7 10.0 4.4

4 13.6 11.9 8.6 -

5 - 13.6 - -

6 - 18.0 - -

7 - 150.3 - -

8 - 15.9 - -

Test Totals 56 230 34 27

The minimum number of pool turnovers was also analyzed. For the purpose of illustration, the 

following simplifying assumptions were made (which may or may not be applicable to particular 

test conditions); the strainer filtration efficiency is constant, the debris within the test tank is 

uniformly distributed within the pool, and no debris settles within either the tank or the 

recirculation piping. For this case, debris concentration within the pool could be represented by 

the following equation

where c(t) = the time-dependent debris concentration

co = the initial debris concentration

ε = the strainer filtration efficiency

N = the number of pool turnovers

Based on this equation, the analytical decrease in tank debris concentrations vs. the number of 

pool turnovers is illustrated in Figure 5.7-4 at several filtration efficiencies. The figure shows 

that five turnovers are adequate to ensure filtration when the bed filtration efficiency is near 1,

but many more turnovers are needed for the lesser filtration efficiencies that could be 

associated with finer particulates. Filtration efficiency for the debris bed and suspended 

material is dependent on the porosity of the bed, which changes with time. The results in Table 

5.7-1 and Figure 5.7-4 are in general agreement that, depending on filtration efficiency, more 

than 10 turnovers may be needed before reaching a relative steady state in the head loss. The 

table and figure represent a simplified presentation of filtration as a function of tank turnovers. 

In test setups, other factors may influence the rate of filtration. Therefore, testing should use 

these other factors in addition to the number of tank turnovers for determining test termination.

N

o c t c e −ε ( ) =
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Figure 5.7-4. Analytical Debris Concentration as a Function of Pool Turnovers

If a head loss test is terminated on the basis of the rate of head loss increase dropping below a 

minimum criterion, but the head loss is continuing to increase, a method of estimating the head 

loss at the end of the strainer mission time would be required. The head loss test represented 

in Figure 7-23 of NUREG/CR-6808 is from a test in which head loss increased somewhat 

linearly throughout a 24-hr test period. The rate of head loss increase should be shown to be 

significantly decreasing at termination, or steady at a value below the test termination criteria, 

and the final head loss should be extrapolated appropriately. Alternately, the head loss may be 

decreasing at termination. For some cases, if the test has been run for an extended period and 

the head loss continues to increase relatively linearly, an extrapolation from that point may be 

appropriate. The staff generally considers linear extrapolation of the data near the end of the 

test to be conservative. Alternate extrapolation methods are to apply a curve fit to the test data 

or perform a more sophisticated numerical analysis of the test data. It is important that the test 

flow rate be tightly controlled when determining whether the head loss rate increase has 

decreased below a termination criterion minimum because a slight reduction in flow rate would 

also result in a lower rate of head loss increase. The extrapolation methodology should ensure 

that all data points collected during the test are enveloped within the curve. 

It is also important to select a representative data range for performing the extrapolation. Data 

from much earlier in the test than those within the test termination criteria window may have to 

be considered because some tests have had relatively short periods of steady head loss or 

even short periods of decrease while increasing over the long term. The NRC staff has 

observed many longer-term tests that seemed to have no increase in head loss for significant 

periods, but actually had slowly increasing head loss. Variations in the time range of data used 

for extrapolation can result in significant differences in the extrapolated final head loss. 

It may be beneficial to perform the extrapolation in real time on a lab test computer. Calculation 

of the second derivative of the head loss would illustrate whether the increase in head loss was 

actually slowing. Running a head loss test to the mission time would provide a more meaningful 

indication of test completion than would using extrapolation techniques. One test, run to the 

Fraction of Debris Remaining in Test Tank

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Number of tank Turnovers

Debris Fraction

 ε = 1

 ε = 0.9

 ε = 0.7

 ε = 0.5

 ε = 0.3

 ε = 0.2

 ε = 0.1
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mission time, could be compared to shorter tests (under similar test conditions) to determine an 

appropriate extrapolation method. The level of concern for this issue depends on the margins 

between the test design head losses and the licensee's NPSH and flashing margins. However, 

it is expected that extrapolations be conducted conservatively to account for uncertainties in the 

process. 

In summary, final head loss values can be extrapolated or based on maximum head loss values 

obtained over a sufficient test period. Evaluators should ensure that they have considered

sufficient information to have reasonable assurance that the head loss test evaluations have 

realistically or conservatively determined maximum strainer head loss over the required mission 

period. Test termination criteria should contribute to that high confidence. Criteria based on 

stability and predictability in test conditions are generally acceptable (e.g., specified number of 

turnovers, plus limits on changes in head loss in a given period). If a test reaches a maximum 

head loss value and the head loss decreases for a significant period of time the test may be 

terminated and the maximum value used as the design basis head loss. To estimate in the final 

head loss from the point of termination, the staff found that a linear curve fit and extrapolation of 

the head loss trend to the mission time (e.g., 30 days) are acceptable. It may be acceptable to 

use other criteria or methods if justified, as discussed above. Additional confidence can be 

gained by running the test for a period after the stability criteria are met. The staff’s acceptance 

of linear extrapolation is based on the relatively little data available for longer term tests. 

Although some long-term head loss tests have been conducted, the behavior of debris beds 

over the long term is not well understood. However, the staff believes that the use of linear 

extrapolation provides a conservative extrapolation methodology. 

5.7.8 Post-Test Data Scaling and Analysis

After completion of head loss testing, the resulting data may have to be scaled to alternative 

conditions from the specific conditions of the tests. The need to perform post-test data scaling 

or data extrapolation has included: (1) head loss extrapolation to the mission time if the testing 

was not extended to the mission time, (2) scaling of the head loss data to the postulated plant 

sump pool temperatures from the test temperature, and (3) scaling of the test data for deviations 

between the test strainer module and the actual replacement strainer design. In addition, it may 

be useful to perform post-test analysis to better characterize the performance of the surrogate 

debris in the test relative to the expected performance of the plant debris.

5.7.8.1 Temperature Scaling

Vendor head loss testing is typically performed with water that is at relatively low temperatures 

compared to the plant sump or suppression pool temperatures following a postulated LOCA. 

Methods for temperature scaling have ranged from simply applying the ratio of the water 

viscosities to applying a head loss correlation such as the NUREG/CR-6224 correlation. 

However, if the test debris bed incurred pressure-driven mechanical disruptions, such as 

boreholes, then the scaling of these head losses cannot be based on viscosity or the standard 

head loss correlations that are based on debris bed uniformity. If pressure driven bed 

discontinuities occur during testing, it may be difficult to show that these disruptions would occur 

at lower pressures associated with the higher water temperatures in the plant. 

Because boreholes and channeling may not be easily observed or detected, it is recommended 

that flow sweeps be conducted at the end of the test to verify that the head loss varies relatively 

linearly with flow. Increasing the flow is more likely to create disruptions to the bed by 

increasing head loss. Therefore decreasing the flow at the end of the test is the preferred 

method to verify bed uniformity (flow and head loss change linearly). The primary temperature-
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affected parameter is water viscosity, which increases at colder temperatures. Therefore, the 

test head losses are typically substantially reduced when applied to the plant condition at higher 

temperature. If the pressure drop across the strainer changes significantly more than linearly a 

viscosity based correction is likely not justified. 

In summary, the temperature scaling method used to correct head loss data at test temperature 

should conservatively take into account the water viscosity change and any potential debris-bed 

morphology changes that occur during testing due to the higher differential pressures developed 

at lower test temperatures.

5.7.8.2 Deviations between Test Module and Actual Replacement Strainer

If the strainer test conditions did not accurately represent the plant replacement strainer, then 

scaling may be necessary to account for deviations. For example, if the design of the test 

strainer module was specified before the design of the replacement strainer was finalized, but 

the total area of the replacement strainer module was increased or decreased during 

finalization, then the test head loss may need to be scaled on the basis of screen area. In 

another example, the problematic materials had been included in the test specifications may be 

removed from containment. In this case, it may be desirable to scale the test head losses for 

the alternative but similar debris load, with respect to debris type and quantity. The scaling 

methods to account for these types of changes can be much more complex than simple 

temperature-based viscosity scaling. Scaling for a reduction in approach velocity should be 

relatively easy to justify. However, increasing approach velocity may be more difficult to 

evaluate due to the potential for bed compression caused by higher flow velocities. Scaling for 

significant differences in debris types and quantities is also challenging. In some cases, it may 

be conservative to analytically substitute a less problematic material for a more problematic 

material (e.g., coatings particulate for calcium silicate), but it would not be acceptable in any 

case to analytically substitute a more problematic material for a less problematic material (e.g., 

calcium silicate for coatings particulate). Due to the complexities involved in some scaling for 

situations that are not well understood, or that cannot be conservatively estimated by the scaling 

analysis, retesting with appropriate parameters is recommended. When analytical head loss 

scaling is performed, the greater the difference between the tested conditions and the plant 

conditions, the greater the uncertainty associated with the scaling.

In summary, scaling methods should conservatively correct the head loss data, taking into 

account the actual strainer debris loading and approach velocity. For most cases, if the plant 

debris loading is increased or the strainer hydraulic conditions worsen (e.g., increase in 

approach velocity), retesting is a conservative method of ensuring prototypical results. If 

conditions are only slightly more challenging than those tested, some conservative extrapolation 

of test results may be accepted, but adequate understanding of the change is required. 

Alternatively, if head loss is reduced due to removal of debris, decreased approach velocity, or 

increased strainer size, conservative calculations or retesting could be performed. 
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5.7.8.3 Post-Test Debris and Debris Bed Characterization

A licensee may find it useful to perform post-test analysis on its head loss data with the 

objective of better characterizing surrogate test debris, especially if the head loss behavior of a 

particular type of debris is not well understood. Such characterization would support the 

licensee's position that the surrogate is representative (or conservative) of the plant material it 

represents. An analysis of the behavior of specific materials may require more than one test 

with different debris combinations to collect sufficient data for the evaluation. Also, examination 

of the post-test debris bed could provide useful information regarding the debris bed 

morphology. If significant debris bed degradation occurs during the testing, the viscosity-based 

temperature scaling methodology should not be used. As discussed above, flow sweeps are 

useful for determining whether temperature scaling based on viscosity can be justified. 

5.7.8.4 Clean Strainer Head Loss

Most strainer vendors calculate losses associated with portions of the plant strainer that cannot 

be modeled during testing due to size considerations. In general, the NRC staff has found the 

calculations to be performed in accordance with industry-accepted hydraulic calculations. Such 

calculations have been considered an acceptable methodology by the staff. However, some 

clean strainer head loss calculations have been based on testing, and the head loss did not 

follow theoretical head loss models. In some of these cases, the testing was performed on 

strainers that have significant geometrical variance from the strainers proposed for installation. 

The staff subsequently reviewed testing of strainers with similar geometries to those proposed 

for installation and validated that the correlations being used by the vendor provided 

conservative estimates of clean strainer head loss. If the clean strainer head loss cannot be 

calculated by accepted theoretical methods, testing should be provided that clearly 

demonstrates the head loss behavior of the clean strainer. 

5.7.9 Qualification Testing of PWR Replacement Strainer Head Loss 

At the onset of the GSI-191 resolution, there was no NRC staff accepted methodology for 

conducting strainer qualification testing. Each vendor independently developed its approach to 

head loss testing, with the NRC staff intermittently observing the vendor testing and providing 

comments. The process was one of evolution in which test observations resulted in new 

learning and ideas that were passed back to the vendors. This section discusses aspects of the 

qualification testing that turned out to be of lesser importance than originally anticipated, as well 

as the important aspects, all of which are integrated into this state-of-the-art methodology. This 

section is a review of the governing aspects that should be the focus of qualification testing.

At the beginning of strainer testing, vendors typically believed that thin-bed debris beds could 

not develop on their strainers due to the complexity of the strainer geometries. However, this 

thinking was largely based on previous testing with small strainers and associated faster 

approach velocities. Under these conditions large pieces of debris could accumulate on the 

strainer and debris could accumulate preferentially on selected surfaces due to approaching 

flow velocities and/or gravitational settling. Typical large passive PWR replacement strainer 

approach velocities are so low that the approaching debris consists primarily of suspended 

fibers and particles that are not significantly affected by gravity. Further, the very low velocities 

allow the debris to accumulate relatively uniformly even if the initial accumulations are nearer 

the pump connection to the strainer. As a result, thin-bed formations are not only possible on 

these complex strainers but they may be the most likely and problematic type of bed formation 

in PWRs. 
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The NRC staff has observed testing and/or seen test photos of instances in which substantial 

head loss was caused by a relatively thin and relatively uniform layer of debris (i.e., thin bed) on

each of the PWR replacement strainer designs. Figure 5.7-5 shows a very non-porous thin-bed 

accumulation on a PCI replacement strainer prototype that caused 28 ft of head loss before the 

vendor reduced pump flow to avoid its damage (Smith, 2008a). This photo shows some 

bridging of the strainer disks by larger pieces of fibrous debris, but the primary cause of head 

loss was the relatively thin and relatively non-porous layer coating all screening surfaces. The 

vendor postulated that the head loss may have been higher than expected due to the use of 

walnut shell flour as a coatings surrogate. The GE strainer design is a similar stacked-disk 

strainer and the staff also observed thin-bed formation on a GE prototype (NRC, 2006) 

indicating that a thin-bed debris accumulation can cause severe head losses. Testing by 

Atomic Energy of Canada Ltd. (AECL) for their finned strainer design was based on thin beds 

causing the most severe head losses (ADAMS #ML062020596). AECL performed many 

scoping tests whose results indicated that thin bed accumulations were more problematic than 

thicker beds. The Alion top-hat strainer design is quite different from the disk or fin design, and 

thin-bed accumulations have been observed on this design, as well. (ADAMS #ML072420575). 

Another unique design is the Control Component Inc. (CCI) pocket strainer design, for which a 

thin-bed formation is shown in Figure 5.7-6. A chemical-effects thin bed caused a head loss 

that peaked at about 9 ft on a CCI strainer (ADAMS #ML072420572).

Figure 5.7-5. Non-Porous ThinBed on PCI Replacement 

Strainer(from Smith, 2008a)
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Figure 5.7-6. Thin-bed on CCI 

Pocket Strainer Design

The process of developing the head loss test methodology included staff observations of vendor 

procedures that did not adequately test for thin-bed head losses which can be significant. In 

order to adequately test for the formation of a thin bed for a large PWR replacement strainer, 

testing must include features so that almost all of the debris approaching the strainer will 

approach the strainer as fine suspended matter. This is because the buoyant debris typically 

does not factor into the head losses and the floor transported debris will essentially remain on 

the floor. Although, this trend is typical, outlier situations can require alternative considerations, 

such as a strainer in a pit where floor-transported debris may fall onto the strainer or 

strainer/debris load combinations that do not have enough fine debris to fully cover the strainer 

surface. 

Therefore, the key feature of simulating realistic debris accumulation is to ensure that the 

suspended matter is prototypically or conservatively represented. Further, the non-suspended 

matter must not be artificially forced to accumulate on the strainer by non-prototypical agitation 

or debris addition methods that affect debris accumulation on the strainer. Testing has 

demonstrated that the most severe head losses are associated with a relatively slow 

accumulation process that allows the debris to systematically seek the locations of higher flow 

through a debris bed and slowly plug these locations. Rapid bulk accumulations can leave 

channels within a bulky debris bed that would not exist for slow accumulations. Moreover, the 

fiber bed accumulates more uniformly in the presence of particulates than without the particulate 

because particulate filtration increases localized head losses and forces the flow toward 

uncovered surfaces. In conclusion, thin-bed head losses are accurately simulated with only 

suspended matter approaching the strainer, with the particulate added first and the fibrous 

debris introduced very slowly. Given the large number of uncertainties associated with head 

loss testing and its inputs, the assurance of strainer qualification should include a thin-bed test 

based on these features. In the absence of a thin-bed test the acceptance of vendor 

qualification testing requires judgment that can add considerable uncertainty to the strainer 

acceptance. Examples of inappropriate testing practices observed by the staff have included:

• Testing in which the intended suspendable fibrous fines were simulated with larger 

shreds of fibrous insulation. In one case the only fibrous debris was latent fibers and 

these fibers were simulated with NUKON® shreds, resulting in a potentially severe 

underrepresentation of latent fiber accumulation because the shreds did not transport to 
5-119

the strainer (NRC, 2007a). Other observations of non-prototypically coarse fiber 

preparation were common prior to the NRC providing expectations for fine debris 

characteristics in testing. 

• Use of non-prototypical agitation to force fibrous shreds to accumulate on the strainer 

rather than settling to the tank floor, with the objective of maximizing debris quantities on 

the strainer. This practice has been observed to prevent the formation of a thin bed in 

tests that were intended to identify thin bed head losses. When a relatively large fibrous

shred enters a gap between disks, within a cylinder, or an interior pocket it can settle 

onto a horizontal surface because the agitation that drove it to the gap is no longer 

influencing the shred. This creates a non-uniform accumulation with respect to the 

surfaces of other orientations. In one situation, accumulations of debris that settled

between horizontal disks created a damming effect. The result was a pressure 

differential that was subsequently relieved by the dam being forced inward clearing a 

portion of screen of debris and relieveing the overall strainer head loss (NRC, 2008a). 

This test did not adequately represent the intended thin bed, and the observed 

phenomenon was likely non-prototypical of what would occur in the plant. 

• Similarly, fibrous shreds have been introduced directly in front of strainers to enhance

debris accumulations, also with the effect of negating the formation of an effective thin 

bed. In this situation, the shreds entering the pockets settled to the horizontal surfaces 

of the strainer. This condition created non-uniformities between the horizontal surfaces 

and the surfaces of other orientations, thereby precluding the formation of an effective 

thin bed (NRC, 2008f).

• Particulates were observed to be introduced as buckets of dry powder that appeared to 

agglomerate, thereby under-representing the suspended particulate (NRC, 2006). 

• The staff has observed cases where the debris preparation did not match the results of 

the transport evaluation (fiber pieces too large or not assured to be conservatively fine). 

• Flow in test facilities have been observed to be non-conservative with respect to the

plant resulting in non-conservative transport. 

• Agglomeration of debris resulting in non-conservative transport and head loss has been 

observed. 

Head-loss testing experience has shown that the large PWR replacement strainers with their 

inherently slow screen approach velocities, typically less than 0.01 ft/s, cannot be effectively 

blocked by fibrous debris alone due to the high porosity of the fibrous debris, even if the strainer 

was to become completely engulfed in fibrous debris. Regarding particulates, not only are thin 

beds capable of causing severe head losses, but the type of particulate is important. A thin 

layer of fine hardened particles, such as latent debris or coatings, which would have a bed 

porosity in the neighborhood of 80%, is not too likely to cause the severe head losses. Coarse 

particulates would cause substantially less head loss than would the fine particulates. The 

primary issue is the more problematic particulates, such as calcium silicate, Microtherm, Min-K, 

and chemical-effects precipitates. Confidence that a specific strainer blockage issue has been 

resolved can be greatly increased when these types of particulates are not present in the 

containment in significant quantities.
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5.7.10 Qualification Testing of BWR Strainer Head Loss

The BWROG developed the strainer resolution methodology referred to as the Utility Resolution 

Guidance (URG) (NEDO-32686), which the NRC staff reviewed and subsequently issued a 

safety evaluation report (NRC-SER-1998). The URG included technical support documentation 

addressing strainer head loss. The BWROG sponsored head loss testing of a variety of test 

module designs, including a truncated cone strainer, a small PCI stacked disk strainer, a large 

PCI stacked disk strainer, a 20-point star strainer, a 60-point star strainer, and a self-cleaning 

strainer. The BWROG developed a head loss correlation based primarily on fiber and sludge 

(fine corrosion products typically found in suppression pools) but also included “bump-up” 

factors to account for other miscellaneous types of debris. The URG stated that the bump-up 

factor correlation was only valid at lower debris loadings (without explicitly defining “lower debris 

loadings”). The staff review found the BWROG bump up factor correlation to be unreliable, 

incomplete, and unacceptable for plant analyses. Other vendors including General Electric 

(GE), Enercon, and ABB (Asea Brown Boveri/Combustion Engineering) conducted scaled 

strainer module tests and developed head loss correlations that were considered applicable to 

their respective strainers. Based on knowledge that emerged from PWR testing the BWROG 

and NRC are reviewing the need to re-evaluate BWR strainer head loss on a plant specific 

basis. 

Whereas the PWR strainer head losses were determined by performing strainer module tests 

using plant-specific debris types and loads, BWR head losses were typically determined using 

head loss correlations based on generic vendor tests. In at least one plant, the strainer 

qualification was based entirely on head loss analyses. The NRC staff reviewed the results of 

head loss testing conducted by the BWROG as presented in the URG, a test report by GE, and 

head loss testing reviewed during the auditing process. The NRC staff conducted formal audits 

of four licensees, including (1) the GE strainer installed at Duane Arnold (Mark I BWR 

containment); (2) the PCI strainer installed at Dresden (Mark I); (3) the ABB strainer installed at 

Limerick (Mark II); and (4) the Enercon strainer installed at Grand Gulf (Mark III).

Based on these audit reports, it is clear that the licensees and vendors typically believed that 

thin beds could not develop on their respective strainers due to the complexity of the strainer 

geometries. The fact that thin beds were discovered to have occurred in the Perry and Limerick 

incidents (which were part of the reason for the regulatory actions to improve strainer 

performance) was attributed to the simpler strainer designs that existed at that time. PWR 

strainer testing has subsequently shown that the complex strainer designs cannot preclude the 

formation of a thin bed. For BWRs, evaluation of thin-bed formation is complicated by the effect 

of the vent downcomer depressurization turbulence. 

The BWR resolutions did not address the potential severity of particulate insulation debris, e.g., 

calcium silicate. Due to the very fine nature of pulverized calcium silicate dust, it was generally 

assumed that this fine dust would not be filtered; therefore head loss testing with calcium silicate 

like particulates was not performed until late in the resolution process. Licensees typically 

screened out smaller quantities of calcium silicate debris as being unimportant compared to the 

larger quantities of other debris types, and/or performed analyses using assumed head loss 

properties that may have underestimated head losses associated with calcium silicate like 

particulates. 

Chemical effects were not considered during the BWR resolutions in the 1990s. Although the 

BWR post-LOCA environments are less likely to result in significant chemical products, the 

potential extent of chemical effects should be determined and accounted for if necessary. Head 
5-121

loss testing and strainer qualification conducted during the BWR resolution was performed to a 

different set of standards than during the PWR resolution. Because of the lessons learned 

during the implementation of strainer improvements at PWRs, the BWROG and NRC staff are 

currently revisiting several areas to determine whether further actions are required at BWRs to 

ensure adequate strainer performance. One of the main areas being evaluated is strainer head 

loss testing which also includes issues regarding the debris included in the vendor tests, the 

debris preparation, and whether the debris used in testing adequately represents the plants’ 

conditions. 

5.8 Debris Head Loss Correlations

The NRC developed the head loss correlations presented in NUREG/CR-6224 and NUREG1862. The NUREG/CR-6224 correlation was developed as an analytical tool to support the 

resolution of the BWR strainer issue but was also used during the GSI-191 resolution as an 

analytical scoping and test data extrapolation tool. The NUREG-1862 correlation was 

developed during the GSI-191 resolution specifically to address concerns raised by the ACRS 

regarding analytical estimation of head-loss-associated debris beds containing calcium silicate.

The NUREG/CR-6224 correlation was implemented in two separate user-friendly software 

packages and made available for industry use, as well as the NRC staff. These software 

packages are the NUREG/CR-6224 Correlation and Deaeration Software Package, and the 

BLOCKAGE 2.5 code. The first development was BLOCKAGE 2.5, which includes a fairly 

complete set of BWR strainer blockage evaluation models, as well as the NUREG/CR-6224 

correlation (NUREG/CR-6370 and NUREG/CR-6371 are the Blockage 2.5 User and Reference 

Manuals). The models include drywell and wetwell debris transport and probabilistic models 

that calculate debris accumulation and head loss on multiple suppression pool strainers at the 

same time. The probability model calculates an overall plant strainer blockage probability based 

on user input weld break probabilities and the code’s determination of whether or not each 

specific weld break would lead to a blocked strainer. A key component is the model for 

suppression pool debris resuspension and settling. This model calculates debris concentrations 

for each type and size categorization, which are subsequently used to predict debris 

accumulation on each strainer based on the debris concentrations and pump flow rates. The 

NUREG/CR-6224 Correlation and Deaeration Software Package was developed by extracting 

the head loss correlation model from the BLOCKAGE 2.5 code and adding models to estimate 

deaeration from flows passing through a bed of debris. Both software packages have a userfriendly graphics user interface. The NUREG-1862 correlation was not developed into a 

software package.

There are basic limitations for the use of all such analytical correlations. Specifically, the head 

loss predictions are only as good as the correlation input parameters. At least two of the input 

parameters can only be determined by using an applicable head loss correlation to deduce the 

parameter from applicable head loss data. These two parameters are the debris bed porosity 

and the debris bed constituent specific surface areas. Since these parameters should be 

deduced using an appropriate head loss correlation, they should then be used in conjunction 

with that correlation. To make matters more complicated, a typical strainer blockage calculation 

will have multiple types of debris (such as fibrous insulation, latent fibers, coatings particulates, 

calcium silicate, dirt, etc.), and the experimentally determined head losses will include 

synergistic effects among the debris types that are difficult to simulate analytically. Therefore, 

the analytical correlations are useful for scoping purposes such as the initial sizing of a new 

strainer design or the extrapolation of head loss test data from the test conditions to alternate 

conditions, such as a slightly smaller or larger strainer area. The greater the variance between 
5-122

the calculation parameters used in the correlation and the corresponding validating test 

parameters, the greater the uncertainty introduced into the correlelation results.

It should also be pointed out that each of these correlations has inherent assumptions built into 

their respective developments. For example, both correlations assume that particulate debris

cannot be deformed under the range of pressures encountered in a strainer debris bed. 

Particulates such as dirt or iron oxide corrosion products can be observed to be very rigid when 

observed under a microscope. When these particles are compressed in a solid layer they do 

not deform once the particles make complete contact such as in a thin layer of dirt particles. 

Some materials, such as calcium silicate derived from limestone and diatomaceous earth 

(fossilized plankton), has a fine crystalline structure that can undergo shape changes under 

pressure. These changes can affect head loss correlation predictions involving calcium silicate 

(i.e., the bed porosity and specific surface area could have a pressure dependency which is not 

modeled).

The NUREG/CR-6224 Correlation and Deaeration Software Package is presented first because 

this package had greater use and a wider peer review. Second, the BLOCKAGE 2.5 code is 

briefly presented followed by the more recent NUREG-1862 correlation.

5.8.1 NUREG/CR-6224 Correlation

5.8.1.1 NUREG/CR-6224 Correlation and Deaeration Software Package

The NUREG/CR-6224 head loss correlation was originally developed during a volunteer plant 

parametric study, completed in 1995, for the resolution of the BWR ECCS strainer blockage 

issue. For this study, the correlation was implemented into a computer program named 

BLOCKAGE 2.5 (NUREG/CR-6370, NUREG/CR-6371), which included models for debris 

generation, debris transport, risk assessment, and debris head loss. In 2004, for use in the 

resolution of the GSI-191 PWR sump strainer blockage issue, the basic NUREG/CR-6224 head 

loss correlation, as programmed into BLOCKAGE 2.5, was extracted and implemented as a 

stand-alone program that solved only the head loss calculation. A user-friendly graphical user 

interface was also developed. In 2005, this program was expanded to include a deaeration 

model to estimate the deaeration that occurs when the pressure of the water deceases as the 

water flows through a bed of debris. This final program, referred to as the “NUREG/CR-6224 

Correlation and Deaeration Software Package,” was publically released by the NRC in June 

2005 via the NRC Public Document Room. Program installation also installs a user’s manual, 

sample problems, and reference materials, along with the executables. 

NUREG/CR-6224 Head Loss Correlation

A semi-theoretical NUREG/CR-6224 correlation was developed for predicting head loss through 

fibrous debris beds based on the fundamental principles of porous media filtration and 

hydraulics (NUREG/CR-6224). The correlation was developed for single-phase water flow and 

for a uniform-thickness homogeneous layer of fibrous debris with or without interspersed 

particulate, but it is also applicable to a layer of particulate debris supported in place with 

minimal fibers overlaying a strainer mesh or strainer holes, sufficient for effective filtration (i.e., a 

“thin bed” of debris). The general equation, valid for laminar, transient, and turbulent flow 

regimes, is formulated as
5-123

where C = 4.1528 x 10-5 (ft-H2O/in.)/(lbm/ft2

-s2) [units conversion constant]

Sv = specific surface area = 1.71 x 105 ft2

/ft3 for NUKONTM

εm = mixture porosity

μ = dynamic viscosity (lbm/s-ft)

U = velocity (ft/s)

ΔH = head loss (ft-H2O)

ρw = water density (lbm/ft3

)

ΔLo = uncompressed fiber bed thickness (in.)

ΔLm = actual bed thickness (in.)

The first term of two on the right-hand side, which is linear with flow velocity, reflects the viscous 

effects associated with pressure loss, and the second term, which is a function of the square of 

the velocity, reflects the effects of inertia. In the laminar flow associated with large passive 

strainers, where the velocities through the debris bed are typically less than 0.01 ft/s, the 

pressure loss is dominated by the first term. The ratio of the actual bed thickness (ΔLm) to the 

uncompressed thickness (ΔLo) reflects the compressibility of the fibrous debris bed under 

pressure (the larger the pressure differential, the greater the bed compression).

The supporting constituent equations, which complete the correlation, include an equation for 

the compressibility of the fibrous debris bed, an equation that provides a material contact 

compressibility limit, and equations for calculating the mixture properties of porosity, specific 

surface area, and densities. The mixture porosity depends upon the porosities of the 

uncompressed fiber bed, the entrapped particulate, and the bed compression and is calculated 

from:

where ρf = density of an individual fiber (175 lbm/ft3 for fiberglass)

ρp = density of each individual particle

η = ratio of the mass of particulate to mass of fiber in the bed

εo = uncompressed fiber bed porosity

The next equation is used to estimate the compressibility of the debris bed. 

where co = the “as-fabricated” bulk fiber density (2.4 lbm/ft3 for NUKON® fiber)

 c = actual bulk fiber density under pressure (lbm/ft3).

[ ] 















∆

∆ 



 



 − = − + − +

∆

∆

o

m

w

m

m

v m m v

o L

L C S U S U

L

H 2 1.5 3 2 (1 ) 3.5 (1 ) 1 57(1 ) 0.66 ρ

ε

ε

ε ε μ

m

o

o

p

f

m L

L

∆

∆ =1 − (1+ η)(1− ε )

ρ

ρ

ε
5-124

The coefficients α and γ can be specified in the software package input by the user. The values 

developed for these coefficients during the NUREG/CR-6224 study were α = 1.3 and γ = 0.38.

There is a practical limit to the fiber bed compression, particularly whenever significant 

particulate is embedded in the fiber matrix. The particulate cannot be compressed beyond its 

bulk granular density (e.g., approximately 65 lbm/ft3 for BWR suppression pool sludge 

consisting of iron oxide corrosion products). The limiting compression equation incorporated 

into the software package is:

where, cgran = the bulk granular density of the particulate (lbm/ft3).

For thin-bed debris beds, the bed porosity is limited to correspond to the porosity of the granular 

particulate, which is:

The solution of the general NUREG/CR-6224 correlation equation and its supporting equations 

require an iterative solution, which is discussed in NUREG/CR-6371.

Programming Verification and Correlation Validation

Correlation programming verification was conducted for the BLOCKAGE 2.5 code (NUREG/CR6371) by comparing code results to the results of analytical solutions. This verification is 

extended to the NUREG/CR-6224 Correlation and Deaeration Software Package, since the 

applicable correlation programming is common to the two programs. 

The validity of the NUREG/CR-6224 correlation was assessed against limited experimental data 

involving NUKON® and BWR suppression-pool iron oxide sludge during the NUREG/CR-6224 

study and the correlation was shown to perform reasonably well against that data. Validation 

against experimental data involving NUKON® and calcium silicate particulate (NUREG/CR6874) proved more challenging. Calcium silicate particulate has a crystalline structure subject 

to potential deformation, whereas iron oxide particles behave like small, hardened rocks and are 

unlikely to deform under differential pressures expected across strainers. During the calcium 

silicate tests, the fiber bed compression was measured, whereas it was not measured during 

the iron oxide testing; therefore, the compression function was not independently validated 

during the earlier NUREG/CR-6224 study.

The validity of the correlation predictions depends upon knowing appropriate values for input 

into the correlation. One important property that should be experimentally determined is the 

specific surface area of the particulate. The specific surface area strongly affects hydraulic 

flows through the particulate, as does the bed porosity. The experimental determination is done 

by adjusting this input parameter and others and comparing the results to the experimental data 

until the correlation fits the data reasonably well. Once agreement is reached the input values 

in conjunction with the correlation can be used with reasonable success to predict head losses 

for comparable debris compositions. Note that the densities can typically be independently pre-

∆ = ∆ (η +1)

gran

o

m o c

c L L

p

gran

m

c

ρ

ε =1−
5-125

determined to a reasonable accuracy. The test data from a thin-bed test provide a reasonable 

basis for ascertaining the particulate specific surface area because the bed compression and 

fiber properties are not issues for the thin-bed case. Calcium silicate is a substantially more 

difficult type of particulate for which to determine the appropriate correlation input values than 

less deformable particulates like iron oxide. The iron oxide particulates are hardened particles 

that will not change shape under the kinds of pressures found in a typical debris bed, whereas 

calcium silicate particulate with its crystalline structure could change shape under debris bed 

head loss pressures (i.e., the surface area could become somewhat dependent on head loss).

An independent ACRS technical assessment of the correlation identified deficiencies, with

which the NRC staff generally agreed, in the formulation of the correlation. The assessment 

pointed out that there were variations in the trends of the results when the correlation, as 

originally formulated, was applied to the head loss test data for calcium silicate in NUREG/CR6874, which was intended to ascertain the specific surface area for calcium silicate. The three 

identified formulation deficiencies listed in Table 5.8-1 could have contributed to these 

variations.

First, the denominator in the porosity expression of the inertia effects term should have been 

cubed, i.e., instead of (1- εm)/εm, it should have been (1-εm)/εm3. The primary reason for this 

change was to put the formulation in agreement with the more classical theoretical forms, such 

as the Ergun equation. An NRC comparison with test data indicated that the more classical 

form was a somewhat better fit to the data. The inertia effects term, which is a function of the 

velocity squared, has the most impact when the flows are faster and turbulent in nature. For the 

large passive strainers, the flow rates through the debris bed are generally much too slow for 

this correlation correction to have a significant effect on the calculation estimates.

The second and third formulation deficiencies related to the correlation’s ability to predict the 

compression of the bed of fibrous debris. The second deficiency dealt with the formulation of 

the compression function that related pressure to the bed compression ratio, and the third 

deficiency dealt with the formulation of the compression limiting equation. The compression 

function of the NUREG/CR-6224 correlation related the bed compression ratio to the head loss 

per unit bed thickness whereas the ACRS review stated that it would be more correct to relate 

the compression ratio only to the head loss. In addition, the ACRS review noted that the 

compression function did not calculate a compression ratio of one when the head loss was zero 

(which, in addition to not being correct, caused difficulties with the iterative numerical solution of 

the correlation’s set of equations). This deficiency suggested a compression function of a 

different form that would go to one when the head loss is zero, i.e., ΔLo/ΔLm=1+αΔLoφΔHγ. 

The ACRS noted that the compression-limiting equation had been oversimplified for debris 

types such as calcium silicate and provided a more detailed derivation, as presented in Table 

5.8-1.

Table 5.8-1. Deficiencies Identified in Formulation of NUREG/CR-6224 Correlation

Specific Concern NUREG/CR-6224 ACRS Comment

Porosity expression in inertia 

effects term, specifically, εm in the 

denominator should be cubed

(1- εm)/εm (1- εm)/εm

3

Formulation of compressibility 

function

ΔLo/ΔLm=α(ΔH/ΔLo)

γ ΔLo/ΔLm=αΔHγ

Formulation of compression limiting 

function

ΔLm/ΔLo= (co/cgran) (η+1) ΔLm/ΔLo=(co/cgran)(η+cgran/ρf)
5-126

The most appropriate form of the compression function really depends upon which form does 

the best job of predicting the head loss data and could depend somewhat on the type of fiber. 

The data reduction of the calcium-silicate head loss data presented in NUREG/CR-6874 (for the 

final and most valid series of tests) applied the correlation to a thin-bed calcium silicate debris 

bed, where the bed compression was not an issue, to ascertain an effective specific surface 

area for the calcium silicate particulate. Then, the correlation was applied to other test series to 

determine how well the correlation was performing overall. The comparative results for the 

original NUREG/CR-6224 correlation with the test data are shown in the upper plot in Figure 

5.8-1, where the horizontal axis represents the experimentally measured compression ratio, and 

the vertical axis represents the calculated compression ratio. If a data point was correctly 

estimated by the correlation, then that point in the plot would reside on the 45° line. This upper 

plot shows substantial data scatter both above and below the 45° line. Using the compression 

formulation suggested above (i.e., ΔLo/ΔLm = 1 + αΔLoφΔHγ) along with the other two ACRS 

suggested formulation corrections, the data scatter is greatly reduced, as shown in the lower 

plot in Figure 5.8-1. Given the quality of the test data compression measurements, this is a 

reasonably good result. Obtaining quality head loss data for calcium silicate was more difficult 

than for suppression pool sludge due to issues with particle filtration and particle deformation 

associated with calcium silicate; therefore, these comparisons represent a reasonably good test 

of the correlation’s capabilities, both as originally programmed in the software package and the 

potential improvements to the original correlation.

Applicability of Correlation

The head loss predictions of the NUREG/CR-6224 correlation are only as good as the validity of 

the input parameters and depend upon whether or not a realistic debris bed can be treated as 

one-dimensional, uniform thickness, and homogeneous, with single phase water. Further, the 

most appropriate formulation of the compression function and associated coefficients may 

depend somewhat upon the type of fibers in the debris bed. The large passive strainers in use 

at the plant have varied strainer geometries that may affect debris bed uniformity and onedimensionality. Instead of forming in a homogeneous manner, the bed could contain 

stratification due to the relative timing of arrival of the various debris constituents. Under some 

conditions, debris beds can develop channeled flow through bed penetrations known as 

boreholes. Realistic plant debris beds may consist of multiple fiber types and particulate types 

so that even if the appropriate correlation input parameters are developed for each debris type, 

the agglomeration of debris could have synergistic effects not accounted for by means of testing 

with individual components. Additionally, complex geometry strainers are likely to collect debris 

non-uniformly with the degree of non-uniformity depending on the strainer design and debris 

transport. The correlation assume a uniform debris bed. Although the NUREG/CR-6224 

correlation is certainly suitable for scoping calculations, given all these uncertainties, the 

qualification of plant strainers should necessarily be based on experimentation. However, when 

properly applied, the correlation can often be used to extrapolate experimental data from the 

test conditions to alternative conditions not too far removed from the test conditions such as a 

different water temperature, a variation in debris load, or strainer flow velocity. However, the 

further the extrapolation from the test condition, the greater is the uncertainty.
5-127

Original 

NUREG/CR6224 

Correlation

Revised 

NUREG/CR6224 

Correlation

Figure 5.8-1. Performance Comparison of Original and Revised Correlations

The ACRS identified deficiencies in the formulation of the NUREG/CR-6224 correlation listed in 

Table 5.8-1 do not significantly affect the predictions for thin-bed debris beds associated with 

the typical large plant strainer, where the velocity of flow through the bed of debris is typically 

less than 0.01 ft/sec. At these low velocities, the inertial velocity squared term with the εm3 

correction becomes irrelevant. Because a thin bed consists of very little fiber, the two 

deficiencies associated with fiber bed compression do not apply either. Since thin beds tend to 

form from the fine suspendable fibers and particulates, which are not significantly affected by 

gravity, they tend to form relatively uniformly on surfaces of all orientations. As such, the quality 

of the head loss prediction depends upon knowing the appropriate specific surface areas of the 

agglomerated particulate. If the debris bed forms uniformly the performance of a complex 

geometry strainer can perform in a manner quite similar to the flat-plate strainer. In this 

situation, head loss data taken with a small-scale closed loop head loss test apparatus may 

closely approximate similar debris loads on complex strainers. 

0

0.5

1

1.5

2

2.5

3

3.5

4

0 0.5 1 1.5 2 2.5 3 3.5 4

ΔLo/ΔLm -Experimental

ΔLo/ΔLm - Predicted

Test 6B

Test 6E

Test 6F

Test 6H

Test 6I

Line

α = 1.3

γ = 0.38

0

0.5

1

1.5

2

2.5

3

3.5

4

0 0.5 1 1.5 2 2.5 3 3.5 4

ΔLo/ΔLm - Experimental

ΔLo/ΔLm - Predicted

Test 6B

Test 6E

Test 6F

Test 6H

Test 6I

Line

α=0.65

Φ=0.35

γ=0.45
5-128

The set of constituent equations used in the correlation to combine the input properties of 

density and specific surface area for multiple components into a single set of numbers for use 

by the main correlation equation is based on the assumption of hardened materials that do not 

deform under pressure. Particulates that can deform under pressure (or with moisture 

absorption) can pack into the small spaces among the hardened particulate, thereby creating a 

low porosity medium for which this correlation will most likely underpredict the associated head 

loss. The user should beware of this limitation. 

Deaeration Model

A deaeration model was added to the software package to estimate the evolution of dissolved 

air as the water flows through a bed of debris. The software was designed to calculate 

conservative estimates of deaeration given plant specific conditions. The containment sump 

pool water will contain dissolved air due to its contact with the containment atmosphere. As 

pumped recirculation water flows through the recirculation strainer and debris bed, the pressure 

decrease can be significant enough for dissolved air to evolve from the flow, thereby generating 

air bubbles consisting of both air and water vapor. Excessive voiding can result in pump 

cavitation. In addition, the void fraction, if high enough, could invalidate the head loss 

predictions from the NUREG/CR-6224 correlation or those attained during plant specific tests 

under conditions other than those predicted for the plant. Deaeration has been observed in 

both NRC-sponsored and industry-sponsored head loss testing, which is typically conducted at 

temperatures much colder than would be expected in a plant sump pool. This deaeration 

resulted in substantial air buildup immediately downstream of the test strainers. At higher water 

temperatures, the vapor contribution can increase substantially.

The complete deaeration model (see Information Systems Laboratories, 2005) is included in the 

software package installation. The key assumptions included in the deaeration model are:

1 Henry’s law and the ideal gas law are both applicable.

2 The dissolved air composition is based on standard composition dry containment air.

3 The concentration of the dissolved air in the containment sump water is always at its 

equilibrium saturation level both before and after the sump strainer.

4 The decompression process through the strainer debris bed is isothermal.

5 The void gases are saturated with water vapors.

6 The hydrostatic pressure downstream of the strainer equals containment pressure plus 

sump pool hydrostatic head minus strainer and debris head losses.

A key limitation to this deaeration model is the isothermal assumption. If substantial water 

vaporizes while passing through the debris bed, the water temperature will begin to drop 

accordingly. Therefore, in a situation where the sump-pool water temperature begins to 

approach the boiling point, a debris bed depressurization could cause sufficient vaporization 

that the prediction from the Henry’s-law based deaeration model prediction would not be valid 

due to the isothermal assumption. In addition to the input parameters required to solve the 

head loss correlation, this deaeration model requires input of the containment pressure and the 

depth of the pool above the sump strainers to calculate the hydrostatic pressure at the sump 
5-129

strainer surface. For conservatism, the height of the water above the minimum submergence 

for the entire surface of the strainer should be used for pool depth in the deaeration calculation.

5.8.1.2 BLOCKAGE 2.5 Code

The BLOCKAGE 2.5 code was developed by the NRC as a tool to evaluate licensee compliance 

regarding the design of suction strainers for ECCS pumps in BWRs, as required by NRC 

Bulletin 96-03. The BLOCKAGE code was developed to predict whether or not accumulation of 

debris on the pump suction strainers, following a LOCA, would lead to loss of ECCS pump 

NPSH in a BWR. The code included a transient temperature-dependent suppression pool 

model to credit sedimentation, the ability to simultaneously track multiple debris types 

accumulating on the strainers associated with multiple pumps and multiple common headers 

and estimated head losses on each strainer employing user-selected optional head loss 

correlations, including the NUREG/CR-6224 correlation. 

BLOCKAGE 2.5 allows the user to simulate debris generation and the subsequent transport of 

multiple types of debris, including fibers, particles, and metal shreds by specifying the 

characteristics of each debris type. The debris could originate from target destruction in the 

drywell (e.g., insulation), non-target related drywell sources (e.g., latent), and wetwell sources 

(e.g., latent sludge). The user can specify a given quantity of debris for transport or use a threezone destruction model to calculate the generation of insulation debris from insulation targets 

based on the user input of target diameters, lengths, and locations. The user specifies a 

destruction fraction for each of the three zones. The debris transport from the drywell to the 

wetwell can be modeled as location-dependent and time-dependent and is split between two 

discrete time intervals referred to as the “blowdown period” and the “washdown period.” 

The debris entering the pool immediately becomes suspended in the pool where it can be 

deposited onto a strainer, pass through a strainer and be trapped within the primary system, or 

settle to the floor of the wetwell. Debris existing in the wetwell at the time of the pipe break is 

assumed to initially reside on the wetwell floor, where it is subject to resuspension by the 

turbulent primary-system depressurization flows. The wetwell debris transport model accepts 

debris transported from the drywell by debris type, subdivides the debris of each type into 

settling velocity groups, and independently determines the transport of each velocity group for 

each debris type within the suppression pool. The terminal velocity at which debris settles in a 

still pool of water is a function of the size of the individual debris pieces and the type of debris. 

The BLOCKAGE models require that the terminal settling velocity function be subdivided into 

discrete intervals or groups for each type of debris. The user enters a table of characteristic 

settling velocities associated with each size grouping in the debris size distribution.

The debris transport within the suppression pool, including the deposition of debris on the 

strainers and the debris concentration within the pool, is calculated separately for each discrete 

debris size for each debris type. The suppression pool is treated as single volume of water (i.e., 

debris concentration does not vary with location within the pool). Several model parameters 

supplied by the user, which are time-dependent, include the calculational time step, the pump 

flow rates, the drywell debris transport rates, the suppression pool temperature, and the 

suppression pool resuspension and settling rates. 

Several independent ECCS pumping systems can be modeled simultaneously, with each 

system consisting of multiple pumps on a common header attached to a single equivalent 

strainer. The ECCS pump and header models in BLOCKAGE 2.5 allow the user to tailor the 

strainer blockage calculation to the plant specific ECCS pumping systems. As many as eight 
5-130

independent pumping systems could be modeled in a single calculation. A single pumping 

system consists of multiple pumps (or a single pump) attached to a common header that draws 

water from a single strainer. The strainer areas of the multiple strainers attached to a common 

header are combined and represented as the single strainer, and the flow through the 

equivalent strainer is the combined flow of the operating pumps attached to the common 

header. As many as four pumps could be attached to the common header. Each pump 

attached to a common header is modeled with a separate flow capacity and a separate NPSH 

margin, but all pumps use a common time-dependent flow multiplier. Each pump provides 

ECCS flow to the reactor until strainer blockage head losses exceed its available margin of 

NPSH, causing the pump to fail and its flow to cease. Each pump is considered to fail due to 

cavitation when the strainer head loss exceeds its temperature-dependent NPSH margin. The 

calculation of the strainer head loss is based on the total flow of the pumps still operating on the 

common header, but the cavitation failure of each pump is determined independently of the 

other pumps. 

A debris bed filtration model determines the quantity of debris entrained in the pump flow that is 

deposited on the strainer and the quantity of debris that passes through the strainer and may be 

retained within the primary system. The fraction that is deposited onto the strainer is called the 

“strainer filtration efficiency.” The filtration efficiencies are a function of the type and size of 

debris and the thickness of fibrous debris bed already deposited onto the strainer. The debris 

passing through the strainer and debris bed will be carried by the ECCS flow to the reactor 

vessel and associated piping, where some debris will likely be trapped and other debris may be 

returned to the drywell or suppression pool. The retention efficiency determines how much of 

the debris passing through the strainers is retained in the primary system and not returned to 

the containment. One minus this efficiency is immediately returned to the pool. The retention 

efficiency is a function of the type and size of debris.

Debris accumulation on the ECCS strainer resists further flow through the strainers, thereby 

impeding the delivery of ECCS coolant to the reactor core. The BLOCKAGE code contains 

models to estimate the flow resistance, referred to as “pump head loss.” The head loss for each 

strainer is calculated independently of the other strainers. BLOCKAGE 2.5 contains four 

optional head loss correlations, which may be selected by the user to model the head loss for a 

debris cake consisting of fibrous and particulate debris. One correlation should be selected and 

is applied to all of the strainers in the model throughput the entire calculation. The four 

correlations are the semi-theoretical NUREG/CR-6224 correlation, the empirical BWROG 

correlation (Boiling Water Reactor Owners Group, 1994), and two generic correlations. The 

NUREG/CR-6224 correlation was discussed in Section 5.8.1. The two generic correlations 

allow the use of user-supplied coefficients that allow users to implement their own solution. The 

BWROG correlation represented early work that is now be considered obsolete. BLOCKAGE 

2.5 also contains an additive term for estimating head loss due to metallic debris on the strainer, 

which can be added to any of these four head loss correlations. The failure of the ECCS to 

provide long-term cooling to the reactor core is flagged whenever the total ECCS flow capability 

drops below a user-specified minimum flow rate. 

The BLOCKAGE code can evaluate a single-break scenario or a large number of break 

scenarios to determine plant-wide risk. Two sizes of pipe break scenarios are considered, 

large and medium LOCAs. The BLOCKAGE code has two models for calculating the pipe weld 

break frequency for particular welds. These models are referred to as the “weld method” and 

the “plant method.” The weld method specifies the weld break frequencies as a function of pipe 

diameter and weld type. The weld break frequencies are input to the calculation by the user as 

a list of break frequencies that are a function of the pipe diameter and the type of weld. The 
5-131

diameters are grouped into classes to reduce the size of the table. The plant method specifies 

the break frequencies for all weld breaks for a specific diameter pipe. Then the break frequency 

for an individual pipe weld break is determined by using weighting factors that are specified by 

the diameter class and the weld type. When selected by the user, the code writes several 

probability reports that provide information regarding the plant-wide strainer blockage 

probabilities correlated by pipe diameter, piping system, and break location. The code’s 

graphical user interface can be used to create a wide variety of time-dependent plots. 

5.8.2 NUREG-1862 Correlation

The NRC sponsored head loss testing of debris beds consisting of fibers and calcium silicate 

insulation debris to determine the head-loss characteristics associated with calcium silicate 

insulation debris (NUREG/CR-6874). Experiments confirmed that calcium silicate insulation 

could degrade into very fine particulates in the containment environment after a LOCA, and that 

debris beds formed by a combination of fine calcium silicate particulates and fibrous insulation 

on a sump strainer can cause substantial head loss across the sump strainer. 

Analysis of the test data using the NUREG/CR-6224 correlation recommended that head loss 

parameters such as particle density, the sludge density, and the specific surface area, be used 

in conjunction with the correlation for analysis of debris beds containing significant calcium 

silicate. The analysis noted uncertainties associated with the test parameters and also 

variability in the manufacture of the particular brand of calcium silicate insulation tested. A 

technical review by the ACRS raised concerns regarding the application of the NUREG/CR6224 correlation and the NUREG/CR-6874 methodology for calculating head loss through 

debris-covered sump strainers. The concerns specific to the formulation of the correlation were 

discussed in Section 5.8.1.1. The ACRS also expressed concerns with the NUREG/CR-6874 

methodology use of a different specific surface area for calcium silicate when the correlation 

was applied to a thin bed rather than when applied to a thicker bed containing a higher ratio of 

fiber to particulate debris. These concerns launched an effort to develop a new and improved 

head loss correlation that was largely based on debris beds of fiber and calcium silicate. This 

new correlation became the NUREG-1862 correlation. The NRC also sponsored additional 

testing conducted at PNNL (NUREG/CR-6917). The data from the PNNL tests formed the basis 

for validation of the NUREG-1862 correlation.

The NUREG-1862 correlation consists of a set of equations derived to calculate the pressure 

drop for flow across a compressible porous debris bed composed of thermal insulation such as 

fiberglass fibers (NUKON®) and calcium silicate (CalSil) particles. The equations account for 

the kinetic and viscous contributions to pressure drop. The compressibility of the porous 

medium debris bed is considered by initially assuming an irreversible, inelastic process followed 

by elastic behavior with constant compressibility. Semi-empirical relations and constants 

required to solve the flow and compression relations were determined from available test data. 

The solution of the set of equations involves an iterative procedure developed to estimate the 

pressure drop across a debris bed composed of one debris type (e.g., fibers) by applying the 

flow and compression relations to a one-volume, homogeneous debris bed model. This iterative 

solution procedure was successful in providing estimates of an upper bound pressure drop for 

the available test data for a debris bed composed of two types of debris using a two-volume, 

nonhomogeneous model in which the particles are assumed to concentrate or saturate a part of 

the fiber bed. The pressure drop across a debris bed composed of two debris types (e.g., fibers 

and particles) depends on the distribution of the two debris types in the bed. For a debris bed 

composed of two debris types, procedures have been developed to estimate the lower bound 
5-132

pressure drop by using the one-volume, homogeneous model, and to estimate the upper bound 

pressure drop by using a two-volume, nonhomogeneous model in which the particles are 

assumed to concentrate or saturate a part of the fiber bed. 

Whereas the NUREG/CR-6224 correlation was based on the assumption that the debris bed 

could be treated as a homogeneous distribution of fibers and particles in a single layer of 

uniform thickness, the NUREG-1862 correlation allows the debris bed to be divided into two 

separate homogeneous layers with different particulate concentrations. For the correlations in 

NUREG-1862 to be valid, the pressure downstream of the strainer must remain above the 

saturation pressure at the sump water temperature.

The pressure drop (∆pdebris bed) in a debris bed of thickness ∆Ldebris bed consisting of a 

single debris type is given by a modified Ergun equation:

(5.8.1)

where b = 1.95 for a cylindrical fibrous bed, 3.89 for a spherical particle bed

c = 0.071 for a cylindrical fibrous bed, 0.13 for a spherical particle bed

Sv = specific surface area

ρ = fluid density

μ = fluid absolute viscosity

ε = porosity

V = approach flow velocity upstream of strainer

= Void ratio

K(X) = a dimensionless permeability function

For flows perpendicular to a cylinder axis with (X>1x10-4 and ε<0.995) 

(5.8.2)

and for a bed composed of spherical particles with (X>1x10-4 and ε<0.995)

(5.8.3)

Equation (5.8.1) can be rewritten as

(5.8.4)

where msolid = mass of solid material in the debris bed=

∆pdebrisbed

∆Ldebrisbed

= μVSV

2 X3

K(X)(1+ X)

2

(1− ε)

2

ε

3 +

bρV2

Sy

6

1− ε

ε

3

(1− ε )μSy

6ρV





 





c

∆pdebrisbed

∆Ldebrisbed

= μVSV

2

K(X)

msolid

A∆Ldebrisbedρsolid

(1− ε)

2

ε

3 +

bρV2

Sy

6

1− ε

ε

3

(1− ε )μSy

6ρV





 





c
5-133

= density of solid material in the debris bed

A = debris bed cross-sectional surface area=

The viscous term (first term on the right-hand side) of the head loss Eq. (5.8.1) or Eq. (5.8.4) is 

the dominant contributor to pressure drop for sump strainer approach velocities that are less 

than 0.061 m/s (0.2 ft/s). The viscous term contributes more than 90% of the total pressure 

drop for all of the calculational results provided in NUREG-1862. At approach velocities of less 

than 0.0305 m/s (0.1 ft/s), the viscous term contributes an even larger percentage of the 

pressure drop. Consequently, it can be argued that the kinetic term could be omitted from the 

head loss calculation for typical PWR large strainer approach velocities.

For a homogeneous bed consisting of two debris types (NUKON® and CalSil), the total 

pressure drop is obtained by adding the two pressure drops similar to Eq. (5.8.1) or Eq. (5.8.4), 

one using Eq. (5.8.3) and the cylindrical fibrous bed constants for NUKON® fibers and the other 

using Eq. (5.8.4) and the spherical particle constants for CalSil. 

Debris Bed Properties

The calculational procedure developed in NUREG-1862 employs pressure drop calculations 

across a debris bed composed of either one or two calculational control volumes. The onevolume method should be used for calculating head loss across a debris bed composed of a 

single debris type. The one-volume approach does not represent the best calculational method 

for beds with multiple debris types and non-homogeneous debris distributions because 

hydraulic and mechanical pressures can vary non-uniformly within the debris bed. The twovolume method overcomes this limitation by calculating the debris bed flow and compression by 

assuming the presence of two compressible calculational control volumes for the debris bed.

Testing has shown that a bed can be initially formed at an approach velocity of 0.1 ft/s (0.0305 

m/s) with conditions close to a uniform NUKON®/CalSil distribution. However, the uniform 

condition was not maintained with flow passing through the debris bed, when the particles tend 

to redistribute from a uniform condition to one in which the particles are concentrated in the fiber 

in a portion of the debris bed. Testing has shown that the homogeneous debris bed produces 

the lower bound head loss. This condition (homogeneous unsaturated debris bed) can be 

modeled using the one-volume calculational approach. The homogeneous debris bed with a 

uniform distribution of NUKON® fibers and CalSil particles can be modeled by using Eq. (5.8.1) 

or Eq. (5.8.4) to calculate the debris bed pressure drop.

A heterogeneous locally saturated debris bed represents a more stable reconfiguration of 

particles in a fiber bed. The upstream portion of the debris bed is considered to be composed 

entirely of fibers, and the downstream portion is considered to contain the maximum 

concentration of particles that the fiber bed can hold under a specific flow condition. 

(The maximum particle concentration volume can be located anywhere within the debris bed; 

however, for calculation purposes, the maximum particle concentration volume is assumed to 

be present on the downstream side of the debris bed.) Testing has shown that this bed 

configuration typically results in a larger upper bound head loss. The two-volume calculational 

method should be used to model this bed configuration to account for the two different debris 

distributions within the debris bed. 
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A homogeneous saturated debris bed is a subset of the locally saturated debris bed. In this 

configuration, the fiber bed is completely saturated with particles. In other words, every part of 

the fiber bed contains particles. The one-volume method can be used to model this 

configuration because the saturated debris bed is closest to a true homogeneous condition with 

uniform distribution of fiber and particles. However, if the debris bed is heterogeneous and 

locally saturated with particles, a two-volume approach is proposed to calculate the head loss. 

In either approach, the initial bed conditions, flow parameters (determined from experimental 

studies and described in NUREG-1862), and material parameters need to be known to calculate 

the pressure drop across a porous medium debris bed.

A heterogeneous oversaturated debris bed represents the case where the debris bed contains 

more particles than are required to saturate the fiber bed. It is postulated that the downstream 

portion of the bed is composed of fiber saturated with particles. The upstream portion of the 

bed is composed entirely of particles. The two-volume calculational method should be used to 

solve for this condition because of the various debris distributions in the bed.

To apply the calculational approach recommended in NUREG/CR-1862, several debris bed 

initial conditions, parameters, and material parameters should be known. The following specific 

information is needed to calculate the pressure drop across a porous medium debris bed:

• Constituent masses of the material in the test debris beds

• Initial thickness of the debris bed at bed formation 

• Debris material properties such as density and specific surface area, as well as the 

multipliers and exponents in the kinetic term of the porous medium pressure drop 

equation

• Maximum concentration of particulate debris in a fibrous debris bed, a condition called 

the “maximum particle concentration”

• Material-specific compression parameter, necessary to predict the porous media debris 

bed compression and expansion

• Flow velocity

The values for these parameters were obtained by comparing the predictions made using the 

calculational approach with head loss data from tests at PNNL (NUREG/CR-6917), Los Alamos 

National Laboratory/University of New Mexico (LANL/UNM) (NUREG/CR-6874), and Argonne 

National Laboratory (NUREG/CR-6913).

Compressibility of a Debris Bed

The material compressibility, a measure of the mechanical strength of the material, affects fluid 

flow in a porous medium. Gels and fibers are compressible materials that present unique 

problems in relating fluid flow and applied pressure because bed porosity can change 

throughout the bed as conditions vary. The geometry of a porous medium can change because 

of (1) deformation of the solid matter, (2) rearrangement of the individual particles or fibers as a 

result of movement, bending, or slipping, and (3) disintegration and subsequent rearrangement 

of the solid material. Bending, slipping, and disintegration are essentially irreversible processes. 

Therefore, these deformation mechanisms produce non-recoverable volume reductions. The 

degree of non-recoverable deformation is especially pronounced during an initial compression 

and decreases as the deformation is increased.
5-135

A porous medium composed of material such as fibers, particles, or gel exhibits hysteresis 

during compression-recovery cycles. This phenomenon is difficult to model in a numerical 

calculation; therefore, the assumption is made in NUREG/CR-1862 that the first compression is 

an irreversible process, and that after first compression, the porous medium is elastic with 

constant compressibility. Further, by assuming the volume of the solid material to be 

incompressible, the compressibility of the porous medium can be related entirely to the void 

volume instead of the total volume.

Initial Bed Thickness

The above considerations allowed the derivation of the initial thickness for a NUKON®/CalSil 

bed at a reference approach velocity:

(5.8.5)

where ∆Linitial = debris bed thickness at a reference bed formation approach velocity of 

about 0.0305 m/s (0.1 ft/sec) 

A = is debris bed cross-sectional surface area

mNUKON = NUKON mass in the debris bed

m CalSil = CalSil mass in the debris bed

ρNUKON = NUKON (fiber) material density 

ρCalSil = CalSil (particle) material density 

The values for the initial void ratios of the solid constituents at bed formation were determined 

from tests conducted at PNNL; these are XNUKON = 30 and XCalSil =6.2. These constants, together 

with Eq. (5.8.5), provide a reasonable prediction of formation debris bed thickness for NUKONonly and NUKON/CalSil debris beds at an approach velocity of 0.0305 m/s (0.1 ft/sec) over the 

range of temperatures from about 19 to 82°C (66.2 to 179.6°F). The assumption of constant 

compressibility allows the void ratios and bed thickness after the first compression to be 

calculated from the compressibility model. 

Debris Bed Material Properties

For predictive calculations, the material densities of the NUKON fibers and the CalSil particles 

were assumed to be the same as those recommended in NUREG/CR-6874. Because PNNL 

verified the appropriateness of these density values, they are recommended for predictive 

calculations. CalSil insulation can include fiber material such as fiberglass and cellulose. The 

CalSil fibers are assumed to possess the same material density as fiberglass.

If the specific surface area (Sv) is calculated using the manufacturer-specified fiber diameter and 

the geometric definition for a packed bed composed of cylindrical fibers oriented perpendicular 

to the flow direction, Sv =4/∆p, the following values result.

Sv = 4 / 0.00026 in. = 605,694 m-1 = 184,615 ft-1 without binder material

Sv = 4 / 0.00028 in. = 562,430 m-1 = 171,429 ft-1 with binder material

PNNL performed independent measurements of the NUKON fiber diameters. These 

measurements indicated that the fiber diameters range between 5 and 15 μm. The diameters 

result in the following range of SV values. 
5-136

Sv = 4 / 5x10-6 m = 800,000 m-1 = 243,840 ft-1 for 5-μm-diameter fibers

Sv = 4 / 15x10-6 m = 266,667 m-1 = 81,280 ft1 for 15-μm-diameter fibers

However, not all of the fibers in a NUKON debris bed are expected to be oriented perpendicular 

to flow. Consequently, the Sv value that results from the assessment of test data (which is 

recommended for application in the developed calculational method) can differ from the 

theoretically calculated value. Based on re-analysis of the PNNL data, NUREG-1862 

recommends the following values of Sv:

984,252 m-1

/ 300,000 ft-1 for NUKON fibers

2,132,546 m-1

/ 650,000 000 ft-1 for CalSil particles

984,252 m-1

/ 300,000 ft-1 for fiberglass fibers in CalSil

The equations used for determining the first irreversible compression of the debris bed equation 

and the elastic relaxation of the debris bed after the first compression employ a material specific 

parameter, N. The value of the parameter should be determined from test data. A value of 

0.236 was recommended for N, which was determined by using data obtained from testing at 

PNNL, from the tests performed by LANL at UNM, and from the ANL testing.

Comparison with Data and Conclusions

The iterative procedure developed to solve the flow and compression relations using a onevolume model for a homogeneous debris bed has been successful in conservatively estimating 

the pressure drop for PNNL, ANL, and LANL/UNM tests with regard to flow across a debris bed 

composed of one debris type (e.g., NUKON fibers).

The one-volume head loss predictions for a homogeneous NUKON/CalSil debris bed provide a 

reasonable lower bound pressure drop when compared to available test data. For debris beds 

composed of particles and fibers, the two-volume calculational method can predict upper bound 

pressure drops for larger CalSil concentration and can provide an adequate estimate of 

pressure drop, in the correct order of magnitude, for debris beds with lower CalSil concentration. 

Pressure drop across a debris bed depends on water temperature as well as on the flows and 

temperatures to which the debris bed has been exposed. The developed calculational method, 

generally, predicts higher pressure drop at lower liquid temperature, a result that follows 

classical theory expectations.

5.9 Chemical Effects

5.9.1 Introduction

The NRC initiated this study in response to a concern raised by the ACRS during its review of 

staff activities related to the resolution of GSI-191 in February 2003 (NUREG/CR-6868). 

Specifically, the ACRS raised the concern that chemically induced corrosion products have the 

potential to impede ECCS recirculation after a LOCA. Under this study, several small-scale 

head loss tests were conducted to determine whether debris generation and sump strainer head 

loss can be affected by chemical interactions between the ECCS recirculation water and 

exposed metal surfaces. Head loss flow tests were conducted in a small-scale (10 liters), 

vertical, closed-loop circulation, hydraulic test system built for measuring the head loss across a 
5-137

fiber-laden strainer. The principal conclusions of this study are that it is possible for gelatinous 

materials, if formed, to transport to PWR sump strainers, and that such materials can increase 

head loss across a fibrous debris bed. These results lend credibility to the concerns raised by 

the ACRS. Figure 5.9-1 shows head loss vs. materials concentration. The measured head loss 

increases with the metal concentration. In Figure 5.9-2, the measured head loss with chemical 

precipitates was normalized by the head loss without chemical precipitates. In the case of 

aluminum, the head loss with chemical precipitates is almost two orders of magnitude higher 

than that without chemical effects. 

Even though this study showed the significance of chemical effects, the scope is limited; only 

sodium hydroxide was used as a pH buffering agent, metal salts (as nitrate forms) were added 

to the test loop, and the corrosion/leaching tests for zinc were not successful because of the 

quiescent condition. This study included only separate-effects tests for each potential stage of 

the progression (i.e., quiescent-immersion corrosion/leaching tests, and artificially induced 

saturation/precipitation combined with transport/head loss flow tests) (NUREG/CR-6868). As a 

result, this study did not include integrated tests to demonstrate the complete progression of 

chemical effects from metal corrosion to the ultimate formation of precipitation products. As an 

independent peer review panel recommended, integrated chemical effects testing was needed. 

Three NUREG reports described in the following sections are follow-on studies to implement the 

findings in this study. 

Figure 5.9-1. Head Loss 

versus Materials 

Concentration 

(NUREG/CR-6868)
5-138

Figure 5.9-2. Ratio of 

Measured Head Loss With 

And Without Chemical 

Precipitates as a Function 

of Metal Ion 

Concentration 

(NUREG/CR-6868)

5.9.2 Integrated Chemical Effects Test

The Integrated Chemical Effects Test (ICET) project was a joint effort by the NRC and the 

nuclear utility industry (NUREG/CR-6914). The ICET attempted to simulate the chemical 

environment in a containment water pool after a LOCA and monitored the chemical system for 

30 days to identify the presence, composition, and physical characteristics of chemical products 

that formed during the tests. The primary objectives were to (1) determine, characterize, and 

quantify chemical-reaction products that may develop in the containment sump under a 

representative post-LOCA environment, and (2) identify and quantify any chemical precipitates 

that might be produced during the post-LOCA recirculation phase. No measurements of head 

loss were made in the tests. This section is primarily based on an earlier review documented in 

the Appendix B of NRC Staff Review Guidance (NRC, 2008c).

5.9.2.1 Test Conditions

All of the ICETs were conducted in an environment that attempted to simulate containment pool 

conditions during recirculation. The tests included an initial 4-hr spray phase to simulate 

containment spray interaction with the unsubmerged materials. The materials present in this 

environment typically included higher ende amounts of submerged and unsubmerged 

aluminum, copper, concrete, zinc, carbon steel, and insulation samples. Representative 

amounts of concrete dust and latent debris (dirt) were also added. Insulation samples consisted 

of NUKON fiberglass and calcium silicate (CalSil) material. Water was circulated through the 

bottom portion of the test chamber during the entire test to achieve representative flow rates 

over the submerged specimens. 

The amounts of material in the test were scaled to the liquid volumes of the test chamber and 

the containment sump volume. For most materials, scaling was in terms of the surface area of 

material to the sump volume, but for insulation materials, the scaling was in terms of the volume 

of material to the sump volume. The relative amounts of material were based on an informal 

survey of a number of plants (NUREG/CR-6914). More-detailed plant survey information made 

available after testing indicated the amount of insulation (e.g., CalSil) in these tests may have 
5-139

been too high to be representative. The ratios of material to sump volume are in most cases 

larger than would be expected for a typical plant, although the values are not necessarily 

bounding. The ratios of the material quantities to sump water volume are summarized in Table 

5.9-1.

The physical and chemical parameters that defined the tank environment are summarized in 

Tables 5.9-2, 5.9-3, and 5.9-4. Of the chemical parameters listed, only boric acid, lithium 

hydroxide, and hydrochloric acid were present in all five tests. Hydrochloric acid (HCl) can be 

formed from the degradation of cable insulation material. The initial test solution pH was 

different in each test, and it varied from ≈7.3 in. Test 2 to ≈9.8 in. Test 4. The predetermined 

amounts of chemicals were added for each test, and no attempt was made to control or alter the 

resulting pH during the test.

Table 5.9-1. Material Quantity/Sump Water Volume Ratios for ICETs (NUREG/CR-6914)

Material Ratio Value

(ratio units)

Submerge

d Material 

(%)

Unsubmerg

ed Material 

(%)

Comments

Zinc in galvanized 

steel

8.0 (ft2/ft3) 5 95 Accounts for grating and duct work that 

might be submerged.

Inorganic zinc 

primer coating 

(non-topcoated)

4.6 (ft2/ft3) 4 96 Addresses both non-topcoated zinc 

primer applied, as well as zinc primer 

exposed by delamination of a topcoat.

Inorganic zinc 

primer coating 

(topcoated)

0.0 (ft2/ft3) - - Epoxy-based topcoats prevent 

interaction of the zinc primer with sump 

and spray. Exposure of zinc primer to 

sump and spray fluids due to local 

failures of epoxy-based topcoats is 

accounted for in the non-topcoated zinc 

coatings.

Aluminum 3.5 (ft2/ft3) 5 95 Aluminum is generally not located at 

elevations inside containment where it 

may be submerged.

Copper (including 

Cu-Ni alloys)

6.0 (ft2/ft3) 25 75 Majority of surface area associated with 

CRDM coolers and instrument air lines 

(containment fan coolers for Cu-Ni 

alloys). 

Carbon steel 0.15 (ft2/ft3) 34 66

Concrete (surface) 0.045 

(ft2/ft3)

34 66 The submerged value accounts for 

limited damage to floor and wall surface 

areas that will be submerged due to 

primary RCS piping being elevated 

above the containment floor.

Concrete 

(particulate)

0.0014 

(lbm/ft3)

100 0

Insulation material 

(fiberglass or 

calcium silicate)

0.137 

(ft3/ft3)

75 25 The submerged value accounts for 

most of the fiberglass remaining in 

areas where it will wash down into the 

sump pool.
5-140

Table 5.9-2. Physical Parameters for ICETs (NUREG/CR-6914)

Physical Parameters Test Value

Tank Water Volume 949 L (250 gal)

Circulation Flow 100 L/min (25 gpm)

Spray Flow 15 L/min (3.5 gpm)

Sump Temperature 60°C (140°F)

Table 5.9-3. Chemical Parameters for ICETs (NUREG/CR-6914)

Chemical Concentration

Boric acid (H3BO3) 2800 mg/L as borona

Trisodium phosphate (TSP-Na3PO4·12H2O) (Tests 

2 & 3)

As required to reach pH 7 in simulated 

sump fluid

Sodium hydroxide (NaOH) (Tests 1 & 4) To reach pH 10 in simulated sump fluid

Sodium tetraborate [Borax] (STB-Na2B4O7·10H2O) 

(Test 5)

To reach boron concentration of 2400 

mg/L in Test #5

HCl 100 mg/La

LiOH 0.7 mg/La

a

Concentrations applicable to Tests 1-4. Concentrations for Test 5 were 2400 mg/L boron, 43 

mg/L HCl, and 0.3 mg/L LiOH.

Table 5.9-4. Test Series Parameters (NUREG/CR-6914)

Test Temp 

(°C)

pH 

Control

pHa Boron 

(mg/L)

Notes

1 60 NaOH 10 2800 100% fiberglass insulation test. High 

pH, NaOH concentration as required by 

pH.

2 60 TSP 7 2800 100% fiberglass insulation test. Low pH, 

trisodium phosphate (TSP) 

concentration as required by pH.

3 60 TSP 7 2800 80% calcium silicate/20% fiberglass 

insulation test. Low pH, TSP 

concentration as required by pH.

4 60 NaOH 10 2800 80% calcium silicate/20% fiberglass 

insulation test. High pH, NaOH 

concentration as required by pH.

5 60 STB 8 to 

8.5

2400 100% fiberglass insulation test. 

Intermediate pH, sodium tetraborate 

(Borax) buffer. a

Values shown were the target pH for Tests 1-4. Value for Test 5 is in the expected range.

The materials described in Table 5.9-1 were introduced to the tank as 373 flat-metal coupon 

samples (40 submerged) and one submerged concrete sample. Flow rate and temperature 

were controlled to maintain target values of 25 gpm and 60°C. The value of 25 gpm was 

chosen to yield fluid velocities over the submerged coupons from 0-3 cm/s. Daily water 

samples were obtained for measurements of pH, turbidity, total suspended solids, kinematic 
5-141

viscosity, and shear-dependent viscosity, as well as for chemical analyses. In addition, 

microscopic evaluations were conducted on water-sample filtrates, precipitates, fiberglass, 

CalSil, metal coupons, and sediment.

When the water reached the desired temperature, test-specific chemicals were dissolved into 

the water. Latent debris, concrete, test coupons, and insulation samples were then placed in 

the tank. Once the solution temperature reached 60°C, the test commenced with initiation of 

the tank sprays. During the 4-hr spray period, additional chemicals were added if required. 

The tests ran for 30 days. Water samples, insulation samples, and metal coupons were 

analyzed after the test. 

5.9.2.2 Overall Results

Solution samples from Tests 1 and 5 produced precipitates upon cooling to room temperature, 

whereas samples from Tests 2, 3, and 4 did not. A precipitate formed at the test temperature of 

60°C in Test 3. The Test 1 precipitates occurred much more quickly and were present in 

greater quantities than the Test 5 precipitates. Except for precipitates seen on the first day of 

Test 3, no precipitates were visible in the test solutions at the test temperature of 60°C. 

Turbidity measurements were taken at 60°C and 23°C. In Tests 2, 3, and 4, measurements at 

both temperatures produced similar results, consistent with the assumption that the turbidity is 

due to physical particulates and independent of temperature. During the first 4 hr of Test 3, a 

large increase in turbidity was seen, and corresponded to the visible precipitates in that test. In 

Tests 1 and 5, turbidity at 23°C rose higher than the 60°C values, consistent with the presence 

of a precipitate at the lower temperature.

The precipitates in Tests 1 and 5 are primarily amorphous forms of Al(OH)3, which is supported 

by x-ray diffraction (XRD) measurements and earlier literature referenced in the same report 

NUREG/CR-6915). The precipitate in Test 3 is a calcium phosphate (NUREG/CR-6914). 

Calcium phosphate is the name given to a family of minerals containing calcium, phosphorus, 

and oxygen (and sometimes hydrogen). They are all highly insoluble in the moderately alkaline 

solutions of interest. 

Daily samples were analyzed for aluminum, calcium, copper, iron, magnesium, nickel, silicon, 

sodium, and zinc. The solution samples were completely mixed before the inductively coupled 

plasma (ICP) atomic emission spectroscopy (AES) measurements. Thus, the results are 

representative of the solution plus any precipitate present. In Test 1, aluminum and sodium 

were present in greater concentrations than were all other tested elements. In Test 2, silicon 

and sodium were the dominant elements in solution. Silicon, sodium, and calcium were present 

in the greatest concentrations with the Test 3 solution. In Test 4, silicon, sodium, calcium, and 

potassium were present in solution in the greatest concentrations. Sodium, aluminum, calcium, 

and silicon were the elements of highest concentration in the Test 5 solution.

Turbidity was measured to study suspended solids. In all of the tests, turbidity peaked within 

the first few hours of testing and decreased to lower values within 24 hr. By the second day of 

testing, the turbidity decreased to very low values. The turbidity measurements remained at 

these low values for the duration of the tests. Tests 3 and 4 had higher values of turbidity early 

in the test than did the other tests because CalSil particulate was added to the tank before test 

initiation. Turbidity reached a very high peak early in Test 3 due to the formation of a calcium 

phosphate precipitate .
5-142

Insulation debris, which was composed of fiberglass or a mixture of fiberglass and CalSil, was 

analyzed after completion of each test. Three types of deposits were found on the fiberglass 

samples: flocculants, films, and webbing. Particulate deposits were confined to the exteriors of 

the samples and were physically attached or retained. Flocculent deposits were found 

throughout the samples and were more prevalent on the fiberglass interior. It is likely that the 

film or webbing deposits that were observed in Tests 1 and 4 were caused by the drying 

process since new fiberglass dipped in solution produced a similar film appearance. The 

amounts of deposits seen on the fiberglass insulation varied from test to test because of 

differing solution chemistry. The greatest deposition occurred in Test 3, followed in order by 

Tests 1, 4, and 2. Test 5 samples had the fewest deposits. Test 1 experienced the largest 

amount of corrosion on the submerged coupons. No significant corrosion of the submerged 

coupons was observable in Tests 2-5, except for the aluminum coupons in Test 5. None of the 

tests showed significant corrosion on the unsubmerged coupons. Sediment on the tank bottom 

at the end of the tests also varied. Tests 3 and 4 had the most sediment, most of it attributable 

to the large amount of crushed CalSil added to the tank. In Test 3, there were also significant 

amounts of chemical precipitate. Tests 1, 2, and 5 produced the least sediment, which was 

composed largely of materials from the insulation used (fiberglass) and debris added to the 

tank. 

5.9.2.3 Solution Chemistry

Each test had a target pH that was attributable to specific chemical requirements, as given in 

Table 5.9-4. The actual measured pH values are shown in Figure 5.9-3 and are relatively 

constant throughout the tests except for Test 3. In Test 3, the pH increased from the initial pH 

by approximately 0.8 units. In this test, the formation of Ca3(PO4)2 removed phosphate from 

the solution early in the test, which diminished the buffering capacity of the system. Without 

adequate buffering, the system pH could be more easily affected as varying chemical reactions 

occurred. 

The only metal coupons that showed significant corrosion in any of the tests were the aluminum 

coupons in Tests 1 and 5 and the uncoated carbon steel coupons in Test 1. It should be noted 

that the post-test weight loss measurements listed in NUREG/CR-6914 were performed after air 

drying without cleaning the coupons. The measured aluminum concentrations during Tests 1 

and 5 are shown in Figure 5.9-4. Aluminum concentrations in the other tests were below the 

detection limit of the ICP measurements. The pH in both Tests 1 and 5 was in the range of high 

aluminum solubility. Test 1 had a higher pH, which is consistent with the higher observed 

corrosion rate. In both Tests 1 and 5, the aluminum levels increased fairly steadily for about 15 

days, and then stayed relatively constant for the remainder of the test. Although the pH in Test 

4 was also high, the aluminum levels in solution were less than 1 mg/L. As will be discussed 

later, this low level of corrosion is probably due to the presence of high amounts of Si in solution 

from dissolution of the large amount of CalSil insulation in Test 4. The pH in Test 2 corresponds 

to a solubility minimum for Al(OH)3, which is consistent with the very low levels of dissolved 

aluminum in this test.
5-143

Figure 5.9-3. 

Measured pH During 

ICETs (NUREG/CR6914).

Figure 5.9-4. Measured 

Aluminum 

Concentrations in Tests 

1 and 5 (NUREG/CR6914).

The concentrations of zinc and copper were very low compared to the concentrations of 

aluminum in Tests 1 and 5. Neither zinc nor copper appeared as either adsorbed or 

precipitated species in these tests. Calcium levels were high in Tests 3 and 4, due to the 

addition of a large amount of CalSil in those tests. The solubility of CalSil (mostly calcium 

silicate CaSiO3) decreases with increasing pH. This may partly explain why the dissolved Ca 

levels at long times are lower in Test 4 than in Test 3 (see Figure 5.9-5). However, the higher 

pH in Test 4 may also lead to increased dissolution of fiberglass, and the resulting increase in 

dissolved siliconlevels (Figure 5.9-6) may also result in a decrease in dissolved Ca. The 

dissolved calcium in the tests without CalSil additions is probably due to leaching from concrete 

dust and other concrete sources. The drop in the calcium level early in Test 3 is due to the 

removal of Ca from solution by precipitation of Ca3(PO4)2. The amount of TSP added in Tests 

2 and 3 is about 4 g/L. Fully dissolved, this would give P levels greater than 300 mg/L. For 

CalSil loadings greater than about 2 g/L, the amount of Ca3(PO4)2 that can be formed is limited 

by the amount of phosphate available. Thus, in Test 3, the measured phosphate levels from 

day 1 to day 30 were less than 1 mg/L. All the phosphate has been removed from solution by 

precipitation of Ca3(PO4)2. Although the precipitation of Ca3(PO4)2 removed Ca from 

solution
5-144

Figure 5.9-5. Measured 

Calcium Concentrations 

in Tests 1-5 

(NUREG/CR-6914).

early in Test 3, because of the large amount of CalSil present in the test (19 g/L), dissolution of 

the CalSil continued until reaching the equilibrium solubility limit corresponding to the pH. 

Measured silicon concentrations are shown in Figure 5.9-6. They are high in Tests 3 and 4, as 

expected from the large amounts of CalSil in those tests. The silica concentration is also high in 

Test 2, which has only fiberglass insulation and a TSP buffer. It is extremely low in Tests 1 and 

5, and this was somewhat unexpected. Fiberglass solubility increases with pH, and separate 

effects testing (5-6 and 5-7) would suggest significant dissolution of fiberglass in Test 1 and 

somewhat less in Test 5. It appears that dissolved aluminum quickly reacted with the fiberglass 

to coat it, inhibiting further corrosion of the fiberglass (NUREG/CR-6914).

Figure 5.9-6. Measured 

Silicon Concentration in 

Tests 1-5. Note that 

although expressed in 

NUREG/CR-6914 as silica 

(SiO2) concentration, it is 

probably silicon (Si) 

concentration because 

that is what would be 

directly measured by ICP.

5.9.2.4 Precipitation

The two major chemical precipitates observed in the ICETs are Ca3(PO4)2 in Test 3 and some 

form of Al(OH)3 in Tests 1 and 5. The formation of the Ca3(PO4)2 precipitate in Test 3 

occurred very quickly with the addition of TSP through the sprays and is easily replicated in 

separate effects tests when phosphates are added to solutions that contain dissolved calcium. 

No precipitates were observed in Test 2, which also used TSP, but had no CalSil. Concrete 

would be a potential source of dissolved calcium. Figure 5.9-5 shows that the dissolved calcium 

level in Test 2 is lower than that in Test 5. Because leaching of calcium from concrete 

increases with decreasing pH (Lane et al., 2006), this is somewhat unexpected. It is possible 
5-145

that some of the calcium was removed from solution by formation of Ca3(PO4)2. Because this 

compound would form almost immediately as the calcium was leached from the concrete, it 

would probably not be visible as a precipitate in the solution, but would add to the sediment. 

Behavior of the precipitates in Tests 1 and 5 is more complicated. White precipitates were 

observed in solution samples for these tests as the solutions cooled to room temperature, 

whereas no precipitates were observed at 60°C. In Test 1, precipitates became visible after the 

first 8 hr of testing, when the test solution was cooled to room temperature. The amount of 

visible precipitation at room temperature increased, and the precipitates formed more quickly 

during cooling as the test progressed. In Test 5, the precipitates took longer to form (several 

days at room temperature), and the quantities were much smaller than in Test 1. In addition, 

the quantity of Test 5 precipitates was relatively unchanged throughout the test. 

The ICP-AES results indicated that the precipitates were composed largely of aluminum and 

boron. Calcium and sodium were also present in smaller amounts. The ICP analysis cannot 

detect the presence of either oxygen or hydrogen in materials. The precipitates from Tests 1 

and 5 have similar chemical compositions. The precipitate in Test 1 may have a somewhat 

greater proportion of aluminum than in Test 5. The precipitate in Test 5 appears to have a 

larger concentration of calcium. These results are consistent with the relative amounts of 

aluminum and calcium in solution (Figures 5.9-4 and 5.9-5). Transmission electron microscopy 

(TEM) and XRD analysis of the precipitates from Test 1 indicated that they were primarily 

amorphous rather than crystalline, although it was insisted that the XRD refinement revealed 

pseudoboehmite (poorly crystalline AlOOH) (NUREG/CR-6915), and the fundamental particle 

size was about 10 nm. However, much larger agglomerations of these basic particles were 

observed. It should be noted that the poorly crystalline AlOOH identified by XRD was 

performed after drying the precipitate.

Precipitate was not detected visually at the test temperature, 60°C, at any time during Test 1. 

However, the turbidity measurements are supportive of a precipitation in the Test 1 solution at 

room temperature. As the solution cooled from 60 to 23°C, the turbidity was observed to 

increase in a 10-min period from 0.3 NTU at 60°C to significantly higher values at 23°C 

becoming more than 133 NTU during the later stages. Precipitate was also visually observed to 

have formed as the fluid cooled during the draining process at the end of the test. The tank fluid 

appeared cloudy as it exited the drain hose into the post-test holding tank. A surrogate 

precipitate was produced by titrating aluminum nitrate solution with pH 9.5 containing 2800 mg/L 

boron and sodium hydroxide at 25°C. Nuclear magnetic resonance (NMR) analysis was 

performed on this surrogate precipitate, which indicated that a complexation between aluminum 

and boron occurred when the solution cooled below 40°C. Thus, the description of the 

precipitate as Al(OH)3 or AlOOH is a simplification of a more complex situation.

5.9.2.5 Passivation of Aluminum in ICET Solutions

In both Test 1 and Test 5, dissolved aluminum concentrations increased approximately linearly 

with time during the initial part of the test, but then reached pseudo-steady-state values (See 

Figure 5.9-4). Such behavior could be associated either with reaching a solubility limit or 

passivation of the metal coupons. 

Hydrogen is generated as part of the corrosion reaction of aluminum with water. Generation of 

hydrogen is an indication of an ongoing corrosion process. There were some problems with the 

hydrogen measurements during Test 1. However, the data from day 20 until the end of the test 

are at least qualitatively accurate. The hydrogen generation decreased from day 21 to day 26, 

which corresponds to the leveling off of aluminum concentration on day 25 in Test 1. Similarly, 
5-146

the decrease in the hydrogen generation associated with Test 5 at about day 17 is consistent 

with the leveling off of the aluminum concentration in that test. These measurements thus 

support an argument for passivation, not a solubility limit, as the mechanism that produces the 

leveling off of the dissolved aluminum concentration in these tests. 

The results in Test 4 suggest passivation by aluminum silicates, which was evidenced by a 

benchtop Al corrosion coupon testing and x-ray photoelectron spectroscopy analysis 

(NUREG/CR-6915). Passivation by aluminum silicates requires a source of soluble silicates. In 

Test 4, considerable leaching of Si from the fiberglass appears to have occurred, but the 

presence of dissolved aluminum in Tests 1 and 5 appears to significantly inhibit leaching from 

the fiberglass. The initial dissolved silica levels of 100 mg/L in Test 4 seemed to rapidly 

produce passivation of the aluminum. At the dissolved Si levels of ≈8 mg/L seen in Tests 1 and 

5 (Figure 5.9-6), many days are required for passivation to occur, and it is possible that these 

low levels of silica may not have affected aluminum passivation in these tests.

5.9.2.6 Summary and Discussion

Aluminum hydroxides, Al(OH)3 or related forms, and calcium phosphates are the primary 

chemical precipitates in the ICET tests. Significant dissolution of aluminum was observed in 

solutions with pH of 8.0 or greater. The isothermal nature of the ICET tests produces 

nonconservative estimates of the potential corrosion of nonsubmerged materials in the 

containment and the corrosion that occurs early in the accident. Calcium phosphates were 

formed in solutions with TSP and CalSil. 

Concrete and other insulation materials are other potential sources of dissolved Ca that could 

react with TSP to form calcium phosphate. No visible precipitates were observed in the Test 2 

fluid, which had TSP but no CalSil. The measured Ca levels suggest that some calcium 

phosphate may have formed. Rapid formation of calcium phosphate precipitate may be 

especially detrimental because NPSH margins are typically at a minimum near the switchover to 

ECCS recirculation. 

In the plant, the recirculated water is cooled by heat exchangers (e.g., shutdown cooling HX in 

CE plants, RHR or RHR + CS HXs in Westinghouse plants or decay heat coolers in B&W 

plants) The lower temperature in terms of solubility or reaction kinetics can affect formation of a 

precipitate product. Therefore, the temperature-cycling effect by heat exchangers on 

precipitation may need to be further investigated; it was partially investigated by ANL work 

(Bahn et al., 2008b) suggesting that the rapid thermal cycling does not appear to affect chemical 

precipitation. 

The initial aluminum precipitation product is amorphous. Eventually, it will transform to the more 

stable, much less soluble, crystalline form. The crystalline form is much less soluble than the 

amorphous form, and any portion of the precipitate that is transformed would be much less likely 

to redissolve at higher temperatures. However, it is noted that this transformation would take 

time, depending on temperature and solution chemistry. 

The ICET results show that solution chemistries observed in complex multicomponent 

environments are not always consistent with those predicted on the basis of tests in simpler 

environments. Levels of dissolved silica in Test 1 are much lower than would be predicted from 

tests on fiberglass in solutions with comparable pH value (NUREG/CR-6873). Aluminum in 

solution inhibits the dissolution of fiberglass. Low levels of dissolved aluminum in Tests 3 and 4 

provide strong evidence for the potential for passivation of aluminum in solutions with large 
5-147

amounts of Si in solution. In this respect, the large amount of CalSil in the ICET tests is nonconservative. Westinghouse Electric data reported in WCAP-16530-NP (Lane et al., 2006) 

indicate a 75 ppm threshold silica inhibition level for passivation, with a marked decrease in 

aluminum corrosion at a 50 ppm concentration. Aluminum phosphates are also highly insoluble, 

making phosphates a candidate inhibitor (if no CalSil is present) (Lane et al., 2006). 

Passivation also occurred in Tests 1 and 5 after 15 to 20 days. At the low levels of dissolved 

silica in these tests (≈ 8 ppm), it is not clear whether the mechanism of passivation in these 

tests was in any way related to the formation of aluminum silicates. It is also not clear how to 

“credit” passivation in such environments based on the various ratios of aluminum surface area, 

fiberglass volume, pH, other materials, etc. When passivation occurs, use of the average 

corrosion rate over the whole test period gives non-conservative estimates of the amount of 

corrosion that will occur during active dissolution, before the material becomes passivated. 

5.9.3 ICET Aluminum Chemistry

5.9.3.1 Bench-Scale Experiments

The report NUREG/CR-6915 describes the results of an extensive literature search and benchscale experiments that were performed to gain a better understanding of the corrosion of 

aluminum and the formation of precipitation products in environments similar to ICET Test 1 and 

ICET Test 5. It also includes results from a comprehensive examination of both the test 

solutions and precipitates from these two tests. The precipitates were visually examined by 

using both scanning electron microscopy (SEM) and TEM. Supplemental analytical 

measurements were performed with XRD, NMR (both liquid and solid state), and light 

scattering.

5.9.3.2 Summary of Important Results

The precipitates that form as the ICET 1 and 5 solutions cool are agglomerations of nanometersized particles. The size of the agglomerations grows with time. The precipitate is highly 

hydrated, consisting of about 90% water by mass.

The XRD and TEM analyses of the precipitates of ICET 1 and 5 indicate that the precipitates 

were largely composed of amorphous aluminum hydroxide, with a substantial quantity of boron 

adsorbed onto the surface, although the XRD refinement revealed pseudoboehmite, poorly 

crystalline boehmite (AlOOH). Figure 5.9-7 shows TEM micrographs of precipitates formed at 

room temperature in ICET Test 1 solution, suggesting that the constituent particle size is about 

10 nm. The amorphous form is to be expected because of the high concentration of anions in 

the solution; such high concentrations of anions are known to retard crystallization at 

temperatures below 60°C. Also, as discussed in the report NUREG/CR-6915, earlier literature 

showed that the crystallographic phase of aluminum hydroxide precipitation in alkaline solution 

depends on a degree of supersaturation; this is further discussed in an ANL letter report in 

terms of aluminum solubility in alkaline solution (Bahn et al., 2009a). Chemical analysis results 

indicate that up to 35% of the boron from the initial solution may have been adsorbed onto the 

amorphous aluminum hydroxide precipitate. The NMR measurements showed complexation 

between aluminum and boron. This finding corroborates the hypothesis that complexation was 

responsible for impeding the crystallization of aluminum compounds.
5-148

(a) (b)

Figure 5.9-7. TEM Micrographs of (a) Day-15 and (b) Day-30 Filtered Test Sample from 

ICET 1 Solution (NUREG/CR-6915).

Figure 5.9-8 shows the particle size distributions for the aged and precipitated ICET Test 1 

solution at room temperature. As indicated in Figure 5.9-7, the size distribution suggests that 

the precipitates are highly agglomerated. To evaluate the possibility that tiny and colloidal 

particles were present in the ICET Test 1 solution at 60°C, surrogates were prepared by adding 

aluminum coupon into NaOH/boron solution. As shown in Figure 5.9-9, light scattering 

measurements of particle sizes in surrogate solutions simulating ICET Test 1 showed that they 

contain particles with a bimodal size distribution peaking at ≈30 and ≈500 nm. However, this 

result suggests that nanometer-sized aluminum hydroxide precipitates can be formed in 

NaOH/boron solution at 60°C within a relatively short time. The report also states that 

precipitates were noted at 60°C in the surrogate solution after several weeks. Thus, although at 

60°C and pH 9.6, the estimated solubility limit for amorphous aluminum hydroxide is much 

higher than ≈375 mg/L, the solution may contain colloidal and tiny particles dispersed in solution 

rather than only aluminate ions (Al(OH)4–). In acidic solutions, aluminum in solution can exist 

as Al3+, AlOH2+, and Al(OH)4+. In alkaline solutions, aluminate ions (Al(OH) 4–) are the only 

stable form of aluminum. The solubility is a function of the solid hydroxide phase present 

(amorphous or crystalline) and increases with pH in alkaline solutions. The presence of some 

organics and inorganics can increase the aluminum solubility. Solubility can also be affected by 

the particle size presented in the solution.

A review of the literature shows that sodium silicates are effective inhibitors of corrosion of 

aluminum, with an inhibition efficiency of almost 100%. The inhibition is due to the formation of 

an amorphous aluminosilicate film on the metal surface. Microstructural analysis performed on 

the Test 1 and 4 aluminum coupons indicate that the major components are aluminum, oxygen, 

silicon, sodium, and calcium, with small amounts of carbon and magnesium. Silica was present 

to a much larger degree in ICET Test 4 than in Test 1. Thus, in ICET Test 4, the corrosion of 

aluminum was inhibited by the dissolution of calcium silicate. 

A bench-scale test was performed to provide a direct comparison between aluminum corrosion 

in a boric acid/NaOH solution and a boric acid/NaOH with silicates. The silicate addition 

produced virtually instantaneous passivation of the aluminum, and no measurable corrosion 

could be detected. The concentration of the silicate inhibitor is cited as 88.7 mg/L, but it is not 

clear whether this is the concentration of Si or silica (SiO2). 
5-149

Figure 5.9-8. Particle Size 

Distribution for Test 1 

Solution at Room 

Temperature after 4-Month 

Aging (NUREG/CR-6915).

Figure 5.9-9. Particle Size 

Distributions for 

Aluminum/Boron Metal 

Dissolution Surrogate 

Solution at 60°C after 8 hr 

(NUREG/CR-6915).

5.9.3.3 Summary and Discussion

The amorphous forms of Al(OH)3 are more highly hydrated than the crystalline forms. The rate 

of transformation to the more crystalline form is controlled by the rate at which hydroxyl anions 

replace water in the amorphous solid. This may mean that per mole of aluminum, an 

amorphous precipitate may be more effective in producing head loss than a crystalline 

precipitate. Because aluminum in solution exists in different forms in acidic and alkaline 

solutions, it is not clear that the process for producing surrogates such as outlined in WCAP16530-NP (Lane et al., 2006), which starts from an acid solution, will produce precipitates 

comparable to those that could potentially form in an alkaline sump environment (NUREG/CR6915). An ANL letter report showed that the crystal phase of aluminum hydroxide surrogate by 

WCAP-16530-NP appears amorphous with weak indication of poorly crystalline bayerite (Shack, 

2007).

The presence of silicon in solution can lead to inhibition of the corrosion of aluminum. The large 

amount of CalSil in ICET-4 probably produced a concentration of dissolved Si that was not 

representative of what would be found in the post-LOCA environment. Passivation needs to be 

demonstrated for conditions representative of plant-specific conditions. 
5-150

Complete inhibition of aluminum corrosion was demonstrated in a bench test with a 

concentration of silicate inhibitor at 88.7 mg/L. This finding is in reasonable agreement with 

WCAP-16785-NP values (Reid et al., 2007). 

Because aluminum hydroxide precipitates in NaOH/boron solution can exist as colloids, the 

aluminum content of a solution is not a complete measure of the likelihood of precipitate 

formation as a solution is cooled. Although the aluminum concentration in ICET Test 1 remained 

relatively constant from Day 15 to Day 30, precipitates formed much more readily as the 

solution cooled during the later part of the test. 

5.9.4 ANL Head Loss Testing

5.9.4.1 Overview

A test loop was constructed at ANL to study the effects of the chemical products observed in the 

ICET tests on head loss (NUREG/CR-6913). This study considered the effect of head loss at a 

CalSil loading of 19 g/L (ICET 3), along with much lower CalSil loadings lower (0.5 g/L and 

less), which would be more representative of most plant situations.

Most tests in the ICET 3 environments were integrated, and the chemical products were formed 

by the dissolution of calcium silicate insulation reacting with dissolved trisodium phosphate 

(TSP) buffer in the test loop water In the ICET 1 and 5 environments, surrogate chemical 

products were used. Use of the surrogate forms was justified by comparisons with the 

chemistry and other physical characteristics, such as the amorphous structure of the products 

formed in the integral ICET. 

A diagram of the ANL test loop is shown in Figure 5.9-10. Piping in most of the loop is 

chlorinated polyvinyl chloride (CPVC); the clear test section containing the test strainer was 

either LEXAN or clear polyvinyl chloride (PVC). LEXAN has better high-temperature strength; 

PVC is more resistant to NaOH solutions. The heater and cooler sections are stainless steel. 

During operation, temperatures around the loop are typically ±0.6°C (1°F). Loop velocities can 

be controlled over the range from 0.02 to 2 ft/s. The inside diameters of the LEXAN and PVC 

sections are 6.5 and 5.625 in., respectively. Fluid volume in the loop is 119 L (4.2 ft3). At 0.1 

ft/s, the transit time around the loop is about 4 min. The sump strainer in these tests is a flat 

perforated plate; two different perforated plates have been used. Differential pressure 

transducers measure the differential pressures across the strainer and bed.

In scaling the results from the ANL test facility, the mass of chemical product and physical 

debris per unit area of strainer should be considered. The mass of chemical product produced 

scales with fluid volume, while the potential for head loss is characterized by the product mass 

per unit strainer area. A 15 g loading of debris in the LEXAN section corresponds to a loading 

of 0.7 kg/m2. To maintain the same loading per unit area in the PVC section requires 11.5 g of 

debris.

Physical debris and chemicals are introduced to the loop through a charging port at the top of 

the loop. The horizontal configuration of the strainer is not intended to reflect a realistic strainer 

configuration, but rather to permit the development of uniform beds with well defined 

characteristics. Head loss behavior for such beds may not characterize the local head loss 

behavior of more complex, non-uniform beds that might form on realistic strainer geometries.
5-151

In the basic test procedure, the test loop was filled with deionized water and heated to 54°C 

(130°F). Boric acid, LiOH, and a pH control chemical (NaOH, TSP, or STB) were added to 

reach desired concentrations and pH. The loop was held at temperature overnight to deaerate 

the liquid. NUKON and CalSil were used to create the physical debris bed. The insulation 

materials were added as slurries. The NUKON was shredded and processed in a blender; the 

CalSil was ground with a mortar and pestle. Liquid was added to form a slurry. In some cases, 

the slurry was held at temperature for a time before being added to the loop. Pressure drop 

across the bed, flow velocity, and temperature were monitored continuously. In ICET 1 

environments, aluminum nitrate solutions were added to the loop after the physical debris was 

formed. The pressure drop across the bed before addition of the aluminum nitrate solution 

provided a baseline value for pressure drop without chemical effects. In the ICET Test 3 

environments, tests were run without TSP additions to get baseline values for the pressure drop 

due to the physical debris alone.

Figure 5.9-10. Schematic Diagram of ANL Test Loop (NUREG/CR-6913).

5.9.4.2 Solution Chemistry

A series of tests (ICET-3-1 to ICET-3-11) was performed to evaluate the potential for head loss 

due to chemical effects in a TSP-buffered environment. Test conditions are summarized in 

Table 5.9-5. The tests were designed to explore conditions corresponding to a range of debris 

amounts, containment sump residence times, and TSP dissolution times. The two basic 

physical parameters that are affected by these variables are the degree of CalSil dissolution that 

will occur before the formation of the debris bed, and the interaction between the chemical 

products and the physical debris during bed formation. Unlike the ICET-3 integrated test

(NUREG/CR-6914), these tests have excess phosphate available, i.e., the amount of calcium 
5-152

phosphate that can form is limited by the amount of calcium available from dissolution of the 

CalSil.

Benchtop, small-scale dissolution tests of CalSil were performed to identify the potential effects 

of the TSP dissolution rate on the dissolution of CalSil and the subsequent formation of calcium 

phosphate precipitates. Three different histories of TSP addition were studied, with the intention 

of encompassing the range of histories of TSP dissolution expected within an actual 

containment sump:

1 Add TSP before CalSil addition (instantaneous dissolution of TSP).

2 Titrate TSP over 1-hr period into solution after CalSil addition (nominal case).

3 Titrate TSP over 4-hr period into solution after CalSil addition 

(very slow addition of TSP).

Surrogate solutions for ICET-1 environments were developed using aluminum nitrate, 

Al(NO3)3·9H2O. Because in ICET-1 the solutions arise from the dissolution of aluminum in a 

basic solution containing boric acid, the surrogate solutions were prepared by dissolving 

commercial aluminum nitrate, Al(NO3)3·9H2O, powder in a base solution containing 2800 ppm 

B added as boric acid, 0.7 ppm Li as LiOH, and NaOH sufficient to reach a pH of 9.6. 

Aluminum hydroxides, nominally Al(OH)3, make up the principal chemical product with potential 

to cause head loss observed in ICET-1 and -5 environments. Detailed characterization of the 

products formed in ICET Test 1 showed that they are most likely amorphous (NUREG/CR6915). 

Samples of surrogate solutions containing 100, 200, and 375 ppm Al form precipitates at room 

temperature. The precipitates are too fine and too dilute for direct measurement of structure. 

However, when samples were taken through heating and cooling cycles, the sediments would 

redissolve at high temperatures. This finding, together with measurements of the Al level in the 

supernate, suggests that solubility behavior is similar to that expected for amorphous Al(OH)3, 

which suggests that the sediments are amorphous or at least act like amorphous Al(OH)3.

The tests performed in ICET-1- and ICET-5-like environments are summarized in Table 5.9-5. 

For the ICET-1 environments, the dissolved Al levels ranged from 100 to 375 ppm. For the 

ICET-5 environment where the pH is lower, a dissolved Al level of 50 ppm was used (for the 

final portion of this test, this value was raised to 100 ppm).

5.9.4.3 Precipitation

Significant effects on head loss due to chemical products were observed in environments with 

CalSil and TSP buffer (ICET-3) and in environments with significant dissolved aluminum and 

NaOH for pH control (ICET-1). 

In ICET-3 environments, the head losses associated with purely physical debris beds of 

NUKON and CalSil are generally much lower than those that occur across debris beds in which 

some of the CalSil has been replaced with a corresponding amount of calcium phosphate 

precipitate. For a thin NUKON bed (≈3 mm), very large pressure drops were observed for the 

lowest tested CalSil loading, 0.47 kg/m2. However, with thicker NUKON beds (≈12 mm), little 

chemical effect could be observed for CalSil loadings ≤ 0.47 kg/m2. These results show that 

the relationship between head loss and fiber loading for a given particulate loading is highly 

nonlinear and not monotonic. Beds in which no NUKON was present were also examined. In 
5-153

this case, a significant portion of the strainer remains open for the highest strainer loading of 

CalSil tested, 1.2 kg/m2. The pressure drops are very low with this open area.

The dissolution of CalSil and, hence, formation of calcium phosphate would be retarded if all 

TSP could be dissolved before the CalSil addition (i.e., simulating instantaneous TSP 

dissolution). However, even with instantaneous TSP dissolution, the equivalent dissolved Ca 

will exceed 75 mg/L after a few hours for CalSil concentrations as low as 0.5 g/L. Such an 

equivalent dissolved Ca concentration was shown to produce pressure drops on the order of 5 

psi at an approach velocity of 0.1 ft/s across a 0.71 kg/m2 NUKON debris bed.

Amorphous aluminum hydroxides in the ICET-1 environment can have significant effects on 

pressure drop. Pressure drops much greater than would be expected from corresponding 

debris beds in an inert environment have been observed in environments with NaOH buffer for 

dissolved Al levels of 375 and 100 ppm. These high pressure drops can occur with no visible 

precipitates.

Table 5.9-5. Conditions for Head Loss Tests in ICET-3 Environment (NUREG/CR-6913)

Test ID NUKO

N (g)a

Cal

Sil 

(g)

30 

min 

Preso

ak

TSPb

Addition

al 

dissolve

d Ca 

(ppm)

Comment

ICET-3-1 15 15 No Initially in 

loop 200 Simulates initial conditions in ICET-3; precipitates arrive after bed forms

ICET-3-2 15 15 No Initially in 

loop

10, 25, 

50 ppm 

Cad

Parametric test starting with 1/20th 

dissolved Ca of ICET-3: precipitates 

arrive after bed forms

ICET-3-4 7 25 Yes

1/8th 

initially in 

loop; 7/8th 

metered in

None

Minimal CalSil dissolution before initial 

bed formation; continued dissolution as 

test continues

ICET-3-5 7 25 Yes None None Baseline physical debris only

ICET-3-6 15 15 Yes

1/8th 

initially in 

loop; 7/8th 

metered in

None Minimal CalSil dissolution before initial 

bed formation

ICET-3-7 15 15 Yes None None Baseline physical debris only

ICET-3-8 15 0 No Initially in 

loop 43.5c

CaCl2 and NUKON added 

simultaneously; maximum CalSil 

dissolution before bed formation

ICET-3-9 15 0 No Initially in 

loop

9, 18, 

27 ppm 

Cad

CaCl2 added after NUKON bed 

stabilizes; maximizes arrival time of 

precipitates to bed; maximum CalSil 

dissolution before arrival at the bed

ICET-3-10 15 15 Yes

1⁄2 metered 

presoak; 1⁄2 

metered

None

Intended to represent a “typical” 

degree of CalSil dissolution before bed 

formation

ICET-3-11 Replicates ICET-3-7

ICET-3-12 15 5

1⁄2 metered 

presoak; 1⁄2 

metered

None Lower CalSil loading

ICET-3-13 15 5 Yes None None Baseline for ICET-3-12
5-154

ICET-3-14 ICET-3-7 & 11

ICET-3-15 15 10 Yes None None Baseline physical debris only

ICET-3-16-

A1 15 10 Yes

1⁄2 metered 

presoak; 1⁄2 

metered

None Lower CalSil loading

ICET-3-17-

A1 Replicates ICET-3-10

ICET-3-18-

A1 5 10 Yes

1⁄2 metered 

presoak; 1⁄2 

metered

None Thinner NUKON bed

ICET-3-19-

A2 - 25 Yes

1⁄2 metered 

presoak; 1⁄2 

metered

None CalSil/calcium phosphate precipitate 

only debris

a

1 g of debris corresponds to a strainer loading of 47.6 g/m2. b

The total amount of TSP in each test where TSP was added was always 3.4 g/L. Some fraction was 

either dissolved initially in the test loop or metered in during the presoak period. The remaining fraction 

was metered in during a 30-60 min period after the debris was added to the loop. c

Calcium equivalent to full dissolution of 15 g CalSil.

d Calcium additions made incrementally to sequentially reach values of dissolved Ca listed.

Table 5.9-6. Summary of ICET-1 Head Loss Tests with NaOH and STB (NRC, 2008c)

Test ID Description Test 

Section

Strainer

ICET-1-3 NUKON 15.0 g; NaOH; 375 ppm Al A 1

ICET-1-1-

B2_100ppm

NUKON 15.0 g; NaOH; 100 ppm Al B 2

ICET-1-2-

B2_200ppm

NUKON 11.6 g, NaOH; 200 ppm Al B 2

ICET-1-3-

B2_375ppm

NUKON 11.6 g, NaOH; 375 ppm Al B 2

ICET-1-1-

B2_100ppm repeat

NUKON 11.5 g, NaOH; 100 ppm Al B 2

ICET-1-1-

B2_100ppm repeat 

2

NUKON 11.5 g, NaOH; 100 ppm Al B 2

ICET-5-1-

B2_042606

NUKON 11.5 g, STB 1248 g; 50 ppm Al B 2

ICET-3-STB1-A2 NUKON 15.0 g; CalSil 15.0 g; STB 1248 g; 

50 ppm Al

A 2

A: LEXAN test section.

B: PVC test section.

1: Perforated plate with 51% flow area and 3/16 in. holes with 1/4 in. staggered centers.

2: Perforated plate with 40% flow area and 1/8 in. holes with 3/16 in. staggered centers.

Sodium tetraborate buffers seem more benign than NaOH or TSP. A submerged aluminum 

area and sump volume that results in a 375 ppm dissolved Al concentration in a NaOH 

environment results in 50 ppm dissolved Al with a sodium tetraborate buffer. No significant 

head loss was observed in a test that lasted ≈11 days with 50-ppm aluminum and a STB buffer. 

A test with a NUKON/CalSil debris mixture and STB buffer produced much lower head losses 

than observed in corresponding tests with TSP, although tests were not performed over the full 

range of CalSil loadings of interest.
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5.9.4.4 Head Loss in ICET Environments

Pressure drops across the bed for tests with physical debris of 15 g NUKON/15 g CalSil and 

TSP present (ICET-3-6 and ICET-3-10) are compared with the baseline test ICET-3-11, which 

had 15 g NUKON/15 g CalSil but no TSP, in Figures 5.9-11a and b, respectively. In ICET-3-6, 

no TSP was added to the presoak to limit the possible dissolution of the CalSil. This scenario 

was intended to give a lower bound for the amount of calcium phosphate precipitate arriving as 

the debris bed is formed. As expected, the initial pressure drop behavior in ICET-3-6 is very 

similar to the baseline case ICET-3-11, in which no chemical precipitates are present (Figure 

5.9-11a). However, a comparison of the maximum pressure drops reached in ICET-3-6 and 

ICET-3-11 shows that the difference in the pressure drop increases with time. The increased 

pressure drop with time in ICET-3-6 is attributed to the continuing dissolution of CalSil and 

additional formation of calcium phosphate precipitates.

In Test ICET-3-10, some TSP was added during the presoak. This test was intended to give a 

more “typical” amount of calcium phosphate precipitate arriving as the debris bed is formed. 

This results in a much more rapid increase in head loss than in ICET-3-6 (Figure 5.9-11b), 

although the pressure drop in ICET-3-6 eventually approaches the steady-state value obtained 

in ICET-3-10. Pressure drop across a 15 g NUKON bed at 0.1 ft/s is about 0.2 psi. With the 

addition of 15 g of CalSil, but no chemical reaction, the pressure drop at 0.1 ft/s is about 1.2 psi. 

With the addition of TSP, pressure drop across the bed increases to greater than 5 psi even 

though the velocity decreases to less than 0.05 ft/s.

The degree of dissolution that would occur before the debris reached the sump strainer in a 

prototypical situation would presumably be bounded by the ICET-3-6 and ICET-3-8 limiting 

cases, and may be most similar to the ICET-3-10 case. The test results suggest that variability 

in the degree of CalSil dissolution is likely to have a relatively small effect on the chemical 

effects of head loss in this system. Differences in debris transport time would probably have a 

much larger effect on the rate at which the pressure drop increases. The actual amount of head 

loss for a plant-specific case is also dependent on many additional factors such as sump 

strainer debris loading, uniformity of the strainer debris loading, propensity for flow bypass (i.e., 

jetting) through the debris bed, debris bed strainer approach velocity, and transport of chemical 

precipitate not addressed in these tests. 

Test ICET-3-18 used debris loading of 5 g NUKON and 10 g CalSil. This resulted in a thin 

debris bed about 3-4 mm thick. The bed approach velocity and differential pressure across the 

strainer as a function of time for test ICET-3-18-A1 are shown in Figure 5.9-12. This test 

resulted in a rapid buildup of head loss. After 10 min, flow velocity could not be maintained at 

0.1 ft/s and gradually decreased. The thinner bed plugged more rapidly than in either ICER-3-

10 or ICET-3-17, which had 15 g NUKON and 15 g CalSil and was about 12 mm thick. This test 

result is consistent with the classic thin bed head loss behavior observed elsewhere (i.e., a thin 

fiber bed that becomes saturated with particulate can result in high head loss).

Test ICET-3-9 was performed with CaCl2 additions. The pressure drop history in ICET-3-9, 

shown in Figure 5.9-13, suggests a strongly nonlinear relationship between the amount of the 

calcium phosphate precipitate and the pressure drop. The first two additions of CaCl2 in ICET3-9 produced relatively small increases in pressure drop. The third addition resulted in a very 

rapid increase in pressure drop. The total inventory of dissolved Ca added in ICET-3-9 is 

equivalent to complete dissolution of 9 g of CalSil or a CalSil loading of 0.4 kg/m2 of strainer. 

However, the results from ICET-18 (Figure 5.9-12) show that the loading that results in high 

pressure drops will also depend on the thickness of the fiber bed.
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A test was also run with debris loading of 25 g CalSil with no NUKON. The 25 g of CalSil used 

in this test corresponds to a strainer loading of 1.2 kg/m2, which is probably conservative for 

most plants after their sump strainers are updated. Although a portion of flow area was blocked 

by the CalSil, a significant portion of the strainer remained open with this loading. The pressure 

drops were very low as expected with a significant open area. It appeared that, even with a 

heavy loading of CalSil, another source of fiber is necessary to form a bed that can trap the 

CalSil particulate and the associated chemical product.

Figure 5.9-11. (a) Bed Approach Velocities and Differential Pressures across the Strainer 

as a Function of Time for (a) Test ICET-3-6 and -11 and (b) Test ICET-3-10 and -11 (15 g 

load = 0.7 kg/m2) (NUREG/CR-6913).
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Figure 5.9-12. Bed Approach Velocity and Differential Pressure across the Strainer as a 

Function of Time for Test ICET-3-18 (NUREG/CR-6913).

Figure 5.9-13. Bed Approach Velocities and Differential Pressures for ICET-3-8 and -9 

(NUREG/CR-6913).

Because the dissolution rate of CalSil is pH dependent (dissolution is more rapid at lower pH), it 

will depend on the rate at which TSP is added to the system. Tests were performed with TSP 

dissolved in the solution before any addition of CalSil (“instantaneous” dissolution of TSP) and 

with TSP metered in over 1-hr and 4-hr periods. The TSP dissolution history had a larger effect 

at a CalSil loading of 1.5 g/L than at 0.5 g/L. It took substantial time (approximately four days) 

to achieve full dissolution for the 1.5 g/L CalSil loading, while dissolution of the 0.5 g/L loading 

appears to be complete within approximately 1-3 days. However, for both CalSil 

concentrations, substantial Ca dissolution (>75 mg/L) has occurred within a few hours 

regardless of the TSP addition rate.

In the head loss loop tests, virtually all the calcium phosphate precipitates that form are 

transported to the bed. In an actual sump, the precipitates can settle before they reach the 

sump strainer. Settling tests were performed to determine settling rates for calcium phosphate 

under conditions with no bulk directional flow. Tests were performed in a settling tower with an 
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effective height of 71.5 cm. The tower was filled with a solution containing LiOH (0.7 ppm Li), 

and boric acid (2800 ppm B), and TSP (3.4 g/L). A CaCl2 solution was then added to the tower. 

The dissolved Ca reacts with the TSP in the solution to form calcium phosphate precipitate. 

The solution is stirred to get a uniform mixture, and then the precipitates are allowed to settle. 

Two different CaCl2 concentrations were tested. One produced a dissolved Ca inventory 

equivalent to 300 ppm, and the other an inventory equivalent to 75 ppm. The 300 ppm 

inventory is roughly equivalent to full stoichiometric dissolution of a 1 g/L concentration of CalSil;

the 75 ppm inventory is roughly equivalent to full stoichiometric dissolution of a 0.25 g/L 

concentration of CalSil. The settling rate was dependent on concentration. For the 75 ppm 

calcium test, which is more representative of the concentrations of interest, the settling velocity 

was estimated to be 0.8 cm/min.

Pressure drops much larger than would be expected from corresponding debris beds in an inert 

environment have been observed in environments with NaOH buffer for dissolved aluminum 

levels of 375 and 100 ppm (ICET-1 and -5 environments). These high pressure drops can 

occur with no visible precipitates. The increases in pressure drops are much larger than those 

expected due to the small changes in bulk fluid properties, like viscosity, for these solutions.

In short-term laboratory testing with surrogate solutions, the kinetics of the formation of chemical 

products can lead to substantial test-to-test variability. Both tests with 375 ppm dissolved Al 

concentrations resulted in large pressure drops. No high head losses were observed in two 

short (8-10 hr) tests with 100 and 200 ppm Al in solution, respectively. However, two longer (6-

8 day) tests with 100 ppm Al did result in large pressure drops. The pressure drop history in 

one of these tests (ICET-1-1-B2) is shown in Figure 5.9-14.

Samples of the solutions from all the loop tests formed emulsions that settled to the bottom of 

the sample containers when allowed to remain at room temperature for some time. 

Measurements were made with ICP/AES to determine the Al content of the clear supernate 

solutions above the emulsions. Although the solutions appeared perfectly clear, this finding 

does not preclude the possibility that some fine precipitates remain. Thus, the measurements 

may somewhat overestimate the solubility of amorphous Al(OH)3 at room temperature and 

nominally pH 9.6 in sump solutions. The measured values were 32-63 ppm. The variability in 

the results is probably due primarily to small variations in pH. Literature estimates of the 

solubility at room temperature give values of 37-59 ppm for pH values 9.4-9.6, which are 

consistent with the results from the loop tests.

The observation that the solutions in the head loss loop can remain supersaturated for a 

substantial period is consistent with results from ICET 1 (NUREG/CR-6914). Although the 

concentration of aluminum remained constant over the 10-15 days of the test, precipitates 

formed more rapidly and in greater volume as the solution was cooled as the test progressed.

The head loss test in the ICET-5 environment was conducted for ≈11 days. No increase in 

head loss due to precipitate formation was observed. Sodium tetraborate buffers seemed more 

benign than NaOH or TSP. A submerged Al area and sump volume that resulted in a 375 ppm 

dissolved Al concentration in a NaOH environment resulted in a 50 ppm dissolved Al 

concentration with a sodium tetraborate buffer. The 375 ppm concentration resulted in high 

head loss in 0-2 hr. Interaction with NUKON/CalSil debris mixtures produced much lower head 

losses than observed in corresponding tests with TSP, although tests were not performed over 

the full range of CalSil loadings that might be of interest.
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Figure 5.9-14. Pressure and Velocity History in Test ICET-1-1-B2 (100 ppm, repeat 2)

(NUREG/CR-6913).

5.9.4.5 Relationship of ICET to Plant Environments

Although the final level of dissolved Al in ICET 1 was ≈ 375 ppm, actual plant levels of dissolved 

Al for the same environments would “scale” with the amount of Al exposed, which is plant 

specific. In addition, the ICET 1 was run isothermally at a temperature of 60°C (120°F), 

whereas the actual temperatures will vary considerably over the whole course of the accident. 

The amount of Al exposed to the environment depends strongly on whether the sprays are on. 

In most plants, the amount of submerged Al would be a small fraction of the total Al in 

containment. To obtain a better estimate of the range of Al that may be expected in the 

recirculating water, calculations were performed using more realistic thermal histories for 17 

plants for which estimates of the amount of Al in containment were available (NUREG/CR-6914, 

Vol. 1, Appendix C).

The results suggest that the dissolved Al concentration in ICET-1 is conservative, and most 

plants with NaOH buffering would be expected to have dissolved Al concentrations at 30 days 

below 100 ppm. Because of the large amount of aluminum that is exposed to sprays but not 

submerged, one plant, based on the survey results and the preliminary calculations, could have 

a concentration 65 ppm after one day, rising to 80 ppm after 30 days. Although comparable 

time-temperature dissolution history calculations were not performed, the dissolved Al 

concentration in ICET-5 is probably similarly conservative. Based on the corrosion rates 

inferred from ICET-5 and the relative amounts of Al in containment compared to ICET-5, most 

plants with STB buffering would be expected to have dissolved Al concentrations at 30 days 

below 15 ppm.

5.9.4.6 Comments and Observations

Significant effects on head loss due to chemical products were observed in environments with 

CalSil and TSP buffer (ICET-3) and in environments with significant dissolved aluminum and 

NaOH for pH control (ICET-1). 

CalSil dissolves quickly in prototypic environments. The dissolved calcium concentration was 

greater than 75 ppm within a few hours even with 0.5 g/L concentrations of CalSil. 
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Uncertainties in TSP dissolution rates and degree of dissolution of CalSil before bed formation 

have relatively small effects on the dissolution rate of CalSil for CalSil loadings of interest. 

Solubility of calcium phosphate is low over temperature and pH ranges of interest in the sump. 

Thus, precipitate will occur simultaneously with dissolution of CalSil and TSP. Significant 

amounts of precipitate are likely to occur in a relatively short time for TSP plants that have 

sufficient amounts of dissolved calcium in a post-LOCA containment pool. 

Tests with the vertical head loss loop showed that dissolved calcium levels of 10-20 ppm 

(corresponding to 0.03–0.06 g/L of CalSil) had significant increases in head loss due to 

precipitation of calcium phosphate. These test results are consistent with those of WCAP16785-NP (Reid et al., 2007) regarding the highly insoluble nature of calcium phosphate. The 

level of dissolved Ca required for high head loss in environments with TSP depends strongly on 

fiber bed thickness, sump volume, and strainer area. Thin fiber beds (≤3 mm) show a much 

higher head loss. 

If the results from a test facility are scaled up to plant-specific parameters, the mass of chemical 

product and physical debris per unit area of strainer should be considered. The mass of 

chemical product produced should be proportional to the fluid volume while the potential for 

head loss is characterized by the product mass per unit strainer area. Even with a heavy 

loading of CalSil, a source of fiber is necessary to form a bed that can trap the CalSil particulate 

and the associated chemical product. 

The ICET-1 environments gave high losses in tests with Al concentrations down to 100 ppm. 

Post-test measurements suggested that approximately 50 ppm remained in solution at ≈ 75°F, 

pH ≈ 9.6. No visible precipitate was observed in tests with 100 ppm aluminum in solution, even 

though head loss was high. This finding is consistent with results from ICET-1 that precipitates 

are very small. Argonne measurements on filtered/unfiltered solutions in bench tests with 0.2-

μm filters showed no differences in aluminum concentration. The Al(OH)3 precipitates are 

difficult to characterize. 

Results from TEM suggest that precipitates consist of agglomerations of ~10 nm constituent 

particles. ANL measurements gave 19 μm without ultrasonic deflocculation and 2 μm with 

deflocculation, which is consistent with the LANL observations of agglomerates. High hydration 

of products increases effectiveness in plugging of debris bed formed on the strainer. The 

kinetics of Al(OH)3 precipitation are complex. Solutions can maintain a significant amount of 

supersaturation for significant amounts of time (days), and then a relatively rapid increase in 

head loss can occur. The behavior of precipitated aluminum in ANL loop tests and in ICET-1 is 

consistent with an ongoing process of nucleation and growth of products too small to be 

detected visually. In these tests, a large amount of aluminum was removed from solution (more 

than 50 ppm). Subsequent ANL conducted tests with WCAP-16530 AlOOH surrogate product, 

corresponding to 5 ppm aluminum in solution, also showed high head loss (Bahn et al., 2007). 

However, a loop test with a STB buffer suggested somewhat large amounts of product (10–30 

ppm) were required to get high head loss.

Although all the tests were run with a standard thickness of NUKON bed, it is expected that the 

level of dissolved aluminum required for high head loss is expected to depend strongly on fiber 

bed thickness, sump volume, and strainer area. Thin fiber beds could produce a much higher 

head loss for the same mass of chemical product than a thicker bed. 

Head loss tests in the ICET-5 environment showed no measurable increase in head loss due to 

chemical effects with 50 ppm dissolved Al for tests of 12-20 days. An increase of dissolved 
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aluminum to 100 ppm resulted in high head loss. A test with a NUKON/CalSil + STB resulted in 

a head loss characteristic of NUKON/CalSil without chemical effects. The head loss slowly 

decreased with time consistent with dissolution of the CalSil (thus reducing its effectiveness as 

a physical particulate) with no formation of a precipitate product (at a concentration of CalSil of 

0.12 g/L). 

5.9.5 Thermodynamic Modeling 

5.9.5.1 Thermodynamic Simulation Studies

A study was initiated before the ICET program to determine the need for a pressurized test loop 

for ICETs (NUREG/CR-6873). In addition, to assess whether gelatinous products could form 

following a LOCA, gain insights into important parameters, and attempt to predict the ICET 

results, this study performed computer-based thermodynamic simulations of chemical effects. 

The report NUREG/CR-6873 documents the results of experiments to determine corrosion rates 

for metals and leaching rates for concrete and fiberglass, which were used as input parameters 

to the thermodynamic model. Based on the measured corrosion rates, estimated exposed 

surface area, and exposure time, the thermodynamic simulations indicated that the formation of 

dominant solid phases was controlled by the presence of NUKON, aluminum, and concrete. 

The predicted dominant solid phases consisted of potentially amorphous silicate phases such 

as sodium aluminum silicate (NaAlSi3O8), calcium magnesium silicate (Ca2Mg5Si8O22(OH)2), 

calcium silicate (CaSiO3), and silica (SiO2). The formation of NaAlSi3O8 in the presence of 

alkaline solutions could lead to gel formation, which could result in clogging of debris-loaded 

sump pump suction strainers. The thermodynamic simulations indicated that, in alkaline 

simulated containment water at pH 10, corrosion product formation does not differ as hightemperature and -pressure conditions during the initial stages of a LOCA event approach 

steady-state atmospheric pressure conditions, which could support the validity of ICETs without 

a pressurized water loop. 

This study provided initial understanding of the evolution of solution chemistry and possible solid 

phases. However, as identified in the report, there were assumptions and simplifications to the 

thermodynamic model. One simplification is that the model does not consider reaction kinetics, 

which is a common weak point of thermodynamic equilibrium modeling. Another weak point is 

that the modeling results such as chemical speciation entirely rely on what kinds of information 

are included in the code database, for example, the reaction equilibrium constant (K) as a 

function of temperature. In this study StreamAnalyzer© Version 1.2 was used. The modeling 

results need to be benchmarked by one simulation program with those by another 

thermodynamic program, which might contain a different thermodynamic database or 

experimental observations. For this purpose, a follow-on study to compare simulation results 

with ICET observations was conducted by the same authors. The follow-on work was 

documented in a separate NUREG report, as described in the following section.

5.9.5.2 Commercial Simulation Codes

To gain insights into important test parameters and develop the predictive capability of ICET 

results, the NRC initiated a study to evaluate the feasibility of utilizing commercially available 

thermodynamic simulation computer codes to predict the formation of chemical species in a 

typical post-LOCA PWR containment environment (NUREG/CR-6912). As an initial step, not 

only OLI Systems StreamAnalyzer, which had been used in the previous work (NUREG/CR6873), but also three other computer codes were used: EQ3/6, PHEEQC, and Geochemist’s 

Workbench REACT. After the code comparison exercise, three of the codes, EQ3/6, OLI 
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Systems StreamAnalyzer, and PHEEQC were further examined in more detail. The simulations 

by three codes were benchmarked to the ICET experiments, corresponding to five 

representative post-LOCA environments at 60°C (140°F) for times up to 720 hr. After a couple 

of trial predictions, a complete set of blind and informed predictions was attempted using a 

single modeling program, PHEEQC, which provided modeling advantages in terms of its 

flexibility in suppressing the precipitation of specified solids and the ease with which its 

thermodynamic database could be modified. The authors tried to simulate the evolution of 

water chemistry over a 30-day period by dividing the time into multiple steps and at each step 

providing different input data based on corrosion/release rates for each element. Because the 

corrosion/release rates were predetermined and constant over the time period, the code could 

not address properly the time-dependent effect observed in ICETs, such as inhibition effect or 

metal surface passivation, which led to the decrease of the corrosion/release rates.

Results of this study demonstrated that thermodynamic simulation modeling software is broadly 

useful in assessing the potential effects of post-LOCA interaction on sump strainer blockage. 

However, its predictive capability is often hindered by insufficient thermodynamic data for 

relevant phases and aqueous species in the code database, as well as limitations in the kinetic 

data for dissolution of reactive materials in the presence of co-dissolving materials. Based on 

those findings, this study provides some insights for predicting what would happen in 

environments outside ICET tests, although the modeling alone is insufficient to make blind 

predictions with confidence. When thermodynamic simulations were refined using ICET data 

and experimental observations, the predictions broadly agreed with experimental results. 

Overall, prediction of chemical byproduct concentrations and species is most accurate when the 

analytical models are properly benchmarked with experimental data. 

5.9.6 Peer Review of Chemical Effects Studies

The chemical-effects peer review assessment process and a summary of its significant findings 

are discussed in NUREG-1861. Each peer reviewer was asked to provide an individual 

evaluation, based on his or her particular area of expertise. The research projects addressed 

by the peer review included ICET and ICET-follow-up testing and analysis conducted at LANL 

(NUREG/CR-6914, -6915) chemical speciation prediction conducted through the Center for 

Nuclear Waste Regulatory Analyses (CNWRA) at SwRI (NUREG/CR-6873 and NUREG/CR6912), and accelerated chemical-effects head loss testing conducted at ANL (NUREG/CR6913). The chemical-effects peer review evaluated the technical adequacy and uncertainty 

associated with the NRC-sponsored research results, and identified outstanding chemical 

effects issues. Subsequent to the peer review assessment, ANL conducted additional testing 

on chemical effects (Bahn et al., 2007, 2008a, 2008b, 2008c, 2008d, 2009). One head loss test 

was also conducted with in-situ corrosion of aluminum coupon instead of adding chemical 

chemical precipitates (Bahn et al., 2008c), as has been recommended by the peer review.

5.9.6.1 Integrated Chemical Effect Tests

The review focused on a predetermined set of ICET-related technical questions. Those 

questions and the related responses from the peer reviewers are summarized as follows:

Question 1: Have the principal sump pool variables, which affect chemical byproduct 

formation environment, been adequately simulated?

Response: The majority of the reviewers agree that the types of materials that are present in 

PWR containments have been appropriately selected. They also stated that the 

concentrations of chemicals used during the operation of a PWR are 
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approximately in the range of anticipated chemical concentrations. The 

reviewers also noted that other chemical constituents have not been simulated, 

the analysis lacks consideration of redox effects and radiolysis, and the tests did 

not adequately model the steep cyclic temperature transients of recirculating 

coolant or the hot fuel cladding and pressure vessel surfaces. 

Question 2: Many ICET variables were held constant during the experiments. How would 

changes in the most important constant variables affect chemical product 

formation?

Response: In general, the reviewers suggest comprehensive evaluation of the physical, 

chemical, and mineralogical properties of the observed precipitates during the 

experiments, along with detailed evaluation of all of the data to better understand 

the effects of chemical product formation. Some of the reviewers suggest that 

temperature has a significant effect on solubility and the types of compounds that 

will form. They recognize temperature as a difficult aspect to model and 

recommend further work.

Question 3: What variables or materials not simulated by the ICET testing may have the most 

impact on chemical product formation (e.g., coatings, free insulation, flow through 

sediment and other materials on sump strainer, and galvanic effects), and how 

should their effect be characterized by testing or by analysis?

Response: In general, the reviewers think that field visits to operating PWR facilities could 

unearth limitations or omissions not otherwise anticipated. Considerations from 

the reviewers are diverse and are summarized as follows:

• A failure to control or monitor CO2 uptake, which could deviate significantly from the 

actual post-LOCA environment in a PWR

• Presence of suspended solids from the RCS and how they could change their chemical 

form

• Effects of organic coatings to estimate the quantities of coatings involved, their 

properties, and the secondary effects of radiation and hydrothermal reactions (reactions 

with hot water) on the organic materials

• Effects of high- and low-temperature heat transfer surfaces on collection and dissolution 

of solid phases to determine the importance of surface deposition

• Effect of liquid coming into contact with fuel in the reactor vessel to understand heat and 

radiolytic effects

• Effects of silica in the water storage systems and RCS on the total mass of material 

precipitating

• Simulation of the production of hydrogen peroxide (1-20 2, to determine redox potential) 

and nitric acid (HNO3, lowers the pH of the solution)

Question 4: Were the methods used within the ICET program to characterize and analyze 

chemical byproducts sufficient?

Response: The reviewers agree that the methods used within the ICET program were not 

sufficient to characterize and analyze chemical byproducts. Much more serious 

work needs to be done to characterize the physical, chemical, and mineralogical 

properties of the precipitates and coatings as a basis for subsequent conceptual 

and computer modeling. Some XRD and TEM work was performed during the 

course of ICET or during follow-up work, but in general, the tests should have

incorporated the following analytical techniques as part of their standard analysis:
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• Particle size distribution (PSD)

• Fourier transform infrared spectroscopy (FTIR)

• X-ray diffraction (XRD)

• Transmission electron microscopy (TEM)

5.9.6.2 ANL Head Loss Testing

The review focused on a predetermined set of technical questions related to chemical effects 

head loss testing. Those questions and the related responses from the peer reviewers are 

summarized as follows:

Question 1: Is the accelerated head loss testing approach viable for evaluating the effects of 

multiple chemical environments quickly?

Response: The majority of the reviewers agree that the current head loss testing facility is 

insufficiently flexible for evaluation of multiple chemical environments or 

replication of tests to establish reproducibility, and the test loop does not provide 

the same type of stagnant environment that would be encountered in the 

submerged portion of the containment building. Some recommendations are as 

follows:

• Use multiple small bench-scale facilities that could be run simultaneously, with stepped 

variations in critical parameters, so that the sensitivity and magnitude of potentially 

adverse conditions could be rapidly mapped as a function of these parameters.

• A smaller test loop might be designed to model the operation of a vertical strainer, rather 

than the tested perpendicular dead-end strainer.

• A smaller test loop would also allow easier testing at temperatures that vary with time 

and might allow exposed high and low temperature surfaces.

Question 2: What is the best method for incorporating time-dependent effects (e.g., material 

aging, evolving chemical environments) in simulation testing?

Response: The reviewers suggest various methods to incorporate time-dependent effects in 

simulation testing:

• With the variability in individual PWR designs and differing operating histories, there is a 

need to concentrate on the most critical parameters and efficiently study their effects 

though small-scale bench tests. Once the degree of variability and its importance are 

established, small-scale loop and head-loss tests could be conducted on a suitable 

range of variably aged samples. 

• The effect of temperature should be studied through small bench-scale tests, followed by 

limited small-scale loop and head-loss tests. Confirmatory tests using the present 

facilities should be conducted only after assessing the impact of all relevant parameters.

• Kinetic models, coupled with thermodynamic codes, should be considered, making sure 

that the codes accurately simulate radiolysis and redox effects. 

Question 3: What metrics are most appropriate for evaluating the results of simulated 

chemical products with those that formed during the ICET program?

Response: The reviewers identified various metrics for evaluating the results of simulated 

chemical products:
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1 In the filtration/head-loss testing, the aluminum corrosion product was introduced by 

neutralizing aluminum nitrate [AI(N03)3] with sodium hydroxide (NaOH). This method is 

not representative of the way aluminum solids arise in the post-LOCA cooling water 

system. It is proposed that the aluminum be introduced in another manner, either by 

corroding a coupon of aluminum in NaOH or by adding sodium aluminate solution 

[NaAI(OH)4].

2 The testing performed for the ICET program showed the importance of pH, CalSil 

dissolution, borate, aluminum corrosion, phosphate, NUKON fiberglass, and concrete on 

solids formation. The head loss testing could focus on varying these components, plus 

studying the effects of temperature differentials and hot and cold surfaces, to create the 

solids present in the post-LOCA environment.

5.9.6.3 Thermodynamic Modeling

The review focused on a predetermined set of technical questions related to prediction of 

chemical speciation. Those questions and the related responses from the peer reviewers are 

summarized as follows:

Question 1: Is the speciation analysis expected to provide reasonable predictions of chemical 

product formation over a range of possible sump environments? 

Response: The reviewers agree that even though this chemical speciation analysis 

represents a significant improvement over earlier work, it does not exploit 

existing capabilities of the selected codes to their fullest advantage. Specifically, 

two physical effects not modeled were the radiation field from the fuel, and the 

layer of corrosion products on the interior surface of the RCS. The reviewers 

note that concessions had to be made for the seeming lack of CO2 to form lowsolubility carbonates. Reaction rates (kinetics) also are not handled well by the 

modeling software; therefore, the models may not reflect the evolving 

concentration profiles. As the models are refined, they should provide closer 

matching of the observed ICET concentrations, the concentrations observed in 

the supplemental CNWRA testing, and the concentrations in systems not 

replicated in the ICET experiments. In addition, the non-equilibrium 

concentration of radiolysis products (and even species in the absence of 

radiolysis) cannot be addressed by the selected codes.

Question 2: Is the plan for benchmarking these codes using small-scale testing and the ICET 

results appropriate?

Response: The reviewers agree that the plan for benchmarking codes is satisfactory, 

provided that the actual processes are accurately simulated. Some reviewers 

think that the capabilities of the codes currently being used are not being used to 

full advantage and, as a result, the value of the associated experimental studies 

is diminished. In addition, the reviewers note that small-scale testing is a valid 

approach to gain more information, especially on the kinetic and equilibrium 

behaviors of the key solutes and solid phases.

Question 3: What is the most appropriate way to measure the uncertainty associated with 

these codes?

Response: The reviewers suggest various ways to measure the uncertainty associated with 

the codes, noting that it is difficult to measure the overall uncertainty of the output 

of any multi-component chemical simulation, because a large number of 

parameters are involved with widely varying levels of accuracy. First, a 
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sensitivity analysis of empirical or deterministic models is suggested. Second, 

comparison of the code predictions against the results of targeted small-scale 

tests is a feasible way to strengthen the codes and identify and measure their 

uncertainties. Third, the most realistic values should be utilized, and runs should 

be replicated using Monte Carlo methods to determine variations in parameters 

deemed to have the greatest uncertainties and considered to be most critical to 

model output. The cumulative variation in outputs can then be adopted as a 

measure of uncertainty.

5.9.7 Industry Approach to Evaluate Chemical Effects

5.9.7.1 Overview

The Westinghouse report WCAP-16530-NP (Lane et al., 2006) provides a consistent approach 

for plants to evaluate the chemical effects, which may occur post-accident in containment sump 

fluids. The results of this evaluation are intended to provide input on the type and amounts of 

chemical precipitates that may form post-accident. 

Based on containment materials survey for 69 U.S. PWRs, ten material classes were selected 

for dissolution testing at pH values of 4.1, 8.0, and 12.0, in solutions that contained boric acid 

(4400 ppm B) with added TSP, STB, and sodium hydroxide. The dissolution tests were 

conducted at temperatures of 88 and 129°C (190 and 265°F). The dissolution of each element 

from representative materials was estimated by ICP, and precipitation testing was, 

subsequently, conducted by sampling and cooling the dissolution-test solution. The settling 

rates and filterability of precipitates were measured, which provided baseline data for surrogate 

chemical precipitate qualification. The WCAP-16530-NP chemical model was developed based 

on the dissolution testing results. Instructions were provided for preparation of three chemical 

(surrogate) precipitates. 

5.9.7.2 Summary of Important Results

Containment Materials Survey

The containment materials provided on the plant surveys can be divided into fifteen (15) 

material classes based on their chemical composition. Ten of these material classes were 

selected for the dissolution testing, and eleven representative materials were tested, as shown 

in Table 5.9-7.
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Table 5.9-7. Containment Material Classification Summary (from WCAP-16530-NP)

Material Class Materials in Class Representative Material

Aluminum Aluminum alloys, aluminum coatings Aluminum (pure)

Aluminum silicate Cerablanket, FiberFrax Durablanket, Kaowool, MatCeramic, Mineral Fiber, PAROC Mineral Wool FiberFrax Durablanket

Calcium silicate Asbestos, CalSil insulation, Kaylo, Marinite, Mudd, 

Transite, Unibestos CalSil insulation

Carbon Steel All carbon and low alloy steels SA 508 Cl 2

Concrete Concrete Ground Concrete

E-glass Fiberglass insulation, NUKON, Temp-Mat, Foamglas, 

Thermal Wrap

NUKON, Unspecified 

Fiberglass

Amorphous Silica Min-K, Microtherm Min-K

Interam E Class Interam E Class Interam E-5

Mineral wool Min-Wool, Rock Wool Min-Wool

Zinc Galvanized steel, zinc coatings Galvanized Steel

Copper All copper alloys None

Nickel All nickel alloys None

Organic Mastics CP-10, ThermoLag 330-1 None

Other Organics Armaflex, Kool-Phen, Benelex 401, RCP motor oil None

Reactor Coolant 

Oxides Nickel ferrite and other oxides None

Dissolution Testing

Eleven containment materials were dissolution tested: seven insulation materials, plus 

aluminum, zinc, carbon steel, and ground concrete. The total time for the dissolution testing 

was 30, 60, or 90 minutes at either 88 or 129°C (190 or 265°F). 

Elemental analysis was performed using ICP for Al, Fe, Zn P, S, Si, Ti, Mg, and Ca on all 

materials tested. The ionic material of greatest concentration after the equilibration tests was 

aluminum followed by silicon and calcium, as shown in Figure 5.9-15. For this figure, the total 

mass of each element release in the design matrix dissolution tests was calculated by summing 

the releases for all times, temperatures, and pH levels. Released mass of Al increased with 

solution pH. Figure 5.9-16 shows the total mass releases from each tested materials. 

Figure 5.9-15. Comparison of 

Total Mass Released during 

Dissolution Testing by 

Element (Lane et al. 2006).
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Figure 5.9-16. Comparison of 

Total Mass Released from the 

Tested Materials (Lane et al. 

2006).

Precipitation Testing

Precipitation testing was performed following the dissolution testing. The solution from the 

dissolution testing was transferred and cooled down, or the solution was mixed with other pHbuffering agents, such as TSP or sodium tetraborate. Precipitate formed in thirteen of the sixty 

tests performed, and none of the 13 precipitates settled rapidly; thus, all of the precipitates 

would be expected to be transported to the sump strainer. Analysis of the 13 precipitated 

materials with SEM and energy dispersive x-ray spectroscopy (EDS) identified their chemical 

compositions. The “best guess” for the precipitates identified six different types: hydrated 

aluminum oxyhydroxide (AlOOH), sodium aluminum silicate (NaAlSi3O8), calcium aluminum 

silicate, calcium phosphate, sodium calcium aluminum silicate, and Zn2SiO4 (willemite). Among 

them, the major chemical precipitates were determined to be aluminum oxyhydroxide, sodium 

aluminum silicate, and calcium phosphate. The precipitate identification is based on chemical 

composition analysis by SEM/EDS, but any TEM or XRD analysis to characterize 

crystallographic phases was not reported. Therefore, for example, “aluminum oxyhydroxide 

(AlOOH)” in WCAP-16530-NP (Lane et al., 2006) should be considered as a common name for 

the aluminum hydroxide family, including the amorphous phase. Precipitate filterability was also 

assessed, by calculating filter cake coefficients.

Chemical Model

For each chemical species, concentration data generated during dissolution testing at specific 

conditions were used in a regression analysis to develop release rate equations as a function of 

temperature, pH, and the concentration of that species. Release rate equations were 

developed for each predominant containment material for each chemical species. For example, 

different functions were used to calculate calcium release from calcium silicate and concrete. 

Using the WCAP-16530-NP (Lane et al., 2006) chemical model for precipitate formation, CalSil 

dissolution is greatest at pH values between 5.6 and 8.5, and decreases above 8.5. However, 

this is offset by a reverse effect with pH seen by aluminum corrosion. Aluminum release was 

highest at pH 12.0 and lowest at pH 4.1. 

The chemical model conservatively assumes all dissolved aluminum precipitates as hydrated 

AlOOH and/or sodium aluminum silicate and all dissolved calcium in phosphate solutions 

precipitates as calcium phosphate. This assumption appears reasonable for calcium phosphate 
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because of the low solubility but highly conservative for aluminum because ICET 1 and 5 testing 

(NUREG/CR-6914), ANL solubility tests (Bahn et al., 2008b), subsequent Westinghouse 

solubility study (Lane et al., 2006), and other publications suggest that a significant amount of 

dissolved aluminum would not precipitate but may stay dissolved in solution or form extremely 

small-size colloidal particles, which would not induce head loss across the debris bed on the 

sump strainer. 

Since corrosion of aluminum resulted in the greatest mass released during the dissolution 

testing, the release rate equation for aluminum incorporated into the chemical model needs to 

be carefully evaluated. Equation 6-2 in WCAP-16530-NP, the expression for aluminum, is a fit 

to a combined data set including ICET 1 average release rate. As shown in Figure 5.9-17, the 

WCAP-16530-NP chemical model underpredicts the aluminum release for the active corrosion 

part of ICET 1. However, since the 30-day total aluminum release is conservative compared 

with ICET 1 and the WCAP-16530-NP chemical model assumes 100% precipitation of released 

aluminum, using this chemical model to estimate the 30-day total mass of chemical precipitates 

for chemical-effects head loss testing appears to be reasonable if the total precipitates are 

added at the beginning of the testing. 

Figure 5.9-17. Aluminum 

Concentrations with Time 

Estimated by WCAP-16530-NP 

Chemical Model in 

Comparison with Actual 

Measured Concentrations in 

ICET 1 (Lane et al. 2008).

The WCAP-16530-NP chemical model assumes that sodium aluminum silicate would precipitate 

first if there is dissolved silicate, and then the remaining aluminum would precipitate as AlOOH, 

which is based on the thermodynamic analysis in NUREG/CR-6873. As discussed in a previous 

section, the thermodynamic analysis suggested sodium aluminum silicate precipitation if 

aluminum, NUKON, and concrete are present together. This analysis might be correct but 

needs to be carefully evaluated because the ICETs did not indicate any formation of sodium 

aluminum silicate precipitate, and thermodynamic modeling is highly dependent on the 

adequacy of its thermodynamic database. However, if the filterability of the sodium aluminum 

silicate is comparable with that of AlOOH, which is claimed in this Westinghouse report, the 

assumption of sodium aluminum silicate formation in the model would be acceptable. 

Comparison of two precipitates in terms of filterability was performed by ANL head loss testing 

and is further discussed in one of the following sections.

The chemical model is based on single effects and does not consider multiple materials effect. 

The ICETs indicated some multiple materials effects, such as Al corrosion inhibition by 

dissolved silicate (ICET 4) and Si release inhibition by dissolved Al (ICET 5). However, the 

ICET Results Compared to Predictions 

Calculated pH Value (No CO2) Used in Modeling

0.0

200.0

400.0

600.0

800.0

1000.0

1200.0

1400.0

0 10 20 30

Days

Al (mg/kg)

WCAP

RAI eq.

ICET 1 Filtered

ICET 1 Unfiltered

From Coupon Mass
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enhancement of release rates by the multiple materials effect was not evidenced. Therefore, 

the chemical model based on single effects appears reasonable.

Surrogate Chemical Precipitate

This Westinghouse report provides instructions on preparing chemical surrogates for three 

major chemical precipitates (AlOOH, sodium aluminum silicate, and calcium phosphate) and 

qualification criteria for the settling rate of these surrogates. If the settling rate is too high, the 

prepared surrogate should not be used in head loss testing. The way to prepare surrogates is 

relatively simple and convenient to follow, but an identification analysis to confirm the 

surrogate’s crystallographic phases was not provided. Rough estimation for surrogate size is 

available, but size distribution measurements in solution are needed, for example, by using a 

laser light scattering method. Argonne letter reports suggest that the AlOOH surrogate in 

WCAP-16530-NP is most likely amorphous (Bahn et al., 2007). 

To prepare AlOOH surrogate, aluminum nitrate is added into water, followed by sodium 

hydroxide. Since in actual post-accident sump conditions aluminum would precipitate in alkaline 

water, it would be more prototypical if sodium hydroxide were added into water first, followed by 

aluminum nitrate. This reverse procedure might raise other issue because of strong caustic 

condition by dissolved sodium hydroxide. As long as the AlOOH surrogate is efficient in 

inducing head loss across the debris bed, this procedural modification may not be necessary. 

Summary and Comments

Important containment material classes were selected on the basis of survey results. Eleven 

representative materials were tested for dissolution and precipitation. From these tests, three 

major chemical precipitates were identified: hydrated AlOOH, sodium aluminum silicate, and 

calcium phosphate. Settling rates and filterability were measured for formed precipitates. 

However, the measurement of filterability, in this study, was not reliable since the model used to 

calculate the filter cake coefficient was determined by calculating a precipitate mass measured 

after drying. These calculations assumed the same degree of hydration between different 

batches of precipitate and between different precipitates. This may not be a valid assumption. 

The chemical model was developed from dissolution testing and can predict total precipitate 

mass during the 30-day mission time under plant-specific conditions. The model assumes that 

all dissolved aluminum would precipitate, and all released calcium would precipitate in 

phosphate solution, which is highly conservative for aluminum precipitation. The WCAP-16530-

NP report provides instructions on preparing each chemical surrogates and qualification criteria 

for the settling rate. The chemical surrogates were poorly characterized in terms of 

crystallographic phases and particle size distributions. However, if these surrogates are highly 

efficient in inducing head loss across the debris bed, detailed surrogate characterization might 

not be necessary. 

5.9.7.3 WCAP-16530 Follow-on Study

Description of Tests and Procedures at CNWRA

The tests in the follow-on study were conducted at CNWRA. These NRC-sponsored tests 

(McMurray and He, 2006) focused on a more detailed evaluation of the dissolution 

characteristics of specific insulation materials and concrete resulting from post-LOCA solutions. 

They also had the objective of attempting to reproduce the results of the Westinghouse tests in 

WCAP-16530-NP (Lane et al., 2006). Original models used by Westinghouse assumed that 
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dissolution rates for the same material classes (e.g., different types of fiberglass insulation) had 

similar dissolution characteristics. The CNWRA tests used different materials (than in the 

Westinghouse tests) from the five insulation classes, recorded their dissolution rates, and then 

compared them to the assumptions made in WCAP-16530-NP. A test was done for a concrete 

coupon in this test. The concrete coupon should be contrasted with a concrete “powder” that 

was used in the WCAP-16530-NP testing regime. The concrete surface area used in this report 

is representative of the upper bound of uncoated concrete in U.S. PWRs. 

Each of the materials was soaked in 4400 ppm boric acid solutions at pH values of 4.1, 8, and 

12 at 265 and 190°F for 90 min. The solutions at pH 8 and 12 were adjusted to their respective 

pH values using NaOH. The test vessels were allowed to cool for approximately 2 hr before 

undertaking chemical and SEM measurements and visual observations of the solutions. 

Additional visual observations of the solutions were made after equilibration at room 

temperature continued for one day and 85 days.

No settled precipitates were visually observed at the end of the cool down phase of the test. 

However the CalSil solutions were cloudy. Only one chemical compound was positively 

identified, Na2CO3 on the surface of the Microtherm material. The exact chemical identity of the 

species creating the cloudy solutions was not ascertained.

Summary of Important Results

The CNWRA tests were a repeat of some of the WCAP-16530-NP methodology tests (Lane et 

al., 2006) and also some new tests to complement these studies. Both groups performed tests 

at the same temperatures and at the same three pH values (4.1, 8.0 and 12.0). We contrast the 

differences results of these tests here.

The first of these differences is the cooling rates afforded to the solutions in contact with the 

simulated containment materials. The Westinghouse methodology maintained the solutions in 

equilibrium with the separate test materials at the test temperature (either 190 or 265°F) while 

performing in-situ filtration through a 0.7 μm filter. The first sets of tests were to determine the 

concentration of various compounds leached from the test materials. Once these samples were 

taken at 0.5, 1.0, and 1.5 hr, another volume of liquid was transferred into settling cones at a 

temperature of 80°F. This second test was to determine the precipitation rate of the cooling 

solutions. These solutions did not have the containment materials in contact with them either 

when sample aliquants were removed or when they were in the cooldown phase. The total 

contact time of the materials with the solutions was 90 min.

In the CNWRA tests the materials were brought to test temperature (either 190 or 265°F) for 90 

min. The cooldown was achieved by equilibration of the sample containers with ambient 

laboratory temperature. These solutions remained in contact with the simulated containment 

materials during the cooldown. The cooldown took approximately two hours, yielding a total 

contact time of the solution with the materials of ≈3.5 hr. At the end of the cooldown period, 

1 mL aliquant was withdrawn through a 0.45 μm filter. The remainder of the leachate solution 

was then decanted from the test vessel and put into separate vessels to observe the settling 

rates at day one and day 85.

The WCAP-16530-NP tests used Teflon containers at 190°F and stainless steel containers at 

265°F, as there were container integrity problems with poly-tetrafluorethylene (PTFE) at 265°F. 

The CNWRA tests were also performed in PTFE vessels at both temperatures andno container 

integrity problems were noted with this material. The WCAP-16530-NP methodology attempted 
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to provide mixing effects by having the reaction vessel placed on a shaker table during the 1.5 

hr equilibration period. Additionally, the WCAP-16530-NP tests fully submerged the materials in 

the solutions at the start of the tests. The CNWRA tests allowed the samples to sink to the 

bottom of the test vessel based on material wetting and gravity. The CNWRA tests also did not 

include any device to enhance mixing or stirring. 

The WCAP-16530-NP methodology employed ground, aged concrete for their tests. The 

CNWRA methodology used solid blocks of concrete. There was no attempt in the SwRI studies 

to use materials identical to the ones in the WCAP studies. In fact, different materials of the 

same insulation class were specifically chosen to see if the tests would bear out the hypothesis 

that all classes of materials in the same insulation type would react the same way. 

No precipitates were observed in any of the test vessels after the 2-hr cooling period. Plantspecific materials were used in all of these solutions. However, the solutions with CalSil were 

cloudy due to the presence of “disaggregation” of the insulation, although there was no visual 

evidence of physical change to the solid material. Following an equilibration period of 85 days, 

none of the solutions had precipitates in them. The CalSil solutions were still cloudy, and the 

only “solid” materials on the bottom were small pieces of the insulation. For the amorphous 

silica class of insulation materials, significant quantities of silica were released from the pH 8 

and 12 solutions vs. the pH 4.1 solutions. For the E-glass classes of insulation materials, 

greater amounts of silica were dissolved at pH 12 than at pH 4.1. For the aluminum silicate 

class of insulation materials, higher concentrations of silica were observed in the pH 12 than in 

the pH 4.1 solutions. The two insulation materials from the aluminum silicate class, Kaowool 

and Durablanket, reacted to the chemical leaching tests the same way. In high pH solutions of 

Microtherm insulation, Na2CO3 formed. It was only found in the pH 12 solution, but the time of 

formation is not known because the hydrated form of the solid is transparent. This compound 

was discovered during the EDS analysis of the Microtherm surface due to the high sodium 

concentration. It was not identified in any of the other solutions. 

Calcium silicate materials demonstrated higher solubilization of calcium at pH 4.1 than pH 8 or 

12, and higher concentrations of potassium and silica at pH 8 and 12 than at pH 4.1. Concrete 

dissolution tests showed that calcium is significantly solubilized at pH 4.1, whereas at pH 12 the 

principal materials solubilized were silica and potassium. All three pH solutions had sulfur 

identified in the ppm range (chemical species was not determined). 

Comments and Observations

Both of the CNWRA and WCAP-16530-NP methodologies (Lane et al., 2006) provide 

information regarding the solution chemistry. The slower cooling in the CNWRA tests better 

represents cooling of a post-LOCA containment pool, while the more rapid cooling in the 

WCAP-16530-NP tests better represents cooling that may occur in an RHR heat exchanger. In 

the WCAP-16530-NP tests, the removal of the containment materials from the solution before 

cooldown is non-conservatem, as it does not represent what happens to the material on the 

sump strainers where the debris will have cooled in the presence of the post-LOCA pool. 

Although materials of the same manufacturer were used for both tests, the materials were not of 

the same production batch. The difference is of some importance, as the insulation is made 

from mined materials with very little chemical treatment to remove natural impurities. These 

impurities would not affect the insulating properties of the material but may make their chemical 

composition slightly different.
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The SEM measurements of the fibers from all the solutions (except Microtherm) after the 

CNWRA test showed no difference with the images of the same materials taken before the test. 

Specifically, SEM observations showed no evidence of dissolution of the material or 

precipitation of other substances. No information on how quickly the turbidity in the solutions 

from CalSil was formed is available in the report with the exception that the cloudy appearance 

of the CalSil solutions was present after the 2-hr cool down and remained even after 85 days. 

These materials were referred to as a “disaggregation” of the bulk insulation and not a 

precipitate. No tests were performed on the filterability of these solutions. No measurements 

were made of pressure drop during the testing period. The chemical tests of the Microtherm 

solution and the SEM of the material indicated that a significant amount of silica had dissolved, 

and an apparent outer layer was formed on the surface of the fibers. Additionally at pH 12, the 

Microtherm had a deposit that was determined by XRD to be Na2CO3. However, it is unclear if 

this material formed during the dry-out of the insulation or if it was formed in situ from solution. 

5.9.7.4 Description of Technical Letter Report on WCAP-16530-NP

This technical letter report (TLR), prepared at ANL (Shack, 2007), reviewed WCAP-16530-NP 

(Lane et al., 2006). It includes some criticisms of the release equations for Al developed in 

WCAP-16530-NP and some comments and observations on the surrogates for Al(OH)3

produced by the procedures described in the report. It also summarizes literature results on the 

solubility of Al(OH)3 in various crystalline and amorphous forms. 

For the most part, the calculations of releases proposed in WCAP-16530-NP seem appropriate. 

The model for calcium release includes a saturation term that is not relevant if phosphate is 

present, but this has little practical effect for the levels of calcium that would be experienced in 

the post-LOCA environment. The release rate models in WCAP-16530-NP are based on “onematerial-at-a-time” dissolution tests and thus may miss important interactions that can occur in 

more complex environments. For example, straightforward application of the silica release 

equation in WCAP-16530-NP would greatly overestimate the release of silica in ICET-1. 

There is excellent agreement between the results of the WCAP-16530-NP aluminum dissolution 

tests and the observed dissolution rate in ICET-1 for days 1–15. However, when comparing 

predictions of the release rate models with data from ICET-1, the average dissolution rate over 

the whole 30 days of the test is used. The recommended Al release model in WCAP-16530-NP 

(Equation 6-2) significantly underestimates releases in ICET-1 over the first 15 days of 

operation (predicted 11.5 mg/L/day and observed 20.8 mg/L/day) and underestimates the 

dissolution data in the tests reported in WCAP-16530-NP. It also underestimates somewhat the 

release rates in ICET-5 (predicted 2.4 mg/L/day and observed 4.1 mg/L/day). 

An alternative release model is given in WCAP-16530-NP (Equation 6-1) that seems to better 

reflect the available data. It should be noted that the coefficients for this equation in Rev. 0 of 

the report are incorrect. Corrected coefficients in the TLR (Shack, 2007) are in excellent 

agreement with the WCAP-16530-NP dissolution data and ICET-1 day 1-15 data. This release 

model seems to over-predict releases in STB environments (predicted 9.4 mg/L/day and 

observed 4.1 mg/L/day). The assumption in WCAP-16530-NP that all dissolved calcium in TSP 

environments forms precipitates is reasonable. The assumption that all dissolved aluminum 

forms precipitates is quite conservative in AI/NaOH and Al/STB environments (ICET-1 and 

ICET-5, respectively). Some crystalline forms of Al(OH)3, such as gibbsite, have very low 

solubilities, but the solubility of amorphous forms in the pH range of interest for sumps is 

significant. However, accurate prediction of solubility limits is difficult since they are sensitive to 
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the choice of the solubility constant and pH. For amorphous materials, literature citations on 

Al/NaOH solubility have values of 14-54 ppm at 25°C and pH 9.5.

Confirmatory tests at ANL showed that the surrogate Al(OH)3 produced by the procedures 

described in WCAP-16530-NP produces very fine precipitates that produce high head loss in 

loop tests. The TLR notes that WCAP-16530-NP does not provide other information, such as 

solubility under changing pH or temperature conditions that might provide information on 

whether the products are crystalline or amorphous. 

Comments and Observations

The report WCAP-16530-NP (Lane et al., 2006) provides useful data/information, especially on 

a wide range of insulation materials not included in ICET. However, care should be taken in 

interpreting the results as they are single-component effects. The study only tests single-effect 

dissolution; in most cases, only one material in the alkaline NaOH/boric acid solution was 

tested. The Equation 6-1 release rate in WCAP-16530-NP (with corrected coefficients) gives 

conservative rates for Al release in all stages of ICET-1 and ICET-5. The Equation 6-2 release 

rate in WCAP-16530-NP (with corrected coefficients) gives non-conservative rates for Al release 

in ICET-1 and ICET-5 before passivation of the aluminum. The assumption in WCAP-16530-NP 

that all dissolved calcium in TSP environments forms precipitates is reasonable. The 

assumption that all dissolved aluminum forms precipitates is quite conservative in AI/NaOH and 

AI/STB environments. 

5.9.7.5 Description of Technical Letter Report on WCAP-16530-NP Surrogates and STB

In the TLR (Bahn et al., 2007), the procedure given in Westinghouse report WCAP-16530-NP 

(Lane et al., 2006) for preparing precipitates representing several insoluble aluminum 

precipitates was used to prepare aluminum oxyhydroxide surrogate product and the properties 

of this product were studied. Only limited characterization of the product was actually 

performed, since a head loss test demonstrated that it is very effective in producing head loss. 

Small-scale tests were also performed to determine the solubility of aluminum in STB solutions 

as a function of temperature at a pH of approximately 8.3. A long-term (35 days) head loss test 

with STB buffer was performed to confirm earlier test results.

The solubility of aluminum in NaOH solutions has been studied extensively. Although the 

crystalline forms such as gibbsite are thermodynamically more stable, experience with ICET-1 

suggests that over the time frames of interest, the solubility is controlled by the formation of 

amorphous products. 

For the pH range of interest the most significant soluble aluminum species is aluminate ion, 

Al(OH)4

-1

. The equilibrium reaction between the solid phase and its supernatant solution is 

given by: 

Al(OH)3 (s) + H2O (aq) → H+ (aq) + Al(OH)4

-1 (aq)

The Al(OH)4

-1 concentration at equilibrium is a function of pH:

log Al(OH)4 – = log K - log H+ = log K + pH

Values of the solubility product constant log K are given by Van Straten et al. (1984) and 

Langmuir (1996) and can be inferred from experiments by ICETs at LANL (NUREG/CR-6915), 
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and ANL bench top and loop tests (NUREG/CR-6913). The data cited in the above research

papers are for aluminum/NaOH systems with no other added chemicals. The data from the 

LANL and ANL tests are for systems with 2800 ppm B and LiOH. The “best estimate” value for 

log K based on experiments in environments containing boron (present as boric acid) is about 

12.2 at room temperature. 

The ICET Test 5 suggests that at a pH of 8.4 the solubility of aluminum in STB solutions is 

about 50 ppm at room temperature (70°F). This value is also consistent with the result of ICET5-1-B2 (the initial ANL loop test with STB buffers), in which no head loss was observed with 50 

ppm after about 12 days of operation at 70°F. These concentrations are much higher than 

suggested by the literature data under these conditions (≈4 ppm), and this anomaly provides 

motivation for the small-scale tests on solubility described WCAP-16530-NP.

Studies on the WCAP-16530-NP Surrogates 

The procedure in WCAP-16530-NP (Lane et al., 2006), in particular the limitations on the 

concentrations and the requirements on the settling rates, does seem effective at producing fine 

precipitates. However, the concentrations in the mixing vessels are still very high compared to 

the concentrations expected in the post-LOCA sump, ANL 100 ppm loop tests, or ICET-1 tests. 

No arguments or data are available to show that they are in any physical sense equivalent to 

the suspensions that would be produced under conditions more representative of those that 

might occur in a post-LOCA sump. Limited X-ray spectra on surrogates similar to those 

developed by the WCAP-16530-NP process suggest that they are most likely amorphous but 

with some indication of crystalline phase.

A head loss test was conducted using the WCAP-16530-NP aluminum oxyhydroxide surrogate. 

The amount of surrogate precipitate added to the test loop would be equivalent to an original 

concentration of aluminum of 5 ppm and that completely precipitated from the 119-liter test loop. 

The pressure increase during the test was extremely rapid, starting just after the few seconds 

necessary for transport of the injected surrogate solid from the mixing tee to the plate with the 

NUKON bed. The pressure drop capacity of the system was exhausted almost immediately. 

No precipitate was visible (≈595 mg was added as solid) in the water approaching the bed, and 

no buildup of precipitate was visible on the bed.

Studies with STB Buffers

Two series of small-scale tests with initial solutions of STB were performed. In the first test 

series, Al(NO3)3 was added periodically to solutions held at constant temperature resulting in 

nominal aluminum concentrations ranging from 10 to 90 ppm. The solutions were carefully 

examined visually for evidence of the formation of precipitates. In the second test series, 

sufficient Al(NO3)3 was added to the solution to cause precipitation and have solid material in 

equilibrium with the supernatant solution. If all the aluminum added would have stayed in 

solution, this condition would have yielded a nominal aluminum concentration of 400 ppm. The 

solutions were then held under isothermal conditions for over 22 days. If the solution reached 

equilibrium with the precipitate during the test, the dissolved aluminum concentration would be 

equal to the solubility of Al(OH)3 under the given conditions.

In the solubility tests at 80°F, visual observation suggested that precipitation began to occur at 

concentrations of aluminum in the range of 55 to 66 ppm. The amount of precipitate at these 

levels was very small and difficult to observe. At levels of 80 ppm and greater, the precipitate 

was easy to see and clearly evident. In the solubility tests at 100°F, visual observation of 
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precipitation was evident at a concentration of 77-80 ppm. Although precipitates were observed 

in the 80°F test at 55-66 ppm of Al, the measured concentration in the supernate increased as 

the nominal concentration was increased. 

This finding suggests that either the kinetics of precipitation is sluggish or the precipitate 

particles are initially smaller than the 0.22 μm filter used to filter the supernate. In the solubility 

tests at 100°F, the increase in the measured concentration as the nominal concentration was 

increased was smaller than in the case of the test at 80°F; this difference may indicate that the 

kinetics of precipitation are faster at the higher temperature.

Precipitation

In the precipitation kinetics tests, all the test solutions were cloudy at the beginning of the tests, 

but the sample at 120°F looked less cloudy than the samples at 80 and 100°F. After 9 days, the 

sediment in 80 and 100°F had largely settled, but the 120°F test was still cloudy with no 

sedimentation. The 120°F test did not show visible sedimentation until 20 days after the test

started. The solution pH was 8.3-8.4 for all the tests. The ICP analysis of samples from the 

tests at the three temperatures shows that after 22 days the solutions had not reached 

equilibrium concentrations.

The tests were shut down after ≈104 days, but unfortunately, the last samples were taken at 22 

days. Because room temperature is not too different from the test temperature for the 80°F test, 

a sample was taken at 134 days from this solution. Since the higher temperature solutions were 

allowed to cool, no long-term data were available. 

Therefore, the concentrations at 100 and 120°F at 134 days were estimated assuming an 

exponential decrease in the supernate concentrations. Figure 5.9-18 plots the measured values 

of aluminum concentration at 22 days for the 80, 100, and 120°F tests, the measured value at 

104 days for the 80°F test, and the extrapolated long-term data for the 100 and 120°F tests as a 

function of temperature. The predicted aluminum solubility based on data in NaOH and boric 

acid solutions is also plotted. The measured results are much higher than the predicted results. 

The reasons for these differences are not clear. Previous small-scale tests with NaOH and 

boric acid at the pH ranges of 9.5-10.0 indicated good agreement with the predicted aluminum 

solubility data (NUREG/CR-6913). 

The predicted results show a monotonic increase of aluminum solubility with increasing 

temperature, but the measured aluminum concentrations in the supernates after 22 days 

showed the highest concentration at the lowest temperature. Rather than a difference in 

solubility, it is likely that the STB solutions can be highly supersaturated at 80°F because the 

precipitation kinetics is slow. For the 100 and 120°F solutions, the kinetics would be faster so 

that the observed aluminum concentration in the supernate could be lower than at 80°F. The 

solubility tests also suggested that the precipitation kinetics is slower at 80°F than at the higher 

temperatures. The processes could also be made more complex by changes in the kinetics of 

the transformation of the precipitates from their initial amorphous form to crystalline forms. 

Because of the slow kinetics, longer-term tests would be needed to get better quantitative 

estimates of aluminum solubility by this approach. 

Since initial head loss tests with STB buffer (NUREG/CR-6913) showed no pressure drop at 50 

ppm dissolved aluminum and a large pressure drop at 100 ppm dissolved aluminum, a second 

head loss test with a STB buffer (ICET-5-2-B2) was performed to evaluate interim 

concentrations. The temperature and pressure history during the test is shown in Figure 5.9-19. 
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The test was run with 50 ppm aluminum at approximately 80°F for ≈ 21 days. No increase in 

pressure drop was observed in the initial test period. After ≈21 days, Al(NO3)3 was added to 

increase the nominal dissolved aluminum concentration to 60 ppm. The test was continued for 

about a day. Then, Al(NO3)3 was added to increase the nominal dissolved aluminum 

concentration to 70 ppm. At this aluminum concentration, a notable pressure increase occurred 

even at 120°F. The pressure drops increased as the temperature was dropped to 100°F and 

then 80°F. The significant increase in pressure drop between 120°F and 80°F with 60 ppm is 

consistent with that expected due to the change in viscosity (≈50 percent). The initial increase 

in pressure drop between 120 and 100°F with 70 ppm (≈20 percent) is also consistent with the 

change in viscosity (≈20 percent). However, the continued increase in pressure drop with time 

at 100°F and 70 ppm is indicative of precipitate formation. The increase in pressure drop as the 

temperature is decreased from 100°F to 80°F (≈30 percent) is consistent with that expected 

from viscosity alone (≈30 percent). The growth in pressure drop with time at 120°F with nominal 

80 ppm Al is clearly faster than with nominal 70 ppm aluminum. The jump in pressure drop as 

the temperature is decreased from 120°F to 100°F with a nominal 80 ppm aluminum (≈40 

percent) is somewhat greater than would be expected from viscosity alone (≈20 percent). The 

jump in pressure drop as the temperature is decreased from 100°F to 80°F with nominal 80 ppm 

aluminum (≈40 percent) is again somewhat greater than would be expected from viscosity alone 

(≈30 percent). The pressure drop increased from ≈0.2 psi at 80°F with a nominal 50 ppm Al to 

1.3 psi with 80 ppm Al, and the difference was still increasing when the test was terminated.

Figure 5.9-18. Measured Al 

Concentration in the Supernate 

after 22 Days from the 80, 100, 

and 120°F Precipitation Kinetics 

Tests, 134-day Extrapolated 

Values, and Predicted Solubility 

(NRC, 2008c).
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Figure 5.9-19. Pressure and Temperature History during Head Loss Test ICET-5-2-B2

(Bahn et al., 2007).

Comments and Observations

The Al(OH)3 surrogate was prepared at ANL according to the WCAP-16530-NP procedure 

(Lane et al., 2006). It was tentatively concluded that the precipitate had a fine crystalline 

structure rather than being truly amorphous. However, regardless of structure, the aluminum 

oxyhydroxide surrogate that was produced was effective in producing head loss. An amount of 

surrogate equivalent to the precipitation of 5 ppm dissolved aluminum resulted in immediate 

blockage of the vertical head loss loop. 

A head loss test with STB (pH ≈8.3) with 50 ppm dissolved aluminum showed no measurable 

head loss increase after 20 days of testing at 80°F. An increase to 70 ppm resulted in the first 

measurable increase in head loss, and an increase to a dissolved aluminum level of 80 ppm 

produced more significant head loss. Tests confirm results seen in an earlier head loss test at 

ANL. The equilibrium solubility limit for aluminum in STB and boric acid solutions with pH ≈ 8.3 

is less than ≈ 50 ppm, but kinetics of precipitation are very sluggish, especially at temperatures 

as low as 80°F.

5.9.7.6 Description of Technical Letter Report on AlOOH and SAS Surrogates

Argonne performed additional testing related to GSI-191 chemical effects as part of technical 

support provided to the NRC (Bahn et al., 2009a). The purpose of these tests was to evaluate 

the properties of chemical precipitates that are used in sump strainer head loss testing by 

certain nuclear industry test vendors. Argonne conducted vertical loop head loss tests to 

evaluate precipitate filterability and bench-type tests and to investigate precipitate 

characteristics such as particle size and settlement rate and solubility. Specific precipitates that 

were evaluated included aluminum oxyhydroxide (AlOOH) and sodium aluminum silicate (SAS) 

prepared according to the WCAP-16530-NP directions (Lane et al., 2006), along with 

precipitates formed from injection of sodium aluminate, calcium chloride, and sodium silicate 

according to the plant-specific test approach. 
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Head Loss Testing

Argonne had previously performed a vertical head loss loop test with the WCAP-16530-NP 

AlOOH precipitate. An additional head loss test using the WCAP-16530-NP AlOOH surrogate 

but at lower concentration was performed. The test confirmed that the surrogate is very 

effective in increasing the head loss across a glass fiber bed. The test result is consistent with 

that of the earlier ANL head loss test with the WCAP-16530-NP surrogate. In the ANL loop, 

only 1.5 ppm Al equivalent of surrogate (29.6 g/m2) can completely plug a glass fiber bed, as 

shown in Figure 5.9-20. 

Figure 5.9-20. Pressure Drop and Strainer Approach Velocity vs. Time in a Loop Test 

using the WCAP16530-NP Aluminum Hydroxide Surrogates (Bahn et al., 2008a).

Tests with the SAS surrogate showed that it is not quite as efficient as the WCAP AlOOH 

surrogate in increasing head loss. At low levels, the SAS surrogate tends to dissolve, especially 

in high purity water. However, in tap water, only 2 ppm Al equivalent SAS surrogate (172 g/m2) 

is needed to generate a significant head loss. Therefore, both surrogates are quite effective in 

the increase of head loss with a glass fiber debris bed. 

Particle Size

The median particle sizes of the WCAP-16530-NP AlOOH surrogates were 13-72 μm, 

depending on the Al concentration in the mixing tank. For the same mixing concentration, the 

particle sizes of the SAS surrogate are larger than those of the AlOOH surrogate. The settling 

rates of the surrogates are strongly dependent on particle size, and the rates are reasonably 

consistent with those expected from Stokes Law or colloid aggregation models. The particle 

size distribution of these surrogates was significantly shifted by ultrasonic vibration (i.e. the size 

became smaller) suggesting that the binding energy between particles in surrogates is relatively 

low so that the flocculated particle can break apart into smaller particles by external forces. 

Compared with the precipitate size formed in the ICET-1 solution at room temperature, the 

WCAP-16530-NP AlOOH surrogates are highly flocculated, but the total Al concentrations are 

different (375 ppm vs. 1000 ppm). The particle size distributions of various surrogates are 

universal, consistent with the predictions of reaction-limited colloid aggregation theory.
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Plant-Specific Approach

Surrogates were also created using the plant-specific procedure. Although aluminum and 

silicate were both added to the solution, the aluminum precipitate formed by the procedure 

probably consisted primarily of aluminum hydroxide, since it would tend to form first in this plantspecific procedure. The characteristics of the precipitates strongly depend on whether in the 

solutions are made using high purity or ordinary tap water and whether silicates are present or 

not. In borated and silicated high purity water the aluminum hydroxide precipitates form 

extremely small particles with sizes of 100-300 nm depending on the total Al concentration. 

These particles are much smaller than the WCAP-16530-NP surrogates. This finding suggests 

that the sodium silicate that is present in the plant-specific procedure could act as a deflocculant 

for the aluminum hydroxide precipitates. In tap water, the aluminum hydroxide precipitates are 

much larger than those formed in the solutions using high purity water, although they are still 

somewhat smaller than the WCAP-16530-NP surrogates. The effect of tap water on precipitate 

size may be attributable to the relatively high ionic strength of tap water due to dissolved cations 

like Ca2+, Mg2+, Na+ and the presence of anions like SO42-

, Cl-, etc. The loop head loss tests 

showed that extremely small aluminum hydroxide precipitates (100-300 nm) produced by using 

borated/silicated high purity water do not cause significant head loss while the 5.7 ppm Al

equivalent of the plant-specific type precipitate made in tap water exhausted the pressure drop 

capacity of the ANL vertical loop. 

5.9.7.7 Description of Technical Letter Report on AlOOH Surrogate Stability at Elevated 

pH

One acceptable method to the NRC staff for conducting chemical effects head loss testing is to 

follow the methodology for creating chemical surrogate material as described in WCAP-16530-

NP (Lane et al., 2006). Many licensees have employed this method. An assumption in WCAP16530 is that the water used in head loss testing remains close to a neutral pH. However, 

during head loss testing, materials such as insulation can leach chemicals that may elevate the 

pH of the water. The NRC staff requested that ANL evaluate the potential impact that elevated 

pH may have on the chemical surrogates created using the WCAP-16530-NP methodology 

(Bahn et al., 2009a).

Bench-scale and loop head loss tests for Al(OH)3 precipitates that can potentially form in sump 

solutions with high levels of dissolved aluminum (Al) have been performed at ANL with 

aluminum oxyhydroxide (AlOOH) surrogates prepared as described in WCAP-16530-NP and 

summarized in a previous section. In previous ANL tests (Bahn et al., 2008a), the 

characteristics of this surrogate were explored only at near neutral water chemistry. The main 

objective of these tests was to evaluate whether or not AlOOH surrogates generated using the 

WCAP-16530-NP procedure are affected by elevated pH.

The stability of the AlOOH surrogate was evaluated by measuring dissolved aluminum 

concentration as a function of time at different pH values. The solubility of the AlOOH surrogate 

in tap water increased with pH. In samples filtered through a 0.02 μm filter, 2.3 ppm Al was 

detected at pH=8.7, while at pH=8.0, the Al concentration was less than the detection limit of 0.5 

ppm. As the solution pH decreased over test time because of carbon dioxide from air, the 

dissolved Al concentration decreased. At pH=9 dissolution occurred rapidly with peak values of 

the dissolved Al found at times less than 4 hr. The dissolution kinetics were somewhat slower 

at pH=8.5. 
5-181

At pH=9.0, the surrogate appears to have a lower solubility in high purity water than in tap 

water, presumably because the higher ionic strength of tap water enhances the Al hydroxide 

solubility.

The surrogates made with tap water followed the reaction-limited-colloid-aggregation theory. 

Although the WCAP-16530-NP AlOOH surrogate particles made with tap water were larger than 

those made with high purity water at the same pH and total Al concentration (2.2 g of AlOOH/L), 

the constituent particle size was smaller than that in high purity water. Reaction-limited-colloidaggregation theory suggests that, although the overall solubility is increased, the higher ionic

strength of tap water may enhance the nucleation of Al hydroxide precipitates.

A vertical-loop head loss test at room temperature with solution pH=9.0 was performed with the 

AlOOH surrogate made with tap water. Figure 5.9-21 shows the pressure drop and flow velocity 

as a function of time. An AlOOH surrogate addition equivalent to the precipitation of 3 ppm Al 

from solution caused a 2.5-psi head loss increase. At this pH and temperature, the head loss 

was very stable over 5 days, even though the bench-scale tests suggest that this amount of Al 

would be soluble under these conditions. In a previous head loss test with the AlOOH surrogate 

at neutral pH, a 1.5 ppm Al equivalent addition was enough to plug the bed. This finding 

suggests that the efficiency of the surrogate on plugging a bed is less at pH=9.0 than at neutral 

pH, as would be expected from the variation of solubility with pH. Dissolution of the AlOOH 

surrogate at an initial solution pH=9.0 to a steady state Al concentration occurred quite rapidly. 

The steady-state concentration was quite stable over time periods on the order of five days. 

After 5 days the solution pH decreased to 8.91. It was further decreased to 7.60 by addition of 

nitric acid. The decrease in pH resulted in an increase in head loss of an additional 3 psi for a 

total head loss of 5.5 psi, but then the head loss gradually decreased and stabilized at 4 psi 

after 2 days. This decrease in head loss was unexpected because of the decreased solubility of 

AlOOH at the lower pH. This result may be due to the higher ionic strength induced by the nitric 

acid addition or the effect of precipitate aging making the precipitates less effective in producing 

head loss or perhaps some debris bed re-distribution over time.

Figure 5.9-21. Pressure Drop Across the NUKON Bed and Approach Velocity as a 

Function of Time for a Vertical-Loop Head Loss Test with Tap Water at Initial pH=9.0 

(Bahn et al., 2009).
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5.9.7.8 Description of WCAP-16785-NP and WCAP-16530-NP Refinement

Description of Tests and Procedures

The chemical dissolution model developed in WCAP-16530-NP (Lane et al., 2006) was 

intended to be generic for all PWRs. In this follow-on report, Westinghouse describes the 

results of tests which further evaluate the inhibition of corrosion in aluminum and aluminum 

alloys in the presence of silicates and phosphates at temperatures of 100 and 200°F. The 

specific areas chosen for testing were silicate and phosphate inhibition of aluminum corrosion, 

the variability in corrosion rates between aluminum alloys, and the solubility of key precipitates 

containing aluminum, silica, and phosphate.

This study uses the generic Westinghouse chemical model and applies to it the ICET program 

parameters to predict the amount of chemical precipitates that will form. This computed result is 

then compared to the results of the ICETs. Task 1 tested the passivation of aluminum corrosion 

by silica (at concentrations of 0, 50, 75, 100, and 125 ppm) at a pH of 8.0 and 200°F. The 

passivation concentration minimum was then tested at various pH values (6.0, 8.0, and 11.0) 

and temperatures (150 and 200°F). This task also tested the effect that silica had on the 

passivation of aluminum in the presence of phosphate. Task 2 tested the corrosion rates of 

various aluminum alloys at pH 8.0. Task 3 measured the passivation of aluminum and its alloys 

by phosphate at pH 8.0 and 200°F. Task 4 measured the solubility of calcium and aluminum 

precipitates at various pH values and temperatures and in the presence of silica.

Summary of Important Results and Conclusions

The WCAP-16530-NP (Lane et al., 2006) investigated the solubility of aluminum silicate, 

aluminum oxyhydroxide, and calcium phosphate precipitates over the range of temperature and 

solution chemistry anticipated in the post-LOCA environment. It also investigated the inhibition 

of corrosion (i.e., passivation) of aluminum metal in environments containing TSP and silica. 

The investigation was focused on aluminum as the major contributor to the ionic content of the 

post-LOCA environment as a result of aluminum corrosion. Aluminum as the major contributor 

to dissolved ionic species following a LOCA is supported by WCAP-16530-NP as well as the 

ICET work documented in NUREG/CR-6914.

All tests were conducted in solutions containing 2500-ppm boron. This was used as the primary 

“test solution.” The range of temperatures and pH conditions tested was selected to bound the 

long-term equilibrium conditions under which the bulk of the material release and subsequent 

precipitate formation occurs.

With this as the test objective, the pH of test solutions was adjusted to the following values: 4.5, 

6.55, 8.0, or 11.0 at the onset of the measurement process. The lowest pH value (pH 4.5) 

occurred in the test solution when a small amount of TSP was added (Task 3). The pH value of 

6.55 was realized when sodium silicate was added such that the silicon concentration was 75 

ppm (Task 1). The pH of ≈8.0 was realized when TSP was added to the solution of boric acid 

(Task 3). The solutions for this test only used TSP for pH adjustment (i.e., no NaOH was added 

to these solutions). For tests of passivation, a separate test solution was adjusted to each of 

the test pH values (using NaOH or TSP), and the temperature was adjusted to either 150 or 

200°F before inserting test coupons. These were used in Tasks 1, 3 and 4.

Task 4 measured the solubility of sodium aluminum silicate, aluminum oxyhydroxide and 

calcium phosphate. In the absence of TSP, with a concentration of 60 ppm aluminum and 178 
5-183

ppm silica, a precipitate formed at both 80 and 140°F at pH 8.0. Solutions containing 99 ppm 

aluminum and 294 ppm silica, with TSP used as a buffer, formed precipitates at pH 8.0 and 

200°F.

Aluminum and silica were added to a solution of 2500 ppm B (pH 8.0 using NaOH) at a 

temperature of 200°F. The precipitate solubility was calculated by incremental additions of the 

aluminum and silica solutions until precipitation occurred. The limit of solubility for NaAlSi3O8 at 

80°F is between 40 and 60 ppm aluminum with 119-178 ppm silica. 

At a solution temperature of 200°F and a maximum aluminum concentration of 98 ppm, no 

precipitates were observed for 30 days at any pH value. No precipitate was observed in the 

140°F test solution at 40 ppm aluminum for up to 30 days at pH 8.0. Solutions of AlOOH just 

below the solubility limit were cycled between 200 and 80°F over a four-day period. No details 

were provided concerning the rate of temperature change during cycling. No precipitation 

occurred. Additionally, the pH was varied from 8.0 to 7.0 and from 8.0 to 9.0 at constant 

temperature (200°F), and no precipitate formation occurred. Calcium phosphate was found to 

be insoluble at all pH, concentrations and temperatures tested. 

The corrosion coupons were immersed for a total of either 12 or 24 hr. Task 1 in this study 

showed the 24-hr corrosion rate of aluminum was lower than the 12-hr corrosion rate of 

aluminum (this is a usual circumstance in corrosion rate measurements) in both solutions 

adjusted with the different buffers. The aluminum corrosion rate decreased over the 

concentration range of 0 to 75 ppm silica from 9.5 mg/m2/min. where it leveled off at <2.0 

mg/m2/min after a 24-hr period.

Similar passivation of aluminum by silica was observed using the same test conditions as above 

with TSP added as the buffer (bringing the solution to pH 8.0). This task also demonstrated that 

the corrosion rate of aluminum in silica solution increased greatly with increasing pH for both 

150 and 200°F tests. 

Task 3 tested the ability of only phosphate to passivate aluminum alloy 1100. At pH 8.0 and at 

200°F, the amount of aluminum dissolved decreased by a factor of 3.6 using TSP. Reductions 

in corrosion were realized at a pH 9.0 as well as at higher temperatures when compared to 

solutions with no phosphates. 

WCAP-16785-NP (Reid et al., 2007) developed an equation for multi-variate aluminum release 

rate for inhibition by silicate and a similar equation for phosphate, which they claim to be valid in 

the pH range of 4.5 to 9.0 and below 200°F. Above pH 9.0, the equation for original aluminum 

release rate should be used. 

Additional tests in Task 1 identified that the Westinghouse model for aluminum corrosion in 

WCAP-16530-NP (Lane et al., 2006) was more conservative than the actual measured 

corrosion rates, evaluated at both temperatures. Task 2 measured the corrosion rates of three 

aluminum alloys: 3003, 5005, and 6061. The corrosion tests were performed for 12 and 24 hr at 

a temperature of 200°F in 2500 ppm boron solution adjusted to pH 8.0 using NaOH. The 

corrosion rates were compared to the rate of aluminum alloy 1100 corrosion. 

The conclusion presented in the WCAP-16530-NP report is that the difference in corrosion rate 

of aluminum alloys (as compared to aluminum metal) under identical conditions as in Task 1 

was negligible. Another conclusion was that, due to the variety of aluminum alloys used in plant 

applications, the net reduction in aluminum-generated precipitates would be low.
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Task 3 tested the passivation of aluminum in TSP-buffered boric acid solution without added 

silica. The aluminum corrosion with silica was one-fifth that without silica. The tests also 

showed a significant decrease in passivation when the TSP solution is brought to pH 9.0. 

Westinghouse again developed a multi-variate equation to model the corrosion as a function of 

pH and temperature. This model, as before, showed that there is significantly less passivation 

from the model than from actual testing. 

Comments and Observations

Additional testing was performed to study TSP and silica inhibition of aluminum corrosion. 

Based on the overall application of inhibition and alloy-specific corrosion rates, it may be 

possible for an individual plant to use these results to demonstrate a lower aluminum release 

rate compared to the WCAP-16530-NP base model (Lane et al., 2006). During corrosion 

testing, however, the aluminum coupons were placed on the bottom of the Erlenmeyer flask. 

This creates a crevice between the flask and coupon over part of the sample, affects the surface 

area of the coupon exposed to the bulk solution, and could introduce variability in results.

The temperatures and pH values at which measurements were made were not exactly the same 

as those of other studies and within this study itself. It was very difficult to make direct 

comparisons of different corrosion rates for aluminum for this reason. As an example the silicate 

inhibition tests were run at 150 and 200°F and at pH values of 6.55, 8.0, and 11.0. The pH of 

6.55 resulted from the addition of basic sodium silicate. Other passivation tests were performed 

at pH 4.5. The pH of all the solutions was measured after precipitation and was at the target pH 

(with the exception of the 6.55 value). This finding indicates that TSP was not the limiting 

reagent in the precipitation reactions. No confirmatory analyses (e.g., XRD) were performed on 

the precipitates. It was assumed that sodium aluminum silicate, aluminum oxyhydroxide, and 

calcium phosphate were the precipitates that formed in those tests, and no others.

As a preliminary effects study, this is a good basis. However, there is a tacit assumption that 

other materials that will be present in the sump environment will have no effect on these 

measurements. Based on the experimental evidence here identifying that the theoretical model 

originally used overestimates the mass of precipitates formed, the assumption of no synergistic 

effects is not justified.

5.9.7.9 Aluminum Chemistry and Aluminum Corrosion Products

Previous ANL head loss tests for Al(OH)3 precipitates that can potentially form in sump solutions 

with high levels of dissolved Al have been performed with surrogates proposed by industry or by 

forming precipitates in situ with Al(NO3)3 as the source of dissolved Al (Bahn et al., 2008c). In a 

post-LOCA environment, the precipitates would be formed in situ with the source of the Al being 

dissolution of Al due to corrosion of Al metal, and NO3– would not likely be present in amounts 

comparable to those encountered when Al(NO3)3 is the source of dissolved Al. The current 

head loss tests were performed with the source of Al being corrosion from Al alloy plates. The 

objective of these tests was to compare head loss associated with precipitate formation from 

aluminum coupon corrosion with those using WCAP-16530-NP precipitates or with precipitates 

formed in situ as a result of chemical injection. 

The head loss tests were performed in the ANL vertical loop with 6061 Al alloy and 

“commercially pure” 1100 Al plates immersed in borated solution. The Al release rate from 

6061 Al alloy in borated water at a pH=9.35 (at room temperature) and 140°F with a flow rate of 
5-185

0.1 ft/sec was similar to predictions based on data from bench-top tests and low-flow rate tests 

with 1100 and 3003 Al alloys. However, the Alloy 1100 corrosion rate was higher than 

predictions based on data from benchtop tests and appears to be flow dependent.

Figure 5.9-22 shows the pressure drop across the debris bed and temperature as a function of 

time. Alloy 6061, when allowed to corrode in a flowing loop, created a significant head loss at 

an Al concentration of 116 ppm with a pH of 9.35 and a temperature of 140°F. An additional 

increase in the head loss was observed when the temperature was lowered from 140 to 80°F. 

Post-test examination revealed that grayish black particles were trapped in the glass fiber bed. 

Stagnant bench-top corrosion tests with Alloy 6061 also showed grayish black particles, which 

were released from the coupon surfaces rather than being generated as a precipitate from the 

solution. Based on microscopic analyses, it was concluded that the grayish black particles were 

intermetallic particles present in the alloy that were released by corrosion of the alloy matrix. 

The intermetallic particles were primarily (FeSiAl) ternary compounds ranging in size from a few 

tenths of a micrometer to 10 μm. The ANL bench-top tests and other loop tests showed that the 

solubility limit for Al(OH)3 at pH=9.35 (at room temperature) and 140°F is significantly greater 

than 116 ppm Al. This result indicates that the head loss at 140°F was induced by the 

intermetallic particles present in the 6061 Al alloy. As the temperature of the loop was 

decreased, additional head loss occurred due to the formation of Al(OH)3 from the decrease in 

temperature (i.e. the dissolved aluminum exceeded its concentration limit at the lower 

temperature). 

Another head loss test was conducted with 1100 Al plates. Figure 5.9-23 shows the pressure 

drop and temperature variation with time. With an Al concentration of 118 ppm in the loop from 

corrosion of 1100 Al plates, no significant increase in head loss was observed at 140°F. Posttest examination for the glass fiber bed and bench-top test results confirmed that Fe-Cu 

enriched intermetallic particles were present in the 1100 Al, which were released and captured 

in the bed during the loop test. The differences in head loss behavior associated with the 

intermetallic particles may be attributed to the sizes of the intermetallic particles in 6061 Al alloy 

being typically larger than those in 1100 Al alloy. At the Al concentration of ≈118 ppm no 

significant increase in head loss was observed in the 1100 Al test until the temperature was 

decreased to 100°F. This increase appeared to be induced by Al hydroxide precipitation, not by 

intermetallic particles. Once the head loss began to increase, a rapid increase in head loss was 

observed, even though the temperature was increased from 100 to 120°F. 
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Figure 5.9-22. Pressure Drop and Loop Water Temperature vs. Time in a Loop Test using 

6061 Al Plates with 2500 ppm B, Initial pH=9.35 Solution, and Temperature of 80°F (Bahn 

et al., 2008c).

Figure 5.9-23. Pressure Drop across the Strainer and Temperature vs. Time in 1100-Al 

Loop Test (Bahn et al., 2008c).

The vertical-loop head loss tests for Al corrosion with 6061 and 1100 Al plates seem to suggest 

somewhat lower solubility than the chemical Al tests. This difference may be due to 

heterogeneous nucleation of Al hydroxide on intermetallic particles and/or on the surfaces of 

preexisting Al hydroxide precipitates. This Al solubility issue is further discussed in a later 

section. The test results suggest that the potential for corrosion of an Al alloy to result in 

increased head loss may depend on its microstructure (i.e., the size distribution and number 

density of intermetallic particles), as well as its Al release rate. 

The increase in head loss due to in situ precipitation of Al(OH)3 observed in these tests seems 

reasonably consistent with that expected from the addition of corresponding amounts of the 

WCAP-16530-NP surrogate. Per unit mass of Al removed from solution, the WCAP-16530-NP 

surrogate appears somewhat more effective in increasing head loss than the Al(OH)3
5-187

precipitates formed in situ by corrosion or chemical addition of Al, and thus it gives conservative 

estimates of the head loss due to the precipitation of a given amount of Al from solution. 

However, in choosing the amount of surrogate that should be used, consideration should be 

given to the potential for additional head losses due to intermetallic particles and the apparent 

reduction in the effective solubility of Al(OH)3 when intermetallic particles are present.

5.9.7.10 Long-Term Al Solubility Test

Long-term Al(OH)3 solubility tests were conducted in solutions containing 2500 ppm B, and 40-

98 ppm Al, using aluminum nitrate or sodium aluminate as the Al source (Bahn et al., 2008b). 

The solution pH values were adjusted to achieve target pH ranging from 7.0 to 8.5. The solution 

temperature was cycled to obtain a temperature history more representative of ECCS 

temperatures during operation in the recirculation mode after a LOCA in a PWR. Figure 5.9-24 

shows the temperature history used in the long-term solubility test. 

Precipitates were observed to form as fine, cloudy suspensions, which showed very little 

tendency to settle; under certain conditions, they formed as flocculated precipitates, which 

appeared on the inner surface of the test flasks. Table 5.9-8 shows the indication of precipitate 

formation under each test condition. The flocculated precipitates had an average diameter of 4-

6 μm. Based on prior ANL head loss tests with surrogates (Bahn et al., 2008a), they would be 

expected to cause significant increases in head loss in glass fiber beds. Very fine precipitates 

associated with the cloudy solutions were less effective at causing head loss in the ANL vertical 

loop with a fiberglass-only bed, but could cause a different head loss response given different 

bed conditions (e.g., in cases where pore sizes are smaller than in fiberglass-only beds). The 

flocculation tendency of the precipitates can be qualitatively explained in terms of ionic strength 

or solution pH based on a colloidal stability theory referred as the Derjaguin, Landau, Verwey 

and Overbeek (DLVO) theory. The effect of solution pH is related to the zeta potential change 

on the particle surface according to this theory, and the effect of the total Al concentration is 

related to the resulting increased particle concentration, which tends to increase flocculation. 

The Westinghouse report WCAP-16785-NP (Reid et al., 2007) also provides 30-day solubility 

data at 140 and 200°F for Al(OH)3. The WCAP-16785-NP estimated that Al hydroxide solubility 

at 140 and 200°F is 40 and 98 ppm, respectively, for pH of 8.0. The Westinghouse tests 

considered limited temperature perturbations, but based on the results in this report from tests 

with increased thermal cycling, these limits still appear to be reasonable. WCAP-16785-NP also 

states that perturbations in pH down to 7.0 did not affect these results. However, those tests in 

which the pH was decreased to 7.0 appear to be short term and were only performed at 200°F 

with 40 ppm Al. The results in this report suggest that the solubility limit at pH=7.0 is less than 

40 ppm, even at 200°F.

The thermal cycling intermittently introduced during the long-term solubility testing did not 

induce rapid precipitation. Thermal cycling did not cause either instantaneous Al hydroxide 

precipitation from clear solution or additional precipitation from already precipitated solution. A 

typical thermal cycling time of 30 min might not be sufficient for incubation of Al hydroxide 

precipitate in the temperature range (60-27°C) of interest. However, this result does not 

necessarily exclude the possibility that precipitation would be enhanced by the thermal cycling 

at a heat exchanger because one ANL loop head loss test showed that the head loss decreased 

but rapidly increased again after the temperature increase from 100 to 120°F. More systematic 

experiments are needed to evaluate this issue. 
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Table 5.9-8. Indication of Precipitate Formation as either a Cloudy Suspension or a 

Flocculate in Test Solutions on Cooling from 200 to 80°F (Bahn et al., 2008b).

Total Al 

Concentration 

(ppm)

Initial Solution pH at Room Temperature Before Adding Al Solution

7.0 7.5 8.0 8.5

98 ●a ● △b NDc

70 ● ● ND ND

55 ● △ ND ND

40 ND △ △ △d

a Solid symbols indicate precipitates were flocculated. 

b Open symbols indicate precipitate was a cloudy suspension and not flocculated.

c ND indicates no test data are available.

d Solution became cloudy after cooling down from 100 to 80°F.

Figure 5.9-24. Typical 

Solution Temperature History 

for the 30-day Al Solubility 

Tests (Bahn et al., 2008b).

5.9.7.11 Aluminum Solubility Curve

A degree of supersaturation of aluminate with respect to aluminum hydroxide having 

crystallographic phase, j, in alkaline environment is given by the equation (Van Straten et al. 

1984)

where and denote the activity of ionic species i and solubility product of aluminum 

hydroxide having crystallographic phase j, respectively. There are several crystalline forms for 

aluminum hydroxide, for example, , pseudoboehmite, boehmite, bayerite, gibbsite and an 

amorphous form. Taking log to the base 10 of the above expression leads to
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In these expressions, p[Al]T denotes the negative log to the base 10 of the activity of aluminate 

ion. The reaction shows that increases with a decrease in pH + p[Al]T; if the solution pH 

increases at a constant aluminum concentration, decreases, and if aluminate ion 

concentration increases at a constant pH, increases. By using the parameter pH + p[Al]T, 

all the test results reported in the ANL long-term solubility tests can be combined in a pH + 

p[Al]T vs. temperature domain (see Figure 5.9-25). In this figure, p[Al]T denotes the negative 

log to the base 10 of the total aluminum content in solution either as dissolved or precipitated 

form in units of mol/kg. At relatively lower concentration, replacing activity with molal 

concentration does not induce a large error. Three distinct regions are revealed: no 

precipitation, non-flocculated precipitation, and flocculated precipitation. Since 

precipitation/non-precipitation was determined by visual observation, extremely fine precipitates 

(<100 nm) might be present in the non-precipitation region. It appears that the boundary of the 

flocculated precipitation region is almost independent of temperature while the boundary 

between the non-flocculated precipitation and no-precipitation regions shows a dependency on 

temperature. 

Figure 5.9-25. Al 

Stability Map in the pH + 

p[Al]T vs. Temperature 

Domain for Solutions 

Containing Boron. Filled 

and open symbols mean 

the occurrence of Al 

hydroxide precipitation 

and no precipitation, 

respectively; pH and 

p[Al]T are the solution 

pH at temperature and 

the negative log to the 

base 10 of the total 

aluminum content as 

dissolved or precipitated 

in units of mol/kg (Bahn 

et al., 2008d).

Since using pH + p[Al]T is a convenient way to display and compare solubility test results 

obtained under various test conditions, previous ANL test results and literature data were 

combined with current long-term solubility test results in Figure 5.9-25. In this figure, the filled 

symbol indicates Al hydroxide precipitation was observed at that test condition, and an open 

symbol indicates Al hydroxide precipitation was not observed. The circle symbols represent the 

ANL long-term solubility test data (Bahn et al., 2008b), including some room-temperature data 

points from the previous ANL report (NUREG/CR-6913). In cases where the precipitates were 

flocculated, a filled square symbol was used. The saturated Al concentrations observed in the 

ICET-1 and -5 (NUREG/CR-6914) are plotted along with the solubility test data at 140 and 
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200°F reported in WCAP-16785-NP (Reid et al., 2007) and the ANL bench-top test data in STB 

solution (Bahn et al., 2007). The previous ANL head loss test data associated with Al hydroxide 

precipitates (NUREG/CR-6913 and Bahn et al., 2008a) including the two Al alloy plate tests 

(Bahn et al., 2008c) are designated by diamond symbols. The boundary between precipitation 

and non-precipitation area appears to be well represented by a straight line that depends on 

solution temperature up to 71°C (160°F). Above 71°C, the dependence of the boundary 

between precipitation and non-precipitation on solution temperature is weaker. The data from 

the loop tests appear to indicate less solubility than bench-scale test data. The loop tests using 

chemical Al sources such as aluminum nitrate are relatively close to the proposed boundary 

shown in Figure 5.9-26. However, two data points obtained from the Al corrosion loop tests at 

49°C are located above the proposed boundary line. 

Based on the solubility data summarized in Figure 5.9-25, bounding estimates of aluminum 

solubility in alkaline environments containing boron were obtained. The Al solubility was 

estimated with and without inclusion of data from the Al corrosion loop tests. The bounding 

curves were drawn based on engineering judgment. 

Because we are interested in alkaline solutions, the chemical form of the dissolved Al is 

Al(OH)4

–

, and p[Al]T can be replaced by –log[Al(OH)4

–

], where log[Al(OH)4

–

] is log to the base 10 

of the molal concentration of Al(OH)4

–

. One mole of Al(OH)4

– has one mole of Al, which is 

equivalent to 26.98 g. 

The upper line in Figure 5.9-25 bounds all data except for the two data points from the Al 

corrosion loop tests and one other data point from another loop test based on chemical 

additions and is given by

where T is the temperature in degrees Fahrenheit. Therefore, the solubility of Al in units of ppm 

can be expressed as:

Estimates of Al solubility as a function of pH and solution temperature based on the above 

expression are shown in Figure 5.9-26. The data in this figure show that the predicted Al 

solubility values form a lower bound on the available solubility data in alkaline solutions 

containing boron, except for the Al corrosion loop tests.

Shifting the solubility estimate upward to bound the two data points from the Al corrosion loop 

tests gives
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The corresponding solubility of Al in units of ppm can be expressed as:

The solubility values based on the above expression are more conservative, i.e., they predict a 

lower value for the amount of Al that can be present before precipitation occurs, shown in Figure 

5.9-27. The data in this figure give a lower bound on all the available solubility data (including 

loop tests) in alkaline solutions. 

Most of the available high temperature (>140°F) data come from long-term Al solubility tests at 

ANL. The test solution was alkaline or near neutral and composed of boric acid and sodium 

hydroxide. Aluminum was added as sodium aluminate. The temperature history was to be 

representative of the temperature of the reactor coolant as it passes through the core, a heat 

exchanger, and the sump after a LOCA. The test durations at higher temperatures (>140°F) are 

short, no more than one day at each temperature. The relatively short test times and the 

presence of boric acid in the test solution should be kept in mind when applying the proposed Al 

solubility curves at relatively high temperatures (>140°F) or in boron-free environments. In a 

boron-free environment the Al solubility may decrease significantly. 

Figure 5.9-26. Al Solubility 

Curves as Functions of pH 

and Temperature without 

Considering Test Data from 

Al Corrosion Loop Tests 

(Bahn et al., 2008d).
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Figure 5.9-27. Al Solubility 

Curves as a Function of pH 

and Temperature with 

Consideration of Test Data 

from Al Corrosion Loop 

Tests (Bahn et al., 2008d).

5.9.7.12 Alternative Buffers

Description of Tests and Procedures

The two most common buffering agents in PWRs are NaOH and TSP. Sodium tetraborate 

(STB) is used in ice condenser plants, although several plants with large dry containments have 

recently switched to STB due to calculated reductions in post-LOCA precipitates with this buffer. 

Both NaOH and TSP can be easily employed as pH control agents for the post-LOCA 

environment. Both form precipitation products in this environment, which can lead to clogging of 

containment sump strainers. The Westinghouse report WCAP-16596-NP (Reid et al., 2006) 

examined the feasibility of using other buffering agents that would not have the deleterious 

effects of strainer clogging. 

The buffering agents that were compared during this testing regime were TSP, sodium 

metaborate (SMB), STB, sodium gluconate (SG), and sodium tripolyphosphate (STPP). The 

stated objectives of the test program were to evaluate selected candidate buffers against the 

following criteria:

• Quantity of material required to adjust pH to target value

• Dissolution rate of the material in water at post-LOCA sump temperatures

• Affordability and ready availability

• Absence of demonstrated deleterious effects, e.g., corrosion to key containment 

structural materials

Other factors evaluated included

• Does not adversely affect the solubility of boric acid or lead to an increase in boric acid 

precipitation on structures.
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• Is resistant to degradation from radiation, elevated temperatures, and humidity, i.e., long 

storage life in the containment environment.

• Is non-hazardous material, i.e., does not create habitability concerns during storage or 

handling.

• Will not cause significant release of metal oxide deposits from the fuel or primary coolant 

system surfaces. 

These objectives were tested using seven steps that attempted to ascertain the properties of the 

buffering agents under a variety of conditions in the post-LOCA environment. The seven steps 

were the following:

1 Dissolution of the buffering agent at 150°F in demineralized water.

2 Adjustment of the pH of boric acid solutions to several different concentrations using the 

buffering agent.

3 Dissolution of the buffering agent at 100°F in 2500 ppm boric acid solution.

4 Assessment of calcium and aluminum effects on a solution containing 2500 ppm boron 

with enough of the buffering agents to bring pH to 8.5.

5 Corrosion test (2 week trial) of the effects of each of the candidate buffer solutions (2500 

ppm boron adjusted to pH 8.0) on pure aluminum and A508 steel (carbon steel).

6 Long-term (30 days) test at elevated (150°F) temperature and 100% or 30% relative 

humidity of candidate buffer solid stability.

7 Solubility stability test with boric acid solutions at boiling by adding each of the candidate 

buffers.

The performance goal for Test 1 on these buffering agents was that the final simulated postLOCA solution would have a pH above 8.0. Although the regulatory position on this issue is that 

the minimum acceptable pH is 7.0, Westinghouse decided to make the requirements for pH 

control more stringent to account for any acidic materials that may form from radiolysis of 

organics (such as cable wrap materials that may contain chlorides) in containment.

Summary of Important Results and Conclusions

Six buffering agents (NaOH, TSP, SMB, SG, STB, and STTP) were identified at the start of this 

project. The important characteristics were solution stability, pH buffering capacity, low 

probability of forming insoluble precipitates or gels, and cost. The overall conclusion was that 

STB is the best alternative to TSP for plants with appreciable calcium-containing materials. 

Buffer TSP is recommended for plants with very little contribution from calcium-containing 

materials. In addition, SMB was identified as a suitable replacement for NaOH, although the 

SMB would need to be in solution due to its solubility characteristics.

Sodium gluconate was eliminated as a possible buffering agent as it did not meet the Test 1 

requirements for final pH. All buffering agents dissolved between two hours and 21 minutes and 

five hours and 20 minutes. As a comparison, the TSP dissolution took place in two hours and 

20 minutes. The buffers TSP, SMB, and STB all used similar mass quantities to achieve pH 

values >8.0 in 2500 ppm boron solutions. Sodium hydroxide took much less, and STPP could 

not achieve a pH of greater than ≈7.5 regardless of mass added. The buffers STB, TSP, SMB 

and STPP all achieved solubility in 2500 ppm boric acid solution at temperatures of 100, 150 

and 200°F, without any precipitation of boric acid. 

All recommended buffers increased the solubility of boric acid. A formal calculation is provided 

to allow plants to accurately estimate the SMB or STB concentration required in the final volume 
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of post-LOCA liquid to achieve an acceptable pH. The buffering agents tested are rated as 

excellent, good, or poor for each of the testing areas and depend upon the environmental 

conditions within the containment building. Table 5.9-9 gives a summary of the results.

Of all the buffering agents tested, TSP caused the least amount of combined corrosion with 

A508 carbon steel and aluminum coupons. Calcium addition to all solutions containing the 

individual buffer in 2500 ppm boron solution yielded a precipitate or suspended floc (except 

NaOH). Aluminum addition to all solutions containing the individual buffer in 2500-ppm boron 

solution yielded a precipitate or suspended floc (except for STPP). Testing at elevated pH 

(initial value of 8.5) and lower concentrations of calcium and aluminum showed that precipitation 

did not occur before threshold values of >177 ppm (STB) or 75 ppm (SMB) for aluminum, and 

>254 ppm for calcium (in both STB and SMB). Values of pH less than 8.0 for SMB and STB 

showed no evidence of precipitation with calcium (of up to 700 ppm Ca). The following 

recommendations were made: STB for use at plants that will have high calcium concentrations 

in the post-LOCA environment, TSP for plants that will have low calcium concentrations in the 

low post-LOCA environment, and SMB as a replacement for sodium hydroxide in any plant that 

currently uses sodium hydroxide. 

The corrosion rates for both aluminum and carbon steel in STPP solution (at pH 7.5) were very 

high relative to other buffering agents. The solution from the carbon steel test was yellow from 

the high level of dissolved Fe ion. 

Table 5.9-9. Summary of Characteristics of Candidate ECCS Buffering Agents 

(Reid et al., 2006) 

Criterion

Buffering Agenta

NaOH TSP STB SMB STPP SG

Precipitate Formation Pb Gc E G E No Data

Quantity required to adjust pH>8.0 E G G E P P

Dissolution Rate N/Ad G G G G G

Affordability/Availability E E E G G G

Corrosiveness G E G G P No Data

Effect on Boric Acid Solubility G G G G G No Data

Environmental Stability G G G G G No Data

Habitability Concern G E G G E E

Oxide/CRUD Release G G G G P P a

E=excellent, G=good, P=poor.

b

NaOH rated P due to elevated Al production.

c

TSP rated P under elevated calcium conditions.

d

NaOH provided as a 50 percent solution.

Comments and Observations

Threshold values for precipitate formation from dissolved aluminum in STB (177 ppm) are 

significantly higher than those observed during longer term bench testing and head loss testing 

at ANL and ICET-5 (about 50 ppm).

The radiolytic stability of the compounds and their solutions was not tested. The two 

recommended buffers, SMB and STB, were not tested under conditions of a radiolytic field. In 
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the presence of gamma radiation sodium metaborate would likely become STB or mono-borate 

anion, although this needs to be tested. 

For Test 1 it is not clear if the dissolution testing was performed under static conditions (i.e., no 

mixing) that would best simulate the effect in containment. Most likely the solution was heated 

by using a hot plate, which would have caused convection currents. In the post-LOCA 

environment, the opposite effect would be occurring because sump water would be cooling 

down (from contact with concrete below the material), and no upward convection would occur. 

Actual simulation of the dissolution based on plant design should be a major consideration in 

the actual testing of any material. If the water is to flow over the solid buffer material, any test 

should also simulate this effect. 

Sodium gluconate is the product of a strong base (sodium hydroxide) and a weak acid (gluconic 

acid). The measured pH for 10 g SG in 1 L of demineralized water was 6.93. The equilibrium 

constant for gluconate anion dissolved in water in equilibrium with gluconic acid is 4 x 10-11, 

which would yield a pH of about 8.1 in demineralized water (O’Neil, 2006). The difference in pH 

indicates that another factor was present in this test that was not considered. 

Test 4 did not add calcium and aluminum together, but separately. Thus, no potential synergic 

effect of the mixture can be assessed from this data. Silica was not used in any of these tests. 

The positive or negative effect of silica or silicates on these test results is unknown. The results 

of the precipitation settling tests and coefficients of filter cake formation tests are reported as: 

“These results do not provide an accurate measure of the precipitate contribution to sump 

strainer head loss.” Thus, there is no quantitative fashion in which these results can be used. 

The Al solubility data in STB are contradicted by ANL work that found that concentrations of 

aluminum at 60-70 ppm yielded precipitate and at 80-100 ppm plugged filters in STB solution. 

While investigating the effects of aluminum concentration on precipitate formation in STB, 

WCAP-16530-NP tests (Lane et al., 2006) showed that the formation of precipitates is 

dependent on the temperature of the solution at the time of the addition of the metal solution. 

Less precipitate was formed when the same amount of dissolved aluminum was added at room 

temperature compared to addition at 60°C. This effect was not studied, so it is not known if this 

is related to precipitation kinetics.

5.9.7.13 Additional Issues on Chemical Effects

Both NRC and industry have sponsored research to provide additional information and develop 

some guidance for evaluating chemical effects (NUREG-1918). The NRC convened an external 

peer review panel to review the NRC-sponsored research and to identify and evaluate additional 

chemical phenomena and issues that were either unresolved or not considered in the original 

NRC-sponsored research.

A phenomena identification and ranking table (PIRT) exercise was conducted to support this 

evaluation in an attempt to fully explore the possible chemical effects that may affect ECCS 

performance during a hypothetical LOCA. The PIRT was not intended to provide a 

comprehensive set of chemical phenomena within the post-LOCA environment. Rather, these 

phenomena should be combined with important findings from past research and informed by 

ongoing research results. 

The PIRT panel identified several significant chemical phenomena. These phenomena pertain 

to the underlying containment pool chemistry; radiological considerations; physical, chemical, 
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and biological debris sources; solid species precipitation; solid species growth and transport;

organics and coatings; and downstream effects. Several of these phenomena may be 

addressed using existing knowledge of chemical effects in combination with an assessment of 

their implications over the range of existing generic or plant-specific post-LOCA conditions. 

Other phenomena may require additional study to understand the chemical effects and their 

relevance before assessing their practical generic or plant-specific implications.

Experimental testing and other studies have been completed to determine the effect of cooling 

water composition, debris sources, and materials corrosion on the nature of the debris, 

presuming no fuel cladding failure. However, ten further topics related to chemical effects were 

identified that deserve additional consideration (NUREG/CR-6988).

The ten topic areas are radiation effects (particularly on material corrosion), differences in 

concrete carbonation between tested systems and existing containment structures, effects of 

alloy variability between tested and actual materials, galvanic corrosion effects, biological 

fouling, co-precipitation, other synergistic solids formation effects, inorganic agglomeration, crud 

release effects (types and quantities), retrograde solubility and solids deposition, and organic 

material impacts. Sufficient data or prior related studies were available to sufficiently address 

some of the questions raised in the 10 topic areas. However, within these ten broad areas, 

topics that merit additional consideration also were identified.

The topic with the greatest perceived influence on ECCS performance is the interactions of 

organic materials (lubricants and coatings) with inorganic solids. The effects of radiolysis on 

redox potential and thus metal corrosion have the next most influence. Of similar influence are 

the effects of biological growth in the post-LOCA system and the impacts of dried borate salts 

on hot fuel cladding and reactor pressure vessel materials. Of lesser, but not insignificant, 

influence are galvanic corrosion, inorganic agglomeration, and crud release effects on 

increasing and altering solids delivered to the post-LOCA coolant. Changes in concrete 

carbonation and differences in alloy corrosion rates were judged to have minor impacts on 

ECCS functionality.

The NRC staff conducted an initial evaluation of phenomena identified by the peer review panel, 

which are summarized in NUREG-1918, and reduced the list to those phenomena that can be 

potential contributors to ECCS performance degradation. The final list is consisted of 41 items 

and tabulated in an NRC evaluation report (NRC, 2011). The NRC staff grouped these 

phenomena into 10 topic areas, which were subsequently evaluated and reported in 

NUREG/CR-6988 by PNNL. A team of NRC staff further evaluated these phenomena using 

existing knowledge and the findings from the industry and NRC-sponsored research. The staff’s 

evaluation of the outstanding issues concluded that the implications of these issues are either 

not generically significant or are appropriately addressed, although several issues associated 

with downstream in-vessel effects remain. The remaining issues are summarized below (NRC, 

2011).

• The deposition of precipitates on reactor fuel and its effects on core cooling

• The effect of physical and chemical debris contained within the core on the ability of the 

coolant to remove heat from the core

• The effect of debris settling on the grid straps to block flow and prevent heat transfer 

from the fuel cladding

• The potential for particulate settling on the grid straps to block flow and prevent heat 

transfer from the fuel cladding
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5.9.8 Summary and Completeness Assessment

Potential chemical effects on the head loss across the debris-loaded sump strainer under a 

post-LOCA condition, raised by ACRS, were experimentally evidenced by small-scale bench 

tests (NUREG-6868), integrated chemical effects tests (NUREG/CR-6914), and vertical loop 

head loss tests (NUREG/CR-6913). Industry’s efforts to address the chemical effects were 

documented in WCAP-16530-NP (Lane et al., 2006). Three main precipitates were identified by 

WCAP-16530-NP: calcium phosphate, aluminum oxyhydroxide, and sodium aluminum silicate. 

The assumption that all released calcium would form precipitates is reasonable. CalSil 

insulation needs to be minimized especially in a plant using TSP buffer, which has already been 

conducted by licensees. The assumption that all released aluminum would form precipitates 

appears highly conservative because ICETs (NUREG/CR-6914 and NUREG/CR-6915), and 

other studies (Bahn et al., 2008b, 2008d, and Reid et al., 2007) suggest substantial solubility of 

aluminum at high temperature and inhibition of aluminum metal corrosion by silicate or 

phosphate. The buffer STB tends to enhance even more the solubility of aluminum 

(NUREG/CR-6914; Bahn et al., 2007; Reid et al., 2006, 2007). This buffer was estimated as a 

good candidate to replace NaOH (Reid et al., 2007).

The WCAP-16530-NP (Lane et al., 2006) is conservative in terms of not only aluminum 

solubility but also filterability of surrogates. The AlOOH and SAS surrogates are quite effective 

in increasing the head loss across the debris-loaded bed and more effective than the 

prototypical aluminum hydroxide precipitates generated by in-situ aluminum corrosion (Bahn et 

al., 2008a, 2008c). The NRC Safety Evaluation of WCAP-16530 (NRC-SER-2007b) also notes 

that some of the conservative assumptions in the WCAP-16530-NP methodology are the basis 

for accepting other chemical effects uncertainties. In the plant-specific surrogate case, 

aluminum hydroxide precipitates were deflocculated by dissolved silicates, which led to fine 

particle size (100-300 nm) and poor filterability by a glass fiber debris bed (Bahn et al. 2008a). 

This result suggests that preparation procedures and test conditions for the chemical surrogates 

different from the one proposed by WCAP-16530-NP (Lane et al., 2006) need to be carefully 

evaluated so that any non-conservatism can be avoided. The NRC Final Safety Evaluation 

Report for WCAP-16530-NP (ML073520891, 2007) notes that some of the conservative 

assumptions in the WCAP-16530-NP methodology are the basis for accepting other chemical 

effects uncertainties.

Modeling efforts to predict possible chemical precipitates formed under a post-LOCA sump 

water condition were documented (NUREG/CR-6873 and NUREG/CR-6912). As discussed in 

other peer-review report (NUREG-1861), thermodynamic modeling is limited by available 

thermodynamic database and cannot predict effects related to reaction kinetics, such as 

aluminum inhibition/passivation. Thermodynamic modeling, therefore, needs to be 

benchmarked by experimental results.

5.10 Downstream Effects

In accordance with Title 10 of the CFR Part 50, Subsection 50.46(b)(5), licensees of domestic 

nuclear power plants are required to provide long-term cooling of the reactor core “after any 

calculated successful initial operation of the ECCS.” Furthermore, the “calculated core 

temperature shall be maintained at an acceptably low value and decay heat shall be removed 

for the extended period of time required by the long-lived radioactivity remaining in the core.” If 

debris collects and clogs or wears components or pathways that support operation of the ECCS 

or CSS, then compliance with this regulation may be affected. In response to this requirement, 

the report “Pressurized Water Reactor Sump Performance Evaluation Methodology” (NEI, 2004) 
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provided the general guidance on evaluating the impact of debris on the ECCS and CSS and 

their components. 

5.10.1 Ex-Vessel Debris Effects

The NEI report provides licensees guidance on evaluating the flowpaths downstream of the 

containment sump for blockage from entrained debris. The guidance specified three issues yet 

to be addressed: (1) blockage of flowpaths in equipment, such as containment spray nozzles 

and tight-clearance valves, (2) wear and abrasion of surfaces, such as pump running surfaces, 

and heat exchanger tubes and orifices, and (3) blockage of flow clearances through fuel 

assemblies. This report identified the starting point for the evaluation to be the flow clearance 

through the sump screen and stated that the flow clearance through the sump screen 

determines the maximum size of particulate debris for downstream analysis. It also stated that 

wear and abrasion of surfaces in the ECCS and CSS should be evaluated based on flow rates 

to which the surfaces will be subjected and the abrasiveness of the ingested debris. The NEI 

report also stated that abrasiveness of debris is plant-specific and therefore should be evaluated 

on a plant-specific basis.

The safety evaluation (SE) of this NEI report by NRC staff (NRC-SER-2004) found that the 

guidance statements did not fully address the potential safety impact of LOCA-generated debris 

on components downstream of the containment sump. In its SE, the NRC staff stated that the 

evaluation of GSI-191 should include a review of the effects of debris on pumps and rotating 

equipment, piping, valves, and heat exchangers downstream of the containment sump related 

to the ECCS and CSS. In particular, any throttle valves installed in the ECCS for flow balancing 

(e.g., HPSI throttle valves) should be evaluated for blockage potential.

The NRC stipulated that the downstream review should first define both long- and short-term 

system-operating lineups, conditions of operation, and mission times. Where more than one 

ECCS or CS configuration is used during long- and short-term operation, each lineup should be 

evaluated with respect to downstream effects.

Evaluations of systems and components are to be based on the flow rates to which the wetted 

surfaces will be subjected and the abrasiveness of the ingested debris. The abrasiveness of the 

debris is plant specific and depends on the site-specific materials that may become latent or 

break-jet-generated debris.

Specific to pumps and rotating equipment, an evaluation should be performed to assess the 

condition and operability of the component during and after its required mission times. 

Consideration should be given to wear and abrasion of surfaces (e.g., pumps running surfaces, 

bushings, and wear rings). Tight clearance components or components where process water is 

used either to lubricate or cool should be identified and evaluated.

Changes in component rotor dynamics and long-term effects on vibrations caused by potential 

wear should be evaluated in the context of pump and rotating equipment operability and 

reliability. The evaluation should include the potential impact on pump internal loads to address 

such concerns as rotor and shaft cracking.

The downstream effects evaluation should also consider system piping, containment spray 

nozzles, and instrumentation tubing. Settling of dust and fines in low-flow/low fluid velocity 

areas may impact system operating characteristics and should be evaluated. The evaluation 
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should include such tubing connections as provided for differential pressure from flow orifices, 

elbow taps, and venturi and reactor vessel/RCS leg connections for reactor vessel level.

Valve and heat exchanger wetted materials should be evaluated for susceptibility to wear, 

surface abrasion, and plugging. Wear may alter the system flow distribution by increasing flow 

down a path (decreased resistance caused by wear), thus starving another critical path. 

Conversely, increased resistance from plugging of a valve opening, orifice, or heat exchanger 

tube may cause wear to occur in another path that experiences increased flow or some flow 

paths to be blocked completely.

Decreased heat exchanger performance resulting from plugging, blocking, plating of slurry 

materials, or tube degradation should be evaluated with respect to hydraulic and heat removal 

capability required by the overall system.

An overall ECCS and CSS evaluation integrating limiting or worst-case pump, valve, piping, and 

heat exchanger conditions should be performed and include the potential for reduced 

pump/system capacity resulting from internal bypass leakage or through external leakage. 

Internal leakage of pumps may be through inter-stage supply and discharge wear rings, shaft 

support, and volute bushings. Piping systems design bypass flow may increase as bypass 

valve openings increase or as flow through a heat exchanger is diverted because of plugging or 

wear. External leakage may occur as a result of leakage through pump seal leak-off lines, from 

the failure of shaft sealing or bearing components, from the failure of valve packing, or through 

leaks from instrument connections and any other potential fluid paths leading to fluid inventory 

loss. Leakage past seals and rings caused by wear from debris fines to areas outside 

containment should be evaluated with respect to fluid inventory, overall accident scenario 

design, and licensing bases environmental and dose consequences.

In response to the NRC guidance, Westinghouse Electric issued WCAP-16406-P, “Evaluation of 

Downstream Sump Debris Effects in Support of GSI-191,” in May 2006.10 The report is intended 

to address the above comments and provide detailed guidance and a consistent approach for 

licensees to evaluate the downstream impact of sump debris on the performance of their ECCS 

and CSS following a LOCA. The report was developed to address the issues identified in both 

the NEI report and the associated NRC SE. 

In December 2007, NRC staff finalized the Safety Evaluation for WCAP-16406-P and 

determined that this report was acceptable for referencing in licensing applications for 

Westinghouse, Combustion Engineering, and Babcock and Wilcox designed PWRs to the 

extent specified and under the limitations delineated in the technical report and the final SE of 

the report (a non-propretary version of the topical report does not exist). 

5.10.2 In-Vessel Debris Effects

The NRC Safety Evaluation on WCAP-16793, Rev. 2 accepted a fibrous debris limit of 15 grams 

per fuel assembly for operating PWRs. Testing demonstrated that in the absence of fibrous 

debris, other types of debris small enough to pass through the ECCS sump strainer did not 

cause a significant head loss. Testing also demonstrated that at some fiber load above 15 

grams, head loss can increase significantly when chemical precipitates are present. For 

 

10The report is proprietary to Westinghouse Electric.
5-200

example, some tests with 20 grams of fiber resulted in relatively high head losses. The NRC 

concluded that at some fiber load above 15 grams that head loss can increase significantly. 

Testing was accomplished using a single, partial height fuel assembly with the core support 

plate modeled in the test rig. The test fuel assemblies consisted of a prototypical inlet nozzle, 

fuel protective filter, and spacer grids (usually 4 or 5 grids), and prototypically sized fuel rods 

and instrument tubes. The assemblies were about one-third full height. Testing was generally 

conducted with room temperature tap water, but some tests were run at about 130°F. Tests 

were run at various flow rates. It was determined that the maximum flow rate resulted in the 

limiting head loss. 

Tests to simulate the fuel response to hot-leg and cold-leg breaks were conducted because 

each condition has different flow conditions and available driving head. The cold-leg break 

condition has a much lower flow rate, but also has less driving head to force coolant into the 

core. It was determined that if a plant meets the hot-leg break fiber limit of 15 grams then the 

cold-leg break will also be acceptable. 

Tests showed that small fibers can become trapped in the spacer grids or fuel filters. These 

fibers are effective at filtering particulate debris and chemical precipitates. If enough fiber 

becomes trapped within a limited volume in the fuel assembly it can capture other debris and 

cause significant head loss. It was observed that the greatest head losses occurred when all or 

most of the debris was trapped at a single elevation within the assembly. 

Fuel assembly testing included Nukon® fiberglass as the fibrous debris and silicon carbide as 

the particulate. The particulate had a nominal diameter of 10 microns. The fiber size 

distribution was based on samples of fibers collected downstream of prototypical strainers 

during testing. Some tests also included microporous type insulation. In these fuel assembly 

tests, microporous insulation behaved similarly to silicon carbide. Aluminum oxyhydroxide 

chemical precipitates (prepared in accordance with WCAP-16530) were added after all 

particulate and fiber debris was added. Tests showed that a relatively small amount of chemical 

surrogate could result in a significant head loss with further additions having little effect. It was 

discovered that the head loss depended on the amount of particulate that was included in the 

test. The particulate to fiber ratio (p/f) was varied. For high flow rate (hot-leg break) cases it 

was determined that a low p/f ratio resulted in the limiting head loss when chemicals were 

added. For lower flow rates (cold-leg break response) a higher p/f ratio resulted in the limiting 

head loss after chemicals were added. Without chemical surrogates added, the p/f ratio that 

results in the highest head loss is different. 

The 15 gram fiber limit, which is applicable to all plants, was determined using the most 

conservative inputs in all areas that were varied during the testing. It is unlikely that the most 

limiting conditions would occur following a LOCA. However, because review of the test program 

identified many uncertainties regarding fuel blockage behavior and a theoretical model for 

blockage behavior has not been developed, the NRC concluded that the limit is appropriate. 

The NRC will review additional information as it becomes available to determine if the limit can 

be increased under plant specific conditions or if the limit should be changed based on updated 

analyses. 

The NRC safety evaluation on WCAP-16793, Rev. 2 contains a number of limitations and 

conditions in Section 4.0 of the document (NRC-SER-2013). 
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5.11 Vendor Head Loss Test Programs

Although the BWR test program occurred prior to the PWR test program, the PWR program is 

discussed first because the PWR tests were more rigorous and the testing included chemical 

effects and particulate insulation materials, such as calcium silicate, thereby providing a more 

complete understanding of the complexities of head loss testing at the onset. Note that the 

PWR program did not depend upon the result of the BWR program.

5.11.1 Strainer Debris Head Loss Testing by PWR Vendors

There were five vendors that supplied large passive replacement strainer to the 69 U.S. PWRs 

for the resolution of GSI-191. These vendors included: (1) Atomic Energy of Canada Limited 

(AECL), (2) General Electric (GE), (3) Performance Contracting Incorporated (PCI), (4) Enercon 

Services, Inc., and (5) Control Component Inc. (CCI). AECL manufactured, tested, and installed 

their strainers. GE conducted head loss testing at Continuum Dynamics Inc. AREVA 

conducted head loss testing for the PCI-manufactured strainers at Alden Research Laboratories 

(ARL). ALION Science and Technology conducted head loss testing on the Enerconmanufactured strainers. CCI conducted the testing on the their strainers with the exception of 

the CCI strainers installed at Arkansas Nuclear One, Units 1 and 2, which were tested by 

Fauske and Associates, LLC. Duke conducted testing for the Enercon strainers installed at 

some of their plants at Wyle Labs. 

The features of the head loss testing that all the strainer vendors have in common include the 

testing of a prototype strainer in a reduced-scale test tank or flume that uses a pump to 

recirculate water through the strainer and tank. The thermal and hydraulic conditions within the 

tank are intended to approach conditions prototypical of the licensee’s sump. The scaling of the 

test strainers is based on maintaining the average screen approach velocity for the test strainer 

module the same as that calculated for the plant strainer. That is, the ratio of test strainer area 

to plant strainer area is used to establish the test pump flow rate to obtain the calculated plant 

approach velocity, and to maintain the same debris amount per unit area between the test and 

the plant. The test strainer prototypes consist of sections, or modules, that are similar to the 

plant strainer designs, but smaller. These reduced scale test strainers maintain key design 

parameters (gap widths, disk dimensions, etc.) of the plant strainer. 

The vendors’ head loss testing programs have commonalities but also substantial differences in 

their respective approaches. All replacement strainers are large passive designs. The vendor 

test procedures evolved during the resolution of GSI-191 as new issues were identified and 

resolved through interactions with the NRC staff.

Typical of all vendors, the test debris quantities are scaled from the plant’s bounding estimates 

of debris predicted to transport to the replacement strainers as determined by the debris 

generation and transport analyses. The scaling from the plant debris loads to the test loads is 

based on the ratio of the effective screen area for the test strainer divided by that of the plant 

replacement strainer. The total replacement strainer screen area is reduced by an area referred 

to as a “sacrificial area,” which accounts for the potential for miscellaneous debris (e.g., tape, 

labels, etc.) to block a portion of the strainer. Sacrificial area is based on an estimation for the 

generation and transport of such debris. The sacrificial are is subtracted from the total strainer 

area resulting in an effective screen area for the accumulation of fibrous and particulate debris. 

During early testing, the preparation of fibrous debris was based on the vendor’s generic debris 

preparation protocol rather than an attempt to match the analytically determined size 

distributions of debris predicted to reach the strainer. Some vendors created finer debris than 
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others. The NRC staff became concerned that some vendors were using non-prototypical 

fibrous debris size distributions in their tests. Staff guidance on fibrous debris size distributions 

for testing was provided to the industry The size distributions for the particulate debris were 

generally based on either the SE-accepted recommendations in the guidance report or plant 

specific data. 

The PWR vendor specific strainer designs and head loss testing procedures are summarized as 

follows

AECL Strainer Design and Testing

The passive AECL Finned StrainersTM consist of perforated corrugated sheets of stainless steel 

welded together to form hollow core fins connected to a common header (NRC, 2006b; NRC,

2007c; NRC, 2007b). The diameter of the perforation holes is typically 1/16 in. and the 

corrugated plate bend angle was 60°. The basic design was modified to create plant-specific 

strainer designs to fit into the individual plant sump. Some fins were shortened to accommodate 

surrounding sump area structures. The water enters the perforated plate surface of each 

strainer “fin” and is collected by a common header for each strainer module. The strainer 

design incorporates orifices designed to force uniformity in the rates of flow across the various 

fins, i.e., the same flow rate through each fin. AECL supplied plant specific designed strainers 

to seven U.S. units.

Tests of prototypical head loss and vortex formation susceptibility were performed with a 

reduced-scale head loss testing apparatus and large-scale prototypical strainer. Tests with the 

reduced-scale head loss loop were performed to determine the thin bed thickness and optimize 

the total surface area and fin pitch for normal debris. In addition, the reduced-scale test loop 

was used to perform chemical-effects and bypass tests. The large-scale test loop was used to 

test strainer prototypes. The reduced-scale test facility consisted of a 90-in.-diameter, open 

plastic tank with a maximum fill height of 56 in. The test strainer was positioned on the floor of 

the tank and was attached to a piping system leading to a pump below the tank. The pump was 

capable of producing a flow rate from 1 to 100 gpm. The large-scale head loss test loop 

consisted of an open lined tank that was 64 in. deep, 8 ft wide, and 19 ft long, and had an 

external piping system connected to a pump; the strainer test module was positioned on the 

floor of the tank. 

The large test loop accommodated a test strainer module that was approximately 1/16 scale, 

based on the screen surface area, with a representative array of full-scale sized fins. The largescale test loop was capable of producing a flow rates from 5 to 3000 gpm. A photograph of an 

AECL large-scale test module is shown in Figure 5.11-1. Plant strainers used the same base fin 

design, but the fin and plenum structures were tailored to the specific plant. Based on the test 

results from the reduced-scale head loss loop, the final strainer module design was tested using 

the large-scale head loss facility to investigate thin-bed and full-debris load head losses. The 

head loss tests were conducted at water temperatures controlled at about 104°F.
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Figure 5.11-1. Photo of AECL 

Large Scale Test Module (NRC, 

2008g, page 39/77)

The AECL testing focused on determining the peak thin-bed head losses by introducing small 

batches of fiber, with the particulate introduced first and then fibrous debris batches added until 

full load objectives were achieved. The test pump was started prior to introducing the 

particulate debris.

AECL used walnut shell flour to simulate coatings and latent particulates based on the rationale 

that the flour’s density of 81 lb/ft3 was close to the typical target coatings density of 94 lb/ft3, 

which would result in a conservative transport to the strainer in the tests. The NRC staff 

accepted the use of walnut shell flour as a surrogate for particulates, even though its particles 

do not phsically represent either coatings particulate or the latent dirt. Walnut shell flour 

particles, which look like little platelets under a microscope, do not well resemble the hardened 

particles of coatings particulates, which look like little rocks. The basis for accepting a nonrepresentative material was that walnut shell flour caused head losses that were either on par or 

conservative relative to the head losses that would be caused by the spherical 10-μm particles 

recommended in the guidance report. In retrospect, walnut shell flour may have been a poor 

surrogate for the coatings particulate because it may cause unrealistically high head losses in 

thin bed formations due to compaction not representative of coatings or latent particles. While 

the measured head losses may have been conservative, the high head losses could cause a 

strainer to unrealistically fail its qualification test. The NRC staff audit report of the suction 

strainer design for Millstone Unit 2 contains a more detailed analysis of the acceptablility of 

walnut shell flour as a coating debris surrogate (NRC, 2007b).

AECL prepared its fibrous debris by first passing the insulation material through a leaf shredder 

and then using a water jet from a pressure washer to further separate the fibers. This process 

generated debris substantially finer than the shredded debris, but only a portion of the 

generated debris truly represented the fines that would prototypically remain suspended in the 

plant sump pool. The adequacy of this debris preparation process can only be gauged by 

comparing the quantity of the debris settling in the test tank to the debris accumulation on the 

strainer. For the audited testing, a majority of such debris introduced into the test tank 

accumulated on the test strainer module. Particulate insulation materials were crushed into 

powder. The test debris was all wetted prior to introduction into the tests.

AECL introduced the debris into their test tank upstream of the strainer in batches consistent 

with determining a peak thin-bed head loss. Mechanical agitation was used near the location of 

the debris introduction to minimize debris settling, and near-field debris settling was reduced to 

acceptable quantities, even though significant fibrous debris settling occurred within the test 
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tank as indicated by the post-test collection of the debris. The settling within the tank could 

have been a concern in situations where the fiber sources were limited and transport of the 

majority of fibers would be needed to attain the bounding head loss. Since the maximum head 

losses for these tests was attained for thin beds, and there was excess fiber available, the 

settling did not adversely affect the results of the tests. The settling of debris such that 

adequate debris is not available to result in the plant’s peak head loss is a potential concern 

with each of the vendor testing programs.

The AECL stability criterion for head loss used to terminate a test was a change of less than 5% 

or 0.1 psi, whichever is greater, and no general steadily increasing trend in pressure within 1.5 

hr. Typically, the minimum number of tank turnovers within 1.5 hours was about 4.5, but the 

testing typically occurred over several days such that the water was visually clearing of 

particulate at termination. Clearing of the water is a good indicator that the tests were conducted 

for an adequately long time before termination. Test head losses were scaled to the plant 

conditions based on the temperature-dependent viscosity.

Once the non-chemical debris beds in the multi-loop test rig had reached a suitably stable head 

loss value, AECL proceeded to introduce chemical debris in batches over an extended period of 

time (ADAMS #ML090410618, 2008). The total duration of the multi-loop rig tests was roughly 

three months. Based on the test results, the licensee recognized that reducing the aluminum 

inventory in containment would be necessary to ensure the conservatism of the limiting 

aluminum concentration assumed for the post-LOCA sump pool. Therefore, aluminum ladders 

were removed from the containment. Since aluminum is an important contributor to chemical 

effects, the NRC staff was interested in comparing the predicted plant-specific aluminum 

release between the AECL method and the WCAP-16530-NP spreadsheet. The licensee 

provided a comparison of aluminum release for the two different methods as a function of pH. 

For a pH of 8.5, which was used to calculate the aluminum release, the AECL method predicted 

a slightly higher aluminum release than the WCAP method.

General Electric Strainer Design and Testing

The GE strainers consist of modules of stacked disks connected via a common header or 

plenum (NRC, 2008a). The disks are constructed of perforated plates. The dimensions and 

number of disks vary with the plant application. The modules can be connected in trains to fit 

plant-specific sumps. The typical perforations in the strainer plate consist of 3/32 in. diameter 

holes. The GE strainer design also incorporates a coarse wire mesh over the strainer surface. 

After water passes through the perforated plates, it flows into the common plenum to the 

recirculation pump suction flowpath. Plant specific strainers were constructed of these disks, 

oriented either vertically or horizontally, and arranged in a manner to fit the plant sump. GE 

supplied plant-specific designed strainers to 11 U.S. units. An example of GE plant strainer is 

shown in Figure 5.11-2.

GE conducted head loss testing with strainer module prototypes in a tank equipped with a 

recirculating pump loop (NRC, 2008a; General Electric, 2007a). Instrumentation included a loop 

flow sensor to monitor the strainer flow rate, a thermocouple to monitor water temperature, a 

differential pressure transducer to measure strainer head loss, and equipment to record these 

measurements. The test tank was sufficiently small with respect to the strainer module that the 

debris settling within the tank was minimized. Debris settling could be reduced with agitation. 

Full debris loads, including those capable of circumscribing the strainer, were tested with the 

prototype strainers. GE testing also included reduced fibrous and particulate loads in varied 
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combinations to determine strainer behavior under different debris loads. Figure 5.11-3 shows 

a photograph of a GE prototype strainer undergoing testing.

Figure 5.11-2. Example 

Plant GE Strainer Design 

(General Electric, 2007a)

Figure 5.11-3. Photograph 

of GE Prototype Test 

Module (General Electric, 

2007a)

In addition, GE conducted small-scale tests in a test loop consisting of a 1250-gal tank that was 

approximately 82 in. diameter and 4.5 ft deep, referred to as “sector tests” because the test 

strainer consisted of a replication of one strainer gap between two disk surfaces, oriented 

horizontally (NRC, 2008a). The bottom of the strainer was located six inches above the tank 

floor. The sector tests were run in two basic modes. Completely stirred tests used agitation to 

maintain the debris in suspension in an attempt to move all debris onto the test strainer. 

Partially stirred tests did not use agitation and, therefore, allowed settling of debris to occur. 

Two variable-speed agitators were used to help prevent settling in the test tank for completely 

stirred tests and to help suspend debris uniformly prior to starting the test strainer flow for 

partially stirred tests. For all tests, a tee in the return line with a valve allowed bypass samples 

to be taken. GE used the sector testing to test debris loads that are insufficient to form a 

circumscribed bed, including thin bed tests.

The GE procedure for preparing fibrous debris evolved from simple shredding toward 

generation of the finer shreds of debris shown in Figure 5.11-4. The improved multiple-pass 
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process created debris that was much finer than the single-pass shredder debris, but still not as 

fine as true prototypical individual fibers. Particulate insulation debris was mechanically 

pulverized into fines for testing.

Figure 5.11-4. Photograph of GE 

Prepared Fibrous Debris (OPPD 

2008)

GE selected suitable test surrogates for plant-specific prototype debris. GE either used the 

specific plant insulations or insulation materials with like properties, such as Transco fibrous 

insulation for NUKON fibrous insulation. GE used Carbo-Zinc to represent the IOZ coating 

debris and ElectroCarb® Black Silicon Carbide as a suffogate for the other types of coating 

debris and for latent particulate; both debris types had a size distribution conservative with 

respect to the guidance report recommendation and SE-accepted value of 10 μm particles. The 

use of Carbo-Zinc for the IOZ coatings debris is acceptable because the source particulate of 

the Carbo-Zinc was actually the base ingredient for the manufacturing of the IOZ paint. The 

silicon carbide density of 94 lb/ft3 would cause the near-field debris settling behavior of the 

surrogate particulate to be prototypical of non-IOZ particulate coating debris because they have 

similar density. The debris samples were weighed, mixed with water in buckets, and poured 

into the test pool. Powders were wetted before introduction.

Prior to the addition of debris to the test loop, the recirculation pump was started, and clean 

head loss was measured. In earlier testing, the recirculation pump was then stopped until the 

debris was added to the test tank (NRC, 2008a). The fiber and particulate debris was added 

into the test loop and kept suspended by agitation until the recirculation pump was started. 

After the recirculation pump was started, head loss data were collected. In addition, bypass 

samples were taken for determination of strainer debris bypass. After it was determined that the 

test head loss termination criteria had been reached, the recirculation pump was stopped, and 

the tank was drained to allow observations of the test article. The NRC staff recommended that 

the pumps be started prior to introducing the debris, and that the particulate be introduced prior 

to the fibrous debris. The circulation of the pumps was intended to uniformly mix the particulate 

in the tank and loop water prior to the accumulation of fibers on the strainer. In later GE testing, 

the fibers were introduced slowly in a multiple batch process after the start of the pumps.
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In some earlier testing, GE introduced debris into their test tank relatively close to the strainer, 

such that the fibrous debris may not have had enough opportunity to disperse before being 

drawn onto the strainer. This practice raised the concern that the location of introduction could 

skew the debris accumulation away from prototypical uniformity. GE subsequently responded 

to staff concerns by introducing the debris in a highly agitated zone away from the strainer so 

that the debris had to transport several feet to reach the strainer.

GE also conducted thin bed testing in a small-scale sector test apparatus and concluded that a 

thin bed had not occurred in their tests. Test results presented during an NRC audit showed 

that sudden drops in the head loss occurred during fully stirred sector testing. Although the 

actual phenomena occurring during the sector head loss tests cannot be known with certainty, 

the NRC staff inferred from test data, showing sudden large head loss reductions, that the 

accumulation of shreds within the sector gap may have caused a blockage to form and then 

give way. If this phenomenon occurred, once the shreds entered the gap and were no longer 

influenced by the turbulence from pool stirring, they would settle onto the lower gap strainer 

surface close to the outer perimeter of the disk, creating a location for debris to collect, 

essentially a dam. Once the dam had built up in the gap at the outer edges of the disk 

sufficiently to cause a substantial head loss across the dam, the debris would be pushed 

inward, partially clearing a portion of the strainer surface. The clearing resulted in a sudden 

decrease in measured head loss across the strainer. Individual fibers are not susceptible to 

gravitational settling and would not have preferentially settled to the lower surface, nor created 

an entrance dam. The NRC staff had observed a thin bed formation in prior prototype testing of 

a GE strainer (NRC, 2006) and also observed thin-bed behavior in later tests. Therefore, the 

staff concluded that a thin bed may form on a GE strainer.

The GE test termination criterion for defining a steady state was that the measured head loss 

increase became less than 1% over a period of 30 min or five turnovers, whichever was greater, 

but the criterion does not apply until all fiber debris has been added to the tank as scheduled. 

However, at this rate of increase the head loss could potentially increase at a rate of 48% in 24 

hr, assuming the rate remained linear. A minimum of five turnovers is adequate to filter the 

fibrous debris that is likely to accumulate on the strainer with a filtration efficiency of nearly 

100%. However, five turnovers is not sufficient for the subsequent filtration of particulates, 

especially the finer particulate where the effective filtration efficiency may be quite low, based 

information documented in the NRC head loss test guidance report (NRC, 2008d). The staff 

recognized these issues and reviewed the test results to ensure that they were conducted for 

adequate lengths of time or that appropriate post-test data extrapolation accounted for potential 

head loss increases. 

PCI Strainer Design and Testing

The PCI strainers consist of modules of stacked disks connected via a common header or 

plenum (NRC, 2007e). The disks are constructed of stainless steel perforated plates, where the 

dimensions and number of disks vary with the plant application. The perforated sheets are 

riveted together along the outside edge and shop welded to a core tube along the inner edges. 

The tube of each module is constructed of stainless steel pipe, and the modules are connected 

together by means of a coupling sleeve fitted over the core tubes and secured by a latch. The 

core tube has holes cut in the pipe wall to admit flow of strained water from the inside of the 

perforated sheets. The holes along the core tube length are sized to maintain a uniform rate of 

flow from disk to disk. The modules can be connected in trains or stacks to fit plant-specific 

sumps. The perforations in the strainer plate consist of holes with a licensee-specified 

diameter. After water passes through the perforated plates, it flows to the common plenum to 
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the recirculation pump suction. Plant-specific strainers were constructed of these disks, 

oriented either vertically or horizontally, and arranged in a manner to fit the plant sump. PCI 

supplied plant specific designed strainers to 17 U.S. units. 

PCI conducted head loss testing with strainer module prototypes in a tank equipped with a 

recirculating pump loop (NRC 2007e; Scott, 2006; Smith, 2008a, 2008b; Hiser, 2008). Earlier 

PCI testing, conducted by AREVA at ARL, was conducted in a test flume approximately 27 in. 

wide, 39 in. high, and about 21 ft long. Later testing was conducted in a larger steel-reinforced 

test flume that was 10 ft wide by 45 ft long, and 6 ft high, and that had an optional 6-ft-deep pit 

at one end. For the larger flume a flow channel was constructed inside the flume to achieve 

prototypical flow approach velocities needed to simulate near-field debris settling. Some tests 

conducted in the larger facility were agitated to prevent settling of debris. Instrumentation 

included a loop flow sensor to monitor the strainer flow rate, a thermocouple to monitor water 

temperature, a differential pressure transducer to measure strainer head loss, and equipment to 

record these measurements. 

In the larger flume, the test module can be either floor-mounted or recessed in a pit-mounted 

configuration. Testing in the PCI flume can be conducted at temperatures up to 120°F. The 

specification of the temperature is an option of the licensee. The testing observed by the staff 

was conducted at about 120°F. Prototypical rising water levels associated with filling the sump 

pool can be simulated. The flow is controlled either by variable-frequency motor controllers or 

flow control valves. The instrumentation includes orifice plate flow meters, pressure taps, and 

temperature probes with the data fed to data acquisition computers. A plant-specific internal 

flume flow channel is constructed of lumber and installed within the outer steel test flume. The 

shape of the flow channel is designed to model the flow velocities that are prototypical of 

average plant strainer approach velocities. The purpose of the internal flow channel is to 

simulate the plant flow conditions so that debris settling within the test flume prototypical of the 

plant can be credited. This settling has been referred to as “near-field debris settling” or the 

“near field effect.” The design of the flow channel associated with the tests observed by the 

staff was based on CFD modeling of the plant sump. The analytical approach to designing the 

shape of the test flume may have resulted in test flow velocities that adequately represented the 

plant flow conditions. However, the staff raised several issues regarding the modeling of the 

plant flow and continues to interact with the test vendor to ensure that the testing is 

representative of conservative with respect to the plant conditions. Whether or not the debris 

settling seen in the tests is prototypical of the plant also depends significantly on whether or not 

the surrogate debris used in the tests was prototypical of the plant debris. In the observed 

testing, most of the heavier debris, including NUKON shreds settled within the flume before the 

flow reached the test strainer modules. In some tests with higher velocities the majority of the 

small fibrous debris transported to the strainer. The vendor has developed a debris preparation 

and introduction methodology that improves these aspects of testing. The test module in the 

testing is composed of full sized disks, and plant specific disk spacing and core tube geometry. 

In one observed test, for example, two vertical strainer module towers were installed in the pit 

below floor level, with the tops of the strainer positioned several inches above the flume floor 

level (Hiser 2008). Each tower had 40 horizontally mounted square strainer disks.

The preparation of the fibrous debris is an issue of importance to the PCI test protocol. PCI 

prepares fibrous debris in the three categories designated as “fines,” “small pieces,” and “large 

pieces,” and then matches the quantities of each category to the licensee’s specific analytically 

determined size distributions Smith, 2010). The small pieces are prepared by passing the 

fibrous insulation through a commercially available wood chipper. This process produces small 

shreds of fibrous debris that also include a certain intermixed amount of essentially individual 
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fiber. The fine fibrous debris is prepared with a second shredder that produces substantially 

finer debris than the common wood chipper. This fine debris is intended to represent the very 

fine fibrous debris that would typically transport as suspended fibers in the plant sump pool (i.e., 

essentially individual fibers). However, a majority of this fine debris still tended to settle in the 

test flume during some tests. The vendor continued to refine the test methodology for testing 

that allowed near-field settling and has developed a method for debris introduction. PCI 

conducted tests with plant-specific foreign debris surrogates such as tape, tags, stickers, and 

label materials transporting in the flume to achieve a prototypical accumulation of such materials 

in the strainer or show that certain types of debis would not transport.

The PCI test procedures evolved to starting the pumps prior to debris introduction (their earlier 

testing varied with the pump starting before and after debris introduction). The PCI test 

termination criteria include 1) less than 1% increase in head loss in 30 min unless otherwise 

directed by the test engineer and 2) a minimum of 15 pool turnovers after all debris has been 

introduced. 

Enercon Strainer Design and Testing

The Enercon replacement strainers consist of several individual “top hat” units connected to a 

manifold (NRC, 2008e). Each top hat unit typically consisted of two concentric hollow cylinders 

(some top hats were designed with a single cylinder) that allow flow through the inner and outer 

surfaces of each cylinder through perforations in the circular plates. Each cylinder annulus 

typically (but not all) contains a bypass prevention material that is similar to steel wool, which 

limits the amount of debris that will pass through the strainer to downstream components. The 

top hat dimensions as installed at Indian Point, for example, included the outer diameter of the 

outer cylinders as either 12 or 12.5 in.; the inner diameter of these cylinders as either 10 or 10.5 

in.; the outer and inner diameters of the inner cylinders as 7 or 7.5 in. and 5 or 5.5 in. 

respectively; and the lengths as 15.5 to 43.5 in. The top hats can be oriented either vertically or 

horizontally. Strainer modules can be interconnected as needed for each plant-specific 

application. Water passes through the perforations, through the steel wool, and into the 

common manifolds. Enercon supplied plant-specific designed strainers to 14 U.S. units. An 

example Enercon plant strainer is shown in Figure 5.11-5.

ALION Science and Technology typically conducted the head loss testing on the Enercon 

manufactured strainers (one strainer test for multiple units was conducted at Wyle Labs). An 

isometric view of the ALION test tank with an Enercon prototype strainer installed is shown in 

Figure 5.11-6. In this configuration, the prototype strainer, consisting of a 3 x 3 array of top hat 

units connected to a common plenum, was enclosed with four plywood walls to control the 

approach of the incoming debris-laden flow. The plywood baffles were also used to ensure that 

the test array was geometrically and volumetrically configured to simulate a section of the plant 

strainer. ALION scaled the test flow rate based on the ratio between the net testing module 

surface area and the actual strainer net surface areas to maintain the plant strainer screen 

approach velocity in the test prototype. The test tank was approximately 6.0 ft high, 6.0 ft wide, 

and 10.0 ft long. Pressure transmitters, a flow meter, and thermocouples were installed to 

measure the head loss, total flow rate, and the water temperature. 
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Figure 5.11-5. H. B. Robinson 

Strainer (NRC, 2008b)

Figure 5.11-6. Isometric View 

of Alion Test Tank with 

Prototype Strainer (NRC, 

2008e)

ALION used the actual plant insulation materials, where practical, or suitable surrogates as 

sources of debris for the testing. NUKON® was used to simulate the latent fibers. NUKON® 

has been accepted as a valid latent fiber surrogate. The latent particulate is simulated with 

silica sand with a size distribution sized according to the recommendation in NUREG/CR-6877. 

The size distribution of the surrogate fibrous debris was based on the vendor’s generic debris 

preparation protocol, rather than attempting to match the plant’s analytically determined size 

distributions. For the prototype tests, the fibrous debris was prepared by processing the fibrous 

insulation through a commonly available leaf shredder and then further refining the wetted 

shredded debris using a paint stirrer. The NRC staff was concerned that the shredded fibrous 

debris in the test did not adequately represent the suspended fibers that were predicted to reach 

the strainer by the transport analysis. Only very fine suspended debris would accumulate on 

the typical licensee strainer due to the very slow approach velocities associated with a large 

replacement strainer. ALION revised their debris preparation procedure so that the resulting 

fibrous debris met staff expectations. The particulate materials were generally obtained in a 

powder form so that no additional preparation was required other than wetting. The method of 

introducing the debris depended upon the plant-specific requirements. The stabilization or test 

termination criteria for the prototype tests were 1% change in head loss in a 1-hr period and a 
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minimum of five pool turnovers having occurred but also subject to the judgment of the test 

coordinator who could extend the test.

ALION also sponsored chemical-effects head loss testing conducted by VÚEZ in a small tank 

designed to represent the containment conditions with respect to pool liquid volume, pool 

chemistry, temperature, materials, and impact on debris head loss (NRC, 2008e). The 

experiment was designed to replicate the corrosive interactions of the spray and pool fluid 

chemistry with those materials and debris sources in containment and resident on the sump 

screen over a 30-day mission time. The experiment attempted to prototypically simulate head 

loss parameters of debris bed thickness and composition and the flow velocity. The debris test 

screen in these small-scale tests was a horizontally mounted flat plate screen with an area of 

0.135 ft2

. Instrumentation measured the pump flow rate, the water temperature, the head loss 

across the debris bed, and the fluid pH level. The water level was monitored. The water 

temperature was regulated to simulate the postulated time-dependent plant sump temperature. 

The pump flow rate was specified to simulate the plant strainer approach velocity. The scaling 

from the plant debris loads to the test loads was based on the ratio of the effective test area for 

the test strainer divided by that of the plant replacement strainer. The prepared fibrous debris 

was combined with the particulate debris to form a slurry. After the tank chemistry, temperature, 

and pump flow conditions were established, the debris slurry was poured directly onto the 

horizontal test screen to form the debris bed with the intent of having all of the debris actually 

accumulate on the screen. However, this method of forming a debris bed was not prototypical 

of the plant since in the plant, the debris would accumulate slowly as the flow carried the debris 

onto the strainer surfaces basically one fiber at a time, which would allow the flow-driven debris 

to slowly patch weak areas of the bed. Forming the debris bed by pouring the debris, rather 

than allowing the flow to form the bed results in beds that form less tightly compacted than 

would be prototypical. The staff observations noted the formation of non-uniform beds and 

inadequate debris preparation. Bulkier and non-uniformly formed debris beds could preclude 

the formation of an effective thin-bed and lead to an incorrect thin-bed conclusion. Since the 

chemical-effects head loss tests are run for the 30-day mission time, there was no need to 

specify any termination criteria associated with head loss increases or the number of pool 

turnovers. The termination criterion was 30 days. The staff ultimatedly did not accept the 

results of this the tests conducted at VUEZ. 

CCI Strainer Design and Testing

The CCI strainers modules consist of a large array of strainer pockets connected via a common 

header or plenum (NRC, 2007d; NRC, 2008f). Each pocket is typically 4.29 in. high, 2.76 in. 

wide, and about 12 in. deep (although these dimensions could be varied). The rear surface of 

each pocket is curved. The total screen area depends upon the number of pockets 

incorporated into each strainer module and the number of modules in the plant strainer. The 

typical diameter of a perforation hole was 2.1 mm (0.082 in.). CCI supplied plant-specific 

designed strainers to 20 U.S. units. Schematics of an individual pocket and a small test strainer 

module are shown in Figure 5.11-7. A photograph of an example installed plant strainer is 

shown in Figure 5.11-8.
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Figure 5.11-7. Schematic of Individual Pocket and Small Test Strainer Module 

(Blumer, 2007)

Figure 5.11-8. Photograph 

of Installed Plant Strainer 

(NRC, 2007d)

CCI typically conducted strainer prototype testing to determine potential head loss from debris, 

with and without chemical effects, using their test flume with three separate rigs: a testing 

module consisting of an array strainer pockets (e.g. 90 pockets), a small test flume with a test 

module consisting of a simulation of six pockets, and a medium-scale multifunctional test loop 

usually consisting of 40 pockets (NRC, 2008f). The choice of test rigs and the size of the 

modular test array depended upon the licensee test objectives and plant strainer design.

The schematics illustrating the multifunctional test rig are shown in Figures 5.11-9 and 5.11-10. 

The multifunctional test loop at CCI consisted of a closed recirculation loop with recirculation 

flow returning at the opposite end of the fume from where the test strainer was used to draw 

flow from the flume. The test tank consisted of a Plexiglas channel about 1.3 ft wide and 4.6 ft 

high and the test strainer was 10 pockets high by four pockets wide. A centrifugal pump 

circulated the water through the loop with the flow regulated using a pump rpm controller and/or 

an upstream valve. Instrumentation included a loop flow sensor to monitor the strainer flow 

rate, a thermocouple to monitor water temperature, differential pressure transducer to measure 
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strainer head loss, and equipment to record these measurements. The large flume apparatus, 

approximately 8.5 ft wide, 9.8 ft high, and about 14.4 ft long, accommodated a larger strainer 

prototype, for example, the 120 pockets strainer used in the Oconee testing (NRC, 2007d).

Figure 5.11-9. Illustration of the Multifunctional Head Loss Test Rig (Blumer 2007)

Figure 5.11-10. Illustration of 

the Multifunctional Head Loss 

Test Rig

(NRC 2008f)

The scaling from the plant debris loads to the test loads was based on the ratio of the effective 

screen area for the test strainer divided by that of the plant replacement strainer. To determine 

the strainer effective screen area, the total replacement strainer screen area was reduced by an 

area referred to as a “sacrificial area” that would, in theory, account for the miscellaneous debris 

(e.g., tape, labels, etc.) that could accumulate on the strainer. This practice was used by most 

strainer vendors. 

CCI used actual plant insulation materials, where practical, or suitable surrogates as sources of 

debris for the testing. NUKON® was used to simulate the latent fibers. CCI used stone flour to 

simulate coatings and latent particulate. 

The CCI preparation of the fibrous debris included baking the insulation at 300°C for 24 hours, 

cutting the insulation into pieces, soaking in water, and then using a high pressure water jet to 

decompose the insulation pieces into pieces smaller than 10 mm (3⁄8 in.). This process seemed 
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to create debris considerably smaller than a single pass through a typical shredder, but the 

debris was still substantially larger than fiber that would remain suspended given typical sump 

pool flow and turbulence conditions. Although the settling behavior may have been corrected in 

later testing, CCI testing reviewed during NRC staff audits showed a fraction of the fibrous 

debris settling to the floor in front of the strainer rather than transporting as the prototypically 

fine fibers most capable of forming an effective thin-bed. The typical thin-bed accumulation of 

fibrous debris on the large PWR replacement strainers is due to suspended fibers primarily, 

which were not well represented by the CCI preparation. The CCI test conclusion, based on 

testing prior to adjusting their debris preparation procedure, that either a thin bed cannot form or 

its head loss would be substantially less than the fully loaded case was likely due to the nonprototypical debris preparation. CCI mechanically crushed the particulate insulations used in 

testing into a powder. The chemical precipitates were either allowed to form in the test loop to 

simulate precipitates under containment sump conditions, or were prepared per the WCAP test 

guidance, depending on the customer. The staff did not completely accept the in-situ method, 

but noted that it did produce significant head losses in some cases. The debris samples were 

weighed, mixed into a wetted homogeneous mixture in buckets, and poured into the test pool.

In the CCI test protocol, the pumps were started and the recirculation flows were established 

prior to introducing debris into the test flume. The early procedure used in the CCI 

multifunctional testing was to introduce the debris in close proximity to the test strainer to reduce 

debris settling within the tank. The wetted debris was slowly poured into the test loop within 

about 1 ft of the strainer entrance. The test strainer perimeter approach velocities of the test 

strainer at this location would be approximately prototypical of the corresponding plant strainer 

velocities. While this approach reduced near field settling, it did not eliminate it. Post-test 

photographs clearly showed varying amounts of both fibrous and particulate debris on the tank 

floor. 

The early CCI approach of introducing the debris in close proximity to the strainer allowed larger 

debris to accumulate in the pockets than would accumulate under plant prototypical conditions 

where only suspended fines would reach the plant strainer. Larger pieces of debris were pulled 

into a pocket as the debris descended in front of the pocket, but once the larger piece was 

inside the pocket, it readily settled to the pocket floor, resulting in a non-uniform accumulation 

with respect to the other pocket surface orientations. Suspended fines would accumulate 

relatively uniformly on all surface orientations. Hence, introducing debris directly in front of the 

test strainer caused non-prototypical debris accumulation that disrupted the formation of a 

prototypical thin bed and thereby compromised the thin bed testing. Later testing prepared the 

fibrous debris more finely and added the debris further from the strainer so that it would 

transport more realistically to the strainer. Figure 5.7-7 shows a relatively uniform accumulation 

on a CCI test strainer, which was the result when debris was introduced far enough away from 

the strainer to allow the heavier debris to settle so that only the suspended fines reached the 

strainer.

The CCI test termination criteria included a 3% or less percentage change in head loss increase 

in 10 min for the thin bed test and 1% in 30 minutes for the full load tests when the head loss 

was less than 1 ft. For a head loss greater than or equal to one foot, the criteria were set at 1% 

in 30 minutes for both thin bed and full load tests. The procedure did not specify a minimum 

number of tank volume turnovers following the final addition of debris. However, the CCI tests 

generally ran for significant lengths of time prior to termination. 
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Comparison of Vendor Head Loss Testing for PWRs

The trend in replacement strainer design has been the implementation of large passive strainers 

withsurface areas up to several thousand square feet. These large strainers distribute the 

debris over a larger area. This philosophy has resulted in thinner debris beds and reduced 

water flow velocities, which in turn, reduce the head loss across the debris. The vendor designs 

vary primarily on how larger screen areas are incorporated into relatively small volumes that can 

be tailored to fit into a specific licensee’s recirculation sump. The qualification testing of these 

strainers involves the replication of the plant post-LOCA strainer environment that would 

surround the strainer. The parameters that need to be prototypically replicated, or 

conservatively treated, include water flow velocities, pool turbulence, temperature, and water 

depth. 

There are limitations to prototypically reproducing the sump pool environment in small-scale 

testing. All vendors conducted prototype tests at reduced temperatures that ranged from room 

temperature to 120°F with the exception of some long term tests where the test attempted to 

replicate the prototypical plant sump temperature profiles as closely as possible. 

The flow approaching the perimeter of these large PWR replacement strainers is typically 

moving slower than 0.1 ft/sec on average. The average velocity of flow through the screen 

surfaces is typically less than 0.01 ft/sec. At these velocities, in the absence of turbulence 

caused by falling water, nearly all debris that would readily settle in the sump pool would have 

settled so that the debris approaching the strainer would consist mainly of suspended fines. 

The suspended fines consisted of the very fine particulate and individual fibers or very small 

fiber shreds. The chief characteristic of the fines was that this debris takes substantial time to 

settle, even in still water, so in the sump pool it would effectively remain in suspension and 

would be relatively uniformly distributed in the water. This condition leads to relatively uniform 

debris accumulations on all active strainer screen surfaces. When holistically considering the 

potential threat to blocking a large plant strainer, a thin bed debris accumulation likely has the 

greater potential to cause significant blockage. Note that some plant may have higher approach 

velocities due to their particular configuration. 

If the licensee transport evaluation conservatively predicted larger pieces reaching the strainer 

in addition to adequately accounting for the suspended fines, this prediction would 

conservatively increase the bounding debris estimate. If the larger pieces of debris were to be 

added to an head loss test flume where the pieces could prototypically settle, these pieces 

should then have no significant effect on the test head loss. However, if these pieces were 

somehow forced to accumulate on the strainer in a non-prototypical manner, their presence on 

the strainer could preclude the formation of a thin-bed and lead to a non-prototypically low head 

loss result. NRC guidance, which has been followed by the test vendors during their latest 

rounds of tests, is designed to minimize the effects of non-prototypical transport of larger debris 

by adding all of the finest debris before moving to larger sizes. The use of staff guidance for 

fibrous debris preparation is another important factor in obtaining realistic thin bed head loss 

values. 

All vendors based their test debris loads on the bounding quantities of debris as determined by 

plant-specific debris generation/transport analyses. The vendors have, in general, made 

reasonable selections for their surrogate debris. In early testing each vendor prepared their 

fibrous debris using a generic method that did not ensure that the debris added to the head loss 

test matched up with the debris predicted by the debris generation and transport analyses to 

arrive at the strainer. AECL and CCI prepared their surrogate fibrous debris using a high-
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pressure jet to separate the fibers after first reducing the insulation to small pieces. This 

process creates debris finer than a single pass through a leaf shredder but potentially not 

prototypical of suspended fibers. Only a portion of this debris may transport as prototypical 

suspended fines. GE, PCI, and ALION all first shredded their debris but then applied different 

secondary processes. GE in a later protocol passed their debris through the shredder a 

minimum of five times until the debris passed their qualification test. PCI created three sizes of 

shredded debris, for which they match the sizes to the licensee size categories, but the PCI 

fines were not sufficiently fine to represent the licensee’s suspended fines. This was potentially 

complicated by the fact that some PCI testing credited near-field settling and some of the debris 

may have settled non-prototypically because it was larger than true fines. After shredding, 

ALION further processed the shreds with a paint stirrer in the prototypes tests, and used a cake 

mixer in the 30-day chemical effects tests. 

The typical vendor fiber preparation methods create debris that contains a portion of individual 

fibers that will transport prototypically as suspended debris. Because none of the vendors 

experimentally ascertained the percentage of the prepared debris that was prototypical of 

suspended fiber they could not verify that the plant specific transport estimates were 

represented in the testing. As an example where this consideration could be critical, consider 

an all-RMI plant where the only fibers that can reach the strainer are latent fibers. Latent fibers 

are assumed to be individual fibers that completely transport to the strainers. Here, the debris 

generation evaluation estimates a given quantity of latent fibers that is assumed to completely 

transport and accumulate on the strainer. The vendor debris preparation methods created 

debris so that some fraction of the debris could settle so that an insufficient quantity might 

accumulate on the strainer. Ensuring the prototypicality of the fibrous debris is very important in 

ensuring valid head loss testing results. For particulate debris, the vendors generally acquired 

particulate in powder form. Microporous insulations were either crushed into a powder or 

purchased in powder form. With the exception of a few specific cases, the treatment of 

particulate debris has not been problematic for head loss testing. 

Issues associated with debris introduction to the test involve the method, the timing and the 

location of debris introduction. Debris introduction must consider the test objectives, which are

typically based on either a thin bed test or a full load test. The vendor debris introduction 

procedures evolved during the GSI-191 resolution. Later vendor protocols made improvements 

to start the pumps to establish the hydraulic conditions prior to introducing the debris; the debris 

was wetted prior to slowing pouring it into the test tank or flume to preclude non-prototypical 

agglomeration of the debris. The debris was typically introduced in batches, with the head loss 

being allowed to stabilize prior to introducing the next batch. 

One difference among the vendor approaches was the location that the debris was introduced 

with respect to the location of the prototype test strainer. With the exception of PCI, the vendor 

approaches were generally designed to minimize debris settling within the test tank or flume. 

Later PCI testing used a flume shaped so that the approaching flow velocities would be 

prototypical of the plant sump. The flume shape was based on CFD analyses of the plant 

sump. Later evaluation showed that in some cases the turbulence predicted for the flume was 

significantly lower than the turbulence predicted for the plant. Had the turbulence levels been 

comparable, the debris settling in the PCI flume should be similar to that in the plant sump pool 

provided the test debris is also prototypical. Further, PCI was the only vendor that chose to test 

the transport and accumulation of the miscellaneous foreign debris such as tapes and labels 

rather than simply including a penalty for miscellaneous debris in the scaling for the test. The 

other vendors introduced debris closer to the test strainer to reduce potential for the debris to 

settle. These vendors also used pool turbulence to reduce the debris settling or actually 
5-217

introduced the debris directly in front of the strainer. Later tests suspended the practice of 

introducing debris too close to the strainer and evaluated added turbulence to ensure that it did 

not affect debris bed formation non-conservatively. 

The adequacy of the debris introduction location with respect to the fibrous debris is directly 

related to the debris size distribution. If fine fibrous debris is prepared prototypically so that it

essentially remains suspended under sump pool conditions its introduction location is not critical

as long as it is not too close to the strainer. However, when a substantial portion of the 

prepared debris readily settles in the test tank, its introduction location when considered in 

conjunction with the quantities introduced is very important. Staff guidance is (1) that the 

suspendable debris be adequately represented, and (2) that larger debris is not to be forced to 

accumulate when that debris would not prototypically accumulate in the plant sump. The PCI 

flume protocol allowed the heavier debris to settle without reaching the sump. Therefore, the 

issue with the PCI methodology is ensuring that the individual fibers are prototypically 

represented in the mix of prepared debris. In the early CCI protocol, the fibrous debris was 

introduced directly in front of the strainer to minimize debris settling, but this protocol essentially 

forced larger debris that would not prototypically reach the strainer pockets to accumulate on 

the pockets floors. This behavior could preclude the formation of a thin bed. A similar situation 

occurred in the GE Waterford head loss testing, where mechanical stirring in the sector testing 

kept shreds in motion until the shreds accumulated in the sector gaps. This type of 

accumulation effectively formed debris dams at the entrance to the gap that subsequently 

shifted inward and cleared a portion of the screen area, which also precluded the formation of a 

thin bed. Vendors have taken actions to reduce the effects of non-prototypical debris 

accumulation on the strainers during testing. 

During the auditing process, the NRC staff encountered a range of vendor attitudes regarding 

thin bed testing. Thin bed testing seems to be a cornerstone of the AECL protocol, where AECL 

consistently tested for thin bed head losses and found situations where the thin bed losses 

exceeded the full load head losses. By contrast, GE, PCI, ALION, and CCI all seem to have 

concluded that thin beds could not form on their respective strainers. The staff had observed 

thin beds on GE and PCI strainers and evidence of potential thin bed accumulations on CCI and 

ALION strainers. The reason that thin beds consistently formed on AECL strainers and not on 

other strainer designs was likely associated with test practices including the concerns described 

in this section. 

The staff identified issues in small- scale testing conducted by ALION and AECL. These 

vendors conducted smaller scale tests over long periods in an attempt to allow chemical 

precipitates to form on a debris bed under conditions similar to those that would occur in a plant. 

The vendors conducted these tests because they believed that the chemical precipitates that 

were added to larger tests resulted in very conservative head loss values. Upon review of the 

test results the staff identified, for some tests, that for a similar debris load, the small-scale tests 

had a significantly lower head loss value than similar larger scale tests before chemical debris 

was allowed to accumulate on the debris bed. Because the small-scale test pre-chemical 

values were lower than the larger scale test values with similar debris loads the staff was 

concerned that the effects of chemicals were not adequately represented in the small-scale 

tests. In some cases the test results were not accepted. In some cases the tests were 

repeated assuring that pre-chemical head loss values were on par with previous larger scale 

test results prior to chemical effects. 
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Test Termination and Post Test Data Scaling

The test termination criteria and subsequent data extrapolation vary considerably from one 

vendor to another. Test data may be extrapolated from the test temperature to the plant sump 

pool temperatures. Results may be extrapolated from test termination to the mission time, and 

also extrapolated to alternative conditions, such as an alternative debris load, to account for 

deviations between the test module and the final replacement strainer design. 

The primary termination criterion of the vendors has been that the rate of head loss increase be 

less than a certain percentage within a specified period of time. This criterion varies from 1% 

increase within 10 minutes to 1% within 60 minutes. The NRC staff observed head loss tests 

that were terminated when the head loss was increasing. One method for adjusting the 

measured head loss at test termination to account for the head loss increases that could occur 

is to extrapolate the head loss to the scenario mission time. Only GE and PCI included mission 

time extrapolations in their respective protocols. However, the staff acceptance review of 

design basis strainer head losses ensured that potential time based increases were accounted 

for. GE, PCI, and ALION methods have a criterion for the minimum number of pool turnovers 

between final debris introduction and test termination to allow debris filtration to occur. It was 

analytically shown that it takes about five pool turnovers to ensure the accumulation of the 

suspended fibers. However, for particulates it can take a substantially longer time to complete 

filtration because the filtration efficiency is much lower for particulates than for fibers. The staff 

recommended at least 15 turnovers between the completion of the debris introduction and test 

termination {NRC 2008d). 

All of the vendors extrapolated head loss test data from the colder test temperatures to the 

warmer plant sump pool temperatures to obtain lower head losses more prototypical of the 

plant. The staff is concerned that certain head loss results may not scale with viscosity when 

pressure-driven bed degradation processes, such as bore holes, are present in the bed. Staff 

guidance is that tests should include flow sweeps to validate whether flow through the debris 

bed is laminar prior to extrapolating test results to higher temperatures.

The ALION protocol included an analytical method for combining chemical effects data from the 

30-day VÚEZ tests with the prototype head loss test results based on applying a bump-up 

factor, determined from the chemical-effects testing, to the prototype head losses. Further, 

ALION used the NUREG/CR-6224 correlation to extrapolate to alternative conditions. The staff 

did not accept the use of the chemical bump-up factor and some of the extrapolations based on 

the 6224 correlation. 

5.11.2 Strainer Debris Head Loss Testing by BWR Vendors

Four strainer vendors supplied replacement strainers to the 35 operating U.S. BWR units. 

These vendors were: (1) GE, who supplied strainers to 12 units, (2) PCI, who supplied strainers 

to 15 units, (3) Enercon, who supplied strainers to 3 units, and (4) ABB Combustion Engineering 

(ABB), who supplied strainers to 4 units (LA-UR-01-1595). All of the replacement strainers were 

large-capacity passive designs. With the exception of the Enercon strainer, the strainer designs 

incorporated cavities, troughs, or traps to collect debris so that relatively large screen areas 

could be fit into relatively small volumes. The Enercon strainer made use of the large available 

space within the Mark III suppression pool to increase the screen areas without the use of 

internal entrapments. The large screen areas reduced the velocity of flow through the debris 

bed and simultaneously reduced the thickness of the postulated bed of debris. 
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The BWROG conducted prototype head loss testing to gather data on alternative ECCS suction 

strainer designs as a possible resolution to the strainer-clogging problem. The strainer head 

loss tests were conducted at the EPRI non-destructive evaluation (NDE) center in Charlotte, 

North Carolina. Supplemental tests to determine the effects of individual debris components on 

head loss and combinations of debris components were conducted at Continuum Dynamics, 

Inc. (CDI) in Princeton, New Jersey. These tests are documented in the URG (NEDO-32686, 

Volume I).

The overall objective of the full-scale test program was to develop and test strainer concepts 

that could be used to resolve the strainer clogging issue. Three specific concepts were 

evaluated: high-capacity passive strainers, strainer backflushing, and an active self-cleaning 

strainer. Testing was also conducted on a truncated cone strainer, similar to those installed at 

typical BWRs, to provide a baseline for comparison. For the passive strainers, the primary 

objective was to determine the capacity of each strainer to accumulate debris without clogging. 

Seven passive strainers and one active self-cleaning strainer were tested to obtain pressure 

loss and performance data as a function of debris type, debris quantity, flow rate, and time. 

The tested strainers were 1) the truncated cone design, 2) the 20-point star design, 3) the 60-

point star design, 4) two-thirds of the 60-point star design (i.e., sheet metal covered one-third of 

60-point star, 5) prototype #1 of the stacked-disk design, 6) prototype #2 of the stacked-disk 

design, and 7) the stacked disk section of the self-cleaning strainer design (in passive mode). 

For passive strainers, tests were conducted to evaluate the maximum fiber and corrosion 

product capacity, the feasibility of backflushing, and the effect of RMI on head loss. Tested 

debris included prototypical fibrous insulation, RMI, simulated corrosion products, and 

miscellaneous debris. The active strainer was tested to evaluate its ability to maintain a clean 

strainer surface area under various debris loadings at design flow rates and the resistance of 

the rotating assembly to start-up after a period at a minimum flow condition.

Two centrifugal pumps connected in parallel with a combined capacity of 10,000 gpm pumped 

water from a 50,000-gal tank and subsequently returned the flow to the tank. The test strainer 

was attached to the pump suction piping. Strainers could be mounted either vertically or

horizontally. Backflushing was performed by aligning one pump to pull water from the tank 

through alternative suction piping and then discharging the water back through the test strainer. 

The primary measurements taken during these tests were 1) strainer head loss, 2) system flow 

rate, 3) the masses of insulation debris, corrosion products and other debris introduced into the 

vessel, and 4) plow/brush rotation rate and strainer torque on the self-cleaning strainer.

The BWROG concluded that (1) corrosion products, when mixed with fibrous insulation, greatly 

increased the head loss over that of fibrous insulation alone, (2) lower approach velocities 

produced lower head losses although the relationship was non-linear over the range of flow 

rates and strainer sizes tested, (3) miscellaneous debris can also create significant increases in 

head loss, (4) thin debris bed tests indicated a fibrous bed thickness slightly greater than 1/8 in. 

was sufficient to cause high head loss on the truncated cone but not the alternative strainer 

designs, (5) the measured amount of fibrous NUKON insulation that passed through the 

truncated cone strainer was 0.4% of the total fiber in the tank for a specific flow rate and strainer 

head loss, and (6) passive strainers can collect significant amounts of fibrous insulation and 

corrosion products with acceptable head loss at the flow rates of interest for BWR ECCS. The 

BWROG also found that a minimum approach velocity is required to keep RMI debris on the 

strainer, and that an RMI debris bed causes less significant head loss than a fibrous/particulate 

debris bed. Backflushing did not always remove accumulated fibrous/particulate debris on the 
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complex strainer designs. The active front portion of the self-cleaning strainer was kept clean 

for all debris types and loadings tested at the design flow rate of 5,000 gpm; however, the 

torque generated by the turbine (rotating cleaning blades) was higher than expected.

The NRC staff reviewed the BWROG testing and found that, while the URG contained valuable 

and useful data for predicting strainer head loss, there were several concerns regarding the 

quality and applicability of these data. One important NRC staff concern regarding the BWROG 

tests was that reasonable steady-state head loss measurements were not achieved in a 

significant number of the tests. This concern is important because the amount of debris on the 

strainer was deduced from known quantities of debris introduced into the water tank by 

assuming that essentially all of the debris was deposited onto the strainer when the test head 

loss was measured. Therefore, the debris bed composition was relatively unknown during 

transient conditions. Direct application of the head loss data obtained for the prototype strainers 

to the plant strainers was not justified because the test modules were not actual prototypes of 

the plant-specific design. In some cases, the debris loads used in the test programs did not 

cover the entire range of debris loads in the plants. This resulted in potential inaccuracies in the 

estimation of strainer head loss. In spite of these reservations, NRC found that use of the data 

obtained from the test programs in plant-specific calculations was reasonable, provided the 

vendor or the licensee used the data within the original range of testing or established a 

theoretical basis for extrapolating the data to other strainer designs or debris loads. 

Subsequent prototype testing by the vendors generally followed the BWROG testing procedures 

which initiated the recirculation pump prior to introducing the debris, used the return flow to keep 

most of the debris in suspension, and terminated the test when the head loss increases slowed 

to an acceptable rate. In general, the test procedures assumed that the head loss would always 

increase with the debris quantities accumulated on the strainer (i.e. the greater the debris load, 

the greater the head loss). While the BWROG concluded that thin beds could not form on the 

alternative strainer designs, the PWR testing demonstrated that thin debris beds can readily 

form on complex strainers and can cause significant head losses, often greater than head 

losses obtained with greater debris loads. Discussions of the limited information available for 

vendor-specific head losses testing follow.

GE Strainer Design and Testing 

The GE stacked-disk BWR ECCS suction strainer uses disks whose internal radius and 

thickness vary over the height of the strainer. The patented GE stacked-disk suction strainer for 

the ECCS pump was designed to have minimum head loss while accumulating a maximum 

quantity of debris within a given volume. The strainer has a central core of varying radius such 

that the flow through the entire central region is maintained at constant velocity. A number of 

perforated disks of varying internal diameters and whose thickness varied with radius surround 

the central core. The spacing between the disks is maintained constant at 1.75 in. The outer 

diameter of the disks is typically constant, but can be varied and still maintain the constant 

velocity core. Figure 5.11-11 is an isometric view of a typical GE stacked-disk strainer with a 

quarter segment removed to illustrate the internal design. GE tested their stacked-disk strainer 

design at the EPRI NDE Center (NEDO-32721-A,).
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Figure 5.11-11. Isometric View of a 

Typical GE BWR Replacement 

Strainer (NEDO-32721-A).

The methodology used for hydraulic design of the GE stacked-disk suction strainer includes the 

calculation of the head loss with a clean strainer, the head loss due to fiber and corrosion 

product laden debris, and the use of bump-up factors to account for miscellaneous types of 

debris. GE conducted hydraulic testing on a GE prototype strainer to determine both cleanstrainer and debris-laden head losses. GE used data from their prototype testing and from the 

BWROG head loss testing (NEDO-32686) to develop a design correlation for the GE strainers. 

This correlation consisted of a dimensionless head loss coefficient that was essentially a linear 

function of the flow velocity, water viscosity, and debris bed thickness divided by the square of 

an inter-fiber distance.

The prototype test strainer was mounted horizontally to a 24-in. tee in a 50,000 gal vessel. Two 

centrifugal pumps capable of producing a total flow of 10,000 gpm were used to provide system 

flow which was controlled by valves on the pump outlets. The flow returned to the vessel 

through a venturi and then through a pipe whose exit was centered in the vessel and directed 

down toward the floor. This pipe orientation prevented material from settling on the vessel floor. 

Instrumentation included a differential pressure transmitter to measure head loss across the 

strainer, differential pressure across the venturi in the return leg of the piping to measure the 

flow rate, and a thermometer to measure the temperature. A schematic of the test facility is 

shown in Figure 5.11-12.

The GE test procedures essentially duplicated the BWROG test procedures. The pumps were 

started and the flow rate established prior to introducing the debris. The flow rate was 

maintained at a nearly constant value determined by the test matrix, unless the strainer 

maximum pressure drop was reached or the pump performance was degraded. After the 

strainer head loss became approximately steady state, the flow rate could be adjusted down 

and up (a flow sweep) to obtain head loss at different flow rates. A run was terminated when 

the strainer head loss became relatively stable or a pre-determined value of head loss was 

achieved (after conducting any required flow sweeps). 

GE provided proprietary design details of the strainer and the hydraulic performance 

characteristics of their strainer to the NRC for review (NEDO-32721P). In addition, the NRC 
5-222

staff performed an onsite audit of the Duane Arnold plant, which is a single BWR/4 unit with a 

Mark I containment. Duane Arnold was the reference plant used in the NUREG/CR-6224 study 

that formed the basis for the resolution of the BWR strainer blockage issue. 

Figure 5.11-12. 

Schematic of the GE 

Test Facility (NEDO32721-A).

These reviews formed the basis for the NRC acceptance of the GE replacement strainers. 

Based on the NRC review, the staff concluded that the test program used by GE for verifying 

the hydraulic performance of the prototype strainer and validating GE’s head loss correlation 

was acceptable; however, the staff expressed concerns regarding the validity and use of this 

correlation. GE adopted an empirical means for correlating the head loss test data for the 

fiber/sludge debris bed. The GE head loss correlation is based on test data generated over a 

narrow range of test parameters, and the GE correlation does not account for the geometric 

effects systematically. After further review, the staff concluded that GE introduced sufficient 

margin to compensate for any deficiencies in the correlation. The staff concluded that extending 

the test results over a narrow parametric range outside the test range is reasonable. 

PCI Strainer Design and Testing

PCI supplied advanced passive stacked-disk strainers to the nuclear industry under the 

trademark Sure-FlowTM strainer. The strainers consist of stacks of coaxial perforated metal 

plate disks that are welded to a common perforated internal core tube. The design maximizes 

the surface area of the perforated plate while keeping the circumscribed area to a minimum. 

The internal core tube is designed to provide structural support and to ensure uniform approach 

flow velocity to all disks. The design of a specific PCI strainer was tailored to fit each plant 

application. Figure 5.11-13 is a photograph of one installed BWR PCI strainer, and Figure 5.11-

14 shows a typical strainer core tube (Rao et al., 2001).
5-223

Figure 5.11-13. PCI 

Stacked Disk Strainer 

Being Installed at Pilgrim 

Nuclear Power Plant

(Rao et al., 2001).

Figure 5.11-14. Core Tube 

Used in the PCI Stacked 

Disk Strainers

(Rao et al., 2001).

PCI conducted prototype testing and used the NUREG/CR-6224 head loss correlation, as 

implemented in an industry proprietary computer code named HLOSS developed by Innovative 

Technology Solutions (ITS) Corp to predict strainer head loss. The overall technical approach 

was to use the prototype test data to validate the head loss correlation and then use the 

correlation to make strainer-specific head loss predictions.

PCI developed two prototype Sure-Flow stacked-disk strainers and tested them at the EPRI 

NDE Center. The test data were published in the BWROG URG (NEDO-32686). One 

prototype, referred to as “Stacked-Disk #1” in the URG, was a 40%-scale prototype with six 

disks, five troughs between the disks, a 13-in. core tube, a 30-in. outside diameter, and a length 

of 2.5 ft. A larger prototype, referred to as “Stacked-Disk #2,” was 4-ft long with a core tube 

diameter of 26 in. and a stack outer diameter of 40 in. Both the BWROG and PCI tested the 

head loss performance of these strainers. 

The tests were conducted by first starting the pumps and establishing the flow rate. Then, the 

debris was introduced. The tests were instrumented to measure strainer head loss, flow rate, 

and water temperature. Return flow was discharged downward at the center of the tank 12 

inches above the tank floor to reduce debris settling. When the pressure drop across the

strainer reached a pre-determined limit or approximate steady state, the value was recorded, 

and if needed, the flow rate was adjusted down and up (a flow sweep) to obtain head loss at 

different flow rates. 
5-224

The NRC staff reviewed the PCI strainer design, performance characteristics, head loss data, 

and the adequacy of the head loss models. The test data were obtained primarily for debris 

beds consisting of NUKON fibrous debris with and without sludge, and for RMI debris. As part 

of this review, the staff explored the adaptation of the NUREG/CR-6224 correlation developed 

for uniform flat screen debris beds to stacked-disk strainers so that the correlation could be 

used by the staff to evaluate the performance of strainers installed at the various operating 

BWR plants. The adaptation of the correlation to a stacked-disk strainer involved the 

implementation of the concept of a variable effective strainer area, where the initial actual 

strainer screen area progressively decreased due to debris accumulation in the disk gaps until 

the debris accumulation area became the strainer circumscribed area (Rao et al., 2001). The 

shape of this effective area curve versus debris accumulation was to be deduced from 

applicable strainer head loss data.

Enercon Strainer Design and Testing

Enercon Services designed and manufactured large capacity passive suction strainers 

specifically for the BWR Mark III containment toroidal suppression pool. Figure 5.11-15 shows 

an individual Enercon module of the Mark III strainer installed at the Grand Gulf Nuclear Station 

(GGNS). These strainer modules were joined together to form a large plant strainer located on 

the floor of the suppression pool, as illustrated in the Figure 5.11-16. The resulting strainers 

have surface areas in excess of 6000 ft2. Enercon tested these strainers at a quarter-scale 

testing facility. 

Figure 5.11-15. Individual 

Enercon Mark III Strainer 

Module (Rao et al., 2001).
5-225

Figure 5.11-16. Illustration 

of Installed Enercon Mark III 

Strainer (Rao et al., 2001).

Prototype replacement strainer testing was conducted at a specially constructed test facility, 

where quarter-scale strainer prototypes were installed. The quarter-scale prototype test strainer 

module differed in construction from the actual plant modules with respect to specifics such as 

the number of ribs and the plate thickness, which affected the scalability of the clean-strainer 

head loss but not the scalability of the screen surface area. Plant hydraulic conditions and 

debris loads were scaled to the prototype strainer size. Specifically the approach velocities 

were maintained the same and the debris loadings per unit area were equal to or greater than 

those expected in the plant.

The NRC staff audited the GGNS strainer clogging resolution and reviewed the Grand Gulf 

head loss testing. The GGNS replacement strainer has a screen area of 6253 ft2 and serves as 

a common header for all six ECCS pumps so that any combination of operating systems can 

draw recirculation water through the same large screen area. All of the prototype tests were 

conducted at 75°F. The data repeatability was acceptable. Head loss variations of 2-ft water or 

less were measured during repeatability tests, and the plant had sufficient NPSH margin to 

account for these uncertainties. The head loss test data indicated that some of the tests might 

not have reached steady state before termination. The licensee accounted for this apparent 

shortcoming by extrapolating to a steady value for the mission time (Rao et al., 2001).

Grand Gulf uses predominantly Mirror-brand RMI cassettes to insulate reactor system piping, 

but substantial inventories of Kaowool, calcium-silicate, and fiberglass insulations are also 

present in the containment. Due to the low strainer approach velocities of approximately 0.016 

ft/sec, RMI debris did not accumulate or remain attached to the strainer. Therefore, the head 

loss concern at Grand Gulf came from the combined effects of fibrous debris (Kaowool and 

fiberglass) and particulate debris (calcium silicate). The combination of these types of debris

resulted in high head losses even though the approach velocity was relatively low. These 

results represented a significant finding because such data had previously not been available. 

ABB Strainer Design and Testing

The large-capacity passive replacement strainers designed by ABB are constructed of a strainer 

plate shaped into longitudinal pleats to extend the plate area and thus reduce the approach 

velocity at the plate. The strainer plates, have 5/8-in. perforations with an overlaying 1/16-in. 
5-226

wire mesh. ABB conducted prototype testing of their design at the EPRI facility. The debris 

loads for the Limerick testing consisted primarily of NUKON and iron oxide corrosion products. 

The design report for the ABB strainer is proprietary. The strainer is described as a strainer with 

pleated surfaces. A correlation algorithm and a scaling factor were developed, based on the 

test data, which the staff found accpetable.
6-1

6 BWR INDUSTRY RESPONSE 

The NRC staff first addressed ECCS clogging issues in detail during its review of Unresolved 

Safety Issue (USI) A-43, “Containment Emergency Sump Performance.” The resolution of USI 

A-43 is documented in GL-85-22, “Potential for Loss of Post-LOCA Recirculation Capability due 

to Insulation Debris Blockage,” dated December 3, 1985. The staff concluded at that time that 

no new requirements would be imposed on licensees. During the 1990s, however, new 

information arose which challenged the adequacy of the NRC’s conclusion that no new 

requirements were needed to prevent clogging of ECCS strainers in BWRs. In July 1992, a 

Barsebäck event demonstrated the potential for a pipe break to generate and transport a 

sufficient amount of debris to the suppression pool to clog the ECCS strainers.

Similarly, in 1993, two events involving the clogging of ECCS strainers occurred at the Perry 

Nuclear Power Plant, a domestic BWR. Both Perry events involved clogging of the RHR pump 

suction strainers by debris in the suppression pool. The debris consisted of glass fibers and 

corrosion products (or “sludge”) that had been filtered from the pool by the glass fibers that had 

accumulated on the strainer. The Perry events demonstrated the deleterious effects on strainer 

pressure drop caused by the filtration of particulates by fibrous materials adhering to the strainer 

surface, a previously unrecognized effect.

The Barsebäck and Perry events led to the development of NRC Bulletin 96-03, the draft for 

which was released for a 60-day public comment on July 31, 1995 (Office of Federal Register, 

1995). During the public comment period, NRC staff resources were diverted from NRC Bulletin 

96-03 to the development of NRC Bulletin 95-02 due to an event at Limerick Generating Station, 

Unit 1. On September 11, 1995, Limerick Unit 1 was operating at 100 percent power when a 

reactor safety relief valve (SRV) spuriously opened. Operators were unable to close the SRV, 

and a manual reactor scram was initiated. During the event, two loops of suppression pool 

cooling were operated to remove heat being released into the pool. During the event, the 

operators observed fluctuating motor current and flow on the “A” loop of suppression pool 

cooling. Cavitation was the apparent cause, and the loop was secured. The “A” pump was 

checked and successfully restarted with no further problems observed. Following the event, a 

diver inspected the condition/cleanliness of the strainers and suppression pool. The diver found 

both “A” loop strainers almost entirely covered with a thin mat of debris, consisting mostly of 

fibers and sludge. The “B” loop strainers had a similar covering, but less of it. Analysis showed 

that the mat primarily consisted of iron oxides and polymeric fibers. The fiber source was not 

identified, but the licensee determined that they did not originate within the suppression pool 

and contained no trace of either fiberglass or asbestos. This event demonstrated the 

importance of FME practices to ensure adequate suppression-pool cleanliness. In addition, it 

re-emphasized that materials other than fibrous insulation could clog strainers.

NRC Bulletin 96-03 was issued on May 6, 1996. It requested BWR licensees to implement 

appropriate procedural measures and plant modifications to minimize the potential for clogging 

of ECCS suction strainers by debris generated during a LOCA. Also issued was RG 1.82, 

Revision 2, “Water Sources for Long-Term Recirculation Cooling Following a Loss-of-Coolant 

Accident,” which presents guidance on plant-specific analyses to evaluate the ability of the 

ECCS to provide long-term cooling consistent with the requirements of 10 CFR 50.46.
6-2

6.1 NRC Bulletin 1995-02

On October 17, 1995, NRC issued NRC Bulletin 95-02 to all holders of BWR operating licenses 

or construction permits. It was issued because the staff was concerned that BWR licensees 

had inadequately maintained suppression pool cleanliness. The concern arose out of the 

Limerick event described above. Limerick had never cleaned the Unit 1 suppression pool. 

Some of the debris that clogged their strainers had apparently been left in the pool during plant 

construction. Clearly, debris in the suppression pool threatened the ability of the pumps that 

draw suction from the suppression pool to adequately perform their safety functions. This 

bulletin was issued to:

1 Alert addressees to complications experienced during the Limerick event.

2 Request addressees to assess the operability of their ECCS and other pumps that draw 

suction from the suppression pool on the basis of suppression pool/suction strainer 

cleanliness, and the effectiveness of the addressee’s FME practices. In addition, 

addressees were requested to implement appropriate procedural modifications and 

other actions (e.g., suppression pool cleaning), as necessary, to minimize foreign 

material in the suppression pool and containment. Addressees were requested to verify 

their operability evaluation through appropriate testing and inspection.

3 Require that addressees report to the NRC whether and to what extent they complied 

with the requested actions. A second report was required upon completion of 

confirmatory test(s) and inspection(s) to provide the results, verify that addressees had 

complied with the requested actions, or indicate completion of any proposed alternative 

actions.

Figure 6.1-1 shows that BWR licensees had, in fact, cleaned their suppression pools. Figure 

6.1-1 does not include Big Rock Point because its design does not have a suppression pool, 

and Browns Ferry, Unit 1, which was in an extended shutdown at the time of the response. 

Tennessee Valley Authority, the licensee for Browns Ferry, stated in their response that they 

would address the bulletin issues for Unit 1 before restarting the plant. 

Figure 6.1-1. NRC Bulletin 95-02 Responses on Last Suppression Pool Cleaning
6-3

The Containment Systems and Severe Accident Branch of NRC performed detailed reviews of 

11 plants and wrote safety evaluations on those responses. Since no safety issues were 

identified in either the preliminary or the detailed reviews, and it was learned that utilities had 

been cleaning their suppression pools, NRC redirected its resources to the completion of NRC 

Bulletin 96-03. The NRC also completed reviews on addional plants. 

NRC concluded that it was appropriate to close this multi plant action (MPA) without further 

review for the following reasons: 

1 Over 85% of the BWRs had been reviewed in detail with no safety concerns identified. 

2 Of the five remaining plants, an inspection visit to two (Perry and Grand Gulf) showed 

suppression pools to be extremely clean. 

3 As part of the review of NRC Bulletin 96-03, a detailed audit of Grand Gulf Nuclear 

Station (GGNS) was performed including FME procedures. The audit team concluded 

that GGNS had implemented an appropriate inspection program to ensure the 

operability of the ECCS (relative to strainer and suppression pool cleanliness). The 

team also implemented appropriate foreign material control procedures to limit the 

potential for clogging the ECCS with materials brought into the drywell or wetwell during 

outage operations. 

4 The NRC issued “Temporary Instruction (TI) 2515/125—Foreign Material Exclusion 

Controls” on August 25, 1994 to determine whether licensees had implemented effective 

procedures to prevent foreign material from inadvertently entering safety systems during 

maintenance activities, outages, and routine operations. After reviewing the FME 

controls at Fitzpatrick and Hatch in response to TI 2515/125, resident inspectors for both 

plants concluded that the FME controls of the licensees were adequate. 

In general, NRC review found that concerns raised by the events at Barsebäck and Perry, as 

well as the NRC‘s focus on strainer issues, had increased awareness of foreign material issues 

among BWR licensees. This heightened awareness resulted in increased attention being given 

to suppression-pool cleanliness even before the issuance of the NRC Bulletin 95-02. This is 

evidenced by the fact that most of the plants had cleaned their suppression pools within the 

three years prior to the bulletin. Limerick had cleaned the Unit 2 suppression pool prior to the 

Unit 1 event, and Unit 1 was scheduled for cleaning at the next refueling outage at the time of 

the event. Only NMP-1 had not recently cleaned their suppression pool, and in response to the 

bulletin, they committed to do so at the next outage of sufficient duration. It should not be 

construed that NMP-1 had any less sensitivity to the issue than the other BWR licensees. Their 

analysis of the plant led them to conclude that they did not need to clean their pool again. In 

1981, they had drained and cleaned the entire torus. Since then, they have minimized any 

potential to introduce debris into the torus. Divers retrieved items that were inadvertently 

dropped into the torus pool by workers. Because NMP-1 uses mostly RMI, NMP-1 staff 

concluded that they were not likely to introduce fibrous material into the torus during outages. 

On this basis, they had concluded that there was no need to clean the torus again. However, as 

noted above, they committed to do so in response to NRC Bulletin 95-02.

6.2 NRC Bulletin 1996-03

NRC Bulletin 96-03 was issued to request licensees to implement appropriate procedural 

measures and plant modifications to minimize the potential for clogging of suction strainers in 

the suppression pool by debris generated during a LOCA. The bulletin identified three 

resolution options. These options were to install one of the following: a large-capacity passive 

strainer, a self-cleaning strainer, or a backflush system. 
6-4

Table 6.2-1 summarizes the actions taken by each licensee. All licensees elected to use option 

1, installation of large-capacity passive strainers. Four different vendor designs were used: the 

GE stacked disk strainer, the PCI “Sure-Flow” stacked disk strainer, the Enercon toroidal 

strainer, and ABB strainer. The total installed strainer surface areas per plant are also shown in 

Table 6.2-1.

At the time of the issuance of the bulletin, the BWROG was developing topical report NEDO32686, “Utility Resolution Guidance for ECCS Suction Strainer Blockage.” The purpose of the 

URG is to provide utilities with (1) guidance on evaluation of the ECCS potential strainer 

clogging issue for their plant, (2) a standard industry approach to resolution of the issue that is 

technically sound, and (3) guidance that is consistent with the requested actions in the bulletin 

for demonstrating compliance with 10 CFR 50.46. The URG included guidance on a 

calculational methodology for performing plant-specific evaluations of potential strainer 

blockage. After reviewing responses to NRC Bulletin 96-03, NRC concluded that all affected 

BWR licensees had designed their new large-capacity passive strainers consistent with the 

criteria in the URG which had been reviewed and approved by the NRC staff.

During the development of NRC Bulletin 96-03, NRC decided not to perform detailed reviews of 

every plant. As a result, the reporting requirements for the bulletin do not contain detailed 

descriptions of proposed resolutions by the licensees. Instead, the staff developed a strategy 

for reviewing the implementation of this bulletin which consisted of conducted a review of the 

URG combined with a sampling of plants. Specifically, the staff first reviewed and issued a 

safety evaluation on the URG. The URG provided a baseline evaluation process for 

determining how much strainer area was needed for each plant. The second component of the 

staff‘s review included detailed audits of four sites to ensure that the application of the URG 

guidelines was consistent with the staff‘s basis for approval of the URG.

The NRC staff conducted audits (Rao et al., 2001) of four sites: Limerick Generating Station, 

Units 1 and 2; Dresden Nuclear Power Station, Units 2 and 3; Duane Arnold Energy Center; and 

Grand Gulf Nuclear Station. The results of these audits showed that these licensees had 

adequately designed their ECCS strainers to withstand the debris loads anticipated during a 

LOCA. No safety concerns were identified at any of the plants. On the basis of the audit 

findings and results of the staff‘s review of the URG, NRC did not consider it necessary to 

perform any additional detailed reviews of licensee resolutions. In addition to the review work 

cited above, the staff performed a number of additional reviews related to the strainer clogging 

resolution. This work included several test programs, both by the NRC and the industry. The 

work was conducted at LANL and reported in Report LA-UR-01-1595 (Rao et al., 2001), which 

summarizes the efforts of the NRC, the NRC’s contractors, and industry to resolve the BWR 

ECCS strainer clogging issue.
6-5

Table 6.2-1. Summary of Strainer Modifications Made in Response to NRC Bulletin 96

Plant Name, Plant Type and 

Containment Type

Stacked Disk Strainer Designs Other 

Strainer 

Design

Type of Review 

Performed by 

NRC

Approxima

Strainer A

per P

Bolt-on

Supplemental 

Supports

Ring Girder 

Mounted

Browns Ferry 2 & 3 BWR/4, Mark I X 1,2,5 119

Brunswick 1 & 2 BWR/4, Mark I X X 1,4 157

Clinton BWR/6, Mark III Toroidal 1 605

Cooper BWR/4, Mark I X 1,7 216

Dresden 2 & 3 BWR/3, Mark I X 1,6 47

Duane Arnold BWR/4, Mark I X 1,6 135

Fitzpatrick BWR/4, Mark I X 1,2 292

Fermi 2 BWR/4, Mark I X 1 232

Grand Gulf BWR/6, Mark III Toroidal 1,2,6 625

Hatch 1 & 2 BWR/4, Mark I X 1,3 111

Hope Creek BWR/4, Mark I X 1,3 378

LaSalle 1 & 2 BWR/5, Mark II X 1,2 50

Limerick 1 & 2 BWR/4, Mark I X 1,6 271

Monticello BWR/3, Mark I X 1,7 122

NMP-1 BWR/2, Mark I X 1 128

NMP-2 BWR/4, Mark II X 1 141

Oyster Creek BWR/2, Mark I X 1,3 142

Peach Bottom 2 & 3 BWR/4, Mark I X 1,2,3 355

Perry BWR/6, Mark III Toroidal 1,2,7 532

Pilgrim BWR/3, Mark I X 1,2,5,7 134

Quad Cities 1 & 2 BWR/3, Mark I X 1,2,5 83

River Bend BWR/6, Mark III X X 1,2 242

Susquehanna 1 & 2 BWR/4, Mark II X 1 134

Vermont Yankee BWR/4, Mark I X 1,2 248

WNP-2 BWR/5, Mark II X 1 82

1) Review of licensee response to NRC Bulletin 96-03 only.

2) Meeting with licensee to discuss licensee’s proposed resolution and strainer sizing criteria.

3) Review of strainer sizing criteria, including performance of confirmatory calculations of estimated debris loadings.

4) Review of strainer sizing criteria and strainer performance characteristics (i.e., head loss), including performance of co

5) Review of strainer sizing criteria and strainer performance characteristics, including performance of confirmatory calcul

license amendment for containment pressure credit in NPSH calculations.

6) Detailed audit of plant resolution of the strainer blockage issue.

7) Site visit.

7-1

7 PWR INDUSTRY RESPONSE

7.1 NRC BULLETIN 2003-01

7.1.1 Introduction

On June 9, 2003 NRC issued NRC Bulletin 2003-01 (03-01), “Potential Impact of Debris 

Blockage on Emergency Sump Recirculation at Pressurized-Water Reactors.” This bulletin was 

addressed to all holders of operating licenses for PWRs and was issued to: 

1 Inform addressees of the results of NRC-sponsored research identifying the potential 

susceptibility of pressurized-water reactor (PWR) recirculation sump strainers to debris 

blockage in the event of a high-energy line break (HELB) requiring recirculation 

operation of the emergency core cooling system (ECCS) or containment spray system 

(CSS).

2 Inform addressees of the potential for additional adverse effects due to debris blockage 

of flowpaths necessary for ECCS and CSS recirculation and containment drainage.

3 Request that, in light of these potentially adverse effects, addressees confirm their 

compliance with 10 CFR 50.46(b)(5) and other existing applicable regulatory 

requirements, or describe any compensatory measures implemented to reduce the 

potential risk due to post-accident debris blockage as evaluations to determine 

compliance proceed.

4 Require addressees to provide the NRC a written response in accordance with 10 CFR 

50.54(f).

The bulletin described the history of the occurrences of sump strainer blockage, the 

corresponding regulatory basis, and the research conducted by NRC on the issue to date. In 

response to the issues associated with the potential post-accident debris blockage concerns 

identified in the bulletin, the NRC requested that individual PWR licensees submit information 

on an expedited basis to document that they had either (1) analyzed the ECCS and CSS 

recirculation functions with respect to the identified post-accident debris blockage effects, taking 

into account the recent research findings, and determined that compliance exists with all 

applicable regulatory requirements, or (2) implemented appropriate interim compensatory 

measures to reduce the risk associated with potentially degraded or nonconforming ECCS and 

CSS recirculation functions while evaluations to determine compliance proceed. 

Conditions at specific PWRs were expected to vary with respect to susceptibility to postaccident debris blockage, and various options were anticipated to be available to addressees for 

preventing or mitigating the effects of debris blockage. For these reasons, addressees that 

were unable to confirm compliance with all existing regulatory requirements within 60 days in 

light of the potential debris blockage effects identified in the bulletin were requested to consider 

a range of possible interim compensatory measures (ICM) and to implement those which they 

deemed appropriate, based upon the specific conditions associated with their plants. The risk 

benefit of certain interim compensatory measures was demonstrated by the NRC-sponsored 

technical report LA-UR-02-7562 (Kern and Thomas, 2003). Possible ICMs proposed in NRC 

Bulletin 03-01 are listed in Table 7.1-1.

In addition to the measures listed, addressees were also requested to consider implementing 

unique or plant-specific compensatory measures, as applicable. Commensurate with the 

potential risk-significance of post-accident debris blockage effects, addressees electing to 
7-2

implement ICMs in response to the NRC Bulletin 03-01 were requested to ensure that the 

interim measures were implemented as soon as practical. 

Table 7.1-1. Interim Compensatory Measures (ICM) and Their Categories

Category Description

ICM 1 Providing operator training on indications of and responses to sump clogging

ICM 2 Making procedural modifications that would delay the switchover to containment 

sump recirculation

ICM 3 Ensuring alternative water sources to refill the RWST or to otherwise provide 

inventory to inject into the reactor core and spray into the containment atmosphere

ICM 4 Undertaking more aggressive containment cleaning and increased foreign material 

controls

ICM 5 Ensuring containment drainage paths are unblocked

ICM 6 Ensuring sump strainers are free of adverse gaps and breaches

Responding to the NRC Bulletin 03-01, all plants stated that they had chosen option 2 and listed 

the ICMs they either implemented or were planning to implement. The plant responses also 

provided the basis for any measures they rejected. 

In response to NRC Bulletin 03-01, the Westinghouse Owners Group prepared a report, WCAP16204 (Westinghouse Electric, 2004). The report provided a list of candidate operator actions 

(COA) recommended for consideration and implementation by the Westinghouse and 

Combustion Engineering designed plants. The possible actions that were proposed by WCAP16204 are listed in Table 7.1-2.

Table 7.1-2. Candidate Operator Actions and Their Categories

Category Description

A1a Implement operator action to secure one spray pump

A1b Implement operator action to secure both spray pumps

A2 Manually establish one train of containment sump recirculation before automatic 

actuation

A3 Terminate one train of safety injection (HPSI/high-head injection) after recirculation 

alignment

A4 Implement early termination of one LPSI/RHR pump before recirculation alignment

A5 Refill of refueling water storage tank

A6 Inject more than one RWST volume by drawing from a refilled RWST or by 

bypassing the RWST

A7 Provide more aggressive cooldown and depressurization following a SBLOCA

A8 Provide guidance on symptoms and identification of containment sump blockage

A9 Develop contingency actions in response to containment sump blockage, loss of 

suction, and cavitation

A10 Implement early termination of one train of HPSI/high-head injection before 

recirculation alignment

A11 Prevent or delay containment spray for SBLOCAs (<1.0 in. dia) in ice condenser 

plants
7-3

Since the WCAP-16204 report was issued after the requested response date for NRC Bulletin 

03-01, NRC requested all Westinghouse- and Combustion Engineering-designed plants to 

provide the discussion of candidate operator actions through requests for additional information 

(RAIs). A response similar to the ICMs, listed in NRC Bulletin 03-01, was requested. That is, 

the plants were to either list the particular actions they had implemented or planned to 

implement, or provide the basis for rejecting specific actions. In addition, a few Babcock & 

Wilcox plants also provided their discussion of the COAs.

7.1.2 NRC Bulletin 2003-01 Database

Argonne National Laboratory (ANL) was tasked by NRC with creating an NRC Bulletin 03-01 

database. The database collected every action, in both ICM and COA categories, discussed by 

each plant in the responses to NRC Bulletin 03-01 and subsequent RAIs from NRC. The 

actions have been categorized for the database in the following types:

• Accepted: meaning that the particular action has either been already implemented by a 

plant or implemented as a result of NRC Bulletin 03-01 response.

• Planned: meaning that in its NRC Bulletin 03-01 response, a plant proposed to 

implement the action in the near future, often by a specified date or at coming refueling 

outage. Although it is expected that the planned actions were later implemented, those 

actions are still distinguished in the database from the accepted actions. 

• Rejected: meaning that this particular action or measure was not implemented by a 

plant. For those actions, a basis for the rejection is recorded in the database.

• Not applicable: meaning that action could not be applied to a plant. Examples include 

responses of a dry atmospheric containment plant to the actions specifically designed for 

ice condenser containments. 

• Not considered: meaning that a plant did not consider a particular action. Usually, this 

type refers to unique or plant-specific actions requested by NRC Bulletin 03-01, in cases 

when the response specifically stated that a plant did not consider any actions (if a plant 

considered some action, but decided not to implement those, such actions would be 

listed as “rejected” in the database). 

The NRC Bulletin 03-01 database was developed using Microsoft Access software. As stated 

above, each record of the database refers to a particular action or compensatory measure 

discussed by a plant. For each action, the information is recorded for the following fields: 
7-4

Plant Name There are two special cases – Arkansas Nuclear One and Millstone – which 

have different plant designs for different units. To have a one-to-one 

relationship between the plant name and its design, it was decided in the NRC 

Bulletin 03-01 database to treat Arkansas Nuclear One Units 1 and 2 and 

Millstone Units 2 and 3 as separate plants. They are referenced as, for 

example, Arkansas Nuclear One 1 in the database. 

Unit This field either states that the action is common for all units of the plant or 

otherwise specifies the unit number the action is applied to. 

ICM/COA This field specifies if the action belongs to either ICMs or COAs.

Category Specifies a category of ICM (numbered “1” to “6” according to Table 7.1-1, plus 

a “plant specific” option) or COA (according to Table 7.1-2, numbered “A1a” to 

“A11”).

Action type “Accepted”, “Planned”, “Rejected”, “Not considered”, or “Not applicable”, as 

described above. 

Action 

Description 

A brief, up to few sentences, description of the action. Additional information 

there may include, for example, a specific procedure reference for procedure 

modification actions, or a basis for rejection for “Rejected” actions. 

ML Number Specifies the ADAMS accession number of the document on which the 

database entry is based, such as licensee response or NRC closure letter. 

Based on the above information, a table of actions is generated in the NRC Bulletin 03-01 

database. This table is automatically integrated in the database with a table specifying 

characteristics of each plant, such as NRC region, reactor supplier, and containment type. As a 

result of such integration, each action is associated with the reactor characteristics. This 

provides an opportunity, for example, to select actions for Westinghouse-designed plants only. 

A total number of 1,084 actions (database records) have been collected for the NRC Bulletin 03-

01 database. The distribution of these records by various fields – such as by reactor, by action 

type, by ICM/COA category – is analyzed in the Database Results section below. These types

of statistics, displayed in various table forms, is one of the two major database’s capabilities. 

The other is the detailed report for records that satisfy user-selected criteria, as described in the 

Appendix A, Section A.1. 

7.1.3 NRC Bulletin 2003-01 Database Results

The detailed results from NRC Bulletin 03-01 database are presented in Appendix A, Section 

A.1. Figure 7.1-1 shows a summary of the database results in the form of the distribution of the 

actions from all plants by ICM/COA categories and type. Figure 7.1-1 demonstrates that 

majority of the ICMs from NRC Bulletin 03-01 have been implemented or were planned for 

implementation. The noticeable exception is ICM 2 (procedural modifications that would delay 

the switchover to containment sump recirculation), where the plants rejected a significant 

portion of such actions. For COAs, the majority of A1a-A4 candidate actions were rejected, 

while most A5-A9 actions were either implemented or planned. Most of the actions in COA A10 

category were either rejected or not applicable. None of the A11 actions was implemented or 

planned. This inference is similar for all reactor types (although COA categories were not 

developed for Babcock & Wilcox plants – see Appendix A for details). 
7-5

Figure 7.1-1. Action Type by ICM/COA Categories

0

10

20

30

40

50

60

70

80

90

1 2 3 4 5 6 7 A1a A1b A2 A3 A4 A5 A6 A7 A8 A9 A10 A11

Accepted

Planned

Rejected

Not applicable

Not considered

 ICM COA
7-6

7.2 NRC Generic Letter 2004-02

7.2.1 Introduction

In Section 4.5 of this report, the contents of the NRC-issued Generic Letter 2004-02 (GL-04-02) 

were presented. In particular, NRC issued this Generic Letter to:

1 Request that addressees perform an evaluation of the ECCS and CSS recirculation 

functions in light of the information provided in the letter and, if appropriate, take 

additional actions to ensure system function. Additionally, addressees were requested 

to submit the information specified in the letter to the NRC. The request was based on 

the identified potential susceptibility of PWR recirculation sump strainers to debris 

blockage during design basis accidents requiring recirculation operation of ECCS or 

CSS and on the potential for additional adverse effects due to debris blockage of 

flowpaths necessary for ECCS and CSS recirculation and containment drainage.

2 Require addressees to provide the NRC a written response in accordance with 10 CFR 

50.54(f).

To assist in determining, on a plant-specific basis, the impact on sump strainer performance and 

other related effects of extended post-accident operation with debris-laden fluids, addressees 

were permitted to use the guidance in RG 1.82, Revision 3, “Water Sources for Long-Term 

Recirculation Cooling Following a Loss-of-Coolant Accident,” dated November 2003. Revision 3 

enhanced the debris blockage evaluation guidance for PWRs provided in Revision 1 to better 

model sump-strainer debris blockage and related effects. Revision 1 replaced the 50% 

blockage assumption in Revision 0 with a comprehensive, mechanistic assessment of plantspecific debris blockage potential for future modifications related to sump performance, such as 

thermal insulation changeouts. This revision was made in response to the findings of USI A-43. 

The staff issued Revision 2 of RG 1.82 after evaluating blockage events such as the Barsebäck 

Unit 2 event mentioned above but for BWRs only. The NRC staff determined after the issuance 

of Revision 2 that research for PWRs indicated that the guidance in that revision was not 

comprehensive enough to ensure adequate evaluation of a PWR plant’s susceptibility to the 

detrimental effects of debris accumulation on debris interceptors (e.g., trash racks and sump 

strainers). This led to the issuance of Revision 3 to address the PWRs. 

In order to better understand the concerns identified in the generic letter, both the NRC and 

industry have conducted extensive research programs in the areas of debris generation, debris 

transport, protective coatings, head loss tests, chemical effects and downstream effects. One 

result from these research prgrams is that the NRC staff concluded that the NUREG/CR-6224 

correlation for suction strainer qualification developed for the BWRs in response to Bulletin 

1995-02 was not accurate enough to use with PWR strainers. Every licensee needed to 

conduct plant specific head loss tests with plant specific prototypical debris. 

Each PWR liscensee has conducted site specific tests as mentioned above and has provided 

the NRC staff a response to the generic letter which summarizes the analyses completed and 

test results which demonstrate qualification of their suction strainers. The remainder of this 

chapter describes the database developed from the generic letter responses.
7-7

7.2.2 Generic Letter 2004-02 Database

To address the sump blockage issues, this knowledge base report collected the initial 

responses of the licensees to GL-04-02, RAIs, and any further correspondence between NRC 

and the licensees up through April 28, 2011 (the date of the latest document incorporated in the 

database). The information was organized in a form of a database. For the database creation, 

the licensee responses were collected in several areas that included: 

• Strainer 

- Previous screen area per strainer and number of strainers per plant

- New screen area with number per plant

- Strainer hole size

- Strainer type and vendor,

- Whether the strainer is vented or not

- Number of trains11 per plant

• Plant modifications in response to GL-04-02, including

- Physical modifications (such as an installation of new strainer)

- Administrative modifications (such as procedure changes)

- Downstream modifications (separately)

• Information on head loss testing, including

- Strainer approach velocity

- Test facility location

- Clean strainer head loss

- Head loss with non-chemical debris

- Full debris head loss

- Thin bed thickness

• Net Positive Suction Head (NPSH)

- NPSH required and available along with NPSH margin for each pump

- Minimum strainer submergence in accidents

- Submergence at switch over to sump circulation and final submergence

• Debris generation, such as

- Amount and composition of latent debris

- Strainer sacrificial area (for tags, etc.)

- Strainer scaling factor for testing,

- Amount of the debris generated and transported to the strainer

- Surrogate debris types and amounts used for testing

- Debris zone of influence

- Chemical buffer

• Downstream effects

 

11 The number of safety trains and strainers per plant varies by plant design. Some plants have separate 

suction strainers for the safety injection and containment spray systems that are in the same train, others 

have a combined strainer. While even others have separate strainers in different parts of the 

containment building, such a one for vapor containment and one for internal recirculation. For the 

purposes of the GL-04-02 database, the definition of “train” is the same as in the licensee responses.
7-8

- Model used for ex-vessel and in-vessel analyses

- Amount of debris that bypasses the strainer

- Fuel type

- Core head loss

For each value or entry from the above list, the source of the information was recorded in the 

database in the form of ML number of the document and the page number. Another field 

indicates whether the information comes from a proprietary document.12 In addition to that, a 

comment field was created in the database for the user to record any related information for 

each entry. 

The exact structure of database entries is different for the different types of the information 

collected. However, in general, each database entry has the following format:

- Plant name

- Unit13 (if a record is applied to all units, 0 is entered in this field)

- Pump or strainer to which the record is applied

- Case (such as SBLOCA)

- The value (such as screen size)

- ML number for the source document

- Page number in that document14

- Proprietary information checkmark

- Comments 

A group of the database fields is often referred to as just “field” in this report. For example, the 

report may refer to New Screen Area field, which actually means a group of the database fields, 

including the actual value for the screen area, ML number, page number, comments, etc.

The detailed description of each field along with the specifics of the information collected for the 

database is presented in Appendix A (Section A.2.3). 

The compilation is linked to a database that includes the NRC region, NSSS supplier, and 

containment type for each plant (the same table that was used for the NRC Bulletin 03-01 

database). That linkage enables the sorting and/or selections of the GL-04-02 database 

records by NSS supplier, for example. 

The GL-04-02 database was developed in the Microsoft Access environment. The user interface 

for the GL-04-02 database is described in Appendix A, Section A.2.1. 

 

12The database capability to distinguish proprietary records has not been used for this report. All the 

information collected in the GL 04-02 databse to date and used in this report come from public sources. 

13Unit is a required field for the GL-04-02 database. For single-unit plants, such as Ginna, “1” is entered 

in the unit field. Thus, in the results presented further in this section, that and other similar plants would 

be shown as “Ginna-1.” 14Page number in the PDF ML document is recorded in the database (as opposed to the page number in 

the original submission). For example, several submissions and/or appendixes can be combined into one 

ML document, each with its own page numbering. Using page number for the entire document avoids 

any possible confusion to what part of the document this page number is applied.
7-9

At the time of this report preparation, the interactions between NRC and the plants regarding the 

GL-04-02 are still in progress. Some of the plants are still submitting RAI responses to NRC. 

For these reasons, the GL-04-02 database, as it is presented in this report, cannot be viewed as 

“finished”; it is expected that new information may be available for the database in the future. In 

addition to the potential for new data to be added, some of the data currently in the database 

may become outdated due to ongoing evaluations. At the time this knowledge base was 

completed the NRC was reviewing the industry guidance for in-vessel resolution so the issue 

had not been completed at most plants. Additionally, some plants had not provided adequate 

information to the staff regarding strainer performance. Therefore, plant changes or additional 

evaluations may be required to address these issues. 

The detailed description of the database field and the information entered into each field in the 

GL-04-02 database are presented in the Section A.2.3 of Appendix A. 

7.2.3 Generic Letter 2004-02 Database Results 

The results obtained with the GL-04-02 database are presented in Appendix A, Section A.2.3. 

Appendix A also provides the detailed describtion of each field in the database along with the 

assumptions made during the database compilation. 

As an example of the GL-04-02 database results, Fig. 7.2-1 compares the new and previous 

strainer screen area for all plants (the exact meaning of the data plotted in Fig. 7.2-1 is provided 

in Appendix A). Overall, Fig. 7.2-1 demonstrates significant increases in strainer screen areas

in response to GL-04-02. It also shows the significant difference in newly installed screen size 

among the plants (and sometimes among the units of the same plant). 

Similar variation between the plants was observed for almost all of the parameters recorded in 

the GL-04-02 database (see Appendix A). For the fields for which no graphs can be plotted (for 

example, for the list of the plant modification), the information is displayed in Appendix A in a 

table form.
7-10

Figure 7.2-1. Total Strainer Screen Area

0 93 186 279 372 465 557 650 743 836

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000

St. Lucie - 1

Surry - 2

Surry - 1

Wolf Creek - 1

North Anna - 1

Palo Verde - 1

Palo Verde - 2

Palo Verde - 3

Millstone - 2

Shearon Harris - 1

Calvert Cliffs - 1

Calvert Cliffs - 2

North Anna - 2

St. Lucie - 2

Turkey Point - 3

South Texas - 1

South Texas - 2

Vogtle - 1

Vogtle - 2

Summer - 1

Oconee - 2

Oconee - 3

Millstone - 3

Oconee - 1

Salem - 1

ANO - 2

Seabrook - 1

Watts Bar - 1

Watts Bar - 2

Salem - 2

Indian Point - 2

Indian Point - 3

Robinson - 2

Ginna - 1

Comanche Peak - 1

Comanche Peak - 2

Waterford - 3

Turkey Point - 4

Palisades - 1

Beaver Valley - 1

Beaver Valley - 2

Callaway - 1

Diablo Canyon - 1

Diablo Canyon - 2

Braidwood - 1

Braidwood - 2

Byron - 1

Byron - 2

Farley - 2

Farley - 1

ANO - 1

Three Mile Island - 1

Davis Besse - 1

Catawba - 1

Catawba - 2

D.C. Cook - 1

D.C. Cook - 2

San Onofre - 2

San Onofre - 3

Point Beach - 1

Point Beach - 2

McGuire - 1

McGuire - 2

Sequoyah - 1

Sequoyah - 2

Crystal River - 3

Fort Calhoun - 1

Prairie Island - 1

Prairie Island - 2

Kewaunee - 1

Screen Size, m2

Screen Size, ft2

Previous Size

New Size
8-1

8 SUMMARY

The containment sumps in PWRs (also known as the emergency or recirculation sump) and 

suppression pools in BWRs, and ECCS and recirculation strainers are integral parts of a safety

systems required to ensure the safety of commercial nuclear reactors. Every nuclear power 

plant in the United States is required by the Code of Federal Regulations (10 CFR 50.46) to 

have an ECCS that is capable of mitigating a design basis accident. 

In PWRs, the containment sump collects reactor coolant and chemically reactive spray solutions 

after a LOCA. The sump serves as the water source to support long-term recirculation for 

residual heat removal, emergency core cooling, containment cooling and pressure control, and 

containment atmosphere cleanup. In BWRs the suppression pool provides the water source. 

This water source, the related pump inlets, and the piping between the source and inlets are 

important safety components. In the event of a LOCA within the containment of a light water 

reactor (LWR), piping thermal insulation and other materials in the vicinity of the break will be 

dislodged by the pipe break and steam/water-jet impingement. A fraction of this fragmented 

and dislodged insulation and other materials, such as paint chips, paint particulates, and 

concrete dust, will be transported to the containment floor by the steam/water flows induced by 

the break and by the containment sprays. Some of this debris eventually will be transported to

and accumulated on the recirculation-sump suction strainers in PWR containments or on the 

pump-suction strainer in BWR containments. Debris accumulation on the sump strainers could 

challenge the plant’s capability to provide an adequate water supply to the ECCS and the CSS 

pumps.

The current state of knowledge has evolved significantly due to the work on PWRs, conducted 

by the NRC and the nuclear industry. The Generic Safety Issue (GSI)-191 study, “Assessment 

of Debris Accumulation on PWR Sump Performance,” was established by the NRC to determine 

if the transport and accumulation of debris in a containment following a LOCA could impede the 

operation of the ECCS in operating PWRs. Assessing the likelihood of the ECCS and CSS 

pumps in domestic PWRs experiencing a debris-induced loss of NPSH margin during sump 

recirculation was the primary objective of the NRC's technical assessment of GSI-191. The 

technical assessment culminated in a parametric study that mechanistically treated phenomena 

associated with debris blockage using analytical models of domestic PWRs generated with a 

combination of generic and plant-specific data. 

This report describes the current status of the knowledge base on emergency core cooling 

sump performance in operating LWRs. The report discusses the substantial knowledge that 

has been developed as a result of the research on issues related to debris clogging of BWR 

suction strainers and PWR sump strainers. The report provides brief background information 

(Sections 1 through 4) regarding these issues. This background information includes a 

historical overview of the resolution of the BWR issue with a lead into the PWR issue, a 

description of the safety concern relative to PWR reactors, the criteria for evaluating sump 

failure, descriptions of postulated accidents, descriptions of relevant plant features that influence 

accident progression, and a discussion of the regulatory considerations. 

Section 5 of the report presents the current state-of-the-art resolution methodology for 

understanding the strainer blockage phenomena and processes that have evolved over the 

years. This section incorporates our current understanding of many of the actions/processes 

that can have an impact on the available NPSH margin in ECCS and CSS. The section 

presents details on pipe break characterization, debris generation and zone of influence, debris 

transport, coatings and coating debris, latent debris, debris accumulation and head loss, debris 
8-2

head loss correlations, chemical effects on head loss, and downstream effects. The section 

also includes a description of the test programs conducted by several vendors in support of 

BWRs and PWRs. 

Section 6 is a summary of industry response by BWR licensees and the closure of NRC Bulletin 

96-03, based on the URG for ECCS suction strainer blockage. Since no safety concerns were 

identified at any of four audited plants and NRC accepted the URG methodology, NRC did not 

consider it necessary to perform any additional detailed reviews of licensee resolutions. In 

addition to the review work cited above, the staff performed a number of additional plant reviews 

related to strainer clogging, including several test programs conducted both by the NRC and the 

nuclear industry. The work is reported in LA-UR-01-1595 (Rao et al., 2001), which summarizes 

the efforts of the NRC, the NRC’s contractors, and industry to resolve the BWR ECCS strainer 

clogging issue.

Section 7 and Apendix A discuss in detail the plant-by-plant PWR licensee responses to NRC 

Bulletin 03-01 and GL-04-02. The licensee responses to the initial generic letter and the 

responses to the requests for information were collected for several areas and put into a

database. Information regarding strainer characteristics, physical and administrative plant 

modifications, head loss test information, chemical effects, NPSH required and available, debris 

characteristics, and downstream effects are included in the database. The collected information 

has been incorporated in user-friendly databases based on Microsoft Access with capabilities

to select various criteria to filter the information, carry out search/sort of the data, and assess 

phenomenon-specific or plant-specific information. 

To organize the information related to the NRC Bulletin 2003-01, a database was developed, 

and information was input on the interim compensatory measures (ICMs) proposed in the 

bulletin with regard to which measures were implemented, planned, or rejected by each plant. 

In addition to ICMs, the database also contains, in a similar manner, the plant responses to the 

candidate operator actions (COAs) proposed by the Westinghouse Owners Group to address 

Bulletin 03-01 issues. Each Bulletin 03-01 database record refers to a single action discussed 

by a plant. A record includes the plant name, unit, ICM/COA category, action type (such as 

“accepted”), a brief description of the action, and the ML number reference for this record. 

The Bulletin 03-01 responses in the database were combined with a table defining design 

features of each plant, such as NSS supplier and containment type. That expanded database 

allows the selection of the Bulletin 03-01 responses by various parameters and their 

combination, such as accepted actions for a given containment type. A user interface was 

developed for the Bulletin 03-01 database to facilitate such selection in an interactive manner. 

The results of a search of the database that satisfy the selected criteria can be displayed in a 

table or in graphical form. In addition to this criteria selection capability, the database also 

provides the statistics covering all the information stored in the database. For example, a total 

number of accepted, planned, or rejected actions can be displayed for each ICM/COA category. 

Based on the Bulletin 2003-01 database results, the following observations were made. A 

majority of ICM measures were either implemented or were planned for implementation by the 

response time. Among the ICM categories (see Table 7.1-1), ICM category 2 displayed the 

largest number of rejected actions. Also, several plant-specific measures were implemented. 

For COA categories (see Table 7.1-2), the majority of COAs for A1-A4 and A10-A11 were either 

rejected or not applicable to a specific plant. In contrast, most of the A5-A9 actions were 

implemented or planned for implementation. This inference is similar for all reactor types 

(although COA categories were not developed for Babcock & Wilcox plants). 
8-3

Similar to the Bulletin 03-01 database, the responses to the GL-04-02, “Potential Impact of 

Debris Blockage on Emergency Recirculation during Design Basis Accidents at PressurizedWater Reactors,” were collected to create a GL-04-02 database. The GL-04-02 database 

includes 28 tables in six areas. Each table contains the information on a particular field, such as 

new screen area, for each plant. The structure of each table changes depending on the 

specifics of the information in that table, but in general the structure of the database records is 

similar to that of the Bulletin 03-01 database. Each record at least contains the plant name, 

unit, the recorded value (such as the screen area), the ML number and page number for the 

source of the information, and a Comments field. In some cases, more than one value is stored 

in the database records. For example, the Debris-Amount table contains information on the 

amount of debris both generated at a break and used in testing. 

A user interface, similar to that of the Bulletin 03-01 database, was developed for the GL-04-02 

database. The interface provides the user with the capability to select various criteria to filter 

the information, carry out search/sort of the information, and select the particular database table 

for which the results are displayed. The results are presented in a table form and can be 

transferred to Microsoft Excel for plotting. The GL-04-02 database also incorporates a table 

defining the specifics of each plant such that the database records can be filtered, based on 

selected design features. 

Based on the information in the GL-04-02 database, the plots of various parameters were 

prepared to compare the results for all the PWR plants in the U.S. For example, the new screen 

size plot shows a significant increase in the screen area for the strainers installed in response to 

GL-04-02. It also shows, however, a significant variation in the size of these new strainers 

among the plants. Similar variations between the plants were observed for almost all of the 

parameters recorded in the GL-04-02 database. For the fields for which no graphs can be 

plotted (for example, the list of the plant modifications), the information is displayed in a table 

form. At the time of this report’s preparation, the work on the resolution of issues associated 

with GL-04-02 was in progress so some information in the database may change. 

In August 2010, NRC issued a document (SECY-10-0113) on closure options for GSI-191. On 

December 23, 2010, NRC issued a memorandum (Vietti-Cook, 2010) stating that two major 

outstanding issues (namely, the size of the zone of influence and quantity of fiber that could 

cause a blockage in the reactor core which could affect long term core cooling) need to be 

resolved jointly by the NRC and industry to achieve closure of the ECCS issue in U.S. PWRs. 

These documents were updated in 2012 by SECY-12-0093 and its related SRM. The 2012 

update proposed a risk-informed approach for GSI-191 resolution, which the Commission 

approved in December 2012. At the time of this NUREG publication a pilot plant submittal is 

under review by NRR staff.

9-1

9 REFERENCES

9.1 NRC Documents Cited

ADAMS Accession No. ML043090005, Response to Advisory Committee on Reactor 

Safeguards on Safety Evaluation of the Industry Guidelines Related to Pressurized Water 

Reactor Sump Performance, November 26, 2004.

ADAMS Accession No ML090410618, North Anna Power Station Audit Report, Corrective 

Actions for Generic Letter 2004-02: Chemical Effects, 2008.

Bulletin 03-01 “Potential Impact of Debris Blockage on Emergency Sump Recirculation at 

Pressurized-Water Reactors,” June 9, 2003.

Bulletin 93-02, “Debris Plugging of Emergency Core Cooling Suction Strainers,” May 11, 1993. 

Bulletin 95-02, “Unexpected Clogging of a Residual Heat Removal (RHR) Pump Strainer While 

Operating in Suppression Pool Cooling Mode,” October 17, 1995. 

Bulletin 96-03, “Potential Plugging of Emergency Core Cooling Suction Strainers by Debris in 

Boiling-Water Reactors,” May 6, 1996. 

DG-1107, “Water Sources for Long-Term Recirculation Cooling Following a Loss-of-Coolant 

Accident,” Draft Regulatory Guide, February 2003. ADAMS Accession No. ML043090005

Evaluation of NEI Guidance on PWR Sump Performance, GSI-191 SER, Rev. 0, U.S. Nuclear 

Regulatory Commission, December 2004. ADAMS Accession No. ML043280007

GL-04-02, “Potential Impact of Debris Blockage on Emergency Recirculation During Design 

Basis Accidents at Pressurized-Water Reactors,” September 2004.

GL-85-22, “Potential for Loss of Post-LOCA Recirculation Capability Due to Insulation Debris 

Blockage,” December 3, 1985.

GL-97-04, “Assurance of Sufficient Net Positive Suction Head for Emergency Core Cooling and 

Containment Heat Removal Pumps,” October 7, 1997.

GL-98-04, “Potential for Degradation of the Emergency Core Cooling System and the 

Containment Spray System after Loss-of-Coolant Accident Because of Construction and 

Protective Coating Deficiencies and Foreign Material in Containment,” July 14, 1998.

IN-88-28, “Potential for Loss of Post-LOCA Recirculation Capability Due to Insulation Debris 

Blockage,” NRC Information Notice, May 19, 1988.

IN-89-77, “Debris in Containment Emergency Sumps and Incorrect Screen Configurations,” 

NRC Information Notice, November 21, 1989.

IN-89-77, Supplement 1, “Debris in Containment Emergency Sumps and Incorrect Screen,” 

NRC Information Notice, December 3, 1993.

IN-92-71, “Partial Blockage of Suppression Pool Strainers at a Foreign BWR,” NRC Information 

Notice, September 30, 1992.

IN-92-85, “Potential Failures of Emergency Core Cooling Systems Caused by Foreign Material 

Blockage,” NRC Information Notice, December 23, 1992.

IN-93-02, Bulletin 93-02, Supplement 1, “Debris Plugging of Emergency Core Cooling Suction 

Strainers,” NRC Bulletin to Licensees, February 18, 1994.
9-2

IN-93-34, “Potential for Loss of Emergency Cooling Function due to a Combination of 

Operational and Post-LOCA Debris in Containment,” NRC Information Notice, April 26, 1993.

IN-94-57, “Debris in Containment and the Residual Heat Removal System,” NRC Information 

Notice, August 12, 1994.

IN-95-06, “Potential Blockage of Safety-Related Strainers by Material Brought inside 

Containment,” NRC Information Notice, January 25, 1995.

IN-95-47, “Debris in Containment and the Residual Heat Removal System,” NRC Information 

Notice, August 12, 1994.

IN-96-10, “Potential Blockage by Debris of Safety System Piping Which Is Not Used during 

Normal Operation or Tested During Surveillances,” NRC Information Notice, February 13, 1996.

IN-96-59, “Potential Degradation of Post Loss-of-Coolant Recirculation Capability as a Result of 

Debris,” NRC Information Notice, October 30, 1996.

IN-97-13, “Deficient Conditions Associated with Protective Coatings at Nuclear Power Plants,” 

NRC Information Notice, March 24, 1997.

LER 50-266/97-006, “Potential Refueling Cavity Drain Failure Could Affect Accident Mitigation,” 

Point Beach Unit 1, February 19, 1997.

LER 50-269/97-010, “Inadequate Analysis of ECCS Sump Inventory due to Inadequate Design 

Analysis,” Oconee Unit 1, January 8, 1998

LER 50-315/98-017, “Debris Recovered from Ice Condenser Represents Unanalyzed 

Condition,” D.C. Cook Unit 1, July 1, 1998

LER 50-346/02-005-01, “Potential Clogging of the Emergency Sump due to Debris in 

Containment,” Davis-Besse Unit 1, December 11, 2002. 

LER 50-346/03-002-00, “Potential Degradation of High Pressure Injection Pumps due to Debris 

in Emergency Sump Fluid Post Accident,” Davis-Besse Unit 1, May 5, 2003.

LER 50-369/90-012, “Loose Material Was Located in Upper Containment during Unit Operation 

Because of an Inappropriate Action,” McGuire Unit 1, August 30, 1990.

LER 50-440/93-011, “Excessive Strainer Differential Pressure across the RHR (Residual Heat 

Removal) Suction Strainer Could Have Compromised Long Term Cooling during Post-LOCA 

Operation,” May 19, 1993.

LER 50-455/97-001, “Unit 2 Containment Drain System Clogged due to Debris,” Byron Unit 2, 

April 17, 1997.

NEA/CSNI/R (95) 11, “Knowledge Base for Emergency Core Cooling System Recirculation 

Reliability,” Prepared by U.S. Nuclear Regulatory Commission for the Principal Working Group 

1, International Task Group, Committee on the Safety of Nuclear Installations, Organization for 

Economic Cooperation and Development Nuclear Energy, February 1996.

NEDO-32686, “Utility Resolution Guidance for ECCS Suction Strainer Blockage,” Boiling Water 

Reactor Owners Group, Rev. 0, November 1996. ADAMS Accession No ML092530500.

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9-3

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9-4

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9-5

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9-6

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9-9

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9-10

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9-11

Rao, D. V., C. J. Shaffer, and R. Elliot, 2001, “BWR ECCS Strainer Blockage Issue: Summary of 

Research and Resolution Actions,” Los Alamos National Laboratory, LA-UR-01-1595, ADAMS 

Accession No. ML012970246.

Reid, R. D., K. R. Crytzer, A. E. Lane, and T. S. Andreychek, 2006, “Evaluation of Alternative 

Emergency Core Cooling System Buffering Agents,” Westinghouse Electric Company, WCAP16596-NP Revision 0, ADAMS Accession No ML062570173.

Reid, R. D., K. R. Crytzer, A. E. Lane, 2007, “Evaluation of Additional Inputs to the WCAP16530-NP Chemical Model,” Westinghouse Electric Company, WCAP-16785-NP, Revision 0, 

ADAMS Accession No. ML072010381.

Scott, M. L., 2006, “Staff Observations Regarding Flume Testing of a Prototype Portion of the 

Proposed Replacement Suction Screen Design for the Comanche Peak Steam Electric Station,” 

Letter to Jared S. Wermiel, Division of Safety Systems, Docket Nos. 50-445 and 50-446, 

ADAMS Accession No..ML061280580.

Scott, P., et al., “Review of GE Nuclear Energy/BWR Owners Group Report on the Evaluation 

for Existence of Blast Waves Following Licensing Basis Double-Ended Guillotine Pipe Breaks,” 

Battelle Columbus, Inc., April 11, 1996, ADAMS Accession No.ML9605140096.

Shack, W. J., 2007, “Technical Letter Report on WACP-16530-NP, Evaluation of Post-Accident 

Chemical Effects in Containment Sump Fluids to Support GSI-191,” NRC Technical Letter 

Report, ADAMS Accession No..ML080650350.

Smith, S. J., 2008a, “Staff Observations of Testing for Generic Safety Issue 191 during February 

12 and February 13 Trip to the Alden Test Facility for PCI Strainer Tests,” Letter to M. L. Scott, 

Safety Issues Resolution Branch, ADAMS Accession No. ML080920398.

Smith, S. J., 2008b, “Staff Observations of Testing for Generic Safety Issue 191 during July 29 

to July 31, 2008 Trip to the Alden Test Facility for PCI Strainer Tests,” Letter to M. L. Scott, 

Safety Issues Resolution Branch, ADAMS Accession No. ML083470317.

Smith, S. J., 2010, “Staff Observations of Testing for Generic Safety Issue 191 during July 12 to 

July 14, 2010 Trip to the Alden Test Facility for PCI Strainer Tests,” Letter to M. L. Scott, Safety 

Issues Resolution Branch, ADAMS Accession No. ML102160226.

Städtke, H., 2006, Gasdynamic Aspects of Two-Phase Flow, Wiley-VCH, Federal Republic of 

Germany.

Van Straten, H. V., B. T. W. Holtkamp, and P. L. de Bruyn, 1984, “Precipitation from Supersaturated Aluminate Solutions: I. Nucleation and Growth of Solid Phases at Room 

Temperature,” J. Colloid Interface Sci. 98, 342-362.

Vietti-Cook, A. L., “Staff Requirements – SECY-10-0113 – Closure Options for Generic Safety 

Issue-191, Assessment of Debris Accumulation on Pressurized Water Reactor Sump 

Performance,” Memorandum to R. W. Borchardt, December 23, 2010, ADAMS Accession No. 

ML072550227.
9-12

Wallis, G., 2004, “The ANSI/ANS Standard 58.2-1988: Two-Phase Jet Model,” ADAMS 

Accession No. ML050830344.

Westinghouse Electric, 2004, “Evaluation of Potential ERG and EPG Changes to Address NRC 

Bulletin 2003-01 Recommendations (PA-SEE-0085),”, WCAP-16204 Rev. 1.

Westinghouse Electric, 2006, Submittal of “Evaluation of Downstream Sump Debris Effects in 

Support of GSI 191,” Rev. 1, WCAP-16406-P ADAMS Accession No. ML072550227.
A-1

Appendix A. NRC BULLETIN 2003-01 AND GENERIC LETTER 

 2004-02 DATABASES

This appendix contains a discussion and summary tables of two Microsoft Access databases 

developed to tabulate PWR liscensees’ responses to NRC Bulletin 2003-01 and Generic Letter 

2004-02. The complete databases are archived in ADAMS at Ascession Nos. ML13170A449 

and ML13170A455, respectively. (When opening these database files from the ADAMS system, 

the user my receive a message “The file does not exist, or you do not have read access to the 

file”. If you see this message just click ok and save the file to your desktop.)

A.1 NRC BULLETIN 2003-01 DATABASE

The description of the Bulletin 2003-01(03-01) Database is provided in Chapter 7.1 of this 

report. Here, only the user interface and detailed results from the database are presented. 

A.1.1 Bulletin 03-01 Database User Interface

A total number of 1,084 actions (database records) have been collected for the NRC Bulletin 03-

01 database. The distribution of these records by various fields – such as by reactor, by action 

type, by Interim Compensatory Measure/Candidate Operator Action (ICM/COA) category – is 

analyzed in the Database Results section below. This type of statistics, displayed in various 

table forms, is one of the two major database’s capabilities. The other is the detailed report for 

records that satisfy user-selected criteria, as described below. A choice between these two 

capabilities is presented to the user of the database in the main database window, as shown in 

Fig. A.1-1. 

In the Database-wide Statistics section, a user can select which particular result is to be 

displayed (Fig. A.1-2). Again, those results are presented in the Result section below. 

Figure A.1-1. Bulletin 03-01 

Database Main Window
A-2

Figure A.1-2. Bulletin 03-01 

Database Database-wide 

Statistics Selection Form

In the Criteria Selection section, a form is opened to assist a user in criteria selection. The 

Criteria Selection form (Fig. A.1-3) allows for interactive selection of a particular criterion for the 

filtering and a combination of various criteria. It also provides word-searching capabilities. The 

ICM, COA, and Action Type sections of the Criteria Selection form provide a possibility to 

choose any records based on these criteria. The ICM and COA sections of the database can 

be turned off completely by clicking on the option button in the corresponding section title bar. 

“Select All” and “Unselect All” buttons are provided in the ICM, COA, and Action Type sections 

to quickly turn on or clear all checkmarks in the corresponding section. The options in these 

sections are independent meaning that any combination of the criteria in these sections can be 

applied to the database records. The help (“?”) buttons in the ICM and COA sections provide 

the description of ICM and COA categories (similar to Tables A.1-1 and A.1-2), respectively.
A-3

Figure A.1-3. Criteria Selection Form of NRC Bulletin 03-01 Database

On the right-hand side of the form, a selection regarding the plants and units can be made. On 

top, the NRC regions of interest can be specified. Plant Selection allows choosing either all 

plants or selecting a specific plant. The Unit Selection group can filter records based on the 

plant unit the actions are applied to. “All” means to display all actions (no filter). The option 

“Include common actions only”, if turned on, will filter out the actions for specific units such that 

only actions described as those applicable to all plant units will be selected. “Specific” option 

means that the actions applicable to the selected plant units are displayed. Unless the “Include 

unit-specific actions only” option is selected, actions applicable to all units will also be displayed. 

The NSS Supplier and Containment Type sections allow filtering the database records by the 

reactor supplier (B&W, CE, or WEST), and containment type (DRYAMB (large dry), DRYSUB

(subatmospheric), or ICECND (ice condenser)), respectively. Either all types or a specific value 

can be selected from the drop down box. In general, the selection options in the right-hand side 

of the form are inter-dependent. For example, if a specific NRC region is selected, then the list 

in the drop down box for the reactor plant would only have the reactor names from this region. 

Similarly, if a specific reactor plant is selected, then the NSS Supplier and the Containment 

Type would already be defined by the reactor selection. Thus, if a specific plant is selected, 

these two sections will be deactivated on the form. If a specific NSS Supplier is selected, then 

the list options in the containment type will be limited to this supplier. Only the Unit Selection 

section is independent from other selections; any selection can be made regardless the other 

options. 
A-4

The Search section of the Criteria Selection form provides an opportunity to look for specific 

words in the Action Description field of the database. Up to five words can be entered in this 

section; only records which have an exact match for non-empty search boxes, in any order, will 

be displayed. For example, to find the records dealing with procedure modifications regarding 

RWST, words “RWST” and “procedure” can be entered in separate boxes of the Search section. 

The search is not case-sensitive. 

When any action is taken in the Criteria Selection form, the database automatically recalculates 

the number of records and number of plants that satisfy the selected criteria. Those two 

numbers are displayed in the corresponding boxes in the lower left-hand side of the Criteria 

Selection form. The statistics of the distribution of the selected records by ICM/COA categories 

and action types can be displayed by clicking on the magnifying glass button next to the record 

count. This is one of the report forms available from the Criteria Selection form. The other 

three types of the report can be displayed by clicking on a corresponding button below the plant 

count. These reports will show the complete database information (i.e., content of all fields) for 

the records that satisfy the selected criteria. The information displayed by these reports is the 

same; only the form of the reports is different. The Report button opens a report when all 

records are displayed in a printer-ready table. (An example of such report is shown in Table 

A.1-6 in the Results section below.) The selected criteria are repeated on top of this report. 

The Form report displays the information on record-by-record basis. The Table report shows 

the information in a table form. The results of the statistical and printer-ready reports can be 

transferred to MS Word or MS Excel for further analysis (with an exception of the selected 

criteria header).

A.1.2 NRC Bulletin 03-01 Database Results

This section presents the results obtained from NRC Bulletin 03-01 database. The results 

presented here are statistical results only in that they usually do not show the details of each 

particular tasks but rather the overall distribution of the tasks either by plants, categories, or 

types. Detailed reports can be generated by the database; they are not presented here due to 

space limitations. 

It is also noted that the results presented here represent a historical snapshot in time and may 

not be valid in future times, unless updated with new information. For example, the actions 

characterized as “planned” for this report are those that were planned for implementation by a 

plant at a time when Bulletin 03-01 response was prepared. It was not verified as part of this 

report whether those commintments were indeed carried out. Similarly, the information 

presented below does not guarantee that the actions described as “completed” would not be 

reversed in future, for example, as a result of design modifications.

Responding to the NRC Bulletin 03-01, all plants stated that they had chosen option 2 and listed 

the ICMs (Table A.1-1) they either implemented or were planning to implement. The plant 

responses also provided the basis for any measures they rejected.
A-5

Table A.1-1. Interim Compensatory Measures (ICM) and Their Categories

Category Description

ICM 1 Providing operator training on indications of and responses to sump clogging

ICM 2 Making procedural modifications that would delay the switchover to containment sump 

recirculation

ICM 3 Ensuring alternative water sources to refill the RWST or to otherwise provide inventory 

to inject into the reactor core and spray into the containment atmosphere

ICM 4 Undertaking more aggressive containment cleaning and increased foreign material 

controls

ICM 5 Ensuring containment drainage paths are unblocked

ICM 6 Ensuring sump strainers are free of adverse gaps and breaches

In response to NRC Bulletin 03-01, the Westinghouse Owners Group prepared a report, WCAP16204 (Westinghouse Electric, 2004). The report provided a list of candidate operator actions 

(COA) recommended for consideration and implementation by the Westinghouse and 

Combustion Engineering designed plants. The possible actions that were proposed by WCAP16204 are listed in Table A.1-2.

Table A.1-2. Candidate Operator Actions and Their Categories

Category Description

A1a Implement operator action to secure one spray pump

A1b Implement operator action to secure both spray pumps

A2 Manually establish one train of containment sump recirculation before automatic 

actuation

A3 Terminate one train of safety injection (HPSI/high-head injection) after recirculation 

alignment

A4 Implement early termination of one LPSI/RHR pump before recirculation alignment

A5 Refill of refueling water storage tank

A6 Inject more than one RWST volume by drawing from a refilled RWST or by bypassing 

the RWST

A7 Provide more aggressive cooldown and depressurization following a SBLOCA

A8 Provide guidance on symptoms and identification of containment sump blockage

A9 Develop contingency actions in response to containment sump blockage, loss of 

suction, and cavitation

A10 Implement early termination of one train of HPSI/high-head injection before 

recirculation alignment

A11 Prevent or delay containment spray for SBLOCAs (<1.0 in. dia) in ice condenser plants

Table A.1-3 shows the distribution of actions by ICM/COA categories for each plant. The plants 

are grouped by NRC region. The total number of actions for each plant is also shown in Table 

A.1-3. Table A.1-4 shows how the same actions are distributed between the action types for 

each plant. 
A-6

Table A.1-5 and Fig. A.1-4 show the distribution of the actions from all plants by ICM/COA 

categories and type. Figure A.1-2 demonstrates that majority of the ICMs from NRC Bulletin 03-

01 have been implemented or were planned for implementation. The noticeable exception is 

ICM 2 (procedural modifications that would delay the switchover to containment sump 

recirculation), where the plants rejected a significant portion of such actions. For COAs, the 

majority of A1a-A4 candidate actions were rejected, while most A5-A9 actions were either 

implemented or planned. Most of the actions in COA A10 category were either rejected or not 

applicable. None of the A11 actions was implemented or planned. 
A-7

Table A.1-3. Action Categories by Plant

Plant

ICM COA

Total 1 2 3 4 5 6 7 A1a A1b A2 A3 A4 A5 A6 A7 A

NRC Region 1

Beaver Valley 22 2 2 3 1 1 1 1 1 1 1 1 1 1 1 1 

Calvert Cliffs 19 2 1 1 1 1 1 1 1 1 1 1 1 1 1 1 

Ginna 27 6 2 1 3 1 2 2 1 1 1 1 1 1 1 

Indian Point 24 6 1 1 2 1 1 1 2 1 1 1 1 1 1 1 

Millstone 2 24 6 1 1 1 2 1 1 1 1 1 1 1 1 1 1 

Millstone 3 33 9 2 5 1 1 2 1 1 1 1 1 2 1 1 1 

Salem 59 8 7 2 12 3 2 1 2 2 2 2 2 2 2 2 2 

Seabrook 24 2 4 1 1 2 2 1 1 1 1 1 1 1 1 1 

Three Mile Island 21 3 2 1 1 1 1 1 1 1 1 1 1 1 1 1 

NRC Region 2

Catawba 25 4 3 2 2 1 1 1 1 1 1 1 1 1 1 1 

Crystal River 17 3 3 3 3 2 2 1

Farley 18 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 

McGuire 25 4 3 2 2 1 1 1 1 1 1 1 1 1 1 1 

North Anna 27 4 3 2 2 2 1 1 1 1 1 1 2 1 1 1 

Oconee 21 4 8 2 2 3 1 1

Robinson 22 3 1 1 2 1 1 1 1 1 1 1 1 1 1 1 1 

Sequoyah 20 1 1 1 1 2 1 1 1 1 1 1 1 1 1 1 1 

Shearon Harris 33 3 2 2 5 6 2 1 1 1 1 1 1 1 1 1 1 

St. Lucie 33 7 3 1 1 2 1 1 2 2 2 2 2 1 1 1 1 

Summer 22 2 2 1 2 1 1 1 1 1 1 1 1 1 1 1 1 

Surry 21 3 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 

Turkey Point 30 3 1 3 4 3 3 1 1 1 1 1 1 1 1 1 1 

Vogtle 19 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 

Watts Bar 27 4 1 1 3 2 1 3 1 1 1 1 1 1 1 1 1 

NRC Region 3

Braidwood 23 2 2 2 2 1 1 1 1 1 1 1 1 1 1 1 1 

Byron 23 2 2 2 2 1 1 1 1 1 1 1 1 1 1 1 1 

Davis Besse 13 1 1 2 2 4 2 1
A-8

DC Cook 32 2 1 1 1 4 2 5 1 1 1 1 1 3 3 1 1 

Kewaunee 26 2 3 2 4 1 1 1 1 1 1 1 1 1 1 1 1 

Palisades 22 1 3 1 2 1 1 1 1 1 1 1 1 1 1 1 1 

Point Beach 22 2 2 1 2 1 1 1 1 1 1 1 1 1 1 1 1 

Prairie Island 25 2 4 2 1 2 1 1 1 1 1 1 1 1 1 1 1 

NRC Region 4

Arkansas Nuclear 

One 1 22 1 2 3 1 1 1 1 1 1 1 1 1 1 1 1 1 

Arkansas Nuclear 

One 2 22 1 2 3 1 1 1 1 1 1 1 1 1 1 1 1 1 

Callaway 23 2 1 2 2 2 1 1 1 1 1 1 1 1 1 1 1 

Comanche Peak 25 3 2 2 3 1 1 1 1 1 1 1 1 1 1 1 1 

Diablo Canyon 23 3 1 2 1 2 1 1 1 1 1 1 1 1 1 1 1 

Fort Calhoun 35 7 7 1 1 1 1 5 1 1 1 1 1 1 1 1 1 

Palo Verde 28 2 1 3 3 2 4 1 1 1 1 1 1 1 1 1 1 

San Onofre 25 4 1 2 4 1 1 1 1 1 1 1 1 1 1 1 

South Texas 28 6 2 5 1 1 1 1 1 1 1 1 1 1 1 1 

Waterford 28 7 1 2 3 2 1 1 1 1 1 1 1 1 1 1 

Wolf Creek 26 6 2 2 2 1 1 1 1 1 1 1 1 1 1 1 

Table A.1-4. Action Types by Plant

Plant Total of 

Record

Accepted Planned Rejected Not 

Applicable

Not 

Considered

NRC Region 1

Beaver Valley 22 10 3 7 2

Calvert Cliffs 19 10 2 6 1

Ginna 27 16 8 1 2

Indian Point 24 16 4 4

Millstone 2 24 16 6 1 1

Millstone 3 33 21 5 4 3

Salem 59 39 7 11 2

Seabrook 24 12 4 5 3

Three Mile Island 21 9 6 4 2
A-9

NRC Region 2

Catawba 25 17152

Crystal River 173 122

Farley 18 10233

McGuire 25 17152

North Anna 27 17262

Oconee 21 10 101

Robinson 22 13621

Sequoyah 208381

Shearon Harris 33 158721

St. Lucie 33 15 1161

Summer 229571

Surry 21 11262

Turkey Point 30 158331

Vogtle 1991531

Watts Bar 27 16281

NRC Region 3

Braidwood 232 11631

Byron 232 11631

Davis Besse 1367

DC Cook 32 20372

Kewaunee 26 10943

Palisades 223 1441

Point Beach 229832

Prairie Island 25 12931

NRC Region 4

Arkansas Nuclear 

One 1

22 113611

Arkansas Nuclear 

One 2

2293811

Callaway 235 1062

Comanche Peak 259853

Diablo Canyon 2394541

Fort Calhoun 35 10 1591
A-10

Palo Verde 28 12 9 6 1

San Onofre 25 18 6 1

South Texas 28 22 5 1

Waterford 28 15 5 7 1

Wolf Creek 26 13 6 6 1

Table A.1-5. Action Types by ICM/COA Category

Action Type

ICM/COA Category Total Accepted Planned Rejected Not Applicable Not Co

ICM 1 147 86 61

2 96 47 21 28

3 80 51 24 4 

4 93 68 25

5 72 55 17

6 56 48 8

7 37 15 8 5 

COA A1a 43 9 6 28

A1b 42 5 2 35

A2 42 1 40 1

A3 42 5 3 33 

A4 42 1 2 24 15

A5 45 29 16

A6 43 26 12 5

A7 41 30 7 2 2

A8 41 31 10

A9 41 23 18

A10 41 2 1 19 19

A11 40 5 34 
A-11

Figure A.1-4. Action Type by ICM/COA Categories

The results in previous tables and figure are generated based on the data from the entire 

database. Below are database results obtained from subsets of the data based on some 

selection criteria. These results utilize the selection criteria capability of the NRC Bulletin 03-01 

database described above. Note that the results presented below show only a fraction of data 

available from the database; an almost unlimited set of results can be generated using various 

combinations of criteria selection and/or search filters. 

Figure A.1-5 compares the distribution of the actions by the ICM/COA categories and type for 

three reactor suppliers. Note that the COA proposed by WCAP-16204 (Westinghouse Electric, 

2004) generally do not apply to Babcock & Wilcox plants, but two B&W plants, Arkansas 

Nuclear One 1 and Three Mile Island still provided a discussion of those actions. That 

information is easily available from the NRC Bulletin 03-01 database report with corresponding 

selection criteria, as demonstrated in Table A.1-6.

0

10

20

30

40

50

60

70

80

90

1 2 3 4 5 6 7 A1a A1b A2 A3 A4 A5 A6 A7 A8 A9 A10 A11

Accepted

Planned

Rejected

Not applicable

Not considered

 ICM COA
A-12

Figure A.1-5. NRC Bulletin 03-01 Database Results by Supplier

0

1

2

3

4

5

6

7

8

9

1 2 3 4 5 6 7 A1a A1b A2 A3 A4 A5 A6 A7 A8 A9 A10 A11

Accepted

Planned

Rejected

Not applicable

Not considered

 ICM COA

B&W

0

5

10

15

20

25

1 2 3 4 5 6 7 A1a A1b A2 A3 A4 A5 A6 A7 A8 A9 A10 A11

Accepted

Planned

Rejected

Not applicable

Not considered

 ICM COA

CE

0

10

20

30

40

50

60

70

1 2 3 4 5 6 7 A1a A1b A2 A3 A4 A5 A6 A7 A8 A9 A10 A11

Accepted

Planned

Rejected

Not applicable

Not considered

 ICM COA

WEST
A-13

Table A.1-6. NRC Bulletin 03-01 Database Report - COA for B&W Plants

Selected Criteria:

ICM - COA - Action type - NRC Region(s): 1 2 3 4 

A1a A6 Accepted Plant(s): All

A1b A7 Planned Unit(s): All

A2 A8 Rejected

A3 A9 Not considered NSS Supplier: B&W

A4 A10 Not applicable

A5 A11 Containment: Any

Action Description Search: <None>

Conditions Satisfied for

24 Records 2 Plants

Plant

NSS 

Supplier Containment

Unit

(s)

ICM/

COA Category

Action 

Type Action Description

Arkansas 

Nuclear 

One 1 B&W DRYAMB

1 COA A1a Accepted

This step is already in current EO

However, ANO-1 does not secure 

reactor building spray pump prior 

sump recirculation, and in respon

sump blockage, one spray pump 

secured if there is indication of a 

containment breach or two spray 

are secured if there is no indicatio

containment breach.

1 COA A1b Accepted

This step is already in current EO

However, ANO-1 does not secure 

reactor building spray pump prior 

sump recirculation, and in respon

sump blockage, one spray pump 

secured if there is indication of a 
A-14

containment breach or two spray 

are secured if there is no indicatio

containment breach.

1 COA A2 Rejected

Automatic actuation of sump 

recirculation is not applicable, and 

transfer of one train of sump recir

early was unacceptable due to ne

positive suction head requiremen

BWST drawdown rate, and valve 

times

1 COA A3 Rejected

Licensee is maintaining the same 

HPSI termination criteria (which a

applicable both before and after s

recirculation) as have been in effe

“ECCS flows shall not be throttled 

the core outlet is not sub-cooled o

than that required for pump prote

(actual sump blockage indication)

1 COA A4 Rejected

Licensee is maintaining the same 

HPSI termination criteria (which a

applicable both before and after s

recirculation) as have been in effe

“ECCS flows shall not be throttled 

the core outlet is not sub-cooled o

than that required for pump prote

(actual sump blockage indication)

1 COA A5 Accepted

Implemented in current operating 

procedures. (see also ICM categ

1 COA A6 Accepted

Covered under current procedure

Additional borated water sources 

made available for injection into th

and they include but are not limite

any remaining or refilled BWST 

inventory, clean waste receiver ta
A-15

BWST, batch boric acid additions 

BWST, delivered offsite sources, 

unborated water via the spent fue

As a last resort, pure unborated w

can be provided to the BWST for 

injection by the LPI pumps. A 

proceduralized method of adding 

inventory to the RCS, bypassing t

BWST, is via normal makeup from 

makeup tank. (see also ICM cate

#3).

1 COA A7 Accepted

Current EOPs expedite cooldown 

a LOCA, but cooldown limits do n

apply when the core exit thermo-c

are not sub-cooled. Forced Flow 

Cooldown Procedure is written fo

plant cooldown under LOCA cond

where sub-cooling margin is adeq

so normal cooldown limits apply. 

term “rapid cooldown” has a spec

procedure-based meaning (a rate 

than technical specification limits)

operators are trained to perform a

cooldowns as quickly as possible 

technical specification limits. (see 

ICM category #2).

1 COA A8 Accepted

This guidance is in the currently 

approved EOPs, which provide de

symptoms of sump blockage as w

indications to monitor. These sym

are lowering sump level and fluctu

in the ECCS pump performance, 

including erratic indication of suct

discharge pressure, flow, and am

(see also ICM category #1).

1 COA A9 Accepted Owners Group interim guidance s
A-16

that whenever ECCS is placed on 

reactor building sump recirculatio

there are symptoms of sump 

degradation, operator should veri

suction lineups, throttle LPI to min

flow rate, if both RBS trains are 

operating then stop one RBS train

evidence of containment breach t

stop all RBS pumps, and refer to 

management. If the sump were to 

procedures would direct the staff 

consider such actions as injecting 

additional coolant into the RCS. (

also ICM category #1).

1 COA A10 Rejected

Not implemented. Licensee is 

maintaining the same vendor HPS

termination criteria (which are app

both before and after sump recirc

as have been in effect, i.e., “ECC

shall not be throttled while the cor

is not sub-cooled other than that r

for pump protection” (actual sump 

blockage indication).

1 COA A11

Not 

applicabl e

Applies only to ice condenser pla

Three 

Mile 

Island B&W DRYAMB

All COA A1a Rejected

Not implemented, since minimal b

relative to an existing long duratio

to switchover (BWST drawdown o

approximately 28 min in the most 

LOCA events) relative to core coo

needs; operator burden early in a
A-17

event; resultant reduction of dose 

mitigation capability; and the abili

eventually throttle the LPSI pump

then securing one or both core sp

pumps (depending on potential do

consequences) should sump clog

indications arise.

All COA A1b Rejected

Not implemented, since minimal b

relative to an existing long duratio

to switchover (BWST drawdown o

approximately 28 min in the most 

LOCA events) relative to core coo

needs; operator burden early in a

event; resultant reduction of dose 

mitigation capability; and the abili

eventually throttle the LPSI pump

then securing one or both core sp

pumps (depending on potential do

consequences) should sump clog

indications arise.

All COA A2 Rejected

Not implemented, since the relativ

long BWST drawdown time allows 

substantial core cooling prior to 

switchover to ECCS recirculation

All COA A3

Not 

considere d

Not considered probably because 

B&W design.

All COA A4 Accepted

Considered the post-switchover L

pump throttling procedures to be 

reasonably similar in effect to CO

(ICM #1)

All COA A5 Planned

Revise the site emergency operat

procedures to incorporate interim 

measures to include initiating BW

after switchover to recirculation by 

September 15, 2005. TMI-1 has e
A-18

procedures for refilling the BWST 

the spent fuel pool and the conde

storage tanks, and the technical s

center guidance procedure curren

being developed will recommend 

alternate injection path using a no

makeup/RCS fill capability to hav

transfer pumps draw from one of 

reactor coolant bleed tanks and p

through the makeup system to the 

(ICM #3)

All COA A6 Planned

Develop guidance for injecting mo

one BWST volume from a refilled 

or for injecting from alternate wate

sources September 30, 2005. (IC

All COA A7 Rejected

Not implemented, since the relativ

long BWST drawdown time allows 

substantial core cooling prior to 

switchover to ECCS recirculation

All COA A8 Accepted

Enhanced the emergency proced

provide the guidance in regard to 

operation after switchover to ECC

sump suction. All the necessary 

indications are readily available to 

operators, including high vibration 

on the LPSI pumps. (ICM #1)

All COA A9 Accepted

Enhanced the emergency proced

provide the guidance in regard to 

operation after switchover to ECC

sump suction. (ICM #1)

All COA A10 Accepted

Already implemented through exis

procedures to shut down HPSI pu

soon as RCS pressure allows (IC

All COA A11

Not 

considered

Not considered probably because 

B&W design.
19

Figure A.1-6 shows a comparison of the distribution of the actions between different 

containment types, such as dry ambient pressure, dry sub-atmospheric, and wet ice condenser.

Figure A.1-6. Results from NRC Bulletin 03-01 Database by Containment Type

0

10

20

30

40

50

60

70

1 2 3 4 5 6 7 A1a A1b A2 A3 A4 A5 A6 A7 A8 A9 A10 A11

Accepted

Planned

Rejected

Not applicable

Not considered

 ICM COA

DRYAMB

0

2

4

6

8

10

12

1 2 3 4 5 6 7 A1a A1b A2 A3 A4 A5 A6 A7 A8 A9 A10 A11

Accepted

Planned

Rejected

Not applicable

Not considered

 ICM COA

DRYSUB

0

2

4

6

8

10

12

1 2 3 4 5 6 7 A1a A1b A2 A3 A4 A5 A6 A7 A8 A9 A10 A11

Accepted

Planned

Rejected

Not applicable

Not considered

 ICM COA

ICECND
A-20

A.2 NRC Generic Letter 2004-02

General description of the GL-04-02 Database is provided in Chapter 7.2 of this report. Here, 

only the user interface and detailed results from the database are presented. 

A.2.1 Generic Letter 2004-02 Database Interface 

The GL-2004-02 database was developed in the Microsoft Access environment. A user 

interface was created to simplify the navigation and use of the database. The main database 

form, which first opens when the database is loaded, is shown in Fig. A.2-1. From there, the 

user can select either to work with the results of the database or to view and modify each 

database record. 

The main database form (Fig. A.2-1) also lists the current date of the database. This capability 

is added to the database since by the time of this report preparation the GL-04-02 was not 

closed and plants continued to provide the information related to the GL-04-02. The current 

date reflects the date of the most recent document used for the database entries. 

Figure A.2-1. Main Form for GL-04-02 Database

In addition, two other options are available from the database main form (defined by smaller 

buttons on the right-hand side of the form). One is to see the database completion report 

(described in Section A.2.2.2). The other is to work with the tables, queries, and forms. This 

option is provided for further database development. 

The data modification mode is initiated by clicking on the View/Modify Data button on the main 

database form. In this mode, all database entries can be modified or deleted. A warning 

message is displayed when this mode is selected. Also in this mode, new entries can be added 

to the database. A data modification form, such as one shown in Fig. A.2-2, is opened. The 

desired database area (such as Strainer) can be selected on the right side of the form. A 

particular field of the database (such as New Size) is selected from the tabs at the top of the 

form, which are updated when new area is selected. In this form, all fields are open and can be 

modified and saved in the database (no dedicated “save” action is needed; the modified data 

are stored in the database instantaneously). The navigation through the records is done by 

clicking on the buttons on the lower side of the form. Built-in capabilities, such as searching, 

filtering, and sorting (available from either Access menu or toolbars) can be used to find the 

specific records. 
A-21

The Exit button is used to return to the main database form.

Figure A.2-2. Data View/Modification Form

In the View Results part of the database interface, two forms are opened (left and top forms in 

Figure A.2-3). The first form, Criteria Selection, allows selecting various parameters and their 

combination for filtering the database records. For example, only records for the plant, which 

belong to NRC Region 4, with NSSS supplied by CE and applicable to units 1 and 2 can be 

chosen to display in the Results form. This form is interactive in a way that each selection 

defines the choices available from other areas. For example, if any selection is made for the 

NRC region, the plant list (available after selecting “Specific” in the Plant area) will display only 

plants that satisfy the region selections. Similarly, if a specific NSSS supplier is selected, only 

containment types available with that selection will be displayed. 

The total number of plants, which satisfy the selected criteria, is shown below for the 

containment type selection on this form. Clicking on the magnifying glass icon next to that 

number will open a window with the list of those plants. This form also allows selection of units 

(English or SI) for the result forms. The Apply button will reload any open result form to reflect 

any changes made to the selection criteria. The Reset button clears any previously made 

selection such that all database records will be displayed. 
A-22

Figure A.2-3. Database Interface: Result View

The second (top) form in the Results view allows choosing the particular part (or table) of the 

database. The database area can be selected by clicking on the corresponding tab at the top of 

this form. In each tab, the buttons showing the available database fields (such as New Size) are 

displayed. In addition, in some cases, combined (modified) results can be viewed, such as 

minimum and maximum or total values of the specific field for each plant. 

Clicking on any of the buttons in the Table selection form opens the Result form below it (an 

example of Strainer New Size is shown in Figure A.2-3). The Results form shows the database 

records in a table form. Only the records that satisfy the criteria from the Criteria Selection form 

are displayed. In addition to that, the Access built-in tool for searching, sorting, and filtering can 

be applied to any field in the Results form. The data from the form (with conservation of any 

applied filters) can be transferred to Microsoft Excel by clicking on the Excel button at the 

bottom of the form (the results presented in Section A.2.3 were obtained by using this 

capability).

The data in the Results form can only be viewed, searched, and filtered. They cannot be 

modified. Any modifications to the Results form (such as sorting) only affect the way the data 

are displayed in this form. Such modifications do not affect the data stored in the database. 

(The View/Modify Data section available from the main database form should be used for data 

modifications.)

A.2.2 Generic Letter 04-02 Database Status

At present, the interactions between NRC and the plants regarding the GL-04-02 are still in 

progress. Some of the plants are still submitting RAI responses to NRC. For these reasons, 
A-23

the GL-04-02 database, as it is presented in this report, cannot be viewed as “finished”; it is 

expected that new or updated information may be available for the database in the future. 

The detailed description of the database field and the information entered into each field in the 

GL-04-02 database are presented in the next section. 

A.2.3 Generic Letter 2004-02 Database Results 

This section presents the compilation of the information stored in the GL-04-02 database. The 

information is presented for each field and covers all database records for that field. Where 

possible, the information is presented in a graphical form; otherwise, it is shown as a table. The 

results are preceded by a description of the specifics of the information collected for the 

database along with any assumptions made for a particular database field. 

Even though the information for some fields may be available from other sources, for this 

database the information was collected exclusively (with the exception of the fuel type) from the 

licensees’ responses to the GL-04-02. For example, the previous screen size refers to the 

strainer screen area installed before GL-04-02 was issued and might be recorded in earlier NRC 

documents. However, for consistency with other fields of the GL-04-02 database, only 

information reported by the plants in the GL-04-02 responses is entered into the database. A 

similar approach was adopted for all other fields. 

Strainer: Previous Size

In this field, the strainer screen area installed prior to GL-04-02 issuance is recorded. The 

screen area is usually provided in square feet (ft2). For the plants that have more than one 

strainer, the screen area is recorded for one strainer and the number of strainers per plant is 

also recorded. If multiple strainers were installed in a plant, then a separate database record is 

created for each strainer indicated by “Pump or Strainer” field. The total strainer area for a plant 

unit (Figure A.2-4) is calculated by the database and the results are presented together with the 

new strainer area described below. 

Strainer: New Size

This field contains the information on the strainer screen area installed in response to the GL04-02. The same approach to the multiple strainers, as for the previous size, is adopted for this 

field. In case when physically one strainer is installed in a plant, but there is a solid plate 

divided (such as for different trains), the strainer is considered to consist of two independent

strainers, each with 50% area (unless otherwise split is stated). If the divider plate has 

perforations in it, the strainers are not treated as independent. For these situations the strainer

is considered to be one strainer with the full screen area alotted to the strainer. 

Similarly to the previous size field, the total area per plant unit is calculated by the database. 

Figure A.2-4 compares the new and previous strainer screen area for all plants. In some cases, 

the previous screen size was not stated in the GL-04-02 responses and it is not included in Fig. 

A.2-4. The light bars show the previous screen size; the dark bars shown the new size. The 

light bars are shown atop of the dark bars to save the space; the dark bars should be 

considered starting from zero (not from where the light bars end). For example, for the Wolf 

Creek-1 plant (fourth line from the top in Fig. A.2-4), the previous screen size is 800 ft2 as 

indicated by the light bar. The new size is 6,600 ft2 and is shown by the location of the end of 
A-24

the dark bar. The same approach with overlapping bars is used for all the figures presented 

further in this section, unless otherwise stated. 

Overall, Fig. A.2-4 demonstrates a significant increase in strainer screen area in response to 

GL-04-02. It also shows the significant difference in newly installed screen sizes among the 

plants (and sometimes among the units of the same plant). 

Strainer: Hole Size

The hole (perforation) size for the newly installed strainers is shown in Fig. A.2-5. The database 

includes the hole size for all strainers reported in GL-04-02 responses. The database was built 

with a capability to display maximum and minimum hole size. However, for all the plants, 

maximum and minimum hole sizes, if reported, are always the same. Therefore, Fig. A.2-5 

displays only one strainer hole size per plant unit.

Strainer: Strainer Type and Vendor

The strainer vendor was recorded for each plant in the GL-04-02 database. A separate table 

was created in the database to indicate the type of the strainer for each vendor (so far, a one-toone relationship between the vendors and types exists). That table is automatically linked to the 

vendor field in the GL-04-02 database such that the strainer type is displayed for each plant in 

every database form where the vendor is displayed, although the strainer type is not stored 

specifically for each plant. 

Table A.2-1 shows the strainer type and the plants where this strainer was installed for each 

strainer vendor. Three plants, listed at the bottom of Table A.2-1, did not report the strainer type 

or vendor in GL-04-02 responses. 

Strainer: Vented

This field records if the strainer is vented or not. In most cases, the strainers are not vented. If 

it it not specifically stated in the response whether the strainer is vented or not, that field was left 

blank in the datatabse. Table A.2-2 lists the plant units for which the strainers were identified as 

vented in GL-04-02 responses. 

Strainer: Number of Trains per Plant

The number of safety trains and the number of strainers per plant varies by plant design. Some 

plants have separate suction strainers for the safety injection and containment spray systems 

that are in the same train, others have a combined strainer. While even others have separate 

strainers in different parts of the containment building, such as one for vapor containment and 

one for internal recirculation. For the purposes of the GL-04-02 database, the definition of 

“train” is the same as in the licensee responses. It is possible, for example, that a plant can 

have a common strainer for all its safety trains. In most cases, there are two safety trains per 

plant. Only one plant, South Texas units 1 and 2, reported three safety trains. 
A-25

Figure A.2-4. Total Strainer Screen Area

0 93 186 279 372 465 557 650 743 836

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000

St. Lucie - 1

Surry - 2

Surry - 1

Wolf Creek - 1

North Anna - 1

Palo Verde - 1

Palo Verde - 2

Palo Verde - 3

Millstone - 2

Shearon Harris - 1

Calvert Cliffs - 1

Calvert Cliffs - 2

North Anna - 2

St. Lucie - 2

Turkey Point - 3

South Texas - 1

South Texas - 2

Summer - 1

Oconee - 2

Oconee - 3

Millstone - 3

Oconee - 1

Salem - 1

ANO - 2

Seabrook - 1

Watts Bar - 1

Watts Bar - 2

Salem - 2

Indian Point - 2

Indian Point - 3

Robinson - 2

Ginna - 1

Comanche Peak - 1

Comanche Peak - 2

Waterford - 3

Turkey Point - 4

Palisades - 1

Beaver Valley - 1

Beaver Valley - 2

Callaway - 1

Diablo Canyon - 1

Diablo Canyon - 2

Braidwood - 1

Braidwood - 2

Byron - 1

Byron - 2

Farley - 2

Farley - 1

ANO - 1

Vogtle - 1

Vogtle - 2

Three Mile Island - 1

Catawba - 1

Catawba - 2

D.C. Cook - 1

D.C. Cook - 2

San Onofre - 2

San Onofre - 3

Point Beach - 1

Point Beach - 2

McGuire - 1

McGuire - 2

Sequoyah - 1

Sequoyah - 2

Davis Besse - 1

Crystal River - 3

Fort Calhoun - 1

Prairie Island - 1

Prairie Island - 2

Kewaunee - 1

Screen Size, m2

Screen Size, ft2

Previous Size

New Size
A-26

Figure A.2-5. New Strainer Hole Size

0.00 0.51 1.02 1.52 2.03 2.54 3.05 3.56 4.06 4.57 5.08

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2

Wolf Creek - 1

ANO - 1

ANO - 2

Beaver Valley - 1

Callaway - 1

Calvert Cliffs - 1

Calvert Cliffs - 2

Fort Calhoun - 1

Ginna - 1

Millstone - 2

Millstone - 3

North Anna - 1

North Anna - 2

Seabrook - 1

St. Lucie - 1

St. Lucie - 2

Summer - 1

Surry - 1

Surry - 2

Kewaunee - 1

Point Beach - 1

Point Beach - 2

Braidwood - 1

Braidwood - 2

Byron - 1

Byron - 2

Palo Verde - 1

Palo Verde - 2

Palo Verde - 3

Oconee - 1

Oconee - 2

Oconee - 3

Salem - 1

Salem - 2

Prairie Island - 1

Prairie Island - 2

Watts Bar - 1

Watts Bar - 2

Waterford - 3

Beaver Valley - 2

Catawba - 1

Catawba - 2

D.C. Cook - 1

D.C. Cook - 2

Diablo Canyon - 1

Diablo Canyon - 2

Farley - 1

Farley - 2

Indian Point - 2

Indian Point - 3

McGuire - 1

McGuire - 2

San Onofre - 2

San Onofre - 3

Shearon Harris - 1

Three Mile Island - 1

Turkey Point - 3

Turkey Point - 4

Vogtle - 1

Vogtle - 2

Comanche Peak - 1

Comanche Peak - 2

Palisades - 1

Sequoyah - 1

Sequoyah - 2

South Texas - 1

South Texas - 2

Crystal River - 3

Robinson - 2

Davis Besse - 1

Screen Hole Size, mm

Screen Hole Size, in
A-27

Table A.2-1. Strainer Vendors and Types.

Vendor Type Plant Name Unit

1 2 3 4

AECL Finned strainer with corrugated, 

perforated stainless steel fins

Millstone

North Anna

Summer

Surry

CCI Pocket Cassette design ANO

Beaver Valley

Braidwood

Byron

Calvert Cliffs

D.C. Cook

Ginna

Oconee

Palo Verde

Salem

Enercon Top hat style Beaver Valley

Catawba

Crystal River

Davis Besse

Indian Point

McGuire

Robinson

San Onofre

Shearon Harris

Three Mile Island

GE Stacked disk Diablo Canyon

Farley

Fort Calhoun

Seabrook

St. Lucie

Turkey Point

Vogtle

Waterford

PCI Stacked disk Callaway

Comanche Peak

Kewaunee

Palisades

Point Beach

Prairie Island

Sequoyah

South Texas

St. Lucie

Turkey Point

Watts Bar

Wolf Creek
A-28

Table A.2-2. Vented Strainers

Plant Name Unit

ANO 2

Comanche Peak 1

Comanche Peak 2

D.C. Cook 1

D.C. Cook 2

Palisades 1

Plant Modifications: Physical 

This field collects the physical plant modifications listed in the GL-04-02 responses. Only 

actions implemented, as a direct response to the GL-04-02, are collected for the database, i.e., 

no prior actions are included. 

For each action, a separate field is provided where it is stated if the action was credited in the 

evaluations for GL-04-02. If it was not clear from the response whether the action was credited 

or not, that field was left blank in the database. 

The entries in this and the following two fields reflect the information provided by the plant in the 

GL-04-02 responses. Similar to Bulletin 03-01 database, no verification was carried out to 

ensure that the commitments listed here were actually fulfilled. 

Table A.2-3 lists all physical plant modifications in the GL-04-02 database. 

Plant Modifications: Administrative

In addition to the physical actions, administrative actions were also recorded in the GL-04-02 

database. Those actions include procedure modifications, training, tagging, etc. Similarly to the 

physical modifications, the database records include a Yes/No field for credited actions. Table 

A.2-4 lists all administrative modifications collected in the database.

Plant Modifications: Downstream

The plant modifications for the components located downstream of the strainer are recorded 

separately in the GL-04-02 database (the physical plant modifications filed excluded 

downstream actions). The database records for the downstream modification also includes 

Yes/No field for such actions. If a plant response explicitly states that no downstream actions 

were needed, then “no” is recorded in that field, and no actions are listed. Table A.2-5 shows 

downstream plant modifications for those plants that provided the list of such actions. Plants 

with an indication that no downstream actions are needed are listed separately in Table A.2-6. 

Table A.2-3. Physical Plant Modifications

Plant Plant Modifications (Physical) Credited?

ANO-1 Insulation replacements and modifications to reduce potential 

debris.

Yes

Original concrete curb surrounding the sump was removed. Yes
A-29

ANO-2 Insulation replacements and modifications to reduce potential 

debris.

Yes

Modifications to refueling canal drain cover. Yes

Several pieces of equipment relocated to accommodate new 

strainer.

Yes

Beaver 

Valley-1

Bell-mouth flanges were added in the sump trench at the 

pump suction inlets for the outside RSS pumps and the low 

head safety injection pumps to reduce the suction head loss.

Yes

Borated Temp-Mat TM insulation encapsulated in RMI on the 

reactor vessel closure head has been replaced with RMI to 

reduce debris loading on the sump strainer.

Yes

Iodine filters, containing a significant amount of thin aluminum 

that would have been submerged, were removed from the 

containments.

Yes

Mitigation of the additional fibrous insulation will be 

accomplished through removal, replacement, analysis or 

design modification prior to startup from the next refueling 

outage (1 R20, Fall 2010).

Yes

New RMI was installed on the replacement steam generators 

and associated piping in the vicinity of the SGs, resulting in a 

reduced quantity of insulation that could contribute to debris 

loading on the sump strainer.

Yes

Quench spray loop seals were modified. Yes

Reactor cavity drain cross bars that have the potential to 

collect debris and block water flow to the containment sump 

were removed.

Yes

Recirculation spray pump test dike was modified. Yes

Replacement of high-pressure safety injection cold leg throttle 

valves to increase the throttle valve gap and thereby reduce 

flow restrictions.

Yes

Support columns for the existing sump screens' frame were 

deleted or relocated.

Yes

Temperature sensors, used to provide containment water 

temperature post LOCA, were relocated.

Yes

Temp-Mat fibrous insulation or calcium-silicate on select 

piping was replaced with RMI.

Yes

Temp-Mat insulation encapsulated in metal jacketing on the 

reactor coolant loop piping was replaced with RMI.

Yes

The start signal for the RSS pumps has been changed from a 

fixed time delay to an Engineered Safety Features Actuation 

System signal based on a refueling water storage tank level 

low coincident with a containment pressure high-high signal to 

allow sufficient pool depth to cover the sump strainer before 

initiating recirculation flow.

Yes

Plant modifications planned to be completed for BVPS-1 

associated with Cal-Sil insulation removal that ensures that 

the requirements of FENOC's revised methodology of 

assuming 100 percent destruction of Cal-Sil to fines is met 

prior to startup from the next refueling outage (1 R20, 

Yes
A-30

Beaver 

Valley-2

Bell-mouth flanges were added in the sump trench at the 

pump suction inlets for the outside RSS pumps to reduce the 

suction head loss. Grating is attached to these flanges for 

vortex suppression.

Yes

Borated Temp-Mat insulation encapsulated in RMI on the 

Reactor Vessel Closure Head flange has been replaced with 

RMI, and Min-K insulation encapsulated in RMI on portions of 

the Reactor Coolant System piping has been replaced with 

Thermal Wrap insulation encapsulated RMI.

Yes

Conduits to containment sump level instruments were 

modified.

Yes

Conduits to containment sump level switches were modified. Yes

Containment sump level transmitters and containment sump 

level switches were relocated locally within the sump.

Yes

Insulation modifications were to be implemented prior to 

startup following the fall 2009 refueling outage (2R14).

Yes

Iodine filters, containing a significant amount of thin aluminum 

that would have been submerged, were removed from the 

containments.

Yes

Modification of high-pressure safety injection cold leg throttle 

valves to increase the throttle valve gap and thereby reduce 

flow restrictions.

Yes

Modifications to the RSS test return lines and supports were 

implemented

Yes

Modifications were performed to shorten a QS line and to 

relocate a QS support.

Yes

Reactor cavity drain cross bars that have the potential to 

collect debris and block water flow to the containment sump 

were removed.

Yes

The sodium hydroxide buffer was scheduled for replacement 

in the fall 2009 refueling outage with sodium tetraborate.

Yes

The start signal for the RSS pumps has been changed from a 

fixed time delay to an Engineered Safety Features Actuation 

System signal based on a refueling water storage tank level 

low coincident with a containment pressure high-high signal to 

allow sufficient pool depth to cover the sump strainer before 

initiating recirculation flow.

Yes

FENOC plans to repair and/or replace the insulation on the 3-

inch and 6-inch PORV supply piping with appropriately applied 

stainless steel jacketing and sure-hold bands. Plant 

modifications, repairing and/or replacing NUKONO insulation 

will be completed on the 3-inch and 6-inch BVPS-2 PORV 

supply piping with appropriately applied stainless steel 

jacketing and sure-hold bands, prior to startup from the next 

refueling outage (2R15, Spring 2011).

Yes

Braidwood-1 A short (nominal 2 in.) curb was installed around the perimeter 

of the modified trash rack.

Yes

Stainless steel grating ("trash rack") 4 ft high with 1-7/8 in. x 

7/8 in. openings installed to enclose openings for both sumps, 

along with debris retainers approx. 14 in. long by 5 in. high.

Yes
A-31

Braidwood-2 A short (nominal 2 in.) curb was installed around the perimeter 

of the modified trash rack to ensure online leakage in 

containment will reach the leakage detection sumps rather 

than enter the ECCS sumps.

Yes

Single level switch assembly inside each sump removed and 

associated cables removed and/or abandoned in place.

Yes

Stainless steel grating ("trash rack") 4 ft high with 1-7/8 in. x 

7/8 in. openings installed to enclose openings for both sumps, 

along with debris retainers approximately 14 in. long by 5 in. 

high.

Yes

Byron-1 A short (nominal 2 in.) curb was installed around the perimeter 

of the modified trash rack to ensure online leakage in 

containment will reach the leakage detection sumps rather 

than enter the ECCS sumps.

Yes

Single level switch assembly inside each sump removed and 

associated cables removed and/or abandoned in place.

Yes

Stainless steel grating ("trash rack") 4 ft high with 1-7/8 in. x 

7/8 in. openings installed to enclose openings for both sumps, 

along with debris retainers approximately 14 in. long by 5 in. 

high.

Yes

Byron-2 A short (nominal 2 in.) curb was installed around the perimeter 

of the modified trash rack to ensure online leakage in 

containment will reach the leakage detection sumps rather 

than enter the ECCS sumps.

Yes

Single level switch assembly inside each sump removed and 

associated cables removed and/or abandoned in place.

Yes

Stainless steel grating ("trash rack") 4 ft high with 1-7/8 in. x 

7/8 in. openings installed to enclose openings for both sumps, 

along with debris retainers approximately 14 in. long by 5 in. 

high.

Yes

Callaway-1 Debris barriers installed in all openings through secondary 

shield wall near emergency recirculation sumps.

Yes

Recirculation sump level indication relocated and modified. Yes

Trisodium phosphate dodecahydrate baskets relocated in 

containment.

Yes

Calvert Cliffs1Calvert Cliffs installed debris interceptors in Unit 1 during the 

spring 2008 refueling outage to shield a portion of the strainer 

surface area from debris. No credit is taken in evaluations for 

these debris interceptors. The debris interceptor in Unit 1 is 

planned for removal in the 2010 refueling outage.

No

The aluminum scaffolding was removed from Unit 1 in 2008 

and Unit 2 in 2009.

Yes

Two pipes in Unit 1 will have insulation removed during the 

2010 RFO. The pipes are the shutdown cooling line insulated 

with mineral wool insulation and the pressurizer relief valve 

line outside of the pressurizer compartment insulated with 

generic fiberglass insulation. 

Yes

By July 2014, replace appropriate mineral wool insulation with 

reflective metal insulation or banded Nukon/Thermal Wrap 

insulation.

Yes
A-32

By July 2014, remove telescoping aluminum ladder from the 

Polar Crane in Containment.

Yes

By July 2014, enlarge the reactor refueling cavity drains to 

reduce post-loss-of-coolant accident water holdup and 

increase strainer submergence.

Yes

By July 2014, ensure Operations has a means of assessing 

containment sump pool temperature.

Yes

By July 2016, replace selected reactor coolant piping and 

reactor coolant pump insulation with reflective metal insulation.

Yes

By July 2014, replace appropriate generic fiberglass insulation 

with reflective metal insulation, banded Nukon/Thermal Wrap 

insulation, Foamglas insulation or coatings.

Yes

By July 2016, add Sure-Hold Bands to appropriate piping 

sections containing existing Nukon insulation, or replace 

existing Nukon insulation on appropriate piping sections with 

reflective metal insulation.

Yes

Calvert Cliffs2The aluminum scaffolding was removed from Unit 1 in 2008 

and from Unit 2 in 2009.

Yes

By July 2014, replace appropriate mineral wool insulation with 

reflective metal insulation or banded Nukon/Thermal Wrap 

insulation.

Yes

By July 2014, remove telescoping aluminum ladder from the 

Polar Crane in Containment.

Yes

By July 2014, enlarge the reactor refueling cavity drains to 

reduce post-loss-of-coolant accident water holdup and 

increase strainer submergence.

Yes

By July 2014, ensure Operations has a means of assessing 

containment sump pool temperature.

Yes

By July 2016, replace selected reactor coolant piping and 

reactor coolant pump insulation with reflective metal insulation.

Yes

By July 2014, replace appropriate generic fiberglass insulation 

with reflective metal insulation, banded Nukon/Thermal Wrap 

insulation, Foamglas insulation or coatings.

Yes

By July 2016, add Sure-Hold Bands to appropriate piping 

sections containing existing Nukon insulation, or replace 

existing Nukon insulation on appropriate piping sections with 

reflective metal insulation.

Yes

Catawba-1 Replacement of the existing orifice plates with smaller 

diameter orifice plates to allow the ECCS throttle valves to be 

opened greater than currently allowed for flow balancing.

Replacement of the fiberglass blankets (NUKON) insulation on 

the bottom bowls of the Unit 1 steam generators with reflective 

metal insulation RMI.

Yes

Replacement of the Microtherm® insulation, previously 

installed on portions of the reactor vessel heads, with RMI.

Yes

Catawba has replaced a significant amount of low-density 

fiberglass (LDFG) insulation in specific areas of lower 

containment with reflective metal insulation (RMI) via Fiber 

Insulation Replacement Projects (FIRP).
A-33

Catawba-2 Replacement of the existing orifice plates with smaller 

diameter orifice plates to allow the ECCS throttle valves to be 

opened greater than currently allowed for flow balancing.

Replacement of the Microtherm® insulation, previously 

installed on portions of the reactor vessel heads, with RMI.

Yes

Catawba has replaced a significant amount of low-density 

fiberglass (LDFG) insulation in specific areas of lower 

containment with reflective metal insulation (RMI) via Fiber 

Insulation Replacement Projects (FIRP).

Comanche 

Peak-1

Drains holes added to the reactor vessel head stand shield 

wall.

Yes

Installation of debris interceptors. Yes

Installation of debris screens and strainers for drains in the 

refueling cavity.

Yes

Installation of water control features to optimize sump 

performance.

Yes

Modifications to minimize water holdup on floors and 

miscellaneous items.

Yes

Revised RWST switchover setpoints and motor operated valve 

modification.

Yes

Comanche 

Peak-2

Drains holes added to the reactor vessel head stand shield 

wall.

Yes

Installation of debris interceptors. Yes

Installation of debris screens and strainers for drains in the 

refueling cavity.

Yes

Installation of water control features to optimize sump 

performance.

Yes

Modifications to minimize water holdup on floors and 

miscellaneous items.

Yes

Revised RWST switchover setpoints and motor operated valve 

modification.

Yes

Crystal 

River-3

A 15-in. high stainless steel debris interceptor was installed.

A flow distributor was added to minimize localized flow 

streaming and to reduce bulk recirculation flow turbulence.

CR3 intended to replace all of the encapsulated mineral wool 

insulation in the LOCA zone of influence within the D-rings 

(HELB zones) with RMI.

CR3 reduced the amount of NUKON fiber in the RB by 40 ft3 

by replacing the Pressurizer Head insulation with Reflective 

Metal Insulation (RMI). The amount of mineral wool fiber was 

also reduced, by removing the majority of insulation on the 

steam generator blowdown lines.

Yes

Over 800 lb of aluminum was removed from containment by 

replacing storage box covers with stainless steel.

Perforated plate (3/16 in. holes) screens were installed in the 

RB floor drains to limit the transport of debris from remote 

areas of containment to the sump area.

RB sump level instrumentation was enhanced, by installing a 

dP cell.
A-34

Refueling cavity drain trash rack was installed.

Stainless steel plate bored with 3/16 in. perforations was 

added to the four scuppers.

The containment sump trash rack was increased in size from 

approximately 55 ft2 of horizontal surface area to 

approximately 100 ft2 of horizontal and 15 ft2 (25 lineal feet) of 

vertical surface areas.

The new steam generators will be provided without the high 

heat aluminum paint that exists on the current steam 

generators, that is Unqualified High Heat Aluminum Paint 

(from 1485 ft2 to 479 ft2 of 10 μm particulate loading).

Yes

The original 1⁄4 in. square mesh sump screen (86 ft2 of flat 

plane screened area) was replaced with a complex geometry 

sump strainer that has an effective surface area of 1139 ft2.

Yes

The remaining 10 ft3 of NUKON insulation will also be 

replaced with RMI (although head loss analyses and testing 

assume that the 10 ft3 of NUKON will remain).

D.C. Cook-1 Blank plate installed in crossover pipe connecting recirculation 

sump with adjacent lower containment sump.

Yes

CalSil insulation removed from pressurizer relief tank (PRT) 

and pressurizer safety and relief valve discharge line.

Yes

Debris interceptors installed on loop compartment side of 

flood-up overflow wall.

Yes

Debris interceptors installed over the drains from hydrogen 

skimmer/containment pressure equalization (CEQ) fan rooms.

Yes

Five existing 10-in.-dia openings in flood-up overflow wall 

modified to reduce head loss.

Yes

Low-density fiberglass on a non-RCS systems relief valve 

discharge line to PRT removed.

Yes

New level instruments installed inside recirculation sump 

enclosures.

Yes

Radiation shields on annulus side of openings in flood-up 

overflow wall modified.

Yes

Recirculation sump vent configuration modified. Yes

D.C. Cook-2 Blank plate installed in crossover pipe connecting recirculation 

sump with adjacent lower containment sump.

Yes

CalSil insulation on PRT drain line removed. Yes

CalSil insulation removed from PRT and pressurizer safety 

and relief valve discharge line.

Yes

Debris interceptors installed on loop compartment side of 

flood-up overflow wall.

Yes

Debris interceptors installed the drains from hydrogen 

skimmer/CEQ fan rooms.

Yes

Five existing 10-in.-dia openings in flood-up overflow wall 

modified to reduce head loss.

Yes

New level instruments installed inside recirculation sump 

enclosures.

Yes

Opening installed on lower containment sump and internals 

from check valves in the West CEQ fan room drain lines were 

removed.

Yes
A-35

Radiation shields on annulus side of openings in flood-up 

overflow wall modified.

Yes

Recirculation sump vent configuration modified. Yes

Several hundred tags, labels, and other materials that 

presented a potentially significant debris source term were 

removed.

Yes

Davis Besse1Cleaned all floor drains and associated drain piping in 

containment to assure no volume holdup.

Yes

Installed a jet deflector as part of the emergency sump 

modification

Yes

Installed refuel canal drain line debris screen. Yes

Installed trash racks at points around containment. No

Modification /installation of cyclone separators for the HPI, 

Low Pressure Injection (LPI), and CS pumps.

Yes

Opened a hole through the sump wall to permit lower strainer 

feed.

Yes

Relocated the sump access ladder and the emergency sump 

water level equipment to remove interferences with strainer 

assembly

Yes

Removed/replaced equipment tags, signs and labels with 

qualified materials.

Yes

Replaced nearly all the fibrous insulation in containment with 

RMI and completely stripped and recoated containment dome.

Yes

Diablo 

Canyon-1

Addition of three 18-in.-high perforated plate debris 

interceptors.

Installation of multiple banding on CalSil piping insulation 

inside the pipe break ZOls.

Installation of RMI and stainless steel jacketed Temp-Mat on 

the replacement SGs.

Installation of stainless steel jacketed Temp-Mat insulation on 

the inlet to pressurizer safety valves.

Installation of stainless steel jacketing on Temp-Mat piping 

insulation inside the pipe break ZOls.

Installation of tray covers to protect the pressurizer heater 

cable insulation in cable trays below the pressurizer.

Modification of the reactor cavity door.

Removal of cable tray fire stops inside the crane wall.

Diablo 

Canyon-2

Addition of three 18-in-high perforated plate debris 

interceptors.

Installation of multiple banding on CalSil piping insulation 

inside the pipe break ZOls.

Installation of RMI and stainless steel jacketed Temp-Mat on 

the replacement SGs.

Installation of stainless steel jacketed Temp-Mat insulation on 

the inlet to pressurizer safety valves.

Installation of stainless steel jacketing on Temp-Mat piping 

insulation inside the pipe break ZOls.

Modification of the reactor cavity door.

Removal of cable tray fire stops inside the crane wall.
A-36

Farley-1 Debris interceptors are installed inside containment for both 

Unit 1 and 2. 

No

FNP installed the largest sized strainers practicable for the 

space available within containment for each unit.

Yes

To prevent the potential for plugging and creating a hold-up 

volume, the refueling cavity drain covers are removed during 

modes requiring ECCS operability.

Farley-2 Debris interceptors were installed inside containment for both 

Unit 1 and 2. 

No

FNP installed the largest sized strainers practicable for the 

space available within containment for each unit.

Yes

To prevent the potential for plugging and creating a hold-up 

volume, the refueling cavity drain covers are removed during 

modes requiring ECCS operability.

Fort 

Calhoun-1

A no-spray configuration, which significantly reduces debris 

transport and lowers flow rates through the sump strainer 

screens, was to be implemented during the 2008 RFO.

During the 2006 RFO, a significant amount of fibrous 

insulation was replaced with RMI during the SG, pressurizer, 

and RPV head replacement projects.

Trisodium phosphate, the previous containment sump buffer, 

was replaced with sodium tetraborate to reduce formation of 

chemical precipitates.

Ginna-1 The existing Johnson screen, which runs the entire width of 

the "B" sump, will be removed to allow for structural 

modifications to the sump in support of adding modules to the 

sump cover. If left in place, the Johnson screen would operate 

in series with the new strainer modules; however, it is a much 

coarser mesh than the 1/16 in. perforated holes in the strainer 

modules and would therefore offer no additional removal of 

debris from the water passing through the strainer.

No

The Ginna containment sump strainer system was to be 

installed during Ginna's April 2008 RFO.

Yes

The reactor cavity drain line isolation valve to the reactor 

coolant drain tank (RCDT) may require manipulation when the 

sump is required to be operable. Therefore, a reach rod was 

to be used to penetrate the sump cover, allowing valve 

operation without entering the sump.

No

The RCDT vent line, with its manual isolation valve, was to be 

routed up through the sump cover to allow operators to vent 

the tank without entering the sump.

No

Indian Point2Installation of a trash rack over the refueling canal drain. Yes

Installation of flow channeling barriers. Yes

Installation of passive strainer assemblies in the internal 

recirculation and vapor containment sumps.

Yes

Replacement of the TSP PH buffers with sodium tetraborate. Yes

Indian Point3Installation of a trash rack over the refueling canal drain. Yes

Installation of flow channeling barriers. Yes

Installation of passive strainer assemblies in the internal 

recirculation and vapor containment sumps.

Yes
A-37

Removal of Kaowool from inside the crane wall. Yes

Replacement of the sodium hydroxide PH buffers with sodium 

tetraborate.

Yes

Kewaunee-1 Four beams in upper pressurizer vault covered with stainless 

steel jacketing.

Yes

Jacketed calcium silicate insulation in submergence zone 

repaired.

Yes

Jacketed fiberglass pipe insulation replaced. Yes

Nonessential equipment labels removed from containment. Yes

Wooden reactor vessel O-ring storage container removed from 

containment.

Yes

The containment refueling cavity drain standpipe will be 

modified to remove the 1 in. x 1 in. grid/grating recessed into 

the top of the standpipe to eliminate the potential for debris to 

be captured on the drain opening.

Yes

The JM Thermobestos insulation (calcium silicate insulation 

with asbestos fibers) in the "A" steam generator vault will be 

secured with stainless steel banding, similar to that performed 

in the "B" steam generator vault (opposite train) to enable use 

of a ZOI size equal to 5.45D.

Yes

Fibrous insulation on the Service Water piping that passes 

through the top of the "B" reactor coolant pump vault will be 

removed.

Yes

Fibrous insulation (Temp-Mat) on the pressurizer surge line 

pipe whip restraints will be removed and replaced with a nonfibrous material.

Yes

McGuire-1 Replacement of the Microtherm® insulation, previously 

installed on portions of the reactor vessel heads, with RMI.

Yes

McGuire is replacing a significant amount of low-density 

fiberglass (LDFG) insulation in specific areas of lower 

containment with reflective metal insulation (RMI) via Fiber 

Insulation Replacement Projects (FIRP).

McGuire-2 Replacement of the Microtherm® insulation, previously 

installed on portions of the reactor vessel heads, with RMI.

Yes

McGuire is replacing a significant amount of low-density 

fiberglass (LDFG) insulation in specific areas of lower 

containment with reflective metal insulation (RMI) via Fiber 

Insulation Replacement Projects (FIRP).

Millstone-2 Calcium silicate insulation was removed from piping and 

equipment in containment such that no calcium silicate 

insulation could be part of the ECCS strainer debris bed for 

any break that would require recirculation. All remaining 

calcium silicate insulation in containment is jacketed with 

stainless steel and is not susceptible to being dislodged by 

any break that would require ECCS recirculation.

Yes

North Anna-1 A drain was installed in the primary shield wall to the incore 

sump room (ISR) in Units 1 and 2 to reduce the water holdup 

volume and to increase the total volume of water available for 

recirculation.

Yes
A-38

CalSil insulation located within the SG cubicles and 

pressurizer room has been replaced with Paroc and TempMat 

insulation in Units 1 and 2.

Yes

Engineered safety features (ESF) circuitry was added to start 

the RS pumps on a CDA signal coincident with a RWST levellow signal. 

Yes

The containment sump level transmitters were modified to 

protect them from clogging due to debris.

- Level transmitters located within the sump have been 

modified by drilling holes through stilling wells at various 

places to prevent the element from clogging, and

- Level transmitters located above the containment floor have 

been provided with debris shields to protect them from 

containment spray generated debris.

Yes

The RWST level instrumentation was modified to change the 

safety injection Recirculation Mode Transfer (RMT) setpoint 

from 19.4% to 16.0% RWST wide range level. This allows 

more energy to be removed from the containment and lowers 

the sump temperature prior to the LHSI pump suction 

switching from the RWST to the containment sump. This 

change also provides a higher water level in the containment 

sump prior to the LHSI pump suction switching to the 

containment sump. The combination of lower sump 

temperature and higher water level provides more NPSH to 

the LHSI pumps, and provides the required volume of water to 

maintain the strainers submerged.

Yes

Two new containment sump strainers (with corrugated, 

perforated stainless steel fins) were installed with a total 

surface area of approximately 4400 ft2 for the RS pumps in 

both units, approximately 2000 ft2 for the Unit 1 LHSI pumps 

and approximately 1900 ft2 for the Unit 2 LHSI pumps. These 

strainers replaced the previous containment sump screens, 

which had a surface area of approximately 168 ft2.

Yes

North Anna-2 A drain was installed in the primary shield wall to the ISR in 

Units 1 and 2 to reduce the water holdup volume and to 

increase the total volume of water available for recirculation.

Yes

CalSil insulation located within the SG cubicles and 

pressurizer room has been replaced with Paroc and TempMat 

insulation in both Units 1 and 2.

Yes

Engineered Safety Features (ESF) circuitry was added to start 

the RS pumps on a Containment Depressurization Actuation 

(CDA) signal coincident with a Refueling Water Storage Tank 

(RWST) Level-Low signal. The Outside RS (ORS) pumps 

start immediately once the coincidence logic is satisfied. The 

Inside RS (IRS) pumps start following a time delay of 120 sec 

once the coincidence logic is satisfied. These changes ensure 

sufficient water is available to meet the RS strainer 

submergence and RS pump net positive suction head (NPSH) 

requirements.

Yes
A-39

Microtherm insulation has been removed from Unit 2 

containment. (No Microtherm insulation was installed in the 

Unit 1 containment.)

Yes

The containment sump level transmitters were modified to 

protect them from clogging due to debris.

- Level transmitters located within the sump have been 

modified by drilling holes through stilling wells at various 

places to prevent the element from clogging, and

- Level transmitters located above the containment floor have 

been provided with debris shields to protect them from 

containment spray generated debris.

Yes

The RWST level instrumentation was modified to change the 

safety injection Recirculation Mode Transfer (RMT) setpoint 

from 19.4% to 16.0% RWST wide range level. This allows 

more energy to be removed from the containment and lowers 

the sump temperature prior to the LHSI pump suction 

switching from the RWST to the containment sump. This 

change also provides a higher water level in the containment 

sump prior to the LHSI pump suction switching to the 

containment sump. The combination of lower sump 

temperature and higher water level provides more NPSH to 

the LHSI pumps, and provides the required volume of water to 

maintain the strainers submerged.

Yes

Two new containment sump strainers (with corrugated, 

perforated stainless steel fins) were installed with a total 

surface area of approximately 4400 ft2 for the RS pumps in 

both units, approximately 2000 ft2 for the Unit 1 LHSI pumps 

and approximately 1900 ft2 for the Unit 2 LHSI pumps. These 

strainers replaced the previous containment sump screens, 

which had a surface area of approximately 168 ft2.

Yes

Oconee-1 Removal of fibrous insulation from areas in containment where 

it would be potentially affected by a pipe break jet (ZOI).

Yes

Replacement of reactor building emergency sump (RBES) 

screens and trash racks with larger strainers.

Yes

Replacement of seal flush orifices and cyclone separators on 

the LPI pumps, HPI pumps, and building spray (BS) pumps.

Yes

Oconee-2 Removal of fibrous insulation from areas in containment where 

it would be potentially affected by a pipe break jet (ZOI).

Yes

Replacement of RBES screens and trash racks with larger 

strainers.

Yes

Replacement of seal flush orifices and cyclone separators on 

the LPI pumps, HPI pumps, and building spray (BS) pumps.

Yes

Oconee-3 Removal of fibrous insulation from areas in containment where 

it would be potentially affected by a pipe break jet (ZOI).

Yes

Replacement of RBES screens and trash racks with larger 

strainers.

Yes

Replacement of seal flush orifices and cyclone separators on 

the LPI pumps, HPI pumps, and BS pumps.

Yes

Palisades-1 Containment sump buffer changed from trisodium phosphate 

to sodium tetraborate.

Yes
A-40

Modifications of containment base slab configuration to 

eliminate choke points.

Yes

Palo Verde-1 Fiberfrax was removed from the containment. The piping 

penetrations in the containment bioshield walls were originally 

sealed with Fiberfrax. 

NUKON insulation has been removed around letdown delay 

coils.

The existing sump temperature element was relocated to 

facilitate the installation of the replacement sump strainers.

The Microtherm (Units 1 and 2) and Min-K (Unit 3) insulation 

was scheduled to be removed from the reactor head in the fall 

2009 RFO for Unit 2, in the spring 2010 RFO for Unit 1, and in 

the fall 2010 RFO for Unit 3.

Palo Verde-2 Fiberfrax was removed from the containment. The piping 

penetrations in the containment bioshield walls were originally 

sealed with Fiberfrax. 

NUKON insulation has been removed around letdown delay 

coils.

The existing sump temperature element was relocated to 

facilitate the installation of the replacement sump strainers.

The Microtherm (Units 1 and 2) and Min-K (Unit 3) insulation 

were scheduled for removal from the reactor head in the fall 

2009 RFO for Unit 2, in the spring 2010 RFO for Unit 1, and in 

the fall 2010 RFO for Unit 3 refueling outage.

Palo Verde-3 Fiberfrax was removed from the containment. The piping 

penetrations in the containment bioshield walls were originally 

sealed with Fiberfrax. 

NUKON insulation has been removed around letdown delay 

coils.

The existing sump temperature element was relocated to 

facilitate the installation of the replacement sump strainers.

The Microtherm (Units 1 and 2) and Min-K (Unit 3) insulation 

was scheduled to be removed from the reactor head in the fall 

2009 RFO for Unit 2, in the spring 2010 RFO for Unit 1, and in 

the fall 2010 RFO for Unit 3 refueling outage.

Point Beach1Reactor cavity drain to be extended away from the strainers, 

or an impingement device to be installed between the strainers 

and the drain to prevent air ingestion.

Yes

Structural modifications to reinforce limiting components to 

carry end thrust loads on strainer assemblies.

Yes

Point Beach2Reactor cavity drain to be extended away from the strainers, 

or an impingement device to be installed between the strainers 

and the drain to prevent air ingestion.

Yes

Structural modifications to reinforce limiting components to 

carry end thrust loads on strainer assemblies.

Yes

Prairie 

Island-1

Capping of abandoned waste liquid disposal pipes located in 

sump.

Yes

Existing components such as cable tray supports were 

relocated and/or reconfigured to clear space for new strainers.

Yes

Trash rack over sump removed. Yes
A-41

Prairie 

Island-2

Capping of abandoned waste liquid disposal pipes located in 

sump.

Yes

Existing components such as cable tray supports were 

relocated and/or reconfigured to clear space for new strainers.

Yes

Trash rack over sump removed. Yes

Robinson-2 Installation involved removal of the original sump screens at 

the sump, removal of the coarse screens at the reactor coolant 

pump bay drain openings, installation of a jet impingement 

shield near the letdown line, and relocation of some interfering 

equipment adjacent to the new strainer.

Yes

Salem-1 PSEG installed a debris interceptor in front of the new strainer 

modules.

Yes

PSEG installed new level switches installed for both units.

PSEG replaced all the calcium silicate insulation within the 

ZOI replaced at Unit 1 and 2 with Transco RMI. Min-K 

insulation also was replaced with Transco RMI wherever 

possible.

PSEG replaced the original strainers. Yes

Salem-2 PSEG installed a debris interceptor in front of the new strainer 

modules.

Yes

PSEG installed new level switches installed for both units.

PSEG replaced all the calcium silicate insulation within the 

ZOI replaced at Unit 1 and 2 with Transco RMI. Min-K 

insulation also was replaced with Transco RMI wherever 

possible.

Original strainers replaced. Yes

Unit 2 steam generators were replaced. The new steam 

generators are insulated with Transco RMI.

Yes

San Onofre-2 Bioshield gate modifications.

Microtherm-to-RMI insulation change-out was performed.

New sump screen installation. Yes

The completed analysis and testing work take credit for the 

reduced quantity of mineral wool insulation on the replacement 

steam generators.

Yes

San Onofre-3 Bioshield gate modifications.

Microtherm-to-RMI insulation change-out was performed.

New sump screen installation. Yes

The completed analysis and testing work take credit for the 

reduced quantity of mineral wool insulation on the replacement 

steam generators.

Yes

Seabrook-1 Additional debris interceptors have been installed on the 

scuppers in the bioshield wall to further reduce the debris that 

can be transported to the sump strainers from a postulated 

LOCA.

Cable tray adhesive labels have been removed to reduce the 

miscellaneous debris that could be generated by labels that 

fail due to a postulated LOCA.

Sequoyah-1 The original containment sump intake structures were 

replaced with advanced designed strainers during the Unit 1, 

outage in the fall of 2007.

Yes
A-42

Sequoyah-2 The original containment sump intake structures were 

replaced with advanced designed strainers during the Unit 2, 

Cycle 14 RFO in the fall of 2006. 

Yes

Shearon 

Harris-1

Installation of a trash rack in the refueling canal drain. During 

RFO14 (fall of 2007), HNP installed a trash rack in the 

refueling canal drain. This trash rack is removable such that it 

can be removed prior to refueling operations and reinstalled 

following completion of refueling operations. This trash rack is 

fabricated of austenitic stainless steel.

Yes

Reinforcement of insulation cassettes containing Min-K. HNP 

had previously told the NRC in the September 01, 2005, 

submittal that it planned to remove the insulation cassettes 

from containment and replace them with a different type of 

insulation. All of these cassettes are on safety-relief valve 

(SRV) loop seals and power-operated valve (PORV) water 

seals in the pressurizer cubicle. HNP did not remove the MinK from containment; instead, HNP reinforced the cassettes 

with stainless steel banding such that a break in one of the 

SRV lines would not affect all of the Min-K insulation in the 

pressurizer cubicle.

Yes

Removal of aluminum fire extinguishers from containment. In 

2003, HNP discovered that the fire extinguishers in 

containment were made of aluminum. These fire 

extinguishers were subsequently removed from containment 

during power operations; this action was completed in RFO14 

Yes

HNP has opted to-replace the Min-K insulation on the 

Pressurizer power operated relief valve (PORV) and safety 

relief valve (SRV) loop seal piping with a low-density fibrous 

insulation material that is less problematic from a sump 

strainer head loss standpoint. The Min-K insulation, that will 

be replaced, represents all Min-K insulation that could be 

damaged by a LOCA.

Yes

St. Lucie-1 The calcium-silicate insulation (cal-sil) on selected piping in 

the containment has been reinforced with a banding system. 

The banding system consists of 11⁄2-in. wide stainless steel 

bands spaced approximately 3 in. on center.

Yes

Summer-1 Debris interceptors removed. Yes

Gate placed across stairwell entrance adjacent to A train 

sump.

Yes

Two vertical trash rack gates in reactor building annulus. Yes

Surry-1 Air ejectors re-installed in LHSI pump cans. Yes

Containment sump level transmitters modified to protect them 

from clogging due to debris.

Yes

Drain drilled in primary shield wall of ISR to reduce the water 

holdup volume.

Yes

Engineered safeguards features circuitry added to start the RS 

pumps.

Yes

Insulation inside containment was found to be damaged, 

degraded or covered with an unqualified coating system and 

was removed or jacketed.

Yes
A-43

Surry-2 Insulation inside containment was found to be damaged, 

degraded or covered with an unqualified coating system and 

was removed or jacketed.Air ejectors re-installed in LHSI 

pump cans.

Yes

Air ejectors re-installed in LHSI pump cans. Yes

Containment sump level transmitters modified to protect them 

from clogging due to debris.

Yes

Drain drilled in primary shield wall of ISR to reduce the water 

holdup volume.

Yes

Engineered safeguards features circuitry added to start the RS 

pumps. 

Yes

Insulation inside containment was found to be damaged, 

degraded or covered with an unqualified coating system and 

was removed or jacketed.

Yes

Three Mile 

Island-1

A new trash rack was installed.

An access ladder was modified to make room for the trash 

rack.

Configuration changes were made to address upstream flow 

concerns: Replacement of the door to the entrance of the Drings and Installation of fuel transfer canal drain strainer.

Normal drain lines were redirected to the new normal sumps.

Piping interferences with the new sump trash rack were 

modified.

Radiation monitor RM-G-21 was elevated above RB flood 

level to make room for the strainer and trash rack.

The “box” strainer assembly was replaced with an array of “top 

hat” strainer modules. 

Yes

23 empty TSP baskets were installed in the RB basement 

prior to or during T1R17. The TSP was added to the baskets 

and the NaOH tank was isolated after Technical Specification 

Amendment no. 263 was approved.

The RB sump level instruments were modified.

The sump was divided into a normal “wet” sump and an ECCS 

“dry” sump.

Turkey Point3CalSil insulation and jacketing on pressurizer relief tank 

replaced with post-LOCA qualified coating..

Yes

Cylindrical core bore beneath refueling cavity to provide 

pathway for piping that connects the strainer assemblies to the 

south ECCS sump suction inlet.

Yes

Filled existing ECCS sump suction inlet pits with reinforced 

concrete.

Yes

Four sections of pressurizer surge line containing Cal-Sil and 

one section containing NUKON replaced with RMI.

Yes

Reactor coolant pump insulation replaced with RMI. Yes

Turkey Point4Cylindrical core bore beneath refueling cavity to provide 

pathway for piping that connects the strainer assemblies to the 

south ECCS sump suction inlet.

Yes

Debris interceptors installed at the exit points at the bioshield 

wall. 

Yes
A-44

Vogtle-1 Removal of cage assembly vortex suppressors in sumps. Yes

Replacement of Min-K insulation with NUKON. Yes

Temperature elements for RHR sumps replaced and 

relocated.

Yes

Vogtle-2 Removal of cage assembly vortex suppressors in sumps. Yes

Replacement of Min-K insulation with NUKON. Yes

Temperature elements for RHR sumps replaced and 

relocated.

Yes

Three electrical interferences for new Unit 2 CS Sump Train A 

Screen relocated/rerouted.

Yes

Two conduit interferences at Unit 2 RHR Sump Train A screen 

rerouted.

Yes

Waterford-3 Nineteen TSP baskets were relocated to allow easier 

installation of the new plenum and strainers, or to eliminate 

interferences with the baskets.

Yes

The housing for the low level switch inside the SI sump was 

relocated to mount on top of the new screen plenum.

Yes

The original box-like SI sump screen that surrounded the 

sump itself was removed and replaced with GE modularized, 

stacked disk strainers.

Yes

The sump partition that separates the two trains of the SI inlets 

was replaced with stainless steel grating.

The tubing for two level transmitters inside the SI sump was 

rerouted to penetrate through the plenum in a designed 

location in order to prevent debris from passing through the 

penetration opening.

Yes

Waterford 3 will replace the fibrous insulation on the current 

steam generators with Reflective Metal Insulation.

Yes

Watts Bar-1 Minor rerouting of electrical conduit during installation of new 

strainers.

Yes

Several large pieces of min-K fiber insulation replaced with 

RMI and others banded.

Yes

Wolf Creek-1 Debris barrier plates have been installed in openings through 

the secondary shield wall that are near the emergency 

recirculation sumps.
A-45

Table A.2-4. Administrative Plant Modifications

Plant Plant Modifications (Administrative) Credited?

ANO-1 Licensee committed to the measurement of latent debris quantities 

every third refueling outage to confirm that latent debris quantities 

used in strainer testing and downstream effects analysis remain 

bounding. This frequency may be relaxes after the first 

measurements, provided the results indicated that an adequate 

level of cleanliness was maintained.

Yes

The coatings program has been upgraded in response to the GL04-02 by expanding the focus beyond the liner plate to include 

periodic walkdown inspections of all readily accessible coatings in 

containment to assess damage or degradation.

Yes

In December 2007, a design modification was implemented to 

reduce the concentration of the sodium hydroxide (NaOH) 

chemical buffer.

Yes

ANO-2 Licensee committed to the measurement of latent debris quantities 

every third refueling outage to confirm that latent debris quantities 

used in strainer testing and downstream effects analysis remain 

bounding. This frequency may be relaxes after the first 

measurements, provided the results indicated that an adequate 

level of cleanliness was maintained.

Yes

The coatings program has been upgraded in response to the GL04-02 by expanding the focus beyond the liner plate to include 

periodic walkdown inspections of all readily accessible coatings in 

containment to assess damage or degradation.

Yes

Chemical buffer change from trisodium phosphate to sodium 

tetraborate to support chemical effects analysis.

Yes

Beaver 

Valley-1

A containment coatings inspection and assessment program and a 

containment-cleaning program became effective for both units in 

April of 2008.

Yes

LOCADM analyses were conducted for both units in accordance 

with WCAP-16793-NP, Revision 1.

Yes

WCAP-16793-NP, Rev. 1, and WCAP-17057-P, Rev. 0, which 

describe the Westinghouse fuel nozzle tests, were reviewed. Both 

units were shown to be enveloped, by testing described within 

those reports.

Yes

Emergency operating procedures for Unit 1 was to be revised to 

enhance the steps that shut down two RSS pumps prior to the 

transfer to recirculation. These procedure changes were to be 

implemented by December 31, 2009.

Yes

Beaver 

Valley-2

The sodium hydroxide buffer was scheduled to be replaced with 

sodium tetraborate in the fall 2009 RFO.

Yes

A containment coatings inspection and assessment program and a 

containment-cleaning program became effective for both units in 

April 2008.

Yes

LOCADM analyses were conducted for both units in accordance 

with WCAP-16793-NP, Revision 1.

Yes

WCAP-16793-NP, Rev. 1, and WCAP-17057-P, Rev. 0, which 

describe the Westinghouse fuel nozzle tests, were reviewed. Both 

Yes
A-46

Plant Plant Modifications (Administrative) Credited?

units were shown to be enveloped by testing described within 

those reports.

Emergency operating procedures will be revised to shut down one 

of the RSS pumps supplying the spray header when the 

containment pressure is reduced below a predetermined value. 

The change will be implemented prior to startup from the fall 2009 

refueling outage.

Yes

Callaway-1 Administrative controls have been added to the plant modification 

process to require a specific response to the following design 

issues (1) added or changed materials that could become postaccident debris, (2) addition or removal of aluminum or zinc from 

the containment building, (3) introduction of unqualified coatings or 

impact on qualified coatings, (4) significantly change amounts of 

exposed surface area of containment structures or equipment, (5) 

change post-accident recirculation water flow paths through 

containment, and (6) changing flood levels or creating new 

submergence levels.

Yes

Changes were made to the containment entry procedure to 

enhance requirements during plant operational modes 1 through 4 

for control of materials during work activities conducted in the 

containment.

Yes

Changes to the scaffold construction and use procedure to 

enhance requirements for control of scaffold tags and materials 

used during work activities conducted in the containment during 

plant operational modes 1 through 4.

Yes

Licensee has implemented a containment latent debris 

assessment program, which utilizes swipe sampling to determine 

the amount of latent debris in the containment building. 

Housekeeping and foreign materials exclusion procedures have 

been revised to target containment building cleaning based on the 

results of the swipe sampling survey.

Yes

Applicant has implemented a containment coatings assessment 

program for monitoring and assessing the containment building 

coatings, including administrative controls on conducting coating 

examinations, including deficiency reporting criteria and 

documentation requirements.

Yes

Licensee has implemented a containment latent debris 

assessment program, which utilizes swipe sampling to determine 

the amount of latent debris in the containment building. 

Housekeeping and foreign materials exclusion procedures have 

been revised to target containment building cleaning based on the 

results of the swipe sampling survey.

Yes

Calvert Cliffs1Valve equipment tags are now made of materials that would sink in 

water and not transport to the containment sump.

Yes

Calvert Cliffs2Valve equipment tags are now made of materials that would sink in 

water and not transport to the containment sump.

Yes

Catawba-1 The modification process and the plant labeling process have been 

enhanced relative to GL-04-02 controls.

Submitted license amendments to the NRC for ECCS Water 
A-47

Plant Plant Modifications (Administrative) Credited?

Management modifications, which include revisions to postaccident response that reduce recirculation flowrates through the 

ECCS Sump Strainer and decrease the predicted volume of 

transported sump pool debris. The license amendment has been 

approved.

Catawba-2 The modification process and the plant labeling process have been 

enhanced relative to GL-04-02 controls.

Submitted license amendments to the NRC for ECCS Water 

Management modifications, which include revisions to postaccident response that reduce recirculation flowrates through the 

ECCS Sump Strainer and decrease the predicted volume of 

transported sump pool debris. The license amendment has been 

approved.

Comanche 

Peak-1

Compensatory actions and modifications to the locked high 

radiation doors in response to NRC Bulletin 03-01 have been 

implemented as permanent changes in procedures.

Yes

A reassessment of containment building protective coatings was 

conducted in support of the response to GL-04-02.

Yes

The plant-labeling program is being evaluated to determine 

suitable material and program changes.

Yes

An upstream effects evaluation was completed, and the refueling 

cavity drains were identified as a potential plugging point.

Yes

An event characterization to evaluate the licensing and design 

basis to establish the design basis events that require emergency 

sump recirculation was completed.

Yes

Bounding debris generation, transport, and loading analyses are 

being performed for both units in support of analysis for the new 

design.

Yes

The ECCS and CSS were to be evaluated for blockage and wear 

concerns.

Yes

Comanche 

Peak-2

Compensatory actions and modifications to the locked high 

radiation doors in response to NRC Bulletin 03-01 have been 

implemented as permanent changes in procedures.

Yes

A reassessment of containment building protective coatings was 

conducted in support of the response to GL-04-02.

Yes

The plant labeling program is being evaluated to determine 

suitable material and program changes.

Yes

An upstream effects evaluation was completed, and the refueling 

cavity drains were identified as a potential plugging point.

Yes

An event characterization to evaluate the licensing and design 

basis to establish the design basis events that require emergency 

sump recirculation was completed.

Yes

Bounding debris generation, transport, and loading analyses are 

being performed for both units in support of analysis for the new 

design.

Yes

The ECCS and CSS were to be evaluated for blockage and wear 

concerns.

Yes

Crystal River3Licensed Operator training has been conducted on indications 

available for recognition of containment sump screen blockage and 
A-48

Plant Plant Modifications (Administrative) Credited?

appropriate response measures.

Multiple and diverse sources to refill the BWST and inventory to 

inject into the RCS have been established.

Aggressive containment cleaning and increased foreign material 

controls have been established.

Training has been provided to the Maintenance organization on the 

importance of RB cleanliness towards the minimization of latent 

debris that could affect sump recirculation, and thus post-accident 

core cooling capabilities including enforcement of the use of mats 

and/or tarps for work activities occurring over open floor grating to 

minimize the spread of foreign material to lower building 

elevations. In addition, a checklist item to discuss housekeeping 

requirements for work inside the RB has been added to 

Administrative Instruction, AI-607, "Pre-job and Post-job Briefings."

The integrity of the RB sump was verified on a refueling outage 

interval of 24 months with the performance of Surveillance 

Procedure SP-175A, "Reactor Building Emergency Sump 

Inspection and Cleaning."

Engineering Change screening criteria includes questions that 

require the engineer to determine if the change will create or alter 

the potential sources of debris which could interfere with ECCS 

suction from the RB sump, and if the change will result in the 

addition of materials in containment that could affect post-accident 

chemical precipitation.

To address the possibility of high sump screen differential pressure 

and sump screen blockage, diverse contingency actions including 

backflush of sump screens were written into EM-225E, "Guidelines 

for Long Term Cooling."

D.C. Cook-1 Extensive testing and analysis were conducted to determine break 

locations, identify and quantify debris sources, quantify debris 

transport, determine upstream and downstream effects, and 

confirm the recirculation function.

Yes

Alternate evaluation methodology used as described in Chapter 6 

of the GR and SER.

Yes

Changes to the licensing basis, including technical specifications, 

made to reflect the plant modifications, and the change to a 

mechanistic sump strainer blockage evaluation.

Yes

Extensive changes to plant programs, processes, and procedures 

made to limit the introduction of materials into containment that 

could adversely impact the recirculation function.

Yes

Monitoring programs established to ensure containment conditions 

will continue to support the recirculation function.

Yes

Conservative measures applied to assure adequate margins 

throughout the actions taken to address the GL-2004-02 concerns.

Yes

D.C. Cook-2 Extensive testing and analysis were completed to determine break 

locations, identify and quantify debris sources, quantify debris 

transport, determine upstream and downstream effects, and 

confirm the recirculation function.

Yes

Alternate evaluation methodology used as described in Chapter 6 Yes
A-49

Plant Plant Modifications (Administrative) Credited?

of the GR and SER.

Changes to the licensing basis, including technical specifications, 

made to reflect the plant modifications, and the change to a 

mechanistic sump strainer blockage evaluation

Yes

Extensive changes made to plant programs, processes, and 

procedures to limit the introduction of materials into containment 

that could adversely impact the recirculation function.

Yes

Monitoring programs established to ensure containment conditions 

will continue to support the recirculation function.

Yes

Conservative measures made to assure adequate margins 

throughout the actions taken to address the GL-2004-02 concerns.

Yes

Davis Besse1Controls on coatings, insulation, and signage have been 

established.

Yes

Procedures have been instituted that require verification of strainer 

integrity and containment cleanliness prior to entering a mode of 

operation that requires ECCS operability.

Yes

Diablo 

Canyon-1

Material exclusion procedures exist to verify that no loose debris is 

left following any activity performed in containment once 

containment integrity has been established.

An aggressive containment-cleaning program has been developed 

and implemented.

PG&E has inspection procedures to assure the containment sump 

screens are free of adverse gaps and breaches.

Classroom and simulator training on indications of, and responses 

to, sump clogging have been included in operator initial and 

requalification training.

Training has been provided to engineering personnel to raise their 

awareness of the more aggressive containment cleanliness 

requirements, the potential for sump blockage, and actions being 

taken to address sump blockage concerns.

Training has been conducted for Emergency Response 

Organization decision makers and evaluators in the Technical 

Support Center on indications of sump blockage and 

compensatory actions.

To ensure that alternative water sources are available to refill the 

RWST, Emergency Operating Procedure (EOP) ECA-I.1, "Loss of 

Emergency Core Cooling," provides two methods to refill the 

RWST: (1) refill from the boric acid blender, and (2) refill from the 

spent fuel pool (SFP) via the SFP pumps.

The following EOP changes have been implemented: EOP E-1.3, 

"Transfer to Cold-leg Recirculation" and EOP E-1, "Loss of Reactor 

or Secondary Coolant."

New EOP ECA-1.3, "Sump Blockage Guideline," was developed to 

provide specific guidance to operators when sump blockage was 

diagnosed to have occurred.

Diablo 

Canyon-2

Material exclusion procedures exist to verify that no loose debris is 

left following any activity performed in containment once 

containment integrity has been established.

An aggressive containment-cleaning program has been developed 
A-50

Plant Plant Modifications (Administrative) Credited?

and implemented.

PG&E has inspection procedures to assure the containment sump 

screens are free of adverse gaps and breaches.

Classroom and simulator training on indications of, and responses 

to, sump clogging have been included in operator initial and 

requalification training.

Training has been provided to engineering personnel to raise their 

awareness of the more aggressive containment cleanliness 

requirements, the potential for sump blockage, and actions being 

taken to address sump blockage concerns.

Training has been conducted for Emergency Response 

Organization decision makers and evaluators in the Technical 

Support Center on indications of sump blockage and 

compensatory actions.

To ensure that alternative water sources are available to refill the 

RWST, Emergency Operating Procedure (EOP) ECA-I.1, "Loss of 

Emergency Core Cooling," provides two methods to refill the 

RWST: (1) refill from the boric acid blender, and (2) refill from the 

spent fuel pool (SFP) via the SFP pumps.

The following EOP changes have been implemented: EOP E-1.3, 

"Transfer to Cold-leg Recirculation" and EOP E-1, "Loss of Reactor 

or Secondary Coolant."

New EOP ECA-1.3, "Sump Blockage Guideline," was developed to 

provide specific guidance to operators when sump blockage was 

diagnosed to have occurred.

Farley-1 Procedural and program controls are in place to ensure materials 

used in the containments will not result in an increase of the debris 

loading beyond the analyzed values. This includes controls for 

containment coatings, labels and insulation.

Procedural changes have been made to ensure that the postLOCA ECCS sump levels are maximized.

Farley-2 Procedural and program controls are in place to ensure materials 

used in the containments will not result in an increase of the debris 

loading beyond the analyzed values. This includes controls for 

containment coatings, labels and insulation.

Procedural changes have been made to ensure that the postLOCA ECCS sump levels are maximized.

Fort Calhoun1Plant procedures, programs, and design requirements were 

reviewed to determine those that could impact the analyzed 

containment or recirculation function configuration. These reviews 

resulted in the identification of those documents that required 

revision or development of new documents to ensure maintenance 

of the inputs and assumptions into the future.

Indian Point-2 Licensing basis change regarding passive failure analyses. Yes

Licensing basis change regarding emergency core cooling system 

valve surveillance requirements.

Yes

The procedure EN-MA-118, "Foreign Material Exclusion," has 

been revised to identify the recirculation and containment sumps 

as FME Level 1 areas, the highest level of cleanliness control.

Yes
A-51

Plant Plant Modifications (Administrative) Credited?

ENN-EE-S-010-1P2 "Electrical Separation Design Criteria" 

standard has been revised to phase out the use of vinyl cable tray 

tags, to exclude the use of new marinate and/or transite, to 

eliminate the use of new cable wrap for separation, and to require 

an Engineering evaluation should a deviation be necessary.

Yes

ENN-EE-S-008-IP, "Electrical Installation Standard" has been 

revised to eliminate unqualified material such as vinyl tags, tape, 

and blankets in new installations.

Yes

A sampling program was initiated to ensure containment dust, dirt, 

and latent debris do not exceed the analyzed quantities evaluated.

Yes

The procedure EN-DC-115, "Engineering Change Development" 

has been revised to screen design changes for impact on GL 

2004-02 compliance. Examples of specific screen items include 

any changes to: insulation, coatings, aluminum, and other 

metallic/non metallic debris sources.

Yes

Several enhancements to the existing Entergy Nuclear Northeast 

fleet procedure, ENN-DC-150, "Condition Monitoring of 

Maintenance Rule Structures", were made. These enhancements 

include a detailed inspection checklist for coatings. A preventative 

maintenance (PM) to visually inspect coating in the Indian Point 

Unit 2 and 3 Vapor Containment Buildings during all future 

refueling outages was created for GSI-191, employing guidance 

from ENN-DC-150. These changes have been incorporated in 

fleet procedure EN-DC-150, Rev. 0. The frequency of the PM 

inspection for GSI-191 is every two (2) years, or every cycle during 

the refueling outage. The process requires any degraded coatings 

be evaluated as acceptable, or repaired prior to exiting the outage.

Yes

Licensing basis change regarding the containment sump pHbuffering agent.Yes

Indian Point-3 Licensing basis change regarding passive failure analyses. Yes

The procedure EN-MA-118, "Foreign Material Exclusion," has 

been revised to identify the recirculation and containment sumps 

as FME Level 1 areas, the highest level of cleanliness control.

Yes

The standard ENN-EE-S-010-1P2, "Electrical Separation Design 

Criteria" standard has been revised to phase out the use of vinyl 

cable tray tags, to exclude the use of new marinate and/or transite, 

to eliminate the use of new cable wrap for separation. 

Yes

The standard ENN-EE-S-008-IP, "Electrical Installation Standard," 

has been revised to eliminate unqualified material such as vinyl 

tags, tape, and blankets in new installations.

Yes

A sampling program was initiated to ensure containment dust, dirt, 

and latent debris do not exceed the analyzed quantities evaluated.

Yes

The procedure EN-DC-115, "Engineering Change Development" 

has been revised to screen design changes for impact on GL-04-

02 compliance. Examples of specific screen items include any 

changes to: insulation, coatings, aluminum, and other metallic/non 

metallic debris sources.

Yes

Several enhancements to the existing Entergy Nuclear Northeast 

fleet procedure, ENN-DC-150, "Condition Monitoring of 

Yes
A-52

Plant Plant Modifications (Administrative) Credited?

Maintenance Rule Structures", were made. These enhancements 

include a detailed inspection checklist for coatings. A preventative 

maintenance (PM) to visually inspect coating in the Indian Point 

Unit 2 and 3 Vapor Containment Buildings during all future 

refueling outages was created for GSI-191 employing guidance 

from ENN-DC-150. These changes have been incorporated in 

fleet procedure EN-DC-150, Rev. 0. The frequency of the PM 

inspection for GSI-191 is every two (2) years, or every cycle during 

the refueling outage. The process requires any degraded coatings 

be evaluated as acceptable, or repaired prior to exiting the outage.

Licensing basis change regarding the containment sump pHbuffering agent.Yes

Kewaunee-1 Fleet GSI-191 Program implemented that designates a Lead 

Person, and Program Owners, and delineates GSI-191 staff and 

management responsibilities.

Yes

Fleet FME procedure instituted that prevents entry of foreign 

material into plant systems.

Yes

Containment inspection procedure is implemented at the end of 

each outage to identify and remove inappropriate material and 

debris from containment, and to ensure portable equipment is 

seismically restrained or properly stored.

Yes

During refueling, radiation protection staff routinely performs 

cleaning of various areas in containment.

Yes

Controlled-area maintenance-staff clean the recirculation sump pit, 

as needed, during refueling outages to remove standing water and 

boric acid residue.

Yes

Procedures established to perform periodic latent debris sampling 

in containment and to quantify the total latent debris in containment 

to ensure the quantity remains below the analyzed limit.

Yes

Procedures established to apply, inspect, and quantify coatings in 

containment.

Yes

Fleet guidance document issued for labeling plant equipment that 

includes labeling equipment in containment.

Yes

Maintenance procedure that provides guidance for applying and 

replacing insulation in containment.

Yes

Plant modification included notification to the GSI-191 responsible 

engineer of modifications to the screen for potential impact relative 

to GSI-191 issues.

Yes

The allowable quantity of latent debris (dirt, dust) in containment 

will be limited to 51 Ibm to prevent formation of a filtering bed of 

fiber on the recirculation strainer when combined with the 

remaining fiber in containment.

Yes

The Dominion fleet latent debris sampling and evaluation 

procedure will be revised prior to the next refueling outage to 

require a sampling frequency of every other refueling outage for 

low-fiber plants that are dependent upon plant cleanliness to 

prevent formation of a filtering bed of fiber on the recirculation 

strainer. The procedure will specify the sampling frequency may be 

relaxed after several consecutive sample results (outages) that 

Yes
A-53

Plant Plant Modifications (Administrative) Credited?

identify minimal or no increasing volume of measured latent debris 

and ample latent debris inventory margin.

McGuire-1 The modification process and the plant labeling process have been 

enhanced relative to GL-04-02 controls.

Submitted license amendments to the NRC for ECCS Water 

Management modifications, which include revisions to postaccident response that reduce recirculation flowrates through the 

ECCS Sump Strainer and decrease the predicted volume of 

transported sump pool debris. The license amendment has been 

approved.

McGuire-2 The modification process and the plant labeling process have been 

enhanced relative to GL-04-02 controls.

Submitted license amendments to the NRC for ECCS Water 

Management modifications, which include revisions to postaccident response that reduce recirculation flowrates through the

ECCS Sump Strainer and decrease the predicted volume of 

transported sump pool debris. The license amendment has been 

approved.

Millstone-2 Containment cleanliness standards have been defined and 

detailed in a station housekeeping procedure.

Yes

Design controls have been put in place to require evaluation of 

potential debris sources in containment created by or adversely 

affected by design changes.

Yes

Insulation specification changes have been made to ensure that 

changes to insulation in containment can be performed only after 

the impact on containment strainer debris loading is considered.

Yes

Millstone-3 Containment cleanliness standards have been defined and 

detailed in a station housekeeping procedure.

Yes

Design controls have been put in place to require evaluation of 

potential debris sources in containment created by or adversely 

affected by design changes.

Yes

Insulation specification changes have been made to ensure that 

changes to insulation in containment can be performed only after 

the impact on containment strainer debris loading is considered.

Yes

North Anna-1 Revised the technical specifications for Units 1 and 2 to support 

the installation of the new strainers and resolution of GSI-191 and 

NRC GL-04-02.

Yes

Replaced the LOCTIC containment analysis methodology for 

analyzing the response to postulated pipe ruptures inside 

containment, including a LOCA and a main steam line break 

(MSLB), with the NRC-approved GOTHIC evaluation methodology 

discussed in Dominion Topical Report DOM-NAF-3-0.0-P-A. The 

change to the GOTHIC code provided margin in LOCA peak 

containment pressure and other accident analysis results.

Yes

Revised the LOCA Alternate Source Term (AST) analysis to 

include the effects from changing the RS pump start methodology 

and other changes identified in License Amendments 250 and 230 

for NAPS Units 1 and 2, respectively, approved by the NRC on 

March 13, 2007 (ADAMS ML070720043).

Yes
A-54

Plant Plant Modifications (Administrative) Credited?

Revised and/or created procedures and programs to ensure that 

future changes to the plant do not adversely affect the ability of the 

new containment strainers to perform their design function.

Yes

Trained operators on the operation of the RS and LHSI systems 

with respect to the new containment sump strainers.

Yes

North Anna-2 Revised the technical specifications for Units 1 and 2 to support 

the installation of the new strainers and resolution of GSI-191 and 

NRC GL-04-02.

Yes

Replaced the LOCTIC containment analysis methodology for 

analyzing the response to postulated pipe ruptures inside 

containment, including a LOCA and a main steam line break 

(MSLB), with the NRC-approved GOTHIC evaluation methodology 

discussed in Dominion Topical Report DOM-NAF-3-0.0-P-A. The 

change to the GOTHIC code provided margin in LOCA peak

containment pressure and other accident analysis results.

Yes

Revised the LOCA Alternate Source Term (AST) analysis to 

include the effects from changing the RS pump start methodology 

and other changes identified in License Amendments 250 and 230 

for NAPS Units 1 and 2, respectively, approved by the NRC on 

March 13, 2007 (ADAMS ML070720043).

Yes

Revised and/or created procedures and programs to ensure that 

future changes to the plant do not adversely affect the ability of the 

new containment strainers to perform their design function.

Yes

Trained operators on the operation of the RS and LHSI systems 

with respect to the new containment sump strainers.

Yes

Oconee-1 Enhancement of plant labeling process to limit potential for tags 

and stickers to become post-accident debris sources.

Yes

Enhancement of plant containment coatings program to ensure 

that degraded coatings identified from maintenance inspections 

are evaluated for potential effects on RBES evaluations.

Yes

Enhancement of FME controls to ensure that any scaffolding 

remaining in containment during power operation is evaluated for 

potential chemical effects.

Yes

Enhancement of plant design change process to ensure that plant 

modifications are evaluated for impact to RBES evaluations

performed in support of GSI-191.

Yes

Revision of technical specifications to remove reference to trash 

racks and screens and to add reference to strainers.

Yes

Revision of UFSAR to update from 50% blockage criteria to debrisspecific RBES evaluation criteria.Yes

Oconee-2 Enhancement of the plant labeling process to limit potential for 

tags and stickers to become post-accident debris sources.

Yes

Enhancement of plant containment coatings program to ensure 

that degraded coatings identified from maintenance inspections 

are evaluated for potential effects on RBES evaluations.

Yes

Enhancement of FME controls to ensure that any scaffolding 

remaining in containment during power operation is evaluated for 

potential chemical effects.

Yes

Enhancement of plant design change process to ensure that plant Yes
A-55

Plant Plant Modifications (Administrative) Credited?

modifications are evaluated for impact to RBES evaluations 

performed in support of GSI-191.

Revision of technical specifications to remove reference to trash 

racks and screens and to add reference to strainers.

Yes

Revision of UFSAR to update from 50% blockage criteria to debrisspecific RBES evaluation criteria.Yes

Oconee-3 Enhancement of the plant labeling process to limit potential for 

tags and stickers to become post-accident debris sources.

Yes

Enhancement of plant containment coatings program to ensure 

that degraded coatings identified from maintenance inspections 

are evaluated for potential effects on RBES evaluations.

Yes

Enhancement of FME controls to ensure that any scaffolding 

remaining in containment during power operation is evaluated for 

potential chemical effects.

Yes

Enhancement of plant design change process to ensure that plant 

modifications are evaluated for impact to RBES evaluations 

performed in support of GSI-191.

Yes

Revision of technical specifications to remove reference to trash 

racks and screens and to add reference to strainers.

Yes

Revision of UFSAR to update from 50% blockage criteria to debrisspecific RBES evaluation criteria.Yes

Palisades-1 Enhancements of programmatic control of LOCA debris sources in 

containment have been implemented.

Yes

Administrative procedure developed to address the use of proper 

labeling of materials inside the containment building.

Yes

Administrative procedure that governs general cleanliness 

requirements in the reactor building revised to state that general 

cleanliness "should be maintained by periodic cleanup efforts of 

the work areas."

Yes

Administrative procedure developed that deals with failures that 

could adversely affect a safety-related or important-to-safety 

structure, system, or component.

Yes

“Technical Specification for Painting” revised to update the 

requirements of coating applications inside containment in 

accordance with current regulatory and industry standards.

Yes

“Technical Specification for Furnishing and Installing Conventional 

Type Insulation” was revised to explicitly require an engineering 

change process for replacing the thermal insulation material inside 

containment (with some exceptions).

Yes

The “Design lnput Checklist” was revised to incorporate a 

“Containment Sump Blockage” design checklist to determine if 

proposed plant modifications affect the containment sump 

analysis.

Yes

“Fire Protection Surveillance Procedure” used to inspect cable tray 

fire stops located in containment was revised to require that a 

visual inspection of the integrity of fire rated assemblies and fire 

protection assemblies be performed every 18 months.

Yes

“Technical Specification Surveillance Procedure” developed to 

require that inspected areas that are painted or coated be 

Yes
A-56

Plant Plant Modifications (Administrative) Credited?

examined for flaking, blistering, peeling or discoloration.

Technical Specification developed to verify that each containment 

sump inlet debris screen, containment sump passive strainer

assembly, and other containment sump entrance pathways are not 

restricted by debris and show no evidence of structural distress or 

abnormal corrosion. This procedure also performs a cleanliness 

inspection of the containment sump, condition assessment of the 

sump level switches, sump drain screen, and the containment 

sump liner.

Yes

General operating procedure developed to require removal of 

caution tags from containment and to perform inspections of 

containment.

Yes

System operating procedure developed to identify senior reactor 

operator inspections in support of containment closeout to ensure 

the integrity of the containment sump envelope and containment 

sump screens, and to remove unauthorized material.

Yes

Permanent maintenance procedure developed to ensure 

containment cleanliness throughout outage and/or online work 

activities in containment and provide guidelines to prepare for the 

final closeout inspection.

Yes

Permanent maintenance procedure developed to provide 

instructions for condition assessments of protective coatings within 

containment and reporting of results.

Yes

Permanent maintenance procedure developed to provide 

instructions for removing and installing containment sump 

envelope passive strainers and debris screens during operating 

modes 5 and 6.

Yes

Engineering Manual Procedure defines the requirements of the 

program that applies to coatings on the interior surfaces of 

containment, exposed surfaces of equipment located in 

containment, and linings of tanks and piping where detachment 

could adversely affect the function of safety-related structures, 

systems or components and thereby impair safe shutdown.

Yes

Permanent maintenance procedure developed to provide 

requirements for application of qualified Service Level I protective 

coatings to surfaces inside, or to systems, structures or 

components that will be installed inside containment.

Yes

Technical Specification surveillance procedure developed to 

ensure a sufficient amount of sump buffering agent is installed 

inside

containment.

Yes

Palo Verde-1 Programmatic controls are in place to verify containment 

cleanliness and ensure that no foreign material is present at the 

ECCS sump strainers prior to containment closure following 

refueling outages. These controls also ensure maintenance of the 

containment cleanliness for any entry into the containment through 

verification of the condition of all areas entered.

Procedures are also in place to control transient materials taken 

into or out of containment during any entry of the containment at 
A-57

Plant Plant Modifications (Administrative) Credited?

power.

Programmatic controls are in place to perform periodic coatings 

assessment walkdowns to verify the condition of the containment 

coatings.

Palo Verde-2 Programmatic controls are in place to verify containment 

cleanliness and ensure that no foreign material is present at the 

ECCS sump strainers prior to containment closure following 

refueling outages. These controls also ensure maintenance of the 

containment cleanliness for any entry into the containment through 

verification of the condition of all areas entered.

Procedures are also in place to control transient materials taken 

into or out of containment during any entry of the containment at 

power.

Programmatic controls are in place to perform periodic coatings 

assessment walkdowns to verify the condition of the containment 

coatings.

Palo Verde-3 Programmatic controls are in place to verify containment 

cleanliness and ensure that no foreign material is present at the 

ECCS sump strainers prior to containment closure following 

refueling outages. These controls also ensure maintenance of the 

containment cleanliness for any entry into the containment through 

verification of the condition of all areas entered.

Procedures are also in place to control transient materials taken 

into or out of containment during any entry of the containment at 

power.

Programmatic controls are in place to perform periodic coatings 

assessment walkdowns to verify the condition of the containment

coatings.

Prairie Island1The minimum level in the refueling water storage tank was 

administratively increased to 90%.

Yes

Additional measures were implemented to provide more 

aggressive requirements for containment closeout and foreign 

material controls.

Yes

The containment closeout procedures were enhanced to include 

specific verifications that containment drainage paths are not 

blocked.

Yes

The post-outage containment inspection procedure specifically 

looked at the sump strainer for evidence of structural distress or 

abnormal corrosion.

Yes

Prairie Island2The minimum level in the refueling water storage tank was 

administratively increased to 90%.

Yes

Additional measures were implemented to provide more 

aggressive requirements for containment closeout and foreign 

material controls.

Yes

The containment closeout procedures were enhanced to include 

specific verifications that containment drainage paths are not 

blocked.

Yes

The post-outage containment inspection procedure specifically 

looked at the sump strainer for evidence of structural distress or 

Yes
A-58

Plant Plant Modifications (Administrative) Credited?

abnormal corrosion.

Robinson-2 To limit the amount of plastic debris in containment, an inspection 

was conducted in RO-24 and plant labeling procedure PLP-050, 

"Plant Labeling, Stenciling, and Signs," was revised to prohibit the 

installation of new, or replacement of existing, plastic tags or labels 

in containment and requires stainless steel or porcelain coated 

stainless steel signs.

Yes

Procedure EGR-NGGC-0005, "Engineering Change," which is 

used for development of plant modifications, was revised to add 

screening questions regarding insulation, aluminum-containing 

material in containment, and flow paths during the recirculation 

phase of an accident.

Yes

Procedure PLP-006, "Containment Vessel Inspection/Closeout," 

was revised to emphasize inspection for latent debris to ensure 

latent debris is maintained within the inputs and assumptions that 

support the GSI-191 issue resolution. PLP-006 is also used for 

identifying additions, deletions, and locations of aluminum in 

containment. The strainer design analysis is based on 400 lbs of 

latent debris in the containment, as compared to an estimated 

202.5 lbs of latent debris in containment. The latent debris in 

containment was estimated in accordance with the NEI 04-07 

methodology.

Yes

Specification L2-M-039, "Piping and Equipment Thermal 

Insulation," was revised to provide guidance to control insulation 

materials used in containment in order to maintain the debris 

source term in accordance with the analysis. Procedure MMM003, "Maintenance Planning," was revised to include guidance for 

maintenance planners to use the new specification for activities 

inside containment involving insulation.

Yes

Salem-1 PSEG revised appropriate Administrative Procedures. As part of 

the newly installed containment sump strainers, PSEG revised its 

administrative procedures to ensure that potential sources of 

debris that may be introduced into containment will be assessed 

for adverse effects on the ECCS and CSS recirculation functions. 

These programmatic controls include requirements related to 

coatings, containment housekeeping, materiel condition, and 

modifications.

Salem-2 PSEG revised appropriate Administrative Procedures. As part of 

the newly installed containment sump strainers, PSEG revised its 

administrative procedures to ensure that potential sources of 

debris that may be introduced into containment will be assessed 

for adverse effects on the ECCS and CSS recirculation functions. 

These programmatic controls include requirements related to 

coatings, containment housekeeping, materiel condition, and 

modifications.

San Onofre-2 Procedural guidance and training; containment cleanliness and 

control of debris sources.

San Onofre-3 Procedural guidance and training; containment cleanliness and 

control of debris sources.
A-59

Plant Plant Modifications (Administrative) Credited?

Seabrook-1 The containment entry procedure has been updated to require that 

any aluminum to be taken into containment should be evaluated 

prior to entry.

The surveillance procedure that inspects the containment 

recirculation sumps has been extensively revised.

Shearon 

Harris-1

Removal of plastic signage from containment. During RFO 14 (fall 

of 2007), HNP removed most of the plastic signage from 

containment. These signs and labels were operator aids for 

locating components. In some cases, the components had 

redundant stainless-steel tags that were left on the components. 

In some other cases, the plastic signs were replaced with 

porcelainized metal tags. In other cases, the plastic signs were 

replaced with stenciling.

Yes

Revised the modification procedure. The corporate modification 

procedure, EGRNGGC-0005, has been revised to add screening 

questions regarding insulation and aluminum-containing material in 

containment as well as regarding flow paths that water would take 

during the recirculation phase of an accident.

Yes

The site deficiency tags are paper tags and represent a potential 

source of debris. The site deficiency tag procedure, AP-038, was 

revised to specifically prohibit the use of deficiency tags in 

containment.

Yes

Revised the containment closeout procedure. The site 

containment closeout procedure, OST-1081, was revised to 

provide a definition of latent debris, acceptance criteria for latent 

debris, and specific steps to assure that any latent debris in 

containment is within the acceptance criteria. Although HNP has 

determined that the quantity of latent debris in containment is 

significantly less than that assumed in the debris generation 

calculation, HNP elected to place a control on the latent debris that 

may be generated inside containment.

Yes

St. Lucie-1 A walkdown to confirm the absence of potential choke points was 

completed.

Yes

Enhancements to programmatic controls have been put in place at 

St. Lucie Unit 1. Engineering procedures have been revised to 

provide guidance to the design engineer working on plant 

modifications to take into account the impact of the design on the 

"containment sump debris generation & transport analysis and/or 

recirculation functions."

Yes

As an enhancement to the existing process for controlling the 

quantities of piping insulation within the containment, the 

engineering specification that controls thermal insulation was 

revised to provide additional guidance for maintaining containment 

insulation configuration.

Yes

New controls have been instituted limiting the permissible quantity 

of unqualified coatings in the containment building.

Yes

St. Lucie-2 Plant walkdowns have been completed to evaluate the potential for 

chokepoints in the flow path from potential break locations to the 

containment recirculation sump, and it was concluded that there 

Yes
A-60

Plant Plant Modifications (Administrative) Credited?

were no chokepoints that would inhibit flow.

Improvements in programmatic controls have been implemented to 

ensure that the potential quantity of post-loss of coolant accident 

(LOCA) debris does not exceed the evaluation assumptions for Net 

Positive Suction Head (NPSH) margins on recirculation 

ECCS/CSS pumps, or the evaluation assumptions in downstream

analysis for components and systems, or for fuel and in-vessel 

effects.

Yes

Summer-1 A cumulative effects program has been established for tabulating, 

controlling and evaluating changes to quantities of insulation inside 

the reactor building.

Yes

A cumulative effects program has been established for tabulating, 

controlling and evaluating changes to quantities of unqualified 

coatings inside the reactor building.

Yes

A Level 1 coatings program for the reactor building has been 

established.

Yes

Licensee is developing an Alternate Source Term LOCA Dose 

Analysis that does not require the assumption of a pump seal 

failure in the event of a LOCA.

Yes

Surry-1 Performed an analysis of clogging for components in ECCS and 

RS flow streams downstream of ECCS and RS strainers.

Yes

Completed analysis of water hold-up in containment to identify 

locations where water will be blocked from reaching the RS and 

LHSI strainers.

Yes

Revised the SPS Units 1 and 2 Technical Specifications to 

increase the containment air partial pressure limits to provide 

analytical margin, including NPSH margin for the RS and LHSI 

pumps.

Yes

Replaced the LOCTIC containment analysis methodology for 

analyzing the response to postulated pipe ruptures inside 

containment, including a LOCA and a MSLB, with the NRCapproved GOTHIC evaluation methodology discussed in Dominion 

Topical Report DOM-NAF-3-0.0-P-A. The change to the GOTHIC 

code provided margin in LOCA peak containment pressure and 

other accident analysis results.

Yes

Revised the LOCA Alternate Source Term analysis to include the 

effects from changing the RS pump start methodology and from 

other modifications associated with the GSI-191 project.

Yes

Revised and/or created procedures and programs to ensure that 

future changes to the plant do not have adverse affects on the 

ability of the new containment strainers to perform their design 

function.

Yes

Trained operators on the operation of the RS and LHSI systems 

with respect to the new containment strainers.

Yes

Surry-2 Performed an analysis of clogging for components in ECCS and 

RS flow streams downstream of ECCS and RS strainers.

Yes

Completed analysis of water hold-up in containment to identify 

locations where water will be blocked from reaching the RS and 

LHSI strainers.

Yes
A-61

Plant Plant Modifications (Administrative) Credited?

Revised the SPS Units 1 and 2 Technical Specifications to 

increase the containment air partial pressure limits to provide 

analytical margin, including NPSH margin for the RS and LHSI 

pumps.

Yes

Replaced the LOCTIC containment analysis methodology for 

analyzing the response to postulated pipe ruptures inside 

containment, including a LOCA and a MSLB, with the NRCapproved GOTHIC evaluation methodology discussed in Dominion 

Topical Report DOM-NAF-3-0.0-P-A. The change to the GOTHIC 

code provided margin in LOCA peak containment pressure and 

other accident analysis results.

Yes

Revised the LOCA alternate source term analysis to include the 

effects from changing the RS pump start methodology and from 

the other modifications associated with the GSI-191 project.

Yes

Revised and/or created procedures and programs to ensure that 

future changes to the plant do not have adverse affects on the 

ability of the new containment strainers to perform their design 

function.

Yes

Trained operators on the operation of the RS and LHSI systems 

with respect to the new containment strainers.

Yes

Three Mile 

Island-1

Revised emergency operating procedures to throttle LPI flow, if 

high strainer differential pressure is observed.

Turkey Point3Engineering procedures have been revised to provide guidance to 

design engineers working on plant modifications to take into 

account the impact of the design on the "containment sump debris 

generation & transport analysis and/or recirculation functions."

Yes

The engineering specification that controls thermal insulation was 

revised to provide additional guidance for maintaining containment 

insulation configuration.

Yes

New controls have been instituted limiting the permissible quantity 

of unqualified coatings in the containment building.

Yes

Turkey Point4The coating specification update ensures that strainer design basis 

coating debris loads will not be exceeded.

Yes

The insulation specification has been revised to enhance 

configuration management controls to ensure that insulation within 

that could become debris does not exceed strainer design inputs.

Yes

Procedures are in place to ensure that the single potential choke 

point, refueling canal drain covers, are removed prior to Mode 4 

restart so that the design basis sump water supply is available.

Yes

Vogtle-1 Procedural and program controls are in place to ensure materials 

used in the containments will not result in an increase of the debris 

loading beyond the analyzed values. They include controls for 

containment coatings, labels and insulation.

Yes

Vogtle-2 Procedural and program controls are in place to ensure materials 

used in the containments will not result in an increase of the debris 

loading beyond the analyzed values. This includes controls for 

containment coatings, labels and insulation.

Yes

Waterford-3 Changes to plant programs, processes, and procedures to limit the 

introduction of materials into containment that could adversely 
A-62

Plant Plant Modifications (Administrative) Credited?

impact the recirculation function, and establish monitoring 

programs to ensure containment conditions will continue to support 

the recirculation function.

Revise Emergency Operating Procedures to include contingency 

actions for a Low Pressure Safety Injection pump failing to trip on 

Recirculation Actuation Signal.

Wolf Creek-1 Changes to the scaffold construction and use procedure to 

enhance requirements for control of scaffold tags and materials 

used during work activities conducted in the containment during 

plant operational modes 1 through 4.

Changes were implemented for design change process 

procedures to ensure that necessary engineering evaluations will 

be performed when preparing a change to the plant design that 

either directly or indirectly affects containment, ECCS, or CSS. 

Administrative controls were added to the plant modification 

process.

Changes were made to the containment entry and material control 

procedure to enhance requirements during plant operational 

modes 1 through 4 for control of materials during work activities 

conducted in the containment and for control of radiological 

postings.

Changes were made to the clearance order procedure to ensure 

that Generic Letter 2004-02 analyses and evaluations are 

considered prior to making future changes to existing requirements 

that clearance order tags are not installed on components inside 

the containment being removed from service (tagged out) during 

plant operational modes 1 through 4.

Changes to the work request procedure to ensure that GL-04-02 

analyses and evaluations are considered prior to making future 

changes to existing requirements that work request tags are not 

installed on components inside the containment.

WCNOC implemented a program to assess the containment latent 

debris.

WCNOC implemented a program to assess the containment 

coatings.

WCNOC implemented changes to Technical Specifications 

Surveillance procedures to ensure that the installed replacement 

strainers would not have openings in excess of the maximum 

designed strainer opening.

Table A.2-5. Downstream Plant Modifications

Plant Plant Modifications (Downstream)

Braidwood-1 Three ECCS safety injection throttle valves modified to avoid potential 

blockage by incorporating a new bonnet, stem, trim assembly, manual 

operator, and locking device.

Braidwood-2 Three ECCS safety injection throttle valves modified to avoid potential 

blockage by incorporating a new bonnet, stem, trim assembly, manual 

operator, and locking device.
A-63

Plant Plant Modifications (Downstream)

Byron-1 Three ECCS safety injection throttle valves modified to avoid potential 

blockage by incorporating a new bonnet, stem, trim assembly, manual 

operator, and locking device.

Byron-2 Three ECCS safety injection throttle valves modified to avoid potential 

blockage by incorporating a new bonnet, stem, trim assembly, manual 

operator, and locking device.

Calvert Cliffs-1 Replacement of all HPSI pump cyclone separators with the tested unit 

was completed by June 30, 2008.

Calvert Cliffs-2 Replacement of all HPSI pump cyclone separators with the tested unit 

was completed by June 30, 2008.

Catawba-1 Modification of the Catawba Unit 1 and 2 Charging and Safety Injection 

line flow orifices, along with an adjustment to the associated throttle valve 

clearances, was required to resolve throttle valve plugging and erosion 

concerns identified by the downstream debris effects evaluations.

Catawba-2 Modification of the Catawba Unit 1 and 2 Charging and Safety Injection 

line flow orifices, along with an adjustment to the associated throttle valve 

clearances, was required to resolve throttle valve plugging and erosion 

concerns identified by the downstream debris effects evaluations.

Crystal River-3 The cyclone separators on the DH and BS pumps have been removed 

and replaced with models that do not need throttled flow. The throttle 

valves were removed as part of the cyclone separator replacement.

The HP auxiliary spray valve has been fully opened based on supporting 

hydraulic analyses.

Davis Besse-1 Modification/installation of cyclone separators for the HPI, LPI, and CS 

pumps.

Farley-1 ECCS branch flow throttle valves have been replaced.

Farley-2 ECCS branch flow throttle valves have been replaced.

Indian Point-3 The IR pumps were replaced during the spring 2007 refueling outage [Ref. 

971 with a double inlet suction style pump. Due to the predicted increased 

sump screen debris load determined by GL 2004-02 related analyses, the 

head losses through the IR sump are also predicted to increase. Based 

on hydraulic and NPSH calculations, due to the increased debris loads the 

original pumps would not have been able to fulfill their safety functions. 

The replacement pumps are demonstrated to have the capability to 

operate without cavitation at the required flow rates assuming maximum 

anticipated sump screen head losses.

Kewaunee-1 The ICS pump Durametallic seal and safety bushing require additional 

evaluation.

Oconee-1 Replacement of HPI, RHR, and BS pump seal flush orifices and cyclone 

separators due to "potential for plugging.”

Replacement of HPI pump internals to soft, wear-susceptible materials.

Oconee-2 Replacement of HPI, RHR, and BS pump seal flush orifices and cyclone 

separators due to "potential for plugging.”

Replacement of HPI pump internals to soft, wear-susceptible materials.

Oconee-3 Replacement of HPI, RHR, and BS pump seal flush orifices and cyclone 

separators due to "potential for plugging.”

Replacement of HPI pump internals to soft, wear-susceptible materials.

Palisades-1 Replacement of HPSI pumps mechanical seals, cyclone separators, and 

CSS valves.
A-64

Plant Plant Modifications (Downstream)

Prairie Island-1 John Crane Type 1/1B mechanical seals in RHR pumps were to be 

replaced with Chesterton 180 mechanical seals.

Prairie Island-2 John Crane Type 1/1B mechanical seals in RHR pumps were to be 

replaced with Chesterton 180 mechanical seals.

Robinson-2 The seal on the CS pump "B" was noted to have a graphite bushing. This 

seal was replaced with a seal using a metallic bushing.

St. Lucie-1 The High Pressure Safety Injection (HPSI) pump seals and cyclone 

separators have been replaced with a seal system that does not use 

cyclone separators or rely on the HPSI pumped water for flushing and 

cooling the mechanical seals. The new seal system recirculates the seal 

cavity water through an external heat exchanger to flush and cool the seal 

faces. The new seal system will prevent the potential failure of shaft seals 

that could be caused by the carryover of debris in the pumped water when 

the HPSI pumps take suction of potentially debris-laden fluid from the new 

containment strainer system in the recirculation mode.

St. Lucie-2 The HPSI pumps were modified by removing the cyclone separator and 

associated piping and by replacing the mechanical seals with a new seal 

design that uses a recirculated seal cavity fluid for flushing and cooling of 

the seal faces.

The CSS pumps were modified by removing the cyclone separator and 

associated piping and by replacing the mechanical seals with a new seal 

design that uses a recirculated seal cavity fluid.

Summer-1 Downstream high head safety injection throttle valve replaced.

Replacement of pump carbon/graphite disaster bushing with an 

acceptable alternative was being investigated.

Surry-1 Holes in stilling well increased and debris shields provided to prevent 

potential blockage of containment sump wide range level indicators.

Surry-2 Holes in stilling well increased and debris shields provided to prevent 

potential blockage of containment sump wide range level indicators.

Three Mile 

Island-1

One modification to DH manual throttle valves was performed during 

T1R17 (Fall 2007) to address a downstream effect concern.

The stacked disk cage design used in the valves contained small 

openings in the disk stack that had the potential to become blocked with 

the small debris that could pass through the Reactor Building Sump 

Strainer. These valve disk stacks were therefore replaced in T1R17 (Fall 

2007) with a new design with larger flow passages less susceptible to 

blockage by fibrous debris.

Turkey Point-4 Containment spray pump mechanical seals modified and their cyclone 

separators removed.

Vogtle-1 Orifices installed in intermediate and high head ECCS lines; associated 

throttle valves adjusted to ensure that no blockage will occur.

Vogtle-2 Orifices installed in intermediate and high head ECCS lines; associated 

throttle valves adjusted to ensure that no blockage will occur.

Watts Bar-2 New throttle valves were procured for installation in the CVCS and SI lines 

to the RCS. The valves will be installed under EDCR 54783. The new 

valves will be opened sufficiently to preclude downstream blockage and 

reduce the number of components that need to be considered for potential 

debris erosion.
A-65

Table A.2-6. Plants with No Downstream Modifications

Plant Name Unit #

ANO 1

ANO 2

Comanche Peak 1

Comanche Peak 2

D.C. Cook 1

D.C. Cook 2

Diablo Canyon 1

Diablo Canyon 2

Fort Calhoun 1

Ginna 1

Indian Point 2

McGuire 1

McGuire 2

Millstone 2

Millstone 3

North Anna 1

North Anna 2

Palo Verde 1

Palo Verde 2

Palo Verde 3

Point Beach 1

Point Beach 2

Salem 1

Salem 2

San Onofre 2

San Onofre 3

Seabrook 1

Sequoyah 1

Sequoyah 2

Shearon Harris 1

South Texas 1

South Texas 2

Turkey Point 3

Waterford 3

Watts Bar 1

Wolf Creek 1

Head Loss: Strainer Approach Velocity

If the value for the strainer approach velocity is provided, it is recorded directly into the 

database. Otherwise, it is calculated as:
A-66

where the “Design Flow” is the flow rate as indicated in the response for each case, where 

applicable, and the “Total Screen Area” is calculated as in Figure A.2-4. 

For this field, multiple entries were allowed for a plant for different strainers and scenarios (such 

as SBLOCA, LBLOCA), where applicable. Figure A.2-6 shows maximum and minimum values 

for the approach velocity for each plant unit.15 In most cases, only one value is provided, such 

that maximum and minimum velocities are equal. 

Head Loss: Test Location

Table A.2-7 shows the head loss test locations as they are recorded in the GL-04-02 database. 

Head Loss: Clean Strainer Head Loss

This field collects the information on the clean (no debris) strainer head loss. If available, the 

head loss is recorded in the database for the entire strainer at the design conditions. In any 

case, the exact assumption and/or conditions used to determine the clean strainer head loss are 

recorded in the Comments field for each entry. 

Table A.2-8 lists the clean strainer head loss data recorded in the GL-04-02 database. The 

table (rather than chart) form is selected in this report since the head loss is a function of many 

parameters (including the flow rate, for example), such that a direct comparison of these values 

between different plants is not meaningful. The same approach is used for other head loss 

fields below. 

Head Loss: Non-Chemical Head Loss

Table A.2-9 lists the GL-04-02 database entries for the head loss testing in which chemical 

debris was not included. 

Head Loss: Full Head Loss

Table A.2-10 presents the database entries for the recorded full-debris (including chemicals) 

head loss. 

Head Loss: Thin Bed

The GL-04-02 database also collected the information, where provided, on the thin bed 

thickness for the head loss testing. In cases where the response indicated “insufficient fiber 

debris to form 1/8 in. thin bed,” 0 is entered in this database field. Figure A.2-7 summarizes the 

database entries for the thin bed thickness. For about half of the plants, no thin bed effect is 

reported. 

 

15Note that min/max values in this and the following figures refer to the range of the database entries. 

This range does not necessarily covers all conditions discussed in the GL 2004-02 submittals. 
A-67

Figure A.2-6. Strainer Approach Velocity

0.001 0.01 0.1

Ginna - 1

Calvert Cliffs - 1

Calvert Cliffs - 2

Robinson - 2

Palisades - 1

St. Lucie - 1

Point Beach - 1

Point Beach - 2

St. Lucie - 2

Surry - 2

Millstone - 3

Oconee - 1

Oconee - 2

Oconee - 3

Surry - 1

Fort Calhoun - 1

Salem - 1

Salem - 2

Shearon Harris - 1

Diablo Canyon - 1

Diablo Canyon - 2

Waterford - 3

Indian Point - 2

Indian Point - 3

Wolf Creek - 1

North Anna - 1

North Anna - 2

Comanche Peak - 1

Comanche Peak - 2

Summer - 1

Seabrook - 1

ANO - 1

San Onofre - 2

San Onofre - 3

Three Mile Island - 1

South Texas - 1

South Texas - 2

Palo Verde - 1

Palo Verde - 2

Palo Verde - 3

Beaver Valley - 1

Callaway - 1

Byron - 1

Byron - 2

Braidwood - 1

Braidwood - 2

Beaver Valley - 2

Kewaunee - 1

Farley - 2

Farley - 1

Vogtle - 1

Vogtle - 2

Prairie Island - 1

Prairie Island - 2

Watts Bar - 1

Watts Bar - 2

Crystal River - 3

Davis Besse - 1

Turkey Point - 3

Turkey Point - 4

Catawba - 1

Catawba - 2

Millstone - 2

D.C. Cook - 1

D.C. Cook - 2

Sequoyah - 1

Sequoyah - 2

ANO - 2

McGuire - 1

McGuire - 2

Strainer Approach Velocity, ft/s

Min Max

0.0003 0.003 0.03 

Strainer Approach Velocity, m/s 
A-68

Figure A.2-7. Thin Bed Thickness 

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0.05625

0.05625

0.05625

0.05625

0.0625

0.0625

0.0625

0.10

0.125

0.125

0.125

0.125

0.125

0.125

0.125

0.125

0.125

0.125

0.125

0.125

0.125

0.125

0.15

0.15

0.25

0.25

0.25

0.25

0.48

0 2.54 5.08 7.62 10.16 12.7 15.24

0 0.1 0.2 0.3 0.4 0.5 0.6

Catawba - 1

Catawba - 2

Comanche Peak - 1

Comanche Peak - 2

Crystal River - 3

Davis Besse - 1

Diablo Canyon - 1

Diablo Canyon - 2

McGuire - 1

McGuire - 2

Oconee - 1

Oconee - 2

Oconee - 3

Palo Verde - 1

Palo Verde - 2

Palo Verde - 3

Prairie Island - 1

Prairie Island - 2

Salem - 1

Salem - 2

San Onofre - 2

San Onofre - 3

South Texas - 1

South Texas - 2

St. Lucie - 1

St. Lucie - 2

Summer - 1

Turkey Point - 3

Turkey Point - 4

Waterford - 3

Watts Bar - 1

Watts Bar - 2

Wolf Creek - 1

Braidwood - 1

Braidwood - 2

Byron - 1

Byron - 2

Calvert Cliffs - 1

Calvert Cliffs - 2

Ginna - 1

Three Mile Island - 1

ANO - 1

ANO - 2

Beaver Valley - 1

Beaver Valley - 2

D.C. Cook - 1

D.C. Cook - 2

Fort Calhoun - 1

Indian Point - 2

Indian Point - 3

Kewaunee - 1

Millstone - 2

Palisades - 1

Point Beach - 1

Point Beach - 2

Sequoyah - 1

Sequoyah - 2

Millstone - 3

North Anna - 1

North Anna - 2

Robinson - 2

Shearon Harris - 1

Callaway - 1

Farley - 1

Farley - 2

Seabrook - 1

Surry - 1

Surry - 2

Vogtle - 1

Vogtle - 2

Thin Bed Thickness, mm

Thin Bed Thickness, in

Not Reported
A-69

Table A.2-7. Head-Loss Test Location

Plant Name Unit Test Location Comments

ANO 1 Fauske and Associates; Westinghouse

ANO 2 Control Components, Inc.; Fauske and 

Associates; Westinghouse

Beaver 

Valley

1 Original testing by CCI superseded by tests at 

Alion Science & Technology

Beaver 

Valley

2 Alion Science & Technology

Braidwood 1 Control Components, Inc., Winterthur, 

Switzerland

Braidwood 2 Control Components, Inc., Winterthur, 

Switzerland

Byron 1 Control Components, Inc., Winterthur, 

Switzerland

Byron 2 Control Components, Inc., Winterthur, 

Switzerland

Callaway 1 Alden Research Laboratory, Inc., Holden, MA

Calvert Cliffs 1 CCI's facility in Winterthur, Switzerland

Calvert Cliffs 2 CCI's facility in Winterthur, Switzerland

Catawba 1 Wyle Laboratories in Huntsville, Alabama

Catawba 2 Wyle Laboratories in Huntsville, Alabama

Comanche 

Peak

1 Testing by Performance Contracting Inc. at 

Alden Research Laboratory, Inc., Holden, MA

Comanche 

Peak

2 Testing by Performance Contracting Inc. at 

Alden Research Laboratory, Inc., Holden, MA

Crystal River 3 Alion Science and Technology, Warrenville, IL

Davis Besse 1 Head loss testing not 

performed. Enercon 

and Alion Science and 

Technology performed 

head loss calculations.

D.C. Cook 1 Control Components, Inc.; Winterthur, 

Switzerland and ALION, Vuez

D.C. Cook 2 Control Components, Inc.; Winterthur, 

Switzerland and ALION, Vuez

Diablo 

Canyon

1 Continuum Dynamics, Inc. facilities in Ewing, 

New Jersey

Diablo 

Canyon

2 Continuum Dynamics, Inc. facilities in Ewing, 

New Jersey

Farley 1 General Electric Hitachi at Continuum 

Dynamics Incorporated/Alion at the Vuez 

facility

Farley 2 General Electric Hitachi at Continuum 

Dynamics Incorporated/Alion at the Vuez 

facility

Fort Calhoun 1 General Electric at Continuum Dynamics 

Incorporated

Ginna 1 CCI's facility in Winterthur, Switzerland Initial head loss testing
A-70

Plant Name Unit Test Location Comments

Indian Point 2 Alion Science and Technology, Warrenville, IL Location is mentioned 

only with regard to 

bypass and chemical 

testing

Indian Point 3 Alion Science and Technology, Warrenville, IL Location is mentioned 

only with regard to 

bypass and chemical 

testing

Kewaunee 1 Alden Research Laboratory, Inc., Holden, MA

McGuire 1 Wyle Laboratories in Huntsville, Alabama

McGuire 2 Wyle Laboratories in Huntsville, Alabama

Millstone 2 AECL’s Chalk River Laboratory in Canada

Millstone 3 AECL’s Chalk River Laboratory in Canada

North Anna 1 AECL’s Chalk River Laboratory in Canada

North Anna 2 AECL’s Chalk River Laboratory in Canada

Oconee 1 CCI's manufacturing facility in Switzerland

Oconee 2 CCI's manufacturing facility in Switzerland

Oconee 3 CCI's manufacturing facility in Switzerland

Palisades 1 Performance Contracting Inc. at Alden 

Research Laboratory, Inc., Holden, MA

Palo Verde 1 Control Components, Inc., Winterthur, 

Switzerland

Palo Verde 2 Control Components, Inc., Winterthur, 

Switzerland

Palo Verde 3 Control Components, Inc., Winterthur, 

Switzerland

Point Beach 1 Testing by AREVA at Alden Research 

Laboratory, Inc., Holden, MA

Point Beach 2 Testing by AREVA at Alden Research 

Laboratory, Inc., Holden, MA

Prairie Island 1 Testing by Performance Contracting Inc. at 

Alden Research Laboratory, Inc., Holden, MA

Prairie Island 2 Testing by Performance Contracting Inc. at 

Alden Research Laboratory, Inc., Holden, MA

Robinson 2

Salem 1 Control Components, Inc., Winterthur, 

Switzerland

Salem 2 Control Components, Inc., Winterthur, 

Switzerland

San Onofre 2 Alion Science and Technology, Warrenville, IL

San Onofre 3 Alion Science and Technology, Warrenville, IL

Seabrook 1 General Electric at Continuum Dynamics 

Incorporated

Sequoyah 1 Alden Research Laboratory, Holden, MA

Sequoyah 2 Alden Research Laboratory, Holden, MA

Shearon 

Harris

1 Alion Science and Technology, Warrenville, IL

South Texas 1 Performance Contracting, Inc., Alden 
A-71

Plant Name Unit Test Location Comments

Research Laboratory at the Alden facility, 

Holden, MA

South Texas 2 Performance Contracting, Inc., Alden 

Research Laboratory at the Alden facility, 

Holden, MA

St. Lucie 1 Continuum Dynamics, Inc.

St. Lucie 2 Performance Contracting, Inc., along with 

AREVA NP, Inc. and Alden Research

Summer 1 AECL’s Chalk River Laboratory in Canada

Surry 1 AECL’s Chalk River Laboratory in Canada

Surry 2 AECL’s Chalk River Laboratory in Canada

Three Mile 

Island

1 Alion Science and Technology, Warrenville, IL

Turkey Point 3 Continuum Dynamics Inc. (non-chemical head 

loss tests); Alion Science and Technology 

(chemical effects testing) at VUEZ

Turkey Point 4 Alden Research Laboratory, Inc., Holden, MA

Vogtle 1 Alion Science and Technology at VUEZ facility Chemical effects 

testing 

Vogtle 2 Alion Science and Technology at VUEZ facility Chemical effects 

testing 

Waterford 3 Alion Science and Technology at Vuez facility 30-day integrated test 

was done at Vuez 

facility, but it is not 

specified for another 

prototype testing with 

Westinghouse 

surrogates (probably 

by GE). 

Watts Bar 1 Framatome ANP at Alden Research 

Laboratory, Inc., Holden, MA

Watts Bar 2 Alden Research Laboratory, Inc., Holden, MA

Wolf Creek 1 Alden Research Laboratory, Inc., Holden, MA

Table A.2-8. Clean Strainer Head Loss

Plant Name Unit Clean 

HL, ft Comments

ANO 1 0.2 The clean head loss without debris is less than 0.2 ft at 

maximum flow based on current draft calculation analysis.

ANO 2 0.33 For design flow of 7065 gpm.

Beaver Valley 1 1.800 Calculated at a flow rate and temperature of 14,500 gpm 

and 100°F.

Beaver Valley 2 0.756 Calculated at a flow rate of 13,636 gpm. (0.923 ft @ 12,600 

gpm)

Braidwood 1 0.090 Value reported as 2.7 mbar.

Braidwood 2 0.090 Value reported as 2.7 mbar.

Byron 1 0.090

Byron 2 0.090
A-72

Plant Name Unit Clean 

HL, ft Comments

Callaway 1 0.651

Calvert Cliffs 1 0.335 10 millibar for the head losses internal to the strainer.

Calvert Cliffs 2 0.335 10 millibar for the head losses internal to the strainer.

Catawba 1 3.700 Clean strainer head loss reported for limiting Unit (Catawba 

1) at 60 ̊F.

Catawba 2 3.700 Clean strainer head loss reported for limiting Unit (Catawba 

1) at 60 ̊F.

Comanche 

Peak 1 1.270 Calculated design value at 120 ̊F.

Comanche 

Peak 2 1.270 Calculated design value at 120 ̊F.

Crystal River 3 0.083

Total strainer head loss, including the friction loss due to the 

inner walls of the top hats, the inner support members, and 

the exit at the bottom of the top hats. The flow rate was 

assumed to be 8696 gpm. The minimum fluid temperature 

was assumed to be 120 ̊F.

Davis Besse 1 0.140

Value for upper strainer reported as 0.06 psi at 11,000 gpm, 

as calculated by Enercon and Alion Science and 

Technology.

Davis Besse 1 2.330 Value reported as 1.01 psi at 11,000 gpm, as calculated by 

Enercon and Alion Science and Technology.

D.C. Cook 1 0.050

D.C. Cook 2 0.050

Diablo 

Canyon 1 1.700 Plenum plus entrance head losses.

Diablo 

Canyon 2 1.700 Plenum plus entrance head losses.

Farley 1 2.217 RHR A-Train, calculated at 120°F.

Farley 1 2.217 RHR B-Train, calculated at 120°F.

Farley 1 1.142 CSS A-Train, calculated at 120°F.

Farley 1 0.250 CSS B-Train, calculated at 120°F.

Farley 2 2.217 RHR A-Train, calculated at 120°F.

Farley 2 2.217 RHR B-Train, calculated at 120°F.

Farley 2 1.142 CSS A-Train, calculated at 120°F.

Farley 2 2.292 CSS B-Train, calculated at 120°F.

Fort Calhoun 1 0.071 SI-12A, the clean head-loss evaluation is based on a 

combination of strainer head loss and piping head loss.

Fort Calhoun 1 0.123 SI-12B, the clean head-loss evaluation is based on a 

combination of strainer head loss and piping head loss.

Ginna 1 0.131

No measurable head loss of the clean strainer surface area 

was recorded. The total clean strainer head loss is 3.91 

mbar or 0.131 ft WC at the containment sump minimum 

temperature of 195°F and 2300 gpm.

Indian Point 2 0.111 IR, LBLOCA or RC-LBLOCA at 3568 gpm.

Indian Point 2 1.026 VC, 6 Inch or RC-6 Inch Break LOCA at 3221 gpm.

Indian Point 3 0.214 IR, LBLOCA or RC-LBLOCA at 4149 gpm.

Indian Point 3 0.101 VC, 6 Inch or RC-6 Inch Break LOCA at 1226 gpm.
A-73

Plant Name Unit Clean 

HL, ft Comments

Kewaunee 1 0.365

McGuire 1 5.71 For the maximum recirculation flow condition (four trains) at 

60°F.

McGuire 1 3.79 For single train RHR/two-train CS operation at 60°F.

McGuire 2 5.99 For the maximum recirculation flow condition (four trains) at 

60°F.

McGuire 2 3.91 For single train RHR/two-train CS operation at 60°F.

Millstone 2 0.094 Calculated value for a total scaled testing flow rate of 6800 

gpm

Millstone 3 0.382 The maximum clean strainer head loss at 100°F.

North Anna 1 0.970 LHSI, clean strainer head loss.

North Anna 1 1.500 RS, short term.

North Anna 1 1.000 RS, long term.

North Anna 2 0.740 LHSI, clean strainer head loss.

North Anna 2 1.500 RS, short term.

North Anna 2 1.000 RS, long term.

Oconee 1 0.006 Clean strainer head loss at 349 gpm and 54°F.

Oconee 2 0.006 Clean strainer head loss at 349 gpm and 54°F.

Oconee 3 0.006 Clean strainer head loss at 349 gpm and 54°F.

Palisades 1 1.026 Calculated values at 212°F and 3591 gpm. 

Palo Verde 1 0.081

Value at a at a flow rate of 11,600 gpm; as the flow rate 

decreases to 6600 gpm, the head loss also decreases to 

0.026 ft. 

Palo Verde 2 0.081

Value at a at a flow rate of 11,600 gpm; as the flow rate 

decreases to 6600 gpm, the head loss also decreases to 

0.026 ft. 

Palo Verde 3 0.081

Value at a at a flow rate of 11,600 gpm; as the flow rate 

decreases to 6600 gpm, the head loss also decreases to 

0.026 ft. 

Point Beach 1 0.590 Calculated value at minimum sump temperature of 72°F. 

Calculated value is 212°F and design flow rate is 0.41 ft.

Point Beach 2 0.590 Calculated value at minimum sump temperature of 72°F. 

Calculated value is 212°F and design flow rate is 0.41 ft.

Prairie Island 1 0.020

Prairie Island 2 0.020

Robinson 2 1.585

The head loss through the strainer was calculated as 1.585 

ft of water, which includes 0.021 ft of water for the head loss 

through a top hat.

Salem 1 2.880 At the two pump operation flow rate was 8850 gpm; the 

head loss through the strainer train and into the suction box.

Salem 2 2.880 At the two pump operation flow rate was 8850 gpm; the 

head loss through the strainer train and into the suction box.

San Onofre 2 0.230

At 60°F; calculated results; the individual top hat strainer 

head loss is not considered part of the "clean strainer head 

loss," since it is included in the prototypical strainer head 

loss testing results.

San Onofre 3 0.230 At 60°F; calculated results; the individual top hat strainer 

head loss is not considered part of the "clean strainer head 
A-74

Plant Name Unit Clean 

HL, ft Comments

loss," since it is included in the prototypical strainer head 

loss testing results.

Seabrook 1 0.353 At 8050 gpm; this value is total head loss including plenum, 

etc.

Sequoyah 1 1.936 Tall stacks C and E, total strainer head loss including 

strainer assembly and discharge flow plenum.

Sequoyah 2 1.936 Tall stacks C and E, total strainer head loss including 

strainer assembly and discharge flow plenum.

Shearon 

Harris 1 0.120

The value of 0.12 ft for the clean strainer head loss was 

determined by prototype testing performed by Enercon with 

the debris bypass eliminator included. The clean strainer 

head losses, as determined by chemical-effects testing 

performed by Alion at the design flow rate, were 0.0404, 

0.0443, and 0.0459 ft (for three tests with the debris bypass 

eliminator), and 0.0163 ft (for one test without the debris 

bypass eliminator).

South Texas 1 1.950 At 128°F.

South Texas 2 1.950 At 128°F.

St. Lucie 1 5.870

A calculated value for clean system head loss at 65°F. A 

clean strainer disc head loss of 0.107 ft was determined by 

testing. The total clean system head loss is 0.107 ft plus 

1.854 or 1.961 ft.

St. Lucie 2 3.603 Worst-case single failure scenario. Including 10% 

uncertainty margin.

Summer 1 0.021 Calculated value (reported as 0.009 psi).

Surry 1 1.690 RS, analytical value at 170°F.

Surry 1 0.900 LHSI, analytical value at 170°F.

Surry 2 1.690 RS, analytical value at 170°F.

Surry 2 0.900 LHSI, analytical value at 170°F.

Three Mile 

Island 1 0.151

At 8800 gpm; this is the total head loss due to the strainer 

assembly support structure and the “top hat” modules 

including the DBE up to but not including the entrance loss 

to the suction pipes.

Turkey Point 3 0.090 At 3750 gpm.

Turkey Point 4 0.480 At 3750 gpm and 170°F.

Vogtle 1 0.175 RHR

Vogtle 2 0.175 RHR

Waterford 3 0.230 At 210°F.

Waterford 3 0.290 At 90°F.

Watts Bar 1 3.620 Calculated value.

Watts Bar 2 0.338

Wolf Creek 1 0.642 Calculated value at 212°F; tested value is 0.3178 ft at 

114.5°F.
A-75

Table A.2-9. Non-chemical Head Loss

Plant Name Unit Non-chemical 

HL, ft

Comments

ANO 1 0.917 Maximum head loss of 11".

ANO 2 0.870 Two-train HPSI and CSS pump flows with partial 

debris loading (conservatively

applied as three days recirculation) and no chemical 

effects.

Beaver Valley 1 4.25 Total Debris and Strainer Head Loss at 212°F.

Beaver Valley 2 5.45 Total Debris and Strainer Head Loss at 212°F.

Braidwood 1 2.280 Reported as 68.1 mbar.

Braidwood 2 2.280 Reported as 68.1 mbar.

Byron 1 2.280 Reported as 68.1 mbar.

Byron 2 2.280 Reported as 68.1 mbar.

Callaway 1 Value not stated.

Calvert Cliffs 1 0.2743 Fiber/participate head loss for 5,000 gpm (strainer 

nominal flow rate - p. 21) = 8.2 mbar.

Calvert Cliffs 2 0.2743 Fiber/participate head loss for 5,000 gpm (strainer 

nominal flow rate - p. 21) = 8.2 mbar.

Catawba 1 Not specified.

Catawba 2 Not specified.

Comanche 

Peak

1 0.472 Calculated design value at 120°F.

Comanche 

Peak

1 0.607 Experimentally measured value at an average 

temperature of 95.1°F.

Comanche 

Peak

2 0.472 Calculated design value at 120°F.

Comanche 

Peak

2 0.607 Experimentally measured value at an average 

temperature of 95.1°F.

Crystal River 3 Not specified.

Davis Besse 1 Head loss testing not performed. No calculated value

reported.

D.C. Cook 1 2.670 Unit I Loop 4 DEGB.

D.C. Cook 2 4.430 Unit 2 Loop 4 DEGB.

Diablo 

Canyon

1 Not specified.

Diablo 

Canyon

2 Not specified.

Farley 1 0.103 RHR A-Train, Debris Head Loss.

Farley 1 0.103 RHR B-Train, Debris Head Loss.

Farley 1 0.112 CSS A-Train, Debris Head Loss.

Farley 1 0.199 CSS B-Train, Debris Head Loss.

Farley 2 0.103 RHR A-Train, Head loss by fiber debris strainer only.

Farley 2 0.103 RHR B-Train, Head loss by fiber debris strainer only.

Farley 2 0.112 CSS A-Train, Head loss by fiber debris strainer only.

Farley 2 0.172 CSS B-Train, Head loss by fiber debris strainer only.

Fort Calhoun 1 2.440 LBLOCA 0.125 in thin bed testing; includes debris and 

clean head losses.
A-76

Plant Name Unit Non-chemical 

HL, ft

Comments

Ginna 1 0.990 95.2 mbar at 20°C was taken as the maximum sump 

strainer head loss due to debris on the strainer. This 

value is equivalent to 29.7 mbar (0.99 ft WC) corrected 

to the minimum containment recirculation pool design 

temperature of 195°F.

Indian Point 2 3.070 Maximum measured value.

Indian Point 3 3.070 Maximum measured value.

Kewaunee 1 Value not stated.

McGuire 1 Not specified.

McGuire 2 Not specified.

Millstone 2 0.059 Unit conversion: the maximum head loss for the worstcase debris load is 0.35 psi.

Millstone 3 5.382 The maximum debris bed head loss (5.1 ft) plus the 

maximum clean strainer head loss of 0.382 ft.

North Anna 1 1.707 LHSI test results prior to Al addition (0.74 psi). Debris 

bed only.

North Anna 1 0.692 RS test results prior to Al addition (0.3 psi). Debris bed 

only.

North Anna 2 1.707 LHSI test results prior to Al addition (0.74 psi). Debris 

bed only.

North Anna 2 0.692 RS test results prior to Al addition (0.3 psi). Debris bed 

only.

Oconee 1 0.026 Nominal debris loaded loss corrected to 212°F, based 

on Unit 1 scaling (largest HL).

Oconee 2 0.026 Nominal debris loaded loss corrected to 212°F, based 

on Unit 1 scaling (largest HL).

Oconee 3 0.026 Nominal debris loaded loss corrected to 212°F, based 

on Unit 1 scaling (largest HL).

Palisades 1 Value not stated.

Palo Verde 1 Not specified.

Palo Verde 2 Not specified.

Palo Verde 3 Not specified.

Point Beach 1 3.066 Corrected to 212°F (design basis). Numerous other 

head loss values are given on pp. 21, 22, 26, 48, 55, 

60, 66, and 135 of ML092150636.

Point Beach 2 3.066 Corrected to 212°F (design basis). Numerous other 

head loss values are given on pp. 21, 22, 26, 48, 55, 

60, 66, and 135 of ML092150636.

Prairie Island 1 Value not stated.

Prairie Island 2 Value not stated.

Robinson 2 3.385 Clean (1.585) + 1.8 ft debris only, adjusted for viscosity 

at 212°F (saturation temperature at 0 psig).

Salem 1 1.090 In Test 5 for Unit 1, the maximum head loss observed 

prior to the addition of chemical precipitates was 32.5 

mbar (1.09 ft) at a temperature of 41.3°C (106°F). 

This is not total strainer head loss. Total is sum of this 

value and component head loss.
A-77

Plant Name Unit Non-chemical 

HL, ft

Comments

Salem 2 8.100 In Test 6 for Unit 2, the maximum head loss observed 

prior to the addition of chemical precipitates was 242.2 

mbar (8.1 ft) at a temperature of 47.6°C (118°F). This 

is not total strainer head loss. Total is sum of this 

value and component head loss.

San Onofre 2 0.330 Mineral wool head loss testing.

San Onofre 3 0.330 Mineral wool head loss testing.

Seabrook 1 Not specified.

Sequoyah 1 0.245 Short, Total Strainer Head Loss. 

Sequoyah 1 1.970 Tall, Total Strainer Head Loss. 

Sequoyah 2 0.245 Short, Total Strainer Head.

Sequoyah 2 1.970 Tall, Total Strainer Head.

Shearon 

Harris

1 0.140 At 83°F.

South Texas 1 Not specified.

South Texas 2 Not specified.

St. Lucie 1 1.920 Strainer head loss, at 210°F.

St. Lucie 2 4.019 Clean+debris bed. Worst-case single failure scenario. 

Including 10% uncertainty margin.

Summer 1 6.280 Experimentally determined value at 104°F. Reported 

as 2.72 psid.

Surry 1 0.600 RS, Experimental value (no temperature stated). 

Reported as 0.26 psid.

Surry 1 0.250 LHSI, Experimental value (no temperature stated). 

Reported as 0.11 psid.

Surry 2 0.600 RS, Experimental value (no temperature stated). 

Reported as 0.26 psid.

Surry 2 0.250 LHSI, Experimental value (no temperature stated). 

Reported as 0.11 psid.

Three Mile 

Island

1 Not specified.

Turkey Point 3 Value not stated.

Turkey Point 4 Value not stated.

Vogtle 1 Value not stated.

Vogtle 2 Value not stated.

Waterford 3 Not specified.

Watts Bar 1 3.65 "Long" Strainer Type "A", Total Strainer Head Loss 

with temperature correction for post-LOCA 

temperatures applied.

Watts Bar 1 3.62 "Short" Strainer Type "B", Total Strainer Head Loss 

with temperature correction for post-LOCA 

temperatures applied.

Watts Bar 2 1.24 Total strainer head loss (clean + debris) with 

temperature correction.

Wolf Creek 1 Not specified.
A-78

Table A.2-10. Full Debris Head Loss

Plant 

Name

Unit Full HL, 

ft Comments

ANO 1 8.000 Maximum value.

ANO 2 3.400 For two-train HPSI and CSS pump flows with full 30-day debris 

loading and chemical effects (3.23 measured with 3.4 ft 

credited).

Beaver 

Valley

1 4.250 Calculated value at 212°F, based on the maximum head loss 

from the several debris mixes tested in the prototype strainer at 

the maximum expected sump flow rate.

Beaver 

Valley

2 5.450 Calculated value at 212°F, based on prototype testing with the 

plant specific debris loading including chemical effects, at the 

maximum expected sump flow rate.

Beaver 

Valley

2 2.680 Experimental head loss based upon Test 5 (approach velocity 

of 0.0104 ft/sec, corrected to 212°F).

Braidwood 1 2.760 Reported as 82.4 mbar.

Braidwood 2 2.760 Reported as 82.4 mbar.

Byron 1 2.760 Reported as 82.4 mbar.

Byron 2 2.760 Reported as 82.4 mbar.

Callaway 1 Value not stated.

Calvert 

Cliffs

1 23.750 The maximum head loss across the strainer perforated 

material and the accumulated debris including chemical 

precipitates is 710 millibar (10.2 psi) 700 millibar for the debris 

bed and strainer perforated face, and 10 millibar for the head 

loss.

Calvert 

Cliffs

2 23.750 The maximum head loss across the strainer perforated 

material and the accumulated debris including chemical 

precipitates is 710 millibar (10.2 psi) 700 millibar for the debris 

bed and strainer perforated face, and 10 millibar for the head 

loss.

Catawba 1 8.200 The maximum projected head loss at 30 days and 90°F with 

maximum flow rate of 16,000 gpm.

Catawba 2 8.200 The maximum projected head loss at 30 days and 90°F with 

maximum flow rate of 16,000 gpm.

Comanche 

Peak

1 1.742 Calculated design value at 120°F.

Comanche 

Peak

2 1.742 Calculated design value at 120°F.

Crystal 

River

3 “<0.1” is provided as the head loss based on head loss testing 

results at about 90°F.

Davis 

Besse

1 Head loss testing not performed. No calculated value reported.

D.C. Cook 1 3.830

D.C. Cook 2 6.800

Diablo 

Canyon

1 3.417 33 in. for the strainer screen and 8 in. for the strainer plenum; 

the maximum measured head loss was 31.5 in. during Test 11-

S-PSG.

Diablo 2 3.417 33 in. for the strainer screen and 8 in. for the strainer plenum; 
A-79

Plant 

Name

Unit Full HL, 

ft Comments

Canyon the maximum measured head loss was 31.5 in. during Test 11-

S-PSG.

Farley 1 3.530 Temperature-adjusted chemical effects head loss value is 

42.4/12=3.53 ft at 120°F. Tested value is 4.61 ft at 96.3°F.

Farley 2 3.530 Temperature-adjusted chemical effects head loss value is 

42.4/12=3.53 ft at 120°F. Tested value is 4.61 ft at 96.3°F.

Fort 

Calhoun

1 3.380 SBLOCA with chemical precipitates; The SBLOCA "not scaled 

for temperature" test head loss is 5.88 ft (70.6 in.) at 100°F; 

3.38 ft was partially scaled to the plant head loss at 196.6°F.

Ginna 1 1.12 Total head loss (clean strainer + debris) under worst case 

conditions, at a flow rate of 2300 gpm.

Indian 

Point

2 21.880 Maximum measured extrapolated value.

Indian 

Point

3 21.880 Maximum measured extrapolated value.

Kewaunee 1 3.280

McGuire 1 15.700 The maximum projected head loss at 30 days and 90°F with 

maximum flow rate of 16,000 gpm.

McGuire 2 15.700 The maximum projected head loss at 30 days and 90°F with 

maximum flow rate of 16,000 gpm.

Millstone 2 2.400 1.04 psi; maximum value in test.

North Anna 1 2.650 LHSI, Short term (after two sump turnovers), 0.93 clean + 1.72 

debris bed.

North Anna 1 8.370 LHSI, Long term, 0.93 clean + 7.44 debris bed.

North Anna 1 2.210 RS, Short term, 1.5 clean + 0.71 debris bed.

North Anna 1 7.280 RS, Long term, 1.0 clean + 6.28 debris bed.

North Anna 2 2.650 LHSI, Short term (after two sump turnovers), 0.93 clean + 1.72 

debris bed.

North Anna 2 8.370 LHSI, Long term, 0.93 clean + 7.44 debris bed.

North Anna 2 2.210 RS, Short term, 1.5 clean + 0.71 debris bed.

North Anna 2 7.280 RS, Long term, 1.0 clean + 6.28 debris bed.

Oconee 1 0.014 Clean + fiber, particulates, and chemicals; as adjusted to 

235.4°F.

Oconee 2 0.014 Clean + fiber, particulates, and chemicals; as adjusted to 

235.4°F.

Oconee 3 0.014 Clean + fiber, particulates, and chemicals; as adjusted to 

235.4°F.

Palisades 1 1.310 Calculated value at 212°F and 3591 gpm.

Palisades 1 4.820 Calculated value at 212°F and 6894 gpm.

Palisades 1 0.740 Experimental value at 111.6°F.

Palo Verde 1 4.330 The total calculated head loss is 4.33 ft WC for the design 

temperature of 193.8°F (the margin is lowest at 193.8°F).

Palo Verde 2 4.330 The total calculated head loss is 4.33 ft WC for the design 

temperature of 193.8°F (the margin is lowest at 193.8°F).

Palo Verde 3 4.330 The total calculated head loss is 4.33 ft WC for the design 

temperature of 193.8°F (the margin is lowest at 193.8°F).

Point 

Beach

1 3.474 Experimental value corrected to 212°F (design basis). 

Numerous other head loss values are given on pp. 21, 22, 26, 
A-80

Plant 

Name

Unit Full HL, 

ft Comments

48, 55, 60, 66, and 135 of ML092150636.

Point 

Beach

2 3.474 Experimental value corrected to 212°F (design basis). 

Numerous other head loss values are given on pp. 21, 22, 26, 

48, 55, 60, 66, and 135 of ML092150636.

Prairie 

Island

1 12.115 Test #2 (twice the design basis debris loading). Measured 

value at 50.1°F.

Prairie 

Island

1 7.766 Test #1. Measured value at 48.0°F.

Prairie 

Island

2 12.115 Test #2 (twice the design basis debris loading). Measured 

value at 50.1°F.

Prairie 

Island

2 7.766 Test #1. Measured value at 48.0°F.

Robinson 2 5.100 Clean + debris + chemical; adjusted for viscosity at 212°F 

(saturation temperature at 0 psig).

Salem 1 4.750 In Test 5 for Unit 1, the maximum head loss prior to observing 

the bore hole which led to the largest pressure drop was 142.0 

mbar (4.75 ft) at a temperature of 46.2°C (115°F). This is not 

total strainer head loss. Total is sum of this value and 

component head loss.

Salem 2 9.780 In Test 6 for Unit 2, the maximum head loss prior to observing 

bore holes was 292.5 mbar (9.78 ft) at a temperature of 45.0°C 

(113°F). This is not total strainer head loss. Total is sum of 

this value and component head loss.

San 

Onofre

2 9.960 Mineral wool debris head loss testing; the maximum measured 

head loss was 9.31 ft, and extrapolated value was 9.99 ft. 

Corrected value for flow and temperature is 9.96 ft at 122°F. 

Full head loss is then 9.96 + 0.23 = 10.19 ft at 122°F.

San 

Onofre

2 4.140 Mineral wool debris head loss testing; corrected value for flow 

and temperature is 4.14ft at 202 ̊F. Full head loss is then 4.14 

+ 0.23 = 4.37ft at 202°F.

San 

Onofre

3 9.960 Mineral wool debris head loss testing; the maximum measured 

head loss was 9.31 ft, and extrapolated value was 9.99 ft. 

Corrected value for flow and temperature is 9.96 ft at 122°F. 

Full head loss including everything is then 9.96 + 0.23 =10.19 ft 

at 122°F.

San 

Onofre

3 4.140 Mineral wool debris head loss testing; corrected value for flow 

and temperature is 4.14ft at 202 ̊F. Full head loss is then 4.14 

+ 0.23 = 4.37 ft at 202°F.

Seabrook 1 0.643 At 8050 gpm; this value is a total head loss including plenum, 

etc.

Sequoyah 1 Detailed evaluations of chemical sump blockage effects are not 

warranted for Sequoyah, as would be the case if a fiber bed 

could form on the sump strainer surface. A 10% percent 

increase in the strainer debris head loss was applied.

Sequoyah 2 Detailed evaluations of chemical sump blockage effects are not 

warranted for Sequoyah, as would be the case if a fiber bed 

could form on the sump strainer surface. A 10% percent 

increase in the strainer debris head loss was applied.
A-81

Plant 

Name

Unit Full HL, 

ft Comments

Shearon 

Harris

1 2.340 Total; adjusted to 212°F to be consistent with the NPSH 

calculations; determined for the limiting break.

South 

Texas

1 6.504 At 171°F, 24 hr post-LOCA.

South 

Texas

1 8.745 For the design-basis debris test, the maximum corrected head 

loss (excluding clean strainer head loss and piping losses) was 

8.745 ft at a flow rate of 355.857 gpm at a corrected 

temperature of 116.3°F.

South 

Texas

2 6.504 At 171°F, 24 hr post-LOCA.

South 

Texas

2 8.745 For the design-basis debris test, the maximum corrected head 

loss (excluding clean strainer head loss and piping losses) was 

8.745 ft at a flow rate of 355.857 gpm at a corrected 

temperature of 116.3°F.

St. Lucie 1 9.780 The total head loss, including piping/plenum, at 210°F.

St. Lucie 2 4.019 Clean + debris bed. Worst-case single failure scenario. 

Including 10% uncertainty margin.

Summer 1 3.150 Experimentally determined value at 104°F.

Surry 1 3.100 RS, experimental value at 196°F.

Surry 1 1.770 LHSI, experimental value at 175°F.

Surry 2 3.100 RS, experimental value at 196°F.

Surry 2 1.770 LHSI, experimental value at 175°F.

Three Mile 

Island

1 1.700 The total strainer head loss including the impact of calcium 

phosphate precipitants is 1.7 ft at 83°F and a flow rate of 8800 

gpm. This head loss value applies for sump temperatures 

above 140°F.

Three Mile 

Island

1 21.300 The total strainer head loss including the impact of calcium 

phosphate and aluminum precipitants is 21.3 ft at 85°F and a 

flow rate of 8800 gpm. This head loss value applies for sump 

temperatures below 140°F.

Three Mile 

Island

1 15.600 Maximum Strainer Head (Case I: Maximum Reactor Building 

Cooling).

Three Mile 

Island

1 12.100 Maximum Strainer Head (Case I: EQ Reactor Building 

Cooling).

Turkey 

Point

3 3.829 Value at 3750 gpm.

Turkey 

Point

4 0.628 Value at 3750 gpm and 170°F.

Vogtle 1 8.460

Vogtle 2 8.460

Waterford 3 3.95 At 90°F with additional margin.

Waterford 3 2.09 At 210°F with additional margin.

Watts Bar 1 No information found. "...will be addressed by implementing 

the test tank protocol similar to the protocol shown in Enclosure 

3."

Watts Bar 2 1.428 Total strainer head loss with temperature correction for PostLOCA temperatures applied (includes CSHL).

Wolf Creek 1 1.724 Testing of the design basis scenario (Test 3B) determined the 
A-82

Plant 

Name

Unit Full HL, 

ft Comments

temperature corrected head loss with the scaled RHR and CSS 

flow at 212°F was 1.724 ft of water.

Net Positive Suction Head (NPSH): NPSH Margin

The GL-04-02 database collected the information on the NPSH for each pump and for each 

reported scenario (such as SBLOCA). If provided, the information was recorded into the 

database for the required NPSH, available NPSH, and NPSH margin. If the NPSH margin is not 

provided, it is calculated in the database as available NPSH minus required NPSH. 

Figure A.2-8 presents the range of the NPSH margin (either reported or calculated) for each 

plant. For three plants, the reported data were insufficient to calculate the NPSH margin. In 

some cases, for example, for Oconee plant, a negative NPSH margin value was provided in the 

GL-04-02 responses and was included in the database as such as it is showing in Figure A.2-8.

(Note that Oconee has credit in their licenseing basis to use containment pressure to offset the 

short term deficit calculated using conservative methods. That type of information, however, is 

not included in the NPSH margin database)

Figure A.2-8 and several following figures show the data in the minimum/maximum range 

fashion. This form was selected for the presentation purposeds for this report only. In the actual 

database, several entires for each plant are allowed (such as NPSH margin for each pump). 

Since it would be impractical to plot each database entry for each plant, the figures below only 

show the range of the actual data recorded in the database as minimum and maximum values 

for each plant. In case of the NPSH margin, the minimum value is considered to be the most 

important parameter, such that the plants are sorted in Figure A.2-8 by the numimum value of 

NPSH margin in the database. 

NPSH: Minimum Strainer Submergence

For this field, the minimum strainer submergence (usually, recorded in inches) was recorded for 

each plant and each case. Figure A.2-9 shows the range of the recorded strainer 

submergences for each plant. 

NPSH: Submergence at Recirculation Switchover

The value of the strainer submergence (in %) at the time of the sump recirculation switchover 

was recorded in this field. For most plants, the GL-04-02 responses stated that the strainer is 

fully submerged at this point. In those cases, 100% was recorded in this field. Plants with 

partial strainer submergence, at least at some conditions (breaks), include Callaway-1, 

Comanche Peak 1 and 2, Diablo Canyon 1 and 2, Farley 1 and 2, Palisades-1, Sequyoah 1 and 

2, and Watts Bar-1. 

NPSH: Final Submergence

This field is similar to the previous one except the submergence is recorded for the final state. 

So far, full submergence was either reported by all plants or was assumed for the database 

entry. 
A

-83

Figure A.2-8. NPSH Margin

-150 15 30 45 60 75 90

-505 10 15 20 25 30

Millstone - 3

Kewaunee - 1

D.C. Cook - 1

Braidwood - 1

Braidwood - 2

Byron - 1

Byron - 2

D.C. Cook - 2

Vogtle - 1

Vogtle - 2

Sequoyah - 1

Sequoyah - 2

Comanche Peak - 1

Comanche Peak - 2

Turkey Point - 4

Palo Verde - 1

Palo Verde - 2

Palo Verde - 3

Watts Bar - 1

Fort Calhoun - 1

Watts Bar - 2

Catawba - 1

Catawba - 2

San Onofre - 2

San Onofre - 3

ANO - 1

Wolf Creek - 1

Summer - 1

Turkey Point - 3

St. Lucie - 1

Beaver Valley - 2

Shearon Harris - 1

Davis Besse - 1

Crystal River - 3

Beaver Valley - 1

Surry - 1

Surry - 2

Palisades - 1

Salem - 1

North Anna - 1

North Anna - 2

Ginna - 1

Calvert Cliffs - 1

Calvert Cliffs - 2

Salem - 2

South Texas - 1

South Texas - 2

Millstone - 2

McGuire - 1

McGuire - 2

Diablo Canyon - 1

Diablo Canyon - 2

Farley - 1

ANO - 2

St. Lucie - 2

Robinson - 2

Waterford - 3

Indian Point - 2

Farley - 2

Seabrook - 1

Three Mile Island - 1

Point Beach - 1

Point Beach - 2

Indian Point - 3

Oconee - 1

Oconee - 2

Oconee - 3

Callaway - 1

Prairie Island - 1

Prairie Island - 2

NPSH Margin, kPa

NPSH Margin, ft

Min NPSH Margin

Max NPSH Margin

Not Reported
A-84

Figure A.2-9. Minimum Submergence

-76 -51 -25 0 25 51 76 102 127 152 178 203 229 254 279 305 330 356 381 406

-30 -20 -10 0 10 20 30 40 50 60 70 80 90 100110120130140150160

Summer - 1

Braidwood - 1

Braidwood - 2

Byron - 1

Byron - 2

Crystal River - 3

Three Mile Island - 1

ANO - 2

San Onofre - 2

San Onofre - 3

Indian Point - 3

Millstone - 2

Oconee - 1

Oconee - 2

Oconee - 3

Beaver Valley - 2

St. Lucie - 1

Wolf Creek - 1

Prairie Island - 1

Prairie Island - 2

ANO - 1

Ginna - 1

Farley - 1

Farley - 2

Fort Calhoun - 1

Shearon Harris - 1

Seabrook - 1

Catawba - 1

Catawba - 2

Robinson - 2

Indian Point - 2

Turkey Point - 3

Turkey Point - 4

Watts Bar - 2

Salem - 1

Salem - 2

Surry - 1

Surry - 2

Vogtle - 1

Vogtle - 2

Beaver Valley - 1

Palo Verde - 1

Palo Verde - 2

Palo Verde - 3

McGuire - 1

McGuire - 2

Point Beach - 1

Point Beach - 2

Waterford - 3

D.C. Cook - 1

D.C. Cook - 2

Davis Besse - 1

Calvert Cliffs - 1

Calvert Cliffs - 2

Kewaunee - 1

South Texas - 1

South Texas - 2

St. Lucie - 2

Millstone - 3

Watts Bar - 1

Callaway - 1

Diablo Canyon - 1

Diablo Canyon - 2

Palisades - 1

Comanche Peak - 1

Comanche Peak - 2

Sequoyah - 1

Sequoyah - 2

North Anna - 1

North Anna - 2

Minimum Strainer Submergence, cm

Minimum Strainer Submergence, in

Min Value

Max Value

Not Reported
A-85

Debris: Latent Debris

In this field, the total amount of latent debris, as well as percentage of fiber, is recorded for each 

plant. Figure A.2-10 shows the total amount of the latent debris and its split between fiber and 

particulate as calculated by the database. Unlike previous plots, the bar lengths in Figure A.2-

10 show the total amount of the debris, and the lengths for each color show the corresponding 

percentage of its components. For example, for ANO-1 plant, the total amount is 100 lbm, with 

15 lbm of fiber and 85 lbm of particulate. To highlight this difference from other plots, the colors 

have been changed in this plot. For Calvert Cliffs plant the latent debris is stated to be all 

particulates. 

Debris: Sacrificial Area

This field records the amount of the strainer area which is assumed to be not available for 

strainer operation due to foreign material (such as tags). The results are presented in Figure 

A.2-11. For Prairie Island plant, no data were reported for this field. Three other plants, St. 

Lucie-2, Wolf Creek-1, and Callaway-1, did not allow for any sacrificial area. Except for the D.C. 

Cook plant, all other plants reported the same sacrificial area for all their strainers, where 

applicable. The D.C. Cook plant reported separate values for its two strainers. Those values 

are shown as maximum/minimum in Figure A.2-11.

Debris: Scaling Factor

This field reports the ratio between the screen area used in tests and the original strainer screen 

area. If this value was reported in a GL-04-02 response, it was entered into the database 

directly. Otherwise, it was calculated as:

provided that all values in the above equation are available. Figure A.2-12 shows the scaling 

factors recorded in the GL-04-02 database. If one test was carried out to represent several 

strainers with different screen area, more than one entry was provided in the database, one for 

each scaling factor. Alternatively, several tests could be carried out with various screen areas 

of testing unit. In such cases, Figure A.2-12 shows the range (minimum and maximum values) 

of the scaling factors for a plant. 

Debris: Amount

Several fields in the GL-04-02 database record the amount of the debris as used in the strainer 

analysis. The amount of the debris generated at a break is recorded in the Debris Amount –

Analysis field for each type of the debris reported by a plant. If several break locations were 

analyzed, the worst case scenario (one that generates most debris) is selected for the database 

entry. Of that generated amount of debris, in general, only a fraction reaches the strainer. The 

latter amount, plus any possible margin for uncertainty, is used to determine the amount of the 

debris used for strainer testing. The Debris Amount – Test field records the amount of the 

debris used in the testing or the amount of the debris used to determine the testing conditions. 

There is a separate field in the database called Scaled? that specifies the meaning of the Debris 

Amount – Test field. If the value is Scaled? is Yes, that means that the debris amount was 

scaled for the testing conditions (with the scale factor described above). Otherwise, the Debris 
A-86

Amount – Test field entry indicates the amount of the debris at full-size strainer (plus any 

uncertainty margin). Such logic was built-in into the GL-04-02 database since not all the plants 

reported the debris amount for the same conditions. In addition, the amounts of the debris are 

usually reported in different units, such that the debris units are recorded individually for each 

debris type. Also, in the situations where several break locations were analyzed, the worst case 

(usually meaning the most debris) was selected for the database entry.

Table A.2-11 shows an example of the debris amount data recorded for a single plant. Similar 

data were recorded for all other plants. The entire table is not reproduced here due to its large 

size – each plant reported 10 to 20 types of the debris, so the full table would include about 

1000 lines. Table A.2-12 shows the surrogate debris types.

In addition to the type of the surrogate debris, the amount of the surrogate debris was also 

recorded where provided by the plants. The format is very similar to the Debris Amount – Test 

field described above.

Debris: Zone of Influence

The data on the debris zone of influence (ZOI) assumed for the strainer analysis were recorded 

in the database for each debris type. The recorded data are provided in Table A.2-13. In some 

cases, several ZOI values were used in different analysis for the same material, as indicated by 

multiple ZOI entires in Table A.2-13.

Debris: Chemical Buffer

The GL-04-02 database collected the information on the chemical (pH) buffer, including sodium 

hydroxide (NaOH), trisodium phosphate (TSP), and sodium tetraborate (STB). The information 

on whether a plant changed the buffer or its concentration in the response to the generic letter is 

also recorded in the database. The data on the chemical buffer is presented in Table A.2-14. 
A-87

Figure A.2-10. Latent Debris Amount

0 100 200 300 400 500 600

Prairie Island - 1

St. Lucie - 2

ANO - 1

Diablo Canyon - 1

Diablo Canyon - 2

Ginna - 1

Kewaunee - 1

Watts Bar - 2

Summer - 1

Oconee - 1

Oconee - 2

Oconee - 3

North Anna - 1

North Anna - 2

Vogtle - 1

Vogtle - 2

Surry - 1

Surry - 2

St. Lucie - 1

ANO - 2

Braidwood - 1

Braidwood - 2

Byron - 1

Byron - 2

Calvert Cliffs - 1

Calvert Cliffs - 2

Point Beach - 1

Point Beach - 2

Turkey Point - 3

Turkey Point - 4

Fort Calhoun - 1

Indian Point - 2

Beaver Valley - 1

Beaver Valley - 2

Callaway - 1

Catawba - 1

Catawba - 2

Comanche Peak - 1

Comanche Peak - 2

Crystal River - 3

D.C. Cook - 1

D.C. Cook - 2

Farley - 1

Farley - 2

McGuire - 1

McGuire - 2

Palisades - 1

Palo Verde - 1

Palo Verde - 2

Palo Verde - 3

Prairie Island - 2

Salem - 1

Salem - 2

San Onofre - 2

San Onofre - 3

Seabrook - 1

Sequoyah - 1

Sequoyah - 2

Shearon Harris - 1

South Texas - 1

South Texas - 2

Watts Bar - 1

Wolf Creek - 1

Millstone - 2

Indian Point - 3

Waterford - 3

Three Mile Island - 1

Robinson - 2

Davis Besse - 1

Millstone - 3

Latent Debris Amount, lbm

Fiber

Particulate

0 45 91 136 181 221 272

Latent Debris Amount, kg 
A-88

Figure A.2-11. Strainer Sacrificial Area

0 9 19 28 37 46 56 65 74 84 93

0 100 200 300 400 500 600 700 800 900 1000

Braidwood - 1

Braidwood - 2

Byron - 1

Byron - 2

Watts Bar - 1

Watts Bar - 2

Millstone - 3

Sequoyah - 1

Sequoyah - 2

Catawba - 1

Catawba - 2

Beaver Valley - 2

Salem - 1

Salem - 2

Beaver Valley - 1

Palo Verde - 1

Palo Verde - 2

Palo Verde - 3

Calvert Cliffs - 1

Calvert Cliffs - 2

McGuire - 1

McGuire - 2

Oconee - 1

Oconee - 2

Oconee - 3

Three Mile Island - 1

North Anna - 1

North Anna - 2

Indian Point - 2

ANO - 1

ANO - 2

Comanche Peak - 1

Comanche Peak - 2

Waterford - 3

Millstone - 2

Seabrook - 1

Summer - 1

Surry - 1

Surry - 2

Diablo Canyon - 1

Diablo Canyon - 2

Ginna - 1

Robinson - 2

D.C. Cook - 1

D.C. Cook - 2

Palisades - 1

Point Beach - 1

Point Beach - 2

Shearon Harris - 1

South Texas - 1

South Texas - 2

Turkey Point - 4

Turkey Point - 3

Kewaunee - 1

Crystal River - 3

St. Lucie - 1

Farley - 1

Farley - 2

Fort Calhoun - 1

San Onofre - 2

San Onofre - 3

Indian Point - 3

Davis Besse - 1

Vogtle - 1

Vogtle - 2

Callaway - 1

St. Lucie - 2

Wolf Creek - 1

Prairie Island - 1

Prairie Island - 2

Screen Sacrificital Area, m2

Screen Sacrificital Area, ft2

Min

Max

Not reported
A-89

Figure A.2-12. Scale Factor for Testing

0 0.05 0.1 0.15 0.2

Summer - 1

Turkey Point - 4

Crystal River - 3

Wolf Creek - 1

St. Lucie - 2

St. Lucie - 1

Shearon Harris - 1

Point Beach - 2

Point Beach - 1

Kewaunee - 1

Millstone - 3

Millstone - 2

Watts Bar - 2

Palisades - 1

Turkey Point - 3

Oconee - 1

Oconee - 3

Oconee - 2

Waterford - 3

Robinson - 2

Comanche Peak - 2

Comanche Peak - 1

Beaver Valley - 2

Indian Point - 2

Indian Point - 3

Beaver Valley - 1

Braidwood - 2

Byron - 2

Braidwood - 1

Byron - 1

D.C. Cook - 2

D.C. Cook - 1

ANO - 1

Ginna - 1

Palo Verde - 1

Palo Verde - 2

Palo Verde - 3

Prairie Island - 2

Prairie Island - 1

Surry - 1

Surry - 2

Salem - 2

Salem - 1

Diablo Canyon - 1

Diablo Canyon - 2

Sequoyah - 1

Sequoyah - 2

Watts Bar - 1

North Anna - 2

North Anna - 1

South Texas - 2

South Texas - 1

Fort Calhoun - 1

San Onofre - 3

McGuire - 2

Calvert Cliffs - 2

Vogtle - 2

Catawba - 1

McGuire - 1

Callaway - 1

San Onofre - 2

Seabrook - 1

Calvert Cliffs - 1

Three Mile Island - 1

Vogtle - 1

Farley - 1

ANO - 2

Farley - 2

Davis Besse - 1

Catawba - 2

Screen Scale for Testing

Min

Max

Not Reported
A-90

Table A.2-11. Example of the Debris Amount Data

Plant 

Name Unit Debris Type Debris

Debris 

Amount 

(Analysis)

Debris 

Amount 

(Test)

Units Scaled?

Millstone 2 Coatings Qualified coatings 32.8 32.8 ft3 No

Unqualified 

coatings 8.8 8.8 ft3 No

Insulation Claremont 

fiberglass 110.1 65.0 ft3 No

Mineral fiber 297.3 297.3 ft3 No

NUKON 1135.1 675.4 ft3 No

Transco 

encapsulated 

mineral wool

159.4 159.4 ft3 No

Transco RMI foil 1239.6 885.5 ft2 No

3 Coatings Margin for coatings 2.1 ft3 No

Qualified concrete 

coatings 1.5 1.5 ft3 No

Qualified steel 

coatings 8.9 8.9 ft3 No

Unqualified 

coatings 10.5 10.5 ft3 No

Insulation Microtherm 1.1 1.2 ft3 No

Transco thermal 

wrap

1219.0 755.2 ft3 No

Table A.2-12. Surrogate Debris Types

Surrogate Debris Debris Type Plant Name Unit

Acrylic chips Degraded epoxy Coatings Point Beach 2

Epoxy chips Chips South Texas 1

2

Other unqualified 

coatings

Unqualified 

coatings

Palisades 1

Acrylic coating Qualified concrete and 

unqualified coatings

St. Lucie 1

Acrylic powder Alkyd Unqualified 

coatings

Palisades 1

Aluminum paint Qualified 

coatings

Palisades 1

Carboline 3912 Qualified 

coatings

Palisades 1

Carboline 890 Qualified 

coatings

Palisades 1

Carboline-Flexxide 

thinner

Qualified 

coatings

Palisades 1

Carboline-Multibond 

120

Qualified 

coatings

Palisades 1
A-91

Surrogate Debris Debris Type Plant Name Unit

Qual. epoxy Coatings Comanche 

Peak

1

2

Qual. Silicone Coatings Comanche 

Peak

1

2

Unqual. Alkyd Coatings Comanche 

Peak

1

2

Aluminum Aluminum Turkey Point 3

Aluminum hydroxide Aluminum hydroxide Chemical Prairie Island 1

2

Aluminum 

Oxyhydroxide

AIOOH Precipitate Chemical Comanche 

Peak

1

2

Aluminum 

Oxyhydroxide

Chemical Crystal River 3

Diablo Canyon 1

2

Farley 1

2

Palo Verde 1

2

3

Salem 1

2

San Onofre 2

3

Seabrook 1

St. Lucie 2

Three Mile 

Island

1

South Texas 1

2

Chem. Precip. Beaver Valley 1

2

NaAlSi308 Precipitate Chemical Comanche 

Peak

1

2

Sodium aluminum 

silicate

Chemical St. Lucie 2

Turkey Point 4

Wolf Creek 1

South Texas 1

2

Chemical debris Kewaunee 1

Amerlock 400 NT Phenolic paint chips Particulate Watts Bar 1

Phenolic, alkyd and 

silicone coatings 

Coatings Watts Bar 2
A-92

Surrogate Debris Debris Type Plant Name Unit

(chips)

Ameron 90HS Chips Farley 1

2

Boric acid Boric acid Chemical Turkey Point 3

Cable insulation Cable insulation Fibrous Kewaunee 1

Calcium carbonate Calcium carbonate Chemical Prairie Island 1

2

Calcium Phosphate Calcium phosphate Chemical Crystal River 3

Farley 1

2

Palo Verde 1

2

3

San Onofre 2

3

St. Lucie 2

Three Mile 

Island

1

Waterford 3

South Texas 1

2

Calcium Silicate Indian Point 2

3

CaI-Sil Insulation Turkey Point 4

Calcium silicate Fibrous ANO 1

2

Beaver Valley 1

2

Cal-Sil Diablo Canyon 1

2

Insulation Point Beach 2

Turkey Point 3

Particulate Fort Calhoun 1

Calcium Silicate 

Powder

Cal-Sil St. Lucie 1

Particulates St. Lucie 2

Calcium Silicate 

smalls and powder

Calcium silicate cloth 

jacketed

Insulation Palisades 1

Calcium silicate 

jacketed

Insulation Palisades 1

Carboline "Special 

Zinc Filler"

Qualified, unqualified, 

and damaged IOZ 

coatings

Particulate Palo Verde 1

2

3

Carbon steel Carbon steel Turkey Point 3

Cerafiber Asbestos Surry 1

2

Cerafiber Fibrous Fort Calhoun 1
A-93

Surrogate Debris Debris Type Plant Name Unit

Ceramic fiber Asbestos Insulation Point Beach 2

Chips (Carboline 

CarboGuard 890/891 

epoxy coating, or 

similar type coating)

Epoxy, curled chips 

(1.5 in)

Chips Wolf Creek 1

Epoxy, fine chips (1/64 

in)

Chips Wolf Creek 1

Coating chips Unqualified Alkyd and 

high heat Aluminum 

coatings

Chips Diablo Canyon 1

2

Unqualified non-OEM 

alkyd (outside ZOI)

Particulate D.C. Cook 1

2

Unqualified non-OEM 

epoxy (outside ZOI)

Particulate D.C. Cook 1

2

Unqualified OEM alkyd 

(outside ZOI),

Particulate D.C. Cook 1

2

Unqualified OEM 

epoxy (outside ZOI)

Particulate D.C. Cook 1

2

Concrete Concrete Turkey Point 3

Dirt Indian Point 2

3

Latent particulate Latent Prairie Island 1

2

Dirt and dust Latent debris Particulate Turkey Point 4

Latent particulate Particulate Waterford 3

Electro Carb black 

silicon carbide

Qualified epoxy 

coatings

Particulate Fort Calhoun 1

Epoxy 4500 chips Epoxy Unqualified 

coatings

Summer 1

Epoxy chips Unqualified epoxy 

Fines (1/64 in.)

Coatings Comanche 

Peak

1

2

Unqualified epoxy fines 

(1/8"-1/4", 1/4"-1/2", 

1/2"-1")

Coatings Comanche 

Peak

1

2

Unqualified epoxy fines 

(6 mil)

Coatings Comanche 

Peak

1

2

Unqualified epoxy large 

(l "-2")

Coatings Comanche 

Peak

1

2

Epoxy particulate with 

a median particle size 

of 10 microns

Qualified coatings Coatings Calvert Cliffs 1

2

Fiber through debris 

chipper

NUKON (Smalls) Fibers St. Lucie 2

NUKON larges Fibrous Wolf Creek 1

NUKON smalls Fibrous Wolf Creek 1

Fiber through debris 

shredder

Latent fiber Fibrous Wolf Creek 1

NUKON (Fines) Fibers St. Lucie 2
A-94

Surrogate Debris Debris Type Plant Name Unit

NUKON Fines Fibrous Wolf Creek 1

Fiber through debris 

shredder (15% Fiber)

Latent Fibers Fibers St. Lucie 2

Fiberglass Fiberglass Insulation Point Beach 2

Owens-Corning 

Fiberglass

Fibrous Salem 1

2

Fiberglass insulation Fiberglass pipe cover Fibrous Kewaunee 1

Glass from fluorescent 

tube.

Light bulbs Foreign 

material

Braidwood 1

Ground silica Coatings Shearon Harris 1

Epoxy (inside ZOI) Particulate Beaver Valley 1

Qualified Carboline 191 

HB

Particulate Beaver Valley 2

Qualified coatings Particulate Crystal River 3

Qualified IOZ Particulate Beaver Valley 2

Qualified Nutec 11S 

Epoxy

Particulate Beaver Valley 2

Qualified Nutec 1201 

epoxy

Particulate Beaver Valley 2

Vi Cryl CP-10 (inside 

ZOI)

Particulate Beaver Valley 1

Ground silica and 

paint chips

Alkyd enamel (outside 

ZOI)

Particulate Beaver Valley 1

Cold galvananizing 

(outside ZOI)

Particulate Beaver Valley 1

Epoxy (outside ZOI) Particulate Beaver Valley 1

IOZ paint (outside ZOI) Particulate Beaver Valley 1

Unqualified Alkyd Particulate Beaver Valley 2

Unqualified Carboline 

191 HB

Particulate Beaver Valley 2

Unqualified Carboline 

4674

Particulate Beaver Valley 2

Unqualified cold 

galvanizing

Particulate Beaver Valley 2

Unqualified IOZ 

coatings

Particulate Beaver Valley 2

Ground silica/silicon 

carbide

Particulate Three Mile 

Island

1

Ground silica/silicon 

oxide flour

Qualified & unqualified 

coatings

Particulate Catawba 1

2

McGuire 1

2

Ground silicon carbide Qualified and 

unqualified coatings

Particulate San Onofre 2

3

High-density fiberglass High-density fiberglass Fibrous ANO 1

IIG Thermo Gold Cal-Sil Particulate Robinson 2
A-95

Surrogate Debris Debris Type Plant Name Unit

Kaylo Particulate Robinson 2

Thermo 12 insulation Particulate Robinson 2

Inorganic Zinc Filler Cold galvanized zinc Coatings Summer 1

Cold galvanizing Unqual. 

Coatings

Summer 1

Inorganic zinc Coatings Summer 1

Unqualified 

coatings

Summer 1

Zinc (MobilZinc 7) Qualified 

coatings

Summer 1

Johns-Mansville 

Cal-Sil

Cal-Sil / Asbestos Insulation Surry 1

2

Kaowool Kaowool Fibrous Diablo Canyon 1

2

Salem 1

2

Knauf ET fibers Thermal-Wrap Fibrous South Texas 1

2

Knauf Pipe Insulation Mineral fiber Insulation Millstone 2

Labels Electromark labels, 

outer laminate area

Labels Comanche 

Peak

1

2

Electromark labels, 

sub-layer

Labels Comanche 

Peak

1

2

Unqualified Labels Labels Comanche 

Peak

1

2

Lead blanket covers 

fiberglass fines

Lead blanket covers 

fiberglass fines

Blanket cover Comanche 

Peak

1

2

Lead blanket covers 

fiberglass large

Lead blanket covers 

fiberglass large

Blanket cover Comanche 

Peak

1

2

Marinite Marinite Diablo Canyon 1

2

Particulate South Texas 1

2

Marinite I powder Marinite XL Particulate Summer 1

Microtherm Microtherm Insulation Turkey Point 3

Millstone 3

Particulate South Texas 1

2

Microtherm 

(pulverized powder)

Microtherm Particulate Waterford 3
A-96

Surrogate Debris Debris Type Plant Name Unit

Mineral Wool Indian Point 2

3

Mineral Wool Fibrous Diablo Canyon 1

2

San Onofre 2

3

Insulation Point Beach 2

Mineral wool fines Mineral wool jacketed Insulation Palisades 1

Min-K Min-K Fibrous Beaver Valley 1

2

Particulate Salem 1

2

Min-K fines (fibrous) Insulation Comanche 

Peak

1

2

Min-K fines 

(particulate)

Insulation Comanche 

Peak

1

2

Min-K (pulverized 

powder)

Min-K Particulate Waterford 3

Min-K fiber Min-K fiber Insulation Watts Bar 1

Mylar chips Unqualified epoxy 

curled (1/2"-2")

Coatings Comanche 

Peak

1

2

Na tetraborate Na tetraborate Chemical Turkey Point 3

NUKON Indian Point 2

3

Fibrous Catawba 1

2

Crystal River 3

McGuire 1

2

Three Mile 

Island

1

Beaver Valley 1

3M-M20C fiber Insulation Watts Bar 1

Fiberglass (fines) Insulation Comanche 

Peak

1

2

Fiberglass (jacketed) Insulation Comanche 

Peak

1

2

Fiberglass (large) Insulation Comanche 

Peak

1

2

Fiberglass (small) Insulation Comanche 

Peak

1

2
A-97

Surrogate Debris Debris Type Plant Name Unit

Fiberglass, Temp-Mat, 

Cerablanket, and 

Latent fiber

Fibrous Diablo Canyon 1

2

Kaowool Fibrous Robinson 2

Latent fiber Fibrous San Onofre 2

3

Latent Indian Point 2

3

Point Beach 2

Prairie Island 1

2

Watts Bar 1

Low Density Fiberglass Fibrous Robinson 2

Nukon Fibrous Salem 1

2

Insulation Point Beach 2

Turkey Point 3

NUKON and Latent 

fiber

Fibrous Palo Verde 1

2

3

South Texas 1

2

Temp Mat Fibrous Robinson 2

NUKON (shredded) Latent fiber Latent fiber Comanche 

Peak

1

2

NUKON fiber Fibrous Seabrook 1

NUKON fiberglass Fiberglass Insulation Surry 1

2

NUKON fines Fibrous Beaver Valley 2

Additional Fiber Fiber Waterford 3

Latent debris, fiber Latent Palisades 1

Latent fiber Fibrous Turkey Point 4

Fiber Waterford 3

Nukon Insulation Turkey Point 4

Fiber Waterford 3

Transco MEI Fiber Waterford 3

NUKON smalls and 

fines

NUKON thermal wrap 

jacketed

Insulation Palisades 1

NUKON unjacketed Insulation Palisades 1

Owens Corning 

Fiberglass Insulation

Fibrous Oconee 1

2

3

Paint chips Chips Crystal River 3

Alkyds Unqualified Prairie Island 1
A-98

Surrogate Debris Debris Type Plant Name Unit

coatings 2

Carboline 195 Qualified 

coatings

Prairie Island 1

2

Carboline Carbozinc 11 Qualified 

coatings

Prairie Island 1

2

Carboline Phenoline 

305 finish

Qualified 

coatings

Prairie Island 1

2

Carboline Phenoline 

305 primer

Qualified 

coatings

Prairie Island 1

2

Unqualified coatings Chips Fort Calhoun 1

Paroc 140E Paroc Insulation Surry 1

2

Paroc Mineral Wool Paroc mineral wool Fibrous North Anna 1

2

PCI Nukon Claremont fiberglass Insulation Millstone 2

Latent fiber Latent Millstone 2

Nukon Insulation Millstone 2

PCI PWR dirt mix Dirt/dust Latent 

particulate

Comanche 

Peak

1

2

Latent debris, 

particulate

Latent Palisades 1

Latent particulate Latent Point Beach 2

Particulate Wolf Creek 1

PCI PWR Dirt Mix 

(85% of Latent Debris)

Latent particulate Particulates St. Lucie 2

Pre-shredded foils 

0.05 mm (0.002 in.) 

thick.

Mirror RMI pieces Insulation Braidwood 1

2

Byron 1

2

Pulverized acrylic 

coating powder

Epoxy coatings, 

polyamide primer 

coatings, alkyd 

coatings, and baked 

enamel coatings

Particulate South Texas 1

2

Pulverized Amerlock 

400 epoxy coating

Qualified epoxy and 

Alkyd

Particulate Palo Verde 1

2

3

PWR dirt mix Latent dirt/dust Particulate Diablo Canyon 1

2

PWR dirt mix and 

Fiberglass tape

Mica tape Diablo Canyon 1

2

RMI (large pieces) RMI (large pieces) Insulation Comanche 

Peak

1

2
A-99

Surrogate Debris Debris Type Plant Name Unit

RMI (small pieces) RMI (small pieces) Insulation Comanche 

Peak

1

2

RMI smalls Transco RMI Insulation Palisades 1

Sand Latent dirt/dust Particulate Palo Verde 1

2

3

SiC; Amerlock 400 NT Alkyd paint Particulate Watts Bar 1

Silicone paint Particulate Watts Bar 1

Sil-Co-Sil Indian Point 2

3

SIL-CO-SIL 53 Coatings Robinson 2

SIL-CO-SIL 53 powder Dense aluminum Unqualified 

coatings

Palisades 1

Sil-Co-Sil Sand Qualified and 

unqualified IOZ 

coatings

Particulate Diablo Canyon 1

2

Silica Sand Latent Robinson 2

Dirt/dust Particulate Beaver Valley 1

2

Dust/dirt Latent Turkey Point 3

Latent dirt/dust Particulate Catawba 1

2

Crystal River 3

McGuire 1

2

South Texas 1

2

Silicon Carbide Particulate Farley 1

2

Seabrook 1

Coatings (non-zinc) Particulate Turkey Point 3

Latent particulate Latent Indian Point 2

3

Particulate ANO 1

Phenolic paint particles Particulate Watts Bar 1

Phenolic, alkyd and 

silicone coatings 

(particulates)

Coatings Watts Bar 2

Qualified and 

unqualified coatings

Coatings Indian Point 2

3

Silicon Carbide + 

Carboline 890 chips

Coatings (total) Particulate ANO 1

2

Silicon Carbide 10-

micron

Qualified coatings Particulate Waterford 3

Unqualified Coatings Particulate Waterford 3

Silicon Carbide and 

Amerlock 400 NT

Alkyds Coatings Sequoyah 1

2
A-100

Surrogate Debris Debris Type Plant Name Unit

Phenolic Coatings Sequoyah 1

2

Silicone Coatings Sequoyah 1

2

Silicon carbide for 

latent particulate

Latent debris Latent ANO 2

Sodium Aluminum 

Silicate

Sodium aluminum 

silicate

Chemical Crystal River 3

Diablo Canyon 1

2

Farley 1

2

Fort Calhoun 1

Palo Verde 1

2

3

Salem 1

2

San Onofre 2

3

Three Mile 

Island

1

Waterford 3

Chemical debris ANO 1

Chemical 

Precipitates

Beaver Valley 1

2

SS RMI foil RMI foil Insulation Summer 1

Stainless Steel Foils Metallic Oconee 1

2

3

Stainless steel wool Lead blanket,lead wool 

Fines

Blanket cover Comanche 

Peak

1

2

Stone Flour Particulate Oconee 1

2

3

Alkyd paint (inside ZOI) Particulate D.C. Cook 1

2

Epoxy paint (inside 

ZOI)

Particulate D.C. Cook 1

2

Latent dirt/dust Particulate Palo Verde 1

2

3

Latent dust/Dirt Latent Ginna 1

Phenolic Coatings Coatings Ginna 1

Qualified and 

unqualified coatings; 

Particulate Salem 1

2
A-101

Surrogate Debris Debris Type Plant Name Unit

latent dirt/dust

Unqualified coatings Coatings Calvert Cliffs 1

2

Unqualified cold 

galvanizing compound

Particulate D.C. Cook 1

2

Stone flour with typical 

particle diameter of 

7.7 μm

Fines Qualified epoxy 

coatings

Braidwood 1

2

Byron 1

2

Tape Tape Miscellaneous 

debris

Comanche 

Peak

1

2

TempMat Indian Point 2

3

Jacketed TempMat Fibrous Kewaunee 1

TempMat Insulation Surry 1

2

TempMat Fibrous Fort Calhoun 1

Beaver Valley 2

Insulation Point Beach 2

Summer 1

TempMat fines TempMat Fibrous Beaver Valley 1

TempMat Supplied by 

GLT Products

TempMat Fibrous North Anna 1

2

Thermal wrap Thermal wrap Fibrous ANO 1

Thermal-Wrap 

Supplied Transco 

Products

Fiberglass 

(unspecified)

Fibrous North Anna 1

2

Transco Thermal-Wrap Fibrous North Anna 1

2

Thermobestos Jacketed thermobestos Fiber/particulate 

mix

Kewaunee 1

Thermo-Lag 330 Thermo-Lag 330 Fibrous Palo Verde 1

2

3

Thermo-Lag powder Thermo-Lag Particulate Wolf Creek 1

Tin Particles Inorganic zinc Coatings Sequoyah 1

2

Inorganic zinc 

(particulate)

Coatings Watts Bar 2

Tin Powder Carboline Carbozinc 11 Qual. coatings Palisades 1

Unqual. 

coatings

Palisades 1

Coatings (zinc) Particulate Turkey Point 4

Inorganic zinc Coatings Kewaunee 1

Inorganic zinc silicate Qualified Palisades 1
A-102

Surrogate Debris Debris Type Plant Name Unit

coatings

IOZ coating Particulate Wolf Creek 1

IOZ Paint Particulate Watts Bar 1

Qualified inorganic zinc Coatings Comanche 

Peak

1

2

Qualified and 

unqualifed IOZ

Particulate South Texas 1

2

Qualified coatings -

steel - epoxy

Coatings St. Lucie 2

Qualified coatings -

steel - IOZ

Coatings St. Lucie 2

Qualified steel coatings St. Lucie 1

Unqualified inorganic 

zinc

Coatings Comanche 

Peak

1

2

Unqualified coatings -

IOZ

Coatings St. Lucie 2

Zinc chromate Qualified 

coatings

Palisades 1

Transco Latent fiber Fibrous Farley 1

2

Fort Calhoun 1

LDFG/NUKON Fibrous Fort Calhoun 1

Transco Encapsulated 

Mineral Wool (Fibrex)

Transco encapsulated 

mineral wool

Insulation Millstone 2

Transco RMI Transco RMI Insulation Prairie Island 1

2

Transco Stainless 

Steel Foil

Transco RMI Metallic North Anna 1

2

Transco Stainless 

Steel RMI Foil

Transco RMI foil Insulation Millstone 2

Transco Tempmat Transco TempMat Fibrous ANO 1

Transco Thermal 

Wrap

Latent fiber Latent Millstone 3

Nukon Insulation Millstone 3

Transco fiberglass Insulation Millstone 3

Transco thermal-wrap Insulation Surry 1

2

Transco Thermal 

Wrap (shredded)

Fiber St. Lucie 1

Transco ThermalWrapLatent fibers Fibrous North Anna 1

2

Tubing Hot tar tubing Miscellaneous 

debris

Comanche 

Peak

1

2
A-103

Surrogate Debris Debris Type Plant Name Unit

Potable Water Tubing Misc. debris Comanche 

Peak

1

2

Uncompressed fibrous 

insulation

Fines Latent debris Braidwood 1

2

Byron 1

2

Wallnut Shells or 

Acrylic Coating

Qualified coatings -

concrete - epoxy

Coatings St. Lucie 2

Unqualified coatings -

epoxy

Coatings St. Lucie 2

Walnut Shell Flour 

(325 mesh)

Alkyds Coatings Summer 1

Coatings (all non-zinc) Particulate Turkey Point 4

Damaged coatings Particulate North Anna 1

2

Enamel Coatings Kewaunee 1

Epoxy Coatings Summer 1

Epoxy (Amercoat 66) Qualified 

coatings

Summer 1

Epoxy (Ameron 89) Qualified 

coatings

Summer 1

Epoxy (Nu-Klad) Qualified 

coatings

Summer 1

Epoxy 4500 Coatings Summer 1

Epoxy 5000 Coatings Summer 1

Epoxy 6129 Coatings Summer 1

Epoxy 6548/7107 Coatings Summer 1

Factory coatings Coatings Kewaunee 1

Latent particles Latent debris Surry 1

2

Latent particulate Latent Millstone 2

3

Particulate North Anna 1

2

Phenolic epoxy Coatings Kewaunee 1

Qualified coatings Coatings Surry 1

2

Qualified coatings Coatings Millstone 2

3

Particulate North Anna 1

2

Unqualified & damaged 

coatings

Coatings Surry 1

2

Unqualified coatings Coatings Millstone 2

3

Particulate North Anna 1

2
A-104

Surrogate Debris Debris Type Plant Name Unit

Walnut shells Alkyd Coatings Point Beach 2

Aluminum Coatings Point Beach 2

Carboline 191 HB 

Epoxy

Particulate Wolf Creek 1

Carboline 195 surfacer 

epoxy

Particulate Wolf Creek 1

Carboline 4674 Acrylic Particulate Wolf Creek 1

OEM/Other unqualified 

Alkyd

Particulate Wolf Creek 1

OEM/Other unqualified 

Epoxy

Particulate Wolf Creek 1

Qualified (ZOI) epoxy Coatings Point Beach 2

Unqualified epoxy Coatings Point Beach 2

WCAP (NaAlSi) Indian Point 2

3

Wollastonite Marinite 36 fines Particulate D.C. Cook 1

2

Marinite 36 large 

pieces

Particulate D.C. Cook 1

2

Marinite 36 small 

pieces

Particulate D.C. Cook 1

2

Wollastonite 520H Unibestos Fibrous Robinson 2

Zinc Zinc in galvanized plate Coatings Turkey Point 3

Zinc Dust Cal-Sil fines Insulation Ginna 1

Qualified degraded IOZ 

coatings

Coatings Ginna 1

Qualified IOZ coatings Coatings Ginna 1

Zinc filler Fines Qualified IOZ 

Coatings

Braidwood 1

2

Byron 1

2

Table A.2-13. Debris Zone of Influence

Plant Name Unit Debris Type Debris ZOI 

(in D)

ANO 1 Coatings Total coatings (qualified and unqualified) 10

Insulation Calcium-silicate (SS cladding, SS banding) 5.45

Transco RMI Foil 2

Transco Temp Mat 11.7

Thermal-Wrap Fiber 17

Thermal-Wrap Fiber (SS cladding, SS 

banding)

5.45

2 Coatings Total coatings (qual. and unqual.) 10

Insulation Calcium-silicate (unbanded) 25
A-105

Plant Name Unit Debris Type Debris ZOI 

(in D)

Calcium-silicate (banded) 5.45

Mirror foil 28.6

Transco RMI foil 2

Transco Thermal Wrap 17

Beaver Valley 1 Coatings Qualified coatings 5

Insulation Benelex 401 2

Calcium silicate [aluminum cladding, 

stainless steel (SS) bands]

5.45

Diamond Power Mirror RMI with standard 

bands

28.6

Encapsulated Microtherm 4

Encapsulated Min-K 28.6

Fiberglas thermal insulating wool 17

Fiberglass 17

Foamglas 28.6

Temp-Mat with SS wire retainer 11.7

Transco RMI 2

Transco Thermal Wrap 17

Transite 1

2 Coatings Qualified coatings 5

Insulation Benelex 401 2

Calcium silicate (aluminum cladding, SS 

bands)

5.45

Diamond Power Mirror RMI with standard 

bands

28.6

Encapsulated Microtherm 4

Encapsulated Min-K 28.6

Fiberglas thermal insulating wool 17

Fiberglass 17

Foamglas 28.6

Temp-Mat with SS wire retainer 11.7

Transco RMI 2

Transco Thermal Wrap 17

Transite 1

Braidwood 1 Insulation Transco RMI 2.0

Tempmat 11.7

Reflective Mirror with Standard Bands 28.6

Nukon (Thermal Wrap) 17.0

Qualified 

epoxy 

coatings

Fines 10

Qualified IOZ 

coatings

Fines 10

2 Insulation Mirror RMI pieces 2.9

17
A-106

Plant Name Unit Debris Type Debris ZOI 

(in D)

28.6

Qualified 

epoxy 

coatings

Fines 10

Qualified IOZ 

coatings

Fines 10

Byron 1 Insulation Transco RMI 2.0

Tempmat 11.7

Reflective Mirror with Standard Bands 28.6

Nukon (Thermal Wrap) 17.0

Qualified 

epoxy 

coatings

Fines 10

Qualified IOZ 

coatings

Fines 10

2 Insulation Mirror RMI pieces 2.9

17

28.6

Qualified 

epoxy 

coatings

Fines 10

Qualified IOZ 

coatings

Fines 10

Callaway 1 Insulation AlphaMat D 28.6

NUKON intact blankets 7

NUKON large fines 7

NUKON small fines 7

RMI large pieces 28.6

RMI small pieces 28.6

Calvert Cliffs 1 Marinite board 9.8

Lead Blankets 2.5

Coatings Epoxy coatings 4

Inorganic zinc coatings without topcoat 10

Insulation Calcium-silicate insulation 5.45

Generic fiberglass insulation 17

NUKON-jacketed w/standard bands 17

NUKON jacketed w/Sure Hold bands 2.4

Temp-Mat insulation 17

Transco mineral wool 17

Transco reflective metal insulation 2

Transco Thermal Wrap 17

2 Marinite board 9.8

Lead Blankets 2.5

Coatings Epoxy coatings 4

Inorganic zinc coatings without topcoat 10
A-107

Plant Name Unit Debris Type Debris ZOI 

(in D)

Insulation Calcium-silicate insulation 5.45

Generic fiberglass insulation 17

NUKON-jacketed w/standard bands 17

NUKON jacketed w/Sure Hold bands 2.4

Temp-Mat insulation 17

Transco mineral wool 17

Transco reflective metal insulation 2

Transco Thermal Wrap 17

Catawba 1 Coatings Protective coatings (epoxy & epoxyphenolic paints)5

Insulation Knauf insulation 17

Mirror RMI 28.6

NUKON insulation 17

Thermal-Wrap insulation 17

2 Coatings Protective coatings (epoxy & epoxyphenolic paints)5

Insulation Knauf insulation 17

Mirror RMI 28.6

NUKON insulation 17

Thermal-Wrap insulation 17

Comanche 

Peak

1 Blanket 

cover

Lead shielding blankets (fiberglass cover) 5

Coatings Qual. epoxy 4

Qual. Inorganic zinc 10

Insulation Fiberglass (jacketed) 17

Min-K fines (encapsulated) 2

RMI 28.6

2 Blanket 

cover

Lead shielding blankets (fiberglass cover) 5

Coatings Qual. epoxy 4

Qual. inorganic zinc 10

Insulation Fiberglass (jacketed) 17

Min-K fines (encapsulated) 2

RMI 28.6

Crystal River 3 Coatings DBA qualified epoxy coatings 4

IOZ 4

Insulation Mineral wool encapsulated in 22 gauge 

corrugated sheet cover (SG and BD only)

17

Mineral wool jacketed with 22 or 24 gauge 

304SS (MS, FW, EFW Only)

4

Mirror with standard bands 28.6

Mirror with Sure-Hold bands 2.4

Unjacketed NUKON-jacketed NUKON with 

standard bands

17
A-108

Plant Name Unit Debris Type Debris ZOI 

(in D)

D.C. Cook 1 Insulation CalSil 6.4

DP RMI 28.6

Marinite I and Marinite 36 17

Min-K 28.6

Transco fiberglass 2

Transco RMI 2

Miscellaneou

s

Electromark labels 9.9

Fireproof tape 17

2 Insulation CalSil 6.4

DP RMI 28.6

Marinite I and Marinite 36 17

Min-K 28.6

Transco fiberglass 2

Transco RMI 2

Miscellaneou

s

Electromark labels 9.9

Fireproof tape 17

Davis Besse 1 Coatings Qualified coatings 5.5

Insulation NUKON, large pieces 17

NUKON, small fines 17

RMI, large pieces 28.6

RMI, small fines 28.6

Diablo Canyon 1 Aluminum tape 28.6

Cable insulation/jackets 5

Cable tray fire stop materials 28.6

Light bulbs 28.6

Miscellaneous debris 28.6

Pressurizer heater cables 5

Qualified coatings 5

Vapor barrier material 3

Insulation Cal-Sil (12 in centers) 5.5

Cal-Sil (3 in centers) 3

Mineral wool 28.6

RMI with standard band 28.6

Temp-Mat with SS wire mesh, 

encapsulated in SS cladding

3.7

Temp-Mat with SS wire retainer 11.7

Transco RMI 2

2 Aluminum tape 28.6

Cable insulation/jackets 5

Cable tray fire stop materials 28.6

Light bulbs 28.6

Miscellaneous debris 28.6

Pressurizer heater cables 5
A-109

Plant Name Unit Debris Type Debris ZOI 

(in D)

Qualified coatings 5

Vapor barrier material 3

Insulation Cal-Sil (12 in centers) 5.5

Cal-Sil (3 in centers) 3

Mineral wool 28.6

RMI with standard band 28.6

Temp-Mat with SS wire mesh, 

encapsulated in SS cladding

3.7

Temp-Mat with SS wire retainer 11.7

Transco RMI 2

Farley 1 Coatings Qualified coatings 4

Insulation Mirror RMI 28.6

Transco RMI 2

2 Coatings Qualified coatings 4

Insulation Mirror RMI 28.6

Transco RMI 2

Fort Calhoun 1 Coatings Epoxy 5

Insulation CalSil 6.4

LDFG/NUKON 17

LDFG/NUKON (banded) 3

RMI 17.1

Temp-Mat 11.7

Ginna 1 Coatings Qualified coatings 5

10

Insulation CalSil 6.4

RMI 2

Temp-Mat 11.7

Thermal Wrap 17

Indian Point 2 Coatings DBA-qualified/acceptable epoxy 4

Insulation Asbestos with cloth 28.6

Asbestos with jacket 6.4

Fiberglass 17

NUKON 17

RMI 28.6

TempMat 11.7

Transco blanket 17

3 Coatings DBA-qualified/acceptable epoxy 4

Insulation Asbestos with jacket 6.4

Calcium silicate with cloth 28.6

Calcium silicate with jacket 6.4

Fiber (Marinite) board /transite 6.4

Fiberglass 17

Mineral wool with jacket 17

NUKON 17
A-110

Plant Name Unit Debris Type Debris ZOI 

(in D)

RMI 28.6

Temp-Mat 11.7

Kewaunee 1 Coatings Enamel 10

Factory coatings 10

Inorganic zinc 10

Phenolic epoxy 10

Fiber/particul

ate mix

Jacketed Thermobestos 5.45

Fibrous Cable insulation 17

Fiberglass pipe cover 17

Jacketed TempMat 17

Insulation RMI (foils) 28.6

RMI (intact pieces) 28.6

McGuire 1 Coatings Protective coatings (epoxy & epoxyphenolic paints)5

Insulation Mirror RMI 28.6

NUKON insulation 17

Thermal-Wrap insulation 17

Unjacketed NUKON 17

2 Coatings Protective coatings (epoxy & epoxyphenolic paints)5

Insulation Mirror RMI 28.6

NUKON insulation 17

Thermal-Wrap insulation 17

Unjacketed NUKON 17

Millstone 2 Coatings 10

Insulation Cal-Sil 5.45

Transco RMI 2

Unjacketed NUKON, NUKON with standard 

bands Knaupf

17

3 Coatings 5

Insulation Min-K 28.6

Unjacketed NUKON, jacketed NUKON with 

standard bands

17

North Anna 1 Coating 5

Insulation Paroc mineral wool 5.4

Temp-Mat 11.7

Transco RMI 2

Transco Thermal-Wrap 17

2 Coating 5

Insulation Paroc mineral wool 5.4

Temp-Mat 11.7

Transco RMI 2

Transco Thermal-Wrap 17
A-111

Plant Name Unit Debris Type Debris ZOI 

(in D)

Oconee 1 Coatings 10

Insulation Generic fiberglass 28.6

RMI 28.6

2 Coatings 10

Insulation Generic fiberglass 28.6

RMI 28.6

3 Coatings 10

Insulation Generic fiberglass 28.6

RMI 28.6

Palisades 1 Insulation Calcium silicate cloth jacketed 28.6

Calcium silicate jacketed 5.45

Low-density fiberglass jacketed 17

Low-density fiberglass unjacketed 17

Mineral wool jacketed 17

NUKON thermal wrap jacketed 7

NUKON unjacketed 17

Transco RMI 2

Qual. 

coatings

Aluminum paint 10

Carboline 3912 10

Carboline 890 10

Carboline Carbozinc 11 10

Carboline-Flexxide thinner 10

Carboline-Multibond 120 10

Inorganic zinc silicate 10

Zinc chromate 10

Palo Verde 1 Coatings Qualified epoxy coatings 4

Qualified IOZ 5

Insulation Equipment Transco RMI 2

Min-K/Microtherm 28.6

NUKON 17

Piping RMI 28.6

Temp-Mat 11.7

Thermo-Lag 28.6

2 Coatings Qualified epoxy coatings 4

Qualified IOZ 5

Insulation Equipment Transco RMI 2

Min-K/Microtherm 28.6

NUKON 17

Piping RMI 28.6

Temp-Mat 11.7

Thermo-Lag 28.6

3 Coatings Qualified epoxy coatings 4

Qualified IOZ 5
A-112

Plant Name Unit Debris Type Debris ZOI 

(in D)

Insulation Equipment Transco RMI 2

Min-K/Microtherm 28.6

NUKON 17

Piping RMI 28.6

Temp-Mat 11.7

Thermo-Lag 28.6

Point Beach 1 Insulation Asbestos 10

CalSil 14.5

Fiberglass 5.5

Mineral Wool 8

NUKON 2.4

Temp-Mat 11.8

2 Insulation Asbestos 10

CalSil 14.5

Fiberglass 5.5

Mineral Wool 8

NUKON 2.4

Temp-Mat 11.8

Prairie Island 1 Coatings Carboline 195 10

Carboline Carbozinc 11 10

Carboline Phenoline 305 finish 10

Carboline Phenoline 305 primer 10

Qualified coatings total 10

Insulation Mirror RMI (standard bands) 28.6

Mirror RMI large debris (standard bands) 28.6

Misc. fiber 5.4

Transco RMI 2

Transco RMI (large debris) 2

2 Coatings Carboline 195 10

Carboline Carbozinc 11 10

Carboline Phenoline 305 finish 10

Carboline Phenoline 305 primer 10

Qualified coatings total 10

Insulation Mirror RMI (standard bands) 28.6

Mirror RMI large debris (standard bands) 28.6

Misc. fiber 5.4

Robinson 2 Coatings 10

Insulation Asbestos 28.6

Cal-Sil 5.5

Kaowool 28.6

Kaylo 28.6

Low-density fiberglass 28.6

NUKON 17

RMI 2
A-113

Plant Name Unit Debris Type Debris ZOI 

(in D)

Temp-Mat 11.7

Unibestos 28.6

Salem 1 Coatings Qualified epoxy coatings 5

Insulation Jacketed NUKON 7

Transco RMI 2

2 Coatings Qualified epoxy coatings 5

Insulation Jacketed NUKON 7

Transco RMI 2

San Onofre 2 Coatings Qualified epoxy coatings 5

Insulation Microtherm 4

SS encapsulated mineral wool 4

Transco RMI 2

3 Coatings Qualified epoxy coatings 5

Insulation Microtherm 4

SS encapsulated mineral wool 4

Transco RMI 2

Seabrook 1 Coatings Qualified concrete coating 4

Qualified steel coating 4

10

Insulation Insulation Jacketing 7

Jacketed NUKON 7

Transco RMI 2

Unjacketed NUKON 17

Sequoyah 1 Coatings Epoxy and epoxy-phenolic paints 10

Insulation Mirror RMI 28.6

2 Coatings Epoxy and epoxy-phenolic paints 10

Insulation Mirror RMI 28.6

Shearon Harris 1 Coatings Qualified coatings 5

Insulation Microtherm 28.6

Min-K 4

Mirror RMI 28.6

NUKON 17

Temp-Mat 11.7

Thermal-Wrap 17

South Texas 1 Coatings Qualified epoxy/IOZ coatings 5

Insulation Marinite 2

Microtherm 28.6

NUKON 7

Thermal-Wrap 7

Transco RMI 2

2 Coatings Qualified epoxy/IOZ coatings 5

Insulation Marinite 2

Microtherm 28.6

NUKON 7
A-114

Plant Name Unit Debris Type Debris ZOI 

(in D)

Thermal-Wrap 7

Transco RMI 2

St. Lucie 1 Coatings Qualified coatings 4

Insulation CalSil reinforced 3

CalSil unreinforced 5.45

NUKON 17

RMI 2

Transco Thermal-Wrap 17

2 Coatings Qualified coatings 4

Insulation Cal-Sil 5.45

Fiberglass (NUKON/Knaupf) 17

Foamglass 17

Jacketing 17

Mirror RMI 28.6

Transco RMI 2

Summer 1 Insulation RMI 28.6

Qual. 

coatings

Epoxy (Amercoat 66) 4

Epoxy (Ameron 89) 4

Epoxy (Nu-Klad) 4

Zinc (MobilZinc 7) 4

Surry 1 Asbestos 7

Coatings Qual. coatings 10

Insulation CalSil/asbestos 7

Cloth insulation jacketing 11.7

Fiberglass 17

Metal insulation jacketing 11.7

Paroc 5.4

Silicone Foam 28.6

TempMat 17

Transco RMI foil 2

Transco Thermal Wrap 17

2 Asbestos 7

Coatings Qual. coatings 10

Insulation CalSil/asbestos 7

Cloth insulation jacketing 11.7

Fiberglass 17

Metal insulation jacketing 11.7

Paroc 5.4

Silicone foam 28.6

TempMat 17

Transco RMI foil 2

Transco Thermal Wrap 17
A-115

Plant Name Unit Debris Type Debris ZOI 

(in D)

Three Mile 

Island

1 Coatings Qualified coatings 5

Insulation Jacketed NUKON 7

ThermoLag 330-1 28.6

Transco RMI 2

Unjacketed NUKON 17

Turkey Point 3 Coatings Qualified - concrete 4

Qualified - steel 4

Insulation CaI-Sil 5.45

Fiber 17

Microtherm, 28.6

RMI/jacketing 28.6

4 Coatings Qual. concrete 4

Qual. steel 4

Insulation CaI-Sil 5.45

NUKON (piping) 17

NUKON (Steam Gen.) 7

RMI Darchem/Transco 2

RMI mirror 28.6

Insulation 

jacketing

Mirror 28.6

RMI Darchem/Transco 2

Vogtle 1 Insulation Jacketed NUKON 8

Qual. 

coatings

Concrete coatings 4

Steel coatings 4

2 Insulation Jacketed NUKON 8

Qual. 

coatings

Concrete coatings 4

Steel coatings 4

Waterford 3 Coatings Qualified coatings 4

Insulation Jacketed NUKON 17

MEI 4

Microtherm 28.6

Min-K 28.6

Transco RMI 2

Unjacketed NUKON 17

Watts Bar 1 Fire barrier 3M-M20C fiber 11

Insulation Min-K fiber 10

RMI (stainless steel) 28.6

Particulate 3M M20C particulate 11

Alkyd paint 10

Carboline 295 10

Epoxy paint 10

Min-K Si0 2 10

Min-K TiC 2 10

Phenolic paint 10

Silicone paint 10
A-116

Plant Name Unit Debris Type Debris ZOI 

(in D)

2 Coating Protective Coatings (epoxy and epoxyphenolic paints)10

Insulation RMI 28.6

Wolf Creek 1 Coatings Qualified epoxy coatings 4

Unqualified coatings under destroyed 

insulation

10

Untopcoated IOZ primers 5

Insulation Cerablanket 28.6

Foamglass 28.6

Jacketed NUKON 5

Min-K 0

RMI with standard band 28.6

Thermal Wrap 5

Thermo-Lag 28.6
A-117

Table A.2-14. Chemical Buffer

Plant 

Name

Units

Sodium Hydroxide (NaOH)Trisodium Phosphate (TSP)Sodium Tetraborate (STB)Changed

Comments

ANO 1

In December 2007, a design modification was 

implemented to reduce the concentration of the 

sodium hydroxide (NaOH) chemical buffer.

ANO 2

The chemical buffer was changed to STB from 

TSP during the 2R19 refueling outage (spring 

2008).

Beaver 

Valley 1

Not clearly stated: "BVPS-1 and BVPS-2 are most 

closely represented by the conditions in ICET #4 -

fiberglass and calcium silicate insulation, and 

sodium hydroxide (NaOH) pH buffer."

Beaver 

Valley 2

BVPS-2 will be changing buffers from sodium 

hydroxide to sodium tetraborate during the fall 

2009 refueling outage.

Braidwood 1, 2

Byron 1,2 

Callaway 1

Calvert 

Cliffs 1

During the 2010 Refueling Outage the Unit I buffer 

was changed to sodium tetraborate decahydrate 

(STB).

Calvert 

Cliffs 2 The buffer material change was completed during 

the refueling outage in 2009 for Unit 2.

Catawba 1,2

Comanche 

Peak 1,2 Changed concentration of NaOH.

Crystal 

River 3

D.C. Cook 1,2

Davis 

Besse 1

Diablo 

Canyon 1,2

Farley 1,2

Fort 

Calhoun 1

Trisodium phosphate (TSP), the previous 

containment sump buffer was replaced with 

sodium tetraborate (STB) to reduce formation of 

chemical precipitates

Ginna 1

Indian 

Point 2 STB replaces TSP in Unit 2 

Indian 

Point 3 STB replaces NaOH in Unit 3
A-118

Plant 

Name

Units

Sodium Hydroxide (NaOH)Trisodium Phosphate (TSP)Sodium Tetraborate (STB)Changed

Comments

Kewaunee 1

McGuire 1,2

Millstone 2,3

North Anna 1,2

Oconee 1,2,3

Palisades 1

The containment sump buffer was changed from 

trisodium phosphate (TSP) to sodium tetraborate 

(STB)

Palo Verde 1,2,3

Point 

Beach 1,2

Prairie 

Island 1,2

Robinson 2

Salem 1,2

San Onofre 2,3

Seabrook 1

Sequoyah 1,2

Shearon 

Harris 1

South 

Texas 1,2

St. Lucie 1

St. Lucie 2

Summer 1

Surry 1,2

Three Mile 

Island 1

TMI Unit 1 filled the 23 installed TSP baskets with 

the TSP buffer chemical, and isolated the NaOH 

Tank, containing the removed buffer.

Turkey 

Point 3,4

In the September 1, 2005 response to GL 2004-

02, future plans to change the buffering agent to 

TSP prior to startup from the Turkey Point fall 

2006 refueling outage were discussed. Based 

upon the review of the IN, this buffer change will 

not be implemented.

Vogtle 1,2

Waterford 3

Watts Bar 1,2

Wolf Creek 1

Green shaded box indicates which buffer type is used

Red shaded box indicates the buffer type was changed
A-119

Downstream: Models

This field records the models used for the analysis of the components located downstream of 

the strainer. The models used for the ex-vessel and in-vessel analyzes are recorded separately 

in the GL-04-02 database.. In both cases, the models are grouped by exact spelling of the 

database entry such that “WCAP-16793-NP” and “WCAP-16793-NP, Revision 0”, for example, 

are treated as different entries.

Downstream: Strainer Bypass

This field records the amount of the debris that bypasses the strainer. The primary goal is to 

collect the bypass amount characterized in parts per million (ppm). Table A.2-15 shows all the 

data provided for the strainer bypass in ppm units. In addition to that data, all other information 

relative to the bypass characteristics of strainers were collected in this field. In that case, the 

Bypass Amount field was left blank, and all additional information was reported in the 

Comments. 

Downstream: Fuel Type

The GL-04-02 database also incorporates the fuel type currently loaded in the reactors. That 

information was provided directly by NRC (i.e., it wasn’t collected from GL-04-02 responses) in 

the form shown in Table A.2-16. That table was included entirely, without any modifications, 

into the GL-04-02 database. Table A.2-17 shows the same information grouped by the fuel 

type.

Downstream: Core Head Loss

The intent of this field was to collect the information on the pressure loss through the core. 

However, only one plant, Diablo Canyon, has reported a value of 2 ft (measured value at 41.1 

gpm) for the core head loss in GL-04-02 responses. No other plant provided the information on 

the core head loss.
A-120

Table A.2-15. Strainer Bypass Amount

Plant 

Name

Unit Debris Bypass 

Amount, 

ppm

Comments

Comanche 

Peak

1 Coatings 5927.36 Consists of qualified and unqualified epoxy, 

qualified CZ-11, and unqualified inorganic zinc 

and alkyd.

Fibrous 1.54 Consists of fiberglass, lead blanket fiberglass, 

Min-K, lead wool, and latent fibers.

Particulate 39.67 Consists of Min-K and latent particulate.

2 Coatings 5927.36 Consists of qualified and unqualified epoxy, 

qualified CZ-11, and unqualified inorganic zinc 

and alkyd.

Fibrous 1.54 Consists of fiberglass, lead blanket fiberglass, 

Min-K, lead wool, and latent fibers.

Particulate 39.67 Consists of Min-K and latent particulate.

Diablo 

Canyon

1 Coatings 278.2 The mass of debris in the recirculating fluid that 

passes through the sump is characterized in 

terms of parts per million (ppm).

Fibrous 8.2 The mass of debris in the recirculating fluid that 

passes through the sump is characterized in 

terms of parts per million (ppm).

Particulate 87.2 The mass of debris in the recirculating fluid that 

passes through the sump is characterized in 

terms of parts per million (ppm).

2 Coatings 278.2 The mass of debris in the recirculating fluid that 

passes through the sump is characterized in 

terms of parts per million (ppm).

Fibrous 8.2 The mass of debris in the recirculating fluid that 

passes through the sump is characterized in 

terms of parts per million (ppm).

Particulate 87.2 The mass of debris in the recirculating fluid that 

passes through the sump is characterized in 

terms of parts per million (ppm).

Ginna 1 497.8 The heat exchangers, orifices, and spray nozzles 

were evaluated for the effects of erosive wear for 

a constant debris concentration of 497.8 ppm over 

the mission time of 30 days.

Indian 

Point

2 822.1

3 818.6

Salem 1 Particulate 390 Test 4; Initial concentration was 3320 ppm and it 

decreased to 390 ppm after 3.5 hrs. Bypass 

samples were taken starting after the first fibers 

were introduced into the test loop from a sample 

line downstream of the strainer in the horizontal 

return line. After the initial sample, samples were 

taken every 3 minutes beginning with the initiation 

of the test until 15 samples had been taken. After 

the 15th sample was taken, a sample was taken 
A-121

Plant 

Name

Unit Debris Bypass 

Amount, 

ppm

Comments

at 1 hour and then samples were taken every 30 

minutes until the end of the test. The samples 

were taken in 500 ml bottles. Also, for 

downstream wear evaluation, 1.4% of the bypass 

factor was utilized.

2 Particulate 390 Test 4; Initial concentration was 3320 ppm and it 

decreased to 390 ppm after 3.5 hrs. Bypass 

samples were taken starting after the first fibers 

were introduced into the test loop from a sample 

line downstream of the strainer in the horizontal 

return line. After the initial sample, samples were 

taken every 3 minutes beginning with the initiation 

of the test until 15 samples had been taken. After 

the 15th sample was taken, a sample was taken 

at 1 hour and then samples were taken every 30 

minutes until the end of the test. The samples 

were taken in 500 ml bottles. Also, for 

downstream wear evaluation, 1.4% of the bypass 

factor was utilized.

South 

Texas

1 Coatings 744 The mass of debris in the recirculating fluid that 

passes through the sump is characterized in 

terms of parts per million (ppm). For downstream 

effects, the total initial debris concentration 

comprised of the individual debris concentrations 

is defined as the ratio of the solid mass of the 

debris in the pumped fluid to the total mass of 

water that is recirculated by the ECCS and CSS.

Fibrous 5.6 The mass of debris in the recirculating fluid that 

passes through the sump is characterized in 

terms of parts per million (ppm). For downstream 

effects, the total initial debris concentration 

comprised of the individual debris concentrations 

is defined as the ratio of the solid mass of the 

debris in the pumped fluid to the total mass of 

water that is recirculated by the ECCS and CSS.

Particulate 72.6 The mass of debris in the recirculating fluid that 

passes through the sump is characterized in 

terms of parts per million (ppm). For downstream 

effects, the total initial debris concentration 

comprised of the individual debris concentrations 

is defined as the ratio of the solid mass of the 

debris in the pumped fluid to the total mass of 

water that is recirculated by the ECCS and CSS.

2 Coatings 744 The mass of debris in the recirculating fluid that 

passes through the sump is characterized in 

terms of parts per million (ppm). For downstream 

effects, the total initial debris concentration 
A-122

Plant 

Name

Unit Debris Bypass 

Amount, 

ppm

Comments

comprised of the individual debris concentrations 

is defined as the ratio of the solid mass of the 

debris in the pumped fluid to the total mass of 

water that is recirculated by the ECCS and CSS.

Fibrous 5.6 The mass of debris in the recirculating fluid that 

passes through the sump is characterized in 

terms of parts per million (ppm). For downstream 

effects, the total initial debris concentration 

comprised of the individual debris concentrations 

is defined as the ratio of the solid mass of the 

debris in the pumped fluid to the total mass of 

water that is recirculated by the ECCS and CSS.

Particulate 72.6 The mass of debris in the recirculating fluid that 

passes through the sump is characterized in 

terms of parts per million (ppm). For downstream 

effects, the total initial debris concentration 

comprised of the individual debris concentrations 

is defined as the ratio of the solid mass of the 

debris in the pumped fluid to the total mass of 

water that is recirculated by the ECCS and CSS.

Watts Bar 1 Coatings 593

Fibrous 3

Particulate 308

Total 

debris

903

2 Coatings 593

Fibrous 1

Particulate 241

Total 

debris

835

Wolf Creek 1 Chemical 13 The mass of debris in the recirculating fluid that 

passes through the sump is characterized in 

terms of parts per million (ppm).

Coatings 26 The mass of debris in the recirculating fluid that 

passes through the sump is characterized in 

terms of parts per million (ppm).

Fibrous 85 The mass of debris in the recirculating fluid that 

passes through the sump is characterized in 

terms of parts per million (ppm).

Particulate 14 The mass of debris in the recirculating fluid that 

passes through the sump is characterized in 

terms of parts per million (ppm).
A-123

Table A.2-16. Fuel Type

Plant Name Unit

Westinghouse/CEAREVA

AREVA Fuel Type AREVA 

LA

ANO 1 FALSE TRUE Mark-BHTP

2 TRUE FALSE

Beaver Valley 1 TRUE FALSE

2 TRUE FALSE

Braidwood 1 TRUE TRUE Adv. Mark-BW(A) LAs

2 TRUE TRUE Adv. Mark-BW(A) LAs

Byron 1 TRUE FALSE

2 TRUE FALSE

Callaway 1 TRUE FALSE

Calvert Cliffs 1 TRUE TRUE Adv. 14x14 HTP LAs

2 TRUE TRUE Adv. 14x14 HTP LAs

Catawba 1 TRUE TRUE Adv. Mark-BW MOX 17x17 LAs

2 TRUE TRUE Adv. Mark-BW MOX 17x17 LAs

Comanche 

Peak 1 TRUE FALSE

2 TRUE FALSE

Crystal River 3 FALSE TRUE Mark-BHTP

D.C. Cook 1 TRUE FALSE

2 TRUE FALSE

Davis Besse 1 FALSE TRUE Mark-BHTP

Diablo 

Canyon 1 TRUE FALSE

2 TRUE FALSE

Farley 1 TRUE FALSE

2 TRUE FALSE

Fort Calhoun 1 TRUE TRUE 14x14 HTP

Ginna 1 TRUE FALSE

Indian Point 2 TRUE FALSE

3 TRUE FALSE

Kewaunee 1 TRUE FALSE

McGuire 1 TRUE FALSE

2 TRUE FALSE

Millstone 2 FALSE TRUE 14x14 HTP

3 TRUE FALSE

North Anna 1 TRUE TRUE Adv. Mark-BW 17x17

2 TRUE TRUE Adv. Mark-BW 17x17
A-124

Plant Name Unit

Westinghouse/CEAREVA

AREVA Fuel Type AREVA 

LA

Oconee 1 FALSE TRUE Mark-BHTP

2 FALSE TRUE Mark-BHTP

3 FALSE TRUE Mark-BHTP

Palisades 1 FALSE TRUE 15x15 HTP

Palo Verde 1 TRUE TRUE 16x16 HTP LAs

2 TRUE TRUE 16x16 HTP LAs

3 TRUE TRUE 16x16 HTP LAs

Point Beach 1 TRUE FALSE

2 TRUE FALSE

Prairie Island 1 TRUE FALSE

2 TRUE FALSE

Robinson 2 TRUE TRUE 15x15 HTP

Salem 1 TRUE FALSE

2 TRUE FALSE

San Onofre 2 TRUE TRUE 16x16 HTP LAs

3 TRUE FALSE

Seabrook 1 TRUE FALSE

Sequoyah 1 TRUE TRUE Mark-BW 17x17 LAs

2 TRUE TRUE Mark-BW 17x17

Shearon 

Harris 1 FALSE TRUE 17x17 HTP

South Texas 1 TRUE FALSE

2 TRUE FALSE

St. Lucie 1 FALSE TRUE 14x14 HTP

2 TRUE FALSE

Summer 1 TRUE FALSE

Surry 1 TRUE FALSE

2 TRUE FALSE

Three Mile 

Island 1 FALSE TRUE Mark-BHTP

Turkey Point 3 TRUE FALSE

4 TRUE FALSE

Vogtle 1 TRUE FALSE

2 TRUE FALSE

Waterford 3 TRUE FALSE

Watts Bar 1 TRUE FALSE

Watts Bar 2 FALSE Unit 2 is not operational yet

Wolf Creek 1 TRUE FALSE
A-125

Table A.2-17. Plants by Fuel Type

Fuel Type Plant Name Unit

1 2 3 4

AREVA ANO

Crystal River

Davis Besse

Millstone

Oconee

Palisades

Shearon Harris

St. Lucie

Three Mile Island

Westinghouse/CE ANO

Beaver Valley

Byron

Callaway

Comanche Peak

D.C. Cook

Diablo Canyon

Farley

Ginna

Indian Point

Kewaunee

McGuire

Millstone

Point Beach

Prairie Island

Salem

San Onofre

Seabrook

South Texas

St. Lucie

Summer

Surry

Turkey Point

Vogtle

Waterford

Watts Bar

Wolf Creek

Both Braidwood

Calvert Cliffs

Catawba

Fort Calhoun

North Anna

Palo Verde

Robinson

San Onofre

Sequoyah




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NUREG/CR-7172 Knowledge Base Report on Emergency Core Cooling Sump Performance

in Operating Light Water Reactors