NUREG-1918

Phenomena Identification and 

Ranking Table Evaluation of 

Chemical Effects Associated 

with Generic Safety Issue 191 

Office of Nuclear Regulatory Research 
This page intentionally left blank. 
NUREG-1918 

Phenomena Identification and 

Ranking Table Evaluation of 

Chemical Effects Associated 

with Generic Safety Issue 191 

Manuscript Completed: August 2008 

Date Published: February 2009 

Prepared by 

R.T. Tregoning1

, J.A. Apps2, W. Chen3, C.H. Delegard4, R. Litman5, 

D.D. MacDonald6

 

1

U.S. Nuclear Regulatory Commission 

 Washington, DC 20555-0001 

2

Lawrence Berkeley National Laboratory 

1 Cyclotron Road 

Berkeley, CA 94720 

3

Dow Chemical Co. 

2301 N. Brazosport Blvd. 

B-1603 

Freeport, TX 77541 

4

Pacific Northwest National Laboratory 

P.O. Box 999 

Richland, WA 99352 

5

Radiochemistry Laboratory Basics 

28 Hutchinson Drive 

Hampton, NH 03842 

6

Pennsylvania State University 

201 Steidle Building 

University Park, PA 16802 

J.P. Burke, NRC Project Manager 

NRC Job Code N6100 

Office of Nuclear Regulatory Research 
This page intentionally left blank.
ABSTRACT 

The U.S. Nuclear Regulatory Commission (NRC) issued Generic Letter 2004-02, 

“Potential Impact of Debris Blockage on Emergency Recirculation during Design Basis 

Accidents at Pressurized-Water Reactors (PWRs),” on September 13, 2004, as the 

primary vehicle for addressing and resolving concerns associated with Generic Safety 

Issue 191, “Assessment of Debris Accumulation on PWR Sump Performance.” 

Additionally, the NRC staff developed a safety evaluation of industry-developed 

guidance to provide an accepted method for evaluating PWR sump performance as 

requested in Generic Letter 2004-02. However, the safety evaluation and the industry 

guidance document provide little guidance for assessing chemical effects. The 

licensees are to address chemical effects on a plant-specific basis. 

Both the NRC and industry have sponsored research to provide additional information 

and develop some guidance for evaluating chemical effects. The NRC convened an 

external peer review panel to review the NRC-sponsored research conducted through 

the end of 2005 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 

emergency core cooling system performance during a hypothetical loss-of-coolant 

accident (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. It is 

anticipated that knowledge gained by ongoing and completed research will be 

considered along with the PIRT recommendations to identify and resolve existing 

knowledge gaps so that a more accurate chemical effects evaluation can be performed. 

The PIRT panel identified several significant chemical phenomena. These phenomena 

pertain to the underlying containment pool chemistry; radiological considerations; 

physical, chemical, 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. 

iii 
This page intentionally left blank.

iv 
FOREWORD 

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

has sponsored a series of research projects to inform the NRC’s regulatory decisions 

regarding the potential for chemical products to degrade emergency core cooling system 

(ECCS) performance in a pressurized water reactor (PWR) following a loss-of-coolant 

accident (LOCA). Specifically, the NRC has used the research to support the staff 

evaluation of licensee responses to Generic Letter (GL) 2004-02, “Potential Impact of 

Debris Blockage on Emergency Recirculation during Design Basis Accidents at 

Pressurized-Water Reactors (PWRs).” This GL is the principal vehicle for resolving 

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

Sump Performance.” The NRC convened an external panel to review the NRCsponsored research conducted through the end of 2005 and to broadly identify and 

evaluate additional chemical phenomena and issues that were either unresolved or not 

considered in the original NRC-sponsored research. NUREG-1861, “Peer Review of 

GSI-191 Chemical Effects Research Program,” issued December 2006, summarizes this 

review. 

The NRC also conducted a phenomena identification and ranking table (PIRT) exercise 

between March 2006 and June 2006 to more fully evaluate additional chemical effects 

that may affect ECCS performance. The PIRT panelists independently ranked the 

significance and current knowledge associated with chemical phenomena most likely to 

(1) contribute to sump screen clogging, (2) affect downstream component performance, 

(3) impact core heat transfer, or (4) degrade structural integrity. The PIRT identified and 

evaluated over 100 chemical effects phenomena. These phenomena pertain to the 

underlying containment pool chemistry; radiological considerations; physical, chemical, 

and biological debris sources; solid species precipitation; solid species growth and 

transport; organics and coatings; and downstream effects. This report focuses on those 

phenomena and their possible implications that one or more PIRT panelists identified as 

being potentially significant. In addition, the report identifies phenomena requiring 

additional consideration or evaluation. 

Since this PIRT was completed, the NRC staff has initially evaluated the more than 

40 phenomena that at least one PIRT panelist judged highly significant in this report. 

The staff expects some phenomena to improve ECCS performance and others to have 

no effect. The staff identified approximately 16 issues potentially deleterious to ECCS 

performance that merited additional scoping analysis to understand their significance. 

NUREG/CR-6988, “Final Report—Evaluation of Chemical Effects Phenomena in 

Post-LOCA Coolant,” summarizes this scoping analysis and has been able to resolve all 

but a few of these 16 phenomena. 

The staff is continuing to resolve issues associated with the potentially deleterious 

phenomena identified in this PIRT to assess their impact on ECCS performance. As 

part of this assessment, the staff will consider, as appropriate, plant-specific post-LOCA 

environments and conditions, results from additional vendor testing conducted since the 

conclusion of this scoping study, and additional evaluation to characterize the 

significance of these remaining issues with respect to the principal factors 

(e.g., particulate, chemical, and fiber concentrations) and conservatisms that licensees 

have used to address GL 2004-02. The staff will document the disposition of these 

remaining issues upon completion of this assessment. 

v 
This page intentionally left blank.

vi 
CONTENTS 

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

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

EXECUTIVE SUMMARY ................................................................................................. ix 

ACKNOWLEDGMENTS.................................................................................................. xv 

ABBREVIATIONS AND ACRONYMNS ..........................................................................xvi 

1 INTRODUCTION......................................................................................................1 

1.1 Description of Generic Safety Issue 191 ............................................................1 

1.2 Chemical Effects Background and Related Recent Research ...........................2 

1.2.1 ICET Program............................................................................................3 

1.2.2 ICET Precipitates: Physical Characteristics and Head-Loss Testing .......4 

1.2.3 Thermodynamic Analytical Simulations.....................................................6 

1.2.4 Industry-Sponsored Testing and NRC-Sponsored Confirmatory 

Evaluation..................................................................................................6 

1.2.5 Coatings Evaluation...................................................................................8 

1.3 Phenomena Identification and Ranking Table Motivation ..................................8 

2 PIRT OBJECTIVES AND SCOPE..........................................................................11 

3 PIRT APPROACH..................................................................................................13 

3.1 General PIRT Process .....................................................................................13 

3.2 Chemical Effects PIRT .....................................................................................15 

3.2.1 Panel Selection........................................................................................15 

3.2.2 Issue Definition and Background Information..........................................16 

3.2.3 Scenario Development ............................................................................17 

3.2.4 Chemical Effects Evaluation Criteria .......................................................19 

3.2.5 PIRT Issue Development.........................................................................20 

3.2.6 PIRT Issue Assessment ..........................................................................22 

4 CHARACTERIZATION OF PIRT FINDINGS AND USE OF RESULTS.................25 

5 RESULTS...............................................................................................................27 

5.1 Underlying Containment Pool Chemistry .........................................................39 

5.1.1 Effect of Boron.........................................................................................39 

5.1.2 Temperature and pH Evolution and Variability ........................................40 

5.1.3 Issues Related to Post-LOCA Buffering ..................................................41 

5.1.4 Dissolved Hydrogen Concentrations .......................................................43 

5.1.5 PIRT Research Recommendations .........................................................44 

5.2 Radiological Considerations.............................................................................45 

5.2.1 Effect of Radiolysis on Chemical Environment........................................45 

5.2.2 Effect of Radiation on the Properties of Solid Species ............................49 

5.2.3 PIRT Research Recommendations .........................................................49 

5.3 Physical, Chemical, and Biological Debris Sources .........................................49 

5.3.1 Debris Generation ...................................................................................50 

5.3.2 Physical Debris........................................................................................52 

5.3.3 Post-LOCA Chemically Induced Debris...................................................54 

5.3.4 Biological Debris......................................................................................59 

5.3.5 PIRT Research Recommendations .........................................................60 

5.4 Solid Species Precipitation...............................................................................63 

5.4.1 Post-LOCA Precipitation Mechanisms ....................................................63 

5.4.2 Thermal Effects .......................................................................................64 

5.4.3 PIRT Research Recommendations .........................................................66 

5.5 Solid Species Growth and Debris Transport ....................................................67 

5.5.1 Particulate Growth and Agglomeration....................................................68 

5.5.2 Settling and Deposition............................................................................69 

vii 
5.5.3 PIRT Research Recommendations .........................................................70 

5.6 Coatings and Organics.....................................................................................71 

5.6.1 Coatings ..................................................................................................71 

5.6.2 Organics ..................................................................................................73 

5.6.3 PIRT Research Recommendations .........................................................75 

5.7 Downstream Effects .........................................................................................77 

5.7.1 ECCS Pumps ..........................................................................................77 

5.7.2 RHR Heat Exchangers ............................................................................78 

5.7.3 Reactor Core ...........................................................................................79 

5.7.4 PIRT Research Recommendations .........................................................83 

6 CONCLUSIONS.....................................................................................................85 

6.1 Underlying Containment Pool Chemistry .........................................................86 

6.2 Radiological Considerations.............................................................................86 

6.3 Physical, Chemical, and Biological Debris Sources .........................................86 

6.4 Solid Species Precipitation...............................................................................87 

6.5 Solid Species Growth and Debris Transport ....................................................88 

6.6 Organics and Coatings.....................................................................................88 

6.7 Downstream Effects .........................................................................................89 

7 REFERENCES.......................................................................................................91 

APPENDICES 

Appendix A: Curriculum Vitae for PIRT Panelists.........................................................A-1 

Appendix B: Principal Physical Attributes of the LOCA Accident Sequence ................B-1 

Appendix C: PIRT Issue Summary .............................................................................. C-1 

Appendix D: PIRT Response Tables ........................................................................... D-1 

Appendix E: PIRT Panelist Evaluations of T1 Phenomena ..........................................E-1 

Appendix F: PIRT Panelist Evaluations of T2 Phenomena ..........................................F-1 

Appendix G: PIRT Panelist Evaluations of T3 Phenomena ......................................... G-1 

Appendix H: PIRT Panelist Evaluations of T4 Phenomena ......................................... H-1 

Appendix I: PIRT Panelist Evaluations of T5 Phenomena ...........................................I-1 

FIGURES 

Figure 1: General PIRT Process....................................................................................14 

TABLES 

Table 1: PIRT Panelists...............................................................................................16 

Table 2: Selected Post-LOCA Plant Parameters ........................................................19 

Table 3: Containment Pool Buffering Agents and pH Ranges ....................................19 

Table 4: Importance Ranking Scheme ........................................................................22 

Table 5: Knowledge Assessment Ranking Scheme....................................................22 

Table 6: Categorization of PIRT Phenomena..............................................................26 

Table 7: Summary Rankings for T1 Phenomena ........................................................28 

Table 8: Summary Rankings for T2 Phenomena ........................................................29 

Table 9: Summary Rankings for T3 Phenomena ........................................................31 

Table 10: Summary Rankings for T4 Phenomena ........................................................34 

Table 11: Summary Rankings for T5 Phenomenon ......................................................38 

Table 12: Additional Phenomena Identified Separately from the PIRT Exercise ..........38 

Table 13: Post-LOCA Containment Pool Temperatures................................................ 40 

viii 
EXECUTIVE SUMMARY 

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

Sump Performance,” was established to assess the potential for debris transport and 

accumulation of debris generated during a loss-of-coolant accident (LOCA) to impede or 

degrade emergency core cooling system (ECCS) performance in operating commercial 

pressurized-water reactors (PWRs). The U.S. Nuclear Regulatory Commission (NRC) 

issued Generic Letter (GL) 2004-02, “Potential Impact of Debris Blockage on Emergency 

Recirculation During Design Basis Accidents at Pressurized-Water Reactors (PWRs),” 

on September 13, 2004, as the primary vehicle for addressing and resolving concerns 

associated with GSI-191. Additionally, the NRC staff developed a safety evaluation (SE) 

of the May 28, 2004, Nuclear Energy Institute report, “Pressurized Water Reactor 

Containment Sump Evaluation Methodology.” This SE provides one NRC-approved 

method for evaluating PWR sump performance as requested in GL 2004-02. However, 

the SE does not provide specific guidance for evaluating chemical effects to address 

concerns initially raised by the Advisory Committee on Reactor Safeguards. The SE 

specifies that licensees address chemical effects on a plant-specific basis. 

Both the NRC and industry have sponsored research to provide additional information, 

and develop some guidance for evaluating chemical effects. These programs 

collectively have demonstrated that, under certain conditions, chemical precipitates can 

form that may significantly affect head loss across ECCS containment sump strainer 

screens. Some metrics or thresholds have also been established to indicate when 

significant head loss increases can result. 

The NRC convened an external peer review panel to both review the NRC-sponsored 

research conducted up through the end of 2005 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 process followed the general approach that has been used and refined over 

the last several years at the NRC. The first step was to select the panelists and provide 

relevant background information on post-LOCA scenario and emergency system 

functions and operations. The issues and objective of the PIRT were then defined, and 

the LOCA scenario was characterized at distinct time intervals after the initial pipe break 

to provide a framework for developing issues. Next, the following four technical 

evaluation criteria were established for ranking chemical phenomena most likely to do 

the following: 

(1) contribute to sump screen clogging, 

(2) affect downstream component performance, 

(3) impact core heat transfer, or 

(4) degrade structural integrity. 

Brainstorming was used to identify phenomena for consideration. The panelists 

completed the PIRT evaluation independently to identify the significance and knowledge 

level associated with each phenomenon. Rankings were finalized after discussing the 

rationales behind the independent rankings for those issues. Despite the discussions, 

ix 
occasional strong dissenting opinions arose among experts or even between one expert 

and the rest of the group. 

The PIRT results are not intended to represent a comprehensive set of chemical 

phenomena or issues within the post-LOCA environment. Instead, these phenomena 

should be considered in the context of important findings from past research (Section 

1.2) and informed by research completed since the PIRT was conducted. It is 

anticipated that knowledge gained by related research will be considered along with the 

PIRT recommendations to identify and resolve existing knowledge gaps so that a more 

accurate review of the chemical effects evaluations in the GL 2004-02 licensee 

submittals can be performed. 

The PIRT phenomena fall into one of four different classifications. The first class 

(Category I) represents those phenomena or issues that are generally known or have 

been demonstrated to be significant by prior research. Additional aspects associated 

with these issues (i.e., variables and parameters) have also been well characterized. 

The second class (Category II) includes phenomena or issues that either are expected 

to be significant by the PIRT panelists or have been demonstrated to be significant by 

prior research. However, their implications with respect to ECCS performance are not 

well known. The third category (Category III) includes phenomena that are potentially 

significant but are not well understood, and the ECCS performance implications are 

highly uncertain. The fourth category (Category IV) represents phenomena that have no 

engineering significance as determined by both the aggregate PIRT rankings and 

individual rankings and justifications. Categories II and III summarize issues where 

further research could be used to address remaining uncertainties. 

The significant PIRT issues are grouped topically in the report. These issues pertain to 

underlying containment pool chemistry; radiological considerations; physical, chemical, 

and biological debris sources; solid species precipitation; solid species growth and 

transport; organics and coatings; and downstream effects. A summary of issues is 

provided at the end of each topical area discussion. Emphasis is placed on those issues 

falling into Categories II and III that may benefit from additional evaluation. 

Several of these issues (Category II) can be addressed using existing knowledge 

associated with the chemical effect. Additional analysis may be needed only to assess 

the implications of these issues over the range of existing generic or plant-specific postLOCA conditions. Other issues (Category III) may require additional study to more fully 

understand the chemical effects and determine if they are relevant. Then, the practical 

generic or plant-specific implications can be assessed. These issues are summarized 

below for each topical area. 

Underlying Containment Pool Chemistry 

• Additional investigation on the effect of concentrated boron salts within the 

reactor pressure vessel (RPV) could determine whether any significant corrosion 

of the reactor vessel internals and fuel cladding occurs in the post-LOCA period. 

• Also, the effects of concentrated borate on the types, amounts, and properties of 

chemical precipitates that could form within the RPV should be considered. 

• Plant-specific hydrogen ion concentration (pH) and temperature history should be 

considered in combination with various postulated debris mixtures within the 

x 
buffered environment. This evaluation would provide a necessary foundation for 

accurately determining the dissolved species, material corrosion and dissolution 

rates, and precipitate formation based on solubility and kinetic considerations. 

Variability in important factors should also be evaluated to determine the effect of 

changes or uncertainty in the underlying environment. 

• Additional scoping calculations are needed to assess the magnitude and relative 

effect of hydrogen production from a variety of sources, including the Schikorr 

reaction, to determine if dissolved hydrogen plays a significant role. 

Radiological Considerations 

• Consideration of radiological effects is warranted to first understand the 

magnitude of the concentrated radioactive fields in the post-LOCA environment. 

Then, the effects of changes in the reduction-oxidation potential on the 

containment pool chemistry, material corrosion rates, and chemical speciation 

and solubility can be evaluated. 

• The likelihood of transport and accumulation of activated species at the sump 

screen debris bed should be assessed to determine the strength of the resulting 

radiation field. Localized chemical effects resulting from radionuclides trapped 

within the debris bed and the effect of radiation on the properties of precipitated 

solid species should then be considered. 

Physical, Chemical, and Biological Debris Sources 

• The possibility and extent of corrosion product spallation from reactor vessel 

walls, primary system piping and components, and fuel cladding surfaces under 

conditions that would occur under post-LOCA thermal and mechanical shock 

should be examined. 

• The possibility that potential chemical precipitates could form due to retrograde 

solubility at the hot reactor fuel clad surface, and subsequently spall, should be 

investigated. 

• Plant-specific debris sources, dissolved calcium concentrations, and sump 

environmental conditions should be considered to assess the implications of 

calcium carbonate formation from atmospheric carbon dioxide on both the solid 

species inventory and, more importantly, its effect on precipitation kinetics. 

However, the amount of carbon dioxide provided by the air in the containment 

vessel may produce only negligible calcite compared with containment pool 

debris generated from other sources (e.g., fiberglass insulation, concrete, ir 

calcium silicate insulation). 

• Realistic, plant-specific containment pool environment, materials, and 

concentrations should be considered to identify the appropriate corrosion 

acceleration or inhibition factors. One acceleration factor that should be studied 

is the catalytic effect of possible containment materials such as copper and 

citrate (or potentially other hydroxy organic-acid anions, if present). 

• Possible corrosion inhibition effects include concrete and other non-metallic 

material aging products. Specifically, phosphate, chromate, dichromate, silicate, 

xi 
and borate can inhibit aluminum corrosion and deposition of copper on aluminum 

may inhibit or accelerate corrosion. It will be important to understand plantspecific conditions in order to credit these inhibition effects. 

• The effect of significant alloying additions in nuclear structural materials and 

debris or compositional changes in nonmetallic materials within the containment 

on the material dissolution rates should be considered. This evaluation should 

also determine whether significant dissolved concentrations of alloying or 

secondary elements are present that could alter chemical effects. 

• Galvanic couples that may exist within the containment pool, caused by direct 

contact between dissimilar metals, should be identified and evaluated to 

determine if they alter material corrosion rates. 

• The viability and potential consequences of biological growth in a post-LOCA, 

borated-water environment should be investigated. If significant growth is 

possible within 30 days, an understanding of important post-LOCA variables that 

may accelerate or retard the biological growth rate would be necessary to both 

identify locations within the ECCS where growth is possible and evaluate the 

associated implications. 

Solid Species Precipitation 

• A realistic or conservative assessment of relevant combinations of time, 

temperature, pH, and ionic strength should be performed to determine the types, 

sizes, and concentrations of solid precipitates that may form under plant-specific 

conditions and to determine the significance of ripening through polymerization 

on these precipitates. 

• Precipitation studies should also consider solid species precipitation that results 

from the cooling of the ECCS water at the heat exchanger and heating within the 

RPV. 

• Research could also be useful to identify whether conservative or realistic postLOCA environmental conditions are sufficient to foster co-precipitation, and to 

characterize any species that form. 

Solid Species Growth and Debris Transport 

• Variability in important post-LOCA variables (i.e., materials, temperatures, pH, 

buffering systems, etc.) should also be evaluated to determine if the effect on 

agglomeration is significant. This study could be used to demonstrate that both 

chemical precipitates created in single-effects or integrated-effects testing and 

surrogate precipitates produced outside the testing environment are 

representative of materials that form in post-LOCA conditions. 

• Research on transport phenomena may be necessary to validate reducing the 

suspended solid particulate caused by settling and deposition. Variability in the 

plant design, containment materials, containment flow rates and turbulence, 

pH buffer, and the chemical conditions present caused by various hypothetical 

pipe breaks are important considerations that may affect the settling rates of 

containment pool debris. 

xii 
Organics and Coatings 

• The potentially significant coating issues to address, as indicated by the PIRT 

panelists, are leaching from metallic coatings and the decomposition of organics 

within coatings by thermolysis and radiolysis under either realistic or conservative 

post-LOCA conditions. 

• More general research in the effects of organics should be preceded by a 

realistic assessment of possible post-LOCA organic sources (e.g., oils, greases, 

electrical insulations, plastic coatings, paints, etc.) and concentrations in the 

containment pool. If sufficient organic sources exist, additional research would 

then be useful to determine the leaching behavior of these sources and to 

examine the ability of the organic materials to coalesce and/or bind inorganic 

solids as they cool within the post-LOCA containment pool and consequently 

affect flow through the sump strainer screen. 

• The interaction between organic materials and inorganic solids may increase the 

buoyancy of inorganic solids such that it restricts settling but not so great as to 

promote flotation. Additional study would need to determine if organic buoyancy 

can occur within the range of post-LOCA conditions existing at PWR plants and if 

the effect suspends, but does not float, significant debris concentrations that 

would otherwise settle. The engineering impact of organic buoyancy is 

significantly diminished if settling of containment pool solids is not credited in a 

chemical effects evaluation. 

• The implications of hydrothermal hydrolysis under either realistic or conservative 

post-LOCA conditions have not been studied. The most susceptible coatings 

and insulation materials could be evaluated to determine the propensity for 

interactions among hydrothermal hydrolysis byproducts and with other 

containment pool species. 

Downstream Effects 

• The corrosion and erosion characteristics (i.e., hardness and particle size) of 

chemical products and concentrations could be assessed to determine if pump 

seal and internal components can be adversely affected. Magnetite and other 

similar particles created during crud release are expected to potentially be the 

most detrimental. 

• The pertinent chemical effects related specifically to heat exchanger performance 

are deposition and clogging. A conservative analysis of deposition may be 

sufficient to determine if adequate heat exchanger design margins remain. The 

precipitation kinetics could be studied to determine if solid species concentrations 

at these lower temperatures are less than assumed from either aqueous 

concentrations or solubility considerations. Evaluation of the flow conditions at 

the tube inlet location may also provide information to evaluate the propensity for 

heat-exchanger clogging. 

• Evaluation of the chemical products that precipitate and subsequently adhere to 

the reactor fuel could be useful to determine deposit thickness and heat transfer 

characteristics. The propensity for spallation of chemical products from the fuel 

xiii 
cladding could also be studied to evaluate the additional solid products that may 

be formed and their implications for either reactor core or sump screen clogging. 

• The effect of the physical and chemical solid debris, both formed within and 

transported to the reactor core, on the heat capacity of the ECCS coolant water 

should also be considered. However, it is expected that the debris loading would 

have to be significant before the heat capacity is affected. Therefore, 

conservative engineering evaluations may be sufficient to assess the impact on 

the core thermal and hydraulic transfer. 

• Implications of flow blockages in locations other than the reactor core inlet nozzle 

and localized heating effects within individual fuel elements should also be 

considered. It may be possible to use analysis or credit existing operator actions 

to demonstrate that acceptable fuel heat transfer is maintained. 

• It will be important to be mindful of potential synergistic effects related to reactor 

core temperature increases stemming from the downstream effect phenomena 

when evaluating chemical precipitation within the containment pool, at the heat 

exchanger, or within the reactor core. 

• The production of hydrogen, hydrogen peroxide, oxygen, and hydroxyl anion 

within the reactor core should be considered when evaluating the reductionoxidation potential of the ECCS water and other applicable post-LOCA chemical 

effects. 

These issues will be resolved separately by the NRC staff as part of the closure process 

for GSI-191. The following additional information will be considered in resolving each of 

the issues above: 

(1) plant-specific post-LOCA environments and conditions, 

(2) research findings from industry-sponsored and NRC-sponsored chemical-effect 

studies completed subsequent to the PIRT, 

(3) chemical effects evaluation guidance developed by the NRC, and 

(4) additional scoping analysis to characterize the significance of these remaining 

issues with respect to the principal factors (e.g., particulate, chemical, and fiber 

concentrations) and conservatisms that licensees have used to address 

GL 2004-02. 

Consideration of this information was either unavailable at the time of the PIRT or 

outside the scope of this exercise. If consideration of items 1–4 above is insufficient to 

resolve the issues identified in this report, more in-depth evaluation and study may be 

required. The disposition of the issues identified in this report will be documented 

separately. 

xiv 
ACKNOWLEDGMENTS 

The principal authors of this report gratefully acknowledge the assistance of several 

people who integrally contributed to both the peer review of U.S. Nuclear Regulatory 

Commission (NRC)-sponsored chemical effects research and the phenomena 

identification and ranking table (PIRT) exercise. Two peer review/PIRT meetings were 

held, one at Argonne National Laboratory (ANL) and one at the Center for Nuclear 

Waste Regulatory Analysis (CNWRA). These meetings were graciously and efficiently 

hosted, and the assistance of the participating support staff at each organization is 

appreciated. There were several presenters at each meeting who provided critical 

technical information to the panel. Dr. Bruce Letellier of Los Alamos National Laboratory 

(LANL), B.P. Jain of the NRC, John Giscoln of the Electric Power Research Institute, 

and Tim Andreychek of Westinghouse summarized the post-loss-of-coolant accident 

(LOCA) sequence and conditions. Dr. Letellier gave the presentation, “Principal 

Physical Attributes of the LOCA Accident Sequence” (Appendix B) which was used both 

as reference information and to help establish the framework for the PIRT. Each of the 

laboratories conducting NRC-sponsored activities also provided current research 

summaries at each meeting, as follows: Dr. Bill Shack and Dr. Jong-Hee Park for ANL, 

Dr. Bruce Letellier and Dr. Marc Klasky for LANL, and Dr. Vijay Jain and Dr. Jude 

McMurry for CNWRA. 

Several other individuals provided technical information during the meeting to support 

issue formulation and evaluation. These include the aforementioned presenters and 

Ralph Architzel, Shanlai Lu, and Paul Klein of the NRC’s Office of Nuclear Reactor 

Regulation. Dr. Bruce Letellier of LANL was integral in helping to formulate the PIRT 

framework, organize issues, facilitate brainstorming and discussion, take meeting 

minutes, and determine evaluation strategies. Ann Ramey Smith and Paulette Torres of 

the NRC’s Office of Regulatory Research are also thanked for creating tabular 

summaries of the issues formulated during the brainstorming sessions. Paulette Torres 

is also appreciated for summarizing and collating the peer review findings in 

NUREG-1861. This is a necessary companion document. 

Finally, the authors wish to thank the various NRC reviewers of this document. They 

include NRC staff Ching Ng, John Burke, Ervin Geiger, Paul Klein, Shanlai Lu, John 

Lehning, Ralph Architzel, and Matthew Yoder and former NRC staff Steven Unikewicz. 

Their contributions have made this a more accurate and comprehensive document. 

xv 
This page intentionally left blank.

xvi 
ABBREVIATIONS AND ACRONYMNS

 10 CFR 50.46 

 ACRS 

 Ag 

 Al 

 AlNa12SiO5

 Al(OH)3 

AlO(OH) 

 ANL 

 Al2PO4(OH)3 

 

 B 

 BO3

- 

 BWR 

 

 Ca 

 Ca2+

 Ca3(PO4)2

 CaCl2

 CaCO3

 Ca(OH)2

 Cal-Sil 

 CH3CO2

-

 C3H4OH(COO)3

3-

 Cl 

 CNWRA 

 Co 

 CO2

 CO3

2-

 C2O4

2-

 Cr 

 CrO4

2-

 Cr2O7

2-

 C-S-H 

 CSS 

 Cu 

 DBA 

 

 ECCS 

 EDS 

 EPRI 

 

 F 

 Fe 

 Fe3O4

 FeOOH 

 Fe(OH)2

 Fe(OH)3

 FSAR 

Title 10, Section 50.46 of the Code of Federal Regulations

Advisory Committee for Reactor Safeguards 

silver 

aluminum 

sodium aluminosilicate 

aluminum hydroxide 

aluminum oxyhydroxide 

Argonne National Laboratory 

augelite 

boron 

perborates 

boiling-water reactor 

calcium 

calcium cations 

calcium phosphate 

calcium chloride 

calcium carbonate 

portlandite 

calcium silicate 

acetate 

citrate 

chlorine 

Center for Nuclear Waste Regulatory Analysis 

cobalt 

carbon dioxide 

carbonate 

oxalate 

chromium 

chromate 

dichromate 

calcium silicate hydrate 

containment spray system 

copper 

design-basis accident 

emergency core cooling system 

energy Dispersive Spectroscopy 

Electric Power Research Institute 

Fluorine 

iron 

magnetite 

iron oxyhydroxide 

iron(II) hydroxide 

iron(III) hydroxide 

final safety analysis report 

xvii 
 GL generic letter 

 GSI-191 Generic Safety Issue 191 

 H hydrogen 

 HAsO4

2-/H2AsO41- arsenate 

 HELB high-energy line break 

 HCO3

- bicarbonate 

 HNO3 nitric acid 

 H2O2 hydrogen peroxide 

 HPO4

2-/H2PO41- phosphate 

 ICET integrated chemical effects testing 

 In Inconel® 

LANL Los Alamos National Laboratory 

 LB large break 

 LOCA loss-of-coolant accident 

 

 Mg magnesium 

 Mn manganese 

 Mo7O24

6- molybdate 

N2 atmospheric nitrogen 

 NaBO2 sodium metaborate 

 NaOH sodium hydroxide 

 Nb niobium 

 NEI Nuclear Energy Institute 

 Ni nickel 

 NO3

- nitrate 

 NPSH net positive suction head 

 NRC Nuclear Regulatory Commission 

 NRR Office of Nuclear Reactor Regulation 

 NUKON® commercial fiberglass insulation 

 

 O oxygen 

 OH hydroxyl radicals 

 

 pH hydrogen ion concentration 

 Pb lead 

 PIRT phenomena identification and ranking tables 

 PW R pressurized-water reactor 

 PZC point of zero charge 

 

 RCP reactor coolant pump 

 RCS reactor coolant system 

 Redox reduction-oxidation 

 RHR residual heat removal system 

 RMI reflective metal insulation 

 RPV reactor pressure vessel 

 RWST refueling water storage tank 

xviii 
 S sulfur 

 Sb antimony 

 SCC stress corrosion cracking 

 SE safety evaluation 

 SiO2 silicon dioxide 

SiO4

4- and SiO32- silicates 

 SO4

2- sulfate 

 SS stainless steel 

 STB sodium tetraborate 

 

 TH thermohydraulic 

 TMI Three Mile Island 

 TSP trisodium phosphate 

 

 WCAP Westinghouse Commercial Atomic Power 

 

 Zn zinc 

 ZOI zone of influence 

 Zr zirconium 

 ZrO2 zirconium oxide 

xix 
1 INTRODUCTION 

1.1 Description of Generic Safety Issue 191

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

Performance,” [1] was established to assess the potential for debris transport and 

accumulation of debris generated during a loss-of-coolant accident (LOCA) to impede or 

degrade emergency core cooling system (ECCS) performance in operating commercial 

pressurized-water reactors (PWRs). The ECCS is required to meet the criteria of 

Title 10, Section 50.46, “Acceptance Criteria for Emergency Core Cooling Systems for 

Light-Water Nuclear Power Reactors,” of the Code of Federal Regulations

(10 CFR 50.46) [2]. In 10 CFR 50.46(b)(5), the U.S. Nuclear Regulatory Commission 

(NRC) requires that licensees design the ECCS with capability for long-term cooling. 

After successful initiation, the ECCS must provide adequate cooling to maintain the peak 

cladding temperature below 2200 °F, limit cladding oxidation, limit hydrogen (H) 

generation, and sustain a core geometry that is amenable to cooling. 

A common hypothetical scenario addressed by GSI-191 is as follows. A high-energy 

line break (HELB) inside PWR containment damages and dislodges materials near the 

break such as thermal insulation, coatings, and concrete. Actuation of the containment 

spray system (CSS) then washes a fraction of this debris and preexisting debris in 

containment (referred to as latent debris) down onto the containment floor. 

Simultaneously, the containment floor is gradually filling with CSS, reactor coolant, and 

borated water injected from the refueling water storage tank (RWST). The borated water 

is injected into the reactor to ensure core cooling and provide acceptable boron 

concentration to ensure shutdown margin that terminates fission in the core. The postLOCA debris comingles with water from these various sources as the containment fills. 

At some time, depending on the size of the break, the RWST is depleted, and ECCS 

pump operation is changed to draw water from the containment sump and recirculate the 

existing debris-laden water that has accumulated within the containment floor pool. 

Once recirculation starts, a fraction of containment pool debris is transported to the 

sump screen where it either accumulates or is ingested into the pump suction line. If 

debris accumulates on the sump screen, the head loss across the screen will increase. 

If enough debris accumulates, the concern is that it could reach a critical loading such 

that the net positive suction head (NPSH) is insufficient to ensure the successful 

operation of the ECCS and CSS pumps. 

Alternatively, debris that passes through the sump screen raises additional concerns, 

which are collectively referred to as “downstream effects.” For instance, the debris could 

plug or cause excessive wear of close-tolerance components or deposit on surfaces 

within the ECCS or CSS. Plugging or wear might cause a component to degrade to the 

point where its performance characteristics fall below the design-basis requirements. 

Also, debris blockage at flow restrictions within the ECCS could impede coolant 

recirculation through the reactor core, leading to inadequate core cooling. Debris could 

also deposit on the reactor fuel, reducing the efficiency of heat transfer to the circulating 

fluid. 

1 
Chemical effects could also occur during one or several stages of this hypothetical 

scenario. Chemical effects are broadly defined as any chemically induced phenomenon 

that might contribute to either head loss across the sump screen or deleterious system 

performance caused by downstream effects. Possible chemical effects include the 

formation of chemical by-products (e.g., precipitates, scale, reduction-oxidation (redox) 

and dissolution) caused by the interaction of containment materials with the post-LOCA 

environment and degradation of containment materials caused by chemical processes 

within the post-LOCA environment. Containment materials literally encompass all 

materials present in containment and notably include LOCA-generated debris, latent 

debris, structural materials for reactor system components (e.g., piping, reactor pressure 

vessel (RPV), steam generators, heat exchangers, reactor internal structures, etc.), 

containment structural materials, ECCS pump, valve, and heat-exchanger internal 

components, intact insulation and electrical materials, and reactor fuel. 

On September 13, 2004, the NRC issued Generic Letter (GL) 2004-02, “Potential Impact 

of Debris Blockage on Emergency Recirculation during Design Basis Accidents at 

Pressurized-Water Reactors (PWRs),” [3] as the primary vehicle for addressing and 

resolving concerns associated with GSI-191. The GL requested that all PWR licensees 

use an NRC-approved method (1) to perform a mechanistic evaluation of the potential 

for post-accident debris blockage and operation with debris-laden fluids to impede or 

prevent the recirculation functions of the ECCS and CSS following all postulated 

accidents for which these recirculation functions are required and (2) to implement plant 

modifications or other corrective actions that the evaluation identifies as necessary to 

ensure system functionality. 

Additionally, the NRC staff developed a safety evaluation (SE) [4] of the May 28, 2004, 

Nuclear Energy Institute (NEI) report, “Pressurized Water Reactor Containment Sump 

Evaluation Methodology,” dated May 28, 2004 (see enclosures to transmittal letter in 

[5]). The NEI report, as modified by the SE, provides one NRC-approved method for 

evaluating PWR sump performance as requested in GL 2004-02. The SE specifies that 

nuclear plant licensees address chemical effects on a plant-specific basis. Licensees 

can use existing information and generic test results by providing technical justification 

demonstrating the applicability to their plant(s). Licensees also have the option of 

pursuing plant-specific testing and analysis. However, the SE does not provide a 

specific method that is considered acceptable for evaluating chemical effects. The staff 

has prepared draft evaluation guidance (see enclosures to transmittal letter in [6]) for 

licensees’ chemical effect analyses to ensure that chemical effect issues are adequately 

resolved within the context of the GL 2004-02 responses. 

1.2 Chemical Effects Background and Related Recent Research

The Advisory Committee for Reactor Safeguards (ACRS) initially recommended that an 

adequate technical basis should be developed to resolve associated sump performance 

issues related to chemical reactions [7]. This recommendation was based, in part, on 

the gelatinous material that was observed in a water sample taken from the bottom of 

the Three Mile Island (TMI) containment following the accident in 1979 [8]. It has not 

been possible to determine the direct relevance of this finding to post-LOCA chemical 

effects because of the atypical nature of the TMI event. A significant amount of 

Susquehanna River water leaked from service water system relief valves and was mixed 

with the reactor coolant system (RCS) water in containment. The river water in the TMI 

2 
configuration was used to provide emergency cooling to service water systems [9]. An 

additional confounding factor was that the containment water samples were collected 

approximately 5 months after the event, allowing more time for solid species reactions to 

occur than in the 30-day post-LOCA period of most concern. In order to assess 

chemical effects in post-LOCA PWR environments, the NRC and the nuclear industry 

have sponsored a number of research programs. 

1.2.1 ICET Program 

An initial limited-scope study was performed by Los Alamos National Laboratory (LANL) 

to evaluate potential chemical effects occurring following a LOCA [10]. This study 

assessed the potential for chemically induced corrosion products to impede ECCS 

performance. In some of these tests, aluminum (Al), zinc (Zn), or iron (Fe) nitrates were 

added to the test water to induce chemical precipitation between the metals and other 

anionic species in order to assess the associated head loss. The tests showed that gel 

formation with a significant accompanying head loss across a fibrous bed was possible, 

although the test conditions and evolution of chemical species were not prototypical of a 

post-LOCA PWR environment. 

Therefore, a more comprehensive integrated chemical effects testing (ICET) program 

was conducted under the joint sponsorship of the NRC and the Electric Power Research 

Institute (EPRI) [11]. The primary objectives for the ICET test series were to (1) 

determine, characterize, and quantify chemical reaction products that may develop in the 

containment pool under a representative post-LOCA environment and (2) determine and 

quantify any amorphous or gelatinous material that could be produced during the postLOCA recirculation phase. 

The ICET program consisted of five 30-day tests with each test representing a unique 

environment. Each environment was intended to represent a portion of the commercial 

PWR plants such that the entire series would broadly characterize containment pool 

materials and conditions applicable to the existing US PWR nuclear plants after a 

hypothetical LOCA. Representative types and amounts of submerged and unsubmerged 

materials were evaluated based on plant surveys [12]. The primary variables that 

changed during each test were the buffering agent (i.e., sodium hydroxide (NaOH), 

sodium tetraborate (STB), or trisodium phosphate (TSP)) and the insulation materials 

(i.e., 100 percent fiberglass or 80 percent calcium silicate (Cal-Sil) and 20 percent 

fiberglass). 

Companion thermodynamic simulations and corrosion and leaching studies were 

conducted at the Center for Nuclear Waste Regulatory Analysis (CNWRA) at the 

Southwest Research Institute [13] to determine the need for a pressurized test loop and 

the efficacy of isothermal testing to evaluate long-term (i.e., several days) chemical 

effects in ICET. The study predicts that the high-temperature and pressure conditions 

existing during the initial stages of a LOCA have a negligible influence on the long-term 

chemical effects. Based on this work, the ICET program was conducted at atmospheric 

pressure and a constant temperature. A temperature of 60 °C was chosen for ICET to 

broadly represent the steady-state sump temperatures predicted for several plant 

configurations [12]. 

3 
1.2.2 ICET Precipitates: Physical Characteristics and Head-Loss Testing 

The ICET results indicate that (1) chemical reaction products with varied quantities, 

consistencies, attributes, and apparent formation mechanisms were found in each unique 

ICET environment; (2) containment materials (metallic, nonmetallic, and insulation 

debris), hydrogen ion concentration (pH), buffering agent, temperature, and time are all 

important variables that influence chemical product formation; and (3) changes to one 

important environmental variable (e.g., a pH adjusting agent or insulation material) can 

significantly affect the chemical products that form. Specifically, amorphous aluminum 

hydroxide (Al(OH)3) [14] precipitates were observed upon cooling in ICET Tests 1 and 5 

and similar Al-based products were observed in the Tests 1, 4, and 5 fiberglass insulation 

along with other particulate deposits on the outside of the insulation bundles. Calcium 

phosphate (Ca3(PO4)2) was observed within the test solution within 1 hour of initiating 

ICET Test 3, and similar products were apparent in fiberglass insulation in Tests 2 and 3 

along with other particulate deposits on the outside of the insulation bundles. Another 

notable observation occurred on the eighth day of ICET Test 3 when the turbine-type flow 

meter stopped working. Scale and precipitation deposits, which were later determined to 

be a mix of Cal-Sil and Ca3(PO4)2, had accumulated on the turbine inside the flow meter, 

preventing the turbine from moving [11]. 

The ICET program provided insights and initial understanding of the solution chemistry 

and of the types and amounts of chemical reaction products that could form in the ECCS 

containment pool. However, while the ICET program demonstrated that plant-specific 

differences in important variables could significantly alter the observed chemical effects, 

it was difficult to extrapolate the results to other conditions based on the limited testing 

performed. Subsequently, the NRC sponsored follow-on work at LANL to more fully 

understand the formation of the amorphous Al(OH)3 precipitate in NaOH and STB 

environments (ICET Tests 1, 4, and 5). Additionally, this work evaluated the behavior of 

Al over a broader range of conditions (i.e., pH, temperature, and solution age) that might 

exist throughout the PWR following a LOCA [14]. 

Examination of the precipitates of ICET Tests 1 and 5 revealed largely amorphous 

Al(OH)3 with a substantial quantity of boron (B) (up to 35% of the initial dissolved B) 

adsorbed onto the surface. Complexation between Al and B was found to be 

responsible for impeding the crystallization of Al compounds. Aluminate ions (Al(OH)4

-

) 

are the only stable form of Al in an alkaline solution. The solubility is a function of solid 

hydroxide phases and increases with pH in alkaline solutions. The presence of some 

organics and inorganics can also increase the Al solubility. The solubility can also be 

affected by the discrete particle size in the solution [14]. Nanometer-sized particles were 

found in the ICET Tests 1 and 5, and transmission electron microscopy measurements 

revealed that colloids, with a mean radius of 65 nm, did exist at ambient temperature in 

these solutions. This work also found that the corrosion of Al in ICET Test 4 was 

inhibited by sodium silicate formed by the dissolution of Cal-Sil. 

Although the ICET program demonstrated that chemical products could form under these 

representative post-LOCA conditions, there was no evaluation of the head-loss 

characteristics or downstream implications of chemical products observed during testing. 

Therefore, the NRC sponsored further research at Argonne National Laboratory (ANL) to 

evaluate the head loss associated with chemical byproducts observed during the ICET 

series and to understand the effect of relevant changes within the post-LOCA environment 

on head loss, chemical byproduct formation, and the physical characteristics of these 

4 
byproducts [15]. In contrast to the focus on Al of the LANL ICET follow-on study [14], the 

initial ANL research focused on conditions affecting Ca3(PO4)2 formation and settling within 

TSP environments (ICET Tests 2 and 3). 

The ANL testing demonstrated that calcium (Ca) from representative Cal-Sil insulation 

loadings and with representative TSP dissolution rates caused significant pressure drop 

across a test bed when the amount of dissolved Ca was greater than 25 ppm (6.2x10-4

M). Also, significant head loss may result from the precipitation of Ca3(PO4)2 which 

forms either within the containment pool and is transported to the sump screen, or from 

continued Cal-Sil dissolution within a sump screen debris bed. The head losses 

associated with pure physical debris beds of commercial fiberglass insulation 

(NUKON®) and Cal-Sil were generally much smaller than those that occurred across 

debris beds in which some of the Cal-Sil was replaced with a corresponding amount of 

Ca3(PO4)2 precipitates. Debris beds formed solely from Ca3(PO4)2 in a TSP-buffered 

environment caused little pressure drop as the precipitate by itself did not form a 

continuous debris bed across the test screen. 

Testing demonstrated that the Cal-Sil dissolution rate (for the concentrations studied) is 

not strongly dependent on the TSP dissolution rate for realistic TSP dissolution rates. 

However, even for a Cal-Sil suspended-solid concentration as low as 0.5 g/l, the 

dissolved Ca concentration reached levels within a few hours that led to significant head 

loss in these tests. Settling tests of Ca3(PO4)2 under no bulk directional flow found that 

at higher dissolved Ca concentrations (300 ppm (7x10-3 M)) the precipitates can 

agglomerate and settle more quickly. However, approximately one-half of the total 

precipitate settles more slowly than the agglomerated precipitate. At a lower dissolved 

Ca concentration (75 ppm (1.9x10-3 M)), the estimated settling velocity is 0.8 cm/min. 

ANL also evaluated head loss from Al precipitates that were intended to be similar to the 

amorphous Al(OH)3 precipitates in ICET Tests 1 and 5. Dissolved Al from aluminum 

nitrate was used to produce dissolved the Al concentrations which were observed in ICET 

more expeditiously than in a 30-day test. The testing also demonstrated that head loss in 

NaOH environments could be significant down to 100 ppm (4x10-3 M) of dissolved Al, even 

though visible precipitate is not apparent. Also, head loss was shown to be a strong 

function of the precipitate solubility limit, which varies with Al concentration, temperature 

and time at temperature. 

These initial studies [15] also indicated that no significant head loss in STB-buffered 

solutions at a pH of approximately 8.3 occurs unless the dissolved Al is greater than 

50 ppm (2x10-3 M). Post-LOCA containment pool dissolved Al concentrations higher than 

50 ppm (2x10-3 M) are not expected in most plants. Follow-on testing was performed to 

characterize the long-term solubility limits and head-loss characteristics of Al precipitates 

in STB-buffered environments [16]. The findings suggest that a concentration of 50 ppm 

(2x10-3 M) Al can be maintained in STB-buffered solutions with a pH of 8.4 at 70–80 °F for 

periods of at least 20 days without the formation of significant amount of precipitate 

product, or head loss. In these tests, concentrations greater than 70 ppm (3x10-3 M) 

caused measurable head loss. 

5 
1.2.3 Thermodynamic Analytical Simulations 

In parallel with the experimental programs at LANL and ANL, CNWRA was contracted to 

evaluate the feasibility of using commercially available thermodynamic simulation codes 

for predicting chemical species formation in a typical PWR post-LOCA containment 

environment [17]. Specifically, CNWRA evaluated codes initially through blind prediction 

of the ICET series using the existing thermodynamic speciation database associated with 

each code and either published corrosion or leaching rate data or rates experimentally 

determined by CNWRA using small-scale testing. Follow-on calibrated analysis of the 

ICET series was conducted by disallowing solid precipitation of species that were not 

observed in ICET. 

Results of this study indicate that thermodynamic simulation codes can be broadly useful 

in assessing the potential effects of post-LOCA interaction on sump screen blockage. 

However, their predictive capability is often hindered by insufficient thermodynamic data 

for relevant phases and aqueous species in the code database and by limitations in the 

kinetic data for the dissolution of reactive materials in the presence of co-dissolving 

materials. Prediction of chemical byproduct concentrations and species by these codes is 

most accurate when the system is in equilibrium. But they can be quite inaccurate if 

equilibrium has not been achieved. However, benchmarking the results using relevant 

experimental data can determine if the predicted species and concentrations are 

representative for carefully defined conditions. 

1.2.4 Industry-Sponsored Testing and NRC-Sponsored Confirmatory Evaluation 

The nuclear industry has also sponsored a study to provide input to plant licensees on the 

type and amounts of chemical precipitates that may form post-LOCA for testing of 

replacement sump screens. The study evaluated leaching and corrosion data of various 

containment materials over a wider range of pH and temperature conditions than those 

tested in the ICET program [18]. The materials, pH, and temperature conditions were 

determined via plant surveys. The study partitioned containment materials into 15 material 

classes based on their chemical composition and tested 1 material from the 10 classes 

presumed to have the potential for causing chemical effects in the containment sump: Al, 

aluminum silicate, Cal-Sil, carbon steel, concrete, electrical grade glass (i.e., E-glass), 

amorphous silica, Interam E class insulation, mineral wool, and Zn. 

Single-material, single-effect dissolution testing was conducted and the largest dissolved 

concentrations consisted of Al, silicon (Si), and Ca. Based on this, it was assumed that 

these elements are the most likely to form precipitates. Subsequent room temperature 

single-material (and a few dual-material) precipitation and filterability tests of materials 

containing these elements were conducted and precipitates from the following materials 

were observed for certain pH values: Al, Fiber Frax insulation, galvanized steel, fiberglass 

insulation, concrete, mineral wool, and Cal-Sil (when TSP buffering was used). The 

STB-buffered tests did not induce any additional precipitates. The three principal 

precipitates were assumed to be aluminum oxyhydroxide (AlO(OH)), sodium 

aluminosilicate (AlNa12SiO5), and Ca3(PO4)2 based on energy dispersive spectroscopy 

(EDS) analysis. None of the precipitates settled readily. These test observations are 

generally consistent with the earlier NRC-sponsored studies discussed above [11 and 

14-16]. 

6 
The results from these studies are being used for the following two related applications: 

(1) to develop a tool for predicting the amount of chemical products in specific plant 

environments, and 

(2) to develop a procedure for generating chemical surrogates for use in large-scale 

validation testing simulating individual plant configurations. 

The predictive tool is based on the experimental testing results for determining the 

dissolution rate of species under plant conditions. All dissolved materials that form 

during each time step are then assumed to precipitate instantaneously into Ca3(PO4)2, 

AlO(OH), and/or AlNa12SiO5. The particular precipitates depend on the plant materials 

and type of buffer. Methods and acceptance criteria are largely aimed at ensuring that 

agglomeration does not occur. These criteria are provided for producing surrogate 

precipitates that are intended to behave similarly to the above precipitates during 

strainer testing. 

The NRC recently published a safety evaluation [19] of the Westinghouse Commercial 

Atomic Power (WCAP) report [18]. To support this safety evaluation, the NRC 

sponsored research to confirm certain aspects of the WCAP report and the intended 

applications of the results. Specifically, leaching and precipitation studies were 

conducted by CNWRA [20]. The three main objectives of these studies were (1) to 

examine the assumption that sample materials selected in the WCAP report [18] were 

sufficiently representative that their dissolution characteristics could be generalized from 

one product to the others in the same materials class, (2) to more definitively 

characterize any observed precipitates, and (3) to obtain leaching test data for concrete 

with a sample-to-solution ratio that was more representative of actual plant conditions 

than that in the WCAP report [18]. 

In general, the CNWRA results did not contradict the assumption that the leaching 

behavior of an individual material in a given materials class is representative of all 

materials in the class. However, not all materials were tested to conclusively validate 

this assumption either. Additionally, except for some of the Cal-Sil tests, the dissolved 

concentrations of elements in the CNWRA test leachates were similar to or lower than 

those measured in the WCAP report [18]. It was speculated that either differences in 

actual materials, age or storage conditions, or the greater agitation of samples used in 

the WCAP report [18] may have led to the differences in the dissolution results. 

More importantly, no visible, settled precipitates were observed to 85 days after 

dissolution in any of the CNWRA tests at room temperature, even for experiments using 

the same materials and test conditions in which precipitates formed in the WCAP report 

[18]. Thermodynamic simulations of the CNWRA leachant concentrations often verified 

that the CNWRA solutions were unsaturated with respect to likely low-temperature 

species. Alternatively, in some cases supersaturation with solid species was predicted. 

However, corresponding filterability or head-loss testing was not performed to determine 

whether microscopic solids existed. Finally, leaching from concrete coupons was more 

dilute than that measured in the WCAP report [18] for a ratio of the material area to 

coolant volume that was conservative compared to plant survey information. No 

supersaturation solid phases were observed to precipitate in this testing either, nor were 

any of these phases predicted by thermodynamic modeling. 

7 
Research at ANL [16] was sponsored to evaluate the physical characteristics and 

head-loss performance of WCAP surrogate Al precipitates relative to the precipitates 

generated during earlier NRC-sponsored tests. The study determined that the Al ionic 

concentration affects the precipitate size. Higher-concentration solutions produce larger, 

denser precipitates that settle more rapidly. The WCAP surrogate preparation 

procedures do produce fine precipitates, and the addition of a small amount of 

precipitate equivalent to 5 ppm (2x10-4 M) of dissolved Al resulted in immediate, 

significant head loss across a fiberglass debris bed. However, the precipitates did have 

a different appearance than those in earlier testing [11 and 15], and the ANL study did 

not attempt to determine whether these surrogates are representative of precipitates 

produced under post-LOCA conditions. 

1.2.5 Coatings Evaluation 

The ICET Program did include representative quantities of inorganic Zn-coated carbon 

steel specimens in the test chamber [12]. These specimens were included to represent 

materials having Zn-rich primer applied without an additional topcoat and materials with 

Zn-rich primer exposed because of delamination of the topcoat [12]. No other topcoated 

specimens were included in ICET, primarily because choosing a “representative” coating 

was not possible given the variety of qualified and unqualified [21] systems that exist in 

containment. Limited testing [22] shows that several qualified epoxy systems are not 

expected to leach substantially in alkaline environments. However, this testing typically 

measured only chloride (Cl), fluoride (F), total halogens, and sulfate concentrations in 

the analysis of the leachate analysis. Additionally, these test solutions were not 

representative of post-LOCA borated containment pool chemistries and were not 

exposed to post-LOCA radiation conditions. 

Argonne National Laboratory conducted a limited open-literature search [23] for 

information on the leaching characteristics of coatings in nuclear power plant 

environments. Coating supply companies were also contacted for information on the 

leaching characteristics of coatings in representative PWR post-LOCA environments. 

The survey generally found little information on leachability, leaching rate, and the 

potential leaching constituents of such coatings as a function of temperature, pH, and 

radiolytic conditions. The bulk of the qualification testing was conducted to demonstrate 

that the coatings do not fail under (1) design-basis accident (DBA) pressures and 

temperatures [21] and (2) radiation exposures expected over the plant’s service life [24]. 

Although the ANSI standard [21] implies that coating samples should be irradiated 

before DBA testing, this is not an explicit requirement. Subsequent testing of qualified 

[25] and unqualified (i.e., original equipment manufacturer) [26] coating specimens has 

evaluated the impact of radiation-induced aging on coating failure under DBA conditions. 

1.3 Phenomena Identification and Ranking Table Motivation

The various research programs summarized above have significantly advanced the 

understanding of chemical effects with the post-LOCA containment environment. There 

is increased knowledge of material dissolution behavior in post-LOCA environments for 

a variety of common insulation and metallic materials through both single-effect and 

integrated testing. These programs collectively have also demonstrated that, under 

certain conditions, chemical products can form and significantly affect head loss across 

fibrous debris beds. Furthermore, these programs have also provided some 

understanding about the variables affecting the formation of Ca3(PO4)2 or amorphous 

8 
Al(OH)3 precipitates observed during ICET. Additionally, some metrics or thresholds 

have been established to indicate when significant increases in head loss can result 

from those precipitates. 

However, there are several fundamental issues that have not been addressed by these 

research activities. For instance, the effect of several materials that are expected to 

exist in containment (e.g., coatings, organics, activated species, etc.) and the influence 

of certain post-LOCA conditions (e.g., realistic post-LOCA containment temperature 

profiles, flow through sediment, galvanic effects, radiolytic effects, and the ratio of the 

containment air to pool volume) on chemical effects have not been addressed by ICET 

or other research programs. Also, ICET and other programs held important variables 

constant in a given test, and a complete range of plant-specific conditions for important 

variables has not been studied. It was also not possible to quantify either the mass of 

various chemical precipitates or the exact conditions leading to precipitation of these 

species under representative post-LOCA conditions in order to more readily assess 

plant-specific implications. 

The general concern is that in a plant-specific environment under actual post-LOCA 

conditions, significantly different chemical effects than those observed and studied 

based on the ICET and other single-effect testing observations may occur. This concern 

is buttressed by the fact that the ICET Test1 NaOH environment created amorphous 

Al(OH)3 precipitates that significantly affected head loss in fiberglass debris beds for the 

ICET quantities of submerged Al. However, one test variable change in ICET Test 4—

the addition of substantial Cal-Sil insulation—minimized Al corrosion through silicate 

surface inhibition [14], and an amorphous Al(OH)3 precipitate did not form. Further, the 

ability of chemical effects to degrade ECCS component performance downstream of the 

sump screen (i.e., downstream effects) was not addressed in any of these activities. 

To address these concerns, the NRC convened a panel of five experts spanning a range 

of applicable technical disciplines. The panel had two objectives. The first objective was 

to review the NRC-sponsored research conducted through the end of 2005. The 

programs reviewed were (1) the ICET program [11] and follow-up analysis [14], 

(2) chemical speciation analysis [17], and (3) accelerated chemical effects head-loss 

testing [15]. Technical summaries of these projects can be found in Sections 1.2.1–

1.2.3. Specifically, the reviewers were asked to comment on the general quality of the 

research and the applicability of the results for interpreting post-LOCA chemical effects 

in PWRs. The review findings are summarized in [27] and individual reviews from all the 

reviewers are provided in the appendices. 

Generally, the reviewers concluded that the ICET program was broadly representative of 

plant chemical conditions and did identify some important contributing materials and 

chemical interactions. The reviewers also indicated that the chemical speciation 

analysis did demonstrate the difficulties with using commercially available codes without 

proper calibration and consideration of the chemical species that may develop in the 

post-LOCA environment. A fundamental problem with such codes is that they calculate 

the species composition at the minimum of the Gibbs energy of the system. If the 

system is not at the minimum Gibbs energy, use of these codes may lead to erroneous 

results. The reviewers agreed that more rigorous code development would be 

necessary to develop an adequate assessment tool that models the kinetics associated 

with these environments. 

9 
The reviewers shared the view that although the large-scale chemical effects head-loss 

testing project demonstrated that head-loss implications from ICET-observed products 

can be significant, more work is needed to quantify the effects. There was also a 

general opinion that additional smaller scale testing should be conducted to allow more 

rapid evaluation of chemical phenomena that have not been considered and that the 

range of applicability of the current results should be extended to understand the effects 

of key variables such as time, temperature, and pH. This latter work would allow the 

results to be interpreted and applied to specific plant post-LOCA environments. 

Additional findings and recommendations are contained in [27]. 

The second objective of the peer review panel was to identify additional chemical 

phenomena and issues that were not considered in the original NRC-sponsored 

research and that formed the basis for many of the concerns identified earlier in this 

section. A phenomena identification and ranking table (PIRT) exercise was conducted 

to achieve this objective and fully explore the possible chemical effects that may affect 

ECCS performance during a hypothetical LOCA scenario. The remainder of this report 

details the objective of the PIRT exercise, the approach for selecting the experts and 

conducting the PIRT, and a summary of potentially significant phenomena or issues that 

were identified. Most of these phenomena or issues were identified during the PIRT, but 

there were a few unique issues raised in the individual peer reviews contained in [27] 

that have been incorporated as well. The intent is that these phenomena and issues will 

be addressed, as appropriate, to ensure that chemical effects are adequately considered 

in the demonstration of acceptable ECCS performance as requested in GL 2004-02 [3]. 

There have been several nuclear applications that have used the PIRT process. 

Examples include the scaling of thermohydraulic codes [28], the development of various 

light-water reactor accident scenarios [29, 30, and 31], the assessment of containment 

coatings research issues [32], fission product transport during the manufacturing, 

operation, and accident life-cycle phases associated with tristructural-isotropic (TRISO) 

fuel [33]. Most recently the NRC’s Office of Nuclear Regulatory Research used the 

PIRT process to assess aging materials degradation in commercial PWR and boilingwater reactor (BWR) plants [34]. Additionally, several PIRT exercises were conducted 

to evaluate debris transport in wet and dry containments during a LOCA to identify 

important phenomena to address within the context of GSI-191 [35 and 36]. 

10 
2 PIRT OBJECTIVES AND SCOPE 

The principal objective of the PIRT exercise was to fully explore the possible chemical 

phenomena (e.g., solids, films, precipitates and effects), which could occur during a 

hypothetical LOCA scenario that may affect ECCS performance and possible reactor 

fuel damage caused by inadequate heat removal. Chemical effects were examined 

starting at the RCS pipe break, which initiates the LOCA, through the ECCS injection 

phase and CSS initiation, through the onset of ECCS recirculation, and up to 30 days 

after the accident. Time periods beyond 30 days were not considered in this analysis 

because the required reactor decay heat removal rate is typically low by this time, and 

ECCS margins are typically large. Thirty days also provides sufficient time for licensees 

to implement any necessary additional emergency mitigation measures to ensure 

adequate core cooling. Hence, this is a convenient termination point for the scenario. 

However, as stipulated in 10 CFR 50.46, the licensee still has the responsibility for 

ensuring long-term reactor core cooling beyond this timeframe. 

The PIRT process identified the following three types of issues: 

(1) issues that had been demonstrated during the previously research activities, 

(2) remaining issues or questions related to this prior research, and 

(3) entirely new issues that have not been previously addressed. 

The PIRT was focused on identifying issues that could significantly affect ECCS 

performance by either altering sump screen clogging and head loss, affecting 

downstream component performance, modifying the reactor core heat transfer, or 

influencing structural integrity of important components. The PIRT also identified the 

state of knowledge associated with each issue so that more mature, or known, issues 

could be separated from issues that are not currently as well understood. Although the 

focus of the PIRT was on identifying potentially deleterious chemical effects, several 

advantageous, or potentially advantageous, chemical effects were also identified and 

evaluated. 

11 
This page intentionally left blank.

12 
3 PIRT APPROACH 

 

The PIRT process followed the general approach that has been used and refined over 

the last several years [37]. The first step was to select the panelists and provide 

relevant background information. The issues and objective of the PIRT were then 

defined, and the LOCA scenario was defined using distinct time intervals after the initial 

pipe break to provide context for the issue development. Next, the evaluation criteria 

were established in concert with the panelists. 

Once the framework was established, brainstorming among the panelists and facilitators 

was used to identify phenomena for consideration. Summary tables of phenomena were 

then created and reviewed by the experts to clarify issues in the attempt to develop 

common understanding on the definition and implications associated with each issue. 

The summary table review was also used to reach consensus among the panelists on 

the final phenomena to be evaluated. The panelists independently completed the PIRT 

evaluation to identify the significance and knowledge level associated with each 

phenomenon. Discussion was held after the initial individual evaluations for issues 

where the initial independent rankings revealed a strong difference of opinion among the 

experts or where just one dissenting opinion existed. The PIRT rankings were then 

finalized after this discussion. More details on the PIRT process used to identify and 

evaluate post-LOCA chemical effects on ECCS performance are provided subsequently. 

3.1 General PIRT Process

The PIRT process was originally developed in the late 1980s [28] to characterize issues 

associated with scaling thermal-hydraulic codes and assessing uncertainty. The 

process has evolved over subsequent applications into a relatively mature technique 

[34]. A PIRT is fundamentally based on expert opinion. As such, enlisting experts with 

the requisite technical expertise and experience is a critical step in the process. The 

PIRT follows a structured process that is documented for accuracy and to enhance 

clarity. The PIRT often initially attempts to identify all relevant technical factors or issues 

within a given technical area (e.g., chemical effects). Technical factors or issues are 

defined as processes, phenomena, condition, characteristics, etc. that may exist within 

the technical area and alter the implications. The PIRT then seeks informed opinions 

about the significance and knowledge levels associated with the issues identified. 

Informed opinions are provided as both quantitative rankings and qualitative justifications 

that support the rankings [37]. 

The PIRT outcomes are meant to be fluid and capture the state of knowledge existing at 

a particular time. Significant issues can be validated or changed as additional insights, 

data, and experience are acquired [37]. A PIRT can be conducted at any point during 

the evaluation of a specific technical area. The most opportune time is when decisions 

are needed to determine the general direction of future research and analysis within the 

technical area. 

A PIRT can be used to identify fundamental issues that should be initially addressed 

when a technical area is first being considered. It is expected that changes in the PIRT 

outcomes are more likely for these issues when either the science is immature or great 

13 
uncertainty exists. In mature technical areas, a PIRT can be used to determine which, if 

any, issues remain in order to gain sufficient understanding before developing final 

solutions. Alternately, the PIRT can be conducted after scoping and other initial 

research activities have been completed in order to identify what future work is needed. 

This last alternative is most applicable to post-LOCA chemical effects. Research has 

clearly indicated that various chemical effects can be significant. Several potential solid 

species precipitates have also been identified and some significance metrics or 

thresholds have been established for the formation and implication of these precipitates. 

The nine identified formal steps in a PIRT process [37] are summarized in the Figure 1

flowchart. While the flowchart depicts a serial progression between each of the steps, 

iteration among the various steps is more common. Steps 1–5 are typically defined by 

the sponsor or facilitator of the PIRT. The expert panel provides the information 

developed in Steps 6–8 in concert with a facilitator. Documentation is shown as Step 9, 

but in reality it occurs throughout the process to capture important decisions, definitions, 

and ideas that are necessary to complete the PIRT. 

Step 1

Issue Definition

Step 2

PIRT Objectives

Step 4

Hardware Scenario

Step 5

Evaluation Criterion

Step 3

Background Information

Step 6

Identify Phenomena

Step 7

Importance Ranking

Step 8

Knowledge Level

Step 9

Document PIRT

Step 1

Issue Definition

Step 2

PIRT Objectives

Step 4

Hardware Scenario

Step 5

Evaluation Criterion

Step 3

Background Information

Step 6

Identify Phenomena

Step 7

Importance Ranking

Step 8

Knowledge Level

Step 9

Document PIRT

Figure 1: General PIRT Process 

It is informative to briefly step through the general process as described in [37]. Issue 

definition (Step 1) describes the primary motivation for conducting the PIRT. It defines 

the technical area or most global issue that the PIRT will address. The stated PIRT 

objectives (Step 2) provide the specific outcome or results being sought. The focus, 

content, and uses of the PIRT follow from the objectives. Background information 

(Step 3) relates to relevant information developed before that PIRT that can be used as 

a basis for determining the PIRT outcomes. Some examples of background information 

are design information, calculations, experimental data, or presentations by the experts. 

14 
The next step (Step 4) is to identify the hardware and/or configuration that are affected 

by the issue and define the scenario to be evaluated. This scenario could be real or 

hypothetical and describes the conditions that the hardware encounters. It can often be 

helpful to divide the scenario into major phases [37]. The evaluation criteria (Step 5) are 

used to judge the relative importance of each phenomena or issue. These criteria 

should be directly related to implications associated with the scenario in the previous 

step. Ideally, the criteria are explicit, easy comprehended and measurable [37]. 

The phenomena or technical issues are identified next (Step 6). These issues are 

developed by the experts and are informed by their experience and by background 

information associated with the issue (Step 3). It is important that no ranking or 

evaluation of these phenomena occur at this step so that uncensored brainstorming can 

occur. Also, the issues should have precise written definitions after this step. These 

definitions help ensure that the experts have a consistent, common definition for 

evaluating the issue (Steps 7 and 8). The definitions can also be important in resolving 

ranking inconsistencies. 

The significance or importance ranking is performed by each expert (Step 7) with 

respect to the evaluation criteria (Step 5). Brief written rationales are also provided to 

support each importance rank. Any number of ranking schemes is appropriate. In 

practice, consistent application of the scheme has proven to be more important than the 

specifics of the scheme [37]. This experience favors a simpler scheme. The knowledge 

assessment (Step 8) is then provided for each phenomenon or issue. Once again, 

written rationale is used to support the knowledge assessment, and simple assessment 

schemes are favored for consistency. As mentioned, PIRT documentation (Step 9) 

occurs during all previous steps, but it is especially important to summarize the specific 

PIRT approach for the technical area addressed and to document the findings. 

3.2 Chemical Effects PIRT

The chemical effects PIRT followed the general PIRT framework described in the 

previous section. The specific application of the PIRT process for chemical effects is 

subsequently described. 

3.2.1 Panel Selection 

Expert selection was performed within the initial effort to conduct a peer review of NRCsponsored research activities [27]. In general, the specific technical expertise common 

to both the peer review and PIRT was initially identified by NRC staff and contractors 

conducting NRC-sponsored research (Section 1.2). Technical expertise was sought in 

areas such as gelatinous material and amorphous product formation and 

characterization, analytical chemistry, metallic corrosion and leaching processes, 

experimental chemical testing and analysis, theoretical chemistry and speciation 

prediction; industrial filtration processes, and fluid treatment processes. 

Once the required expertise was determined, the selection criteria were determined. 

The primary selection criteria were to collectively aggregate the most relevant and 

highest quality technical expertise while spanning all the identified technical areas. An 

objective was also to provide approximately equal representation among the technical 

areas so that the opinions consistent within, and possibly unique to, one particular 

discipline were less likely to dominate. Another selection criterion was organizational 

15 
experience. Broad organizational representation and experience was sought so that 

different perspectives were available. Specifically, candidates were sought from 

academia, the nuclear industry, research laboratories, chemical processing industries, 

and filtration industries. It was determined that at least one of the experts should have 

nuclear plant experience in order to provide relevant, practical guidance to the remaining 

group members about the conditions prevalent in commercial nuclear plants. 

The NRC staff, contractors, the ACRS, and nuclear industry representatives provided 

recommendations for suitable candidates with expertise in one or more of the identified 

technical areas. Staff then screened the initial pool based on the evaluation criteria. A 

list of 17 candidates was then developed and most were contacted to gauge availability 

and interest. Each candidate supplied a resume with information relevant to the 

evaluation criteria. The candidate resumes and independent recommendations were 

then used to evaluate candidates with respect to the evaluation criteria and make the 

final panel selections. The list and areas of technical expertise of the peer review and 

PIRT panelists are provided in Table 1. Curriculum vitae are provided in Appendix A. 

Table 1: PIRT Panelists 

Name Affiliation Areas of Technical Expertise 

John 

Apps 

Senior Scientist, 

Earth Sciences Division, 

Lawrence Berkeley National Laboratory 

• Geochemical modeling 

• Gel formation and characterization 

• Chemical speciation modeling 

• Nuclear waste isolation 

Wu 

Chen 

Senior Specialist, 

Dow Chemical Company 

• Fluid/particle separation 

• Industrial filtration processes 

Calvin 

Delegard 

Senior Scientist, 

Pacific Northwest National Laboratory 

• Experimental testing and analysis 

• Analytical chemistry 

• Nuclear material safeguards 

Robert 

Litman 

Analytical Chemist, 

Radiochemistry Laboratory Basics 

• Analytical chemistry 

• Metallic corrosion processes 

• Nuclear industry experience 

Digby 

Macdonald 

Distinguished Professor and Director of 

the Center for Electrochemical Science 

and Technology, Pennsylvania State 

University 

• Electrochemistry and thermodynamics 

• Metallic corrosion processes 

• Experimental testing and analysis 

3.2.2 Issue Definition and Background Information 

The PIRT was initiated with a presentation at the PIRT kick-off meeting to articulate and 

develop the PIRT framework (Steps 1–5 in Figure 1). The issue (Step 1, Figure 1) was 

defined as follows: Operating experience, experimental testing, and analysis have 

demonstrated that chemical effects in post-LOCA containment environments may 

contribute to an inability to adequately cool the reactor core after a LOCA. 

The PIRT objective (Step 2, Figure 1) was to identify chemical phenomena (e.g., solids, 

films, precipitates, and effects) which could lead to deleterious ECCS performance and 

possible reactor fuel damage caused by inadequate heat removal in a post-LOCA 

16 
environment. See Section 2 for more detail. It was also indicated that the PIRT report 

would summarize the phenomena evaluated and indicate those significant or potentially 

significant phenomena that should be considered to ensure that chemical effects are 

appropriately addressed when evaluating ECCS performance. 

Most of the background information necessary to conduct the PIRT (Step 3, Figure 1) 

had been previously provided to the experts as part of the general peer review. Two 

separate meetings were held before the PIRT to address panelist questions, conduct 

general discussion, and seek a common understanding of the issues. A presentation 

was provided during each meeting to review the PWR post-LOCA accident sequence. 

Current technical reports (e.g., NUREG/CR publications, test reports, and quick look 

reports) pertaining to the NRC-sponsored chemical effects research that has been 

conducted to date (summarized in Sections 1.2.1–1.2.3) were provided before each 

meeting. Additionally, presentations and discussions were held during the meeting with 

the panelists and the contractors conducting each research program. Finally, NRC 

personnel knowledgeable in ECCS performance and related GSI-191 issues were 

available at each meeting to address questions. More information on the specific 

background information is provided in [27]. 

3.2.3 Scenario Development 

The post-LOCA scenario (Step 4, Figure 1) was presented at both PIRT meetings to 

provide the framework or basis for the exercise. The primary objectives of the 

presentations were to describe the principal physical attributes of the LOCA sequence 

and describe the function of important ECCS and related plant hardware. The scenario 

in the presentation at the second PIRT meeting (Appendix B) was partitioned into five 

distinct functional phases for subsequent assessment purposes, and a timeline was 

associated with each functional phase. The first phase (T1) spans the time from when 

the LOCA initiating event occurs at time zero (e.g., a pipe rupture) to the end of the 

blowdown, or pressure reduction, phase after approximately 30 seconds. Most of the 

LOCA containment pool debris is generated during this phase caused by the impact of 

the two-phase (i.e., steam plus concentrated boric acid solution), high-pressure jet 

emanating from the pipe break. This phase ends when the RPV and RCS pressures are 

largely equal to the containment pressure. 

The second, or ECCS injection, phase (T2) occurs when the RWST injects borated 

water into the system to provide initial reactor core cooling just after the break. At the 

beginning of this phase, for almost all plants, the CSS activates as well to decrease the 

containment building pressure and temperature. This phase typically lasts from the end 

of blowdown (30 seconds) to approximately 20 minutes after the pipe break (for a largebreak LOCA) when the RWST water has been depleted. Additional debris is created 

and washed into the containment pool by the CSS. Containment pool buffering is also 

initiated during this phase. The intended function of the buffering system is to render 

any radioactive iodine that has escaped from the RCS nonvolatile within the containment 

pool so that gaseous releases to the environment are minimized. It is important to note 

that the method of introduction of the buffering agent will determine whether the initial 

post-LOCA debris is exposed to acidic or buffered containment pool solutions. For TSP 

and ice condenser plants, the containment pool is initially (i.e., within the first hour or so) 

expected to be predominantly acidic as localized dissolution of the buffering agents 

occurs. Buffering in the NaOH plants should initiate more rapidly on a global scale 

because it is introduced through the CSS. 

17 
The third, or early ECCS recirculation, phase (T3) was defined between 20 minutes to 

24 hours for the purpose of this exercise. The onset of ECCS recirculation occurs at 

approximately 20 minutes once the RWST water has been depleted for a large-break 

(LB) LOCA. The ECCS recirculation phase draws suction from the containment pool 

water. The water is then passed through the ECCS pumps into heat exchangers for 

heat rejection and back into the RPV for cooling the reactor core. The circuit is 

completed once water has spilled back out through the break and into the containment 

pool. This phase is assumed to terminate after about 24 hours because containment 

temperatures would have decreased from nearly saturated steam conditions (> 260 °F) 

at the onset of recirculation to well below the boiling point (< 180 °F) after 24 hours. 

Containment debris migrates to the sump screen and can accumulate on the sump 

screen or become ingested into the ECCS pump suction line during this phase. 

The fourth and fifth phases of the event were deemed the intermediate ECCS 

recirculation (T4) and long-term ECCS recirculation (T5) phases, respectively. The 

intermediate phase was defined as 24 hours to 15 days, whereas the long-term phase 

was defined from 15 to 30 days. These additional phases were chosen to identify 

different time scales associated with corrosion or other mechanisms that may be 

important over the intermediate (T4 phase) and long-term (T5 phase) periods. Note that 

there are no new system requirements that delineate these phases. The ECCS is 

designed and expected to operate consistently from the onset of recirculation until 

circulating water cooling of the core is not required (i.e., 30 days for purposes of this 

exercise). 

The only physical change in the system over this time period is that containment pool 

temperatures are continually decreasing, albeit much more slowly than decreases up to 

24 hours. After 15 days, the containment temperature is expected to be less than 

165 °F whereas after 30 days, the temperature is expected to be less than 145 °F. The 

exact temperature depends on a number of factors, including plant design, number of 

operating ECCS trains, and the temperature of the coolant water supplied to the ECCS 

heat exchangers. See Table 13 in Section 5 for more details on the post-LOCA 

temperature ranges. 

The general plant physical layout and configuration was provided to the panel in order to 

provide the appropriate context for evaluating the post-LOCA scenario. The functional 

requirements of the ECCS components at each post-LOCA phase were described along 

with possible implications of component failure. Functions and characteristics of other 

important plant systems like the reactor vessel and containment were also discussed. 

Finally, important post-LOCA parameters related to chemical effects that could affect 

ECCS performance were characterized. These variables include containment pool pH 

and buffering agent, containment materials, containment temperatures, sump inlet flow 

rate, containment pool height, sump configuration, and debris volumes. Representative 

values pertaining to each parameter were provided to the panel along with ranges to 

encompass plant-specific variability. The values for some of these parameters are 

summarized in Table 2 and Table 3, whereas more details are provided in Appendix B. 

These values and ranges were based on industry survey information available at the 

time of the PIRT. Values and ranges for some of these variables (e.g., insulation 

percentages and debris transport amounts) may be, or have been, altered because of 

plant modifications that were made to demonstrate acceptable ECCS performance as 

18 
requested in GL 2004-02. The likely changes and their impact were also discussed with 

the panel. 

Table 2: Selected Post-LOCA Plant Parameters 

Parameter 

Minimum 

Value 

Mean 

Value 

Maximum 

Value 

Containment volume (1x106 ft3) 1.3 2.6 9.9 

Painted area (1x105 ft2) 0.2 3.2 6.5 

Level 1 coatings (1x105 ft2) 0.4 3.0 6.5 

Debris transported to sump screen (1x102 ft3)

1 0.01 7.1 33.8 

Containment floor area (ft2) 0.2 1.5 9.1 

Maximum pool height (ft) 3.5 8.1 21 

Sump flow rates (1x104 gpm) 0.6 1.3 2.0 

Recirculation switchover times (min) 20 34 60 

B concentration (1x103 ppm) 2.0 2.7 4.4 

Reflective metal insulation in containment (%) 0 47 98 

Fiberglass insulation in containment (%) 1 42 100 

Mineral wool insulation in containment (%) <10 25 60 

Cal-Sil insulation in containment (%) 0 7 59 

1

 Not including reflective metal insulation debris 

Table 3: Containment Pool Buffering Agents and pH Ranges 

Buffer Type 

NaOH TSP STB 

Initial containment pH range 4–5 

Buffered containment pH range 8.5–10.5 7–8 8–9 

3.2.4 Chemical Effects Evaluation Criteria 

The chemical effect evaluation criteria (Step 5, Figure 1) were defined in order to judge 

the relative importance of each phenomenon to be assessed. Three levels of evaluation 

criteria were defined to establish a link between the regulatory requirements and specific 

technical concerns that coincide more closely with the panelists’ collective expertise. 

The regulatory requirements contained within 10 CFR 50.46 represent the highest-level 

criteria. This includes requirements that the peak cladding temperature stay below 

2200 o

F, that maximum cladding oxidation remain below 17 percent of the total 

thickness, that maximum H generation remain less than 1 percent of a hypothetical 

amount if all metal in the cladding cylinders were to react, that the core remains 

coolable, and that long-term cooling is maintained for an extended period of time [2]. As 

mentioned, a 30-day time period was assumed in this PIRT exercise as being sufficient 

for demonstrating that long-term cooling is maintained. 

More specific, functional level criteria were defined next. Meeting these requirements 

ensures that the 10 CFR 50.46 regulatory requirements are satisfied. These criteria 

include maintaining adequate NPSH upon consideration of debris loading at the sump 

strainer screens, maintaining the sufficient functioning of pumps, valves, heat 

exchangers, and other components downstream of sump strainer screen; and 

maintaining adequate heat transfer from the reactor fuel. 

19 
The lowest level criteria were next defined. These criteria are detailed technical effects 

commensurate with the background, experience, and expertise of the PIRT panelists. 

The purpose in defining these criteria was to aid the PIRT panelists in evaluating 

chemical phenomena (or issues) that would most likely affect the functional level and, 

consequently, the regulatory requirements. These criteria are effects that (1) contribute 

to sump screen clogging, (2) affect downstream component performance, (3) impact 

core heat transfer, and (4) degrade structural integrity. The panelists were specifically 

requested to use the preceding criteria to identify and rank the significance of 

post-LOCA chemical phenomena 

3.2.5 PIRT Issue Development 

Several underlying assumptions were used in developing the list of phenomena 

evaluated in the PIRT (Step 6, Figure 1). It was first assumed that effects of major fuel 

damage caused by failure of the ECCS to reject heat from the reactor fuel would not be 

considered. This assumption was made because the purpose of this PIRT is to 

understand how chemical effects may lead to ECCS performance failures, not how 

ECCS failures may lead to more severe fuel failures. This latter scenario is beyond the 

plants’ existing design basis, but it is assessed in severe accident analysis. 

It was also assumed that only degraded ECCS performance caused by chemical effects 

would be considered in the PIRT. Issues unrelated to chemical effects are currently 

addressed within the GSI-191 resolution process. An example is pump degradation 

caused by ingested physical debris. These issues are not related to chemical effects. 

However, they were discussed to provide context for assessing additional possible 

contributions caused by chemically induced effects. For instance, the failure to maintain 

the NPSH margin because of sump screen clogging by fibrous debris was not 

specifically evaluated by the PIRT. However, it was discussed that fibrous debris beds 

may be present and serve as a filter for trapping particulate and chemical byproducts. 

This debris may also contribute to chemical effects through reactions within the debris 

bed that may further alter the NPSH margin or pump performance. The panelists were 

asked to evaluate both the significance of any additional debris bed reactions and any 

enhanced chemical byproduct loading that may be filtered by a fibrous debris bed at the 

sump screen. 

Once the assumptions governing issue identification in the PIRT were established, a 

brainstorming session was used to identify issues (Step 6, Figure 1) associated with 

each period sequentially in the post-LOCA sequence. For instance, chemical effects 

associated with the first phase of the LOCA scenario (T1 is 0 to 30 seconds) were 

discussed first. The panelists identified mechanisms, issues, or phenomena, which may 

occur during this time period, and which could have implications with respect to the 

previously defined evaluation criteria. In the T1 phase, issues such as the impingement 

of a high-pressure two-phase jet containing borated reactor water, elevation of 

containment pressure and temperature, and the wash down of debris by the highpressure jet were identified for subsequent evaluation. 

The panelist who initially identified each issue led a short discussion to clarify the 

definition and identify possible implications associated with that issue. The issue title, 

definition, and possible implications were captured on flipcharts and in electronic 

summary tables during the brainstorming session. This brainstorming procedure was 

20 
conducted for all five post-LOCA time periods defined in Step 4 over an approximately 

1-1/2-day period. After the meeting, additional descriptions and implications for 

phenomena were added to the summary tables based on meeting notes, flip chart 

content, and meeting transcripts. Also, implications that were not explicitly discussed 

during brainstorming were added to the summary tables for the panelists’ consideration. 

The summary tables were then forwarded to the PIRT panelists for review. 

Comments received from the panelists on the summary tables were incorporated and an 

updated version of the summary tables was developed. A conference call was held 

approximately 3 weeks after the brainstorming meeting. The purposes of this 

conference call were to (1) clarify and correct definitions and implications associated 

with the summary table phenomena, (2) identify additional issues for evaluation that 

panelists identified after the brainstorming meeting, (3) finalize the summary tables, and 

4) provide instructions for completing the PIRT assessments. The final summary issue 

tables are contained in Appendix C. 

Issues were not generally assessed during this brainstorming phase. However, a few 

issues were discarded or moved to other periods when they were inconsistent with the 

physical attributes associated with the time period of interest. For instance, the issue of 

organic radiolysis leading to carbonate (CO3

2-) formation was initially identified during 

brainstorming for the ECCS injection phase (T2), which lasts from 30 seconds to 

20 minutes. After some discussion, the panelists decided that significant CO3

2- from 

organic radiolysis would evolve only over much longer times. The panelists then 

decided to move this issue to the long-term ECCS recirculation phase (T5). The 

updated summary tables (Appendix C) reflect the phases that the PIRT panelists 

determined by consensus for each phenomenon. 

It should be also noted that issues raised in one phase could be active in other periods 

as well. Quite often, phenomena were specifically indicated only in the time period 

during which it first occurs. However, the panelists were instructed to assess the 

integrated significance of particular phenomena for issues spanning multiple phases. 

For instance, the fiber and particle debris mix associated with the break was identified as 

a phenomenon that is created in T1, yet has implications for T1–T5. 

On occasion, the panel did separately identify some related phenomena in multiple time 

periods when the implications were distinct or the physical process warranted separate 

consideration during each time period. For instance, pH control was identified as a 

phenomenon for consideration during both the ECCS injection (T2) phase and the 

recirculation time (T3) phase. In the ECCS injection phase, NaOH-buffered plants have 

just begun to inject NaOH, whereas STB and TSP-buffered plants are just beginning to 

experience buffer dissolution. During recirculation, pH control through buffering is 

expected to be completed in all plants within about 4 hours. Therefore, the pH evolution 

in the containment pool is expected to start out as acidic (i.e., pH is approximately 4 to 5) 

at the beginning of T2 and then become basic (i.e., pH in the range of 8 to 10) by the 

end of T3. There are also several processes (e.g., radiolysis and hydrolysis of organic 

material) occurring simultaneously that may also affect the solution’s pH. Because the 

implications associated with acidic and basic pH levels are different, the panelists 

decided to specifically evaluate the effect of pH in both time periods. 

21 
3.2.6 PIRT Issue Assessment 

The assessment phase (Steps 7 and 8, Figure 1) used simple three-level ranking 

schemes to evaluate the significance or importance (Table 4) and the level of knowledge 

of the issues (Table 5) associated with each phenomenon evaluated by the PIRT 

panelists (Appendix C). It was agreed that three ranking levels provide sufficient 

distinction among issues without being needlessly complicated. PIRT panelists were 

instructed to perform importance ranking solely with respect to the four detailed 

evaluation criteria listed in Section 3.2.4. Table 4 provides the definitions and highlights 

the critical distinction between ranking levels. Issues that have a controlling, moderate, 

or minimal impact on evaluation criteria were to be rated high, medium, or low, 

respectively. 

Table 4: Importance Ranking Scheme 

Rank Value Definition 

High (H) 3 Phenomenon has a controlling impact on one 

or more of the evaluation criteria 

Medium (M) 2 Phenomenon has a moderate impact on one or 

more of the evaluation criteria 

Low (L) 1 Phenomenon has a minimal impact on one or 

more of the evaluation criteria 

The knowledge assessment in Table 5 is only slightly more complicated. The panelists 

were to consider both the level of understanding associated with each issue and the 

underlying uncertainty related to chemical effects in the post-LOCA scenario. For 

instance, continuing with the pH analogy, the effect of buffering on pH control may be 

generally well understood. However, plant-specific issues such as containment pool 

mixing, materials in the containment pool, and the effect of radiolysis may create large 

uncertainty in the actual pH during the accident at any one plant. The panelists 

therefore needed to weigh both contributions of general understanding and plant-specific 

variability or uncertainty to rank the level of knowledge. Known issues are determined to 

be those where engineering analysis can be performed to understand the practical 

ramifications. Issues that are unknown represent candidates for additional research, 

especially if the importance ranking is high. 

Table 5: Knowledge Assessment Ranking Scheme 

Rank Meaning 

Known (K) Sufficient understanding to make assessment of 

practical ramifications; small uncertainty exists. 

Partially known (PK) Partial knowledge and understanding; moderate

to large uncertainty remains. 

Unknown (UK) Totally unknown or very limited knowledge; 

uncertainty cannot be characterized.

22 
The PIRT panelists were instructed to provide brief rationales identifying the primary 

reason(s) for the importance and knowledge assessment rankings provided for each 

phenomenon. The initial PIRT assessments were also to be completed independently. 

Six PIRT tables were provided to the panelists for completing the assessment (Appendix 

D). The first table (Table D-1, Appendix D) was created to provide a means for 

organizing the assessment. The specific implications associated with individual 

phenomena (Appendix C) were summarized, and broader implication categories were 

created to group the phenomena by their possible effects at critical plant locations 

(i.e., containment pool, sump screen, ECCS pumps, ECCS heat exchangers, and 

reactor core). The post-LOCA time periods were also identified so that effects 

associated with issues at distinct times could be identified. The table was intended to 

help the panelists graphically assess each issue’s importance based on the number and 

type of implications, the relevance to critical locations, and the time periods associated 

with the mechanism. This table was optional, but a few of the panelists did use it to help 

develop their assessments. 

The remaining five PIRT tables (Tables D-2–D-6) are analogous to the summary tables 

(Appendix C). There is a PIRT table for each time period and each row corresponds to 

an issue as in the summary table. Remaining columns are for panelists to indicate their 

importance ranking and rationale along wit their knowledge assessment ranking and 

rationale. 

The panelists submitted their initial assessments, and the results were summarized. 

Numerical quantities of 3, 2, and 1 were assigned to high-, medium-, and low-ranked 

issues, respectively, from each panelist. Also, scores of 3, 2, and 1 were assigned to 

unknown, partially known, and known knowledge rankings, respectively. A few panelists 

chose to rank some issues at levels between those that are identified in Table 4 and 

Table 5 (e.g., issue importance ranked as medium/high). In these instances, an average 

numerical score between the two identified levels (e.g., 2.5 for a medium/high 

importance ranking) was assigned. Then, summary statistics were created for each 

issue. First, the average score, between 1 and 3, was determined for each ranking. All 

panelists were equally weighted in determining this average. Additionally, responses 

were binned to determine the number of high, medium, and low (and unknown, partially 

known, and known) responses for each issue. If a panelist’s response fell between two 

identified levels (e.g., medium/high), the response was always binned with the higher 

importance or knowledge ranking. For example, responses that were marked 

medium/high were binned in the high category, and responses marked unknown to 

partially known were binned into the unknown category. 

These summary issue rankings and the initial independent PIRT assessments provided 

by each panelist were distributed to all the panelists. The preliminary results where then 

discussed in two separate conference calls. The objectives of these calls were to 

(1) summarize issues that the majority of panelists ranked as being highly significant and 

(2) identify and discuss issues that one or two panelists ranked as highly important but 

were judged less significant by the remainder of the panelists. Discussion centered on 

identifying reasons for differences in the individual importance rankings for these issues. 

The primary outcome of the group discussion was to determine which issues should be 

identified as significant and which could be considered less important. All significant 

issues are summarized in Section 5 of this report. Further discussion revealed that 

23 
typically either one of two reasons occurred for divergent opinions. The most common 

reason was that panelists either misunderstood the issue definition or did not take into 

consideration some relevant background information. Panelists provided updated 

rankings in these cases, as appropriate, based on their new understanding of the issue 

(Appendices E–I). Note that the rationale was not always updated for the adjusted 

rankings indicated in Appendices E–I. There were only a few issues where a significant 

technical difference of opinion remained among more than one PIRT reviewer after 

further discussion. In these cases, the divergent rationale provided by the reviewers is 

summarized in Section 5. 

There were other issues that were highly ranked by only one panelist. The high-ranking 

panelist for each issue determined if additional discussion of the rationale behind the 

high ranking was needed. Additional discussion was particularly useful if the highranking panelist believed that others did not appropriately consider his rationale. The 

alternative was that the panelist could agree with the lower rankings of the remaining 

PIRT members based on their technical justifications and additional clarification of the 

phenomenon. Typically, panelists adjusted their high rankings downward based on 

other panelists’ justifications, as documented in Appendices E–I. A few panelists did 

retain their high ranking and rationale after additional discussion among the PIRT panel. 

In no instance was the dissenting panelist able to convince other panelists to elevate 

their rankings based on the dissenter’s justification, although the importance of a few 

issues in other time periods was reaffirmed. Those issues having a single high ranking 

are also summarized as significant issues for consideration in Section 5. The rationale 

associated with both high and lower significance rankings are also summarized in this 

section. 

24 
4 CHARACTERIZATION OF PIRT FINDINGS 

AND USE OF RESULTS 

Four different classifications capture the results of the PIRT evaluation, and they are 

summarized in Section 5. The first category (Category I) represents those phenomena 

or issues that are generally known, or have been demonstrated, to be significant by prior 

research (Section 1.2). However, some additional aspects associated with these issues 

(i.e., variables and parameters) still need to be considered to accurately assess relevant 

chemical effects in either a generic or a plant-specific analysis. An example of this type 

of phenomenon is the evolution of the containment pool pH caused by the addition of a 

buffer, radiolysis of the water, and containment pool temperature decreases during the 

post-LOCA scenario. The PIRT evaluation reaffirmed the great importance of pH and 

temperature for assessing which chemical effects will occur in the post-LOCA 

containment environment. Additionally, assuming radiolytic effects on pH are 

inconsequential (Section 5), the evolution of pH and temperature with time are generally 

known by the licensees for their plant-specific reactor chemistry, ECCS chemistry, and 

buffering system. Therefore, it is possible to address the influence of pH and 

temperature on post-LOCA chemical effects. 

The second category (Category II) includes phenomena or issues that are either 

expected to be significant by the PIRT panelists or have been demonstrated to be 

significant by prior research (Section 1.2). However, the implications of these 

phenomena with respect to ECCS performance are not well known. Additional aspects 

of these issues (i.e., variables and parameters) should be evaluated in order to 

accurately assess the relevant chemical effects either generically or in a plant-specific 

analysis. More research or analysis could also be used to better characterize the issue 

by identifying significant thresholds or ranges for critical parameters and comparing 

those with conditions existing in plant environments. 

For example, an understanding of the particular insulation materials in the containment 

pool after the break debris is an important consideration that will determine the type and 

significance of chemical effects that will occur. This mix could both alter the containment 

pool chemistry and the debris bed formation on the sump screen, which would lead to 

variability in the capture efficiency of chemical byproducts by the debris bed. The 

importance of this phenomenon was demonstrated in ICET [11]. Severe Al corrosion 

occurred during Test 1, whereas almost no corrosion was evident in Test 4. The only 

difference was that the copious amount of Cal-Sil that was present in ICET Test 4 

increased the concentration of dissolved silica, which in turn precipitated on the Al 

surface and inhibited Al corrosion [14]. However, the threshold and range of dissolved 

silicate necessary to inhibit Al corrosion is not known (as a function of surface area), nor 

is there an understanding of what silicate sources in the containment (e.g., Cal-Sil and 

insulation) can lead to Al corrosion inhibition. 

The third category (Category III) includes phenomena that are potentially significant, but 

are not well understood, and the ECCS performance implications are highly uncertain. 

These issues require more research, analysis, or evaluation within the context of specific 

post-LOCA plant environments to accurately consider the effects. Conservative scoping 

analyses could be performed initially to determine if either critical parameter ranges, 

25 
bounding values, or threshold values that are necessary for the issue to be significant 

are representative of commercial plant conditions. If conservative analysis cannot be 

used to evaluate the significance, more refined research or analysis may be necessary. 

For example, the effect of radiolysis on the redox potential of the containment pool 

chemistry has not been considered in prior research. The PIRT panelists identified this 

as a potentially significant consideration. Scoping calculations could be performed to 

conduct a first-order conservative assessment of the significance of radiolysis. If the 

conservative assessment cannot demonstrate that radiolysis has an insignificant effect 

on the redox potential, more rigorous analysis or consideration may be required. 

The fourth category (Category IV) represents phenomena that are insignificant as 

determined by both the aggregate and individual PIRT rankings and justifications. This 

class includes all the issues evaluated during the PIRT but not deemed significant. An 

example is unsubmerged material corrosion. The PIRT panel thought that these 

contributions were generally insignificant compared to dissolved contributions to the 

containment pool chemistry from submerged materials. The Category IV phenomena 

are summarized in the results tables (Section 5), but are not discussed within this report. 

Table 6: Categorization of PIRT Phenomena 

Category Phenomena Implications 

 I Significant Known 

 II Significant Not well known 

 III Potentially significant Not well known 

 IV Not significant Not applicable 

It is important to note that the PIRT used the prior research results (Sections 1.2.1–

1.2.3) as a starting point for the exercise and did not reaffirm those findings. Instead, 

important research findings were discussed, and less obvious aspects that may not have 

been considered in the earlier research were evaluated. For example, Al corrosion was 

demonstrated to be important in the ICET testing [11]. The PIRT did not reassess this 

finding, but instead it evaluated phenomena that might alter Al corrosion rates and 

precipitation such as alloying, inhibition, catalytic effects, co-precipitation, etc. 

Therefore, the PIRT results are not intended to be a comprehensive set of chemical 

phenomena or issues within the post-LOCA environment. These phenomena should be 

combined with important findings from past research (Sections 1.2.1–1.2.3) for 

developing a more comprehensive list. 

Additionally, since the PIRT was completed, additional research has been conducted by 

the nuclear industry and additional research has been sponsored by the NRC (see 

Sections 1.2.4–1.2.5). In some cases, this additional research has further defined 

critical post-LOCA variables and parameters for specific phenomena. For example, 

industry-sponsored testing has measured Al corrosion rates under a broader range of 

pH and temperature conditions than in ICET [18]. It is therefore anticipated that the 

knowledge gained by past and ongoing research (Section 1.2) will be considered with 

the PIRT recommendations to identify and resolve existing gaps so that the implications 

of chemical effects on ECCS performance.can be adequately understand and evaluated. 

26 
27 

5 RESULTS 

The individual PIRT rankings and rationale provided by each panelist are summarized in 

several appendices to this report (i.e., Appendix E–Appendix I). The first tables in each 

appendix replicate the issue definition and implication tables for each time period 

contained in Appendix C, and individual rankings were developed using the PIRT 

evaluations (Appendix D). Average importance and knowledge rankings were calculated 

as detailed in Section 3.2.6. These average rankings are summarized in Table 7–Table 

11 along with the individual panelist rankings. The categories assigned to each PIRT 

phenomenon, as discussed in Section 4, are also included in these tables. There were 

also a few additional phenomena identified by individual panelists in their review of 

chemical effects research sponsored by the NRC [27]. Although these issues were 

raised after the PIRT was completed, the most significant ones are summarized in Table 

12 to develop a more comprehensive list of issues for consideration. 

This section will focus on discussing those issues summarized in Table 7–Table 12 that 

a majority of the PIRT reviewers believe are highly significant and have not been 

specifically addressed within activities sponsored by the NRC (Section 3.2.5). In many 

instances, consensus was reached on these issues and the rationale supporting the 

rankings will be summarized. After discussion, a few issues still had one or two 

panelists who believed that the issue remains highly significant even through the 

remainder of the panelists disagreed (Section 3.2.5). These issues and the competing 

rationale used to support either the high or lower rankings will also be presented. 

However, in this summary, the issues are presented topically. Similar or identical issues 

in distinct time periods are combined under one topical entry. These topical areas do 

not represent a complete nor unique phenomenological description of chemical effects in 

the post-LOCA environment. They are merely used for grouping the significant 

outstanding issues. Significant issues were identified pertaining to the underlying 

containment pool chemistry; radiological considerations; physical, chemical, and 

biological debris sources; solid species precipitation; solid species growth and transport; 

organics and coatings; and downstream effects. This report also discusses unique 

phenomena within each topical area as appropriate. 

At the end of each topical area discussion, a summary of issues that could benefit from 

additional research is provided. This summary is largely intended to capture those 

phenomena falling in Categories II or III (Section 4) because Category I phenomena are 

expected to be sufficiently mature to allow for engineering evaluation. Recall that 

Category II phenomena (Section 4) are generally well known and expected to be 

significant, but the implications with respect to either generic or plant-specific ECCS 

performance are not well known. Category III phenomena (Section 4) are potentially 

significant but are not well understood, and the ECCS performance implications are 

highly uncertain. The PIRT knowledge rankings and the supporting rationales are used 

to assign each significant phenomenon in Categories I, II, or III. Items with higher 

knowledge rankings (i.e., there is less known about the phenomenon) have generally 

been assigned to higher categories. 
Table 7: Summary Rankings for T1 Phenomena 

Issue Phenomena 

Average 

Importance

(H, M, L)1 JA2 WC2 CD2 RL2 DM2

Average 

Knowledge 

(K, PK, UK) 3 JA WC 

T1-1 Crud release 2.4 L M H H H 1.6 PK PK T1-2 RCS coolant conditions at break 2.4 L M H H H 1.4 K K T1-3 pH variability 2.4 L M H H H 1.4 K K T1-4 Localized B concentration in jet 1.9 L/M M M L H 1.8 PK PK T1-5 RCS fluid creates “oxidizing environment” 1.6 L L L M H 1.6 K PK T1-6 Jet impingement 2.2 H L H L H 1.8 PK PK T1-7 Break proximity to organic sources 1.9 M/ H L M L H 2.0 UK PK T1-8 Break proximity to secondary systems 1.2 L M L L L 2.2 UK PK T1-9 Debris mix particle/fiber ratio 2.6 H H H M M 1.6 PK K 

T1-10 Hydrogen peroxide effects 1.4 L L L M M 1.4 PK PK T1-11 Nuclei formation 1.2 L L M L L 2.0 UK PK 

28 

1 High (H), medium (M), low (L) (see Table 4 in Section 3). 2 John Apps (JA), Wu Chen (WC), Calvin Delegard (CD), Robert Litman (RL), Digby Macdonald (DM). 3 Known (K), partially known (PK), unknown (UK) (see Table 5 in Section 3). 4 See Table 6 in Section 4. 
Table 8: Summary Rankings for T2 Phenomena 

Issue Phenomena 

Average 

Importance 

(H, M, L) JA WC CD RL DM 

Average 

Knowledge (K, PK, UK) JA WC CD 

T2-1 Hydrogen sources within containment 1.2 L L L L M 1.6 PK PK PK T2-2 ECCS injection of B 2.2 H L H M M 1.4 K PK K T2-3 Containment spray corrosion 1.6 L M L M M 1.2 K K K T2-4 NaOH pH control 2.2 M L H H M 1.0 K K K T2-5 STB pH control 1.6 M L M L M 1.0 K K K T2-6 TSP pH control 2.2 M L H H M 1.0 K K K T2-7 Containment spray transport 2.4 H H M L H 2.0 PK PK PK T2-8 Containment spray CO2 scavenging 1.9 L/M M M M 1.2 PK K T2-9 Debris dissolution begins 2.2 M L H M H 1.4 K PK K 

T2-10 Carbonate concentration 1.7 L/M L M M M 1.6 PK PK K T2-11 Containment pool mixing 2.0 H L L M H 1.7 UK/ PK PK K T2-12 Boric acid corrosion of exposed concrete 1.4 L M M L L 2.2 UK PK PK T2-13 Fe and Ni radiological reaction 2.0 L M M M H 1.8 PK PK PK 

29 
30 

Issue Phenomena 

Average 

Importance 

(H, M, L) JA WC CD RL DM 

Average 

Knowledge (K, PK, UK) JA WC CD 

T2-14 Hydrolysis 1.2 L L L L M 2.2 UK PK PK T2-15 Organic complexation 1.7 L/M L H L M 2.0 PK PK PK T2-16 Organic sequestration 1.6 L M M L M 2.2 UK PK PK T2-17 Auxiliary component cooling line failure 1.7 L/M L M M M 2.2 PK PK PK T2-18 Polymerization 2.5 H M M M/H H 1.8 PK PK K T2-19 Co-precipitation 1.7 L/M M M L M 1.8 PK PK K T2-20 Radiolytic environment 2.0 L L M H H 1.8 PK PK UK T2-21 Inorganic agglomeration 2.2 M/H L M M/H H 1.6 PK PK K T2-22 Galvanic effects 1.6 L/M M L M 1.8 PK UK T2-23 Deposition and settling 2.3 M/H M L H H 2.2 UK PK UK T2-24 Organic agglomeration 2.3 L/M H H L H 2.6 UK PK UK 
Table 9: Summary Rankings for T3 Phenomena 

Issue Phenomena 

Average 

Importance 

(H, M, L) JA WC CD RL DM 

Average 

Knowledge (K, PK, UK) JA WC 

T3-1 TSP pH control 1.8 L M H L M 1.2 PK K T3-2 NaOH pH control 2.2 H M H L M 1.0 K K T3-3 STB pH control 2.2 H M H L M 1.0 K K T3-4 NaOH injection 1.7 L/M L M M M 1.6 PK PK T3-5 Cable degradation 1.5 L M L M 1.8 PK T3-6 Radiolytic environment 2.3 L/M M H M H 1.8 PK PK T3-7 Fiberglass leaching 2.0 M M M M M 1.0 K K T3-8 Secondary system contamination 1.5 L/M L M L M 1.8 UK PK T3-9 Flow-induced nucleation 1.3 L/M L L M L 2.0 UK PK 

T3-10 Turbulent mixing 1.5 L/M M M L L 2.2 UK PK T3-11 Quiescent settling of precipitate 2.4 M H M M H 2.2 UK K T3-12 Electrostatic scavenging 1.4 L L L L H 2.2 UK PK T3-13 Chemically induced settling 1.7 M/H L L L H 1.8 PK PK 

31 
32 

Issue Phenomena 

Average 

Importance 

(H, M, L) JA WC CD RL DM 

Average 

Knowledge (K, PK, UK) JA WC 

T3-14 Agglomeration and coagulation 2.3 M/H H L M H 1.8 PK PK T3-15 Particulate nucleation sites 1.8 M L L M H 2.2 UK UK T3-16 Additional debris bed chemical reactions 1.9 L/M L M M H 2.4 UK UK T3-17 

Sump screen: high localized chemical concentrations 

1.6 L L M M M 2.2 UK PK 

T3-18 Sump screen: fiberglass morphology 1.6 L L M M M 2.0 PK PK T3-19 ECCS pump: seal abrasion 2.0 L L H H M 2.0 UK K T3-20 Heat exchanger: solid species formation 2.4 M L H H H 1.6 PK K T3-21 Heat exchanger: deposition and clogging 2.1 M/H L H L H 1.6 PK K T3-22 Reactor core: fuel deposition 2.1 M/H L H L H 1.6 PK K T3-23 Reactor core: hydrogen increases 1.5 L L L H 1.5 PK T3-24 Reactor core: diminished heat transfer 2.1 M/H L H L H 1.8 UK K T3-25 Reactor core: blocking of flow passages 2.3 M/H M H L H 2.0 UK K T3-26 Reactor core: particulate settling 2.1 M/H L H L H 2.0 UK K 
33 

Issue Phenomena 

Average 

Importance 

(H, M, L) JA WC CD RL DM 

Average 

Knowledge (K, PK, UK) JA WC 

T3-27 Reactor core: precipitation 2.3 M/H M H L H 2.0 PK PK T3-28 Exposed, uncoated concrete dissolution 1.4 L M M L L 1.4 PK PK T3-29 Coatings dissolution 1.6 L L M M M 2.4 PK UK T3-30 Boric acid corrosion 1.7 L/M L M M M 1.8 PK PK T3-31 CO2/Carbonate radiolysis 1.0 L L L L 2.0 PK 
Table 10: Summary Rankings for T4 Phenomena 

Issue Phenomena 

Average 

Importance 

(H, M, L) JA WC CD RL DM 

Average 

Knowledge (K, PK, UK) JA WC 

T4-1 Source term: unsubmerged materials 1.0 L L L L L 1.6 PK PK T4-2 Submerged source term: Pb shielding 2.0 L H L M H 1.8 PK PK T4-3 Submerged source term: Cu 1.9 L/M M M M M 2.6 UK PK T4-4 Submerged source term: Fe 1.8 L H L H L 1.6 PK PK T4-5 

Submerged source term: Al, decreased concentrations 

1.4 L L M L M 1.8 PK K 

T4-6 

Submerged source term: Al, increased concentrations 

2.2 H H M L M 1.6 PK K 

T4-7 Submerged source term: Fiberglass dissolution 1.6 M L M M L 1.6 K PK T4-8 Submerged source term: Fiberglass inhibition 1.8 M L M M M 1.8 PK PK T4-9 Submerged source term: Zn passivation 1.2 L L M L L 1.8 PK PK 

T4-10 Submerged source term: Zn corrosion products 1.4 L M M L L 1.8 PK PK T4-11 Submerged source term: Zn co-precipitation 1.2 L L M L L 2.0 PK PK T4-12 Zinc hydroxide dissolution (zincate) 1.4 L M M L L 1.8 PK PK 

34 
35 

Issue Phenomena 

Average 

Importance 

(H, M, L) JA WC CD RL DM 

Average 

Knowledge (K, PK, UK) JA WC 

T4-13 Submerged source term: Zn-based coatings 1.4 L M M L L 2.2 PK PK T4-14 Source Term: seal table corrosion 1.0 L L L L 2.2 PK PK T4-15 Submerged source term: fire barriers 1.2 L L M L L 2.8 UK UK T4-16 Submerged source term: organic buoyancy 1.9 M/H L H L M 2.2 PK UK T4-17 Submerged source term: coatings 2.0 L L H M H 2.6 UK UK T4-18 Submerged source term: RCP oil tank failure 2.2 M M M M H 2.2 UK PK T4-19 Submerged source term: biofilm formation 1.2 L L M L 2.6 UK UK T4-20 

Submerged source term: biologically enhanced corrosion 

1.2 L L M L 2.4 UK PK 

T4-21 

Submerged source term: biologically enhanced H2

embrittlement 

1.5 L L M M 2.8 UK UK 

T4-22 

Submerged source term: biological growth in debris beds 

1.8 L L H M 2.6 UK UK 

T4-23 Submerged source term: electrical insulation 1.4 L M L L M 1.8 UK PK T4-24 Reactor core: fuel spalling 1.7 L/M L M M M 1.8 UK PK 
36 

Issue Phenomena 

Average 

Importance 

(H, M, L) JA WC CD RL DM 

Average 

Knowledge (K, PK, UK) JA WC 

T4-25 Radiological effects: debris bed accumulation 1.9 L/M L M M H 2.4 UK UK T4-26 

Radiological effects: dissolution and oxidation changes 

1.6 L L M L H 2.6 UK UK 

T4-27 

Radiological effects: radiolytic affect on biofilms 

1.2 L L L M 2.4 UK PK 

T4-28 Radiological effects: redox potential changes 2.1 L/M M M M H 2.0 PK PK T4-29 Radiological effects: corrosion rate changes 1.9 L/M M M L H 1.8 PK PK T4-30 Radiological effects: agglomeration 1.5 L/M L M M L 2.8 UK UK T4-31 CO2/O2 air exchange 1.4 L L M M L 1.8 PK PK T4-32 ECCS pumps: erosion/corrosion 2.4 M M H M H 1.8 PK K T4-33 ECCS pumps: seal degradation 2.2 M M H M M 2.0 UK K T4-34 Heat exchanger: secondary contaminants 1.2 L L L M L 1.6 UK PK T4-35 Heat exchanger: precipitate formation 2.3 M/H L H H M 1.8 PK K T4-36 pH drop in containment pool 1.4 L M L L M 1.8 PK PK 
37 

Issue Phenomena 

Average 

Importance 

(H, M, L) JA WC CD RL DM 

Average 

Knowledge (K, PK, UK) JA WC 

T4-37 Reactor core: continued deposition/precipitation 2.2 M/H L H L/M H 2.0 PK PK T4-38 Reactor core: fuel deposition spalling 2.2 M L H M H 2.2 UK UK T4-39 Transport phenomena: amorphous coating 1.9 L/M H H L L 2.0 PK PK T4-40 

Transport phenomena: precipitation/coprecipitation 2.2 M M H M M 2.0 UK PK 

T4-41 Transport phenomena: metallic scouring 1.5 L/M M L L M 2.0 UK PK 
38 

Table 11: Summary Rankings for T5 Phenomenon 

Issue Phenomena 

Average 

Importance 

(H, M, L) JA WC CD RL DM 

Average 

Knowledge (K, PK, UK) JA WC 

T5-1 Organic radiolysis 1.5 L M L M 2.2 UK 

Table 12: Additional Phenomena Identified Separately from the PIRT Exercise 

Issue 

Number Phenomena Description Implica

S-1 Conversion of N2 to HNO3 Radiolysis converts atmospheric N2 to HNO3 within sump pool. The pH in sump pool decreas

production. Buffering is not sreduction. 

S-2 Presence of silica Silica in the water storage systems and the RCS affects chemical product formation 

1. Silica in the water storage can combine with Mg, Ca, anretrograde solubility. 2. Silica can have an effect omaterial precipitating. 

S-3 

Material aging and alloying effects 

1. The exposed concrete faces and dust in the containment building are aged and will be carbonated. 2. Corrosion rate data exhibits wide variability depending on the specific corrosion conditions and the alloy. 

1. Numerous metallic alloys available. 2. Aging and alloying could arates. 3. Aging could affect the soliare formed. 

S-4 

Advanced metallic corrosion understanding 

Issues include 1. Understanding corrosion under the wideranging LOCA conditions (jet impingement - immersion), 2. Synergistic corrosion effects 3. The effect of hypochlorite on corrosion 4. Effects of phosphates/salts on corrosion. 

Phenomena could substantia
5.1 Underlying Containment Pool Chemistry

5.1.1 Effect of Boron 

The B concentration present within the containment pool can have an effect on coolant 

chemistry and subsequently material corrosion rates. It also specifically plays a role in 

the precipitation of Al(OH)3 or AlO(OH) as a result of adsorption [14]. One consideration 

is that the B concentrations at the time of the break can be highly variable (T1-2, Table 

7). Boron concentrations can range from 2000-4000 ppm (0.2–0.4 M) at the beginning 

of the fuel cycle to 50 ppm (5x10-3 M) at the end of fuel cycle. At the beginning of the 

fuel cycle (high B), the RCS water that impinges on materials is acidic (i.e., pH is 

approximately 4.5) and hot. 

One PIRT panelist is concerned about the possibility that the boric acid solution can 

become concentrated through droplet evaporation within the high-temperature jet 

emanating from the pipe break to form a highly corrosive borated aerosol solution (T1-

4, Table 7). These conditions were postulated by the PIRT panel to be representative of 

conditions existing at Davis-Besse that led to the significant erosion of the carbon-steel 

reactor head [38]. The variability in the B concentrations over the fuel cycle would imply 

that this effect could be more severe early in the fuel cycle. Although one panelist is 

concerned that corrosion rates could be elevated, other panelists are not concerned 

because of the limited area affected by the jet impaction and because the affected 

materials will largely be unsubmerged above the containment pool water level. This 

effect is also expected to be transient and will diminish as the reactor pressure 

equilibrates (typically within 1 minute) and as the temperature decreases below the 

boiling point. Therefore, the other panelists believe that longer-term chemical effects will 

dominate. 

The initial differences in RCS B concentration during the fuel cycle become less distinct 

as ECCS injection starts within seconds after the break. The ECCS injects borated 

water (2800 ppm (0.26 M) of B) into the RCS to cool the reactor and ensure that the 

fission process is terminated. If the break occurs at the end of the fuel cycle, B 

concentrations are still expected to be greater than 1500 ppm (0.14 M) after the end of 

the injection phase (approximately 20 minutes). This high B concentration results in an 

initial containment pool pH of 4.5 to 5.5, depending on the temperature. 

The effects of B on the containment pool pH (T1-3, Table 7) can be readily determined if 

the B levels are known as a function of time. The initial acidic conditions will accelerate 

corrosion of many submerged metallic components over the first several minutes of the 

accident and the effects of both high and low B should be considered to accurately 

account for differences in the dissolved concentrations of products resulting from 

corrosion and/or leaching. 

 

However, as containment pool buffering and ECCS B-injection continues, the B levels 

will become more uniform, and the containment pool pH will become basic. These 

conditions should be established within the first 20 minutes after the break, and the pH 

should be stabilized by the buffering within 1 to 4 hours after the break [12]. The exact 

time required for stabilization is a function of the buffering system and the rate of mixing 

within the containment pool. Therefore, differences in initial corrosion products species 

39 
concentrations caused by variable B early in the break should become less important as 

the accident sequence progresses. 

The PIRT panelists identified another mechanism for creating concentrated boric acid 

within the RPV through borated water evaporation in contact with hot reactor fuel (T3-27, 

Table 9). Post-LOCA concentration of boric acid within the reactor core caused by water 

evaporation is a well-known phenomenon. It is less clear whether it would be sufficient 

locally to affect corrosion of the fuel cladding, vessel cladding, or other internal 

components. The boric acid may facilitate dissolution of iron (Fe) and nickel (Ni) from 

reactor internal components and zirconium (Zr) from the fuel cladding. These cations 

could subsequently precipitate as fine hydroxides at lower temperatures within the 

containment pool or at the heat exchanger (Section 5.4.2). The other more subtle effect 

of continued boric acid concentration in the reactor would be to diminish the B 

concentration in the containment pool. 

The ICET experiments [14] also demonstrated that B can play a large role in controlling 

precipitate of the Al corrosion products (T2-2, Table 8). Boron apparently caused the 

amorphous Al(OH)3 precipitate in ICET Test 1 to remain amorphous for much longer 

times than without B [14]. An item for further consideration is to understand how realistic 

B concentrations (considering all effects identified in this section) affect precipitation of 

other chemical species that may exist in the post-LOCA environment. Thermodynamic 

data for B complexes in solution are insufficient and many B complexes are inadequately 

characterized for adequate modeling of B chemistry in cooling water following a LOCA. 

5.1.2 Temperature and pH Evolution and Variability 

A related phenomenon is the temperature and pH evolution that occurs within the 

containment pool during the post-LOCA scenario (T1-3, Table 7). Simulated 

temperatures that summarize the results from approximately six distinct analyses are 

provided in Table 13 at various times after a hypothetical LB LOCA [12 and 39]. 

Temperature ranges are provided because the actual temperature/time profile is a 

function of many variables, including the plant type, the reactor power, the ECCS design, 

the availability of ECCS trains, the break size, the break location, and the heat 

exchanger inlet temperature. These ranges are therefore representative of a post-LOCA 

scenario, but they do not necessary apply to any plant-specific pipe break scenario. 

Table 13: Post-LOCA Containment Pool Temperatures 

Post-LOCA Time 

< 10 seconds 1 hour 12 hours 1 day 15 days 

Temperature 

range (o

F) 190–270 150–255 135–210 125–180 115–165 

Although the containment pool temperature often peaks several minutes after the break, 

it is instructive to note that the peak temperature is not reached in certain simulations 

until approximately 1 hour after the LOCA has occurred. Additionally, the containment 

pool temperatures in these simulations remain significantly above ambient conditions for 

several weeks. Simulations conducted out to 30 days indicate that little additional 

temperature drop (approximately 5 o

F) may occur after 15 days. 

40 
Although the temperature is highest relatively soon after the break, the minimum 

containment pool pH occurs at the beginning of the post-LOCA period. As discussed in 

Section 5.1.1, the high initial B concentration (caused by ECCS injection and/or breaks 

at the beginning of the fuel cycle) results in a pH of 4.5 to 5.5. The pH then rises with 

time as buffering agents are added. Depending on the pH buffering system, the final 

steady-state containment pool pH can vary between 7 and 11 and is established 

between 1 to 4 hours after the LOCA [12]. The time necessary to reach the uniform, 

steady-state pH is a function of the rate at which the buffer is introduced and the time 

required for it to become well mixed within the containment pool. 

The relationship between the containment pool temperature and pH is critical for 

understanding chemical effects. The initial acidic pH range enhances corrosion and/or 

dissolution of certain materials (e.g., Zn, Cal-Sil), whereas other materials (e.g., Al and 

NUKON®) are more susceptible within the basic pH range. Significant material 

corrosion or dissolution may alter the pH [15] and affect the dissolution rate of other 

materials. Material dissolution and/or corrosion are also generally accelerated at higher 

temperatures. Additionally, the solubilility of solid phases can depend strongly on 

temperature. Lower temperatures promote the precipitation of chemical species with 

prograde solubilities (i.e., those that decrease with temperature such as Al(OH)3), 

whereas higher temperatures favor precipitation of chemical species having retrograde 

solubility (e.g., calcium carbonates (CaCO3) and AlNa12SiO5). The extent of prograde to 

retrograde solubility depends also on the composition of the aqueous phase. 

Knowledge of how the pH and temperature evolve as a function of time for different postLOCA debris constituent scenarios is necessary to understand the interdependency 

among pH, temperature, and the post-LOCA debris constituents (Section 5.3) for plantspecific conditions. Evaluating a single pH and temperature history is not likely 

sufficient, and determining credible ranges resulting from different LOCA scenarios 

allows for a more thorough evaluation of likely chemical effects. Once these ranges are 

determined, corrosion and dissolution effects and possible subsequent precipitate 

formation can be more accurately assessed to determine the impact of chemical effects. 

5.1.3 Issues Related to Post-LOCA Buffering

It is instructive to describe the various buffering systems because these bear directly on 

both the pH evolution (Section 5.1.2) and the types of chemical byproducts that may 

precipitate. Commercial plants primarily employ these systems to sequester radioactive 

iodine in the aqueous liquid phase using one of the following four methods: 

(1) NaOH injection through containment sprays (T2-4, Table 8; T3-2, Table 9) 

(2) TSP dissolution from containment floor baskets (T2-6, Table 8; T3-1, Table 9) 

(3) for ice condenser plants, STB release as ice melts to provide containment cooling 

(T2-5, Table 8; T3-3, Table 9) 

(4) STB use as a powder from containment floor baskets for plants without ice 

condensers 

As mentioned, the containment pool pH increases as the LOCA continues because of 

the progressive addition of chemical buffers. The pH values after buffering will stabilize 

41 
once the buffering addition is completed and the buffer becomes well mixed within the 

containment pool. 

For plants using NaOH buffering, the NaOH is injected into the initial containment spray. 

The pH of the spray is initially high (the pH is greater than 9.5 and up to 10.5) during the 

approximately 20-minute NaOH injection phase. The final containment pool pH is 

alkaline with an expected pH range of 8.5-10.51

. This pH is conservatively assumed to 

be established within 4 hours, which coincides with the time that the coolant is 

recirculated once through the ECCS. However, in many plants, the pH is expected to 

stabilize within 1 hour because the NaOH is well dispersed initially by the sprays. 

Buffering in other plants occurs by dissolution of TSP from containment floor baskets. 

The dissolution begins once the containment pool water reaches the bottom of the 

basket. This time is variable depending on the plant configuration, but the onset of 

dissolution is expected within 20 minutes. As dissolution begins, initially high pH is 

present near the baskets. The relatively quiescent containment pool likely precludes 

significant mixing until ECCS recirculation begins (T2-11, Table 8). Complete mixing is 

expected within 4 hours after the coolant is recirculated once through the ECCS. The 

final pool pH range for plants using a TSP buffer is approximately 7–8. 

Ice condenser plants are designed to release STB with the ice melt from elevated 

containment baskets during a LOCA. For a LB LOCA, as the ice begins to melt but 

ECCS recirculation has not yet begun, the pH directly under the baskets may be higher 

(approximately 9) than the bulk of the containment pool. However, after recirculation 

begins, mixing begins to equalize the STB concentration. The containment pool pH 

reaches steady state (i.e., when the pH is between 8–9) after the ice bed has completely 

melted (generally within 1 hour for a LB LOCA), and the STB has been well mixed 

throughout the pool. Steady-state conditions should be established in the containment 

pool within a few hours after the LB LOCA [12]. 

The concerns raised by the panelists regarding chemical effect vary for each of these 

buffering approaches. The NaOH buffering results in the most alkaline environment of 

all the buffering agents. One panelist is concerned about ionic species contributions 

resulting from corrosion of unsubmerged materials by the high pH spray within about 4 

hours of the accident (T2-3, T2-4; Table 8). This panelist believes that the corrosion will 

significantly increase the containment pool dissolved metal content because of the large 

unsubmerged material surface area. Other panelists believe that the time period 

associated with unsubmerged corrosion is too short to provide significant contributions. 

The ICET observations indicated that predominant metallic contributions at high pH were 

caused by submerged Al components and that the unsubmerged contributions were 

insignificant [11]. 

A more universal concern with NaOH is for longer time periods, more than 1 day after 

the LOCA (T3-2, Table 9). During this time, the containment pool will be well mixed, and 

the high pH may promote corrosion of metals like Al and the leaching of silica and other 

constituents from insulating materials such as NUKON® and Cal-Sil. Corrosion of Al, 

the leaching of silica, and the subsequent production of Al(OH)3 precipitates were 

 

1

 Note that this upper pH value is less than the value reported in the final safety analysis report 

(FSAR) for some plants. The higher FSAR estimates used by some plants apparently did not 

account for the buffering capacity of the boric acid. 

42 
observed during ICET Test 1 [11]. Interestingly, much less silica leached from NUKON® 

than would be predicted from single-material testing. This has been attributed to 

“passivation” of the NUKON® by Al [17] (See Section 1.2 for more details). Although the 

panelists agreed that these significant observations should be considered when 

evaluating chemical effects, they did not identify additional phenomena related to NaOH 

buffering that require further consideration. 

Concerns related to TSP buffering stem from the observations in the ICET Test 3 that 

large amounts of Ca3(PO4)2 precipitated within the first hour upon introducing TSP (T2-6, 

Table 8) [11]. The precipitation of Ca3(PO4)2 has also been shown to lead to significant 

head loss under certain conditions [15]. It was demonstrated in ICET Test 3 that the 

phosphate was depleted within 1 day or less because of the presence of excess 

dissolved Ca concentrations in solution [15]. This rapid depletion may not occur in TSPbuffered containment pools with smaller dissolved Ca concentrations. However, as long 

as sufficient dissolved Ca is present such that the reaction is phosphate limited, it is 

expected that Ca3(PO4)2 concentrations similar to ICET Test 3 will be precipitated during 

the post-LOCA period. 

Concentrations of dissolved Ca below the point where the reaction become Ca-limited, 

will proportionately decrease the Ca3(PO4)2 concentration. However, for these lower 

dissolved Ca concentrations, other solid species may be formed between available 

metal cations and phosphate anions. As demonstrated by the ICET experiments, the 

time period associated with these phosphate reactions can be short and may proceed to 

completion within 1 day depending on specific cation and anion concentrations (See 

Section 1.2 for more details). The PIRT panelists identified no additional concerns with 

TSP buffering beyond the observations from the ICET and chemical effects head-loss 

testing. 

Buffering with STB raised the least concern among the PIRT panelists (T2-5, Table 8; 

T3-3, Table 9). The spray and containment pool chemistry is more neutral (the pH is 

less than 8.5) in plants using STB buffering than for those using NaOH buffering. 

Therefore, corrosion of some materials is decreased. Although corrosion is diminished, 

precipitate formation can still occur, especially upon cooling. Precipitation was observed 

in ICET Test 5 [11], but it occurred later in the test (several days after the test initiated), 

took longer to form upon cooling (1 day or more), and was generally less concentrated 

when compared to the ICET Test 1 results [11]. Additionally, the STB does not form 

insoluble materials with dissolved ions (like Ca) as does TSP [40]. Therefore, STB may 

be the most benign buffering system. 

5.1.4 Dissolved Hydrogen Concentrations 

At least one PIRT member strongly believed that an accurate accounting of dissolved H2

concentrations is important for determining the underlying ECCS water chemistry (T2-1, 

Table 8). His contention is that the reduction /oxidation (redox) potential is a function of 

the amount of dissolved H. Hydrogen sources within the containment include the RCS 

inventory, the corrosion of metallic materials including the reactor fuel cladding (Section 

5.7.3.3), and the Schikorr reaction. 

The possible generation of H from the Schikorr reaction 

3Fe(OH)2 → Fe3O4 + H2 + 2H2O

43 
and related chemical transformations might contribute significantly to the H inventory in 

containment immediately after a LOCA. Additional H in the containment pool caused by 

this reaction is beneficial in one sense because it may decrease the redox potential and 

inhibit corrosion. This is the reason H is added to PWR and BWR primary coolant 

circuits. Another positive attribute of the Schikorr reaction is that it decreases gelatinous 

iron(II) hydroxide (Fe(OH)2), which may react with other components (e.g., Si(OH)4) to 

produce mixed oxides/oxyhydroxides and mixed hydroxides that may be more 

detrimental than Fe(OH)2. One possible downside of this reaction is that magnetite 

(Fe3O4) is produced. However, Fe3O4 may be a less deleterious chemical effect than 

Fe(OH)2. On balance, this panelist appears to stipulate that this is a beneficial chemical 

effect assuming that H concentrations do not lead to deflagration or other nonchemical 

effects. 

Other PIRT panelists, however, stipulated that the H concentration is small initially and 

that the dissolved H additions from metallic corrosion will decrease with time. 

Additionally, the following points were provided to argue that H would not be an effective 

reducing agent in this environment: 

• H is not a very effective reducing agent in the absence of a catalyst (such as 

platinum metal), 

• H partitioning into the containment building atmosphere renders it largely inert, 

and 

• Containment buildings have H recombiners that start at approximately 2% H in 

the containment atmosphere. These low levels result in negligible dissolved H to 

affect the redox potential. 

Most panelists indicated that estimating these effects should be straightforward. 

5.1.5 PIRT Research Recommendations

Several issues within this section require further consideration to ensure that chemical 

effects are appropriately addressed. Some additional investigation on the effect of 

concentrated B within the RPV is warranted. The B concentration could be estimated 

through scoping calculations. Then, literature surveys may be used to determine if these 

concentrations significantly affect the corrosion rates for reactor vessel internals and fuel 

cladding. Additionally, existing research may indicate whether these concentrations alter 

the types, amounts, and properties of chemical precipitates that could form within the 

RPV. The important role of B in controlling the formation of Al(OH)3 precipitates was 

previously demonstrated in the ICET experiments. 

As discussed, it is vital to consider each plant-specific pH and temperature history in 

combination with various postulated debris mixtures within the buffered environment. 

This evaluation is necessary to accurately determine the dissolved species, material 

corrosion and/or dissolutions rates, and formation of precipitates based on solubility and 

kinetic considerations. Variability in the pH and temperature history should also be 

evaluated. Unfortunately, this assessment does not lend itself well to generic 

considerations because of expected differences in the post-LOCA coolant water 

44 
conditions among the U.S. PWRs. It will therefore be necessary to evaluate conditions 

existing at each plant. 

Additional scoping calculations could be used to assess the magnitude and relative 

effect of H production from a variety of sources, including the Schikorr reaction. The 

objective of this analysis is to determine if dissolved H2 plays a significant role in the 

containment pool chemistry or if these effects can be neglected. 

5.2 Radiological Considerations

Radiological considerations fostered much discussion and a general agreement among 

the PIRT panelists that these effects have not been sufficiently addressed to understand 

their implications on subsequent post-LOCA chemical effects. Issues fall within the 

following two categories: (1) the effect of radiolysis on the post-LOCA cooling water 

chemical environment and (2) the effect of radiation on the physical and chemical 

properties of solid species that could form in this environment. 

There are expected to be two significant radiation sources. The reactor fuel itself is the 

largest source. Although active fission reaction ceases after a LOCA, gamma radiation, 

caused by the radioactive decay in the fuel, is still in the 1x106

 rad/h. The other 

prominent source of gamma radiation is from activated debris and chemical species. 

Neutron-activated corrosion products and deposits form on the fuel and reactor coolant 

internal components. A percentage of these deposits will spall from the surface as a 

result of the post-LOCA pressure/temperature blowdown transient and will be released 

into the cooling water. 

Based on the energy released, some of the more important activation isotopes that may 

be expected in the post-LOCA cooling water include sodium-24 (24Na), beryllium-7 (7

Be), 

chromium-51 (51Cr), cobalt-58 and cobalt-60 (58,60Co), manganese-54 and manganese56 (54,56Mn), 95,97Zr, 55,59Fe, 59,63Ni, niobium-95 and niobium-97 (95,97Nb), antimony-125 

(

125Sb), 65Zn, and silver-110m (110mAg). The species and concentrations present will 

depend on plant-specific coolant chemistry, buffering agents, and the containment 

materials present (e.g., insulation, structural materials and cabling). The radiation fields 

associated with these species are likely to be significant compared to the radiation from 

intact fuel if species become concentrated at the sump screen. At least one PIRT 

panelist estimates that radiation fields on the order of 103

 1xrad/h would be present in 

the sump screen. This estimate is based on the dose measured on reactor coolant resin 

beds and filters following a normal shutdown where fission and corrosion products are 

concentrated within the beds. 

5.2.1 Effect of Radiolysis on Chemical Environment 

The more general concern associated with activation product decay from the reactor fuel 

and potentially spalled activated species (e.g., Ni, Fe, Sb, Mn, and Ag) is related to the 

radiolysis of the post-LOCA cooling water and dissolved constituents (T2-20, Table 8; 

T3-6, Table 9; T4-28, Table 10). Radiolysis is the dissociation of molecules by radiation. 

It is the cleavage of one or several chemical bonds resulting from exposure to highenergy flux. In the post-LOCA environment, water will form H, oxygen (O), hydrogen 

peroxide (H2O2), hydroxyl radicals (OH•), and a number of other, minor products caused 

by radiolysis. However, the O and H gaseous radiolysis products will be quickly 

removed from solution by heat and agitation leaving only H2O2 and OH• in solution. 

45 
Both of these species are strong oxidizing agents (i.e., they have a high tendency to 

accept electrons from other species). 

Radiolysis can subsequently modify the redox potential of the water depending on the 

relative amounts of H, O, and H2O2 produced. The redox potential is the tendency of the 

medium, via the electroactive chemical species present, to acquire or lose electrons and 

thereby be reduced or oxidized, respectively. The H2O2 and O concentrations can build 

in the solution to potentially yield a more oxidizing environment than deaerated or even 

oxygenated water. The redox potential is a property of the environment by virtue of the 

ensemble of species contained within it and is not the sole property of any given 

species. Therefore, it is most readily calculated using the Mixed Potential Model [41] 

and corresponds to the situation where no oxidation of any substrate occurs. 

Experimentally, this situation is most closely achieved when using a platinum or gold 

indicator electrode. 

As the redox potential becomes more positive, or oxidizing, an oxidizing specie's affinity 

for electrons increases. For metallic materials, changes in the redox potential can 

substantially alter the corrosion rates (T4-26, T4-29; Table 10). The redox potential also 

can alter the speciation of dissolved chemicals and consequently the solution 

concentration of the corresponding elements. This effect has been prominent in the mild 

steel-lined Hanford waste storage tanks that contain a mixture of different phases having 

different chemical species. The rate of tank-wall corrosion is affected by the redox 

potential defined by presence and radiolysis of nitrate, nitrite, and hydroxide in the 

waste. Plutonium solubility is also affected by radiolysis of these same three species 

and its solubility can be sharply increased by chemical oxidants [42, 43]. 

As another example, the stress corrosion cracking (SCC) of sensitized Type 304 

stainless steel (SS) in the primary coolant circuit of BWRs is entirely driven by the high 

redox potential of the coolant, which is caused by the accumulation of O and H2O2

through radiolysis and the loss of H through coolant boiling in the core. The redox 

potential and subsequent effects on SCC have been successfully determined in BWR 

primary coolants in which at least four redox couples are present [41]. This work is the 

basis for specifying a critical, primary circuit corrosion potential of -0.23 volts based on 

the standard H electrode (VSHE). For potentials more negative than this value, sensitized 

304 has been demonstrated to be resistant to SCC [41]. 

Several of the panelists expect radiolysis to begin quickly, during the ECCS injection 

phase (T2-20, Table 8). They stipulate that H2O2 production will begin almost 

immediately after the break, because the H control within the RCS will be lost, and much 

of the initial dissolved H in the RCS coolant will transition to gaseous H upon exposure 

to the containment atmosphere (T1-5, Table 7). As a result, Fe, Ni, and Co (and 

possibly other metals like Al) will be more easily oxidized and will precipitate oxides, 

oxyhydroxides, and hydroxides. 

The presence of H2O2 in solution will promote further oxidation of Fe(OH)2 to Fe3O4 or to 

iron oxyhydroxide (FeOOH). However, local depletion of H2O2 could also cause Fe(OH)2

oxidation to Fe3O4 and H through the Schikorr reaction. The H thus generated would 

contribute to the total H inventory, which would help sustain reducing conditions as 

discussed in Section 5.1.4. The formation of perborates (BO3

-

) from the reaction of 

sodium metaborate (NaBO2), NaOH, and H2O2, is also possible under radiolytic 

conditions [44]. Perborates are oxidizing agents and could therefore oxidize metals. 

46 
Because most participating redox reactions will be in a state of disequilibrium, the 

oxidation state of the system can only be defined in terms of mixed potentials. 

The PIRT panelists expect radiolysis to be most significant during the early recirculation 

phase, from 20 minutes to approximately 1 day (T3-6, Table 9). Subsequent to this, 

radiolysis is expected to continue, but equilibrium may eventually be reached (T4-38, 

Table 10). As mentioned previously, high redox potentials can substantially elevate the 

metallic corrosion rates and alter chemical speciation and the solubility of compounds. 

Several panelists believe that the radiolytic effects on the redox potential could 

fundamentally impact the containment pool chemistry. However, other panelists believe 

that the oxidizing potential of the containment pool is already high which may mitigate 

the severity of this effect. 

Another corrosion rate enhancing mechanism (for Al, Fe, and SS) promoted by 

radiolysis is the formation of hypochlorite or hypochlorous acid by radiolysis of Clbearing water (T4-29, Table 10; S-4, Table 12). Both of these compounds are strong 

oxidants. The PIRT panelists expect that effect could become active during the 

intermediate ECCS recirculation time, after 1 day or more. Most of the panelists believe 

that the impact of this effect is modest because containment pool Cl concentrations are 

expected to be low. The ICET test plan [12] indicated that a HCl concentration of 

100 ppm (3 x 10-3 M), which corresponds to about 70 pounds of insulation degradation, 

represents Cl concentration released during cable radiolysis. Actual plant Cl 

concentrations could be lower than this value if significantly less cable insulation 

undergoes radiolysis. However, if Cl concentrations greater than 100 ppm (3 x 10-3 M) 

are present, hypochlorite formation could be significant. At least two panelists expect 

that the effect of radiolysis will be secondary for inorganic materials because the 

environment is already strongly oxidizing and that organic materials are more 

susceptible to radiolytic effects than inorganic materials (Section 5.6). 

Although radiolysis induced by the activation product decay from the reactor fuel 

promotes global radiolytic effects, localized effects are possible because of radionuclide 

transportation and accumulation within the sump screen debris bed (T3-16, Table 9; 

T4-25, Table 10). This concentration of radionuclides (hundreds of Curies have been 

postulated) could locally alter the debris bed chemical environment. The radioactive flux 

becomes more concentrated than if it was dispersed throughout the containment pool, 

and the radiolytic reaction may not reach steady state as debris continues to 

accumulate. Two panelists believe that this concentration will create a locally higher 

oxidizing environment through production of H2O2. Reduced species will transform into 

oxidized species and increase the likelihood of precipitation or co-precipitation of oxides. 

As with the global effects, two panelists stated that radionuclide concentration will 

minimally affect the inorganic chemistry and species formation, but it will have a greater 

impact on organic materials (Section 5.6). These panelists believe that local radiolysis 

will not significantly affect the already high oxidation state such that the corrosion rates 

and solid species precipitation observed in the ICET series would remain largely 

representative of the post-LOCA environment. However, radiation fields could cause 

organic materials to either decompose or polymerize and harden, depending on the 

material. Decomposed organics could also coat fiberglass insulation fibers to reduce 

leaching as the post-LOCA events continue. Another possible effect is that local 

radiation could cause glass embrittlement of NUKON® fibers, which would cause longer 

fibers to break. 

47 
Decay of the activation products may also contribute to the reducing potential of the 

post-LOCA solution through another mechanism. All radionuclide products formed in the 

reactor are negatron emitters. A negatron is a high-energy electron that originates in the 

nucleus. Although each individual radioactive decay yields only one electron, the 

interaction of the one highly energetic electron with water causes ionization events in 

water on the order of 1x104

. In other words, one decay electron yields about 

1x104

 electrons in water. Gamma emitters also contribute to electron production. The 

presence of kiloradians worth of radioactive beta emitters in the containment pool will 

also produce significant numbers of electrons that may shift the redox potential towards 

a reducing environment—but only at interfaces between solid and aqueous phases—as 

compared to the same environment without decay products. However, this effect is 

expected to be beneficial because an environment that is less oxidizing will reduce 

metallic corrosion and leaching rates. 

Traditionally, however, modeling of redox potential effects has considered only the 

chemical radiolysis products that are produced (e.g., H, H2, OH, H2O2, HO2, and O2), 

because these are the longer lived species that form as a result of electron 

bombardment and capture. Also, only these species, and not electrons, can participate 

in charge transfer reactions at the surface that leave the two phases (i.e., aqueous and 

solid) electrically neutral. The number of particles of each radiolysis product in the 

system, produced upon the absorption of 100 eV of energy from the primary radiation (α, 

β, γ, and n radiation), is specified by the G-value. 

Another related observation is that electron emission can occur from a negatively 

polarized metal surface in contact with an aqueous environment. However, the aquated 

electrons, so produced, appear to remain closely associated with the metal surface, 

probably for charge reasons, whereas the chemical radiolysis products are free to 

disperse throughout the aqueous phase. Thus, the overall effect of this electron 

emission is not expected to enhance or diminish the redox potential in the containment 

pool. 

The previous discussion has focused on the radiolysis of water and the effects on the 

global and local redox conditions, but radiolysis also converts atmospheric nitrogen (N2) 

into nitric acid (HNO3) within the containment pool (S-1, Table 12). The HNO3 acts to 

decrease the pool pH. One panelist stated that this effect, if the radioactive dose rate is 

sufficiently high in the containment pool, could overwhelm the plant’s buffering capability. 

This panelist also conducted initial conservative scoping calculations that predicted a 

precipitous pH drop caused by this effect that would lead to massive corrosion of 

structural materials [27]. Plant licensees are required to account for radiolysis, including 

that of atmospheric N2, in designing the buffering system of the pool in an alternative 

source term analysis [45]. A method for calculating pH to account for this and other 

radiolytic phenomena is also described in [46]. However, these calculations do not 

consider the effects on pH from all the various debris types existing in the post-LOCA 

containment pool. It is also not clear if the calculation accounts for the variability of boric 

acid concentration and acidity as a function of temperature and cation concentration. In 

light of these additional factors, some additional evaluation of the calculation methods 

described in [46] may be useful to validate that the containment pool pH does will not 

become acidic as a result of HNO3 formed by the radiolysis of atmospheric N2. 

48 
5.2.2 Effect of Radiation on the Properties of Solid Species 

Another possible effect is that these radiation fields may alter the types and properties of 

solid phases that form (T4-25, Table 10). Such characteristics that could be affected by 

the radiation dose include the precipitate size, composition, morphology, and aging 

mechanisms. A specific example that may illustrate the effects of radiation on solid 

species is the observed decomposition of the neutron poisoning material (Boraflex®) in 

PWR spent fuel pools [47]. The borated, spent fuel pool pH is approximately 4.5. In the 

pools, reactive silica is created by the degradation of the silicone rubber polymer and 

silica filler material that comprises Boraflex®. However, similar Boraflex® degradation 

has not been observed in long-term testing (i.e., approximately 6 months) in either 

borated, aqueous environments or under radiation exposure in dry air environments, 

although it is not reported if the solution was analyzed for silica or other degradation 

products. The implication is that the degradation observed in the spent fuel pool results 

either from radiation exposure or from radiolysis-induced oxidants like H2O2 within the 

borated solution, and not from simple dissolution of the silica filler material. 

The form of the dissolved silica may also be affected by aqueous, radiation exposure. It 

is hypothesized that the radiation from the spent fuel causes the silicone rubber polymer 

to hydrolyze and, together with the silica filler, dissolve as reactive silica. In spent fuel 

pools (pH approximately 4.5), reactive silica is present in solution at concentrations up to 

about 110 ppm. In contrast, the solubility of reactive silica in water (pH approximately 7) 

is about 51 ppm (1.8x10-3 M) as Si or 110 ppm (1.8x10-3 M) as silicon dioxide (SiO2) 

[48]. Although solubility is affected by pH and other variables independent of radiation, it 

is also possible that the solubility has been affected by the radiation by changing the 

physical characteristics (e.g., precipitate size, composition, and morphology) of he silica. 

More study would be necessary to validate this hypothesis and verify the actual effects 

of radiation on the decomposition of Boraflex® in this example, and other debris in the 

post-LOCA containment pool. Some panelists also believe, based on similar arguments 

presented in Section 5.2.1, that the effect of radiation on the form and properties of 

organic materials could be more significant than any effects on inorganic material 

properties. 

5.2.3 PIRT Research Recommendations

The ECCS performance implications associated with all the radiological issues 

discussed in this section are highly uncertain at this point. More consideration of 

radiological effects is warranted to first understand the magnitude of the radioactive 

fields that could be produced. Then, the effects of changes in the redox potential on the 

containment pool chemistry, material corrosion rates, and chemical speciation and 

solubility could be evaluated. Also, the likelihood of transport and accumulation of 

activated species to the sump screen debris bed should be assessed to determine the 

radiation field which could be concentrated at the sump screen. Any localized chemical 

effects that may result from radionuclides trapped within the debris bed and the effect of 

radiation on the properties of precipitated solid species could then be explored. 

5.3 Physical, Chemical, and Biological Debris Sources

This section describes the types and quantities of debris that is created in the 

post-LOCA environment. Debris sources include physical debris (e.g., fibrous insulation, 

particulate insulation, and latent debris), chemically induced debris (e.g., oxides and 

precipitates), or debris created by biological growth. Debris generation is an important 

49 
consideration in any post-LOCA analysis of ECCS operability because it defines the 

amount of debris that will exist in the post-LOCA containment environment. The ECCS 

must contend with the debris load that is transported to the sump screens and either 

accumulates on the screen or is ingested into the ECCS pumps. Conservative 

guidelines have been established to analyze and address many aspects of debris 

generation and most physical debris sources [4]. This section will focus on important 

effects related to debris generation and debris sources that are not currently considered 

in existing guidelines, or that have not been fully evaluated in NRC-sponsored or 

industry-sponsored research activities. These effects generally result from or are related 

to chemical or biological processes that may be active in the post-LOCA environment. 

5.3.1 Debris Generation 

The PIRT raised several issues related to physical debris generation, which may alter 

the post-LOCA physically induced (Section 5.3.2) and chemically induced (Section 5.3.3) 

debris. The first relates to the initial impingement of the two-phase jet emanating from 

the broken pipe (T1-6, Table 7). This, of course, is one important source for physical 

debris generation. Physical debris is also generated by containment spray actuation, 

and post-LOCA pressure/temperature transients within the containment building and 

within the reactor coolant loop. 

Initial guidance for calculating post-LOCA debris generation is largely based on single 

liquid phase jet testing [4]. However, limited validation of insulation and coating debris 

damage or debris sizes from more representative two-phase jets [49] has suggested 

that the existing guidance is generally conservative. The size distribution of the 

insulation debris can affect both transport properties and chemical reactivity. Smaller 

sizes enhance transportability and reactivity [50 and 17]. In the absence of additional 

validation testing, the guidance requires that small debris sizes be assumed. 

Conservative debris concentrations are also calculated using the guidance unless 

corrosion inhibition or other advantageous effects (see below) can be demonstrated. 

The debris caused by the jet resulting from metallic erosion, or the ablation of other 

materials like concrete, is not specifically considered in the guidance [4]. This 

phenomenon will govern the contributions of these materials in the early post-LOCA time 

period, before corrosion and leaching becomes important. Jet impingement could also 

initiate pitting corrosion, which could accelerate the corrosion of normally passivated 

materials like SS. However, the PIRT panelists generally recognized that corrosion, 

erosion, and ablation caused by jet impingement (e.g., Section 5.1.1) will likely be 

inconsequential because of the short time duration of the jet (i.e., approximately 30 s) 

and the relatively small affected volume relative to the rest of the containment. 

The pipe break location is another important consideration. Breaks in different locations 

will create different debris characteristics such as the total debris mass, the particle/fiber 

mixture, and the debris composition. Of course, the physical debris characteristics affect 

the size (thickness), compressibility, and head loss associated with the physical debris 

bed that forms on the sump screen [51]. This phenomenon is the focus of the current 

guidance [4] that requires licensees to consider both high-fiber and high-particulate 

loading to demonstrate that acceptable NPSH margins are maintained in light of 

expected variability in the actual post-LOCA conditions. 

50 
Analogously, significantly different quantities of material (e.g., Cal-Sil and fiberglass 

insulation) can fundamentally alter the chemical effects (T1-9, Table 7). This impact was 

observed upon comparison of ICET Tests 1 and 4. The biggest difference between 

these tests was the inclusion of Cal-Sil insulation in ICET Test 4, yet substantial 

submerged Al corrosion occurred in ICET Test 1, whereas very little occurred in ICET 

Test 4. The lack of corrosion in ICET Test 4 was caused presumably by Al surface 

passivation by silica [14]. 

This result implies that, as with physical debris combinations, it is also necessary to 

consider the chemical ramifications arising from different break sizes and locations. A 

conservative or bounding analysis would not credit corrosion inhibition or other 

synergistic effects that reduce chemical effects. Such an analysis should need to 

consider only break scenarios that generate the maximum debris concentrations 

(e.g., insulation and latent debris) that contribute to post-LOCA chemical effect(s). 

These scenarios may or may not correspond to scenarios that generate the most 

physical debris or the highest ratio of particulate/fiber loading as required in the current 

guidance [4]. 

Conversely, if inhibition or other synergistic effects are to be credited for decreasing 

certain chemical effects, it is not sufficient to merely consider break scenarios that 

generate conservative concentrations of the debris that contribute to chemical effects. 

This practice may mask other, more realistic chemical effects. In a realistic analysis, 

break scenarios that generate less debris concentrations may induce the most onerous 

chemical effects 

The following examples illustrate these points. A hypothetical plant using NUKON® 

fibrous and Cal-Sil particulate insulation could expect the greatest dissolution of Ca and 

Si by considering break scenarios resulting in high concentrations of each constituent 

within the containment pool. If this plant uses TSP buffering, then this scenario should 

produce conservative concentrations of Ca3(PO4)2 precipitate. However, if the plant 

used NaOH buffering and has substantial submerged Al, this scenario may actually aid 

Al surface passivation and diminish the Al(OH)3 chemical byproducts that form [11]. For 

a NaOH-buffered plant that wishes to credit Al surface passivation, it may be more 

appropriate to consider an alternative break scenario that considers lesser quantities of 

Cal-Sil particulate insulation. This scenario may lead to more significant Al corrosion 

and the formation of Al(OH)3 caused by insufficient dissolved SiO2 to induce Al surface 

passivation. 

As another example, consider a hypothetical plant having Al reflective metal insulation 

(RMI)2

 that uses NaOH buffering. The most challenging chemical effects debris mixture 

could result from a break scenario producing sufficient fibrous debris to form a 

contiguous layer across the sump screen and the greatest quantity of Al RMI that settles 

within the containment pool. In this scenario, little additional particulate may be needed 

to cause head loss caused by the formation of Al(OH)3 as demonstrated in the ANL 

testing [15]. 

These examples demonstrate that it is equally important to consider break scenario 

conditions, which result in the greatest challenges caused by chemical effects, 

separately from scenarios that may result in the most challenging fibrous/particulate 

 

2

 Most reactor buildings in PWR plants do not contain Al RMI.

51 
physical debris mixtures. Small variations in the containment pool chemical constituents 

are likely not significant assuming that contributions of all containment materials (e.g., 

eroded concrete, fiberglass, paint and polymer debris, and metal corrosion products) are 

appropriately considered. What is important is considering breaks that generate 

significantly different concentrations or combinations of materials. 

The PIRT panelists also recognized the importance of containment spray actuation in 

transporting post-LOCA-generated insulation debris, latent debris, and coating debris to 

the containment pool (T2-7, Table 8). Submerged insulation debris within the 

containment pool, as demonstrated in the ICET tests [11], is expected to be a principal 

contributor of dissolved chemical species that contribute to various chemical 

phenomena. The latent debris concentration should be limited in those plants that have 

improved cleanliness procedures. Such procedures are identified as a possible interim 

compensatory measure [52] to reduce the potential risk caused by post-accident debris 

blockage as the generic letter evaluations [3] are proceeding. Therefore, latent debris 

may only be significant for plants that have little other fibrous or particulate debris 

sources. Contributions to debris from coating are expected to vary tremendously among 

plants as a function of the relative amounts of qualified and unqualified coatings in 

containment. The initial jet impingement emanating from the pipe break is assumed to 

fail both qualified and unqualified coatings within each respective zones of influence 

(ZOI) [4]. However, qualified coatings are assumed to remain intact outside of their ZOI, 

whereas unqualified coatings are assumed to fail outside of their ZOI [4]. Therefore, a 

substantial quantity of unqualified coating debris could be produced. 

The current guidance for physical debris transport is conservative in that bounding 

quantities of physical debris are assumed to be transported to the containment pool [4]. 

However, as with the rationale for considering multiple break scenarios, the maximum 

quantity of physical debris at the sump screen may not result in the most deleterious 

chemical effects. Therefore, it is important in a realistic chemical analysis to consider 

scenarios where physical debris may be sequestered from the containment pool as a 

function of the break location, debris location, and the containment configuration 

(T1-9, Table 7). Debris that may significantly contribute to either advantageous or 

deleterious chemical effects (e.g., Cal-Sil) may be more amenable to sequestration. For 

example, silicates could lead to inhibition of Al corrosion if present in sufficient quantities 

[53]. However, inhibition might not occur if substantial Cal-Sil or other silicate debris 

sources did not reach the containment pool. As with debris generation considerations, 

conservative analyses that do not credit either debris sequestration, corrosion inhibition, 

or other advantageous synergistic chemical effects may only need to evaluate scenarios 

that generate the maximum debris types and quantities that may contribute to chemical 

effects. 

5.3.2 Physical Debris 

As mentioned in Section 5.2, activated species that spall from reactor component 

internals and fuel represent a particulate source. One principal activated species source 

is from Fe and Ni oxides (mixtures of nickel ferrite, magnetite, nickel oxide and 

hematite), more commonly called “crud,” formed during corrosion of the RCS piping 

The crud layer is approximately 125 μm thick. It is postulated that these oxides could be 

dislodged by the hydraulic shock associated with the pipe break (T1-1, Table 7). These 

materials are observed during normal shutdown transients that produce less severe 

hydraulic shock. Plant data provided by one of the PIRT panelists for three reactor 

52 
shutdowns indicated that Ni concentrations of approximately 9 ppm (2x10-4 M) were 

observed between 30 and 50 hours after shutdown. The Fe concentrations were 

approximately 0.6 ppm (1x10-5 M) and occurred between 15 to 20 hours after shutdown 

[47]. These concentrations were corroborated by a study of French PWR shutdown 

chemistry that also documented the release of 58Co and 60Co [54]. 

One panelist postulated that up to 100 ppm (approximately 2x10-3 M) of Ni and Fe could 

be released just after the pipe break as a result of the more severe LOCA pressure and 

temperature shock. The following postulated scenario (T2-13, Table 8); that could lead 

to these concentrations The initial oxide layer breaks off, fresh metal is exposed and the 

exposed reduced Ni and Fe combines with air and forms additional oxides that spall off 

because of the continued pressure/temperature fluctuations. Thus, the cycle is 

repeated. This process could continue for 1 day or longer until RCS piping cools down. 

This process may also be enhanced if either hot STB or boric acid acts as a flux to 

dissolve the Fe3O4 layer from the reactor vessel wall or zirconium oxide (ZrO2) from the 

clad fuel. However, the RCS temperature may be too low to initiate this phenomenon 

[27]. If these crud particulates are transported to the sump screen, they could contribute 

to NPSH reduction from additional particle loading. Also, these Fe and Ni activation 

products could concentrate at the sump screen and may result in local radiation dose 

rates on the order of kiloradians per hour. This radiation flux could then alter the local 

chemical environment and solid species formation and properties (Section 5.2). Finally, 

over the course of the post-LOCA mission time, the crud materials may change their 

chemical form, including the formation of ferric hydroxide (a strongly flocculating 

material) that could produce deleterious chemical products. 

However, at least one panelist believes that although the initial crud burst quantities may 

be appreciable, subsequent concentrations caused by continued generation and 

spallation will be relatively small compared to the other solid species present within the 

containment pool. A few panelists also believe that the crud particles will settle in a 

relatively quiescent pool given their high densities. This would diminish radiation 

concentration and particulate loading effects at the sump screen. Another panelist 

suggested that a positive effect of these crud particulates is that their high density will 

promote agglomeration of other insoluble materials. 

Spallation of the reactor core fuel cladding ZrO2 (T4-24, Table 10) or deposited chemical 

products is another potential source for activated material (T3-22 and T3-27; Table 9; 

T4-37 and T4-38; Table 10). Possible post-LOCA chemical products that could be 

deposited on the fuel clad include organics, Al, B, Ni, Fe, Zn, Ca, magnesium (Mg), 

silicates (SiO3

2- and SiO44-), and CO32--based deposits. Solid species could precipitate 

on the fuel cladding because of retrograde solubility (Section 5.4.2.2) or solvent 

evaporation near the fuel. Additional solids that form either in the containment pool or 

heat exchanger (Section 5.4.2.1) will also be present. Note that most of the preexisting 

solids, especially those that would be transported through the sump screen, are 

expected to be fine particulates. These products could bind on the fuel cladding as the 

coolant water bearing the dissolved and suspended solids flashes to steam. The 

deposited solids could then undergo higher temperature hydrothermal reactions and 

self-cementation or caking. The characterization of crud found on PWR fuel cladding 

from operating reactors [55] provides evidence to support this hypothesized post-LOCA 

fuel deposition scenario. The referred study found organic and aluminosilicate deposits 

in addition to nickel ferrites on fuel cladding surfaces. 

53 
As the deposits thicken with time, thermal shock and mechanical vibration caused by the 

post-LOCA recirculating water could cause the deposits to spall (T4-38, Table 10). As 

the fuel surface continues to cool, spallation from the surfaces will continue. This 

phenomenon is observed in spent reactor fuel pools as samples from the bottom of the 

pools exhibit increased concentrations of spalled fuel deposits over the first several 

months of storage [47]. Spalled fuel deposits could either contribute to clogging within 

the reactor core (Section 5.7.3.2), or they could be transported to and contribute to sump 

screen head loss. Transportation may be aided if the spalled deposits are particulates 

or are curved flakes resulting from the fuel shape. A positive consequence of spallation 

is that it will improve the heat transfer of the reactor fuel (Section 5.7.3.1). However, at 

least one panelist believes that spalled deposits from the reactor fuel are not likely to 

generate a significant amount of solid material compared to the other chemicallyinduced 

debris constituents. 

5.3.3 Post-LOCA Chemically Induced Debris 

5.3.3.1 CO2 Absorption 

Much like physical debris that is generated at the onset of the LOCA, chemically induced 

debris is expected to form early, and throughout, the post-LOCA scenario. Air 

entrainment within the containment pool—caused by coolant water emanating from the 

break and pool turbulence in addition to atmospheric scrubbing from containment spray 

(T2-8,Table 8) —will cause carbon dioxide (CO2) absorption beginning soon after the 

LOCA and before the onset of sump recirculation. It is worth noting that the large 

containment-air-to-pool-volume ratio that exists in plants was not simulated in the ICET 

program. With the dissolution of post-LOCA debris (e.g., Cal-Sil, concrete, and 

fiberglass), Ca cations (Ca2+) would build up in solution. Because the pH-buffered 

recirculating cooling water eventually becomes alkaline (i.e., the pH is between 7–10), 

the absorbed CO2 would accumulate predominantly as the bicarbonate ion, which would, 

in turn, react with Ca2+ to precipitate CaCO3. Both the absorption of CO2 and 

precipitation of CaCO3 would tend to depress pH, which, together with the depletion of 

Ca2+ from solution, would enhance the continuing dissolution of insulation materials. 

However, the pH buffers in solution would mitigate pH changes, and eventual depletion 

of CO2 in the air of the containment building would limit further calcite precipitation. 

Preliminary calculations by some of the PIRT panelists suggest that approximately 

several hundred pounds of finely divided CaCO3 particulate may be produced through 

the uptake of atmospheric CO2 in a containment building (T2-10, Table 8). This quantity 

is likely negligible (i.e., less than 1 percent) of the total debris introduced into the 

containment pool following a LOCA. Additionally, depending on the buffering chemical, 

the CaCO3 may simply replace other finally divided Ca precipitates like Ca3(PO4)2. The 

hydrated lime, Ca3(PO4)2, and calcite solids are physically similar and are unlikely to be 

significantly different in affecting either sump screen flow or downstream ECCS 

performance. Therefore, calcite formation may only be a principal consideration if 

conditions do not foster precipitation of these other species and if other debris loading 

sources are small (i.e., less than a few thousand pounds). 

However, the CaCO3 could assume a secondary role by serving as a site for 

heterogeneous nucleation and growth of other chemical phases (e.g., Ca phosphates 

and silicates) early in the post-LOCA cooling cycle (T2-10, Table 8). Thus, although 

calcite from atmospheric CO2 may produce a negligible amount of solid material, its 

effect on precipitation kinetics could be significant. For this reason, a few PIRT 

54 
reviewers recommended that the relative impact of CO2 absorbed from the air and the 

effect of subsequent calcite formation should be assessed. The accurate assessment of 

these implications requires consideration of plant-specific debris sources, dissolved Ca 

levels, sump environmental conditions, and the quantity of fresh air in containment that 

replenishes the CO2 supply that may have been exhausted by precipitation. 

5.3.3.2 Dissolution and Corrosion 

Debris dissolution and metallic corrosion also would begin just after the LOCA as 

materials are impacted by and then immersed within the containment pool water. These 

are the major mechanisms for creating the ionic species existing in the containment pool 

(T2-9, Table 8). The dissolved, ionic species could subsequently react and precipitate to 

form new, solid phases that were not originally in the containment pool. Therefore, 

corrosion and dissolution will determine the total inventory of solid material in the 

containment pool. The importance of metallic corrosion and debris dissolution is well 

known and has been demonstrated in the ICET program for representative post-LOCA 

environments [11] and also in less-complex, separate effects testing [17 and 18]. 

The focus of this prior research has often been the evaluation of conservative amounts 

of representative containment materials. It may also be necessary to study the corrosion 

and/or dissolution and precipitation for realistic amounts of important plant-specific 

materials in simulated post-LOCA environments. The chemical products determined 

from conservative material concentrations may suffice for assessing a dominant 

chemical reaction that is not expected to be altered significantly by other chemical 

additions. In other situations, using conservative material concentrations may mask 

more likely chemical effects that could alter the solid species and phases that form. 

For instance, ICET Test 3 included a bounding amount of Cal-Sil insulation that led to 

the rapid elimination of dissolved PO4

3- ions (within 1 day) through the formation of 

Ca3(PO4)2. Although it was demonstrated that Ca3(PO4)2 can result in significant head 

loss [15], it was not possible in ICET Test 3 to form other PO4

3- products that may have 

different implications for environments containing much less dissolved Ca from Cal-Sil or 

other sources. 

Knowledge of realistic chemical mechanisms also allows more accurate evaluation of 

the time period associated with possible solid-species precipitation. The minimum 

NPSH pump margin and maximum required ECCS cooling rates occur at the onset of 

recirculation and represent the principal design considerations. Greater system margin 

is available as time increases past the onset of recirculation. The ICET Test 3 [11] and 

subsequent head-loss testing [15] demonstrated that significant quantities of Ca3(PO4)2

can form within an hour of the initiating LOCA event. However, in ICET Tests 1 and 5, 

significant quantities of Al(OH)3 solid was not observed until several days had passed. 

Therefore, accurate consideration of precipitation formation could be used to 

demonstrate that an acceptable margin exists. Conservative assumptions of the time to 

form precipitates (e.g., instantaneously) could always be used in the evaluation as long 

as the actual solid species precipitates, as described in the above paragraph, are 

known. 

5.3.3.2.1 Nonmetallic Dissolution 

The implications on ECCS performance associated with dissolution of nonmetallic 

physical debris within the containment pool are not always straightforward. On one 

55 
hand, leaching may reduce the debris mass that contributes to sump screen head loss if 

the leachant remains dissolved. This phenomenon was observed in mixed fiberglass, 

Cal-Sil debris beds in STB environments [15]. Calcium silicate dissolution decreased 

the measured head loss across the test screen after some time. Conversely, some 

fiberglass or particulate dissolution may allow greater physical debris bed compression 

which can increase head loss (T3-18, Table 9). Leachants (e.g., Si, Al, Mg, Ca, and 

cations or oxyanions) may also react with other components in the containment pool to 

form voluminous gel-like products that may have onerous head loss and downstream 

effect implications (T3-7, Table 9). This issue underscores the need to consider the 

synergistic effects created by debris dissolution and metallic corrosion. 

The effect of aging on the leaching process for nonmetallic materials, especially 

concrete, is another consideration (S-3, Table 12). Ordinary Portland cement reacts with 

water to form principally calcium silicate hydrate (C-S-H) (i.e., CaO-SiO2-H2O) “gel” and 

portlandite (Ca(OH)2). It is these phases that should be considered if fresh concrete 

were to be leached by the recirculating coolant. However, neither the exposed concrete 

faces nor concrete dust in the containment building are likely to be fresh. After 30 years 

of atmospheric exposure, a substantial fraction, if not all, of both the exposed C-S-H gel 

and the portlandite will be carbonated [56]. Exposed carbonated cementitious materials 

would most likely be converted to a mixture of amorphous silica and either vaterite or 

aragonite, both forms of CaCO3 [57]. 

5.3.3.2.2 Metallic Corrosion 

The implications on ECCS performance associated with metallic corrosion are similarly 

complex. Bulk Al corrosion and the formation of Al(OH)3 precipitates upon cooling were 

observed in ICET Test 1 [11]. These precipitates were later demonstrated to have 

significant head loss implications [15] at the ICET concentrations. The ICET Test 5 also 

exhibited significant Al corrosion. However, significant Al corrosion was not apparent in 

ICET Tests 2, 3, and 4. Additionally, significant corrosion of other metallic components 

was not observed in any of the ICET tests. See Section 1.2 for more details. 

Although all panelists agree that Al corrosion is important in the post-LOCA environment, 

a few believe that higher Al corrosion rates are possible if affected by galvanic coupling, 

by electrolytic deposition, or by catalysis of other metals like copper (Cu) (T4-6, Table 

10). Copper was included in the ICET program, which may imply that the electrolytic 

deposition effect, as described below, or any potential catalytic effect has already been 

accounted for at the Cu surface area to water volume ratios used in ICET. Higher Cu 

ratios may therefore be required to trigger these effects. The catalytic effect of greater 

amounts of Cu, or other materials not in the ICET program, has not been studied. 

The panelists do not expect Cu by itself to corrode significantly unless the post-LOCA 

environment is highly oxidizing (T4-3, Table 10). This expectation was confirmed in the 

ICET series where minimal Cu corrosion was observed. However, besides catalytic 

effects mentioned above, Cu can accelerate or inhibit corrosion of other metals. 

One way in which Cu can alter the corrosion rates of other materials is by forming a 

galvanic couple (T2-22, Table 8). A galvanic couple is created when a structural 

material and Cu are in electrical contact and submerged within an ionic solution. Less 

noble metals than Cu can then preferentially corrode through anodic dissolution. For the 

prominent containment materials, the materials ranked by decreasing nobility are as 

56 
follows: Cu, Fe, Zn, and Al. Thus, Al is more likely to corrode than other materials and 

can actually inhibit corrosion in other materials if a galvanic coupling is present. Copper 

is used, uncoated, as the grounding straps for many large structural components. 

Therefore, the possibility for a galvanic couple between these components exists if they 

are submerged during a LOCA. One panelist believes, however, that precipitates could 

be attracted to the Cu grounding straps and form a coating that would diminish the 

galvanic couple. Galvanic effects have not been studied in the ICET series or in other 

related research projects (Section 1.2). 

A mechanism that decreases corrosion rates is Cu deposition on the surface of other 

materials. Copper ion deposition was observed on Al coupons in ICET Tests 2 and 3, 

and the measured Al solution concentration was below the detection limits in these tests 

[11]. Therefore, corrosion inhibition through Cu ion deposition may have occurred. It is 

difficult to know which, if any, of these possibly competing Cu effects are important 

without further analysis. 

Iron, or steel, corrosion was not particularly prevalent during the ICET series and other 

testing in alkaline environments (T4-4, Table 10). Under the oxidizing conditions present 

in the ICET series, the dissolution of metallic Fe (i.e., in steel) might be expected to lead 

to immediate oxidation with precipitation of Fe oxides under oxidizing alkaline conditions 

as oxidation of Fe2+ is catalyzed by OH-

 [58 and 59]. However, Fe passivation could 

occur if Fe3O4 precipitates on exposed steel surfaces under alkaline conditions, as is 

suggested by [13]. This mechanism could explain why little Fe corrosion was evident 

during the ICET series. At lower pH (i.e., pH of approximately 7), Fe2+ is expected to 

accumulate in the aqueous phase, but the presence of O during ECCS coolant 

recirculation should ensure that any Fe precipitate would occur in the Fe(III) state. The 

PIRT panelists do not expect that Fe would precipitate in the Fe(II) state as reported in 

[60]. 

Lead (Pb) is an element that was not included in the ICET series, but it was evaluated by 

the PIRT (T4-2, Table 10). Lead blanketing or Pb wool is used to shield radiation hot 

spots during containment outage operations. One panelist estimated that several 

hundred pounds of Pb may be used in blankets. Although the blankets are usually 

covered with a protective plastic coating, it is expected that the coating will be 

penetrated in many places as a result of normal operational wear and tear. However, 

much of this Pb should be removed after an outage. Additionally, under typical 

post-LOCA containment conditions, Pb corrosion is expected to be low (on the order of 

ppb to low ppm). Passivation of the surface through formation of complex Pb silicates is 

also possible. 

Acetate (CH3CO2

-

) present within containment could enhance Pb dissolution and cause 

lead carbonate percipitation within the containment pool. The PIRT panelists largely 

agreed that the Pb chemical contributions were extremely plant-specific and these 

effects are only potentially significant if large quantities of both unprotected Pb (greater 

than several hundred pounds) and CH3CO2

- are present in the containment pool. Lead 

can also induce cracking in SS components, but this mechanism should not degrade 

ECCS operability over 30 days. 

Another variable not simulated within the ICET test series is the behavior of silica in the 

RWST and the RCS (S-2, Table 12). The concentration of silica in the RWST may be as 

high as 3 ppm (5x10-5 M), and in the RCS the silica concentration will be in the range of 

57 
0.3 to 3.0 ppm (0.5 to 5x10-5 M). Because silica in combination with Mg, Ca and Al can 

form materials with retrograde solubility, silica can have an effect on the total mass of 

material precipitating. The dissolved silica could react with other species leading to the 

formation of secondary precipitates. At least one PIRT panelist believed that these 

contributions could be important. Although this concentration of silica in the RWST 

should be considered when accounting for dissolved silica levels, it should be noted that 

silica levels in the ICET series generally exceeded 10 ppm (2x10-4 M) for all tests. 

Therefore, the additional contribution resulting from RCS and RWST silica may be 

insignificant compared to silica from other containment debris sources. 

5.3.3.2.3 Dissolution Rate Inhibition and Acceleration 

Other than the ICET program, most of the characterization and analysis to date in the 

post-LOCA environments has used separate effect testing to evaluate corrosion. The 

complex interaction between dissolution processes of combined, or multiple, materials or 

second order effects resulting from variations in the trace chemicals of the containment 

water have not been addressed. Examples of synergistic dissolution rate effects 

observed in the ICET series include the inhibition of NUKON® fiber leaching by 

dissolved Al, inhibition of Al corrosion by dissolved silica (T4-8, Table 10), and possible

suppression of Al corrosion by Cu deposition. Another possible synergistic effect 

discussed previously is galvanic corrosion (Section 5.3.3.2.2) and concrete aging 

(Section 5.3.3.2.1). Some other examples of synergistic dissolution rate effects that the 

PIRT panelists believe may be relevant (e.g., S-4, Table 12) within the post-LOCA 

environment follow.

The impact on the Al corrosion rate caused by typical water constituents has been 

previously studied [61]. The constituents whose effects were evaluated included Cl, 

nitrate (NO3

-

), sulfate (SO4

2-), carbonate/bicarbonate (CO32-/HCO3-

), H2O2, CH3CO2

-

, 

oxalate (C2O4

2-), citrate (C3H4OH(COO)33-), arsenate (HAsO42-/H2AsO41-), phosphate 

(HPO4

2-/H2PO41-), silicates (SiO44- and SiO32-), chromate/dichromate (CrO42-/Cr2O72-), 

molybdate (Mo7O24

6-), and mixtures of these species. Individual tests that were 

conducted at 92 °C (198 °F) with 100 ppm of the respective constituents, showed that 

only citrate increased corrosion rate, whereas phosphate decreased the corrosion rate. 

Significantly, H2O2 had no effect on the Al corrosion rate. Additional testing of Cl 

concentrations up to 10,000 ppm (0.3 M) and mixtures of 100 ppm Cl-

(3x10-3 M) and 

100 ppm H2O2 (3x10-3 M) also had no effect on the Al corrosion rate. 

Further Al corrosion tests have studied corrosion inhibition from phosphate [61 and 62] 

(S-4, Table 12). Initial work showed that measurable corrosion inhibition occurred with 

as little as 5 ppm (5x10-5 M) phosphate and postulated that the inhibition occurred 

because of surface deposition of a protective layer of aluminum phosphate [61]. 

Subsequent X-ray diffraction studies of an Al surface exposed to 5 ppm (5x10-5 M) 

phosphate at 195°C (383°F) for 24 days confirmed the formation of the aluminum 

phosphate compound augelite, Al2PO4(OH)3. This surface compound forms at 

phosphate concentrations down to 0.5 ppm (5x10-6 M) [62]. Some salts including 

chromates, dichromates, silicates (as in ICET Test 4), and borates are also reported to 

inhibit Al corrosion [63]. 

Material alloying may also influence corrosion rates (S-3, Table 12). Corrosion data for 

various containment metals was extracted from the published literature and tabulated 

[60]. The corrosion rates varied widely and were a function of the specific corrosion 

58 
conditions and the nature of the alloy subject to corrosion. Numerous different Al (and 

other metallic) alloys are commercially available and in use, but the variability in alloy 

dependent corrosion rates and cation concentrations has not been addressed in the 

NRC-sponsored testing. Given the corrosive environment of alkali borate solutions, at 

least one PIRT panelist expects that the nature of the alloy may not significantly alter 

corrosion, at least for Al. This intuition is buttressed by industry testing of several 

common nuclear Al alloys [53], which demonstrated only nominal corrosion rate 

differences. However, this has not been demonstrated for other metallic materials. A 

related consideration is the cation concentration or other chemical effects resulting from 

the alloying constituents. This consideration may only be important if substantially 

different alloying constituents other than those tested in ICET and other related 

programs are present or if significant alloying additions are present. 

These various studies indicate that the chemical constituents within the containment 

pool environment and material alloying can alter the basic corrosion potential of 

materials, either advantageously or disadvantageously. It will therefore be necessary to 

consider plant-specific differences in the baseline containment pool environment and 

containment materials to determine if corrosion accelerators or inhibitors may be 

present. An evaluation of significant alloying additions in nuclear materials and 

additional study (i.e., consideration of prior research or bench-top testing) could be 

performed to determine if either significant corrosion rate differences or dissolved 

concentrations of alloying elements are possible. 

5.3.4 Biological Debris 

The propensity for bacteria or other biota to grow in preexisting debris beds located on 

the sump strainer screen or elsewhere within the ECCS was considered by the PIRT 

(T4-22, Table 10). Significant bacterial growth may be important if it creates additional 

debris that contributes to sump screen clogging or detrimental performance of 

downstream components like pumps and valves. The scenario postulated by the PIRT 

is that containment environments contain a large amount of biological materials 

(i.e., fungi, bacteria, and spores) because refueling occurs typically in the spring and fall 

with the refueling hatch open and the containment building under negative pressure to 

prevent gaseous or particulate radioactive releases. Under normal operating conditions, 

these materials do not affect the performance of the closed nuclear systems. 

In the post-LOCA period however, initial temperatures will not be sufficiently high to 

sterilize the interior of the reactor containment building. As a result, as the reactor and 

surrounding component temperatures decrease, the warm moist conditions, augmented 

in some cases by phosphate buffering, will be conducive to growth of algae and perhaps 

other life forms. Sump screen debris beds and other similar locations are preferential 

locations for trapping and concentrating the biological materials and the organic food 

sources necessary to sustain their life. The proximity of the materials and food sources 

may foster growth of products like polysaccharides that are sticky and tenacious. 

According to one panelist, polysaccharides are known to cause fouling in other power 

plant systems, especially on SS surfaces. With time, these biological materials may 

develop contiguous mats and participate in blocking flow through the sump screens. 

The panelists did not reach a consensus concerning the plausibility and impact of this 

proposed scenario within a 30-day time period. One panelist questioned whether 

biological materials could even survive and grow in the post-LOCA borated 

59 
(approximately 2500 ppm (0.23 M)) water solution. He noted that borates are used as 

algae stats to inhibit growth. There was also disagreement about the time and 

temperatures needed for significant growth if biological materials do form. One panelist 

believes that biological growth will begin immediately and could increase exponentially 

such that significant challenges to both heat transfer and flow may exist within 15 days. 

Other panelists believed that growth would occur much more slowly and not be 

important over a 30-day time period. 

However, it should be noted that significant biological debris was found in the Three Mile 

Island (TMI-2) post-LOCA containment when it was opened which contradicts the above 

notion that biological materials may not survive or grow in these environments. 

However, river water was mixed with the RCS and ECCS water, which would not be 

expected in most post-LOCA PWR containment pools [9]. Also, this observation was 

made from containment water samples taken several months after the LOCA occurred 

[8]. It is unknown how much of this debris was present over the 30-day time period most 

critical for ECCS recirculation performance. Given the PIRT uncertainty and lack of 

direct observational experience, this is an area where additional study could shed light 

on the extent of biological growth within the post-LOCA environment. 

5.3.5 PIRT Research Recommendations

A number of issues identified within this section should be considered to thoroughly 

evaluate both generic and plant-specific chemical effects related to debris generation 

and to physical, chemical, and biological debris sources. Several of these issues can be 

addressed by understanding existing chemical effects over the range of appropriate, 

actual post-LOCA conditions at the plant. This study can be used to identify which 

issues remain relevant. Other issues may require additional study to more fully 

understand the particular chemical effects in order to make a determination of generic or 

plant-specific relevance. 

Although the debris generation guidance provided in [4] requires an evaluation of 

conservative concentrations of the main types of expected physical debris, one of the 

PIRT panelists believes that integrated testing should be performed to quantitatively 

measure effects associated with physical debris generation. Specially, the test should 

simulate the initial RCS two-phase jet to consider the debris generated during the initial 

10 s of the LOCA from different insulation materials and components. Then debris 

sizes, degradation, and chemical effects should be characterized. 

This type of integrated testing certainly represents one approach that could be attempted 

to more realistically simulate the post-LOCA environment and conditions. However, 

there are a large number of variables (e.g., debris type, distance from break, break size, 

plant configuration, environmental conditions, and debris age) that affect debris 

quantities, sizes, and post-LOCA effects. Additionally, there are large uncertainties 

associated with these variables and large plant-specific differences among these 

variables. These factors conspire to increase the complexity associated with this type of 

testing. Therefore, a conservative consideration of the applicability of existing debris 

generation and degradation (Section 1.2) may be more appropriate. 

However, no prior testing has evaluated the physical debris concentrations and 

characteristics from crud production and reactor fuel clad spallation. Additional 

evaluations could be performed to examine the possibility and extent of corrosion 

60 
product spallation from reactor vessel walls and from fuel cladding surfaces under 

conditions that would occur under post-LOCA thermal and mechanical shock. Spallation 

of both initial deposits and deposits that continue to form (Section 5.3.2) in the postLOCA period should be considered when evaluating the total debris concentration. This 

activated debris concentration will also determine the radiation fields (Section 5.2) 

present within the containment pool and, more importantly, at the sump screen. 

Evidence of these deposits is apparent in post-shutdown analysis of reactor water 

chemistry and in spent fuel pools upon continued fuel cooling, but larger quantities could 

be expected in a LOCA because of the higher pressure/temperature shock. 

Although the composition of reactor vessel crud deposits are well known (Fe and Ni 

oxides), there are a host of potential chemical precipitates that could form either in the 

coolant by retrograde solubility or on the reactor fuel clad surface by water evaporation. 

The nature of these deposits can first be determined through consideration of the 

dissolved species and suspended solids that are present within the ECCS cooling water. 

A thorough study will likely require a plant-specific evaluation of materials and various 

break conditions to characterize the ECCS cooling water chemistry. Then, the effect of 

the higher reactor core temperatures on the ECCS cooling water chemistry can be 

investigated to determine if new solid species form and whether solid species 

suspended within the cooling water can adhere and/or subsequently spall from the fuel. 

Research could also be conducted to determine whether these products are likely to 

settle within the reactor core, the lower plenum of the reactor vessel, or the containment 

pool. Settling within the reactor core may result in additional flow blockage and impede 

fuel cooling, but settling is much more likely within the containment pool because of the 

generally lower flow velocities. Containment pool settling will reduce the debris load that 

could contribute to either sump screen clogging or subsequent downstream effects. 

Other implications from, and the possible study of, spalled reactor fuel clad deposits are 

discussed in Section 5.7.3. 

Research is also needed to evaluate the debris generated by post-LOCA chemical 

effects. As discussed, several types of precipitates were observed in the ICET testing 

[11] that have been subsequently studied to evaluate some important properties 

(e.g., settling, solubility, and particle size) [15] and the potential for sump screen head 

loss [15]. However, other chemical effects were not considered or properly accounted 

for in the ICET. 

Calcite formation from atmospheric CO2 was one phenomenon not properly simulated in 

ICET because the free headspace to water surface area and volume were not scaled to 

containment ratios. Calcite precipitate loading may only be important for plants with 

significant sources of dissolved Ca (e.g., Cal-Sil, exposed concrete, and fiberglass 

insulation) that use a buffer other than TSP. Plants with TSP buffering already contend 

with Ca3(PO4)2. However, for all plants, the calcite may also serve as a site for 

heterogeneous nucleation and growth of other chemical phases (e.g., Ca phosphates 

and silicates) early in the post-LOCA cooling cycle. Thus, although calcite from 

atmospheric CO2 may produce a negligible amount of material in plants, its effect on 

precipitation kinetics could be significant. It may be necessary to consider plant-specific 

debris sources, dissolved Ca levels, and sump environmental conditions to evaluate the 

significance of this phenomenon. 

61 
The NRC-sponsored research also did not rigorously study the synergistic effects on 

metallic corrosion and nonmetallic dissolution under post-LOCA conditions. 

Single-effects testing under the premise of developing conservative corrosion rates has 

been instructive [18]. However, synergistic effects can either increase corrosion rates 

through catalytic effects or decrease corrosion rates through passivation or other 

mechanisms compared to these single-effects values. Integrated tests using generally 

conservative material quantities, such as ICET, provide some evidence of synergistic 

effects, but conservative concentrations of materials can also mask or inhibit corrosion of 

other materials in these tests. This phenomenon could alter the types and amounts of 

any precipitates that form in the tests compared to the actual containment environment. 

Realistic, plant-specific containment pool environment, materials, and concentrations 

should be considered to identify the appropriate corrosion acceleration and inhibition 

factors. One acceleration factor that should be studied is the catalytic effect of other 

materials that are not in the ICET program but may exist within containment. Copper is 

one possible catalytic material, but it would need to be present in greater quantities than 

in the ICET tests because no catalytic effect was observed in these tests. Examination 

of Al corrosion acceleration caused by citrate and other hydroxyl-organic acid anions 

(e.g., glycolate and HOCH2CO2

-

) is only a concern if significant sources of these anions 

are expected. Possible corrosion inhibition effects that could be evaluated include the 

aging of concrete and other nonmetallic materials; the presence of phosphate and salts 

such as chromates, dichromates, silicates, and borates on Al inhibition; and the 

possibility and threshold for corrosion inhibition or acceleration through Cu ion 

deposition. Although corrosion inhibition is largely beneficial, it will be important to 

demonstrate that testing or evaluation conditions are representative of service conditions 

so that the results are relevant and proper credit can be determined. 

Another corrosion inhibition or acceleration aspect that should be considered is the 

effect of alloying additions in nuclear structural materials and debris within the 

containment pool. First, knowledge of the particular material form and composition is 

needed in the assessment. Then, consideration of prior research or additional 

bench-top testing can be used to determine whether significant corrosion rate 

differences occur compared to unalloyed materials evaluated in ICET [11] and 

single-effects testing [18]. This testing could augment the information developed for Al 

alloys in [53] and should also determine whether significant dissolved concentrations of 

alloying elements are generated through corrosion. These alloying additions could form, 

or aid in the formation of, solid species. 

Galvanic effects should be also considered. These were not considered in the ICET 

series. Galvanic effects can accelerate corrosion of less noble materials while inhibiting 

corrosion of more noble materials. Galvanic couples existing within the containment 

pool (caused by direct contact between dissimilar metals) should be identified on a 

plant-specific basis. There is a wealth of existing information on galvanic effects [64], 

but limited testing of the strongest galvanic couples under simulated containment pool 

conditions could be used to verify the applicability of identified corrosion rates. 

Finally, research would be useful in determining if biological growth is a viable 

post-LOCA debris source that has significant implications. Screening tests could initially 

be performed to determine if growth is possible in post-LOCA borated water solutions 

containing organic sources at representative temperature profiles. A wide range of 

borate concentrations, organic substances, and temperature profiles could be evaluated 

62 
to most effectively bracket plant-specific conditions. If growth is demonstrated within 

30 days, representative changes in important variables (e.g., flow rate) that may 

accelerate or retard the biological growth rate could be evaluated to assess possible 

quantities of biological materials that could form at the sump screen debris bed or other 

downstream locations. 

5.4 Solid Species Precipitation

This section discusses several issues evaluated by the PIRT, which may affect the 

formation or precipitation of solid species from previously dissolved ionic species 

contained within the post-LOCA containment pool. Simply, precipitation occurs when 

the solubility of a specific solid phase is exceeded in solution. However, precipitation 

can depend on a complex interaction of multiple synergistic variables such as time, 

temperature, pH, and other species in solution. It should be noted that precipitation, as 

defined in this section, is the creation of small (nanometer to sub-micrometer size) 

particles suspended within the ECCS coolant. Issues related to the growth or 

agglomeration of these initially small particles are discussed in Section 5.5. 

Precipitation, along with growth or agglomeration, is likely needed to form solid species 

that are large enough to have significant implications for ECCS performance. 

5.4.1 Post-LOCA Precipitation Mechanisms 

Inorganic polymerization (T2-18, Table 8) is the process by which hydrolyzed cations link 

together, generally through oxo (-O-) bridges and dehydration, to form chains and 

networks. With sufficient growth, colloidal particles will result. Condensation 

polymerization occurs when the covalent bonds are rearranged such that monomers (the 

basic building blocks) are connected and water is expelled. The PIRT panelists expect 

the precipitation process to be a principal mechanism for the formation of solids in the 

post-LOCA containment pool, as demonstrated in the ICET testing [14]. This process 

may also be necessary to form particles large enough to tangibly affect ECCS 

performance. The PIRT panelists hypothesized the following possible scenario 

describing this process. 

Polymerization may begin early in the post-LOCA scenario (within 20 minutes of the 

initiating event) as cations are introduced in the containment pool. Any of the cations 

that can induce precipitation in the post-LOCA environment are candidates for 

polymerization including Al, Fe, Si, Zn, Cu, Ca, and boric acid. Extensive information is 

available for the hydrolysis and precipitation of solids from solutions containing simple 

cations, such as Al3+ and Fe3+, but less information is available for more complex 

systems (e.g., precipitation of aluminosilicates). The conditions of polymerization for 

these materials are a function of the ionic species and concentrations, time, 

temperature, and pH. It is therefore necessary to either realistically or conservatively 

consider applicable combinations of these principal variables to determine whether solid 

species precipitation and ripening through polymerization occurs. This evaluation could 

be useful in determining the type and concentrations of precipitates that form under 

plant-specific conditions. 

Precipitation is fostered by the existence of heterogeneous nucleation sites within the 

containment pool (T3-15, Table 9). Conversely, a dearth of these sites can delay 

precipitation. Nucleation sites include dirt particles, coating and insulation debris, and 

biological debris. All panelists believe that it is a foregone conclusion that the 

63 
containment environment would contain a plethora of heterogeneous nucleation sites to 

foster precipitation. Additionally, it is expected that standard laboratory environments 

and simulations should also contain sufficiently representative types and amounts of 

nucleation sites unless extreme cleanliness is practiced. Therefore, although these sites 

are important, they exist naturally and in both laboratory and post-LOCA environments. 

As mentioned previously, classical precipitation will not occur unless the solubility limit 

for a particular solid species is exceeded. However, the co-precipitation of other species 

is possible below the solubility limit of those species (T2-19, Table 8). Co-precipitation 

occurs when a normally soluble ion becomes either included or occluded into the 

crystalline structure of an insoluble material. This process is well-known as an analytical 

technique for isolating certain radioactive materials. Water clarification processes make 

extensive use of this process by hydrolyzing and polymerizing Al ions to produce a 

gelatinous precipitate that co-precipitates other matter (e.g., ions, colloids, or even 

particles) [27]. 

After a LOCA, it is envisioned that various oxides, oxyhydroxides, and hydroxides of 

elements, such as Al, Zn, Fe, Si, and Ca, will be present in the system. These species 

have widely differing associated electrical charges and the relative charges on the 

different particles may change drastically with pH. It may therefore be necessary to 

characterize the surface charge characteristics of all components to determine whether 

mixed oxides, oxyhydroxides, and/or hydroxides can co-precipitate [27]. Radionuclides 

could also be co-precipitated through this mechanism. 

There was no general consensus reached among the PIRT panelists on the importance 

of co-precipitation. Several panelists, citing a lack of evidence for co-precipitation in the 

ICET series, considered this issue to be less important than many of the other chemical 

effects previously discussed. However, at least one panelist believes that the ICET 

series may not have adequately simulated post-LOCA co-precipitation conditions, and 

that further research is warranted. Another panelist is concerned that the mass of 

iron(III) hydroxide (Fe(OH)3) present will increase (e.g., from crud production, Section 

5.3.2), and have a significant effect on coagulating and precipitating other materials. 

Research could be used to identify if either conservative or realistic post-LOCA 

environmental conditions are sufficient to foster co-precipitation and to characterize the 

species that form in concert with Fe(OH)3 or other species. The research focus should 

be on identifying conditions that significantly alter either the precipitate concentration or 

the nature of the species that would form individually compared to other integrated [11] 

or single-effects testing [18]. 

5.4.2 Thermal Effects 

Most of the previous discussion of chemical effects has focused on chemical processes 

that occur within, or are transported to, the containment pool. The containment pool 

water temperature (Table 13) is expected to peak between 190 °F and 270 °F soon (i.e., 

within 1 hour) after the hypothetical pipe break and then gradually decrease over the 

representative 30-day mission time for the ECCS recirculation system. After 15 days, 

the temperature range is expected to be between 115 °F and 165 °F. 

Although the containment pool temperature will slowly decrease as the radioactive 

decay heat is removed from reactor fuel, ECCS water passing through the sump screen 

encounters two notable thermal transients during the residence time necessary for the 

64 
water to complete a cycle through the ECCS cooling loop. First, the temperature 

decreases as coolant water passes through the residual heat removal (RHR) heat 

exchangers. The exact temperature decrease is a function of several variables 

(e.g., cooling water temperature, inlet water temperature, heat exchanger efficiency, and 

flow rates), but an approximately 30 °F decrease compared to the containment pool 

temperature is typical. Second, after passing through the heat exchangers, fluid is 

injected into the RCS and is heated as it is circulated through the RPV. The exact 

temperature increase within the reactor core will also depend on several variables 

(e.g., reactor and ECCS design and operability, break location, and time after the LOCA) 

and will diminish with distance from the fuel. However, a representative temperature 

adjacent to the reactor fuel is approximately 130°F above the containment pool 

temperature. 

These two thermal transients may induce various chemical effects depending on the 

dissolved and solid chemical species entrained in the ECCS flow. Chemical effects and 

implications that impact the heat exchanger performance and heat removal from the 

reactor fuel are discussed separately in Sections 5.7.2 and 5.7.3.1. Additionally, reactor 

fuel deposition and spalling have been previously discussed in Section 5.3.2. Chemical 

effects related to solid species precipitation from the cooling thermal transient at the heat 

exchanger and the heating transient induced by the reactor fuel are characterized in this 

section. 

The principal concern is that the thermal cycle existing within the ECCS coolant loop 

provides a mechanism for continued generation of solid species precipitation. Metallic 

corrosion and nonmetallic leaching could continue to generate dissolved ionic species 

which are then precipitated from the solution as solids by either the cooling or the 

heating transient. Under these conditions, precipitate formation will continue as long as 

complete precipitate redissolution at the containment pool temperature does not occur, 

and corrosion and/or dissolution continues to generate dissolved concentrations above 

the solubility limit of the precipitating species. 

5.4.2.1 RHR Heat Exchanger (Cooling Transient) Effects 

Chemical species having normal solubility profiles may be dissolved in the containment 

pool at higher temperatures. However, these chemical species may precipitate in the 

heat exchanger because of the approximately 30 °F temperature drop (T3-20, Table 9; 

T4-35, Table 10). Some possible solid species that could form include Al(OH)3, FeOOH, 

and amorphous SiO2

3

. The lower temperature at the heat exchanger outlet could also 

facilitate the development of macroscale coatings and/or suspended particulates. 

Single-species solubility relationships can provide some information about the possible 

precipitated species, but co-precipitation effects (Section ) may also be an 

important consideration. 

5.4.1

The primary implication of precipitation within the RHR heat exchangers discussed in 

this section is that they could contribute to head loss at the sump screen. Head loss 

would only result if the species remain insoluble at higher temperatures as they circulate 

through the ECCS loop through the reactor core and back into the containment pool, 

although some fraction of the ECCS flow will not pass through the core but go directly to 

 

3 Any colloidal silica that is formed will be changed to silicate because of radiolytic hydration within 

the reactor core. 

65 
the sump through the break. Precipitated materials from the heat exchanger will not 

have a chance to redissolve at higher temperatures for this fraction of ECCS flow. 

Additionally, the precipitates would need to be suspended within the ECCS flow so that 

they do not settle before reaching the sump screen. 

The PIRT panelists generally agreed that solid species precipitation caused by the heat 

exchanger transient is a highly important phenomenon that could impact ECCS 

performance. This high ranking is based on the knowledge that changes in solubility 

(with temperature or pH) are a principal driving force promoting precipitation. 

Additionally, the solubility of those species that are most likely precipitated decreases 

with temperature. Some initial work has been conducted to investigate solubilities of 

species identified in ICET and single effects testing [14, 15, and 53]. However, coprecipitation and other effects have not been considered and more systematic solubility 

studies may be required to cover the spectrum of relevant chemical species and plantspecific variables. 

5.4.2.2 Reactor Core (Heating Transient) Effects 

The higher temperature within the RPV and, most importantly, at reactor core fuel 

cladding surfaces could cause materials with retrograde solubility (e.g., organics, Al, B, 

Ni, Fe, Zn, Ca, Mg, SiO2, and CO2-based deposits) to precipitate (T3-27, Table 9; 

T4-38, Table 10). Some of these precipitates may form within the ECCS coolant water 

away from the fuel cladding but the highest concentrations will occur adjacent to the fuel 

cladding itself. These precipitates could then bind to the reactor fuel surface through 

caking and self-cementation as discussed in Section 5.3.2. As with low-temperature 

precipitation, co-precipitation effects (Section 5.4.1) may also be an important 

consideration within the RPV. 

One implication of precipitation within the RPV is that additional precipitate could be 

created and transported to the sump screen that would then contribute to head loss. 

Spalling of reactor fuel cladding deposits (Section 5.3.2.) could also create additional 

solid products which contribute to sump screen head loss. Precipitated or spalled 

materials passing through the sump screen may degrade the performance of ECCS 

components downstream from the screen as well (Section 5.7). 

The majority of the PIRT panelists also identified solid species precipitation caused by 

the reactor core thermal transient as an important phenomenon that requires additional 

study. As with cooling transients, this phenomenon is highly ranked because changes in 

solubility (with temperature or pH) are a principal consideration leading to precipitation. 

Little NRC-sponsored or industry-sponsored research has been performed to date to 

evaluate the retrograde solubility of possible precipitated species. 

5.4.3 PIRT Research Recommendations 

Several issues related to the precipitation mechanisms discussed in this section could 

be clarified through additional study to determine either their generic or plant-specific 

relevance. The conditions leading to polymerization are a function of the ionic species 

and concentrations, time, temperature, and pH. Therefore, it will be necessary to either 

realistically or conservatively assess relevant combinations of these principal variables 

to determine if solid species precipitation and ripening through polymerization occurs 

under plant-specific conditions. 

66 
Such a study could also consider solid species precipitation caused by the cooling of the 

ECCS water at the heat exchanger and heating within the RPV. Associated research to 

evaluate effects of pH and temperature history variability, as recommended in Section 

5.1.5, could be performed simultaneously. Investigation of retrograde solubility 

precipitation could also be combined with the research discussed in Section 5.3.5 to 

evaluate reactor fuel clad deposition and subsequent spallation. 

As with the research described in Section 5.1.5, it is difficult to generically assess solid 

species precipitation caused by high- and low-temperature transients because of he 

expected differences in the post-LOCA environment among the PWR plants. Therefore, 

it may be necessary to assess plant-specific temperature, material, and other relevant 

environmental conditions (e.g., pH). It may be possible to design testing to either 

separately evaluate conditions at each plant or to conservatively bracket conditions at all 

plants or among groups of similar plants (i.e., those using the same chemical buffers). 

Research could also be useful to identify if either conservative or realistic post-LOCA 

environmental conditions are sufficient to foster co-precipitation and to characterize the 

species that form. The initial research focus should be on identifying relevant conditions 

that could significantly alter either the precipitate concentration or the nature of the 

species that have been observed in single-effects [18] and integrated-effects testing [11]. 

Follow-on testing could then more systematically evaluate these conditions to determine 

if significant implications result from co-precipitation. 

5.5 Solid Species Growth and Debris Transport

This section discusses several issues related to both growth and maturation of solid 

species precipitates (Section 5.4) and how these and other chemical phenomena affect 

debris transport. Issues related to debris transport include chemical implications for the 

transport of physical debris into and within the containment pool and the transport of 

chemical precipitates. Debris transportability is an important consideration because it 

ultimately governs the physical and chemical debris concentrations and the debris 

characteristics, which affect ECCS performance in recirculation mode. If it remains 

stable and intact, debris that does not transport to the sump screen may have a minimal 

impact on ECCS performance. 

The pipe break that initiates the LOCA will create insulation, coating, corrosion products, 

and other physical debris (Section 5.3), which may be transported into the containment 

pool. Once containment sprays are initiated, additional quantities of this debris may be 

washed into the containment pool. Containment sprays may also wash additional latent 

debris, corrosion products, and failed coatings that were not directly created by the water 

jet into the containment pool. As previously discussed in Section 5.3.1, the panelists 

universally recognized that debris transported by the containment spray was an 

important contributor to the containment pool chemistry and associated chemical effect 

implications. 

Other than creating debris, water emanating from the pipe break and containment 

sprays forms the pool in the bottom of the containment. The containment pool fills for 

approximately 20 minutes during a LB LOCA before water from the RWST is exhausted 

and the ECCS begins recirculating coolant water. During the time before recirculation, 

there is no directional flow within the containment pool toward the sump screens. In 

67 
addition, the pool is expected to be relatively quiescent as it fills except for areas where 

the water from the pipe break flows into the pool (T2-11, Table 8). These areas are 

expected to exhibit substantial turbulence and mixing. Localized turbulence may also 

occur during this period near the surface as containment spray water impacts the 

containment pool surface. 

Directional flow toward the sump screen begins once recirculation starts. This is the 

mechanism by which the physical and chemical debris that has been transported to, or 

created within, the containment pool can be transported to the sump screen. The debris 

will then either be filtered or will pass through the sump screen into the ECCS inlet 

piping. There are several chemical mechanisms that the PIRT panelists identified that 

may affect the transport of physical and chemical debris both within the containment 

pool to the sump screen or downstream of the sump screen if it is ingested. These 

mechanisms have been separated into particulate growth and agglomeration and other 

chemical and physical settling and deposition effects. 

Current guidance [4] is generally conservative and sufficient to address the generation 

and transport of most physical debris (except for additional sources discussed in 

Section 5.3.2) into the containment pool. However, the transport of chemical products is 

not explicitly considered. As discussed previously (Section 5.3.1), pipe break scenarios 

that provide the greatest physical debris transport may not result in the most deleterious 

chemical effects. Therefore, it is important for a realistic chemical effect evaluation to 

consider transport scenarios that provide the greatest chemical effect challenges. 

Consideration of various transport scenarios may not be necessary for conservative 

evaluations that assume that all physical and chemical sources are transported to the 

sump screen and/or downstream of the sump screen. 

5.5.1 Particulate Growth and Agglomeration 

Precipitation is a process involving the formation of small submicroscopic or microscopic 

solid particulates. The impact and important variables affecting precipitation have been 

previously discussed (Section 5.4). However, the growth (ripening) of these particles 

through aging and/or their aggregation or coagulation to form larger clumps of 

particulates (agglomeration) determines the physical size and cohesiveness of the solid 

species (T2-21, Table 8; T3-14, Table 9). Conditions that promote ripening and/or 

agglomeration of precipitated solid species within the containment pool will lead to larger 

particulates that may be less vulnerable to transport (T4-40, Table 10). Although bigger 

particulates could decrease sump screen blockage if a large percentage settles, the 

larger particles that do transport are more likely to contribute to head loss across the 

sump screen. In addition, the larger particulates trapped on the sump screen will form a 

cake that is more effective at trapping smaller particles. As a result, head loss can 

increase with time instead of reaching steady-state. 

The PIRT panelists typically ranked the effects of particulate aging and growth on 

transportability as being of moderate to high importance. Most panelists confirmed that 

particulate growth can be a beneficial phenomenon that would reduce screen blockage if 

particulate sizes that limit transportability are reached. One panelist commented that as 

the concentration of several species increases over time, the aging of insoluble materials 

should generally increase the size, density, and crystalline nature of these materials [47]. 

This process would be promoted throughout those portions of the containment pool 

characterized by either a relatively low flow rate or stagnant conditions. However, one 

68 
panelist indicated that the effect is highly dependent on the plant design and pH buffer 

and may therefore be difficult to credit generically. 

Agglomeration encompasses both inorganic and organic aggregation mechanisms. 

Inorganic agglomeration (T2-21, Table 8; T3-14, Table 9) is the process whereby 

colloidal particles (1–100 nm in diameter) that are formed by cation polymerization 

(Section 5.4.1) are electrically bound to create larger particle clusters and eventually 

visible precipitates. Organic agglomeration describes the ordering of organic colloidal 

particles (1–100 nm in diameter) into larger clusters. However, the presence of organic 

species can also either increase or decrease the likelihood of inorganic agglomeration. 

Organic acids or oil can promote inorganic agglomeration by binding smaller inorganic 

particulates into clusters (T2-24, Table 8). This mechanism is analogous to the manner 

in which soap coagulates dirt particles and is defined here as organic binding. Organic 

species can also discourage inorganic agglomeration through absorption (T2-15, Table 

8). More discussion of organic agglomeration effects is contained in Section 5.6.2. 

The importance of inorganic agglomeration was generally highly rated by the PIRT 

panelists. Inorganic agglomeration is sensitive to many variables including the pH of the 

point of zero charge (PZC) of the species, the ionic strength of the fluid, particle shape 

factors, and particle sizes. If a multi-component system contains particles of opposite 

charge, the particles will coagulate to form macroscopic precipitates. This electrostatic 

agglomeration occurs when the solution pH lies between the PZC of the different 

particles. Even if the particles are not oppositely charged, increasing the ionic strength 

of the medium will cause the electrical double layers of solid particulate to shrink to the 

extent that the attractive van der Waals forces will overcome electrostatic repulsion and 

coagulation will occur as in Al water clarification technology [65]. 

Most panelists agreed that inorganic agglomeration is most likely necessary to form 

particles large enough to degrade ECCS performance and that it could occur quickly if 

conditions were favorable. This stipulation implies that particulate growth and aging, by 

itself, may not be sufficient to degrade ECCS performance. At least one panelist 

believes that inorganic agglomeration contributed in the formation of the visible 

precipitates observed in ICET and other testing (Section 1.2), but does not require 

separate study. 

5.5.2 Settling and Deposition 

This section considers other important physical and chemical processes that affect the 

transportability of both chemical products and physical debris. Settling is defined as a 

lack of transport of either physical debris or chemical products within either the 

containment pool or the ECCS. Deposition refers to chemical products that are 

deposited on debris, component, or structural surfaces within the containment 

atmosphere, the containment pool, or the RCS. Deposition on the reactor fuel and 

within the heat exchanger is also discussed in Sections 5.3.2, 5.4.2, 5.7.2, and 5.7.3. 

Both settling and deposition (T2-23, Table 8) can potentially remove substantial 

quantities of material that could otherwise be either trapped on the sump screen and 

contribute to head loss or affect downstream ECCS performance. Deposition can also 

inhibit metallic corrosion or nonmetallic leaching (Section 5.3) which would decrease the 

species present in the cooling water. Except for settling and deposition within the RPV 

or RHR heat exchangers (Sections 5.3.2, 5.4.2, 5.7.2, and 5.7.3), these are beneficial 

69 
chemical phenomena. The challenge is in reliably determining how much credit can be 

given to settling and deposition in either generic or plant-specific post-LOCA conditions. 

The containment pool directional flow rates during recirculation will be on the order of 

0.05 ft/s (or less) in most existing PWR plants after the sump screens have been 

enlarged. This low flow rate should be prevalent through the bulk of the containment 

pool except for regions impacted by the flow of water through the pipe break. Obviously, 

low flow conditions are more conducive to settling of both chemical products and 

physical debris (T3-11, Table 9). Additionally, the containment floor is a maze of 

components bolted to the concrete floor such that the path of containment water from 

the break to the containment sump is less likely to involve linear, unidirectional flow. 

There are also drop out areas on the containment floor. These features provide trapping 

surfaces, flow stagnation regions, and longer flow paths, which all help retain chemical 

products within the containment pool. The PIRT panelists generally believe that the 

quiescent nature of the containment pool and the containment floor features are highly 

important and beneficial in reducing the impact of chemical effects. 

Chemically induced settling (T3-13, Table 9) of solid debris can also be promoted by 

chemical species that attach to or coat the debris. Some examples provided by the 

PIRT panelists include the possibility of coating fiberglass fibers with Al to shift the PZC 

and enhance agglomeration, thus forming a hydrophobic organic coating on particulates, 

or forming an amorphous silica coating (T4-39, Table 10) on the surface of chemical 

precipitates (e.g., Al(OH)3 and FeOOH). These effects have the added potential benefit 

that they could inhibit further chemical reactions for those materials. It was observed 

that Al species coated fiberglass and inhibited leaching in both ICET testing [11] and 

separate dissolution studies [17]. 

The average importance ranking was medium for chemically induced settling. One 

panelist commented that the amount of potential precipitate removed by precipitation on 

surfaces within containment is likely to be small in relation to material precipitating in 

suspension. However, the panelist also cautioned that the effect is dependent on pH 

and the buffering chemicals. Although one panelist thinks that amorphous silica will be 

precipitated given sufficient silicate sources (e.g., Cal-Sil), another panelist believes that 

flow through the core will produce radiolytic effects (Section 5.2) that will preclude its 

formation. 

5.5.3 PIRT Research Recommendations 

The PIRT identified agglomeration as an important mechanism for defining the 

characteristics, properties, and subsequent implications of precipitates that form during 

the post-LOCA scenarios. Therefore, it is necessary to understand those post-LOCA 

environmental variables that may affect agglomeration including solid species precipitate 

types and concentrations, the PZC of these species, and the ionic fluid strength. 

Variability in important post-LOCA parameters (e.g., materials, temperatures, pH, and 

buffering systems) should also be evaluated to determine if the effect on agglomeration 

is significant. Although it may be possible to conduct this evaluation generically, a plantspecific consideration should be more accurate given the variability in containment 

materials and conditions. This study may be particularly important for demonstrating 

that chemical precipitates in single-effects [18] or integrated-effects [11] laboratory 

testing are representative of products expected during a post-LOCA event. Similarly, it 

70 
should be demonstrated that surrogate precipitates produced outside the testing 

environment [18] are representative of post-LOCA chemical species. 

The transport phenomena discussed in this section generally benefit ECCS performance 

by removing physical debris and chemical products from circulation by settling or 

deposition4

. Therefore, no research is necessary to assess their adverse implications. 

However, research may be necessary if these phenomena will be used to justify 

reducing the amount of suspended solid particulate in a chemical effects evaluation. It 

may be possible to study transport phenomena generically assuming that a parametric 

study can appropriately encompass the plant-specific variability in important transport 

variables such as plant design, containment materials, containment flow rates, pH buffer, 

and the chemical conditions resulting from appropriate hypothetical pipe break 

scenarios. Plant-specific analysis could also be used to decrease variability stemming 

from differences among plants. 

A possible research strategy, if credit for settling is desired, could be to evaluate those 

precipitate characteristics (e.g., particle sizes, cluster sizes, and waters of hydration) 

under conditions that would least likely promote agglomeration. The conditions could be 

determined through testing or possibly analysis. Settling of the precipitate could then be 

evaluated under containment floor flow rates to determine the settling rate. Containment 

floor turbulence (e.g., under the break flow) should also be considered as a source to 

promote particulate suspension. Head loss from suspended solids could also be studied 

using the supernatant from above settling tests to evaluate cake formation and the rate 

of head loss across the sump screen. 

The NRC-sponsored settling tests of Ca3(PO4)2 provide an example of some of the 

issues associated with performing these tests. These tests were conducted in a large 

settling column [15]. The column was filled with a borated water solution containing 

TSP. Calcium chloride (CaCl2) was introduced into the solution to form Ca3(PO4)2. The 

solution was stirred to get a uniform mixture and then the precipitates were allowed to 

settle without further agitation. Two different CaCl2 concentrations were tested to 

provide a higher (300 ppm (7x10-3 M)) and lower (75 ppm (1.9x10-3 M)) dissolved Ca 

inventory. In this simple test, the 300-ppm (7x10-3 M) concentration resulted in, on 

average, larger particles and faster settling times than the 75 ppm (1.9x10-3 M) 

concentration [15]. Thus, this simple test demonstrated the effect of precipitate 

concentration on both agglomeration and settling. However, one panelist was critical of 

the applicability of the results of that test because the conditions were not sufficiently 

representative of the post-LOCA containment pool. A particular concern was that the 

test flow rates were not matched with containment flow rates to ensure similar 

hydrodynamic forces. 

5.6 Coatings and Organics

5.6.1 Coatings 

Coatings existing within containment represent possible additional physical debris 

sources. Generally conservative guidance for considering the effects of physical coating 

debris is provided [4] for the evaluation of ECCS performance. However, both coatings 

and organic materials can impact the chemical effects that occur within, or are 

 

4

 Possible adverse effects related to deposition are discussed in Sections 5.3.1, 5.4.2, and 5.7

71 
transported to, the ECCS cooling water. Both inorganic (e.g., Zn-based) and organic 

(e.g., epoxy-based) coatings exist within containment. One concern is that these 

coatings leach chemicals as a result of being submerged in the containment pool 

environment after the LOCA (T3-29, Table 9; T4-17, Table 10). The coatings could 

either be intact on the substrate or loose within the containment pool as chips or smaller 

particulate. The implication is that coatings may create additional chemical species 

(e.g., chlorides or organics) within the containment pool. Some PIRT panelists 

mentioned that the most likely coatings that could leach significant quantities of 

deleterious materials include Pb-based paints (present in older containment buildings), 

phenolics, and vinyl coatings. 

There has generally been little testing on leachant species and rates from nuclear-grade 

coatings [23]. The ICET series did incorporate inorganic Zn-coated steel to simulate 

material with a Zn-rich primer (T4-13, Table 10) that was either without a topcoat, or the 

topcoat had failed [12]. However, none of the previous NRC-sponsored or industrysponsored testing (Section 1.2) has more broadly considered the chemical effect of 

coatings, principally because of the tremendous variability of types and quantities in 

nuclear plants. 

The testing that has been done has evaluated only a few qualified epoxy and primer 

coatings and most often has examined only leachable Cl, F, sulfur (S) (or sulfate), and 

total halide contributions under a high-pH (i.e., 13), high-temperature (i.e., 95 °C), 

non-borated environment [22]. Chloride concentrations up to nearly 700 ppm (0.02 M) 

have been measured in this testing, but more typical concentrations fall between 100–

200 ppm (3–6x10-3 M). Fluoride concentrations are generally less than 1 ppm (3x10-5 M) 

but have been measured as high as 100 ppm (3x10-3 M). The total organic halide 

concentration, when reported, is often around 1 ppm. The S or sulfate concentrations 

are often less than 100 ppm (3x10-3 M), but peak as high as 800 ppm (0.02 M) [22]. 

Note that the approximately scaled containment pool concentrations associated with 

these measured test concentrations can be determined by dividing the above 

concentrations by 50. One panelist notes that these leaching tests measure the Cl, F, 

and sulfate ionic concentrations. There are likely organically bound halogens and S in 

these coatings that mask the total element concentration. 

Considering the general lack of applicable testing information in post-LOCA 

environments, the PIRT panelists appeared divided on the importance of the leaching of 

coatings on chemical effects. One panelist indicated that most coatings should be 

resistant to dissolution, and concentrations of any dissolved species from coating 

dissolution should also be minor. Therefore, in his opinion, the overall effect on the 

ECCS coolant composition and formation of secondary precipitates is likely to be small. 

Another panelist indicated that this effect would be important only if various 

metallic-based (e.g., Pb) coatings are present. Alternatively, one panelist believes that 

although coatings may not lead to significant precipitate quantities, the decomposition of 

organics within coatings by thermolysis and radiolysis could affect the organic 

complexation (Section 5.6.2) and agglomeration (Sections 5.5.1 and 5.6.2) of other 

inorganic chemical products. Another panelist believes that leaching from coatings may 

substantially add to the ionic loading of the containment sump water if organically bound 

halogens and S are contained in these materials, which are then disbanded from their 

molecules by radiolysis. This panelist cited the degradation of the spent fuel pool resin 

into soluble sulfates that occurs within a few months at low doses (i.e., radians to 

72 
kiloradians). This process will be accelerated by the higher radiation flux present in the 

post-LOCA environment. Other panelists indicated that these effects would be 

inherently plant-specific and could only be evaluated by testing specific qualified and 

unqualified coating systems to evaluate both chemical and radiolytic dissolution 

characteristics in post-LOCA environments. 

5.6.2 Organics 

The PIRT panelists generally indicated that organics could significantly affect the nature, 

properties, and amounts of chemical byproducts that form in the post-LOCA containment 

environment. The biggest uncertainties relate to the possible organic sources and 

concentrations that are located within containment and present in the containment pool 

after a break (T1-7, Table 7; T2-17, Table 8). Coatings, discussed above, and insulation 

debris (e.g., fiberglass and Cal-Sil) represent obvious organic sources, but other less 

obvious sources may also be present. 

Organics stemming from fiberglass and Cal-Sil insulation were included to some extent 

in the ICET experiments. Both the fiberglass and Cal-Sil were heat treated to simulate 

temperature profiles existing in service and representatively bake off some of the organic 

resins. However, dissolved organic materials were likely present in the ICET solution 

based on the pigmented solution color (yellowish to rust colored) observed in each 

test [11]. The organics were attributed to decomposition products of the phenol 

formaldehyde resin-based polymer that coats the fiberglass insulation tested in the ICET 

program. The total organic content was measured in ICET Test 2. The baseline 

measurement at the onset of testing was 0.2 mg/L, increased to 7.3 mg/L by day 15, and 

then more slowly increased to 7.9 mg/L by the end of the test at day 30 [11]. 

Another possible organic source discussed in the PIRT is the reactor coolant pump 

(RCP) oil and small oil reservoirs for other pumps located inside the containment 

building. The scenario evaluated in the PIRT (T1-7 Table 7; T4-18, Table 10) 

considered the overflow, failure, or leakage of oil and other organics from either the RCP 

oil collection tanks or lube oil systems. This ingress could be caused by either a 

preexisting damage within the system or LOCA-induced damage. The oil collection 

tanks are more likely to fail, especially if the pipe break occurs in close proximity, 

because they are fabricated from approximately 1⁄2-inch carbon steel with epoxy coating. 

However, these tanks only typically contain a few gallons of residual oil. The RCP lube 

oil systems contain a bigger source of oil (approximately 250 gallons per pump), but 

these systems are less likely to fail unless there is leakage or direct LOCA impact. 

The panelists agreed that a relatively large release of oil caused by an RCP oil system 

failure might significantly affect containment pool chemistry if oil concentrations on the 

order of parts-per-million are generated. The oil could alter metallic corrosion and/or 

nonmetallic dissolution rates and species (Section 5.3.3.2), precipitation and/or coprecipitation (Section 5.4.1), particle buoyancy, agglomeration and/or complexation 

(below). The tanks could also provide organic food sources for bacterial growth (Section 

5.3.4). The potential for RCP oil reservoir damage or leakage during the LOCA should 

be considered for these reasons. 

The three related organic effects that affect the size of solid particulate clusters include 

organic agglomeration (T3-14 Table 9; T2-24, Table 8), organic binding (T2-24, Table 8), 

and organic complexation (T2-15, Table 8). As with inorganic agglomeration (Section 

73 
5.5.1), these phenomena impact the transport properties of solid species precipitates 

(Section 5.5.2) and also the likelihood that particulates are captured at the sump screen, 

within the heat exchanger, the RPV, or in downstream locations. Particulate transport 

could also be affected by organic buoyancy (T4-15, Table 10). 

As previously discussed (Section 5.5.1), organic agglomeration describes the ordering of 

organic colloidal particles (1–100 nm in diameter) into larger clusters. Organic binding 

describes the formation of smaller inorganic particulates into clusters surrounding 

organic acids or oils. The importance of both organic agglomeration and binding was 

also generally highly rated by the PIRT panelists, but there is more uncertainty 

surrounding this ranking. One panelist indicated that if organic materials act as glues to 

accrete and grow solid particles (or act as surfactants), then large coagulated particles 

may be formed. However, another panelist indicated that organic agglomeration 

depends greatly on the type and magnitude of organics existing within the containment 

pool. A third panelist expects the concentration of organics to be low. The large 

uncertainty surrounding this issue implies that additional consideration is likely 

necessary to determine the scope and applicability of these phenomena. 

Conversely, organic complexing agents act to inhibit agglomeration. Aliphatic acids are 

well-known complexing agents and are a likely class of organic decomposition product 

within the post-LOCA environment. The action of these complexing agents can occur 

either by adsorption onto solid surfaces or by interaction in solution with metal ions. 

Organic surface complexation occurs if organic molecules (i.e., amines, acids, and 

heterocycles) adsorb on surfaces of ions or solids and inhibit the subsequent 

precipitation or growth of those species. Solid species may precipitate, but they remain 

relatively small in size (nano-scale) because of the inhibition caused by the adsorbed 

organics. These species are therefore less likely to agglomerate or grow to macroscopic 

sizes. Solute complexation effectively enhances solid species solubility limits. 

Precipitates that do form will grow more slowly and can grow to greater size although the 

quantity of total solids will be lower. Solute complexation could increase the 

transportability of these metal ions but decrease the likelihood that they are trapped at 

the sump screen or another location within the ECCS. In this regard, the implications of 

organic complexation are counter to those associated with organic agglomeration or 

binding. 

The average importance ranking for organic complexation was medium,although there 

was disagreement among the panelists on the significance. Two panelists argued that a 

minimal amount of organic acid will exist in the post-LOCA containment pool and organic 

complexation will not be significant. However, two panelists indicated that radiolysis of 

organics could yield organic acids (or CO2) and that these conditions have yet to be 

studied. Another panelist indicated that even minor amounts of organic acid can 

possibly have a significant effect on surface reactivity and hence complexation. This 

panelist indicated that the phenol formaldehyde resin-based insoluble polymer coating 

NUKON® fiberglass could dissolve into an alkaline aqueous phase that could inhibit 

solid species nucleation and growth. The uncertainty and disagreement surrounding this 

issue implies that additional consideration is warranted, especially if this phenomenon is 

credited for enhancing solubility limits of the expected precipitates. 

Organic buoyancy describes a mechanism whereby organic materials coat existing 

precipitates (e.g., Al(OH)3) or physical debris (e.g., Cal-Sil and fiberglass) to increase the 

buoyancy. This effect could enhance the transport of particulates or chemical by74 
products to the sump screen. The PIRT panel, on average, rated this particular 

phenomenon to be of medium importance, although there was again significant 

uncertainty: two panelists provided high rankings and two others provided low rankings. 

The justification for the high rankings was that increased buoyancy has the potential to 

transport more solids to the sump screen without affecting particulate sizes. Therefore, 

larger particles, which are more likely to be trapped at the sump screen, could be 

transported than without the buoyancy effect. 

The organics also could act as surfactants that could sorb onto the particle surfaces, 

cause the particles to become hydrophobic, and give the now-coated particles greater 

affinity for air bubbles, which could cause them to float as the coolant suspension 

becomes aerated by agitation. This phenomenon would be akin to flotation which is 

used in mineral milling to separate ore particles for further beneficiation or processing. 

The low rankings were justified, in part, on the stipulation that increased buoyancy would 

most likely cause the particulates to float. If the sump screen is fully submerged, floating 

particulates would not affect head loss significantly, and they would be less likely to be 

ingested into the ECCS pump. Therefore, they would be much less detrimental than 

would suspended debris. One panelist also speculated that if these particles were 

ingested into the ECCS pump, they would be ground up by the impellers and would have 

little detrimental effect on downstream ECCS components. This issue may only have 

practical ramifications if any buoyancy increase restricts settling but does not cause 

particulates to float. Within this buoyancy range, this effect could suspend and promote 

transport of solids that would normally settle within the containment pool. 

The last potentially significant organics and coating phenomenon for consideration is the 

hydrothermal hydrolysis of various organic and/or inorganic coating and insulation 

materials (T2-14, Table 8). One of the panelists [65] identified this phenomenon 

separately from the PIRT exercise. This panelist stipulated that hydrothermal hydrolysis 

could partially de-polymerize polymeric materials, producing materials ranging from 

small molecules to colloids. These colloids could subsequently aggregate to form gels. 

The potential practical impact on ECCS performance is that the de-polymerized 

materials could be more likely to transport and contribute to larger head loss at the sump 

screen than could the original product forms. At least one panelist doubts that this effect 

is significant. The elevated containment temperatures necessary for this phenomenon 

are relatively brief. Depolymerization would also require thermodynamic destabilization, 

which is unlikely in the temperature range under consideration. This reaction may only 

be possible within the reactor core. Additional evaluation of possible effects under either 

conservative or reasonably representative post-LOCA conditions would be required to 

assess this phenomenon. 

5.6.3 PIRT Research Recommendations 

There is a general lack of knowledge about the identity of leachant species and rates of 

release from nuclear grade coatings under the chemical and radiolytic conditions present 

in the post-LOCA containment environment. Generic coatings research is also 

complicated by the variety of coating systems present within PWR containments. 

Therefore, plant-specific evaluation of qualified and unqualified containment coating 

systems is likely to be a more effective approach, which will undoubtedly first require an 

accounting of the types and quantities of coatings present within containment. 

Potentially, the most significant issues to address, as indicated by the PIRT panelists, 

75 
are leaching from metallic coatings and the decomposition of organics within coatings by 

thermolysis and radiolysis. The objective should be to determine the types and 

concentrations of the leachants (including organics) that are liberated under either 

realistic or conservative post-LOCA conditions. 

More general consideration of the effects of organics first requires a realistic assessment 

of possible organic sources and concentrations that may exist in the containment pool. 

Insulation and coating debris are known to contain organics, but an accounting of other 

sources (e.g., oils and greases) is necessary to understand the concentrations and types 

of species. This may require plant-specific evaluation unless it can be demonstrated 

that concentrations are sufficiently low for the types of organics that may exist in 

containment. 

If sufficient organic sources (e.g., electrical insulations and plastic coatings) are 

available, the influence of organic agglomeration and/or binding could be significant. 

Additional research would then be useful to determine the leaching behavior of either 

specific organics (if sources are limited) or samples from representative organic classes 

(if sources are prevalent) within the post-LOCA containment environment. An analogous 

sampling strategy was used in the Westinghouse Owners Group single-effects chemical 

testing [18]. Research should then examine the ability of the water-treated organic 

materials to coalesce and/or bind inorganic solids (e.g., thermal insulation materials) as 

they cool. 

Organic complexation is largely an advantageous effect that will minimize ECCS 

degradation by effectively enhancing the solubility limits. Therefore, no research is 

recommended unless credit for this effect is desired. Organic buoyancy may also be 

beneficial unless the buoyancy increase is sufficient to restrict settling, but not so great 

to promote floatation. Research would be needed to determine if organic buoyancy or 

flotation can occur within the range of post-LOCA conditions existing at PWR plants and 

if the buoyancy suspends, but does not float, significant debris concentrations that would 

otherwise settle. If the effect can be demonstrated, it may be possible to calculate the 

suspended debris if the inorganic and organic particulates types and sizes are known. 

This effect becomes less important if the settling of containment pool solids is not 

credited in a chemical effects evaluation. 

The implications of hydrothermal hydrolysis under either realistic or conservative 

post-LOCA conditions may also require some additional consideration. No previous 

NRC-sponsored or industry-sponsored research has evaluated this effect. A literature 

and theoretical scoping analysis could be initially used to define its importance. The 

next step would entail identifying susceptible organic and/or inorganic coatings and 

insulation materials by screening their physical and chemical properties. After 

screening, the most susceptible materials could be evaluated to determine the 

propensity for interactions among the various constituents produced by hydrothermal 

hydrolysis to ascertain whether even more resilient (i.e., less susceptible to thermal 

hydrolysis) byproducts form. Both interactions among hydrolysis byproducts and with 

other containment pool species should be addressed [65]. 

It is important to note that the reaction of the products of hydrothermal hydrolysis are 

often solids themselves and their reaction with other solids, particularly those having a 

zeta potential of opposite sign (equivalent to having PZC values that are on opposite 

sides of the pH of the medium), will be assisted by the electrostatic interaction between 

76 
the particles. Furthermore, because the rates of these reactions are often controlled or 

significantly affected by mass transport, rheological properties, which tend to control the 

interpenetration of gel-like hydrolyzed material, are also significant. 

5.7 Downstream Effects

Some possible chemical and biological products that may form within the RCS or ECCS 

have been discussed (Section 5.3). These products may increase the debris loading 

that is transported to the sump screen. Most of the phenomena in the preceding 

sections have considered possible contributions of chemical effects to the head loss 

associated with debris that is trapped by the sump screen. However, this debris could 

also pass through the sump screen, become ingested within the ECCS pump suction 

line, and potentially travel through the remainder of the ECCS cooling loop. New 

chemical products could also be created by thermal cooling and heating transients at the 

heat exchanger and near the reactor core, respectively (Section 5.4.2). Either ingested 

debris or newly created chemical products have the potential to degrade ECCS 

components downstream of the sump screen. These considerations are globally 

referred to as downstream effects. 

The evaluation guidance supporting GL 2004-02 requests that downstream effects be 

addressed in the licensees’ safety evaluations [4]. General industry approaches also 

exist for conducting the necessary evaluation within the RPV [66] and in all other 

downstream components and locations [67]. Much of the existing evaluation guidance, 

especially in [67], addresses the effects of physical debris but does not explicitly provide 

guidance for considering chemical effects. However, the NRC staff is currently 

reviewing [66] to ensure that potential chemical effects are appropriately considered. 

The PIRT panel did consider how chemical effects could degrade performance in 

downstream components. The PIRT panelists believe that the ECCS pumps, the RHR 

heat exchangers, and the reactor core are the three major downstream components that 

are either the most likely to contribute to chemical effects or the most susceptible to 

chemical effects. The potentially significant chemical phenomena identified by the PIRT 

that are associated with each of these locations are discussed in this section. These 

PIRT results are intended to inform staff review [66]. 

5.7.1 ECCS Pumps 

Debris that passes through the sump strainer screen is ingested into the ECCS pump 

suction leg and then passes through the pump. The PIRT identified potentially 

significant phenomena resulting from physical debris and chemically induced solids 

passing through the pump. The first group combines chemical phenomena that may 

promote pump seal abrasion or degradation. The second phenomenon analogously 

considers corrosion or erosion of the ECCS pump internals. 

Pump seal abrasion (T3-19, Table 9; T4-33 Table 10) could result from abrasive wearing 

or scouring of the seals. Abrasion caused by physical debris is a prominent 

consideration in the downstream evaluation guidance [67]. However, chemical products 

can also contribute to abrasion, and the effect of chemical products is not addressed in 

the industry guidance [67]. Magnetite from crud generation and spallation from the RCS 

system (Section 5.3.2) was one example of a hard material cited by the panelists that 

could abrade the seals. Seal degradation could also result from leaching of the pump 

77 
seal materials caused by immersion within the post-LOCA buffered containment 

environment. The implications associated with these phenomena are similar. Additional 

particles could directly contribute to head loss across the sump screen and/or deposition 

and clogging within the reactor core or heat exchanger. Dissolved species from these 

phenomena could also form additional solid precipitates, and the additional species 

could contribute to co-precipitation. Pump seal abrasion or degradation could also 

degrade pump performance, possibly to the point of inoperability. 

The PIRT panelists indicated that the importance of these phenomena, on average, fell 

between medium and high. The panelists almost unanimously agreed that the impact of 

pump seal particulates or leachants on either the formation or promotion of additional 

solid species or degradation elsewhere in the ECCS would be small. Only a small 

amount of material would be generated if the entire seal disintegrated. The more 

prevalent concern is failure of the ECCS pump seals caused by crud or other chemical 

products. In general, the panelists believe that additional consideration may be 

warranted to consider this effect. 

Corrosion or erosion of other pump metallic internals (T4-32, Table 10) is technically 

analogous to nonmetallic pump seal degradation or abrasion. The internals most 

susceptible to corrosion or erosion are tight tolerance components such as bearings, 

wear rings, and impellers. As with pump seal degradation, these components could be 

eroded by Fe3O4 particles from crud generation (Section 5.3.2) or corroded as a result of 

immersion within the post-LOCA buffered containment environment. The redox potential 

of the debris-laden fluid also affects the corrosion and/or erosion of these internal 

components. 

The panelists’ expectations of the implications of internal corrosion and/or erosion of 

these components were also similar to seal degradation. Panelists did not expect that 

particulate or dissolved species generated by pump internal corrosion and/or erosion 

would exist in sufficient quantities to significantly alter chemical solid species formation 

or otherwise degrade ECCS performance during the 30-day post-LOCA time period 

considered in the PIRT analysis. The most likely cited implication was that significant 

erosion or corrosion could ultimately lead to pump failure well beyond this 30-day time 

period. One panelist also indicated that any two-phase flow through the pumps would 

also enhance metallic erosion. 

However, the average importance ranking of this phenomenon provided by the PIRT 

panel was high, greater than the ranking for seal degradation. The higher ranking is 

justified by the tight tolerance, and therefore higher speed, of fluid passing within and 

through these internal components and by the greater importance of these components 

to pump operability compared to pump seals. Therefore, the proper consideration of 

erosion and corrosion of pump internals may be important if chemical solid particulates 

are harder or more concentrated than the physical particulates that are evaluated as part 

of the downstream effects evaluation [67]. Any assessment of chemical effects will likely 

need to be plant specific given the variability in pump designs and materials and other 

relevant post-LOCA conditions. 

5.7.2 RHR Heat Exchangers 

After ECCS coolant water has passed through the ECCS pump, it is transported through 

several valves and piping until it reaches the RHR heat exchanger. The PIRT panel 

78 
identified several chemical phenomena that could occur at the heat exchanger. Most 

effects stem from the approximately 35 °F to 40 °F temperature drop at the heat 

exchanger outlet. This is effectively the lowest temperature within the ECCS 

recirculation loop. The possibility of chemical precipitation (or co-precipitation) of 

species having decreasing solubility with decreasing temperature (T3-20, Table 9; 

T4-35, Table 10) was previously discussed in Sections 5.1.2, 5.4.1, and 5.4.2.15. The 

implications pertaining to the additional solids inventory on NPSH at the sump screen 

were also discussed in these sections. 

However, a few other phenomena were identified by the PIRT panel that could directly 

degrade heat exchanger performance. One phenomenon (T3-21, Table 9) is surface 

deposition on the heat exchanger tubes from a combination of previously formed debris 

(i.e., chemical precipitate and physical debris) that passed through the sump screen and 

newly precipitated chemical species resulting from the temperature drop at the heat 

exchanger. This concern is supported by the Cal-Sil and Ca3(PO4)2 deposits that were 

observed in ICET Test 3 even without a significant temperature drop [11]. These 

deposits caused the impeller-type flow meters to fail on the eighth day of the 30-day test. 

Another related phenomenon identified by the PIRT is clogging near the inlet of the 

close-packed heat exchanger tubes from both physical debris and chemically induced 

solid species (T3-21, Table 9). 

Both phenomena could cause decreased flow through the heat exchanger core and/or 

diminished heat transfer between the ECCS and heat exchanger cooling water. 

Diminished cooling of the ECCS water could ultimately decrease the capacity of the 

ECCS water to remove heat from the reactor core. The PIRT panel generally 

considered both these phenomena to be important as three of the five panelists provided 

a high ranking. Rationale supporting the high rankings included the argument that 

precipitates are most likely in the heat exchangers because of the temperature decrease 

from the inlet to the outlet. Subsequently, any precipitates that form may degrade the 

hydrodynamic and thermal performance of the heat exchanger. 

However, at least one panelist who provided lower rankings agreed that deposition and 

clogging have been observed during long-term operation. However, the magnitude of 

the lost heat capacity will depend significantly on the type and properties of any 

precipitates. This panelist justified his lower ranking on the basis that heat exchanger 

performance would not degrade significantly during the first 24 hours because of the 

substantial design margins. Further, beyond 24 hours, the decay heat loading is 

significantly reduced so that the margins are even greater. These phenomena may 

require additional consideration of the margin and operating history associated with the 

heat exchangers to assess their significance. Industry guidance for evaluating heat 

exchanger performance is provided in [67]. 

5.7.3 Reactor Core 

The fuel cladding surface is approximately 120 °F hotter than the sump pool temperature 

during the post-LOCA event. The function of the ECCS is to remove decay heat from 

the reactor fuel during a LOCA. In common LOCA scenarios, the ECCS cooling water is 

initially injected into the RPV through the cold leg of the reactor coolant loop to cool the 

 

5

 Note that the precipitation would need to be rapid given the relatively short residence time at the 

RHR heat exchanger. 

79 
reactor fuel. The ECCS water flows through the inlet nozzle of the reactor core, upwards 

through the vessel core, and out of the vessel through the hot leg. The water travels 

around the reactor coolant loop and flows back into containment at the pipe break 

location. During latter phases of the LOCA, this flow path is typically reversed such that 

the cooling water is injected into the hot leg. Operators may continue to change flow 

from hot-leg to cold-leg injection based on core thermocouple readings. 

As previously mentioned, the ECCS cooling water will contain physical debris, any solids 

developed by chemical processes elsewhere in the ECCS cooling system 

(e.g., containment pool and heat exchangers), and dissolved ions from corrosion, 

dissolution, erosion, or other processes. The PIRT panel identified several significant 

phenomena related to chemical phenomena and processes that could occur as this fluid 

passes through the RPV. The implications of these phenomena can be categorized as 

follows: 

A. phenomena that directly affect the heat transfer properties of the fuel or the 

ECCS water, 

B. phenomena that increase blockage and decrease coolant flow within the RPV, 

and 

C. synergistic effects on the containment pool environment. 

5.7.3.1 Effects on Fuel or ECCS Water Heat Transfer Properties 

Precipitation of retrograde soluble chemical species (Section 5.4.2.2), deposition, and 

subsequent spalling of physical and chemical solids (Section 5.3.2) have previously 

been discussed in terms of their potential additional contribution to sump screen head 

loss. However, both of these mechanisms could also directly affect heat transfer from 

the reactor fuel (T3-24, Table 9). The effects of precipitation of solid phases with 

retrograde solubility (T3-27, Table 9; T4-37, Table 10) would increase the concentration 

of solids within the core. Subsequent deposition (T3-22, Table 9; T4-37, Table 10) of 

these and other previously produced chemical species could decrease the fuel’s heat 

conduction values. After deposition, these solids could continue to build up and may 

potentially spall from the reactor fuel clad at some point. 

The panelists raised the following three unique scenarios related to the propensity of 

deposits to spall and the possible implications: 

(1) Deposits spall and add to the additional solid species inventory within the ECCS 

loop (Section 5.3.2) but spallation restores some of the original heat conduction 

properties of the fuel (T4-38, Table 10), 

(2) Deposits spall and simultaneously remove cladding which releases fission 

products to containment (T4-24, Table 10), and 

(3) Deposits remain on the reactor fuel cladding and may continue to build up, which 

decreases the heat transfer from the fuel. 

80 
Although three of the five PIRT panelists provided high importance rankings for fuel 

deposition, none of them speculated on which of these scenarios is more likely. 

However, a dissenting panelist believes that fuel deposition will not occur to any 

significant extent. There have been no studies of reactor fuel deposition as part of either 

NRC-sponsored or industry-sponsored research programs. Prior research has focused 

on evaluating chemical phenomena occurring at temperatures associated with the 

containment pool and have not addressed higher temperature phenomena that are 

representative of the reactor core. Therefore, additional consideration is necessary to 

determine if deposition can occur to any significant extent. If so, the implications, extent, 

and likelihood of each of these defined scenarios should also be evaluated. 

Physical and chemical solid debris within the ECCS coolant water could also diminish 

the fluid’s heat capacity and degrade the ability of the coolant to remove heat from the 

core. This phenomenon may be more severe at the bottom of the reactor because of 

the settling of particulate chemical products (T3-26, Table 9) and debris. Settling is 

more likely in the core because, for cold-leg injection, the upwards coolant flow rate is 

relatively low. 

One example of a possible phenomenon in this category is borate precipitation caused 

by localized boiling at the fuel elements within the two-phase water/vapor region in the 

core. As the coolant water is vaporized, the B and possibly other species, remains. 

Borate precipitation is possible if concentrations increase above the solubility limit. 

These precipitates may subsequently adhere to the fuel elements and diminish heat 

transfer within the two-phase region. Alternatively, these precipitates may spall from the 

fuel and either travel back to the sump strainer and possibly contribute to head loss or 

settle within the core. Precipitates that settle may contribute to diminished heat transfer 

or blockage below the two-phase region of the core. Greater dissolved B concentrations 

are also expected toward the bottom of the core as a result of stratification from boiling 

and the relatively low coolant flow rate within the core. These higher B concentrations 

may promote additional B precipitation below the two-phase region of the core. 

Three of the five PIRT panelists provided high importance rankings for these related 

phenomena. The high rankings were based on the adverse effect on core cooling and 

potential damage to the fuel. However, accurate evaluation of these related phenomena 

requires an understanding of the debris concentrations, types, and sizes in order to 

determine the heat transfer effects. One panelist commented that engineering 

evaluations may be sufficient to assess the impact on the core thermal and hydraulic 

transfer. An initial conservative or bounding analysis may be useful generically to 

determine if heat transfer remains sufficient. If this bounding analysis is not sufficient, 

additional plant-specific evaluation could be employed. Other mitigative strategies, such 

as reversing ECCS coolant injection flow (Section 5.7.3.2), might also be effective in 

addressing these phenomena. 

5.7.3.2 Effects of Flow Blockages 

Spalled fuel deposition products (Section 5.3.2) and precipitated retrograde soluble 

chemical species (Section 5.4.2.2), which do not deposit on the fuel, could also settle 

within the RPV. In one sense, settling within the vessel can be advantageous because 

the solids are sequestered and are not transported back to the sump screen where they 

could contribute to head loss. However, settling can also be potentially deleterious if 

flow passages to the fuel elements are either globally or locally impeded (T3-25, Table

81 
9). Reduced flow within the RPV, if significant, has the potential to diminish heat transfer 

from the fuel. 

Three out of five PIRT panelists again provided high importance rankings for these 

related phenomena. The rationale supporting the high rankings is that significant flow 

blockage could globally or locally degrade the ability of heat to be dissipated from the 

fuel elements, which might then lead to cladding failure. Justification for the low 

importance ranking was based on the likelihood of mitigating these effects through 

operator action. Current ECCS design also allows for hot-leg injection. Common plant 

operation calls for reversing flow after approximately 8 to 24 hours of a LOCA by 

switching from cold-leg to hot-leg injection [68]. Thereafter, flow injection can be 

periodically alternated between the hot and cold legs. 

Flow reversal is used, in part, to mitigate concerns about borate precipitation caused by 

localized boiling at the fuel elements (Section 5.7.3.1). This action is intended both to 

partially back-flush the fuel element channels to clear debris that may be causing 

blockage and to redistribute and redissolve borate. Of course, flow reversal will also 

resuspend some percentage of any solids that have settled in the RPV back into the 

main flow. These solids might then be transported back to the containment pool. 

Core flow blockage could also result from physical and chemical debris formed 

downstream of the RPV that is transported through the ECCS. Sources include debris 

that passed through the sump screen, solids formed within the heat exchanger 

(Section 5.4.2.2), and spalled deposits from elsewhere in the RCS piping (Section 5.3.2). 

These solids, during cold-leg injection, must first pass through the reactor core inlet 

nozzle and the lower plenum debris screen. The lower plenum debris screen possesses 

a larger mesh size than the sump screens, which reduces the likelihood of debris 

retention at the core inlet nozzle. However, solids may still be trapped at the screen or 

in other locations within the core (e.g., fuel grids, grid straps, and baffle holes) that serve 

as primary or secondary flow passages. 

Suspended solids formed downstream of the RPV travel with the flow during cold-leg 

injection, whereas spalling or settling deposits from the fuel core travel against the 

prevailing upward flow. These different flow paths may result in preferential settling 

locations for each type of solid based on its physical and chemical characteristics. As 

before, the practical implication of either locally or globally restricting flow to the core is 

that heat transfer from the fuel could be diminished. The significance of this 

phenomenon was also ranked highly by three of the five panelists using similar rationale 

as that used to justify the importance of flow blockages from settling solid species 

(above). 

These potential core blockage phenomena should be considered when evaluating ECCS 

performance. However, some initial evaluation of flow blockage at the reactor core inlet 

nozzle has been completed [69]. This study predicts a small, global temperature 

increase (approximately 5 °F) at the highest temperature fuel element only after the flow 

through the reactor core inlet nozzle is substantially blocked (approximately 95 percent 

of the flow area). This study did not address the effects of either a debris bed covering 

the inlet nozzle or localized fuel spacer blockages. Therefore, additional consideration 

of the impact of these effects on fuel element cooling is warranted. 

82 
5.7.3.3 Synergistic Effects on Containment Pool Environment 

Water temperatures within the reactor core resulting from either elevated fuel 

temperatures or higher core inlet temperatures (caused by degraded heat exchanger 

efficiency) could impact chemical effects within the remainder of the ECCS. Higher core 

temperatures could increase or initiate precipitation of species with retrograde solubility 

(Section 5.4.2.2). Higher containment pool temperatures may also lead to more 

dissolution or corrosion of submerged materials, resulting in higher ionic concentrations 

of dissolved species [47]. Therefore, the chemical equilibrium initially established will be 

altered to yield different precipitate concentrations or possibly new precipitates that were 

not originally present [47]. The concentration of precipitates could increase with higher 

temperatures if the dissolution rate of extant materials increases more rapidly than the 

solubility of secondary precipitates or vice versa. If ECCS coolant temperatures do 

increase, the implications can be considered only by evaluating the solubility (Sections 

5.1.2 and 5.4), retrograde solubility (Section 5.4.2.2) and corrosion and/or dissolution 

processes (Section°5.3.3.2) for plant-specific materials and conditions. 

Another synergistic effect considered by the PIRT is related to H increases within the 

reactor core. Hydrogen concentration increases as cladding oxidation progresses 

(T3-23, Table 9). This effect is already a design-basis consideration as it must be 

demonstrated that hydride formation does not compromise fuel ductility [2] and that H 

deflagration is avoided in containment [70]. The unique aspect of this phenomenon 

raised in the PIRT is that additional H from this reaction could affect the redox potential 

and other chemical processes as previously discussed (Sections 5.1.4 and 5.2.1). 

The significance of this phenomenon was ranked as low by three of the five PIRT 

panelists. The low ranking was justified by the rationale that this phenomenon will only 

liberate significant H early in the post-LOCA period as the hydrolysis rate decreases as 

the fuel is cooled. Additionally, any H2 that forms will partition into the containment 

building atmosphere quickly where it is relatively inert. Therefore, it has minimal effect 

on the redox potential. The only high ranking was justified by the rationale that H within 

containment must be accounted for in order to accurately determine the redox potential 

and then evaluate the subsequent effects. Therefore, it is recommended that this source 

of H be considered when evaluating the redox potential of the containment pool water 

and applicable post-LOCA chemical effects. 

5.7.4 PIRT Research Recommendations 

The pump performance evaluation [67] already requires that the effects of debris-laden 

ECCS water on wear, corrosion, and erosion be considered. As plant-specific chemical 

products and concentrations are determined (Sections 5.1 and 5.3), the wear 

characteristics (i.e., hardness and particle size) should be assessed to determine if 

significant additional degradation results from these products. Other than Fe3O4 and 

other similar particles created during crud release (Section 5.3.2), most other chemical 

solids generated in the post-LOCA period are expected to be less detrimental than 

existing physical debris, particulates from insulation, coatings, and latent debris. 

Demonstration of acceptable heat exchanger performance is also part of the downstream 

effects evaluation [67]. The only pertinent chemical effects related specifically to heat 

exchanger performance are deposition and clogging. It may be possible to evaluate 

depositional effects by considering that conservative deposit concentrations are uniformly 

distributed within the tubes to determine the reduction in heat removal compared to the 

83 
requirements imposed by the LOCA scenario. Heat exchanger tube clogging is most likely 

at the heat exchanger tube inlet. Evaluation of the flow conditions at this location should 

provide information to evaluate the propensity for clogging. If the evaluations credit 

chemical species solubility as a function of temperature, it may be necessary to consider 

the formation of additional solids as the recirculating temperature decreases. Another 

important consideration for these evaluations is the time is takes for either limiting deposit 

thicknesses or flow obstructions to occur with postulated combinations of chemical and 

physical debris. These evaluations may benefit from the fact that deposition and clogging 

are expected to worsen over time, and heat exchanger margins increase with time as the 

temperature of the core decreases. 

The impact of phenomena within the reactor core is the downstream area where additional 

fundamental study would be most beneficial because previous NRC-sponsored and 

industry-sponsored research has largely not addressed chemical effects at these high 

temperatures. Evaluation of the chemical products that precipitate and then deposit onto 

the reactor fuel (Section 5.4.2.2) could be used to determine deposit thicknesses and heat 

transfer characteristics. Spalling propensity could also be evaluated (Section 5.7.3) to first 

determine the additional solid products that could be formed and then assess their 

implications for either reactor core cooling (Section 5.7.3) or sump screen clogging 

(Section 5.3.2). Smaller scale modeling of the RCS using heated, nonradioactive fuel 

surrogates could be used to evaluate the significance of these phenomena. Any such 

evaluation should identify conditions necessary for spalling of the corrosion film on the 

reactor fuel, investigate settling propensity of these materials, and assess potential 

flocculating effects of these materials. 

The effect of the physical and chemical solid debris, both formed within and transported 

to the reactor core, on the heat transfer capacity of the ECCS coolant water is another 

consideration that is expected to be evaluated [66]. Engineering evaluations may be 

sufficient to assess the impact on the core thermal and hydraulic transfer. An initial 

conservative or bounding analysis may be sufficient to generically determine if heat 

transfer remains acceptable. It may also be possible to credit mitigation strategies such 

as reactor flow reversal from hot-leg injection in this analysis. If a bounding analysis is 

not sufficient, plant-specific evaluation could be used to determine applicable margins. 

There has been some generic consideration given to the global effects of partial flow 

blockage at the reactor core inlet nozzle [69]. However, the implications of uniform 

blockage, blockages in other locations, and localized heating effects within individual fuel 

elements have not been considered. Existing operator actions to reverse ECCS 

injection flow may also help mitigate flow blockages and could be credited if 

appropriately demonstrated. Alternatively, analysis could be used to determine whether 

there are locations within the core that are more susceptible to flow blockage effects. 

Those locations could then be analyzed using conservative assumptions (as in [69]) to 

determine the significance of these phenomena. 

Finally, it will be important to consider potential synergistic effects related to reactor core 

temperature increases stemming from the phenomena discussed in this section when 

evaluating chemical precipitation within the containment pool (Sections 5.1.2 and 5.4), at 

the heat exchanger (Section 5.7.2), or within the reactor core (Section 5.7.3). As 

previously discussed (Section 5.2.1), H production within the core should be assessed 

when evaluating the redox potential of the containment pool water and applicable 

post-LOCA chemical effects.

84 
6 CONCLUSIONS 

The NRC convened an external peer review panel to both review the NRC-sponsored 

research conducted through the end of 2005 and to identify and evaluate additional 

chemical phenomena and issues that were either unresolved, or not considered in the 

original NRC-sponsored research. A 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 process followed the general approach that has been used and refined over 

the last several years at the NRC. The following four technical evaluation criteria were 

established for ranking chemical phenomena most likely to do the following: 

(1) contribute to sump screen clogging, 

(2) affect downstream component performance, 

(3) impact core heat transfer, or 

(4) degrade structural integrity. 

The panelists independently completed the PIRT evaluation to rank the significance and 

knowledge level associated with each phenomenon that was evaluated. These rankings 

were then finalized after discussing the rationales behind the independent rankings for 

those issues resulting in a strong difference of opinion among experts. 

The PIRT results are not intended to represent a comprehensive set of chemical 

phenomena or issues within the post-LOCA environment. Instead, these phenomena 

should be considered in the context of important findings from past research 

(Section 1.2) and informed by research completed since the PIRT was conducted. It is 

anticipated that knowledge gained by related research will be considered along with the 

PIRT recommendations to identify and resolve existing knowledge gaps so that a more 

accurate review of chemical effects evaluation in the GL 2004-02 licensee submittals 

can be performed. 

The significant PIRT issues that were identified are grouped topically in the report. 

Significant issues were identified by the PIRT panel pertaining to the underlying 

containment pool chemistry; radiological considerations; physical, chemical, and 

biological debris sources; solid species precipitation; solid species growth and transport; 

organics and coatings; and downstream effects. At the end of each topical area 

discussion, a summary of issues that could benefit from additional evaluation is 

provided. 

Several of these issues can be addressed using existing knowledge associated with the 

chemical effect. Additional analysis may only be needed to assess the implications of 

these effects over the range of existing generic or plant-specific post-LOCA conditions. 

Other issues may require additional study to more fully understand the chemical effects 

and determine if they are relevant. Then, the practical generic or plant-specific 

implications can be assessed. These issues are summarized below for each topical 

area.

85 
6.1 Underlying Containment Pool Chemistry

• Additional investigation on the effect of concentrated boron salts within the RPV 

could determine whether any significant corrosion of the reactor vessel internals 

and fuel cladding occurs in the post-LOCA period. 

• Also, the effects of concentrated borate on the types, amounts, and properties of 

chemical precipitates that could form within the RPV should be considered. 

• Plant-specific pH and temperature history should be considered in combination 

with various postulated debris mixtures within the buffered environment. This 

evaluation would provide a necessary foundation for accurately determining the 

dissolved species, material corrosion and/or dissolution rates, and precipitate 

formation based on solubility and kinetic considerations. Variability in important 

factors should also be evaluated to determine the effect of changes or 

uncertainty in the underlying environment. 

• Additional scoping calculations are needed to assess the magnitude and relative 

effect of H production from a variety of sources, including the Schikorr reaction, 

to determine if dissolved H plays a significant role. 

6.2 Radiological Considerations

• Consideration of radiological effects is warranted to first understand the 

magnitude of the concentrated radioactive fields in the post-LOCA environment. 

Then, the effects of changes in the redox potential on the containment pool 

chemistry, material corrosion rates, and chemical speciation and solubility can be 

evaluated. 

• The likelihood of transport and accumulation of activated species (Section 6.3) at 

the sump screen debris bed should be assessed to determine the strength of the 

radiation field. Localized chemical effects resulting from radionuclides trapped 

within the debris bed and the effect of radiation on the properties of precipitated 

solid species should then be considered.

6.3 Physical, Chemical, and Biological Debris Sources

• The possibility and extent of corrosion product spallation from reactor vessel 

walls, primary system piping and/or components, and fuel cladding surfaces 

under conditions that would occur under post-LOCA thermal and mechanical 

shock should be examined. 

• The possibility that potential chemical precipitates could form as a result of 

retrograde solubility at the hot reactor fuel clad surface and subsequently spall 

should be investigated. 

• Plant-specific debris sources, dissolved Ca concentrations, and sump 

environmental conditions should be considered to assess the implications of 

86 
CaCO3 formation from atmospheric CO2 on both the solid species inventory and, 

more importantly, its effect on precipitation kinetics. However, the amount of CO2

provided by the air in the containment vessel may produce only negligible calcite 

compared to containment pool debris generated from other sources (e.g., 

fiberglass insulation, concrete, and Cal-Sil). 

• Realistic, plant-specific containment pool environment, materials, and 

concentrations should be considered to identify the appropriate corrosion 

acceleration or inhibition factors. One acceleration factor that should be studied 

is the catalytic effect of possible containment materials such as copper and 

citrate (or potentially other hydroxy-organic acid anions, if present). 

• Possible corrosion inhibition effects include concrete and other nonmetallic 

material aging products. Specifically, phosphate, chromate, dichromate, silicate, 

and borate can inhibit Al corrosion and deposition of Cu on Al may inhibit or 

accelerate corrosion. It will be important to understand plant-specific conditions 

in order to credit these inhibition effects. 

• The effect of significant alloying additions in nuclear structural materials and 

debris or compositional changes in nonmetallic materials within the containment 

on the material dissolution rates should be considered. This evaluation should 

also determine whether significant dissolved concentrations of alloying or 

secondary elements are present that could alter chemical effects. 

• Galvanic couples that may exist within the containment pool as a result of direct 

contact between dissimilar metals should be identified and evaluated to 

determine if they alter material corrosion rates. 

• The viability and potential consequences of biological growth in a post-LOCA 

borated-water environment should be investigated. If significant growth is 

possible within 30 days, an understanding of important post-LOCA variables that 

may accelerate or retard the biological growth rate would be necessary to both 

identify locations within the ECCS where growth is possible and evaluate the 

associated implications. 

6.4 Solid Species Precipitation

• A realistic or conservative assessment of relevant combinations of time, 

temperature, pH, and ionic strength should be performed to determine the types, 

sizes, and concentrations of solid precipitates that may form under plant-specific 

conditions and the significance of ripening through polymerization on these 

precipitates. 

• Precipitation studies should also consider solid species precipitation caused by 

the cooling of the ECCS water at the heat exchanger and heating within the RPV 

(Section 6.3). 

• Research could also be useful to identify whether conservative or realistic 

post-LOCA environmental conditions are sufficient to foster co-precipitation and 

to characterize any species that form.

87 
6.5 Solid Species Growth and Debris Transport

• Variability in important post-LOCA variables (e.g., materials, temperatures, pH, 

and buffering systems) should also be evaluated to determine if the effect on 

agglomeration is significant. This study could be used to demonstrate that both 

chemical precipitates created in single-effects or integrated-effects testing and 

surrogate precipitates produced outside the testing environment are 

representative of materials that form in post-LOCA conditions. 

• Research on transport phenomena may be necessary to validate reducing the 

suspended solid particulate caused by settling and deposition. Variability in the 

plant design, containment materials, containment flow rates and turbulence, pH 

buffer, and the chemical conditions present resulting from various hypothetical 

pipe breaks are important considerations that may affect the settling rates of 

containment pool debris.

6.6 Organics and Coatings

• The potentially significant coating issues to address, as indicated by the PIRT 

panelists, are leaching from metallic coatings and the decomposition of organics 

within coatings by thermolysis and radiolysis under either realistic or conservative 

post-LOCA conditions. 

• More general research in the effects of organics should be preceded by a 

realistic assessment of possible post-LOCA organic sources (e.g., oils, greases, 

electrical insulations, plastic coatings, and paints) and concentrations in the 

containment pool. If sufficient organic sources exist, additional research would 

then be useful to determine the leaching behavior of these sources and examine 

the ability of the organic materials to coalesce and/or bind inorganic solids as 

they cool within the post-LOCA containment pool and consequently affect flow 

through the sump strainer screen. 

• The interaction between organic materials and inorganic solids may increase the 

buoyancy of inorganic solids such that it is sufficient to restrict settling but not so 

great as to promote flotation. Additional study would need to determine if organic 

buoyancy can occur within the range of post-LOCA conditions existing at PWR 

plants and if the effect suspends, but does not float, significant debris 

concentrations that would otherwise settle. The engineering impact of organic 

buoyancy is significantly diminished if settling of containment pool solids is not 

credited in a chemical effects evaluation. 

• The implications of hydrothermal hydrolysis under either realistic or conservative 

post-LOCA conditions have not been studied. The most susceptible coatings 

and insulation materials could be evaluated to determine the propensity for 

interactions among hydrothermal hydrolysis byproducts and with other 

containment pool species. 

88 
6.7 Downstream Effects

• The corrosion and erosion characteristics (i.e., hardness and particle size) of 

chemical products and concentrations could be assessed to determine if pump 

seal and internal components can be adversely affected. Magnetite and other 

similar particles created during crud release are expected to potentially be the 

most detrimental. 

• The pertinent chemical effects related specifically to heat exchanger performance 

are deposition and clogging. A conservative analysis of deposition may be 

sufficient to determine if adequate heat exchanger design margins remain. The 

precipitation kinetics could be studied to determine if solid species concentrations 

at these lower temperatures are less than those assumed from either aqueous 

concentrations or solubility considerations. Evaluation of the flow conditions at 

the tube inlet location may also provide information to evaluate the propensity for 

heat exchanger clogging. 

• Evaluation of the chemical products that precipitate and subsequently adhere to 

the reactor fuel (Sections 6.3 and 6.4) could be useful to determine deposit 

thickness and heat transfer characteristics. The propensity for spallation of 

chemical products from the fuel cladding could also be studied to evaluate the 

additional solid products that may be formed and their implications for either 

reactor core or sump screen clogging. 

• The effect of the physical and chemical solid debris, both formed within and 

transported to the reactor core, on the heat capacity of the ECCS coolant water 

should also be considered. However, it is expected that the debris loading would 

have to be significant before the heat capacity is affected. Therefore, 

conservative engineering evaluations may be sufficient to assess the impact on 

the core thermal and hydraulic transfer. 

• Implications of flow blockages in locations other than the reactor core inlet nozzle 

and localized heating effects within individual fuel elements should also be 

considered. It may be possible to use analysis or to credit existing operator 

actions to demonstrate that acceptable fuel heat transfer is maintained. 

• It will be important to be mindful of potential synergistic effects related to reactor 

core temperature increases stemming from the downstream effect phenomena 

(Section 5.7.3.3) when evaluating chemical precipitation within the containment 

pool, at the heat exchanger, or within the reactor core. 

• Hydrogen, H2O2, O2, and OH-

 production within the reactor core should be 

considered when evaluating the redox potential of the ECCS water (Section 6.2) 

and other applicable post-LOCA chemical effects. 

89 
This page intentionally left blank.

90 
7 REFERENCES

[1] R. Emrit, R. Riggs, W. Milstead, J. Pittman, and H. Vandermolen, “A Prioritization 

of Generic Safety Issues,” NUREG-0933, U.S. Nuclear Regulatory Commission 

(NRC), Washington, DC, October 2006. 

[2] U.S. Code of Federal Regulations, “Acceptance Criteria for Emergency Core 

Cooling Systems for Light-Water Nuclear Power Reactors,” Section 50.46, 

Title 10. 

[3] Generic Letter 2004-02, “Potential Impact of Debris Blockage on Emergency 

Recirculation during Design-Basis Accidents at Pressurized-Water Reactors,” 

September 13, 2004. 

[4] Safety evaluation by the Office of Nuclear Reactor Regulation related to the NRC 

Generic Letter 2004-02, Nuclear Energy Institute (NEI) guidance report 

(proposed document number NEI 04-07), “Pressurized Water Reactor Sump 

Performance Evaluation Methodology,” Revision 0, December 6, 2004. 

[5] A. R. Pietrangelo (NEI), letter to J. H. Hannon (NRC), “Pressurized Water 

Reactor Sump Performance Evaluation Methodology,” (proposed document 

number NEI 04-07), May 28, 2004 (Agencywide Documents Access and 

Management System (ADAMS) Accession No. ML041550279). 

[6] W.H. Ruland (NRC), letter to A.R Pietrangelo (NEI), “Draft Guidance for Review 

of Final Licensee Responses to Generic Letter 2004-02, ‘Potential Impact of 

Debris Blockage on Emergency Recirculation During Design Basis Accidents at 

Pressurized-Water Reactors,’” September 27, 2007 (ADAMS Accession 

No. ML072600337). 

[7] M. Bonaca (Advisory Committee for Reactor Safeguards), memorandum to W.D. 

Travers (NRC Executive Director for Operations), “Proposed Resolution of GSI–

191, Assessment of Debris Accumulation on PWR Sump Pump Performance,” 

February 20, 2003 (ADAMS Accession No. ML030520101. 

[8] W.D. Shults (Oak Ridge National Laboratory), Analytical Chemistry Report to 

J.A. Daniel (General Public Utilities Service Corporation), September 14, 1979. 

[9] Electric Power Research Institute, Nuclear Safety Analysis Center, “Analysis of 

Three Mile Island—Unit 2 Accident,” NSAC-1, March 1980. 

[10] B.C. Letellier, “Small-Scale Experiment: Effects of Chemical Reactions on 

Debris-Bed Head Loss,” NUREG/CR-6868, U.S. Nuclear Regulatory 

Commission, Washington, DC, March 2005 (ADAMS Accession 

No. ML050900260). 

91 
[11] J. Dallman, B.C. Letellier, J. Garcia, J. Madrid, W. Roesch, D. Chen, K. Howe, 

L. Archuleta, and F. Sciacca, “Integrated Chemical Effects Test Project: 

Consolidated Data Report,” NUREG/CR-6914, Volumes 1–6, U.S. Nuclear 

Regulatory Commission, Washington, DC, September 2006. 

[12] T.S. Andreychek, “Test Plan: Characterization of Chemical and Corrosion 

Effects Potentially Occurring Inside a PWR Containment Following a LOCA,” 

Revision 13, Westinghouse Electric Company, Monroeville, PA, July 2005 

(ADAMS Accession No. ML052100426). 

[13] V. Jain, X. He, and Y.M. Pan, “Corrosion Rate Measurements and Chemical 

Speciation of Corrosion Products Using Thermodynamic Modeling of Debris 

Components To Support GSI-191,” NUREG/CR-6873, U.S. Nuclear Regulatory 

Commission, Washington, DC, April 2005 (ADAMS Accession 

No. ML051610123). 

[14] M. Klasky, J. Zhang, M. Ding, B.C. Letellier, D. Chen, and K. Howe, “Aluminum 

Chemistry in Prototypical Post-LOCA PWR Containment Environment,” 

NUREG/CR-6915, U.S. Nuclear Regulatory Commission, Washington, DC, 

October 2006 (ADAMS Accession No. ML062400465). 

[15] K. Kasza, J.H. Park, B. Fisher, J. Oras, K. Natesan, and W.J. Shack, “Chemical 

Effects Head-Loss Research in Support of Generic Safety Issue 191,” 

NUREG/CR-6913, U.S. Nuclear Regulatory Commission, Washington, DC, 

September 2006 (ADAMS Accession No. ML062280415). 

[16] C.B. Banh, K.E. Kasza, and W.J. Shack, “Technical Letter Report on Follow-on 

Studies in Chemical Effects Head-Loss Research; Studies on WCAP Surrogates 

and Sodium Tetraborate Solutions,” Argonne National Laboratory, Argonne, IL, 

February 15, 2007 (ADAMS Accession No. ML070580086). 

[17] J. McMurry, V. Jain, X. He, D. Pickett, R. Pabalan, and Y.M. Pan, “GSI-191, 

PWR Sump Screen Blockage Chemical Effects Tests-Thermodynamic 

Simulations,” NUREG/CR-6912, U.S. Nuclear Regulatory Commission, 

Washington, DC, September 2006 (ADAMS Accession No. ML060230442). 

[18] A.E. Lane, T.S. Andreychek, W.A. Byers, R.J. Jacko, E.J. Lahoda, and 

R.D. Reid, “Evaluation of Post-Accident Chemical Effects in Containment Sump 

Fluids to Support GSI-191,” Westinghouse Commercial Atomic Power 

(WCAP)-6530-NP, Revision 0, Westinghouse Electric Company, 

Monroeville, PA, February 2006 (ADAMS Accession No. ML060890509). 

[19] Final safety evaluation by the NRR, “WCAP-16530-NP, Final Safety Evaluation 

of Post Accident Chemical Effects in Containment Sump Fluids to Support 

GSI-191,” Pressurized Water Reactor (PWR) Owners Group Project No. 694, 

December 21, 2007 (ADAMS Accession No. ML073520891). 

[20] J. McMurry and X. He, “Supplementary Leaching Tests of Insulation and 

Concrete for GSI-191 Chemical Effects Program,” Technical Letter Report 

92 
IM 20.12130.01.001.320, Center for Nuclear Waste Regulatory Analyses, 

San Antonio, TX, November 2006 (ADAMS Accession No. ML063330573). 

[21] American National Standard N101.2, “Protective Coatings (Paints) for Light 

Water Nuclear Reactor Containment Facilities,” American Institute of Chemical 

Engineers, New York, New York, NY, 1972. 

[22] F.P. Schiffley, II letter to the NRC, PWR Owners Group responses to the NRC 

second request for additional information on WCAP-16530, "Evaluation of 

Chemical Effects in Containment Sump Fluids to Support GSI-191," OG-07-129, 

April 3, 2007 (ADAMS Accession No. ML070950119). 

[23] K. Natesan and R. Natarajan, “Survey on Leaching of Coatings Used in Nuclear 

Power Plants: Letter Report,” Argonne National Laboratory, Argonne, IL, 

September 13, 2006 (ADAMS Accession No. ML062560368). 

[24] American National Standard N5.12, “Protective Coatings (Paints) for the Nuclear 

Industry,” American Institute of Chemical Engineers, New York, NY, 1974. 

[25] R.L. Sindelar, M.E. Dupont, N.C. Lyer, P.S. Lam, T.E. Siddmore, P.R. Utsch, and 

P.E. Zapp, “Degradation and Failure Characteristics of NPP Containment 

Protective Coating Systems—Interim Report,” Westinghouse Savannah River 

Company Topical Report (WSRC-TR)-2000-00079, March 2000. 

[26] Electric Power Research Institute Report No. 1011753, “Design Basis Accident 

Testing of Pressurized Water Reactor Unqualified Original Equipment 

Manufacturer Coatings,” September 2005 (ADAMS Accession 

No. ML071130069). 

[27] P.A. Torres, “Peer Review of GSI-191 Chemical Effects Testing Program,” 

NUREG-1861, U.S. Nuclear Regulatory Commission, Washington, DC, 

December 2006 (ADAMS Accession No. ML063630498). 

[28] B.E. Boyak, R. Duffy, P. Griffith, G. Lellouche, S. Levy, U. Rohatgi, G. Wilson, 

W Wulff, and N. Zuber, “Quantifying Reactor Safety Margins: Application of 

Code Scaling, Applicability, and Uncertainty Evaluation Methodology to a 

Large-Break, Loss-of-Coolant Accident,” NUREG/CR-5249, U.S. Nuclear 

Regulatory Commission, Washington, DC, December 1989. 

[29] B.E. Boyack, A.T. Motta, K.L. Peddicord, C.A. Alexander, R.C. Deveney, 

B.M. Dunn, T. Fuketa, K.E. Higar, L.E. Hochreiter, S. Langenbuch, F.J. Moody, 

M.E. Nissley, J. Papin, G. Potts, D.W. Pruitt, J. Rashid, D.H. Risher, R.J. Rohrer, 

J.S. Tulenko, K. Valtonen, N. Waeckel, and W. Wiesenack, “Phenomenon 

Identification and Ranking Tables (PIRTs) for Rod Ejection Accidents in 

Pressurized Water Reactors Containing High Burnup Fuel,” NUREG/CR-6742, 

U.S. Nuclear Regulatory Commission, Washington, DC, September 2001. 

[30] S.M. Bajorek, A. Ginsberg, D.J. Shimeck, K. Ohkawa, M.Y. Young, 

L.E. Hochreiter, P. Griffin, Y. Hassan, T. Fernandez, and D. Speyer, “Small 

93 
Break Loss of Coolant Accident Phenomena Identification and Ranking Table 

(PIRT) for Westinghouse Pressurized Water Reactors”, Ninth International 

Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-9), 

San Francisco, CA, October 3–8, 1999. 

[31] R.K. Ratnayake, L.E. Hochreiter, S. Ergun, A.J. Baratta, “Identification and 

Ranking of Phenomena Leading to Peak Cladding Temperatures in Boiling Water 

Reactors during Large-Break Loss of Coolant Accident Transients,” Proceedings 

of the 10th International Conference on Nuclear Engineering (ICONE 10), Paper 

No. ICONE 10–22288, American Society of Mechanical Engineers, New York, 

NY, April 2002. 

[32] J.R. Cavallo, T.S. Andreychek, J. Bostelman, B. Boyack, G. Dolderer, and 

D. Long, “PWR Coatings Research Program Phenomena Identification and 

Ranking Tables,” Industry Coatings PIRT Report No. IC 99-02, June 16, 2000 

(ADAMS Accession No. ML003733475). 

[33] R.N. Morris, D.A. Petti, D.A. Powers, and B.E. Boyack, “TRISO-Coated Particle 

Fuel Phenomenon Identification and Ranking Tables (PIRTs) for Fission Product 

Transport Due to Manufacturing, Operations, and Accidents,” NUREG/CR-6844, 

Volume 1, U.S. Nuclear Regulatory Commission, Washington, DC, July 2004. 

[34] P.L. Andresen, F.P. Ford, K. Gott, R.L. Jones, P.M. Scott, T. Shoji, R.W. Staehle, 

and R.L. Tapping, “Expert Panel Report on Proactive Materials Degradation 

Assessment,” NUREG/CR-6923, U.S. Nuclear Regulatory Commission, 

Washington, DC, February 2007. 

[35] B.E. Boyack, T.S. Andreychek, P. Griffith, F. E. Haskin, and J. Tills, "PWR Debris 

Transport in Dry Ambient Containments-Phenomena Identification and Ranking 

Tables (PIRTs)," LA-UR-99-3371, Revision 1, Los Alamos National Laboratory, 

Los Alamos, NM, July 1999. 

[36] B.E. Boyack, T.S. Andreychek, P. Griffith, F.E. Haskin, and J. Tills, “PWR Debris 

Transport in Ice Condenser Containments- Phenomena Identification and 

Ranking Tables (PIRTs)”, LA-UR-99-5111, Revision 1, Los Alamos National 

Laboratory, Los Alamos, NM, December 1999. 

[37] G.E. Wilson and B. E. Boyack, “The Role of the PIRT Process in Experiments, 

Code Development, and Code Applications Associated with Reactor Safety 

Analysis,” Nuclear Engineering and Design, Volume 186, pp. 23–37, 1998. 

[38] A.T. Howell (NRC), memorandum to W.F. Kane (RC), “Degradation of the 

Davis-Besse Nuclear Power Station Reactor Pressure Vessel Head Lessons 

Learned Report,” September 30, 2002 (ADAMS Accession No. ML022740211). 

[39] W. Arcieri, R. Beaton, D. Fletcher, and J. Lehning, “Calculation of Sump Fluid 

Temperature During Loss of Coolant Accidents at a Sample Nuclear Power 

Plant,” Revision 1, Information Systems Laboratories, Inc., Rockville, MD, 

May 2006 (ADAMS Accession No. ML061510478). 

94 
[40] R.D. Reid, K.R. Crytzer, A.E. Lane, and T.S. Andreychek, “Evaluation of 

Alternative Emergency Core Cooling System Buffering Agents,” 

WCAP-16596-NP, Westinghouse Electric Company LLC, Pittsburgh, PA, 

July 2006. This report is available as Attachment 1, “Response to Request for 

Additional Information Related to the License Amendment Request on Change of 

Containment Building Sump Buffering Agent from Trisodium Phosphate to 

Sodium Tetraborate,” letter from J.A. Reinhart to the NRC, September 6, 2006, 

(ADAMS Accession No. ML062570173). 

[41] D.D. Macdonald and M. Urquidi-Macdonald, "The Electrochemistry of Nuclear 

Reactor Coolant Circuits, "Encyclopedia of Electrochemistry, (A.J. Bard and 

M. Stratmann eds.), Volume 5, Electrochemical Engineering, (D.D. Macdonald 

and P. Schmuki, eds.), Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, 

Germany, pp. 665–720, 2007. 

[42] J.R. Divine, W.M. Bowen, D.B. Mackey, D.J. Bates, and K.H. Pool, "Prediction 

Equations for Corrosion Rates of A-537 and A-516 Steels in Double Shell Slurry, 

Future PUREX, and Hanford Facilities Wastes," PNL-5488, Pacific Northwest 

National Laboratory, Richland, WA, 1985. 

[43] S.B. Clark and C.H. Delegard. "Plutonium in Concentrated Solutions," Chapter 7 

in Advances in Plutonium Chemistry -- 1967-2000, (D. Hoffman, ed.), American 

Nuclear Society, La Grange Park, IL, 2002. 

[44] N. Wiberg, Inorganic Chemistry, Academic Press, San Diego, CA, 2001, p. 980. 

[45] U.S. Nuclear Regulatory Commission, “Alternative Radiological Source Terms for 

Evaluating Design Basis Accidents at Nuclear Power Reactors,” Regulatory 

Guide 1.183. 

[46] E.C. Beahm, R.A. Lorenz, and C.F. Weber, “Iodine Evolution and pH Control,” 

NUREG/CR-5950, U.S. Nuclear Regulatory Commission, Washington, DC, 

December 1992. 

[47] R. Litman, “Evaluation of Integrated Chemical Effects Testing,” Appendix D to 

P.A. Torres, “Peer Review of GSI-191 Chemical Effects Testing Program,” 

NUREG-1861, U.S. Nuclear Regulatory Commission, Washington, DC, 

December 2006 (ADAMS Accession No. ML063630498). 

[48] W.L. Lindsay, Chemical Equilibria in Soils, Wiley Interscience, New York, NY, 

1979. 

[49] J.P. Burke (NRC), letter to A.L. Hiser, Jr. (NRC), “Review of Southwest Research 

Institute’s Technical Letter Report for Contract NRC-03-07-046,” June 26, 2008, 

(ADAMS Accession No. ML081780515). 

[50] C.J. Shaffer, D.V. Rao, M.T. Leonard, and K.W. Ross, “Knowledge Base for the 

Effect of Debris on Pressurized Water Reactor Emergency Core Cooling Sump 

95 
Performance,” NUREG/CR-6808, U.S. Nuclear Regulatory Commission, 

Washington, DC, February 2003 (ADAMS Accession Nos. ML030780733 and 

ML030920540). 

[51] C.W. Enderlin, B.E. Wells, M. White, F. Nigl, A. Guzman, D.R. Rector, T.J. 

Peters, and E.S. Mast, "Experimental Measurements of Pressure Drop Across 

Sump Screen Debris Beds in Support of Generic Safety Issue 191," 

NUREG/CR-6917, U.S. Nuclear Regulatory Commission, Washington, DC, 

January 2007. 

[52] NRC Bulletin No. 2003-01, “Potential Impact of Debris Blockage on Emergency 

Sump Recirculation at Pressurized-Water Reactors,” U.S. Nuclear Regulatory 

Commission, Washington DC, June 9, 2003 (ADAMS Accession 

No. ML031600259). 

[53] R. Reid, “Incorporation of Additional Plant Inputs in the Chemical Effects 

Spreadsheet PA-SEE-0354,” PWR Owners Group Presentation at the public 

meeting with NEI, PWR Owners Group, licensees, and sump strainer vendors to 

discuss the resolution of Generic Safety Issue 191, April 18, 2007. Meeting 

information can be accessed at http://www.nrc.gov/reactors/operating/opsexperience/pwr-sump-performance/public-mtgs/2007/index.html. 

[54] F. Dacquait, C. Andrieu, M. Berger, J-L Bretelle, and A. Rocher, "Corrosion 

Product Transfer in French PWRs During Shutdown," Société Française 

d'Energie Nucléaire (SFEN)-Chimie Conference on Water Chemistry in Nuclear 

Reactor Systems, Avignon, France, 2002. 

[55] Y.L. Sandler, “Structure of PWR Primary Corrosion Products,” Corrosion,

Volume 35, Number 5, pp. 205–208, 1979. 

[56] L.J. Parrot and D.C. Killoh, “Carbonation in 36 Year Old, In-Situ Concrete,” 

Cement and Concrete Research, Volume 19, pp. 649–655, 1989. 

[57] P.A. Slegers and P.G. Rouxhet, “Carbonation of the Hydration Products of 

Tricalcium Silicate.” Cement and Concrete Research, Volume 6, pp.381–388, 

1976. 

[58] P.C. Singer and W. Stumm, “Oxygenation of Ferrous Iron: The Rate Determining 

Step In The Formation of Acid Mine Drainage,” Federal Water Pollution Control 

Administration Research Series Report, National Technical Information Service 

Report No. PB-189-233, 1968. 

[59] P.C. Singer and W. Stumm, “Acid Mine Drainage: The Rate Determining Step,” 

Science, Volume 167, pp. 1121–1123, 1970. 

[60] V. Jain, L. Yang and K. Chiang, “Chemical Speciation, Using Thermodynamic 

Modeling, during a Representative Loss-of-Coolant Accident Event,” Center for 

Nuclear Waste Regulatory Analyses Report CWNRA 2004-07, Revision 1, 

Center for Nuclear Waste Regulatory Analyses, San Antonio, TX, 2004. 

96 
[61] V.H. Troutner, “Uniform Aqueous Corrosion of Aluminum—Effects of Various 

Ions,” HW-50133, Hanford Atomic Products Operation, Richland, WA, 1957. 

This report can be accessed at 

http://www2.hanford.gov/ddrs/search/RecordDetails.cfm?AKey=D8506811. 

[62] C. Groot, “Phosphoric Acid Corrosion Inhibition in Present Reactors,” HW-50219, 

Hanford Atomic Products Operation, Richland, WA, 1957. This report can be 

accessed at 

http://www2.hanford.gov/ddrs/common/findpage.cfm?AKey=D8370590. 

[63] L.L. Shreir, R.A. Jarman, and G.T. Burstein. Corrosion, Volume 1, 

“Metal/Environment Reactions,” Butterworth-Heinemann, Oxford, UK, 1994. 

[64] M.G. Fontana, Corrosion Engineering, McGraw-Hill, New York, NY, 1986. 

[65] D.D. Macdonald, “Characterization of Chemical and Corrosion Effects Potentially 

Occurring Inside a PWR Confinement Following a LOCA,” Appendix E to 

P.A. Torres, “Peer Review of GSI-191 Chemical Effects Testing Program,” 

NUREG-1861, U.S. Nuclear Regulatory Commission, Washington, DC, 

December 2006 (ADAMS Accession No. ML063630498). 

[66] T.S. Andreychek, M.D. Coury, A.E. Lane, K.F. McNamee, R.B. Sisk, D. Mitchell, 

P.V. Pyle, W.A. Byers, K.J. Barber, D.P. Crane, M.E. Nissley, D.J. Fink, 

G. Wissinger, H. Dergel, B.G. Lockamon, and P.A. Sherburne, "Evaluation of 

Long-Term Cooling Considering Particulate, Fibrous and Chemical Debris in the 

Recirculating Fluid,” WCAP-16793-NP, Revision 0, Westinghouse Electric 

Company, LLC, Pittsburgh, PA, May 2007 (ADAMS Accession 

No. ML071580139). 

[67] Safety evaluation by the NRR on Topical Report WCAP-16406-P, Revision 1, 

“Evaluation of Downstream Sump Debris Effects in Support of GSI-191,” PWR 

Owners Group Project No. 694, December 21, 2007 (ADAMS Accession 

No. ML073520295). 

[68] NRC Information Notice 93-66, “Switchover to Hot Leg Injection Following a Loss 

of Coolant Accident in Pressurized Water Reactors,” U.S. Nuclear Regulatory 

Commission, Washington, DC, August 16, 1993. 

[69] W.J. Krotiuk, D. Helton, and C. Boyd, “Post-LOCA PWR Core Inlet Blockage 

Assessment,” NRC Office of Nuclear Regulatory Research, Safety Margins 

Branch Analysis Report, U.S. Nuclear Regulatory Commission, Washington, DC, 

February 2007 (ADAMS Accession No. ML070860521). 

[70] U.S. Code of Federal Regulations, “Standards for Combustible Gas Control 

Systems in Light-Water-Cooled Power Reactors,” Section 50.44, Title 10. 

97 
APPENDIX A 

Curriculum Vitae for PIRT Panelist 
John Anthony Apps 

EDUCATION 

Ph.D., 1970 (Geology) Harvard University, Cambridge, Massachusetts. 

A.M., 1965 (Geology) Harvard University, Cambridge, Massachusetts. 

B.Sc. (First Class Honours) 1961 (Mining Geology), A.R.S.M., Imperial College of Science and 

Technology, London University, England. 

EXPERIENCE (Approximately last 20 Years) 

SENIOR SCIENTIST EMERITUS, Geochemistry Department, 01/26/04 - present. Earth Science 

Division, Lawrence Berkeley National Laboratory, University of California, Berkeley, California. 

Investigator to evaluate the geochemistry of the unsaturated zone, fate of cementitious 

materials, fate and transport of long-lived actinides and the temperature effects on radionuclide 

adsorption at the planned DOE high-level nuclear waste repository at Yucca Mountain, 

Investigator with K. Pruess and Xianfu Xu to evaluate CO2 sequestration in deep saline aquifers 

(DOE-OBES) 

Co-editor with Chin-Fu Tsang of a book on underground injection science and technology for 

the U.S. EPA. 

STAFF SCIENTIST, TERM, Geochemistry Department, Earth Science Division, Lawrence 

Berkeley National Laboratory, University of California, Berkeley, California. 10/01/01 – 09/30/03 

(Returned to full-time employment status) 

Investigator to evaluate the geochemistry of the unsaturated zone at the planned DOE highlevel nuclear waste repository at Yucca Mountain, Nevada. Investigator to model the 

geochemistry of the Drift Scale Test at Yucca Mountain (DOE-YMP) 

Investigator with K. Pruess and Xianfu Xu to evaluate CO2 sequestration in deep saline aquifers 

(DOE-OBES). 

Co-convenor with Chin-Fu Tsang of an International Conference on Underground Injection 

Science and Technology (UIST) for the U.S. EPA 

SENIOR SCIENTIST EMERITUS, Geochemistry Department, 06/98 – 09/30/01. Environmental 

Remediation Technology Department, 02/94 – 06/98. Earth Science Division, Lawrence 

Berkeley National Laboratory, University of California, Berkeley, California. 

Investigator to evaluate the geochemistry of the unsaturated zone at the planned DOE high 

level nuclear waste repository at Yucca Mountain, Nevada. Investigator to model the 

geochemistry of the Drift Scale Test at Yucca Mountain (DOE-YMP) 

Investigator with K. Pruess and Xianfu Xu to evaluate CO2 sequestration in deep saline aquifers 

(DOE-OBES) 

Co-principal investigator (with George Moridis), Containment of Contaminants Through Physical 

Barriers from Viscous Liquids Emplaced Under Controlled Viscosity Conditions (DOE-EM-50); 

Co-principal investigator (with Chin-Fu Tsang), Investigation of the Geochemistry of Hazardous 

Waste Disposal by Deep Underground Injection, (EPA-ODW); and the Calico Hills Project 

(DOE-YMP). 

 A-2
STAFF SENIOR SCIENTIST, Geochemistry Group, Earth Sciences Division, Lawrence 

Berkeley Laboratory, University of California, Berkeley, California, 10/82 - 10/31/93. (Elected 

early retirement). 

Principal or co-principal investigator on the following projects: 

Coordination with Russian scientists with respect to radioactive remediation at Cheliabinsk, 

Russia, (with Chin-Fu Tsang), (DOE-EM and DOE-OBES); 

Investigation of the geochemistry of hazardous waste disposal by deep underground injection, 

(EPA-ODW); 

Modeling the leaching of fly ash, (EPRI); Oxygen consumption in compressed air energy 

storage reservoirs, (EPRI) 

Evaluation of ground and surface water contamination from mining operations in California, (The 

State of California); 

Investigation of near field rock-water interactions and radionuclide transport, (NRC-Research); 

Abiogenic methane formation, (DOE-OBES); 

Geochemical aspects of the seismic stability of fractures, (DOE) 

Appointed VISITING PROFESSOR in the Department of Material Science and Mineral 

Engineering, University of California, Berkeley, 8/85 

RECENT HONORS 

Outstanding Performance Award, Lawrence Berkeley National Laboratory, 1996 

Article I. INTERNAL COMMITTEES 

Lawrence Berkeley Laboratory Staff Committee, 1982-1985. 

Earth Science Division Professional Staff Committee, 1978-1987, 1990-present. 

Lawrence Berkeley Laboratory Library Committee, 1984-1987. 

Lawrence Berkeley Laboratory Technical Advisory Committee for the Environmental Restoration 

Program, 1994-present. 

PUBLICATIONS 

About 50 peer reviewed papers, numerous Government Agency, Laboratory and Company 

reports, co-editor of two books, and two patents. 

EXTRA-MURAL ACTIVITIES (Approximately last 20 Years) 

National Research Council, Board of Mineral Resources. Member, Committee on Accessory 

Elements. Chairman, Panel on Non Bauxitic Aluminum Ores, 1978-1979. 

National Research Council, Committee on Radioactive Waste Management. Member, Panel on 

Savannah River Plant Wastes, 1979-1982. 

American Chemical Society, Petroleum Research Fund Advisory Board, 1978-1981. Chairman, 

Geosciences Committee, 1980-1981. Member, Policy Committee, 1980-1981. 

Department of Energy. Member, OBES Earth Science Advisory Committee, (Sewing Circle), 

1979-1982. 

Department of Energy, Office of Nuclear Waste Isolation. Member, Engineering Review Group, 

1983-1986. 

 A-3
Department of Energy, Office of Technology Development, Facilitator, Soil Washing Workshop, 

Las Vegas, NV, August 28-29, 1990. 

Nuclear Regulatory Commission, Advisory Committee on Nuclear Waste Isolation, 1989-1993 

Department of Energy, Fernald Environmental Management Project. Uranium Soils Integrated 

Demonstration Advisory Group: Waste Treatment and Disposal, 1991-1994. 

American Institute of Hydrology, Organizing Committee for the 4th Joint USA/CIS Conference on 

Hydrology, San Francisco, Nov 8-11, 1999 

Consulted for Rockwell-Hanford Operations (BWIP), the Office of Nuclear Waste Isolation, (US 

DOE), US Nuclear Regulatory Commission, US Environmental Protection Agency, US 

Department of Justice, E.I. Du Pont de Nemours Inc., ALCOA, URS Corp., Dames and Moore, 

Woodward-Clyde and others. 

 A-4
Wu Chen 

Sr. Specialist 

Dow Chemical, U. S. A. 

B-1603, Freeport, TX 77541 

(979) 238-9943 

(979) 238-0651 (FAX) 

wuchen@dow.com 

EDUCATION 

 Ph.D. Chemical Engineering 1986 University of Houston 

 M.S. Chemical Engineering 1984 University of Houston 

 B.S. Chemical Engineering 1979 National Taiwan University 

EXPERTISE

• Solids/liquid Separation (filtration, sedimentation, centrifugation and business 

development) 

• Solid handling (storage, transport) 

• Particle formation, Characterization, Coagulation and flocculation 

• Slurry handling 

• Process development, Project management, Bioprocessing, Bioseparation 

• Certified 6-Sigma black belt 

• People Skill, Leadership training, Marriage counseling 

AFFILIATIONS

* Dow Chemical, U. S. A. (1988-PRESENT) 

Engineering & Process Science, Solid Processing, Freeport, TX (1993 - present) 

 Project Leader, Research Leader, Sr. Specialist 

 - Established the solid handling lab. in Freeport (lab. set up, development, equipment 

procurement, and project management). 

 - Lead in all aspects of solid handling (fundamentals, tool/guideline development, laboratory 

evaluation, pilot test, process design, capital project, and plant trouble shooting) 

Industrial Biotechnology, San Diego, CA (2001 - 2003) 

 - Led the implementation of α-Amylases manufacturing process - process development, 

project management, and plant start up 

 - Imported/exported equipment and material, for process implementation in Mexico City. 

Resins Research, Freeport, TX (1991 - 1993) 

 Project Leader 

 - Conducted process research for epoxy products. 

 - Served as a subject matter expert for global solid separation. 

Epoxy Manufacturing, Freeport, TX (1988 - 1991) 

 Sr. Process Engineer 

 - Conduct process development and plant trouble shooting. 

 - Implemented centrifuge & other process technologies into production plants. 

* University of Houston (1986-1988) 

 A-5
 Research Associate 

 - Managed solid liquid separation lab. 

 - Led research in mechanism of flow through compressible, porous beds in solid-liquid 

separation operations-- sponsored by the U. S. Dept. of Energy. 

 

PROFESSIONAL ASSOCIATIONS INVOLVEMENT

American Filtration & Separation Society 

- Awarded Well Shoemaker Award - for significant contributions in leadership and service 

(2005). 

- Awarded Frank Tiller Award - for significant technical achievement (2002) 

- Served as the society Chairman (2003) 

- Served on Board of Directors (1998-2004) 

- Served as the Education Committee Chairman (2004-present) 

- Served as National conference chair (1996, 2000) 

American Institute of Chemical Engineers 

- Served as the course leader/instructor for the solid/liquid separation course (1995-present) 

U.S. National Renewable Energy Laboratory (NREL) 

- Served as a consultant to evaluate the cellulosic ethanol process (2007) 

U.S. Nuclear Regulatory Commission 

- Served as a consultant for technology review (2005-2006) 

Life Strategy 

- Served as in instruct on personality/people skill (1999-present) 

- Served as a counselor on leadership (2000- present) 

- Served as an Instructor/counselor on marriage (1998-present) 

 * course offerings include: Houston, Shanghai, WuHan and Beijing. 

SELECTED PUBLICATIONS

1. Chen, W. and W. P. Li, “Expression”, Perry’s Chem. Eng. Handbook, 8th Edition, to be 

published (2008) 

2. Tiller, F. M., W. P. Li and W. Chen, "Solid-liquid Separation," Chapter 14, Chemical 

Engineering Handbook, Chapman & Hall, to be published (2007). 

3. Chen, W. “Analyses of Compressible Suspensions for an Effective Filtration and 

Deliquoring”, Drying Technology J. 24, 1251-1256 (2006). 

4. Kraipech, W, W. Chen and T. Dyakowski,”The Performance of the Empirical Models on 

Industrial Hydrocyclone Design”, International J. of Mineral Processing, 80, 100-115 (2006). 

5. Chen, W., F. Parma and W. Schabel,”Testing Methods for Belt Filter Press Biosludge 

Dewatering”, Filtration, Vol. 5, No. 1 (2005). 

6. Chen, W.,"Selecting Membrane Filtration System", Cover Story, Chemical Eng. Progress, 

Dec. (2004). 

7. Chen, W.,"The Use of Hydrocyclone Models in Practical Design", 9th World Filtration 

Congress, April 19-22, New Orleans, LA (2004). 

 A-6
8. Chen, W., F. J. Parma, A. Patkar, A. Elkin and S. Sen, "How to Select a Membrane 

Filtration System," AFS Annual Conference, June 18-20, Reno, NV (2003). 

9. Kraipech, W. and W. Chen, "Modeling the Fish-Hook Effect of the Flow within 

Hydrocyclones," AFS Annual Conference, May 1-4, Tampa, Florida (2001). 

10. Chen, W., N. Zydek, F. Parma, "Evaluation of Hydrocyclone Models for Practical 

Applications," Chem. Eng. J., Vol 80, 295-303 (2000). 

11. Chen, W. and A. Probst, "Scale-up of Gravity Clarifiers and Thickeners from a Dynamic 

Simulator," AFS Annual Conference, March 14-17, Myrtle Beach, South Carolina (2000). 

12. Keller, K. and W. Chen, "Solid-liquid Separation: Addressing the Crisis," Chem. Processing, 

Vol. 63, No.1, Jan. (2000). 

13. Tiller, F. M. and W. Chen, "How to Use Filter Aids," Chem. Processing, June (1999). 

14. Chen, W., "Filter Media Selection from an End User’s Point of View," Keynote Speech, 

Filtration 98, International Conference of INDA, Dec. 3, Atlantic City, New Jersey (1998). 

15. Chen, W., "Solid-liquid Separation via Filtration," Chem. Eng., Cover Story, Feb. (1997). 

16. Chen, W., "Sedimentation," Chapter 14, Handbook of Powder Science and Technology, 2nd 

Ed., Chapman & Hall (1997). 

17. Chen, W., "The Measurement of Cake Compressibility and Its Application in Chemical 

Industry," the 7th World Filtration Congress, May 20-23, Budapest, Hungary (1996). 

 A-7
Calvin H. Delegard 

Professional Activities

Twenty-five years (1970; 1972-1976; 1979-1987; 1992-present) in applied/process 

chemistry and nuclear materials safeguards at the Hanford Site. 

• Plutonium process and waste chemistry (speciation, separation, purification, 

processing) 

• PUREX and Plutonium Finishing Plant process chemistry 

• Environmental chemistry of radionuclides (Co, Sr, Tc, Cs, U, Np, Pu, Am) 

• Technical liaison with the Institute of Physical Chemistry, Russian Academy of 

Sciences, on chemistry of the actinides and technetium in alkaline media, on K 

Basin sludge treatment/disposal, chromium phase dissolution, and uranium metal 

corrosion 

• Hanford tank waste chemistry (bulk and radionuclide components) 

• Tank farm evaporator chemistry (concentration and crystallization) 

• Organic decomposition reactions in tank waste (e.g., gas generation in 

101-SY) 

• Tank waste treatment chemistry (ozonation, electrolysis, 

calcination/dissolution, leaching/sludge washing) 

• Material corrosion; Zr and other metals in nitric acid; copper and mild steel in 

basalt groundwater 

• Chemical characterization, processing, and U metal corrosion of K Fuel Storage 

Basins sludge 

• Domestic (234-5) and design of int’l. (Hanford, RFES, SRS) nuclear materials 

safeguards 

• Development and qualification of plant calorimeters for international safeguards 

• Development of prompt gamma analysis for Pu materials characterization 

• Plutonium materials stabilization for storage. 

Eight years (1976-79; 1987-92), nuclear materials safeguards at the International Atomic 

Energy Agency, Vienna, Austria. 

• International nuclear material safeguards inspection execution 

• Subsidiary arrangements, design information, and facility attachments 

preparation 

• Destructive and non-destructive nuclear materials verification methods 

development. 

Technical Publications

 Contractor and National Laboratory Documents 

• Atlantic Richfield Hanford Company • Los Alamos National Laboratory 

• Rockwell Hanford Operations • Brookhaven National Laboratory 

• Westinghouse Hanford Company • Pacific Northwest National Laboratory 

• B&W Hanford, Duke ESH, B&W Protec, Numatec Hanford 

Symposium Proceedings 

• Institute of Nuclear Science, • Institute of Nuclear Materials 

Boris Kidrič, Vinča, Yugoslavia Management 

 A-8
• American Nuclear Society • American Chemical Society •

 American Society Metallurgical • International Atomic Energy Agency 

 Engineers • Minerals, Metals & Materials Society 

• Waste Management • Russian Conference on 

• Materials Research Society Radiochemistry 

• NATO Advanced Research Workshop • European Safeguards Research 

and Development Association 

Scientific Journals 

• Radiochimica Acta • Journal of Alloys and Compounds 

• Radiochemistry • Journal of Nuclear Material 

• Nuclear and Chemical Waste Management 

Book Chapter – in Advances in Plutonium Chemistry 1967-2000

 

Selected Recent Reports and Articles 

- Budantseva, N., A. Bessonov, I. Tananaev, A. Fedosseev, and C. H. Delegard, 1998, 

“Behavior of Plutonium(V) in Alkaline Media,” Journal of Alloys and Compounds 271-

273:813-816. 

- Budantseva, N. A., I. G. Tananaev, A. M. Fedosseev, and C. Delegard, 1998, “Capture of 

Pu(V), Np(V) and Pu(VI) from Alkaline Solutions by Hydroxides of Pu(IV), Th(IV) and 

La(III),” Journal of Alloys and Compounds 271-273:231-235. 

- Peretroukhine, V. F., and C. H. Delegard, 1998, “Some Comparisons of Plutonium-Bearing 

Radwaste Management in the USA and Russia,” The Environmental Challenges of Nuclear 

Disarmament, NATO Advanced Research Workshop, Cracow, Poland. 

- Barney, G. S. and C. H. Delegard, 1999, “Chemical Species of Plutonium in Hanford Site 

Radioactive Tank Wastes,” in Actinide Speciation in High Ionic Strength Media, D. T. Reed, 

S. B. Clark, and L. Rao (editors), Kluwer Academic/Plenum Publishers, New York. 

- Bredt, P. R., C. D. Carlson, C. H. Delegard, K. H. Pool, A. J. Schmidt, D. B. Bechtold, J. 

Bourges, D. A. Dodd, T. A. Flament, N. N. Krot, and A. B. Yusov, 2000, “Studies of 

Chemical Processing of K Basin Sludge,” Waste Management 2000, Tucson, AZ. 

- Delegard, C. H., S. A. Bryan, A. J. Schmidt, P. R. Bredt, C. M. King, R. L. Sell, L. L. Burger, 

and K. L. Silvers, 2000, “Gas Generation from K East Basin Sludges – Series I Testing,” 

PNNL-13320, Pacific Northwest National Laboratory, Richland, WA. 

(http://www.pnl.gov/main/publications/external/technical_reports/PNNL-13320.pdf). 

- Bryan, S. A., C. H. Delegard, A. J. Schmidt, R. L. Sell, K. L. Silvers, S. R. Gano, and B. M. 

Thornton, 2001, “Gas Generation from K East Basin Sludges – Series II Testing,” PNNL13446, Pacific Northwest National Laboratory, Richland, WA. 

(http://www.pnl.gov/main/publications/external/technical_reports/PNNL-13446Rev1.pdf). 

- Delegard, C., 2001, “K Fuel Basin Sludge – Characterization, Reactions, Retrieval, and 

Storage,” presentation to Washington Group International, Warrington, UK, October 9, 

2001, PNWD-SA-5513, Pacific Northwest Division, Battelle, Richland, WA. 

- Fedoseev, A. M., V. P. Shilov, N. A. Budantseva, A. B. Yusov, I. A. Charushnikova, and C. 

H. Delegard, 2002, “Selective Recovery of Chromium from Precipitates Containing d 

Elements and Actinides: I-III. Effect of O2, H2O2, S2O8

2-,” Radiochemistry 44(4):347-365 

(three articles). 

 A-9
- Clark, S. B. and C. Delegard, 2002, “Plutonium in Concentrated Solutions,” Chapter 7 in 

Advances in Plutonium Chemistry 1967-2000, D. C. Hoffmann, Editor, American Nuclear 

Society, La Grange Park, IL (http://www.ans.org/store/vi-300029). 

- Delegard C. H., S. I. Sinkov, B. K. McNamara, S. A. Jones, G. S. Barney, A. J. Schmidt, and 

R. L. Sell, 2002, “Critical Mass Laboratory Solutions – Precipitation, Calcination, and 

Moisture Uptake Investigations,” PNNL-13934, Pacific Northwest National Laboratory, 

Richland, WA (http://www.pnl.gov/main/publications/external/technical_reports/PNNL13934.pdf). 

- Boak, J., E. A. Conrad, C. H. Delegard, A. M. Murray, G. D. Roberson, and T. J. Venetz, 

2003, “Recommendations on Stabilization of Plutonium Material Shipped to Hanford from 

Rocky Flats,” LA-UR-03-3789, Los Alamos National Laboratory, Los Alamos, NM (http://libwww.lanl.gov/cgi-bin/getfile?00937076.pdf). 

- Schmidt, A. J., C. H. Delegard, S. A. Bryan, M. R. Elmore, R. L. Sell, K. L. Silvers, S. R. 

Gano, and B. M. Thornton, 2003, “Gas Generation from K East Basin Sludges and 

Irradiated Metallic Uranium Fuel Particles – Series III Testing,” PNNL-14346, Pacific 

Northwest National Laboratory, Richland, WA 

(http://www.pnl.gov/main/publications/external/technical_reports/PNNL-14346.pdf). 

- Fazzari D. M., S. A. Jones, and C. H. Delegard, 2003, “Application of Prompt Gamma-Ray 

Analysis to Identify Electrorefining Salt-Bearing Plutonium Oxide at the Plutonium Finishing 

Plant,” PNNL-14409, Pacific Northwest National Laboratory, Richland, WA 

(http://www.pnl.gov/main/publications/external/technical_reports/PNNL-14409.pdf). 

- Delegard C. H., A. J. Schmidt, R. L. Sell, S. I. Sinkov, S. A. Bryan, S. R. Gano, and B. M. 

Thornton, 2004, “Final Report - Gas Generation Testing of Uranium Metal in Simulated K 

Basin Sludge and in Grouted Sludge Waste Forms,” PNNL-14811, Pacific Northwest 

National Laboratory, Richland, WA 

(http://www.pnl.gov/main/publications/external/technical_reports/PNNL-14811.pdf) 

- Yusov, A. B., A. M. Fedosseev, and C. H. Delegard, 2004, “Hydrolysis of Np(IV) and Pu(IV) 

and Their Complexation by Aqueous Si(OH)4,” Radiochimica Acta 92(12):869-881. 

- Shilov, V. P., A. M. Fedoseev, A. B. Yusov, and C. H. Delegard, 2004, “Behavior of Np(VII, 

VI, V) in Silicate Solutions,” Radiochemistry 46(6):574-577. 

Education

BS, Chemistry, with distinction, Phi Beta Kappa, Washington State University, 1970; 

Graduate course work at the University of Colorado (1970-72) and Washington State 

University (1973-present). 

calvin.delegard@pnl.gov, (509) 376-0548 

Pacific Northwest National Laboratory 

PO Box 999, MS P7-25 

Richland, WA 99352 USA 

 A-10
Robert Litman 

28 Hutchinson Drive 

Hampton, NH 03842 

(603) 926-4863 

drbob20@comcast.net 

EDUCATION 

 1. Brooklyn College - B.S., Chemistry (1971) 

 2. City University of New York - PhD, Analytical Chemistry (1975) 

PROFESSIONAL EXPERIENCE

 2002 to now - Independent Consultant 

 1998 to 2002 - Principal Chemist (Engineering), Seabrook Station 

 1996 to 1998 - Chemistry Manager, Seabrook Station 

 1985 to 1996 - Chemistry Supervisor, Seabrook Station 

 1981 to 1985 - Senior Chemistry Training Instructor, Seabrook Station 

 1975 to 1981 - Assistant Professor of Chemistry, University of Lowell 

 1971 to 1975 - Graduate Fellow 'A' City University of New York at 

 Brooklyn College 

 additionally... 

2002 Presented Technology Transfer Award by EPRI for leadership in 

 development of the Primary Water Chemistry Guidelines 

1997 Peer Evaluator at Diablo Canyon Nuclear Power Plant for INPO 

1996 to present- 1. Contract Lecturer and Radiochemistry Consultant for RSCS, 

Inc. as a Senior Chemist 

 2. Independent Contractor working on the Multi-Agency 

 Radiochemistry Analytical Protocols Manual (MARLAP) 

For the EPA (via Sanford Cohen & Assoc.1998-9, The Henry 

Jackson Foundation 1999 and Environmental Management 

Support, Inc. 2001- present). 

1992 to 1996 - 1. Contract Lecturer for Technical Management Services, Inc. 

Teaching "Practical Radiochemistry" 

2. Independent Contractor for USEPA NAREL Montgomery, AL. 

Reviewed technical procedures for accuracy and modified them 

for technical enhancements. Performed independent review of 

laboratory techniques. 

1990 to 1992 - Participated as a Training Instructor in the Water Pollution 

 Control Facility Operator Training Courses given by the 

 State of NH 

 1992 - Received Excellence award from Seabrook Station for 

 maintaining and improving chemistry programs. 

1993 - Coordinated and developed the 1993 Summer program for the 

New Hampshire State Science Teachers Association. 

 A-11
1994 - Appointed as a Peer Evaluator for Seabrook Station Training 

programs by INPO. 

PROFESSIONAL AFFILIATIONS

 1. American Chemical Society (since 1971) 

 2. Sigma Xi, The Scientific Research Society of NA (since 1971) 

 3. ASTM Committee D19-Water (since 1996) 

4. Standard Methods Special Committee on Development of 90Sr Analysis in Water 

RECREATIONAL INTERESTS

 1. USYSA Soccer Coach, 'D' License 

 2. USSF Soccer Referee, Level 8 (1999 NH State Referee of the Year) 

 3. NH State High School Soccer Official 

 4. ASA Softball Umpire 

5. NH State High School Softball Umpire 

 6. NH Seacoast Youth Soccer League- Vice President (2001 to present) 

 7. USYS Referee Training Instructor (2003 - present) 

AREAS OF TECHNICAL EXPERTISE WHILE AT SEABROOK STATION

 I was Seabrook Station’s Principal Chemist during my last five years at the plant. My job 

responsibilities included corrosion control methods, analysis of corrosion mechanisms, 

environmental innovations for biocide effectiveness, long term trending of plant chemistry 

performance parameters, monitoring of trends in plant radiochemical parameters, and 

radiological effluent surveillance oversight. 

 During my tenure at Seabrook the chemistry programs received the highest ratings from 

both the Nuclear Regulatory Commission (NRC) and the Institute of Nuclear Power Operations 

(INPO). We also received the highest ratings from the NHDES for our NPDES program 

compliance. Part of the technical responsibility that I was responsible for was the NPDES 

Permit Renewal Process, evaluation of non-routine discharges and program implementation for 

new biocides and anti-scalants. 

One of the programs I initiated at Seabrook was component inspection. This program 

helped to assess corrosion mechanisms, biological fouling, and effectiveness of general 

corrosion control. The inspections provided a chronology so that from one maintenance period 

to the next an accurate assessment cold be made of the components health. The plant 

engineering group relies on these inspections to help maintain system efficiencies. 

Another important program was the integration of the station’s primary to secondary leak 

response. I worked with computer engineering, operations, Instrument and Control, and 

chemistry personnel to provide control room operators with a continuous monitor, which provide 

a gallon per day read out, as well as a rate of change display. I also provided the training on the 

new system to these groups. 

I participated in the site Environmental Review Board (ERB) and was a team member for 

the successful ISO 14001 Certification Program in 2001. I served as the Chairperson of the 

Laboratory Quality Control and Audit Committee (LQCAC), which each year evaluates the 

laboratory that the station uses for 10CFR50/61 and Bioassay programs. This committee was 

 A-12
comprised of laboratory clients interested in ensuring that the technical programs met regulatory 

requirements. 

I represented the Station on five technical EPRI committees and have made significant 

contributions in those areas since 1998: 

1. Primary Water Chemistry Guidelines 

2. Secondary Water Chemistry Guidelines 

3. Primary to Secondary Leak Guidelines 

4. Stator Coolant System Guidelines 

5. Robust Fuels Working Group 1. 

AREAS OF RESEARCH/INTEREST

 During the six years I was at the University of Lowell, I successfully supervised nine 

undergraduate senior projects eight masters theses and one PhD thesis. These projects were 

centered on environmental analysis and basic analytical/radiochemical techniques. During that 

time I was responsible for initiating a multidisciplinary environmental studies program at the 

master's level. This included staff members from chemistry, biology, civil engineering, chemical 

engineering and earth sciences. 

 I have been an auditor for several nuclear power plant chemistry programs and contract 

laboratory programs for their radiochemical processes and procedures over the past 15 years. 

In that time, I have aided in the development and improvement of these procedures. 

 The 40-hour instructional course in radiochemistry that I teach has been presented 23 

times in the past fifteen years. Attendees at these courses included personnel from state and 

government as well as contract radiochemistry laboratories and nuclear power facilities. This 

has helped me to maintain a current status of the radiochemical practices in use, and where the 

radiochemistry community needs to progress in this area. 

 A-13
Digby D. Macdonald 

Distinguished Professor of Materials Science and Engineering 

Director, Center for Electrochemical Science and Technology 

The Pennsylvania State University 

201 Steidle Bldg. 

University Park, PA 16802 

(814) 863-7772, (814) 863-4718 (fax), ddm2@psu.edu 

(a) EDUCATIONAL BACKGROUND 

B.Sc. (1965) and M.Sc. (1966) in Chemistry, University of Auckland (New Zealand); 

Ph.D. in Chemistry (1969), University of Calgary (Canada).

PROFESSIONAL EXPERIENCE (past 35 years) 

Distinguished Professor of Materials Science and Engineering, 6/2003 – present.

Chair, Metals Program, Penn. State Univ., 6/2001 – 6/2003 

Director, Center for Electrochemical Sci. & Tech., Penn. State Univ., 7/99 – present. 

Vice President, Physical Sciences Division, SRI International, Menlo Park, CA, 1/98 – 7/99 

Director, Center for Advanced Materials, Penn. State Univ., 7/91-3/2000 

Professor, Materials Science and Engineering, Penn. State Univ., 7/91 – 6/03. 

Deputy Director, Physical Sciences Division, SRI International, Menlo Park, CA, 4/87 - 7/91 

Laboratory Director, Mat. Research Lab., SRI International, Menlo Park, CA, 4/87 – 7/91 

Laboratory Director, Chemistry Laboratory, SRI International, Menlo Park, CA, 3/84 – 4/87 

Director and Professor, Fontana Corrosion Center, Ohio State University, 3/79 – 3/84 

Sr. Metallurgist, SRI International, Menlo Park, CA, 3/77 – 3/79. 

Sr. Research Associate, University of Calgary, Canada, 3/75 – 3/77. 

Lecturer in Chemistry, Victoria University of Wellington, New Zealand, 4/72 – 3/75. 

Assist. Research Officer, Whiteshell Nuclear Research Establishment, Atomic Energy of 

Canada Ltd., Pinawa, Manitoba, Canada, 9/69 – 4/72. 

CONSULTING ACTIVITIES (Partial list for the last five years)) 

Integrated Design Technologies 

OLI Systems 

Electric Power Research Institute 

SRI International 

Stone & Webster Engineering Co. 

Science Applications International Corp. 

Framatome 

Metallic Power Inc. 

Los Alamos National Laboratory 

Section 1.02 PATENTS

1. D. D. Macdonald and A. C. Scott, “Pressure Balanced External Reference Electrode 

Assembly and Method”, US Patent 4,273,637 (1981). 

2. D. D. Macdonald, “Apparatus for Measuring the pH of a Liquid”, US Patent 4,406,766 

(1983). 

 A-14
3. S. C. Narang and D. D. Macdonald, Novel Solid Polymer Electrolytes”, US Patent 5,061,581 

(1991). 

4. S. Hettiarachchi, S. C. Narang, and D. D. Macdonald, “Synergistic Corrosion Inhibitors 

Based on Substituted Pyridinium Compounds”, US Patent 5,132,093 (1992). 

5. S. Hettiarachchi, S. C. Narang, and D. D. Macdonald, “Reference Electrode Assembly and 

Process for Constructing”, US Patent, 5,238,553 (1993). 

6. D. D. Macdonald, et al, “Conducting Polymer for Lithium/Aqueous Syst.”, US Prov. Pat. 

60/119,360 (1998). 

7. D. D. Macdonald, et al, “Polyphosphazenes as Proton Conducting Membranes”, US Pat. 

Appl. 09/590,985 (1999). 

8. D. D. Macdonald, et al, “Impedance/Artificial Neural Network Method...”, US Prov. Pat. 

60/241,871 (1999) 

9. D. D. Macdonald, “Electrochemical Conditioning of Wine”, US Prov. Pat. 60/295,080 (2001). 

RESEARCH INTERESTS

• Passivity and passivity breakdown on metals 

• Deterministic prediction of corrosion damage 

• Advanced batteries and fuel cells 

• Chemistry and electrochemistry of supercritical aqueous systems 

• Nuclear power generation 

• Electrocatalysis 

(a) PUBLICATIONS (from approximately 160 published over the past five years and from a 

total of 650 published since 1970.). 

1. Engelhardt, G.R., M. Urquidi-Macdonald, and D. D. Macdonald. “A Simplified Method for 

Estimating Corrosion Cavity Growth Rates”. Corros. Sci., 39(3), 419-441 (1997). 

2. Gao, L. and D. D. Macdonald. “Characterization of Irreversible Processes at the 

Li/Poly[bis(2,3-di-(2-methoxyethoxy)propoxy)phosphazene] Interface on Charge Cycling”. J. 

Electrochem. Soc., 144(4), 1174-1179 (1997). 

3. Sikora, E. and D. D. Macdonald. “Defining the Passive State”. Solid State Ionics, 94, 141-

150 (1997). 

4. Engelhardt, G. R. and D. D. Macdonald, “Deterministic Prediction of Pit Depth Distribution”, 

Corrosion, 54, 469-479 (1998). 

5. Macdonald, D. D., E. Sikora, and J. Sikora, “The Kinetics of Growth of the Passive Film on 

Tungsten in Acidic Phosphate Solutions”, Electrochim. Acta, 43, 2851-61 (1998). 

6. Pensado-Rodriguez, O., J. Flores, M. Urquidi-Macdonald, and D. D. Macdonald, “The 

Electrochemistry of Lithium in Alkaline Aqueous Electrolytes. Part II: Point Defect Model”. J. 

Electrochem. Soc., 146, 1326-1335 (1999). 

7. Engelhardt, G. R., D. D. Macdonald, and P. Millett, “Transport Processes in Steam 

Generator Crevices. I. General Corrosion Model”, Corros. Sci., 41, 2165-2190 (1999). 

8. Macdonald, D. D., “Passivity: The Key to Our Metals-Based Civilization”, Pure Appl. Chem., 

71, 951-986 (1999). 

9. Quiroga Becerra, H., D. D. Macdonald, and C. Retamosa, “The Corrosion of Carbon Steel 

in Oil-in-Water Emulsions Under Controlled Hydrodynamic Conditions”, Corros. Sci., 42, 

561-575 (2000). 

10. Sikora, J., E. Sikora, and D. D. Macdonald, “Electronic Structure of the Passive Film on 

Tungsten”, Electrochim Acta, 45(12), 1875-1883 (2000). 

11. Sikora, E. and D. D. Macdonald, “The Passivity of Iron in the Presence of EDTA. Part I. 

General Electrochemical Behavior”. J. Electrochem. Soc., 147(11), 4087-4092 (2000). 

 A-15
12. Macdonald, D. D., M. Al-Rafaie and G. R. Engelhardt, “New Rate Laws for the Growth and 

Reduction of Passive Films”, J. Electrochem. Soc., 148(9), B343 - B347 (2001). 

13. Macdonald, D. D., “Probing the Chemical And Electrochemical Properties of SCWO 

Systems”, Electrochim. Acta, 47, 775-790 (2001). 

14. Zhou, X.Y., S. N. Lvov, X. J. Wei, L. G. Benning, and D. D. Macdonald, “Quantitative 

Evaluation of General Corrosion of Type 304 Stainless Steel in Subcritical and Supercritical 

Aqueous Solutions via Electrochemical Noise Analysis”. Corros. Sci., 44(2), 841-860 (2002). 

15. Engelhardt, G. and D. D. Macdonald, “unification of the Deterministic and Statistical 

Approaches for Predicting Localized Corrosion Damage. I. Theoretical Foundation”, Corros. 

Sci., 46, 2755 (2004). 

(b) PROFESSIONAL ASSOCIATIONS AND HONORS 

• Selector of the Kuwait Prize for Applied Sciences, 1985. 

• Research Award, College of Engineering, Ohio State University, 1983. 

• The 1991 Carl Wagner Memorial Award from The Electrochemical Society. 

• The 1992 Willis Rodney Whitney Award from The National Association of Corrosion 

Engineers. 

• Chair, Gordon Research Conference on Corrosion, New Hampshire, 1992. 

• W.B. Lewis Memorial Lecture by Atomic Energy of Canada, Ltd., 1993, “in recognition 

of [his] contributions to the development of nuclear power in the service of mankind”. 

• Elected Fellow, NACE-International, 1994. 

• Member, USAF Scientific Advisory Board, Protocol Rank: DE-4 (Lieutenant General 

equivalent), 1993-1997 

• Elected Fellow, The Electrochemical Society, 1995. 

• Elected Fellow, Royal Society of Canada, 1996. (“National Academy” of Canada). 

• Wilson Research Award, College of Earth and Minerals Sciences, Pennsylvania State 

University, 1996. 

• Elected Fellow, Royal Society of New Zealand, 1997. (“National Academy” of New 

Zealand). 

• H. H. Uhlig Award, The Electrochemical Society, 2001. 

• U. R. Evans Award, The British Corrosion Institute, 2003. 

• Appointed Adjunct Professor, Massey University, New Zealand, 2003. 

• Appointed Adjunct Professor, University of Nevada at Reno, 2003. 

• Elected Fellow, World Innovation Foundation, 2004. 

 A-16
 

APPENDIX B 

Principal Physical Attributes of the LOCA Accident Sequence 

Presented at PIRT Panelist Meeting 

San Antonio, Texas March 27, 2006 
 

 
 

 
 

 
 

 
 

 
 

 
 

 
 

 
 

 
 

 
 

 
 

 
 

 
 

 
 

 
 

 
 

 
 

 
 

 
 

 
 

 
 

 
 

 
APPENDIX C 

PIRT Issue Summary
C-2

Table C-1: Debris Generation (0 to 30 s) 

Issue 

Number Phenomena Description Implications 

T1-1 Crud release 

Fe, Ni corrosion oxides (. 125 

Fm layer) from the RCS 

piping are released due to 

hydraulic shock of the failure 

event 

The crud release creates a 

radiolytic environment on materials 

caught on the sump screens which 

could affect subsequent reactions. 

Also, the oxides add particulate 

mass to containment pool, which 

may enhance coagulation. 

T1-2 

RCS coolant 

conditions at 

break 

The RCS coolant chemistry 

varies over the fuel cycle. B 

concentrations . 2000 -4000 

ppm (beginning) to 50 ppm 

(end of fuel cycle) B/Li ratio .

100. The 2-phase jet is at 

temperatures of . 315C to 

120C upon cooling 

Initial reactor water chemistry 

spewing out of the break and 

forming the containment pool will 

have variable B concentration. 

The Li/B ratio is maintained 

approximately constant. 

T1-3 pH variability 

pH @25C at beginning of fuel 

cycle is acidic (4) while closer 

to neutral (7) at end of cycle. 

Similar implications to issue 2; 

variable reactor and initial 

containment pool chemical 

environment. 

T1-4 

Localized B 

concentration 

in jet 

Droplet evaporation within the 

high temperature jet 

emanating from the pipe 

break forms at highly 

concentrated B aerosol 

solution. As boric acid 

concentrates at high 

temperatures (250C - 300C), 

a polymerization appears to 

occur that releases protons 

and causes the system to 

become very acidic. 

1. Corrosion of impacting 

surfaces: enhanced erosion & 

corrosion vs. formation of a 

protective lacquer to limit 

erosion. 

2. May limit B concentration in 

containment pool chemistry 

T1-5 

RCS fluid 

creates 

“oxidizing 

environment” 

Coolant is released as a 

super heated spray once 

break occurs. Hydrogen (25 – 

35 cc/kg of H2 injected as gas) 

transfers to the gas phase. 

1. H2 evaporation creates a more 

oxidizing environment in the 

water phase by raising the 

redox potential. 

2. The partial pressure of H2 is 

lowered because of the large 

volume of the gas phase 

(containment volume) 

compared with the water 

volume being released. This 

also increases the redox 

potential. 
C-3

Issue 

Number Phenomena Description Implications 

T1-6 Jet 

impingement 

Water jet & fine debris within 

jet may impact surfaces and 

chip coatings 

Initiates metallic pitting, corrosion 

and ablation of other materials 

(concrete, insulation) 

T1-7 

Break 

proximity to 

organic 

sources 

RCP oil storage tank is made 

with . 1⁄2” carbon steel with 

epoxy coating (250 gallon per 

pump, but tank may just 

contain leakage). 

Tank failure timing: earlier in postLOCA (jet impingement) vs. later in 

post-LOCA (corrosion) 

Organic sources to containment 

pool would alter chemistry (i.e., 

complexation, etc.) 

T1-8 

Break 

proximity to 

secondary 

systems 

Break near cooling systems 

could result in failure of lines 

containing solvents (i.e., 

Freon) into containment 

environment 

1. Radiolytic decomposition could 

create chlorides and fluorides 

which may impact corrosion 

and containment pool 

chemistry. 

2. Possible effects on pump 

performance 

T1-9 

Debris mix 

particle/fiber 

ratio 

Breaks in different locations 

will create different debris 

characteristics: total mass, 

mixture constituents, 

compositions 

1. Could alter the containment pool 

chemistry. 

2. Could affect debris bed 

formation on the sump screen 

and increase variability of 

chemical product capture 

efficiency. 

T1-10 

Hydrogen 

peroxide 

effects 

Hydrogen peroxide will 

behave much the same as 

H2O and most of it will remain 

in the liquid phase. Additional 

hydrogen peroxide 

evaporates into containment 

vapor space and may cause 

additional corrosion. It 

condenses on cooler surfaces 

and can accelerate corrosion 

there 

1. Could affect how much H2O2 is 

in the containment pool: 

Evaporation & condensation 

could sequester form pool 

droplets could transport back 

to pool. 

2. H2O2 alters containment pool 

chemistry and potentially 

causes changes in oxidation 

states or chemical forms in 

sump water.. 

T1-11 Nuclei 

Formation 

Rapid subcooling and 

evaporation of water from 

effluent of broken pipe 

droplets might lead to 

precipitation of LiOH and 

other species. Concentrations 

increase and temperature 

decreases rapidly 

1. Initial precipitate may be 

formed from species existing 

with in the RCS coolant. 

2. Nuclei could form which could 

enhance precipitation of other 

species within the containment 

pool at a later time. 
Table C-2: ECCS Injection (30 seconds to trecirc)a,b,c

Issue 

Number Phenomena Description Implications 

T2-1 

Hydrogen sources within containment 

H2 concentrations in vapor and containment 

pool include the RCS inventory, Schikorr reaction, corrosion of metallic materials 

Containment pool redox potential idissolved hydrogen which is estabreactions. RCS evaporation may lwith liquid, decreasing redox poten

T2-2 ECCS injection of Boron After pipe break, B (. 2800 ppm) is injected into RCS to cool reactor Provides large B source which ma

reaction products in containment pthe B source will serve as a pH bu

T2-3 Containment spray corrosion Containment sprays for buffering creates wetting & surface films on material surfaces with water containing B, LiOH, H2

Containment spray (up to 4 hours) corrosion formation on unsubmergwhich could contribute to containmconcentrations. Spray pH: NaOH = 8.5 – 10.5 TSP = 4.5 - 5 STB = 4.5 – 5 

T2-4 NaOH pH control NaOH injected through containment sprays. Alkaline containment pool environm

10.5) 

T2-5 STB pH control Released with ice in containment during a LOCA Alkaline containment pool environm

high 9 initially and then decreases – 9) 

T2-6 TSP pH control Contained in basket on containment floor that dissolve Slightly alkaline containment pool 

Initially pH is high (pH = 11) until cwithin about 4 hours (pH = 7 – 8) 

T2-7 Containment spray transport Sprays wash latent debris, corrosion products, insulation materials, & coating debris into containment pool Affect on containment debris sourc

compositions) and contributions to pool environment. 

T2-8 

Containment spray CO2

scavenging 

Containment sprays cause CO2 absorption 

within containment pool and carbonate formation. 

Affect on containment pool concen

T2-9 

Debris dissolution begins 

Debris dissolution begins. Initial expected products include Cal-Sil, cement dust, organic fiberglass binders, epoxy & alkyd coatings, uncoated concrete 

Indicate potential important contribchemical containment pool environtime frame. Dissolution of other prover longer time frames. 
C-5

Issue 

Number Phenomena Description Implications 

T2-10 Carbonate concentration Carbonates in solution are provided by atmospheric CO2, and concrete dust at this point 1. Create nucleation sites for spec

2. scavenge dissolved Ca to imped

compounds to form calcium car

T2-11 Containment pool mixing High velocity, turbulent water flow exists underneath the pipe break location, remainder of the pool relatively quiescent Mixing of aqueous/gas phases at t

enhanced; could aid CO2 absorptio

dissolution/mixing, liquid/vapor exc

T2-12 

Boric acid corrosion of exposed concrete 

Concentrated boric acid solutions in contact with exposed concrete 

1. Calcium boro-silicates may prec2. pH decrease in containment poo

T2-13 

Fe, Ni radiological reaction 

Initial Fe, Ni oxide breaks off due to TH transient. Reduced Ni, Fe is dissolved in RCS, combines with air, oxidizes and forms hematite, maghemite, and magnetite. . Kilorad/hour and higher rad. dose rates arise throughout containment due to dispersal of Fe and Ni activation products. 

1. Solid particulate is added to con

another debris source 

2. High pH will increase the reactio3. Reaction continues until RCS pi

day or more). 

4. Radiolysis products generated t

LOCA cooling system 

T2-14 Hydrolysis Nickel oxide becomes catalyst for producing 

H2 from radiolysis Affects redox potential 

T2-15 Organic Complexation Organic acids become absorbed on surfaces of solids & inhibit solid species growth; example: aliphatic acid Effectively enhances solubility limi

may precipitate, but remain relative(nano-scale). They do not agglommacroscopic sizes. 

T2-16 Organic Sequestration Organic electron-rich atoms combine with soluble metal compounds. Sequesters metal ions so that solid 

precipitation is delayed or does no

T2-17 

Auxiliary Component Cooling Line Failure 

LOCA causes attached or nearby component cooling line failure which could release a number of chemicals into the containment pool (chromates, molybdates (6000 – 1000 ppm in storage tank), nitrites, tolytriazole (25 ppm in storage tank), benzotriazole, hydrazine 

1. The release of these types of ch

increase the ionic strength of thenvironment which may decrea

2. Chemicals may accelerate corro
C-6

Issue 

Number Phenomena Description Implications 

T2-18 Polymerization 

Precursor to precipitation & agglomeration; metals/oxygen bonds, ripen to form covalent bonds, growth until they qualify as ~nanometer particles size: Si, Al, Fe, Boric acid are candidates 

May be necessary to form large enresult in tangible effects on ECCS 

T2-19 Co- precipitation 

Method of precipitation/separation Examples: Ni/Fe/Cr, Al/Si/B; Co/Fe systems; Precipitation of one species leads to precipitation of other species (below solubility limit); Radioactive elements precipitate (at low concentrations), activation products: ex. Strontium, Ni, Silver, Fe, Co, Zr 

More solids species form which coconcentration of chemical products or downstream. 

T2-20 Radiolytic environment 

Radiolysis reaction creates an oxidizing environment and can change solution’s electric potential; H2, O2, and H2O2 balance 

most important for determining redox potential 

Could affect chemistry in containmaffects species which form (e.g., Hof different components @ differen

T2-21 Inorganic Agglomeration 

Formation of larger clumps of smaller particulates: Depends on PZC; ionic strength (the higher the strength the smaller the distance for agglomeration) 

1. May be necessary to form large 

result in tangible effects on ECC

2. Can occur quickly if conditions a3. Existence of organic species ca

decrease likelihood (See T2-24

T2-22 Galvanic Effects 

Electrical contact between metals results in increased corrosion of less noble metals: example: magnetite precipitation on Aluminum 

1. Increases in the corrosion sour

noble (anodic) metal. 

2. Decreases in corrosion source 

(cathodic) metal. 

T2-23 Deposition & Settling 

Possibility that chemical products formed during this time period either settle within containment pools or are deposited on other surfaces 

Potentially remove substantial quafrom transporting to the containmeindicate expected species that are if possible. 
C-7

Issue 

Number Phenomena Description Implications 

T2-24 Organic Agglomeration 

Formation of larger clumps of smaller inorganic particulates nucleating around organic acids or oil (such as soap coagulates dirt particles) 

Coagulated particles can collect on decreasing flow, or collect in other the loading on the sump screen 

a Massive fuel damage is not considered during this time period because the objective is to prevent this through 

of the ECCS system. Radiological and other contributions to the chemical environment from minor amounts of expected to be insignificant compared to crud release and other phenomena listed in these tables. 

b Sump pool temperatures can be as high as 120C initially. After 30 minutes, between 60 – 90C c Phenomena listed in earlier time periods (i.e., T1) may continue to be active or important during this time. 
C-8

Table C-3: ECCS Recirculation (trecirc to 24 hours)a,b

Issue 

Number Phenomena Description Implications 

T3-1 TSP pH control Contained in basket on containment floor that dissolve Slightly alkaline containment pool 

– 8); all TSP dissolved within 1 to 4 

T3-2 NaOH pH control NaOH injected through containment sprays. Alkaline containment pool environm

10.5); pH buffering completed typ

T3-3 STB pH control Released with ice in containment during a LOCA Alkaline containment pool environm

STB should be introduced within a 

T3-4 NaOH Injection NaOH, B laden spray impinges on material surfaces 

1. Solution may accelerate co

metallic/non-metallic surfaces duconcentration. 

2. Solution may inhibit corros

an initial passive layer imperviou

T3-5 Cable degradation The insulation surrounding electrical cables located throughout containment is affected by radiolysis, releasing chlorides. The chlorides affect radiolysis and 

containment pool environment. 

T3-6 Radiolytic environment Radiolysis reaction changes solution’s redox potential; H2, O2, and H2O2 balance; peroxide formation occurring during this time frame. Could affect chemistry in containm

affects species which form - most determining redox potential (e.g., Hmixture of different components @ 

T3-7 Fiberglass leaching Fiberglass-based insulation products begin leaching constitutents; e.g., Si, Al, Mg, Ca, etc. Dissolution source term for produc

contribute to containment pool che

T3-8 

Secondary system Contamination 

SG tube rupture leads to secondary side chemicals being added to containment pool. 

1. Possible additional source 

which could delay precipitation thor by sequestering metal ions. 

2. Could accelerate material c

T3-9 Flow-induced nucleationc Nucleation sites created from cavitation, deareation, air entrainment, turbulence (attachment opportunity) Increases possibility of precipitatio

formation 
C-9

Issue 

Number Phenomena Description Implications 

T3-10 Turbulent mixingc Turbulence in containment pool (such as directly under the break) either inhibits or promotes precipitate formation and growth 

1. Could inhibit growth due to turb

which don’t allow solid species 

2. Could promote formation and g

more opportunity for particles tovercome diffusion. 

3. Affects the solid species conce

containment pool which could loss & other ECCS performanc

T3-11 

Quiescent settling of precipitatec

Quiescent flow regions within containment pool promote settling 

Little flow allows larger size, more particles/precipitates to form which 

T3-12 Electrostatic scavenging 

Material surfaces electrostatically attract particles and lead to deposition/agglomeration on the surface; thin accumulation limited to 2 to 3 layers of material. It is a function of solution PZC and surface and particle charges. 

1. Provides a mechanism for retain

products either in benign areas surfaces) or in areas that may imperformance (e.g., sump screen

2. Surface layer either inhibits or e

corrosion. 

T3-13 

Chemically induced settling 

Chemical species attach to or coat particulate debris which leads to settling. Examples are Al coating on Nukon fiber shifting the PZC, or formation of a hydrophobic organic coating 

Results in less particulate debris atransporting to and either accumulthrough the sump screen. 

T3-14 Agglomeration & Coagulation 

Formation of larger clumps of smaller particulates: Depends on PZC; ionic strength (the higher the strength the smaller the distance for agglomeration); sensitive to many factors including shape factors, maximum particle size. 

1. May be necessary to form larg

result in tangible effects on EC

2. Can occur quickly if conditions 3. Existence of organic species c

likelihood 

T3-15 Particulate nucleation sites 

Particles within containment create nucleation sites for chemical precipitation: examples include radiation tracks; dirt particles; coating debris; insulation debris; biological debris, etc. 

Environment is created which fostespecies that could lead to ECCS d
C-10

Issue 

Number Phenomena Description Implications 

T3-16 

Additional debris bed chemical reactions 

Concentration of radionuclides (100’s of Curies available) acts as a “resin bed” or chemical reactor. A number of possible reactions occur. 

1. Hydrogen peroxide formation 2. Fe+2

→ Fe+3 increase due to in

potential; 

3. Organic materials decompose 4. possible coating of NUKON to 

glass embrittlement (shorter fib

T3-17 

Sump screen: high localized chemical concentrations 

High localized concentrations of certain species drive the reaction efficiency at the sump screen 

1. Effect could be at the exterior s

materials, the internal interstitiaboth 

2. Possible effect on the chemica

within the sump screen bed. 

T3-18 

Sump screen: fiberglass morphology 

Localized chemistry alters the fiberglass contribution to the chemical environment 

1. Possible coating of fiberglass f

leaching/solubility. 

2. Radiation leads to glass embrit

fibers form which can pack mohead loss) and provide additionleaching/reactions. 

T3-19 ECCS pump: seal abrasion 

Abrasive wearing of pump seals (e.g., magnetite - high volume/concentration of mild abrasive) creates additional materials that contribute to sump pool chemistry. 

1. Additional particles that may co

core clogging 

2. Particles may add additional su3. Particles may affect chemical s

T3-20 

Heat exchanger: solid species formation 

Concentrations/species that are soluble at the containment pool temperature precipitate at lower (

ΔT~15-20C) heat exchanger outlet 

temperature. 

1. Species remain insoluble at hig

temperatures and affect ability core. 

2. Species remain insoluble at hig

pool temperatures and cause aupon recirculation. 

T3-21 

Heat exchanger: deposition & clogging 

Solid species which form in the heat exchanger lead to surface deposition and/or clogging within closs-packed head exchanger tubes (5/8” diam.) 

1. Severe clogging/deposition causthrough heat exchanger core and areactor core. 2. Less severe deposition may deand degrade heat flow from the rea
C-11

Issue 

Number Phenomena Description Implications 

T3-22 Reactor core: fuel deposition 

ΔT increase (+70C from sump pool) and retrograde solubility of some species (e.g., Ca silicate, Ca carbonate, zeolite, sodium calcium aluminate) causes scale, build-up on reactor core 

1. Decreases heat conduction va2. Localized boiling occurs due to 

removal. 

3. Deposits spall off, creating add

source. 

T3-23 

Reactor core: hydrogen increases 

H2 builds up in from cladding oxidation 

1. Affect redox potential and chem2. Increases containment hydrog

may lead to conflagration. 

T3-24 

Reactor core: diminished heat transfer 

Insulation debris and chemical products mixed within water cause a reduction in the effective heat transfer capabilities (Cp) of 

mixture. The precipitation of this material is initiated in RHR heat exchanger. 

Ability to remove heat from the fue

T3-25 

Reactor Core: Blocking of flow passages 

Chemical products, in combination with other debris, blocks primary flow passages for getting cooling water through core 

Heat transfer may be impeded; flobypass the lower plenum debris sc

T3-26 

Reactor Core: Particulate settling 

Particulate settling occurs due to relatively low, upwards flow (for cold leg injection) within reactor 

Compacted deposits forms which transfer and water flow, especially reactor fuel. 

T3-27 Reactor Core: Precipitation 

ΔT increase (+70C from sump pool) and retrograde solubility of some species (e.g., Ca silicate, Ca carbonate, zeolite, sodium calcium aluminate) causes precipitation, additional chemical product formation 

1. Products contribute to debris in 

blocks flow passages, impedes 

2. Additional precipitate is created 

sump screen and leads to hea

T3-28 

Exposed, Uncoated Concrete Dissolution 

Dissolution can result in pH increases (depending on surface area) up to 10.5 below concrete surface relatively quickly. 

1. This could result in pH increas

pool over time. 

2. Leaching of concrete elements 

into containment pool. 

T3-29 Coatings Dissolution Dissolution/leaching of epoxy, alkyd, or zinc- based coatings and primers occurs 

1. Additional source term for produ

containment pool chemistry. 

2. Chlorides affect radiolysis and io

containment pool environment. 
C-12

Issue 

Number Phenomena Description Implications 

T3-30 Boric Acid Corrosion 

Concentrated boric acid pooled on unsubmerged portions of large ferritic steel components (e.g., piping RPV, pressurizer, steam generator) continues to cause corrosion of these materials. 

1. Contribute additional Fe ions w

transported to containment poo

2. Could affect coprecipitation an

concentrations 

3. May lead to long-term structura

severe. 

T3-31 CO2/Carbonate Radiolysis 

Radiolysis of CO2 and carbonates could lead 

to the formation of organic acid ligands (e.g., acetate, butyrate, oxalate) This is observed during the leaching of spent fuel by groundwaters containing bicarbonate ions 

1. Phenomena would complex m

solution, thereby enhancing disdiminishing the precipitation of these complexed species. 

2. Could occur within containmen

vessel, or within the sump scre

a Sump pool temperatures are expected to range between 50 – 90C during this time period. b Phenomena listed in earlier time periods (i.e., T1, T2) may continue to be active or important during this time. cBulk flow velocities = 0.005 ft/s to 0.1 ft/s (0.15 – 3 cm/s) 
C-13

Table C-4: ECCS Recirculation (24 hours to 15 days a,b) 

Issue 

Number Phenomena Description Implications 

T4-1 

Source terms: Unsubmerged materials 

Corrosion of various materials (Al, Fe, concrete, Cu, Zn) due to condensation and transport into containment pool; condensation expected due to non-uniform containment temperature 

1. Contributes species to contain2. Condensate chemistry & enviro

corrosion/leaching rates. 

T4-2 

Submerged source terms: Pb shielding 

Any acetates present in containment pool will dissolve Pb, which could lead to formation of lead carbonate particulate. Lead blanketing to shield hot spots and covered with plastic coating, but coating likely destroyed. Several hundred pounds of lead in flat sheets. Some plants still use lead wool. No Pb in ICET program. 

Would provide additional particulatcontainment pool 

T4-3 

Submerged source terms: Cu 

Concern stems not from Cu compounds, but the various effects that Cu may have on other corrosion processes. Cu concentrations evaluated in ICET program; Cu comes from containment air coolers, motor windings and grounding straps. 

1. By forming a galvanic couple, c

of other metals (e.g., Al). 

2. Cu ion deposition can occur wh

corrosion. 

3. Within an oxygenated environm

accelerate corrosion 

T4-4 

Submerged source terms: Fe 

Boron inhibits pitting corrosion on surface of steel structures. Fe concentrations evaluated in ICET program. 

1. Less Fe ions in containment po2. less corrosion and structural w

structures 

T4-5 

Submerged source terms: Al, decreased concentrations 

Less dissolved Al, than in ICET #1, affects the type and quantity of chemical byproducts that form at high pH. 

1. Less corrosion inhibition of ins

greater Si levels. 

2. Less Al corrosion products allo

form within pool 

T4-6 

Submerged source terms: Al*, increased concentrations 

Specific mix of other metals in containment pool leads to more Al corrosion (catalytic effect) at either lower or higher pH 

Increases Al solid species which m
C-14

Issue 

Number Phenomena Description Implications 

T4-7 

Submerged source terms: Fiberglass dissolution 

Dissolution at high pH contributes Silicates, Cu, Na, Al, Mg, B, misc. organics to containment pool. Fiberglass concentrations in ICET test plan 

1. Solid species formation is affec

Na, Al, Mg, B concentrations. 

2. Misc. organics in sump pool af

T4-8 

Submerged source terms: Fiberglass inhibition 

Leaching of fiberglass inhibits corrosion of certain metals (e.g., Al) Less metallic ions within containm

T4-9 

Submerged source terms: Zn passivation 

Zn passivation decreases corrosion passivation of Fe which allows Fe corrosion. 

Galvanized steal/zinc coating; vesdissolve ...; precipitate as silicate; corrosion products; 

T4-10 

Submerged source terms: Zn corrosion products 

Zn oxide and hydroxide corrosion products form which contributes to solid species loading. 

Additional source term that could cscreen clogging and/or downstrea

T4-11 

Submerged source terms: Zn coprecipitation 

Zn may coprecipitate with other species (, notably Fe, Al). Reactor Vessel a possible site for coprecipitation 

Additional source term that could cscreen clogging and/or downstrea

T4-12 

Zinc hydroxide dissolution (zincate) 

Buffered pH containment pool dissolves zinc hydroxide so that other species, particularly silicates, may precipitate 

Zinc silicates may be more likely to transportable, possibly amorphousdownstream effects. 

T4-13 

Submerged source terms: Zn-based coatings 

Leaching of Zn-based primers (primarily inorganic Zn phosphates) creates possibility for additional dissolved Zn in solution 

Lead to formation of zinc oxide/hydcarbonates, or silicates that could loss/downstream effects. 

T4-14 

Source Term: Seal table corrosion 

Multiple materials in seal table (Inconel, SS, plastics, organics) leads to formation of additional dissolved species. Seal table is an area in bottom of core where instruments are inserted into the core. A series of pressure isolation chambers. Generally lower than bottom of containment floor 

Additional dissolved species presecontainment pool 
C-15

Issue 

Number Phenomena Description Implications 

T4-15 

Submerged source terms: Fire barriers 

Silicon-based seals (bisco seals) used at many structural penetration points at fire barriers. These may leach in post-LOCA environment 

Another silicon source term that coformation of chemical byproducts whead loss and downstream perform

T4-16 

Submerged source terms: organic buoyancy 

Organics coat materials (e.g., aluminum, CalSil, fiberglass, etc.) and increase the buoyancy of particulate so that it’s more likely to float 

This could enhance transport of pachemical byproducts to the sump s

T4-17 

Submerged source terms: coatings 

Leaching of submerged coatings to contribute species to the containment pool. Possible sources include Pb-based paints (older containment buildings), phenolics, PVC 

Additional source terms (especially fluorides) which contribute to contachemistry. 

T4-18 

Submerged source terms: RCP oil tank failure 

Overflow, failure, or leakage occurs either by LOCA or preexisting condition. Oils and other organics are released into containment pool. 

Oils and other organics may affect sequestration of metallic species. chemistry and byproduct productio

T4-19 

Submerged source terms: biofilm formation 

Biofilms form which protect against metallic corrosion (by forming passive layer) or lead to production of acids which increase metallic corrosion. Some biofilms can be preexisting in containment from outages. 

1. If decreases metallic corros

containment pool concentradissolved species. 

2. If increases metallic corros

containment pool concentradissolved species. 

3. May eventually lead to SCC 

components. 

T4-20 

Submerged source terms: biologically enhanced corrosion 

General corrosion is enhanced due to biological agents. Examples include polysaccharides and sulfate reducing bacteria which may enhance Fe corrosion. Sulfur or carbon sources contribute to bacteria formation. 

Fe and other metallic corrosion is eincreased concentrations of metallcontainment pool. 
C-16

Issue 

Number Phenomena Description Implications 

T4-21 

Submerged source terms: biologically enhanced H2

embrittlement 

Anaerobic and aerobic bacteria synergistically enhance stress corrosion cracking and hydrogen embrittlement of steels. Sulfur or carbon sources contribute to bacteria formation. 

Structural cracking enhanced whiclead to failure of structural compon

T4-22 

Submerged source terms: biological growth in debris beds 

Bacteria grow in preexisting debris beds located on the sump strainer screen or elsewhere within the ECCS system. 

Increased source term which can cclogging or detrimental performancetc. 

T4-23 

Submerged source terms: electrical insulation 

Chlorides form due to radiological breakdown of cable insulation. This affect was simulated in the ICET experiment. 

1. Additional source term for prod

containment pool chemistry. 

2. Chlorides affect radiolysis and 

containment pool environment

T4-24 Reactor Core: Fuel spalling Zr-oxide layer spalls off reactor fuel due to temp gradient - 50 micron layers exist 

1. Heat transfer depends on bala

deposition, and particulates, paenhance coagulation in core thheat transfer of water. 

2. Additional solid products whic

clogging within the reactor core

3. Additional products which coul

within the reactor core or be trathe sump screen. 

T4-25 

Radiological** effects: debris bed accumulation 

Radio nuclides transport to, accumulate, and become concentrated within the sump screen debris bed altering the local chemical conditions 

1. More concentrated effect than 

containment pool 

2. Directly alter chemical byprodu

sump screen, contributing to h

T4-26 

Radiological** effects: Dissolution & oxidation changes 

Radiolysis leads to changes in the oxidation state in reactor, piping, and containment materials which affects the dissolution rate and the byproducts which form. 

Affects the chemical byproduct southat is present in the containment 
C-17

Issue 

Number Phenomena Description Implications 

T4-27 

Radiological** effects: Radiolytic affect on biofilms 

Radiolysis inhibits the formation and growth of biofilms 

Films may be either advantageous corrosion and chemical byproduct earlier items) 

T4-28 

Radiological** effects: Redox potential changes 

Radiolysis causes changes in the redox potential either in the containment pool or in debris beds (on the sump screen, or within ECCS component) 

Could affect chemistry in containmaffects species which form (e.g., Hof different components @ differen

T4-29 

Radiological** effects: corrosion rate changes 

Low doses and low temperature elevate the corrosion rate through formation of hypochlorite through radiolysis of Cl bearing water. Could increase corrosion rates (esp. pitting corrosion) of Al, SS, Fe. 

Corrosion rate increases could incmetallic and nonmetallic species in chemical byproduct formation. 

T4-30 

Radiological** effects: agglomeration 

Radiolysis enhances agglomeration of chemical species. 

Advantage: Agglomeration could settling rate of product. Disadvantage: Could form produclikely to cause clogging of sump sccomponents. 

T4-31 CO2/O2 air exchange 

Air exchange provides source for CO2 

ingestion within the containment pool. CO2

quantities limited by containment volume. Radiolysis can also promote formation of carbonates. 

Increase solid species in containm

T4-32 

ECCS Pumps: erosion/corrosion 

Chemical byproducts cause erosion or corrosion of pump internals, especially tight tolerance components (bearings, wear rings, impellers, etc.). 

Pump performance degrades, posbeing inoperable. 

T4-33 

ECCS Pumps: seal degradation 

Chemical environment causes leaching/degradation of pump seal materials or chemical byproducts cause seal erosion 

Pump performance degrades, posbeing inoperable. 
C-18

Issue 

Number Phenomena Description Implications 

T4-34 

Heat exchanger: secondary contaminants 

Leaks in heat exchanger tubes allow secondary-side water additives to migrate over to the containment pool. 

Additives in the secondary side wathe chemistry in the containment p

T4-35 

Heat exchanger: precipitate formation 

Drop in temperature leads to the formation of sold species (e.g., AlOOH, FeOOH amorphous SiO2) and ripening such that 

macroscale coatings and/or suspended particulates form. 

1. Create clogging, and less effic

cooling the ECCS recirculating 

2. Form products that may clog re

degrade heat transfer from fue

3. Products form which transport 

screen and lead to head loss. 

4. Particulates act as nucleation s

compounds to precipitate 

T4-36 

pH drop in containment pool 

pH drop due to evolving containment pool chemistry causes Al (and other metallic species) to precipitate. 

Creates solid particulate loading thscreen head loss, heat exchanger core clogging, and additional nucle

T4-37 

Reactor Core: continued deposition/precipitation 

Zn, Ca, Mg, CO2 based deposits, films, and 

precipitates may form at higher temperatures within the reactor core 

1. Diminished heat transfer from t2. Spalling could create additiona

which contribute to clogging wi

3. Spalling could create additiona

which contribute to sump scree

T4-38 

Reactor Core: fuel deposition spalling 

Zn, Ca, Mg, CO2 based deposits and films 

which form on the reactor core spall 

1. Additional solid products which 

clogging within the reactor core

2. Additional solid products which 

screen head loss. 

T4-39 

Transport Phenomena: amorphous coating 

Amorphous silica forms on surface of chemical precipitates (e.g., AlOOH, FeOOH). Coatings increase density and make it less likely for products to transport to sump screen. 

Decreased transportability will resumigrating to or through the sump s

T4-40 

Transport Phenomena: precipitation/co-precipitation 

Precipitation/co-precipitation and ripening of solid species within containment pool creates solid species which are less likely to transport. 

Decreased transportability will resumigrating to or through the sump s
C-19

Issue 

Number Phenomena Description Implications 

T4-41 

Transport Phenomena: Metallic scouring 

Turbulent flow causes chemical films/products to be scour off the surface of metallic components so that they enter the containment pool. 

Increased particulate loading that loss, degrade pump, valve, heat experformance, and/or affect heat trafuel. 

a Sump pool temperatures are expected to range between 50 – 70C during this time period. b Phenomena listed in earlier time periods (i.e., T1, T2, T3) may continue to be active or important during this timc Al, in ICET tests, has provided an important contribution to observed chemical effects both through precipitate 

concentrations and pH and in inhibiting fiberglass leaching. 

d Soluble/insoluble activation species include, for example, Na24, Be7, Cr51, Co58,60, Mn54,56, Zr95,97, Fe55,59, Ni59,63

Cs134,137, and I131,133
C-20

Table C-5: ECCS Recirculation (15 days to 30 days a,b) 

Issue 

Number Phenomena Description Implications 

T5-1 Organic radiolysis Radiolysis of organics leads to carbonate formation 

1. Create nucleation sites for 2. scavenge dissolved Ca to 

other compounds 

3. Additional solid species co

leads to degraded system loss, etc.) 

a Sump pool temperatures are expected to range between 40 – 60C during this time period. b Phenomena listed in earlier time periods (i.e., T1, T2, T3, T4) may continue to be active or important during thiDefinitions:ECCS: Emergency Core Cooling System RCS: Reactor Coolant System Crud: Ni, Fe based oxides that reside on internal RCS piping. RCP: Reactor Coolant Pump LOCA: Loss-of-Coolant-Accident trecirc: Time at which ECCS recirculation pumps are actuated 

TSP: Trisodium phosphate buffering agent {Na3(PO4)} 

STB: Sodium tetraborate buffering agent {Na2B4O7} 

Cal-Sil: calcium silicate insulation TH: Thermohydraulic PZC: pH of Zero Charge In: Inconel (nickel-based alloy) SS: stainless steel RHR: Residual Heat Removal System (also referred to as Decay heat removal system)
APPENDIX D

PIRT RESPONSE TABLES
Table D-1: Implications and Time Table

Location Phenomena/Implication 

Category

Time Period (t = 0 @ pipe break, beginning of LOCA)

0 – 30s 30s - trecirc trecirc– 24h 24h – 15d 15d – 30d

Containment 

Pool

Break Location & 

System Failures

Reactor Chemistry 

Conditions

pH Effects

Radiological Effects

Organic Effects

Redox Potential & 

Effects

Carbonate Formation

Unsubmerged Material 

Corrosion

Submerged Metal 

Corrosion

Submerged Material 

Degradation

Precipitate Formation & 

Growth

Mixing & Flow Effects

Settling & Deposition

Sump Screen Debris Bed Buildup & 

Head Loss
D-3

Debris Bed 

Compaction & Head 

Loss

Debris Bed Reduction 

& Screen By-Pass

Chemical Species 

Generation or 

Reduction

ECCS Pumps Seal Degradation

Internal Component 

Erosion/Corrosion

Chemical Species 

Generation

Heat 

Exchanger

Heat Transfer 

Reduction: Clogging or 

Deposition

Chemical Species 

Generation or 

Reduction

Reactor Core Heat Transfer 

Reduction: Clogging, 

Deposition, or Fluid 

Conditions

In-Core Settling

Chemical Species 

Generation or 

Reduction
D-4

Table D-2: Importance Ranking for T1 Phenomena

Phenomenon Importance*

(H, M, L)

Rationale Knowledge**

(K, PK, UK)

Rationale

T1-1

T1-2

T1-3

T1-4

T1-5

T1-6

T1-7

T1-8

T1-9

T1-10

T1-11

* L = Low, M = Medium, H = High

** K = Known, PK = Partially Known, UK = Unknown
D-5

Table D-3: Importance Ranking for T2 Phenomena

Phenomenon Importance*

(H, M, L)

Rationale Knowledge**

(K, PK, UK)

Rationale

T2-1

T2-2

T2-3

T2-4

T2-5

T2-6

T2-7

T2-8

T2-9

T2-10

T2-11

T2-12
D-6

T2-13

T2-14

T2-15

T2-16

T2-17

T2-18

T2-19

T2-20

T2-21

T2-22

T2-23

T2-24

* L = Low, M = Medium, H = High

** K = Known, PK = Partially Known, UK = Unknown
D-7

Table D-4: Importance Ranking for T3 Phenomena

Phenomenon Importance*

(H, M, L)

Rationale Knowledge**

(K, PK, UK)

Rationale

T3-1

T3-2

T3-3

T3-4

T3-5

T3-6

T3-7

T3-8

T3-9

T3-10

T3-11

T3-12
D-8

T3-13

T3-14

T3-15

T3-16

T3-17

T3-18

T3-19

T3-20

T3-21

T3-22

T3-23

T3-24

T3-25

T3-26
D-9

T3-27

T3-28

T3-29

T3-30

T3-31

* L = Low, M = Medium, H = High

** K = Known, PK = Partially Known, UK = Unknown
D-10

Table D-5: Importance Ranking for T4 Phenomena

Phenomenon Importance*

(H, M, L)

Rationale Knowledge**

(K, PK, UK)

Rationale

T4-1

T4-2

T4-3

T4-4

T4-5

T4-6

T4-7

T4-8

T4-9

T4-10

T4-11

T4-12
D-11

T4-13

T4-14

T4-15

T4-16

T4-17

T4-18

T4-19

T4-20

T4-21

T4-22

T4-23

T4-24

T4-25

T4-26
D-12

T4-27

T4-28

T4-29

T4-30

T4-31

T4-32

T4-33

T4-34

T4-35

T4-36

T4-37

T4-38

T4-39

T4-40
D-13

T4-41

* L = Low, M = Medium, H = High

** K = Known, PK = Partially Known, UK = Unknown
D-14

Table D-6: Importance Ranking for T5 Phenomena

Phenomenon Importance*

(H, M, L)

Rationale Knowledge**

(K, PK, UK)

Rationale

T5-1

* L = Low, M = Medium, H = High

** K = Known, PK = Partially Known, UK = Unknown
APPENDIX E

PIRT Panelist Evaluations of T1 Phenomena:

Debris Generation from Pipe Break to 30s into LOCA
E-2

Table E-1: Debris Generation (0 to 30 s)

Issue 

Number

Phenomena Description Implications

T1-1 Crud release Fe, Ni corrosion oxides (. 125 

Fm layer) from the RCS 

piping are released due to 

hydraulic shock of the failure 

event

The crud release creates a 

radiolytic environment on materials 

caught on the sump screens which 

could affect subsequent reactions. 

Also, the oxides add particulate 

mass to containment pool, which 

may enhance coagulation. 

T1-2 RCS coolant 

conditions at 

break

The RCS coolant chemistry 

varies over the fuel cycle. B 

concentrations . 2000 -4000 

ppm (beginning) to 50 ppm 

(end of fuel cycle) B/Li ratio .

100. The 2-phase jet is at 

temperatures of . 315C to 

120C upon cooling

Initial reactor water chemistry 

spewing out of the break and 

forming the containment pool will 

have variable B concentration. 

The Li/B ratio is maintained 

approximately constant.

T1-3 pH variability pH @25C at beginning of fuel 

cycle is acidic (4) while closer 

to neutral (7) at end of cycle.

Similar implications to issue 2; 

variable reactor and initial 

containment pool chemical 

environment.

T1-4 Localized B 

concentration 

in jet

Droplet evaporation within the 

high temperature jet 

emanating from the pipe 

break forms at highly 

concentrated B aerosol 

solution. As boric acid 

concentrates at high 

temperatures (250C - 300C), 

a polymerization appears to 

occur that releases protons 

and causes the system to 

become very acidic.

1. Corrosion of impacting 

surfaces: enhanced erosion & 

corrosion vs. formation of a 

protective lacquer to limit 

erosion.

2. May limit B concentration in 

containment pool chemistry 

T1-5 RCS fluid 

creates 

“oxidizing 

environment”

Coolant is released as a 

super heated spray once 

break occurs. Hydrogen (25 – 

35 cc/kg of H2 injected as gas) 

transfers to the gas phase. 

1. H2 evaporation creates a more 

oxidizing environment in the 

water phase by raising the 

redox potential. 

2. The partial pressure of H2 is 

lowered because of the large 

volume of the gas phase 

(containment volume) 

compared with the water 

volume being released. This 

also increases the redox 

potential.
E-3

T1-6 Jet 

impingement 

Water jet & fine debris within 

jet may impact surfaces and 

chip coatings

Initiates metallic pitting, corrosion 

and ablation of other materials 

(concrete, insulation) 

T1-7 Break 

proximity to 

organic 

sources 

RCP oil storage tank is made 

with . 1⁄2” carbon steel with 

epoxy coating (250 gallon per 

pump, but tank may just 

contain leakage). 

Tank failure timing: earlier in postLOCA (jet impingement) vs. later in 

post-LOCA (corrosion) 

Organic sources to containment 

pool would alter chemistry (i.e., 

complexation, etc.)

T1-8 Break 

proximity to 

secondary 

systems

Break near cooling systems 

could result in failure of lines 

containing solvents (i.e., 

Freon) into containment 

environment

1. Radiolytic decomposition could 

create chlorides and fluorides 

which may impact corrosion 

and containment pool 

chemistry. 

2. Possible effects on pump 

performance 

T1-9 Debris mix 

particle/fiber 

ratio

Breaks in different locations 

will create different debris 

characteristics: total mass, 

mixture constituents, 

compositions

1. Could alter the containment pool 

chemistry. 

2. Could affect debris bed 

formation on the sump screen 

and increase variability of 

chemical product capture 

efficiency. 

T1-10 Hydrogen 

peroxide 

effects 

Hydrogen peroxide will 

behave much the same as 

H2O and most of it will remain 

in the liquid phase. Additional 

hydrogen peroxide 

evaporates into containment 

vapor space and may cause 

additional corrosion. It 

condenses on cooler surfaces 

and can accelerate corrosion 

there

1. Could affect how much H2O2 is 

in the containment pool: 

Evaporation & condensation 

could sequester form pool 

droplets could transport back 

to pool. 

2. H2O2 alters containment pool 

chemistry and potentially 

causes changes in oxidation 

states or chemical forms in 

sump water..

T1-11 Nuclei 

Formation

Rapid subcooling and 

evaporation of water from 

effluent of broken pipe 

droplets might lead to 

precipitation of LiOH and 

other species. Concentrations 

increase and temperature 

decreases rapidly

1. Initial precipitate may be 

formed from species existing 

with in the RCS coolant. 

2. Nuclei could form which could 

enhance precipitation of other 

species within the containment 

pool at a later time.
Table E-2: Apps T1 Ranking Summary

Issue 

Number

Importance 

(H, M, L)

Rationale Knowledg

e (K, PK, 

UK)

Rationale

T1-1 L Particles would be dense and tend to 

settle out.

PK Extent of release cannot be accurately 

predicted.

T1-2 L Effect is transient. Will be compensated 

by addition of cooling water.

K Plant operating parameters well known.

T1-3 L Effect is transient. Will be compensated 

by addition of cooling water and pH 

buffers.

K Plant operating parameters well known.

T1-4 L/M Effect is transient. Depends on B 

concentration. Will be compensated by 

addition of cooling water and pH 

buffers.

PK Actual behavior during LOCA not 

quantified.

T1-5 L Quantity of H2 is small. K Plant operating parameters well known. 

Predictable outcome.

T1-6 H Principal mechanism for generating 

reactive particulates.

PK Actual extent of damage would vary.

T1-7 M/H Release of oil could significantly affect 

corrosion and debris flotation.

UK Likelihood of release is speculative.

T1-8 L Freon would partition into the 

containment-building atmosphere and 

be relatively non-reactive.

UK Radiolysis in gas phase probably low.

T1-9 H Debris composition and amount would 

strongly affect screen blockage and 

formation of secondary precipitates.

PK Potential damage scenario can be 

postulated. Depends on plant design.
E-5

T1-10 L H2O2 reactive, but quantity present may 

be small. H2O2 may induce passivation 

of metals. Time for reaction to occur is 

limited.

PK H2O2 concentration can be predicted, 

but corrosion rates of metals exposed to 

H2O2 would need to be evaluated.

T1-11 L Particles may re-dissolve. Effect 

probably minor over short time frame.

UK Require evaluation to determine 

whether the phenomenon is significant.
E-6

Table E-3: Chen T1 Ranking Summary 

Issue 

Number

Importance 

(H, M, L)

Rationale Knowledg

e (K, PK, 

UK)

Rationale

T1-1 M PK 

T1-2 M K 

T1-3 M pH will affect the rate of corrosion of 

metals

K 

T1-4 M PK 

T1-5 L PK 

T1-6 L The impact areas may not be that 

significant

PK 

T1-7 L PK 

T1-8 M PK 
E-7

T1-9 H Debris mix definitely affect the amount 

(thickness) and characteristics 

(tightness, compressibility,..) of the cake 

on the sump screen

K 

T1-10 L PK 

T1-11 L PK 
E-8

Table E-4: Delegard T1 Ranking Summary

Issue 

Number

Importance 

(H, M, L)

Rationale Knowledg

e (K, PK, 

UK)

Rationale

T1-1 H Not considered in ICET. Significant 

potential solids source also includes fuel 

surfaces.

PK Crud releases observed during reactor 

shut-down and spent fuel storage.

T1-2 H Boron concentration wide variability and 

high temperature not considered in 

ICET but B has large affect on solids 

corrosion.

PK Knowledge based on ICET results only 

for set B concentration and 

temperature.

T1-3 H Boron concentration wide variability and 

high temperature not considered in 

ICET but B has large affect on solids 

corrosion.

PK Knowledge based on ICET results only 

for set B concentration and 

temperature.

T1-4 M Impact of localized higher B 

concentration limited by small affected 

areas.

PK Studies of higher B concentrations not 

performed.

T1-5 L Dissolved H2 concentration ~25-35 

cm3

/kg water at 0°C and much lower at 

temperature so reducing conditions 

from H2 unlikely.

PK Real issue is overall Eh of system and 

this has not been measured under 

radiolytic conditions.

T1-6 H This phenomenon should add large 

quantities of debris to reactor coolant.

PK Testing needed (it would seem) to judge 

effects of steam jetting on metal, paint, 

insulation, and concrete.

T1-7 M Effects of oil not studied; oil may 

accrete small solids and drift 

downstream to span matted fibers at 

sump screen.

PK Effects of oil to accrete finely particulate 

solids under this system not known but 

example exists in oil spills from oil 

tankers onto beaches.

T1-8 L Freons are chemically rugged and, even 

if released, unlikely to react significantly.

PK Radiolysis may have impact on Freon 

stability but access of Freon to high 

fields may be limited.
E-9

T1-9 H Though important, this question likely 

addressed in sufficient detail in ICET.

K ICET gives good starting point.

T1-10 L H2O2 is not very volatile and is unstable 

to disproportionation to form O2 and 

H2O, especially in the presence of iron.

K Effects of H2O2 in the coolant system 

should be studied but the efficient 

transport of H2O2 out of coolant unlikely 

to have much effect.

T1-11 M This is similar to T1-4, only for LiOH and 

other species.

PK Studies of higher solute concentrations 

not performed.
E-10

Table E-5: Litman T1 Ranking Summary

Issue 

Number

Importance 

(H, M, L)

Rationale Knowledg

e (K, PK, 

UK)

Rationale

T1-1 H Thermo-hydraulic transient and 

formation of hydrogen peroxide absent 

hydrogen overpressure will cause 

significant CRUD release.

K This is similar to an unplanned reactor 

trip event. The exception is water 

temperature during a reactor trip 

remains elevated and hydrogen control 

is maintained minimizing peroxide 

formation.

T1-2 H At beginning of cycle with High [B], pH 

of RCS as it impinges will be fairly 

acidic and hot (high temperature). This 

will cause significantly greater corrosion 

and leaching from impacted materials.

K During the early phase of the break 

reactor coolant without buffering agent 

is sprayed directly onto ZOI where the 

greatest surface area contact will occur 

on insulating materials (principally 

responsible for the precipitates). The 

high temperature will increase leaching 

and solubility of ionic materials.

T1-3 H Same as above. K Same as above. However, this 

changes with time. Final pH is 

significantly different than the initial and 

depending upon the media impacted 

will have different effects.

T1-4 L Although this is technically correct, it will 

have a low overall impact on debris 

generation and reaction with the debris.

K Physical properties of boric acid are 

well established.
E-11

T1-5 M Hydrogen solubility decreases 

dramatically due to pressure drop. 

Within reactor containment if hydrogen 

level gets too high recombiners go on to 

eliminate explosive mixture. With no 

hydrogen in the liquid phase and 

peroxide production in the core, redox 

potential goes positive by 100+ 

millivolts.

K The formation of peroxide is a wellestablished phenomenon in the SFP of 

nuclear power plants. Hydrogen loss is 

a physical property.

T1-6 L Reactor containment buildings are 

‘crowded’. The available coating 

surface that would impacted by the 

initial jet spray is small compared to the 

total surface area of painted surfaces in 

the containment.

PK This is a plant specific parameter. It 

would be more significant for plants that 

had variable insulation types that were 

in close proximity to the break.

T1-7 L This is a possibility depending on where 

the break occurs and the proximity to 

these material sources. The tanks 

themselves are carbon steel and coated 

with epoxy.

PK This is a plant specific parameter.

T1-8 L The projected break vicinity is usually 

distant from component cooling systems 

or secondary systems

PK This is a plant specific parameter. It 

depends on the type of materials in 

closed cooling systems in containment.

T1-9 M This is dependent upon the type and 

amount of insulation adjacent to the ZOI 

of the break

PK This is a plant specific parameter.

T1-10 M The presence of hydrogen peroxide on 

non-submerged surfaces will enhance 

corrosion rates. However this would be 

most significant during the first four 

hours when spray is washing down 

surfaces. After that it will be of much 

less importance.

K The effect of peroxide on metallic 

components corrosion can be estimated 

from corrosion rates.
E-12

T1-11 L The effects of LiOH at ambient 

temperatures will be minimal especially 

since the RWST boron will rapidly put 

the break chemistry into the acidic 

range.

K LiOH is a weak base at room 

temperature. The RCS pH308 C(boron 

1200 ppm and Li 3.5 ppm) is ~7.1 

above a pHneutral of 6.8. The same 

solution is pH of ~5.1 below pHneutral of 

7.0
E-13

Table E-6: MacDonald T1 Ranking Summary

Issue 

Number

Importance 

(H, M, L)

Rationale Knowledg

e (K, PK, 

UK)

Rationale

T1-1 H Radiolysis can considerably modify the 

chemistry of the water in the 

containment pool by raising the redox 

potential. A higher redox potential will 

result in the oxidation of lower valency 

cations (e.g., Fe2+) to higher valency 

cations (Fe3+), which subsequently 

hydrolyze to precipitate solids (e.g., 

FeOOH) that may clog the pump 

screens. The hydrolysis of Fe2+ will 

produce Fe(OH)2, which in turn may 

undergo the Schikorr reaction to form 

magnetite (Fe3O4) and hydrogen. The 

latter will contribute to the total 

hydrogen inventory and will impact the 

redox potential. Some scoping 

calculations of the radiolysis of water 

and stainless steel corrosion potentials, 

performed during the present study for 

illustrative purposes, are summarized in 

the author’s report.

K Radiolysis and mixed potential models 

are available for estimating the redox 

potential in the containment pool, data 

and computer codes are available for 

modeling the hydrolysis of many 

common ions (e.g., Fe3+, Ni2+, Cr3+, 

Cu2+, Zn2+, and Al3+) and the formation 

of the corresponding hydroxides, 

oxyhydroxides, and oxides. 
E-14

T1-2 H The Li/B ratio in the coolant, together 

with the NaOH, TSP, and STB buffers 

stored on the containment floor, will 

determine, to a significant extent, the 

acid/base properties (pH) of the coolant 

in the containment pool. Thus 

knowledge of the Li/B ratio at the time 

of the LOCA is vital for modeling the 

chemistry of the water in the 

containment pool, since it describes the 

“initial state”. The processes that occur 

as the coolant expands adiabatically 

upon a pipe break are also of great 

significance.

PK The Li/B ratio is known precisely at any 

point in the fuel cycle, as are the 

physico-chemical properties of the 

coolant. However, the adiabatic 

expansion of the coolant, upon 

occurrence of a LOCA, accompanied by 

evaporation of water and hydrogen 

transfer from the coolant droplets, is 

expected to significantly modify the 

chemical (e.g., pH) and electrochemical 

(redox potential) properties of the 

coolant that eventually collects in the 

containment pool. The physico 

electrochemical processes involved are 

poorly defined and understood at the 

present time, even at the fundamental 

level.

T1-3 H See T1-2 PK See T1-2.

T1-4 H Concentrated boric acid is known to be 

corrosive to ferrous alloys (e.g., carbon 

steel), as witnessed by the Davis Besse 

reactor head degradation phenomenon, 

and is postulated to be corrosive toward 

many other materials that are 

susceptible to highly acidic conditions. 

Thus, high temperature pH 

measurements on concentrated boric 

acid detected the occurrence of a 

polymerization process that released 

protons (H+

).

PK While the production of highly acidic 

conditions in concentrated boric acid 

have been detected in laboratory 

experiments, so little is known of this 

phenomenon that we do not have the 

capability of modeling the damage that 

concentrated boric acid that is formed in 

a LOCA jet may cause.
E-15

T1-5 H The chemistry of the coolant expanding 

from a LOCA break is determined to a 

significant extent by the redox potential 

of the water (for example, the redox 

potential determines the valency of 

metal corrosion products). In turn, the 

redox potential reflects a balance 

between the oxidizing (e.g., O2, H2O2, 

Fe3+) and reducing (H2, Fe2+) species in 

the solution. Thus, as H2 is transferred 

from the solution to the gas phase, and 

noting that, because H2 has a lower 

molecular weight than do O2 and H2O2, 

the droplets in a LOCA stream will 

gradually become more oxidizing in 

nature. In consequence, Fe2+ will be 

oxidized to Fe3+ and FeOOH will be 

precipitated.

PK Theories have been developed for the 

transfer of gasses from the dissolved 

state in a solution to the gas phase, but 

it is not known whether these models 

can be used to predict gas transfer 

under the “shock” conditions of a LOCA 

or whether the requisite data are 

available for the model parameters to 

allow effective prediction.

T1-6 H The erosion of materials by the LOCA 

jet is deemed to be a significant source 

of debris in the containment pool 

immediately after a LOCA. The rate of 

damage accumulation (debris 

production) is a sensitive function of 

many variables, including jet velocity 

and composition, impact angle, distance 

from the jet source and point of impact, 

and so forth.

K The erosion-corrosion of materials by 

single-phase (liquid, gas) and by twophase (liquid + gas, liquid + solid, and 

gas + solid) jets has been extensively 

studied, at both the theoretical and 

practical levels. Models are available 

(e.g., the Keller equation), but the 

applicability of these models to a LOCA 

scenario has yet to be determined.

T1-7 H See T1-6. K See T1-6.
E-16

T1-8 L The amount of radiation-induced 

damage at the prevailing γ-dose rates 

within the first 30 seconds of a LOCA 

are expected to cause minimal damage 

to chloride- and fluoride-containing 

polymers, so that the release of Cl-

 and 

F-

 from radiolytic processes is likewise 

expected to be minimal, compared with 

other processes (e.g., thermo 

hydrolysis). 

PK The rates of radiation-induced damage 

to many plastics and polymers have 

been characterized over wide ranges of 

conditions. These data are readily 

available in the public domain. 

However, there is the possibility of 

synergistic interaction between radiationinduced damage and thermo hydrolysis 

processes that have not been 

significantly explored.

T1-9 M Small variations in the contents of the 

containment pool are probably not very 

significant at this level of analysis. It is 

expected that all LOCA events will 

produce silicates and alumino-silicates 

(eroded concrete), fiber glass, paint and 

polymer debris, metal corrosion 

products, etc).

PK Depends on the location of the break, 

which is not predictable at the current 

time, other than there being an 

increased likelihood that it will occur at 

a highly stressed point in the main 

coolant line.
E-17

T1-10 M Hydrogen peroxide is a strong oxidizing 

agent and hence is capable of inducing 

severe corrosion on metals, such as Al, 

and on alloys, such as the stainless 

steels. H2O2 may be transferred to the 

containment volume via spray and 

evaporation. Initial rankings changed 

due to following email, rankings 

indicated separately: Please find 

attached a table with my reassessments of some originally "high" 

ratings of issues. On examining these 

issues again, it was evident that I did 

not fully recognize the impact of:

1. Time of exposure after the initial 

LOCA.

2. The amount of the specific material in 

the containment (e.g., zinc).

My re-assessments also reflect the 

results of continuing radiolysis 

modeling, albeit with less-than-optimal 

codes that have been jerry-rigged from 

our reactor modeling work. 

Nevertheless, if the fields are as high as 

Bob indicates, the eventual production 

of nitric acid, in addition to the elevation 

of the redox potential, becomes a 

critical issue.

K The impact that H2O2 can have on the 

corrosion and degradation of materials 

has been studied extensively and many 

data and much information are available 

in handbooks. Furthermore, the 

theoretical basis for predicting corrosion 

rates in environments containing 

hydrogen peroxide is highly developed 

in the form of the Mixed Potential Model 

(MPM) and the Point Defect Model 

(PDM).
E-18

T1-11 L The kinetics of precipitation of solids 

from super-saturated solutions are 

highly dependent upon the type and 

volume density of nuclei. Use of this 

fact is made in numerous industrial 

processes by seeding a solution to 

induce precipitation and hence to 

separate a wanted or unwanted product 

from the system. Thus, the inventory of 

solid products in the containment pool 

within the first 30s of a LOCA will 

depend sensitively on the concentration 

and properties of the nuclei. In the 

absence of effective nuclei, as supersaturated solution may remain 

metastable over extended periods 

(minutes to months). Initial 

rankings changed due to following 

email, rankings indicated separately: 

Please find attached a table with my reassessments of some originally "high" 

ratings of issues. On examining these 

issues again, it was evident that I did 

not fully recognize the impact of:

1. Time of exposure after the initial 

LOCA.

2. The amount of the specific material in 

the containment (e.g., zinc).

My re-assessments also reflect the 

results of continuing radiolysis 

modeling, albeit with less-than-optimal 

codes that have been jerry-rigged from 

our reactor modeling work. 

Nevertheless, if the fields are as high as 

Bob indicates, the eventual production 

of nitric acid, in addition to the elevation 

of the redox potential, becomes a 

critical issue.

PK An enormous literature exists on the 

theory and practice of the nucleation 

and solid precipitation in multicomponent systems, but mostly for 

“simple” systems (e.g., salts). How well 

and how easily these theories and 

experimental databases can be applied 

to LOCA scenarios remains to be 

determined. 
E-19
APPENDIX F

PIRT Panelist Evaluations of T2 Phenomena:

ECCS Injection from 30s into LOCA until 

ECCS Recirculation Begins
Table F-1: ECCS Injection (30 seconds to trecirc)

a,b,c

Issue 

Number

Phenomena Description Implications

T2-1 Hydrogen 

sources within 

containment 

H2 concentrations in vapor and containment 

pool include the RCS inventory, Schikorr 

reaction, corrosion of metallic materials

Containment pool redox potential is a function of 

dissolved hydrogen which is established by the listed 

reactions. RCS evaporation may lead to equilibration 

with liquid, decreasing redox potential

T2-2 ECCS injection 

of Boron

After pipe break, B (. 2800 ppm) is injected 

into RCS to cool reactor

Provides large B source which may affect chemical 

reaction products in containment pool. Specifically, 

the B source will serve as a pH buffer.

T2-3 Containment 

spray corrosion

Containment sprays for buffering creates 

wetting & surface films on material surfaces 

with water containing B, LiOH, H2

Containment spray (up to 4 hours) could enhance 

corrosion formation on unsubmerged metallic species 

which could contribute to containment pool 

concentrations. Spray pH:

NaOH = 8.5 – 10.5

TSP = 4.5 - 5

STB = 4.5 – 5

T2-4 NaOH pH 

control

NaOH injected through containment sprays. Alkaline containment pool environment (pH = 8.5 – 

10.5)

T2-5 STB pH control Released with ice in containment during a 

LOCA

Alkaline containment pool environment. Initially pH is 

high 9 initially and then decreases with mixing (pH = 8 

– 9)

T2-6 TSP pH control Contained in basket on containment floor that 

dissolve

Slightly alkaline containment pool environment. 

Initially pH is high (pH = 11) until complete mixing 

within about 4 hours (pH = 7 – 8)

T2-7 Containment 

spray transport 

Sprays wash latent debris, corrosion 

products, insulation materials, & coating 

debris into containment pool

Affect on containment debris sources (types, amounts, 

compositions) and contributions to the chemical sump 

pool environment.

T2-8 Containment 

spray CO2

scavenging

Containment sprays cause CO2 absorption 

within containment pool and carbonate 

formation.

Affect on containment pool concentrations of CO2

T2-9 Debris 

dissolution 

begins

Debris dissolution begins. Initial expected 

products include cal-sil, cement dust, organic 

fiberglass binders, epoxy & alkyd coatings, 

uncoated concrete

Indicate potential important contributors (if any) to 

chemical containment pool environment during this 

time frame. Dissolution of other products will occur 

over longer time frames. 
F-3

T2-10 Carbonate 

concentration

Carbonates in solution are provided by 

atmospheric CO2, and concrete dust at this 

point 

1. Create nucleation sites for species precipitation

2. scavenge dissolved Ca to impede formation of other 

compounds to form calcium carbonate

T2-11 Containment 

pool mixing

High velocity, turbulent water flow exists 

underneath the pipe break location, 

remainder of the pool relatively quiescent

Mixing of aqueous/gas phases at the break location is 

enhanced; could aid CO2 absorption; buffering agent 

dissolution/mixing, liquid/vapor exchange of species.

T2-12 Boric acid 

corrosion of 

exposed 

concrete

Concentrated boric acid solutions in contact 

with exposed concrete 

1. Calcium boro-silicates may precipitate

2. pH decrease in containment pool possible

T2-13 Fe, Ni 

radiological 

reaction 

Initial Fe, Ni oxide breaks off due to TH 

transient. Reduced Ni, Fe is dissolved in 

RCS, combines with air, oxidizes and forms 

hematite, maghemite, and magnetite. . 

Kilorad/hour and higher rad. dose rates arise 

throughout containment due to dispersal of 

Fe and Ni activation products.

1. Solid particulate is added to containment pool, 

another debris source

2. High pH will increase the reaction.

3. Reaction continues until RCS piping cools down (1 

day or more).

4. Radiolysis products generated throughout postLOCA cooling system

T2-14 Hydrolysis Nickel oxide becomes catalyst for producing 

H2 from radiolysis

Affects redox potential

T2-15 Organic 

Complexation

Organic acids become absorbed on surfaces 

of solids & inhibit solid species growth; 

example: aliphatic acid

Effectively enhances solubility limits. Solid species 

may precipitate, but remain relatively small in size 

(nano-scale). They do not agglomerate or grow to 

macroscopic sizes. 

T2-16 Organic 

Sequestration

Organic electron-rich atoms combine with 

soluble metal compounds.

Sequesters metal ions so that solid species 

precipitation is delayed or does not occur. 

T2-17 Auxiliary 

Component 

Cooling Line 

Failure

LOCA causes attached or nearby component 

cooling line failure which could release a 

number of chemicals into the containment 

pool (chromates, molybdates (6000 – 1000 

ppm in storage tank), nitrites, tolytriazole (25 

ppm in storage tank), benzotriazole, 

hydrazine

1. The release of these types of chemicals could 

increase the ionic strength of the containment 

environment which may decrease gel stability. 

2. Chemicals may accelerate corrosion.
F-4

T2-18 Polymerization Precursor to precipitation & agglomeration; 

metals/oxygen bonds, ripen to form covalent 

bonds, growth until they qualify as 

~nanometer particles size: Si, Al, Fe, Boric 

acid are candidates

May be necessary to form large enough particles to 

result in tangible effects on ECCS performance

T2-19 Coprecipitation

Method of precipitation/separation 

Examples: Ni/Fe/Cr, Al/Si/B; Co/Fe systems; 

Precipitation of one species leads to 

precipitation of other species (below solubility 

limit);

Radioactive elements precipitate (at low 

concentrations), activation products: ex. 

Strontium, Ni, Silver, Fe, Co, Zr 

More solids species form which could lead to greater 

concentration of chemical products at the sump screen 

or downstream.

T2-20 Radiolytic 

environment

Radiolysis reaction creates an oxidizing 

environment and can change solution’s 

electric potential; H2, O2, and H2O2 balance 

most important for determining redox 

potential 

Could affect chemistry in containment pool which 

affects species which form (e.g., Hanford tank: mixture 

of different components @ different phases) 

T2-21 Inorganic 

Agglomeration

Formation of larger clumps of smaller 

particulates: Depends on PZC; ionic strength 

(the higher the strength the smaller the 

distance for agglomeration)

1. May be necessary to form large enough particles to 

result in tangible effects on ECCS performance 

2. Can occur quickly if conditions are right.

3. Existence of organic species can increase or 

decrease likelihood (See T2-24)

T2-22 Galvanic 

Effects

Electrical contact between metals results in 

increased corrosion of less noble metals: 

example: magnetite precipitation on 

Aluminum

1. Increases in the corrosion source term for less 

noble (anodic) metal.

2. Decreases in corrosion source term for more noble 

(cathodic) metal.

T2-23 Deposition & 

Settling

Possibility that chemical products formed 

during this time period either settle within 

containment pools or are deposited on other 

surfaces

Potentially remove substantial quantities of material 

from transporting to the containment sump screen: 

indicate expected species that are most likely to settle, 

if possible.

T2-24 Organic 

Agglomeration

Formation of larger clumps of smaller 

inorganic particulates nucleating around 

organic acids or oil (such as soap coagulates 

dirt particles)

Coagulated particles can collect on sump screen, 

decreasing flow, or collect in other places to decrease 

the loading on the sump screen
F-5

a

 Massive fuel damage is not considered during this time period because the objective is to prevent this through successful operation 

of the ECCS system. Radiological and other contributions to the chemical environment from minor amounts of fuel damage are 

expected to be insignificant compared to crud release and other phenomena listed in these tables. b Sump pool temperatures can be as high as 120C initially. After 30 minutes, between 60 – 90C c Phenomena listed in earlier time periods (i.e., T1) may continue to be active or important during this time.
F-6

Table F-2: Apps T2 Ranking Summary

Issue 

Number

Importance 

(H, M, L)

Rationale Knowledg

e (K, PK, 

UK)

Rationale

T2-1 L Quantity of H2 is small. Partitioning into 

containment building atmosphere would 

render it largely inert.

PK Plant operating parameters well known. 

Behavior of hydrogen generally 

predictable.

T2-2 H B would have a significant effect on 

coolant chemistry.

K ICET series provide useful data on 

chemical interactions with B.

T2-3 L Effect is transient. K ICET series indicates that unsubmerged 

corrosion is generally minor.

T2-4 M NaOH would have a significant effect on 

coolant chemistry, but time period is too 

short for substantial reaction to occur.

K ICET series provide useful data on 

chemical interactions due to presence of 

NaOH

T2-5 M STB would have a significant effect on 

coolant chemistry, but time period is too 

short for substantial reaction to occur.

K ICET series provide useful data on 

chemical interactions due to presence of 

STB

T2-6 M TSP would have a significant effect on 

coolant chemistry, but time period is too 

short for substantial reaction to occur.

K ICET series provide useful data on 

chemical interactions due to presence of 

TSP

T2-7 H Quantity and make-up would strongly 

affect sump screen blockage.

PK Consequences are difficult to predict 

following a LOCA. Evaluations need to 

be made on a case-by-case basis.

T2-8 L/M Quantity of CO2 is low, but could induce 

formation of CaCO3 seeds for nucleation 

and growth of other phases.

PK Amount of CO2 that could be absorbed 

is well known, but the consequent effect 

on nucleation and precipitation is less 

clear.
F-7

T2-9 M Debris dissolution is instrumental in the 

formation of secondary precipitates. 

However, extent of reaction during the 

initial phase would be small

K ICET program has evaluated debris 

corrosion rates.

T2-10 L/M Quantity of CO2 is low, but could induce 

formation of 3 seeds for nucleation and 

growth of other phases.

PK Amount of CO2 that could be absorbed 

is well known, but the consequent effect 

on nucleation and precipitation is less 

clear.

T2-11 H Debris settling would limit sump screen 

blockage.

UK/PK Consequences are difficult to predict 

following a LOCA. Evaluations need to 

be made on a case-by-case basis.

T2-12 L Secondary calcium borosilicates may 

actually protect concrete from further 

damage. However, time period is too 

short for significant reaction to occur.

UK Effect would require study.

T2-13 L Quantities are small. Amounts of 

precipitates are small.

PK Extent and magnitude of the effect 

would require further study.

T2-14 L Effect of H2 would be small. H2 would 

partition into the containment-building 

atmosphere, and would be relatively 

inert. Minimal effect on redox potential.

UK Effect would require evaluation under 

LOCA conditions.

T2-15 L/M Amount of organic acid would be minor, 

but possibly significant effect on surface 

reactivity.

PK Consequences would require further 

study.

T2-16 L Amount of organic acid would be minor, 

and overall effect would be small

UK If the identity and concentrations of 

organic acids are known, then the effect 

on metal solubility could be calculated.

T2-17 L/M Quantities released would be small in 

comparison with circulating volume.

PK The impact of added chemicals would 

require evaluation.
F-8

T2-18 H Precursors to nucleation and 

precipitation.

PK ICET series and associated head loss 

studies provide some information.

T2-19 L/M Co-precipitation of radionuclides could 

lead to their concentration in 

precipitates at the sump screen. 

However, radionuclide concentration is 

likely to be low.

PK Effect of co-precipitation can be 

estimated in some systems. 

Experimental studies would be required 

to determine the impact of coprecipitation in most cases.

T2-20 L Corrosion rates of Al could be enhanced 

by radiation induced elevated oxidation 

state. However, the environment is 

already oxidizing.

PK Effect would require quantification for 

specific LOCA conditions.

T2-21 M/H Could affect sump screen blockage. PK ICET series and associated head loss 

studies provide some information.

T2-22 L/M Could be significant depending on the 

design of the PWR. Short-term effects 

would be small.

PK Phenomenon needs evaluation in the 

context of a LOCA.

T2-23 M/H Settling would affect sump-screen 

blockage.

UK Effect is specific to the plant design.

T2-24 L/M Effect depends on the type and 

magnitude of organics released.

UK Depends on the conditions following a 

LOCA, and plant design.
F-9

Table F-3: Chen T2 Ranking Summary

Issue 

Number

Importance 

(H, M, L)

Rationale Knowledg

e (K, PK, 

UK)

Rationale

T2-1 L PK 

T2-2 L PK 

T2-3 M K 

T2-4 L Too short a time K 

T2-5 L Too short a time K 

T2-6 L Too short a time K 

T2-7 H This affects the amount of debris to the 

sump screen

PK 

T2-8 No 

comment

 No 

comment
F-10

T2-9 L PK 

T2-10 L PK 

T2-11 L PK 

T2-12 M PK 

T2-13 M PK 

T2-14 L PK 

T2-15 L PK 

T2-16 M PK 

T2-17 L PK 

T2-18 M PK 
F-11

T2-19 M PK 

T2-20 L PK 

T2-21 L PK 

T2-22 No 

comment

 No 

comment

T2-23 M PK 

T2-24 H PK 
F-12

Table F-4: Delegard T2 Ranking Summary

Issue 

Number

Importance 

(H, M, L)

Rationale Knowledg

e (K, PK, 

UK)

Rationale

T2-1 L H2 concentration in solution low (see T1-

5) and H2, in the absence of a catalyst 

such as platinum metal, is not a very 

effective reductant.

PK Real issue is overall Eh of system and 

this has not been measured under 

radiolytic conditions.

T2-2 H Boron has demonstrated large effect in 

ICET and other testing.

K Boron has demonstrated large effect in 

ICET and other testing.

T2-3 L H2 was already considered in T2-1; 

other constituents shown to have low 

effects in ICET.

K Already studied by ICET and other 

testing.

T2-4 H The NaOH is large contributor to pH 

balance and solute loading.

K Studied by ICET and other testing.

T2-5 M The sodium tetraborate is a large 

contributor to solutes. I downgraded 

Delegard from high to medium based on 

email stating that this issue is secondary 

in light of the others and/or because it 

has been considered in other time 

frames.

K Studied by ICET and other testing.

T2-6 H The trisodium phosphate is a large 

contributor to solutes.

K Studied by ICET and other testing.

T2-7 M Expect that the loose dust and other 

solids will be relatively small additions to 

the solids loosened by initial spray 

release.

PK Dust and loose debris loading in the 

reactor containment building not 

estimated.
F-13

T2-8 M For CO2 absorption to have a significant 

effect, it must find a Ca2+ source to react 

with. Best source is Cal-Sil. Net effect 

of reacting CO2 with Cal-Sil is 

conversion of Ca(OH)2 solids from 

dissolution/precipitation reaction of CalSil in water with dissolved CO2 to form 

CaCO3, effectively trading one finely 

particulate solid for another.

K CO2 budget in the largest reactor 

containment building is ~170 kg and 

about 50 kg in most reactor 

containments to increase the solids 

loading ~100 kg and 30 kg, 

respectively, by converting Ca(OH)2 + 

CO2 → CaCO3 + H2O. This is likely a 

small contributor to the total solids 

released and generated in a LOCA.

T2-9 H Demonstrated by ICET and other 

testing.

K Demonstrated by ICET and other 

testing.

T2-10 M These effects likely are moderate 

compared with other phenomena.

K These effects likely are already 

demonstrated by ICET and other tests.

T2-11 L Effect of turbulence is better mixing. 

This effect is also achieved by the pump 

and thus is already accounted.

K Effects of mixing built into ICET testing 

in this time frame (note, however, that 

ICET did not simulate the initial, Table 

1, high energy jet impingement).

T2-12 M Effects of borates on concrete (and 

other surfaces such as fiberglass and 

aluminum) important.

PK Lab testing began showing influence of 

boron.

T2-13 M Though title of problem mentions 

radiolysis, text describes chemical 

phenomena. Concentrations of 

dissolved Ni, Fe, and other metals in 

coolant are low and their precipitation 

will add little to the total solids budget.

PK Some phenomenological information 

exists from refueling observations.

T2-14 L The effect of H2, as mentioned in T1-5 

and T2-1, is likely to be small despite 

the additional effects of H radical 

combination of Ni or other surfaces.

PK Real issue is overall Eh of system and 

this has not been measured under 

radiolytic conditions.
F-14

T2-15 H The organic acids, in addition to 

absorbing on surfaces and engaging in 

complexation (as described by T2-16), 

also might act as surfactants to 

coagulate or agglomerate particles. 

Additional rationale in email response: 

(Organic Complexation; which is more 

aptly titled Organic Coating or 

Surfactant): I still believe the effects of 

organic decomposition products that 

deposit onto solid particles could be 

significant on solids growth, both to 

increase growth or agglomeration or 

inhibit further growth or agglomeration. 

The conditions associated with this 

phenomenon have not yet been 

investigated in sufficient detail because 

conditions leading to release of the 

organics (high-temperature water and 

radiolysis) have not yet been studied.

PK The sources of organic acids (and other 

organic species) and their effects have 

not been considered in testing to-date 

but can have large effects on the 

chemical and mechanical properties of 

the largely inorganic coolant system 

behavior.

T2-16 M See T2-15. I downgraded Delegard 

from high to medium based on email 

stating that this issue is secondary in 

light of the others and/or because it has 

been considered in other time frames.

PK See T2-15.

T2-17 M The components in the cooling lines 

may have a significant effect but their 

concentrations are small.

PK Testing needed to see if the 

components have an effect. The effects 

on chromate and molybdate on 

aluminum corrosion could be large.

T2-18 M Demonstrated by ICET and other 

testing.

K Demonstrated by ICET and other 

testing.
F-15

T2-19 M Demonstrated by ICET and other 

testing.

K Demonstrated by ICET and other 

testing.

T2-20 M The effects of radiolysis on the inorganic 

constituents likely are small but likely 

are large for the organic materials (e.g., 

paint, plastics, oils).

UK Testing needed here.

T2-21 M Demonstrated by ICET and other 

testing.

K Demonstrated by ICET and other 

testing.

T2-22 M ICET specifically avoided galvanic 

conditions.

UK Testing of galvanically coupled metals 

needed under post-LOCA conditions.

T2-23 L This actually could be a large effect but 

there does not seem to be a credible 

way to know, for the various reactor 

configurations and LOCA conditions, 

how to model the flow routing and 

catchments and weirs.

UK This potentially important phenomenon 

could afford a way to minimize solids 

transport to the sump screens and 

invites study of methods, outside of the 

scope of the chemical effects testing, to 

exploit this (e.g., “carpeting” the floor 

leading to the sump screen to snag 

solids from the coolant).

T2-24 H See T2-15. This mechanism has a 

large potential to grow solids sizes and 

block sump screen passages.

UK Testing is needed here for both raw 

organic materials (such as lubricating 

oils) and thermally and radiolytically 

degraded organic materials (e.g., 

paints, plastics).
F-16

Table F-5: Litman T2 Ranking Summary

Issue 

Number

Importance 

(H, M, L)

Rationale Knowledg

e (K, PK, 

UK)

Rationale

T2-1 L The rate of hydrogen production due to 

corrosion will decrease with time. 

Containment buildings have hydrogen 

recombiners that eliminate explosive 

potential. Most are set to start at 2% 

hydrogen in the containment 

atmosphere. This will lead to negligible 

dissolved hydrogen to affect ORP.

K Dissolved hydrogen can be calculated 

from containment pressure, % H2 and 

Henry’s Law

T2-2 M The 2800 ppm B will yield a pH of 4.5-

5.5 depending upon temperature. This 

will cause hot, acidic corrosion of metal 

components.

PK This is a plant specific parameter based 

on the components in the ZOI.

T2-3 M This will differ based on the containment 

spray systems. The TSP based spray 

will go for at least 30 minutes with no 

buffering thus pH will be 4.5-5.5; this will 

be significant. In ice condensers and 

NaOH plants the spray will be buffered.

PK This is a plant specific parameter based 

on the type of buffer system used.

T2-4 H For NaOH plants the spray will cause 

accelerated corrosion of unsubmerged 

materials. This means high dissolved 

metals content which subsequently may 

precipitate upon cooling.

K The ICET program has shown that the 

highest TDS will result from the NaOH 

spray program.

T2-5 L The STB plants will have a spray that is 

buffered at a more neutral pH.

K ICET program has shown that the least 

amount of TDS and precipitated 

materials with this spray buffer.
F-17

T2-6 H TSP containment buffer systems 

provide the highest degree of precipitate 

formation.

K The phosphates of the major metal ion 

components of insulation and corrosion 

products form insoluble precipitates. 

This adds to the mass of material that 

can potentially be transported to 

containment screens.

T2-7 L The amount of ‘loose’ debris in 

containment that could be washed into 

the sump is minimal. NRC enforces the 

amount of miscellaneous material that 

can be stored in containment, and that 

material in containment must be 

anchored.

K Each plant will have a good idea of what 

potentially will be removed as debris.

T2-8 M The carbon dioxide concentration of air 

provides an additional 69 pounds of 

insoluble material just from the 

carbonate mass. This does not include 

the counter ion and any co-precipitated 

materials.

K The maximum mass can be calculated 

based on the type of insulation.

T2-9 M The greater the mass of leached 

materials that can contribute to 

insoluble mass the more concern. CalSil and TSP are the worst combination.

K ICET program confirms that the calcium 

phosphate amorphous material provides 

the greatest impediment to flow through 

a filtering medium.

T2-10 M In the alkaline environment of all three 

buffers carbonates will precipitate. It 

appears to be most significant at pH 10 

with NaOH.

K The higher the pH the more effective 

and rapid will be the carbon dioxide 

scavenge.

T2-11 M TSP will have the most significant effect 

since the phosphate concentration will 

be relatively high at sump until the 

recirculation phase is initiated. 

Significant precipitation could occur with 

Cal-Sil if enough damage is done to 

insulation.

K The results of the ICET program confirm 

this.
F-18

T2-12 L Few areas of containment buildings are 

bare. They also have minimal surface 

area. Boric acid will neutralize the 

leached materials from bare concrete 

(which will be basic).

K pH of exposed concrete with 

demineralized water is pH 9-10.5. Boric 

acid will buffer this.

T2-13 M The presence of the insoluble CRUD at 

this phase will have significant effects. 

It will help to agglomerate other 

insoluble materials due to the density of 

this material.

K CRUD layer in PWRs is very susceptible 

to dislodging following thermo-hydraulic 

and pH transient of a reactor trip.

T2-14 L The production of hydrogen would be 

very slow. The hydrogen produced 

would not reach concentrations above 3-

4% due to hydrogen recombiners in 

containment.

K Reaction rate will be based on water in 

contact with the NiO. This is dense 

material and will precipitate. Plant 

design prevents significant hydrogen 

build up.

T2-15 L The likelihood of a large organic 

contribution to the containment volume 

is small regardless of the type of 

insulation or buffering agent. The 

radiolysis of the organics could yield 

organic acids (complexing agents) or 

carbon dioxide (precipitating agents as 

carbonates)

UK No quantitative measure can be 

ascribed to this since it depends upon 

the plant, the plant design, the particular 

organic materials that would be present 

and their susceptibility ot total or partial 

radiolysis.

T2-16 L Same as T2-15 UK Same as T2-15

T2-17 M PWRs have significantly different 

mixtures of chemicals in the component 

cooling water systems, and there are 

significant volumes of these systems in 

the containment building. At this stage 

of the event, radiolysis would not have 

taken place as these compounds would 

not have recirculated through the core.

UK No significant effects are expected in 

the short term due to the short contact 

time which would be found in the sump 

before recirculation
F-19

T2-18 M/H The conditions of polymerization for 

these materials are concentration 

dependent and pH dependent. 

Changed ranking based on following 

email from Litman: "Due to my initial 

misinterpretation of the condition I want 

to change my ratings on both from Low 

to Medium. And if I can take a page 

from Apps’s workbook both should be MH"

PK The concentrations are relatively low 

and the close to neutral pH do not 

provide optimal conditions for 

polymerization.

T2-19 L During this phase coprecipitation is not 

likely to significantly contribute since the 

leaching of the non-metallics occurs 

over a longer period of time.

PK The extent is not possible to predict 

accurately since coprecipitation not a 

thermodynamic property.

T2-20 H Peroxide production will be immediate 

following the break since all hydrogen 

control will be lost. Nickel and cobalt 

will be easily solubilized, iron will 

precipitate as iron hydroxide.

K PWR shutdown data base is an 

excellent source of information for this 

phenomenon.

T2-21 M/H During this time frame, the leaching of 

the precipitating ions from non-metallic 

components has not yet become 

significant. Fibrous materials will begin 

to collect precipitated material but there 

will not be significant amount of 

deposition. Changed ranking due to 

following email from Litman: Due to my 

initial misinterpretation of the condition I 

want to change my ratings on both from 

Low to Medium. And if I can take a 

page from Apps’s workbook both should 

be M-H.

K Results of the ICET program.
F-20

T2-22 L Galvanic corrosion effects during this 

early phase would not at all be 

significant. 

K Galvanic corrosion will not contribute 

significantly ot the mass of precipitated 

material. However, with the significant 

mass of carbon steel, zinc and 

aluminum in containment, it is possible 

that electrical isolation of these 

components will be nullified eventually 

leading to long term component 

degradation/failure.

T2-23 H The stagnant conditions that will exist 

outside the ZOI will promote settling of 

insoluble materials. Additionally, there 

are drop out areas and surfaces where 

precipitates can get trapped, minimizing 

their transport to the sump.

PK Very dependent upon plant 

configuration and materials.

T2-24 L The amount of organics introduced at 

this point is likely to be low.

UK Don’t know immediate effects of specific 

organics on this combination of 

containment chemicals.
F-21

Table F-6: MacDonald T2 Ranking Summary

Issue 

Number

Importance 

(H, M, L)

Rationale Knowledg

e (K, PK, 

UK)

Rationale
F-22

T2-1 M Hydrogen, being a reducing agent, has 

a significant impact of the redox 

potential of the containment pool and of 

wetted surfaces. The redox potential, in 

turn, determines the valency of 

corrosion products and the rates of 

corrosion of many materials. 

Consequently, characterization of 

hydrogen sources within containment in 

the event of a LOCA is vital for 

predicting the chemical environment 

that will exist in the system over the 30s 

to trecirc time frame. Initial rankings 

changed due to following email, 

rankings indicated separately: Please 

find attached a table with my reassessments of some originally "high" 

ratings of issues. On examining these 

issues again, it was evident that I did 

not fully recognize the impact of:

1. Time of exposure after the initial 

LOCA.

2. The amount of the specific material in 

the containment (e.g., zinc).

My re-assessments also reflect the 

results of continuing radiolysis 

modeling, albeit with less-than-optimal 

codes that have been jerry-rigged from 

our reactor modeling work. 

Nevertheless, if the fields are as high as 

Bob indicates, the eventual production 

of nitric acid, in addition to the elevation 

of the redox potential, becomes a 

critical issue.

K The principal sources of hydrogen are 

the inventory in the primary coolant prior 

to the break and corrosion of the highly 

reactive metals (e.g., Al and possibly 

Zn, but not Fe, Cu, Pb, or the stainless 

steels or nickel alloys). Hydrogen may 

also be generated by the Schikorr 

reaction from precipitated ferrous 

hydroxide [3Fe(OH)2 à Fe3O4 + 2H2O + 

H2] and from radiolysis, although the 

relative importance of these sources is 

difficult to predict in a general sense. 

Nevertheless, the kinetics of hydrogen 

release from these various sources are 

well-defined.
F-23

T2-2 M The injection of boric acid of 2800ppm 

concentration (B) is not likely to cause 

ant significant swings in pH of the 

containment pool and hence is not likely 

to significantly affect the corrosivity of 

the pool environment. A possible 

exception is if the boric acid solution 

evaporates in contact with hot fuel to 

form a concentrated, highly corrosive 

wet boric acid melt.

K The impact that boric acid will have on 

the pH of the containment pool is readily 

calculated if the pool components prior 

to the addition can be reasonably 

defined.

T2-3 M Containment spray will contact many 

surfaces after a LOCA and the impact 

that it will have on the corrosion of those 

surfaces may affect the total inventory 

of debris. However, the lowest pH (4.5-

5) is similar to that of acid rain, and 

recognizing that many of the surfaces 

are protected by paint or other coatings, 

it is posited that little damage will occur 

in the time-frame of 30s to trecirc time 

frame.

K Extensive work has been reported on 

the corrosion of materials, including 

painted metals and alloys, under acid 

rain conditions, so that the inventory of 

corrosion products that might be 

generated from this source can be 

estimated. High pH spray (NaOH, pH 

=8.5-10.5) will not significantly impact 

Fe, Ni-based alloys, Cu, Pb, or alloys, 

such as the stainless steels. However, 

the upper end of the pH range may 

significantly enhance the corrosion of 

unprotected Al. Sufficient data are 

available in the literature to ascertain 

the magnitude of the impact.

T2-4 M See T2-3. K See T2-3.
F-24

T2-5 M Sodium tetra borate (Na2B4O7) is a 

buffering agent that is released with ice 

in containment during a LOCA, with the 

specific purpose of pH-buffering the 

pool contents. However, much of the 

required buffering capacity is already 

provided by the coolant boric acid and 

the ECCS boric acid.

K The impact that sodium tetra borate 

(STB) will have on the pH of the 

containment pool is readily calculated if 

the pool components prior to the 

addition can be reasonably defined.

T2-6 M Tri sodium phosphate (Na3PO4) is a 

buffering agent that is released from 

baskets on the containment floor during 

a LOCA with the specific purpose of pHbuffering the pool contents. However, 

much of the required buffering capacity 

is already provided by the coolant boric 

acid and the ECCS boric acid.

K The impact that tri sodium phosphate 

(TSB) will have on the pH of the 

containment pool is readily calculated if 

the pool components prior to the 

addition can be reasonably defined.

T2-7 H The amount of debris that is washed 

into the containment pool will critically 

affect the tendency of the pump screens 

to clog.

UK Depends on the design of the system, 

the inventory of “loose material to begin 

with, and the inventory of material 

produced during the first 30s of the 

LOCA. Likely to be difficult to predict 

with reasonable accuracy.

T2-8 M Absorption of CO2 from the containment 

atmosphere might lead to the 

precipitation of carbonate solids (e.g., 

CaCO3). The inventory of CaCO3 that 

might result is predicted to be several 

hundred kilograms, which could 

represent a sufficiently high amount to 

clog the filters.

K The maximum possible inventory of 

CaCO3 is readily calculated from the 

volume of air in containment and the 

concentration of Ca2+ in and the volume 

of the containment pool contents.
F-25

T2-9 H Debris dissolution will determine the 

total inventory of solid material in the 

containment pool. Furthermore, the 

dissolved species may react and coprecipitate among themselves to form 

new, solid phases that were not 

originally in the pool.

PK Because the pool environment is 

chemically very complex, and because 

dissolution experiments have generally 

been reported only for much simpler 

systems, it is not clear how applicable 

the current experimental database is to 

this problem.

T2-10 M The creation of CaCO3 nuclei for the 

precipitation of other solid phases is a 

matter of great importance in this early 

time frame, as precipitation is expected 

to contribute substantially to the total 

solid phase inventory in the pool. 

Initial rankings changed due to following 

email, rankings indicated separately: 

Please find attached a table with my reassessments of some originally "high" 

ratings of issues. On examining these 

issues again, it was evident that I did 

not fully recognize the impact of:

1. Time of exposure after the initial 

LOCA.

2. The amount of the specific material in 

the containment (e.g., zinc).

My re-assessments also reflect the 

results of continuing radiolysis 

modeling, albeit with less-than-optimal 

codes that have been jerry-rigged from 

our reactor modeling work. 

Nevertheless, if the fields are as high as 

Bob indicates, the eventual production 

of nitric acid, in addition to the elevation 

of the redox potential, becomes a 

critical issue.

PK The precipitation of CaCO3 has been 

studied extensively in the petroleum and 

marine industries, so that the basic 

physical chemistry of the formation of 

carbonate nuclei is well understood. 

However, the kinetics of formation of the 

nuclei are sensitive to the presence of 

various surfactants (e.g., organic acids 

and amines), which may derive from the 

decomposition of insulation, paint, and 

coatings, for example.
F-26

T2-11 H Intense mixing enhances mass transfer 

effects, which, in turn, affects the rates 

of processes such as dissolution 

(including CO2 solution), precipitation, 

and coagulation, all of which impact the 

total solids inventory in the containment 

pool.

PK The basic impact of agitation and mass 

transfer on the kinetics of dissolution, 

solution, precipitation, and to a lesser 

extent coagulation, is fairly well 

understood in general terms, but their 

magnitudes are sensitive to geometrical 

and surface (e.g., presence of 

precipitates) effects. Accordingly, 

mixing effects tend to be highly specific 

to the system under consideration. The 

good news is that powerful finite 

element codes are available for 

predicting mass transfer effects in 

complex geometries.
F-27

T2-12 L Corrosion of concrete by boric acid will 

add to the dissolved species inventory 

in the pool and may lead to the spalling 

of solid concrete. The dissolved 

species may react with other species in 

the pool to precipitate additional solid 

phases that may clog the pump screens 

and the spalled concrete will add to the 

total mobile solids inventory in the pool. 

Initial rankings changed due to following 

email, rankings indicated separately: 

Please find attached a table with my reassessments of some originally "high" 

ratings of issues. On examining these 

issues again, it was evident that I did 

not fully recognize the impact of:

1. Time of exposure after the initial 

LOCA.

2. The amount of the specific material in 

the containment (e.g., zinc).

My re-assessments also reflect the 

results of continuing radiolysis 

modeling, albeit with less-than-optimal 

codes that have been jerry-rigged from 

our reactor modeling work. 

Nevertheless, if the fields are as high as 

Bob indicates, the eventual production 

of nitric acid, in addition to the elevation 

of the redox potential, becomes a 

critical issue.

UK Little appears to be known of the 

corrosion of concrete by boric acid, in 

terms of either the kinetics or the solid 

phases that eventually form.
F-28

T2-13 H Radioactive iosotopes of Fe, Ni, and 

other metals that are ejected from the 

LOCA break in the form of spalled oxide 

particles will eventually find their way 

into the containment pool. The resulting 

radiolysis of water will lead to an 

increase the redox potential, which in 

turn will considerably affect the 

chemistry of the pool environment.

PK While the radiolysis of water can be 

effectively modeled, provided that the 

dose rate can be defined, the processes 

whereby particles of oxide are 

transported within the pool are less well 

understood or defined. Previous work 

on the transport of silt in water supply 

systems may provide a useful basis for 

describing these processes.

T2-14 M If NiO (or other oxides) catalyze the 

production of hydrogen from the 

radiolysis of water, it could have a 

significant impact on the redox potential. 

However, the stoichiometry of the 

overall reaction is such that catalysis 

should also occur in the production of 

oxidizing species, with the net effect 

possibly being moot.

UK If NiO does catalyze the production of 

H2 via the radiolysis of water, the effect 

on the redox potential can be readily 

calculated using the Mixed Potential 

Model. However, as search of the 

literature failed to yield any data or 

reported observations in support to this 

postulate.

T2-15 M Complexing between metal ions and 

certain organic molecules (amines, 

acids, and heterocycles) is well-known 

and would generally increase the 

solubility of solids. Thus, solubility 

products may not be exceeded and 

hence certain solid phases may not 

form when they would form in the 

absence of complexing.

K Large databases exist on the stability 

constants for a wide range of complexes 

between metal cations and organic 

species.

T2-16 M Organic sequestration is the process 

whereby metal ions absorb into organic 

phases, most notably into ion exchange 

materials.

K Large databases exist on the ion 

exchange capacities of a wide range of 

organic polymers containing ion 

exchange groups.
F-29

T2-17 M Auxiliary component cooling line failure 

resulting in the release of oxidizing 

species (chromate, molybdate) and 

organic species (nitrites, hydrazine, 

tolytriazole, benzotriazole) could have a 

very significant effect of the chemistry of 

the containment pool and hence could 

lead to the formation of new solids. 

Initial rankings changed due to following 

email, rankings indicated separately: 

Please find attached a table with my reassessments of some originally "high" 

ratings of issues. On examining these 

issues again, it was evident that I did 

not fully recognize the impact of:

1. Time of exposure after the initial 

LOCA.

2. The amount of the specific material in 

the containment (e.g., zinc).

My re-assessments also reflect the 

results of continuing radiolysis 

modeling, albeit with less-than-optimal 

codes that have been jerry-rigged from 

our reactor modeling work. 

Nevertheless, if the fields are as high as 

Bob indicates, the eventual production 

of nitric acid, in addition to the elevation 

of the redox potential, becomes a 

critical issue.

PK In principle, the impact that oxidizing 

and reducing agents will have upon the 

redox potential and hence upon the 

tendency for high valency precipitates to 

form [e.g., Fe(OH)3 versus Fe(OH)3] 

can be estimated using the mixed 

potential model (MPM), but only if 

exchange current density and transfer 

coefficient data are available for the 

redox reactions. Corrosion rates may 

also be effected, but we note that the 

triazoles are effective corrosion 

inhibitors, particularly of the corrosion of 

copper and copper alloys.
F-30

T2-18 H Polymerization is the process by which 

hydrolyzed cations form a precipitated 

solid, generally via colloids. This 

process of precipitation is welldocumented and understood and is 

expected to be a principal mechanism 

for the formation of solids in the 

containment pool.

PK Extensive data are available for the 

hydrolysis and precipitation of solids 

from solutions containing simple 

cations, such as Al3+ and Fe3+, but few 

data are available for more complex 

systems (e.g., precipitation of aluminosilicates). Provided that chemical 

potential data for the initial state 

(“reactants”) and the final state (the 

precipitate) are available, the Gibbs 

energy minimization technique for 

calculating the system composition at 

equilibrium is most useful, because the 

properties of intermediate species need 

not be known.
F-31

T2-19 M Co-precipitation is the process whereby 

a carrier precipitated phase carries 

down species that would not ordinarily 

form precipitates under the prevailing 

conditions. Co-precipitation can greatly 

increase the volume of a precipitate that 

may form and hence could lead to 

clogging of the pump screens. Initial 

rankings changed due to following 

email, rankings indicated separately: 

Please find attached a table with my reassessments of some originally "high" 

ratings of issues. On examining these 

issues again, it was evident that I did 

not fully recognize the impact of:

1. Time of exposure after the initial 

LOCA.

2. The amount of the specific material in 

the containment (e.g., zinc).

My re-assessments also reflect the 

results of continuing radiolysis 

modeling, albeit with less-than-optimal 

codes that have been jerry-rigged from 

our reactor modeling work. 

Nevertheless, if the fields are as high as 

Bob indicates, the eventual production 

of nitric acid, in addition to the elevation 

of the redox potential, becomes a 

critical issue.

PK Although co-precipitation has been 

extensively studied in analytical 

chemistry, radio chemistry, and in 

product purification and separation 

technology, the work is largely empirical 

in nature and has been performed on 

relatively simple systems (e.g., coprecipitation of radium with barium 

sulfate). The theoretical base is 

insufficiently well-developed to predict 

co-precipitation phenomena in the 

complex systems of interest in a LOCA.
F-32

T2-20 H Water radiolysis produces a variety of 

oxidizing (O2, H2O2, OH) and reducing 

(H2, H, O2

-

, etc) species in nonequilibrium concentrations. These 

species establish the redox potential of 

the environment, which determines the 

tendency for oxidation and reduction 

reactions to occur. Accordingly, water 

radiolysis can have an important impact 

of the chemistry of the pool.

K The radiolysis of water has been 

modeled extensively in nuclear reactor 

technology to estimate the 

concentrations of the principal radiolysis 

products. These concentrations can 

then be used in Mixed Potential Models 

to estimate the redox potential and the 

corrosion potentials of various metals 

and alloys. The corrosion potentials can 

then be used to estimate the general 

corrosion rates and the susceptibilities 

of the metals and alloys to localized 

corrosion processes using the Point 

Defect Model.

T2-21 H Inorganic agglomeration is the process 

whereby colloidal particles (1-100nm in 

diameter) that are formed by cation 

polymerization (see T2-18) come 

together to form larger particles and 

eventually precipitates.

PK Destabilization of colloidal systems 

(“solutions”), usually by increasing the 

ionic strength of the solution, which 

shrinks the thickness of the diffuse layer 

and allows attractive van der Waal 

forces to cause the particles to 

agglomerate, is a well-understood 

phenomenon. However, it is also 

physically complex, particularly for the 

multi-component systems of interest in 

this study. Even with an extensively 

developed theoretical base, it is doubtful 

that meaningful predictions can be 

made.

T2-22 M Galvanic coupling between metals that 

are widely separated in the 

electrochemical series (e.g., Al-Cu, Alstainless steel) enhances the corrosion 

rate of the more active component.

K Galvanic corrosion has been studied 

extensively and is well-understood. The 

process can be modeled using a variant 

of the Mixed Potential Model and the 

corrosion rates of both components of 

the couple can be effectively calculated.
F-33

T2-23 H Deposition and settling are the final 

processes in the precipitation process. 

Settling occurs when the mass of a 

particle becomes so large that it cannot 

be maintained in suspension by 

Brownian motion.

K By knowing the particle density and 

volume, and hence mass, it is possible 

tp predict the maximum size that will 

remain in suspension. However, 

various surfactants, some of which may 

be present in the pool, are known to 

prevent settling/deposition. The 

scientific literature on soaps and 

detergents provides a wealth of 

information on this subject.

T2-24 H Organic agglomeration is the process 

whereby organic colloidal particles (1-

100nm in diameter) that are formed by 

hydrophilic micellation (cf T2-21) come 

together to form larger particles and 

eventually precipitates.

PK Destabilization of organic colloidal 

systems (“solutions”), usually by 

decreasing the pH of the solution, so as 

to protonate the acid groups and hence 

annihilate the repulsive surface charge, 

allows attractive van der Waal forces to 

cause the particles to agglomerate. 

This process is a well-understood 

phenomenon. However, it is also 

physically complex, particularly for the 

multi-component systems of interest in 

this study. Even with an extensively 

developed theoretical base, as with 

inorganic agglomeration (T2-21), it is 

doubtful that meaningful predictions can 

be made.
APPENDIX G

PIRT Panelist Evaluations of T3 Phenomena:

ECCS Recirculation from onset of Recirculation until 

24 hours into LOCA
Table G-1: ECCS Recirculation (trecirc to 24 hours)a,b

Issue 

Number

Phenomena Description Implications

T3-1 TSP pH control Contained in basket on containment floor that 

dissolve

Slightly alkaline containment pool environment (pH = 7 

– 8); all TSP dissolved within 1 to 4 hours post LOCA.

T3-2 NaOH pH 

control

NaOH injected through containment sprays. Alkaline containment pool environment (pH = 8.5 – 

10.5); pH buffering completed typically within 4 hours.

T3-3 STB pH control Released with ice in containment during a 

LOCA

Alkaline containment pool environment (pH = 8 – 9); all 

STB should be introduced within a few hours.

T3-4 NaOH Injection NaOH, B laden spray impinges on material 

surfaces

1. Solution may accelerate corrosion of 

metallic/non-metallic surfaces due to high pH, boron 

concentration.

2. Solution may inhibit corrosion by formation of 

an initial passive layer impervious to future 

corrosion.

T3-5 Cable 

degradation

The insulation surrounding electrical cables 

located throughout containment is affected by 

radiolysis, releasing chlorides.

The chlorides affect radiolysis and ionic strength of 

containment pool environment.

T3-6 Radiolytic 

environment

Radiolysis reaction changes solution’s redox 

potential; H2, O2, and H2O2 balance; peroxide 

formation occurring during this time frame.

Could affect chemistry in containment pool which 

affects species which form - most important for 

determining redox potential (e.g., Hanford tank: 

mixture of different components @ different phases)

T3-7 Fiberglass 

leaching

Fiberglass-based insulation products begin 

leaching constituents; e.g., Si, Al, Mg, Ca, 

etc.

Dissolution source term for producing ions which 

contribute to containment pool chemistry.

T3-8 Secondary 

system 

Contamination

SG tube rupture leads to secondary side 

chemicals being added to containment pool.

1. Possible additional source for organic materials 

which could delay precipitation through complexation 

or by sequestering metal ions.

2. Could accelerate material corrosion.

T3-9 Flow-induced 

nucleationc

Nucleation sites created from cavitation, 

deareation, air entrainment, turbulence 

(attachment opportunity)

Increases possibility of precipitation/chemical species 

formation
G-3

T3-10 Turbulent 

mixingc

Turbulence in containment pool (such as 

directly under the break) either inhibits or 

promotes precipitate formation and growth

1. Could inhibit growth due to turbulent shear forces 

which don’t allow solid species to agglomerate.

2. Could promote formation and growth by providing 

more opportunity for particles to collide and 

overcome diffusion.

3. Affects the solid species concentration within the 

containment pool which could contribute to head 

loss & other ECCS performance degradation.

T3-11 Quiescent 

settling of 

precipitatec

Quiescent flow regions within containment 

pool promote settling

Little flow allows larger size, more stable 

particles/precipitates to form which promotes settling.

T3-12 Electrostatic 

scavenging

Material surfaces electrostatically attract 

particles and lead to 

deposition/agglomeration on the surface; thin 

accumulation limited to 2 to 3 layers of 

material. It is a function of solution PZC and 

surface and particle charges.

1. Provides a mechanism for retaining chemical 

products either in benign areas (e.g., walls, 

surfaces) or in areas that may impact system 

performance (e.g., sump screen, pipe internals).

2. Surface layer either inhibits or enhances material 

corrosion.

T3-13 Chemically 

induced 

settling

Chemical species attach to or coat particulate 

debris which leads to settling. Examples are 

Al coating on Nukon fiber shifting the PZC, or 

formation of a hydrophobic organic coating

Results in less particulate debris and chemical product 

transporting to and either accumulating on or passing 

through the sump screen.

T3-14 Agglomeration 

& Coagulation

Formation of larger clumps of smaller 

particulates: Depends on PZC; ionic strength 

(the higher the strength the smaller the 

distance for agglomeration); sensitive to 

many factors including shape factors, 

maximum particle size.

1. May be necessary to form large enough particles to 

result in tangible effects on ECCS performance

2. Can occur quickly if conditions are right.

3. Existence of organic species can decrease 

likelihood

T3-15 Particulate 

nucleation 

sites

Particles within containment create 

nucleation sites for chemical precipitation: 

examples include radiation tracks; dirt 

particles; coating debris; insulation debris; 

biological debris, etc.

Environment is created which foster formation of solid 

species that could lead to ECCS degradation.
G-4

T3-16 Additional 

debris bed 

chemical 

reactions

Concentration of radionuclides (100’s of 

Curies available) acts as a “resin bed” or 

chemical reactor. A number of possible 

reactions occur.

1. Hydrogen peroxide formation

Fe+2 → Fe+3 2. increase due to increase in redox 

potential;

3. Organic materials decompose

4. possible coating of NUKON to reduce solubility; 

glass embrittlement (shorter fiber);

T3-17 Sump screen: 

high localized 

chemical 

concentrations

High localized concentrations of certain 

species drive the reaction efficiency at the 

sump screen

1. Effect could be at the exterior surface of insoluble 

materials, the internal interstitial void material, or 

both

2. Possible effect on the chemical species which form 

within the sump screen bed.

T3-18 Sump screen: 

fiberglass 

morphology

Localized chemistry alters the fiberglass 

contribution to the chemical environment

1. Possible coating of fiberglass fibers reduces 

leaching/solubility.

2. Radiation leads to glass embrittlement; shorter 

fibers form which can pack more densely (increase 

head loss) and provide additional surface area for 

leaching/reactions.

T3-19 ECCS pump: 

seal abrasion 

Abrasive wearing of pump seals (e.g., 

magnetite - high volume/concentration of mild 

abrasive) creates additional materials that 

contribute to sump pool chemistry.

1. Additional particles that may contribute to reactor 

core clogging

2. Particles may add additional sump screen loading.

3. Particles may affect chemical species formation.

T3-20 Heat 

exchanger: 

solid species 

formation

Concentrations/species that are soluble at 

the containment pool temperature precipitate 

at lower (ΔT~15-20C) heat exchanger outlet 

temperature.

1. Species remain insoluble at higher reactor 

temperatures and affect ability to cool the reactor 

core.

2. Species remain insoluble at higher containment 

pool temperatures and cause additional head loss 

upon recirculation.

T3-21 Heat 

exchanger: 

deposition & 

clogging

Solid species which form in the heat 

exchanger lead to surface deposition and/or 

clogging within closs-packed head exchanger 

tubes (5/8” diam.)

1. Severe clogging/deposition causes flow decrease 

through heat exchanger core and an inability to cool 

reactor core.

2. Less severe deposition may degrade heat transfer 

and degrade heat flow from the reactor core.
G-5

T3-22 Reactor core: 

fuel deposition

ΔT increase (+70C from sump pool) and 

retrograde solubility of some species (e.g., 

Ca silicate, Ca carbonate, zeolite, sodium 

calcium aluminate) causes scale, build-up on 

reactor core

1. Decreases heat conduction values from fuel.

2. Localized boiling occurs due to insufficient heat 

removal.

3. Deposits spall off, creating additional debris 

source.

T3-23 Reactor core: 

hydrogen 

increases

H2 builds up in from cladding oxidation Affe 1. ct redox potential and chemical environment.

2. Increases containment hydrogen concentration; 

may lead to conflagration.

T3-24 Reactor core: 

diminished 

heat transfer

Insulation debris and chemical products 

mixed within water cause a reduction in the 

effective heat transfer capabilities (Cp) of 

mixture. The precipitation of this material is 

initiated in RHR heat exchanger.

Ability to remove heat from the fuel is diminished.

T3-25 Reactor Core: 

Blocking of 

flow passages

Chemical products, in combination with other 

debris, blocks primary flow passages for 

getting cooling water through core

Heat transfer may be impeded; flow is forced to 

bypass the lower plenum debris screens

T3-26 Reactor Core: 

Particulate 

settling

Particulate settling occurs due to relatively 

low, upwards flow (for cold leg injection) 

within reactor

Compacted deposits forms which may impede heat 

transfer and water flow, especially for lower portions of 

reactor fuel.

T3-27 Reactor Core: 

Precipitation

ΔT increase (+70C from sump pool) and 

retrograde solubility of some species (e.g., 

Ca silicate, Ca carbonate, zeolite, sodium 

calcium aluminate) causes precipitation, 

additional chemical product formation

1. Products contribute to debris in reactor core which 

blocks flow passages, impedes heat transfer.

2. Additional precipitate is created which travels to 

the sump screen and leads to head loss.

T3-28 Exposed, 

Uncoated 

Concrete 

Dissolution

Dissolution can result in pH increases 

(depending on surface area) up to 10.5 below 

concrete surface relatively quickly.

1. This could result in pH increase in containment 

pool over time.

2. Leaching of concrete elements (e.g., Ca, Si, etc.) 

into containment pool.

T3-29 Coatings 

Dissolution

Dissolution/leaching of epoxy, alkyd, or zincbased coatings and primers occurs1. Additional source term for products affecting 

the containment pool chemistry.

2. Chlorides affect radiolysis and ionic strength of 

containment pool environment.
G-6

T3-30 Boric Acid 

Corrosion

Concentrated boric acid pooled on 

unsubmerged portions of large ferritic steel 

components (e.g., piping RPV, pressurizer, 

steam generator) continues to cause 

corrosion of these materials.

1. Contribute additional Fe ions which may be 

transported to containment pool.

2. Could affect coprecipitation and solid species 

concentrations 

3. May lead to long-term structural weakness if 

severe. 

T3-31 CO2/Carbonate 

Radiolysis

Radiolysis of CO2 and carbonates could lead 

to the formation of organic acid ligands (e.g., 

acetate, butyrate, oxalate) This is observed 

during the leaching of spent fuel by 

groundwaters containing bicarbonate ions

1. Phenomena would complex metal species in 

solution, thereby enhancing dissolution rates and 

diminishing the precipitation of phases containing 

these complexed species.

2. Could occur within containment pool, reactor 

vessel, or within the sump screen debris bed. a Sump pool temperatures are expected to range between 50 – 90C during this time period.

b Phenomena listed in earlier time periods (i.e., T1, T2) may continue to be active or important during this time. c

Bulk flow velocities = 0.005 ft/s to 0.1 ft/s (0.15 – 3 cm/s)
G-7

Table G-2: Apps T3 Ranking Summary

Issue 

Number

Importance 

(H, M, L)

Rationale Knowledg

e (K, PK, 

UK)

Rationale

T3-1 L Rate of dissolution of TSP will have only 

a transient affect on coolant chemistry.

PK Effect would be specific to the type of 

LOCA and plant design.

T3-2 H Major effect on coolant composition. K Plant operating parameters well known.

T3-3 H Major effect on coolant composition. K ICET series provides some information.

T3-4 L/M Effect is transient. PK ICET series provides some information.

T3-5 L Quantities are small and the system is 

pH buffered.

PK Extent of degradation can be estimated.

T3-6 L/M Some impact on corrosion. PK Specific impact on corrosion requires 

study.

T3-7 M Fiberglass leaching is not extensive 

during the time frame in question.

K ICET series and supplementary lab 

studies provide quantitative information.

T3-8 L/M Volume of contaminants not expected to 

be large.

UK Impact would be LOCA and plant 

specific. Effect of chemistry has not 

been evaluated.
G-8

T3-9 L/M Effect depends on the extent of reaction 

and supersaturation. Likely to 

accelerate rates rather than change 

eventual outcome.

UK Impact would be LOCA and plant 

specific. Additional study would be 

required.

T3-10 L/M Effect depends on the extent of reaction 

and supersaturation. Likely to 

accelerate rates rather than change 

eventual outcome.

UK Impact would be LOCA and plant 

specific. Additional study would be 

required.

T3-11 M Precipitates would not affect sump 

screen performance.

UK Impact would be LOCA and plant 

specific. Additional study would be 

required.

T3-12 L Total amount of material immobilized 

would be small. Could favorably affect 

passivation.

UK Impact would require evaluation and 

experimental study.

T3-13 M/H Adsorption or coating could inhibit 

further reaction.

PK Experiments have already been 

performed in support of the ICET series

T3-14 M/H Could impact sump screen blockage. PK Experiments have already been 

performed in support of the ICET and 

head loss test series

T3-15 M Effect is important, but will happen in 

any case.

UK Very difficult to quantify. Uncontrolled.

T3-16 L/M Overall impact not expected to be great. UK Magnitude and extent of the effect is 

unknown, and would require further 

study.

T3-17 L Chemical reactions within the sump 

screen bed are expected to be 

secondary.

UK Would require further study.
G-9

T3-18 L Effect is likely to be minor during the 

initial 24 hr.

PK ICET series provides some indications 

of the significance of this phenomenon.

T3-19 L Amount of material generated would be 

very small. Pump design should 

prevent this from happening, or at least 

mitigate any effect.

UK Would require characterization.

T3-20 M Potentially adverse effect on cooling. PK Effect could be calculated, but 

experimental verification would be 

required.

T3-21 M/H Potentially serious adverse effect on 

cooling.

PK Effect could be calculated, but 

experimental verification would be 

required.

T3-22 M/H Potentially serious adverse effect on 

cooling.

PK Effect could be calculated, but 

experimental verification would be 

required.

T3-23 L Cooling decreases the rate of 

hydrolysis. Hydrogen would partition 

into the containment-building 

atmosphere become relatively inert.

PK Kinetics should be available to calculate 

the effect as a function of temperature.

T3-24 M/H Adverse effect on core cooling, and 

potential damage.

UK Effects depend on many unknown 

factors. Tests and modeling would be 

required.

T3-25 M/H Adverse effect on core cooling, and 

potential damage.

UK Effects depend on many unknown 

factors. Tests and modeling would be 

required.

T3-26 M/H Adverse effect on core cooling, and 

potential damage.

UK Hydrodynamic calculations would permit 

estimates to be made of material 

settling in terms of amount and location.
G-10

T3-27 M/H Adverse effect on core cooling, and 

potential damage.

PK Kinetics of precipitation should be 

available to allow calculation of amount.

T3-28 L Effect minimized by diffusion and low 

exposed surface area. pH is buffered.

PK Information to quantify this effect is 

probably available in the literature.

T3-29 L Most coatings will be resistant to 

dissolution. Dissolved products would 

be minor in amount.

PK Information to quantify this effect is 

probably available in the literature.

T3-30 L/M Products unlikely to have a major effect 

on corrosion or sump screen blocking. 

Unlikely to cause structural damage 

within first 24 hr.

PK ICET series provide some information.

T3-31 L Effect would be small because of 

relatively low carbonate concentration.

PK Information on radiolysis of carbonate 

probably available to allow calculation of 

the magnitude of the effect.
G-11

Table G-3: Chen T3 Ranking Summary

Issue 

Number

Importance 

(H, M, L)

Rationale Knowledg

e (K, PK, 

UK)

Rationale

T3-1 M K 

T3-2 M K 

T3-3 M K 

T3-4 L PK 

T3-5 No 

comment

 No 

comment

T3-6 M PK 

T3-7 M K 

T3-8 L PK 
G-12

T3-9 L PK 

T3-10 M PK 

T3-11 H K 

T3-12 L PK 

T3-13 L PK 

T3-14 H PK 

T3-15 L UK 

T3-16 L UK 

T3-17 L too low a residence time PK 

T3-18 L should be the same anywhere in the 

sump

PK 
G-13

T3-19 L not likely to add significant amount of 

solids into the system

K 

T3-20 L not enough time K 

T3-21 L not enough time K 

T3-22 L not enough time K 

T3-23 No 

comment

 No 

comment

T3-24 L does not affect solid formation K 

T3-25 M if a piece of large debri goes into core K 

T3-26 L K 

T3-27 M PK 

T3-28 M PK 
G-14

T3-29 L unlikely to form solids UK 

T3-30 L PK 

T3-31 No 

comment

 No 

comment
G-15

Table G-4: Delegard T3 Ranking Summary

Issue 

Number

Importance 

(H, M, L)

Rationale Knowledg

e (K, PK, 

UK)

Rationale

T3-1 H The trisodium phosphate is a large 

contributor to solutes. Additional 

rationale provided in email: The effects 

on solids formation are demonstrably 

large, and within this ~30 second to 30 

minute time frame, as the phosphate 

combines with calcium to form the 

calcium phosphate precipitate that the 

"Head Loss Testing" found to be so 

effective in stopping flow.

K Studied by ICET and other testing.

T3-2 H The NaOH is large contributor to pH 

balance and solute loading.

K Studied by ICET and other testing.

T3-3 H The sodium tetraborate is a large 

contributor to solutes.

K Studied by ICET and other testing.

T3-4 M Shown by ICET and other testing to 

contribute to aluminum corrosion. I 

downgraded Delegard from high to 

medium based on email stating that this 

issue is secondary in light of the others 

and/or because it has been considered 

in other time frames.

K Studied by ICET and other testing.

T3-5 M Cable (insulation) important under 

thermal and radiolytic conditions.

UK Needs testing; see T2-15 and T2-24.

T3-6 H Of most importance for organic 

materials.

UK Needs testing. See T2-20.
G-16

T3-7 M ICET and other testing showed these 

effects.

K Studied by ICET and other testing.

T3-8 M See T2-17. The components in the 

cooling lines may have a significant 

effect but their concentrations are small.

PK Testing needed to see if the 

components have an effect. The 

effects on chromate and molybdate on 

aluminum corrosion could be large.

T3-9 L The conditions of flow to affect 

nucleation were tested by ICET.

K Studied by ICET.

T3-10 M The effects of turbulence were tested by 

ICET. See T2-11.

K Studied by ICET.

T3-11 M This does not lend itself to chemical 

effects testing.

UK This phenomenon could be exploited by 

design of, effectively, cascade settlers 

in the floor of the containment building. 

This, however, seems to be outside the 

scope of the chemical testing.

T3-12 L These phenomena (electrostatic 

scavenging, chemically induced settling, 

agglomeration/coagulation, and 

particulate nucleation sites) are potential 

explanations of observed behaviors but 

are not, in themselves, unexamined 

chemical / physical variables in the postLOCA environment.

PK These phenomena and mechanisms 

should be considered to explain the 

observations from testing.

T3-13 L PK

T3-14 L PK

T3-15 L K
G-17

T3-16 M Radiation fields at the sump screen 

could be enough to harden and crosslink 

organic materials.

UK Testing of the effects of high radiation 

fields needed for sump screen beds. 

Effects expected to be higher for the 

organic materials.

T3-17 M These effects were studied in ICET and 

head loss tests.

PK Such conditions were investigated in 

ICET and head loss testing.

T3-18 M This is a subset of T3-16. UK Testing in radiation field needed.

T3-19 H The contribution of solids eroded from 

the pump seals to the total solids budget 

is minor. However, the failure of the 

recirc pumps would be disastrous.

UK The effects of the recirculating 

suspended solids on the integrity of the 

pumps require testing or at least 

evaluation by pump engineers.

T3-20 H Effects of solids deposition (by solubility 

and caking) on cool surfaces potentially 

can build large particles for transport 

and blockage of sump screen.

UK The effects of cooler surfaces on the 

behavior of the recirculating coolant 

were not examined in testing to-date.

T3-21 H UK

T3-22 H UK

T3-23 L H2 disengages rapidly from hot water 

and is unlikely to affect redox chemistry 

greatly. See T2-1.

PK Real issue is overall Eh of system and 

this has not been measured under 

radiolytic conditions.

T3-24 H These three phenomena could affect 

fuel integrity and cause fuel cladding 

failure. This would increase solids 

loading in the coolant system and hence 

blockage of the sump screen as well as 

increase the radiolytic exposure to the 

post-LOCA environment. The UO2, 

should it escape from the fuel c

ladding, is also very hard and a

brasive and could cause earlier failure of 

pump seals and bearings.

UK Engineering evaluations may be 

sufficient to assess the impact of solids 

deposition and loading of the core 

thermal and hydraulic transfer.
G-18

T3-25 H UK

T3-26 H UK

T3-27 H Effects of solids deposition (by 

retrograde solubility, solvent 

evaporation, or caking) on hot core 

surfaces potentially can build large 

particles for transport and blockage of 

sump screen. Note that borate 

deposition also can increase metal 

attack.

UK The effects of hotter surfaces on the 

behavior of the recirculating coolant 

were not examined in testing to-date.

T3-28 M This phenomenon, though important, 

has been considered in ICET and other 

testing.

K Studied by ICET and other testing.

T3-29 M The decomposition of coatings (e.g., 

paints and electrical insulation) by 

thermolysis and radiolysis, can steeply 

exacerbate solids loading on the sump 

screens. See T2-24. I downgraded 

Delegard from high to medium based on 

email stating that this issue is secondary 

in light of the others and/or because it 

has been considered in other time 

frames.

UK Testing is needed here for both raw 

organic materials (such as lubricating 

oils) and thermally and radiolytically 

degraded organic materials (e.g., 

paints, plastics) to assess their potential 

to agglomerate small sized solids.

T3-30 M Borates at high temperatures are used 

to digest minerals in chemical assay. 

Their effects on hot and unwetted metal 

could be severe.

PK The attack of borates on unwetted 

metal coupons should be tested.
G-19

T3-31 L Free carbonate concentrations likely will 

be low in this calcium-rich coolant 

system.

UK Testing of this mechanism can be part 

of the larger suite of tests on the effects 

of radiolysis in the coolant system.
G-20

Table G-5: Litman T3 Ranking Summary

Issue 

Number

Importance 

(H, M, L)

Rationale Knowledg

e (K, PK, 

UK)

Rationale

T3-1 L TSP will provide adequate buffering 

capacity for the entire fluid volume 

within about 2 hours.

K Based on the system design. The 

recirculation flow rates and volumes 

provide for a 400,000 gallon turnover at 

a minimum of 6,000 gpm of two 

volumes in two hours.

T3-2 L pH in the spray will be at pH 9.5 

immediately upon commencement of 

spray. Water in sump will be at pH of 

9.5 within the next hour (even before 

recirculation begins).

K Based on the system design.

T3-3 L pH in spray may be delayed a few 

minutes until sufficient water has 

passed through the ice condenser to 

dissolve all the STB. After that pH =8.5

K Based on the system design.

T3-4 M Solution will be at pH 9.5 will be warm 

(120-160F) and will be replenished 

rapidly based on the washing effect of 

the spray

K Based on the system design

T3-5 L The cable trays will start to be exposed 

to high levels of radiation at this point. 

However, degradation to chlorides is not 

instantaneous and will occur slowly over 

the next several days.

K Cable insulation does undergo 

radiolysis to yield chlorides; eventually.

T3-6 M Solubility of metal ions will be affected 

by the presence of peroxide.

K PWR shutdown chemistry programs.

T3-7 M The leaching process is time controlled. 

The actual leached concentrations will 

not yet be significant.

K ICET program provides evidence that 

maximum leached concentration do not 

occur until days later.
G-21

T3-8 L A steam generator tube rupture would 

not start to have an effect on the RCS 

and containment until RCS ‘backfill’ 

begins which is late in this time period.

K SG make up is with CST water; this is 

basically demineralized water. All 

PWRS use All volatile treatment(AVT) 

thus during the first few minutes of the 

event the chemicals in the SG would be 

boiled off with secondary steam and into 

the condenser or to the turbine building 

roof.

T3-9 M Linear flow rates are low. Any surface, 

which can ‘trap’ insoluble materials, will 

be able to do so. There is a lot of 

surface area over which the recirculated 

water will flow in containment before it 

reaches the sump.

UK This will be a plant specific and event 

specific parameter.

T3-10 L The affect of turbulence beneath the 

break may be significant. However the 

transit time to the sump would allow for 

re-agglomeration of any suspended 

material.

UK This will depend on the break size, the 

flow out the break, and the precipitate 

formed.

T3-11 M The containment floor in PWRs is a 

maze of components bolted to the 

concrete. The pathway from the break 

to the containment sump is not uniform, 

unidirectional flow. This type of path 

provides more significant opportunity for 

solid phases to agglomerate and settle. 

The flow rate in linear ft/second is also 

very small. This also provides 

additional time for settling.

PK The quiescent portions of the flow path 

to the sump will be dependent upon the 

individual plant design, the location of 

the major precipitate contributors with 

respect to the sump, and the type of 

insulation that was affected during the 

event.

T3-12 L All containment surfaces will be wetted. 

The only significant electrostatic charge 

would most likely result from galvanic 

corrosion effects. Those would be 

minimal during this time frame.

UK This is a very general possibility. The 

PZC of any in place precipitates or 

surfaces would have some effect on the 

attraction of precipitates but the mass 

they would attract due to this 

phenomenon is likely to be small.
G-22

T3-13 L There are a limited number of other 

materials available that will be 

transported in the post-LOCA 

environment

PK The ratio of particle surface area to the 

amount of material that cold potentially 

coat particles is largely unknown. Some 

materials could be organics or oils.

T3-14 M Precipitate aging during this time period 

will be in its early stages.

PK This will be very dependent upon the 

type of precipitate, which in turn is 

dependent upon the type o insulation 

affected and the containment spray 

buffering agent.

T3-15 M Dislodged CRUD from the reactor trip 

will provide a significant source of 

nucleation sites. These particles will 

range in size from <1 micron to >100 

microns. Their density will be on the 

order of 4-6 g/cc.

PK The specific effects of these materials 

on the insulation/buffering agent 

precipitate are as yet unknown.

T3-16 M As the debris bed on the screens or 

filters increases, the level of 

radionuclide activity will increase. This 

will create an oxidizing environment 

(due to oxygen saturation) which will 

transform reduced species into oxidized 

species.

PK Tests using radiation sources with 

precipitated materials need to be 

performed to better establish the effects 

of radiation fields on these materials.

T3-17 M The debris bed will initially concentrate 

those materials which are particulate 

(fiberglass fibers, shards of insulation 

jackets or Cal-Sil, metal and coating 

fragments) and those which are 

insoluble precipitates resulting form 

chemical reactions.

PK The known precipitates that will form are 

capable of trapping other materials as 

well as co precipitating other soluble 

ionic solids.
G-23

T3-18 M Fiberglass consists of several different 

mineral silicates. In an intense radiation 

field, these silicates will be transformed 

into soluble silicate ions. These new 

silicate ions will be transported to 

various containment areas where new 

silicate precipitates may form.

K These are know reactions of silica in 

radiation fields. The precipitation effects 

of containment spray buffering agents 

has already been established through 

the ICET program.

T3-19 H Transport of significant quantities of 

CRUD trapped in agglomerated 

precipitates will occur. Some of these 

materials will get through screens and 

find their ways to the RHR pumps and 

safety injection isolation valves..

K The effects of these types of 

particulates are known. Most pump seal 

faces are hardened surfaces to 

withstand normal service, which does 

not include high levels of abrasive, 

particulate matter.

T3-20 H The recirculated water will have 

relatively high concentrations of ions 

due to leaching of insulation and other 

solid materials in containment. This 

initial solubilization will have occurred at 

temperatures much higher (from 50 to 

200 F) than the RHR heat exchanger 

tubes surfaces.

K Solubility of most of these materials is a 

function of temperature. The exceptions 

are some alumino-silicates and AlOOH. 

These two have retrograde solubility.

T3-21 L The degree of heat exchange capacity 

loss will depend to great deal on the 

type of precipitated material. However, 

during the first 24 hours this should be 

negligible due to design margins 

inherent in the heat exchanger design.

K Plant design characteristics and 

conservativisms put on heat exchanger 

capacities.

T3-22 L During this time period the deposition of 

materials with retrograde solubility will 

begin. However it should not occur to a 

significant extent.

K Kinetic controlled process
G-24

T3-23 L The greatest danger to core clad 

oxidation is during the early phases of 

the event when core uncovery is more 

likely and fuel centerline temperature is 

at its peak.

K Design and operating characteristics of 

PWRS.

T3-24 L During this time period the deposition of 

materials with retrograde solubility will 

begin. However it should not occur to a 

significant extent. However if significant 

debris is transported through the sump 

screens that could block flow in fuel 

channels, this could lead to selected 

fuel assembly overheat conditions.

K Fuel rod design characteristics.

T3-25 L See T3-24 K See T3-24

T3-26 L During cold leg injection (up to 24 

hours) the bottom of the reactor vessel 

will be location for the deposition of solid 

materials. Flow direction changes 1800

at the vessel bottom, which will cause 

denser particulates to be deposited 

there.

K Flow design of reactor core.

T3-27 L Retrograde solubility materials will begin 

to deposit on fuel surfaces.

PK No modeling has been done in any tests 

to determine what the extent of this 

effect is.

T3-28 L The surface area of uncoated concrete 

will generally be small and the effect will 

be small during this limited contact time 

period.

K Plant design. Leach rate characteristics 

of concrete. Leaching of basic 

compounds from concrete will be 

buffered by presence of boric acid.
G-25

T3-29 M There are a variety of different coating 

materials. Their resistance to leaching 

and dis-bondment will depend on the 

their original application and 

qualification process.

PK Different combinations of coatings exist 

at each plant. No concerted effort has 

been made yet to quantify what the 

dissolution characteristics of these 

coatings are.

T3-30 M Boric acid corrosion of carbon steel is a 

significant industry issue. This has the 

potential to generate significant 

quantities of ferric hydroxide.

K Industry experience with boric acid 

corrosion of carbon steel and mild steel 

components.

T3-31 L Carbon dioxide/carbonates are limiting 

reagents in the precipitation reactions. 

The equilibrium process for precipitation 

of these ions will far outweigh the 

radiolytic effects of their decomposition 

to form organic acids. The terminal 

radiolysis reaction of organic acids 

reverts to carbonates.

PK No modeling or testing of this particular 

radiolytic phenomenon with the 

precipitated materials has yet been 

accomplished.
G-26

Table 6: MacDonald T3 Ranking Summary

Issue 

Number

Importance 

(H, M, L)

Rationale Knowledg

e (K, PK, 

UK)

Rationale

T3-1 M See T2-6. K See T2-6.

T3-2 M See T2-4 K See T2-4.

T3-3 M See T2-5. K See T2-5.

T3-4 M Impingement of boron laden, NaOH 

spray on metallic and non-metallic 

components in containment may 

enhance corrosion. Assuming that the 

pH is in the range of 8.5-10.5), the 

metal that will be most likely affected is 

Al and then only at the upper extreme of 

this pH range.

PK The corrosion of Al and other metals in 

mildly alkaline solutions have been 

extensively studied and data are 

available for estimating the corrosion 

rate. Likewise, information is available 

on enhancement of corrosion rate due 

to liquid jet impingement. The situation 

with regard to non-metallic materials is 

less well-defined, but most plastics and 

paints are stable when in contact with 

weakly alkaline solutions (but not when 

in contact with highly alkaline solutions).
G-27

T3-5 M Radiolytic degradation of electrical 

insulation is known to release chloride 

ion, which may induce passivity 

breakdown on various metals and alloys 

(e.g., Al, stainless steel), thereby greatly 

enhancing corrosion rates and the 

formation of corrosion products. Initial 

rankings changed due to following 

email, rankings indicated separately: 

Please find attached a table with my reassessments of some originally "high" 

ratings of issues. On examining these 

issues again, it was evident that I did 

not fully recognize the impact of:

1. Time of exposure after the initial 

LOCA.

2. The amount of the specific material in 

the containment (e.g., zinc).

My re-assessments also reflect the 

results of continuing radiolysis 

modeling, albeit with less-than-optimal 

codes that have been jerry-rigged from 

our reactor modeling work. 

Nevertheless, if the fields are as high as 

Bob indicates, the eventual production 

of nitric acid, in addition to the elevation 

of the redox potential, becomes a 

critical issue.

K The radiolytic degradation of plastic 

electrical insulation (e.g., Poly Vinyl 

Chloride, PVC) has been extensively 

studied and the rate of degradation can 

be estimated if the dose rate is known. 

The impact of chloride ion on passivity 

breakdown of metals and alloys can be 

calculated using the Point Defect Model.

T3-6 H See T2-20. K See T2-20.
G-28

T3-7 M Fiberglass thermal insulation leaching is 

expected to add to the inventory of 

dissolved species and to a decrease in 

the inventory of solids that might clog 

the pump screens. However, the 

dissolved products (Si, Al, Mg, Ca, etc. 

cations or oxyanions) may react with 

other components in the pool to form 

voluminous, gel-like products that would 

have the potential for blocking the 

screens.

K The leaching behavior of fiberglass has 

been extensively studied and it appears 

not to be significant over a 24-hour 

period unless the pH > 10. However, 

little is known of the reactions of 

leachants with other components in the 

containment pool or of the impact that 

these species might have on the pool 

chemistry, in general.

T3-8 M Rupture of steam generator tubes would 

allow the discharge of secondary-side 

coolant into containment. The 

secondary coolant is generally highly 

reducing in nature with hydrazine 

(NH2NH2) as the reducing agent and an 

organic amine (e.g., morpholine) or 

ammonia as the AVT (All Volatile 

Treatment) pH control protocol.

K The secondary chemistry of a PWR is 

very well-defined with models being 

available for calculating important 

properties, such as pH, conductivity, 

etc. Gibbs energy minimization codes 

are also available that could be used to 

estimate the pH and composition of 

primary/secondary mixed systems that 

would result in the event of steam 

generator tube failures.
G-29

T3-9 L Flow induced nucleation is the process 

whereby turbulence in a liquid or 

solution induces the formation of tiny 

bubbles through cavitation. These 

bubbles act as nucleation sites for 

precipitation of solids from super 

saturated solutions. Initial rankings 

changed due to following email, 

rankings indicated separately: Please 

find attached a table with my reassessments of some originally "high" 

ratings of issues. On examining these 

issues again, it was evident that I did 

not fully recognize the impact of:

1. Time of exposure after the initial 

LOCA.

2. The amount of the specific material in 

the containment (e.g., zinc).

My re-assessments also reflect the 

results of continuing radiolysis 

modeling, albeit with less-than-optimal 

codes that have been jerry-rigged from 

our reactor modeling work. 

Nevertheless, if the fields are as high as 

Bob indicates, the eventual production 

of nitric acid, in addition to the elevation 

of the redox potential, becomes a 

critical issue.

K The basic physics is known and a 

variant of the method, sonification, is 

used as a means of inducing 

precipitation in industrial and laboratory 

systems.
G-30

T3-10 L Turbulence in two phase systems is 

characterized by high shear forces 

being imparted to particles that tend to 

oppose agglomeration. In some 

systems, it may lead to an increased 

collision frequency between particles 

and hence may promote precipitation. 

Initial rankings changed due to following 

email, rankings indicated separately: 

Please find attached a table with my reassessments of some originally "high" 

ratings of issues. On examining these 

issues again, it was evident that I did 

not fully recognize the impact of:

1. Time of exposure after the initial 

LOCA.

2. The amount of the specific material in 

the containment (e.g., zinc).

My re-assessments also reflect the 

results of continuing radiolysis 

modeling, albeit with less-than-optimal 

codes that have been jerry-rigged from 

our reactor modeling work. 

Nevertheless, if the fields are as high as 

Bob indicates, the eventual production 

of nitric acid, in addition to the elevation 

of the redox potential, becomes a 

critical issue.

PK This is a very complex phenomenon and 

bit is probably fair to conclude that the 

underlying theory has not been 

developed to the extent that “first 

principles” prediction is possible.

T3-11 H Quiescent settling occurs when the flow 

velocity is so low and hence the 

hydrodynamic forces on particles are 

insufficient to prevent precipitation and 

settling.

PK The basic physics of the process are 

known, but it appears that the models 

are insufficiently well-developed to 

provide quantitative prediction of this 

phenomenon.
G-31

T3-12 H Electrostatic agglomeration occurs 

when the surfaces of different particles 

acquire surface charges of different 

sign, due to the pH of the solution lying 

between the PZCs (pH of zero charge) 

of the two surfaces.

K The process is well understood at both 

the theoretical and practical levels and 

extensive use of this phenomenon is 

made in industry (e.g., electrophoretic 

painting of automobiles). Extensive 

PZC data are available for a wide range 

of oxides, oxyhydroxides, and 

hydroxides, and data are readily 

measured for those phases that have 

not been previously been studied.

T3-13 H See T3-12. The surfaces may be 

modified chemically to change the 

surface charge characteristics and 

hence modify the agglomeration 

characteristics.

K Modification of the surface charges is a 

commonly-practiced technology in 

industry and in the laboratory, so that 

there exists an extensive database 

exists on this subject. .

T3-14 H See T3-12. K See T3-12.

T3-15 H A wide variety of nucleation sites may 

exist in the debris-filled containment 

pool after a LOCA, and these may act 

as sites for the precipitation of various 

phases.

PK The rate of nucleation of a phase onto a 

nucleus is determined by the Gibbs 

energy of nucleation. If this quantity is 

small, nucleation occurs readily, but if it 

is large nucleation is difficult and 

precipitation may not occur at all. The 

general principle is that “like nucleates 

like”; so that a carbonate nucleus will 

tend to nucleate carbonates, for 

example.
G-32

T3-16 H Because radioactive material is 

expected to be trapped in the debris 

bed, the radiolysis of water is expected 

to exert a significant impact on the 

chemistry of the local environment. The 

principal impact will probably be due to 

the generation of hydrogen peroxide, 

which is a strong oxidizing agent that 

will oxidize Fe2+ to Fe3+, for example.

K The radiolysis of water has been 

modeled extensively in nuclear reactor 

technology to estimate the 

concentrations of the principal radiolysis 

products. These concentrations can 

then be used in Mixed Potential Models 

to estimate the redox potential and the 

corrosion potentials of various metals 

and alloys. The impact of radioactive 

species trapped in the debris bed can 

therefore be modeled quantitatively.

T3-17 M If radioactive elements are concentrated 

at the sump screen, it is possible that 

the local redox conditions are such that 

high concentrations of certain species 

may form at that location.

PK The redox potential, which is 

established by the radiolysis of water, is 

readily calculated and the impact of the 

redox potential on the solution chemistry 

may be assessed using various 

computer codes that are commercially 

available. In this way, the 

concentrations of the components in the 

system can be calculated and the 

possibility of highly localized 

concentrations can be assessed.
G-33

T3-18 M The chemical environment within the 

sump screen is expected to significantly 

modify the morphology of fiberglass via 

deposition and etching, thereby altering 

the ability of the fiberglass to trap 

additional debris. Initial rankings 

changed due to following email, 

rankings indicated separately: Please 

find attached a table with my reassessments of some originally "high" 

ratings of issues. On examining these 

issues again, it was evident that I did 

not fully recognize the impact of:

1. Time of exposure after the initial 

LOCA.

2. The amount of the specific material in 

the containment (e.g., zinc).

My re-assessments also reflect the 

results of continuing radiolysis 

modeling, albeit with less-than-optimal 

codes that have been jerry-rigged from 

our reactor modeling work. 

Nevertheless, if the fields are as high as 

Bob indicates, the eventual production 

of nitric acid, in addition to the elevation 

of the redox potential, becomes a 

critical issue.

PK The basic principles of deposition and 

etching are known (PZC, etc.), but the 

data for specific glasses do not appear 

to be currently available.

T3-19 M Abrasion of pump seals could contribute 

to the debris inventory, but it would 

appear to be a relatively minor source in 

comparison with others.

PK The basic principles of abrasion and 

wear (“fretting corrosion”) are wellknown, but the wear rate is a sensitive 

function of the substrate material. To 

this Reviewer’s knowledge, the specific 

materials of interest have not been 

studied in this regard.
G-34

T3-20 H Precipitation of material in heat 

exchangers, because of temperature 

gradients. The precipitated material 

could degrade the hydrodynamic and 

thermal performance of the exchanger.

K The driving force for precipitation is the 

change in solubility, which can be 

effectively modeled using equilibrium 

thermodynamics. This topic is welldeveloped in the oil and gas industry in 

relationship to the production of 

hydrocarbons.

T3-21 H See T3-20 K See T3-20

T3-22 H Deposition of solids on the fuel, due to 

retrograde solubility, will degrade the 

ability of heat to be dissipated from the 

core and hence will lead to enhanced 

fuel temperatures.

K The driving force for precipitation is the 

change in solubility, which can be 

effectively modeled using equilibrium 

thermodynamics. This topic is welldeveloped in the oil and gas industry in 

relationship to the production of 

hydrocarbons.

T3-23 H The reaction of Zr-based cladding with 

water will produce hydrogen and hence 

will contribute to the inventory of this 

gas in containment.

K The reaction of zirconium alloys with 

water at high temperatures has been 

well-characterized (as a result of Three 

Mile Island). The impact of hydrogen on 

the redox potential of the pool 

environment and upon the reaction of 

this gas with oxygen are well-known and 

can be accurately predicted.

T3-24 H The mixing of debris with water will 

reduce the effective heat capacity and 

hence will degrade the ability of the 

coolant to remove heat from the reactor 

core.

K The heat capacity of a mixture can be 

accurately predicted by a mass-based 

mixing rule.

T3-25 H Deposition of debris in coolant channels 

within the core may degrade the ability 

to cool the core in the event of a LOCA.

PK Unlike the deposition of a solid from 

solution, the prediction of blocking of 

channels by solid debris is much less 

certain, because of the complexity of the 

phenomenon.
G-35

T3-26 H Settling of particulate debris in the core 

in low flow areas could result in 

reduction of heat transfer from the lower 

regions of the reactor fuel.

PK While the physics of settling are 

understood, the application of the 

principles to reactors under LOCA 

conditions appears not to have been 

made.

T3-27 H See T3-22 K See T3-22

T3-28 L Dissolution of uncoated concrete may 

result in a pH increase.

K The pH of the containment pool is 

effectively buffered by the coolant boric 

acid, the TSP, and by the STB on the 

containment floor. It is difficult to 

imagine that the dissolution of concrete 

over the time available could 

significantly affect the pH of the 

containment pool.

T3-29 M Dissolution of organic coatings (epoxy, 

alkyd, and Zn-base primers) may 

contribute to the debris inventory.

PK Dissolution products will affect pool 

chemistry, including contributing to 

chloride ion inventory, but the impact 

that these phenomena will have on the 

containment pool are not well-defined.
G-36

T3-30 M Concentrated boric acid is known to be 

highly corrosive toward ferrous alloys, 

as evidenced by the Davis Besse 

incident. Initial rankings changed due 

to following email, rankings indicated 

separately: Please find attached a table 

with my re-assessments of some 

originally "high" ratings of issues. On 

examining these issues again, it was 

evident that I did not fully recognize the 

impact of:

1. Time of exposure after the initial 

LOCA.

2. The amount of the specific material in 

the containment (e.g., zinc).

My re-assessments also reflect the 

results of continuing radiolysis 

modeling, albeit with less-than-optimal 

codes that have been jerry-rigged from 

our reactor modeling work. 

Nevertheless, if the fields are as high as 

Bob indicates, the eventual production 

of nitric acid, in addition to the elevation 

of the redox potential, becomes a 

critical issue.

PK The potential for damage caused by 

concentrated boric acid is clear, but few 

data are available to quantify the effect.

T3-31 L Radiolysis of carbonate solutions could 

result in the formation of organic acids.

K While the radiolytic formation of organic 

acids may be possible under highly 

reducing conditions, in the presence of 

CO2, the reverse is most commonly 

observed – the destruction of organic 

materials to produce CO2.
APPENDIX H

PIRT Panelist Evaluations of T4 Phenomena:

ECCS Recirculation from 24 hours until 15 Days into 

LOCA
Table H-1: ECCS Recirculation (24 hours to 15 days) a,b

Issue 

Number

Phenomena Description Implications

T4-1 Source terms: 

Unsubmerged 

materials

Corrosion of various materials (Al, Fe, 

concrete, Cu, Zn) due to condensation and 

transport into containment pool; 

condensation expected due to non-uniform 

containment temperature

1. Contributes species to containment pool

2. Condensate chemistry & environment governs 

corrosion/leaching rates.

T4-2 Submerged 

source terms: 

Pb shielding

Any acetates present in containment pool will 

dissolve Pb, which could lead to formation of 

lead carbonate particulate. Lead blanketing 

to shield hot spots and covered with plastic 

coating, but coating likely destroyed. Several 

hundred pounds of lead in flat sheets. Some 

plants still use lead wool. No Pb in ICET 

program.

Would provide additional particulate loading within 

containment pool

T4-3 Submerged 

source terms: 

Cu

Concern stems not from Cu compounds, but 

the various effects that Cu may have on other 

corrosion processes. Cu concentrations 

evaluated in ICET program; Cu comes from 

containment air coolers, motor windings and 

grounding straps.

1. By forming a galvanic couple, can facilitate attack 

of other metals (e.g., Al).

2. Cu ion deposition can occur which may inhibit 

corrosion.

3. Within an oxygenated environment, Cu can 

accelerate corrosion

T4-4 Submerged 

source terms: 

Fe

Boron inhibits pitting corrosion on surface of 

steel structures. Fe concentrations evaluated 

in ICET program. 

1. Less Fe ions in containment pool.

2. less corrosion and structural weakening of steel 

structures

T4-5 Submerged 

source terms: 

Al, decreased 

concentrations

Less dissolved Al, than in ICET #1, affects 

the type and quantity of chemical byproducts 

that form at high pH.

1. Less corrosion inhibition of insulation results in 

greater Si levels.

2. Less Al corrosion products allows other species to 

form within pool

T4-6 Submerged 

source terms: 

Al*, increased 

concentrations

Specific mix of other metals in containment 

pool leads to more Al corrosion (catalytic 

effect) at either lower or higher pH

Increases Al solid species which may form.
H-3

T4-7 Submerged 

source terms: 

Fiberglass 

dissolution

Dissolution at high pH contributes Silicates, 

Cu, Na, Al, Mg, B, misc. organics to 

containment pool. Fiberglass concentrations 

in ICET test plan

1. Solid species formation is affected by silicates, Cu, 

Na, Al, Mg, B concentrations.

2. Misc. organics in sump pool affect complexation.

T4-8 Submerged 

source terms: 

Fiberglass 

inhibition

Leaching of fiberglass inhibits corrosion of 

certain metals (e.g., Al)

Less metallic ions within containment pool

T4-9 Submerged 

source terms: 

Zn passivation

Zn passivation decreases corrosion 

passivation of Fe which allows Fe corrosion.

Galvanized steal/zinc coating; vessel site for ...; pH>8, 

dissolve ...; precipitate as silicate; ZnO, ZnOH 

corrosion products; 

T4-10 Submerged 

source terms: 

Zn corrosion 

products

Zn oxide and hydroxide corrosion products 

form which contributes to solid species 

loading.

Additional source term that could contribute to sump 

screen clogging and/or downstream effects.

T4-11 Submerged 

source terms: 

Zn 

coprecipitation

Zn may coprecipitate with other species (, 

notably Fe, Al). Reactor Vessel a possible 

site for coprecipitation

Additional source term that could contribute to sump 

screen clogging and/or downstream effects.

T4-12 Zinc hydroxide 

dissolution 

(zincate) 

Buffered pH containment pool dissolves zinc 

hydroxide so that other species, particularly 

silicates, may precipitate

Zinc silicates may be more likely to contribute (more 

transportable, possibly amorphous) to head loss or 

downstream effects.

T4-13 Submerged 

source terms: 

Zn-based 

coatings

Leaching of Zn-based primers (primarily 

inorganic Zn phosphates) creates possibility 

for additional dissolved Zn in solution 

Lead to formation of zinc oxide/hydroxides, 

carbonates, or silicates that could contribute to head 

loss/downstream effects.

T4-14 Source Term: 

Seal table 

corrosion

Multiple materials in seal table (Inconel, SS, 

plastics, organics) leads to formation of 

additional dissolved species. Seal table is an 

area in bottom of core where instruments are 

inserted into the core. A series of pressure 

isolation chambers. Generally lower than 

bottom of containment floor

Additional dissolved species present within the 

containment pool
H-4

T4-15 Submerged 

source terms: 

Fire barriers

Silicon-based seals (bisco seals) used at 

many structural penetration points at fire 

barriers. These may leach in post-LOCA 

environment

Another silicon source term that could contribute to 

formation of chemical byproducts which could impact 

head loss and downstream performance. 

T4-16 Submerged 

source terms: 

organic 

buoyancy

Organics coat materials (e.g., aluminum, calsil, fiberglass, etc.) and increase the 

buoyancy of particulate so that it’s more likely 

to float

This could enhance transport of particulates or 

chemical byproducts to the sump screen.

T4-17 Submerged 

source terms: 

coatings

Leaching of submerged coatings to contribute 

species to the containment pool. Possible 

sources include Pb-based paints (older 

containment buildings), phenolics, PVC

Additional source terms (especially chlorides, fluorides 

) which contribute to containment pool chemistry.

T4-18 Submerged 

source terms: 

RCP oil tank 

failure 

Overflow, failure, or leakage occurs either by 

LOCA or preexisting condition. Oils and 

other organics are released into containment 

pool.

Oils and other organics may affect complexation and 

sequestration of metallic species. Containment pool 

chemistry and byproduct production are influenced. 

T4-19 Submerged 

source terms: 

biofilm 

formation 

Biofilms form which protect against metallic 

corrosion (by forming passive layer) or lead to 

production of acids which increase metallic 

corrosion. Some biofilms can be preexisting 

in containment from outages.

1. If decreases metallic corrosion, would reduce 

containment pool concentration of certain 

dissolved species. 

2. If increases metallic corrosion, would increase 

containment pool concentration of certain 

dissolved species. 

3. May eventually lead to SCC failures of 

components.

T4-20 Submerged 

source terms: 

biologically 

enhanced 

corrosion 

General corrosion is enhanced due to 

biological agents. Examples include 

polysaccharides and sulfate reducing 

bacteria which may enhance Fe corrosion. 

Sulfur or carbon sources contribute to 

bacteria formation.

Fe and other metallic corrosion is enhanced leading to 

increased concentrations of metallic species within the 

containment pool.

T4-21 Submerged 

source terms: 

biologically 

enhanced H2

embrittlement 

Anaerobic and aerobic bacteria 

synergistically enhance stress corrosion 

cracking and hydrogen embrittlement of 

steels. Sulfur or carbon sources contribute to 

bacteria formation.

Structural cracking enhanced which could weaken and 

lead to failure of structural components.
H-5

T4-22 Submerged 

source terms: 

biological 

growth in 

debris beds

Bacteria grow in preexisting debris beds 

located on the sump strainer screen or 

elsewhere within the ECCS system.

Increased source term which can contribute to 

clogging or detrimental performance of pumps, valves, 

etc.

T4-23 Submerged 

source terms: 

electrical 

insulation 

Chlorides form due to radiological breakdown 

of cable insulation. This affect was simulated 

in the ICET experiment.

1. Additional source term for products affecting the 

containment pool chemistry.

2. Chlorides affect radiolysis and ionic strength of 

containment pool environment.

T4-24 Reactor Core: 

Fuel spalling

Zr-oxide layer spalls off reactor fuel due to 

temp gradient - 50 micron layers exist

1. Heat transfer depends on balance of oxide growth, 

deposition, and particulates, particulates may also 

enhance coagulation in core that may diminish 

heat transfer of water.

2. Additional solid products which contribute to 

clogging within the reactor core.

3. Additional products which could lead to clogging 

within the reactor core or be transported back to 

the sump screen.

T4-25 Radiological** 

effects: debris 

bed 

accumulation

Radio nuclides transport to, accumulate, and 

become concentrated within the sump screen 

debris bed altering the local chemical 

conditions

1. More concentrated effect than if spread throughout 

containment pool

2. Directly alter chemical byproducts formed at the 

sump screen, contributing to head loss.

T4-26 Radiological** 

effects: 

Dissolution & 

oxidation 

changes

Radiolysis leads to changes in the oxidation 

state in reactor, piping, and containment 

materials which affects the dissolution rate 

and the byproducts which form.

Affects the chemical byproduct source term loading 

that is present in the containment pool. 

T4-27 Radiological** 

effects: 

Radiolytic 

affect on 

biofilms

Radiolysis inhibits the formation and growth 

of biofilms

Films may be either advantageous or detrimental to 

corrosion and chemical byproduct formation (see 

earlier items)
H-6

T4-28 Radiological** 

effects: Redox 

potential 

changes

Radiolysis causes changes in the redox 

potential either in the containment pool or in 

debris beds (on the sump screen, or within 

ECCS component) 

Could affect chemistry in containment pool which 

affects species which form (e.g., Hanford tank: mixture 

of different components @ different phases)

T4-29 Radiological** 

effects: 

corrosion rate 

changes

Low doses and low temperature elevate the 

corrosion rate through formation of 

hypochlorite through radiolysis of Cl bearing 

water. Could increase corrosion rates (esp. 

pitting corrosion) of Al, SS, Fe.

Corrosion rate increases could increase the amount of 

metallic and nonmetallic species in containment; alters 

chemical byproduct formation.

T4-30 Radiological** 

effects: 

agglomeration

Radiolysis enhances agglomeration of 

chemical species. 

Advantage: Agglomeration could lead to increase 

settling rate of product.

Disadvantage: Could form products that are more 

likely to cause clogging of sump screens, downstream 

components. 

T4-31 CO2/O2 air 

exchange

Air exchange provides source for CO2 

ingestion within the containment pool. CO2

quantities limited by containment volume. 

Radiolysis can also promote formation of 

carbonates. 

Increase solid species in containment pool.

T4-32 ECCS Pumps: 

erosion/corrosi

on

Chemical byproducts cause erosion or 

corrosion of pump internals, especially tight 

tolerance components (bearings, wear rings, 

impellers, etc.).

Pump performance degrades, possibly to the point of 

being inoperable.

T4-33 ECCS Pumps: 

seal 

degradation

Chemical environment causes 

leaching/degradation of pump seal materials 

or chemical byproducts cause seal erosion 

Pump performance degrades, possibly to the point of 

being inoperable. 

T4-34 Heat 

exchanger: 

secondary 

contaminants 

Leaks in heat exchanger tubes allow 

secondary-side water additives to migrate 

over to the containment pool.

Additives in the secondary side water chemistry alter 

the chemistry in the containment pool.
H-7

T4-35 Heat 

exchanger: 

precipitate 

formation

Drop in temperature leads to the formation of 

sold species (e.g., AlOOH, FeOOH 

amorphous SiO2) and ripening such that 

macroscale coatings and/or suspended 

particulates form.

1. Create clogging, and less efficient heat transfer for 

cooling the ECCS recirculating water.

2. Form products that may clog reactor core and 

degrade heat transfer from fuel.

3. Products form which transport back to sump 

screen and lead to head loss.

4. Particulates act as nucleation sites for other 

compounds to precipitate

T4-36 pH drop in 

containment 

pool

pH drop due to evolving containment pool 

chemistry causes Al (and other metallic 

species) to precipitate.

Creates solid particulate loading that could affect sump 

screen head loss, heat exchanger clogging, reactor 

core clogging, and additional nucleation sites.

T4-37 Reactor Core: 

continued 

deposition/pre

cipitation

Zn, Ca, Mg, CO2 based deposits, films, and 

precipitates may form at higher temperatures 

within the reactor core

1. Diminished heat transfer from the reactor fuel.

2. Spalling could create additional solid products 

which contribute to clogging within the reactor 

core.

3. Spalling could create additional solid products 

which contribute to sump screen head loss. 

T4-38 Reactor Core: 

fuel deposition 

spalling

Zn, Ca, Mg, CO2 based deposits and films 

which form on the reactor core spall

1. Additional solid products which contribute to 

clogging within the reactor core.

2. Additional solid products which contribute to sump 

screen head loss. 

T4-39 Transport 

Phenomena: 

amorphous 

coating

Amorphous silica forms on surface of 

chemical precipitates (e.g., AlOOH, FeOOH). 

Coatings increase density and make it less 

likely for products to transport to sump 

screen.

Decreased transportability will result in less product 

migrating to or through the sump screen.

T4-40 Transport 

Phenomena: 

precipitation/coprecipitation

Precipitation/co-precipitation and ripening of 

solid species within containment pool creates 

solid species which are less likely to 

transport.

Decreased transportability will result in less product 

migrating to or through the sump screen.

T4-41 Transport 

Phenomena: 

Metallic 

scouring

Turbulent flow causes chemical 

films/products to be scour off the surface of 

metallic components so that they enter the 

containment pool.

Increased particulate loading that may increase head 

loss, degrade pump, valve, heat exchanger 

performance, and/or affect heat transfer from reactor 

fuel. a Sump pool temperatures are expected to range between 50 – 70C during this time period.
H-8

b Phenomena listed in earlier time periods (i.e., T1, T2, T3) may continue to be active or important during this time. c

 Al, in ICET tests, has provided an important contribution to observed chemical effects both through precipitate formation at high 

concentrations and pH and in inhibiting fiberglass leaching. d

 Soluble/insoluble activation species include, for example, Na24, Be7, Cr51, Co58,60, Mn54,56, Zr95,97, Fe55,59, Ni59,63, Nb95,97,Sb125, Zn65, 

Cs134,137, and I131,133
H-9

Table H-2: Apps T4 Ranking Summary

Issue 

Number

Importance 

(H, M, L)

Rationale Knowledg

e (K, PK, 

UK)

Rationale

T4-1 L Effect relatively small compared with 

submerged material.

PK ICET series provide some information. 

More is needed to evaluate nonisothermal effects.

T4-2 L Amount of exposed lead not expected to 

be large. Coatings of Pb hydroxycarbonates expected to form. Low 

concentrations of acetate expected in 

recirculating coolant are unlikely to 

cause significant dissolution. Possible 

passivation through formation of 

complex Pb silicates.

PK If cooling water composition can be 

estimated, its impact on lead dissolution 

could be calculated.

T4-3 L/M Copper does not corrode rapidly. 

Dissolved Cu would plate out on Fe and 

Al, but amount available in solution 

would be small.

UK Effect of precipitated Cu on galvanic 

corrosion of other metals requires 

quantification. 

T4-4 L Fe corrosion would be slow. PK ICET series and evaluation at CNWRA 

provide some information.

T4-5 L Decreased Al corrosion would mitigate 

sump screen blockage.

PK ICET series and corrosion studies at 

CNWRA provide some information.

T4-6 H Al corrosion could strongly affect sump 

screen blockage.

PK ICET series and corrosion studies at 

CNWRA provide some information.

T4-7 M Dissolution of fiberglass only moderate. K ICET series and dissolution studies at 

CNWRA provide information.
H-10

T4-8 M Effect of fiberglass dissolution on Al 

corrosion would be variable.

PK ICET series and dissolution studies at 

CNWRA provide some information.

T4-9 L Overall impact would be small PK ICET series and evaluation at CNWRA 

provide some information.

T4-10 L Total Zn dissolution would be small. PK ICET series and evaluation at CNWRA 

provide some information.

T4-11 L Total Zn dissolution would be small. PK ICET series and evaluation at CNWRA 

provide some information.

T4-12 L Total Zn dissolution would be small. PK ICET series and evaluation at CNWRA 

provide some information.

T4-13 L Zn based primers are relatively 

insoluble.

PK ICET series provide some information. 

Additional calculations to evaluate 

primer solubility are needed.

T4-14 L Materials are resistant to corrosion, and 

corrosion products would be small in 

amount.

PK Additional calculations to evaluate alloy 

corrosion are needed. Data may be 

available from manufacturers.

T4-15 L Minor source of contamination. UK No information is available on the 

leaching characteristics.

T4-16 M/H Flotation characteristics are important in 

relation to sump screen blockage.

PK Some information available from head 

loss testing.

T4-17 L Effect on coolant composition and 

formation of secondary precipitates is 

likely to be small.

UK Further review of PWR-specific design 

is required.
H-11

T4-18 M Oil leakage could cause flotation of 

debris and impede metal corrosion.

UK Nature of contaminant release and 

physical and chemical effects require 

evaluation.

T4-19 L Environment is likely to be relatively free 

of biofilms.

UK Would require plant specific 

characterization.

T4-20 L Time frame and temperature would limit 

extent of biological reactions.

UK Would require plant specific 

characterization.

T4-21 L Time frame and temperature would limit 

extent of biological reactions.

UK Would require plant specific 

characterization.

T4-22 L Time frame and temperature would limit 

extent of biological reactions.

UK Would require plant specific 

characterization.

T4-23 L Duration is too short for a major effect. UK Extent of radiolysis would depend on 

plant specific conditions.

T4-24 L/M Spallation of Zr oxides would add only a 

small burden to the particulate load, but 

could contribute to core damage 

through restriction of circulation.

UK Actual behavior would require laboratory 

and pilot testing.

T4-25 L/M Concentration of radionuclides in the 

bed may not have a major impact in 

altering the chemistry of the system 

except perhaps with respect to 

organics.

UK Specific experiments are needed to 

quantify the effect.

T4-26 L Overall effect expected to be small. 

Oxidation state would already be high.

UK Need to evaluate the effect due to 

radiolysis.
H-12

T4-27 L Problem not likely to have a major effect 

during the period in question. Inhibition 

effects would likely be small.

UK Effect would have to be evaluated.

T4-28 L/M Radiolysis would likely enhance the 

oxidation state, but conditions would 

already be oxidizing. There could be an 

acceleration of oxidation reactions.

PK Effect of radiolysis on the oxidation state 

can be estimated, but plant specific 

conditions would be needed to make an 

evaluation.

T4-29 L/M Effect could accelerate Al corrosion. 

Effect likely to be modest as 

concentration of Cl expected to be 

relatively low.

PK Effect could be estimated, but 

experiments are needed to quantify 

rates.

T4-30 L/M Effect could be important, but is difficult 

to quantify.

UK Little is known on the subject.

T4-31 L Effect likely to be small. PK It might be possible to calculate the 

magnitude of this effect.

T4-32 M Effect could be serious, but surely 

pumps are designed to prevent such an 

outcome?

PK Manufacturers should be consulted.

T4-33 M Effect likely to be small. UK Evaluation needed. Manufacturers 

should be consulted.

T4-34 L Effect likely to be small. UK Effect of contaminants would have to be 

evaluated.

T4-35 M/H Could adversely affect heat exchanger 

operation and cause costly repairs.

PK Likelihood of precipitation and type 

could be evaluated
H-13

T4-36 L pH drop in buffered system is likely to 

be small.

PK Could be estimated.

T4-37 M/H Could adversely cooling and core 

damage could occur, with costly repairs.

PK Likelihood of precipitation and type 

could be evaluated.

T4-38 M Spallation would partially restore cooling 

ability. Spallation products not likely to 

constitute a large volume of material.

UK Difficult to estimate spallation. Testing 

would be required.

T4-39 L/M Amount of potential precipitate removed 

by precipitation on surfaces is likely to 

be small in relation to material 

precipitating in suspension. However, 

effect is dependent on pH buffer system 

used.

PK ICET series could provide some 

information. Specific testing would be 

required.

T4-40 M Phenomenon could limit screen 

blockage, but is dependent on plant 

design and choice of pH buffer.

UK Effect would depend on plant specific 

conditions.

T4-41 L/M Corrosion rates could be greatly 

accelerated, especially with respect to 

Al.

UK Effect is difficult to quantify. Much 

depends on the location of the break 

and proximity of exposed metal 

structures.
H-14

Table H-3: Chen T4 Ranking Summary

Issue 

Number

Importance 

(H, M, L)

Rationale Knowledg

e (K, PK, 

UK)

Rationale

T4-1 L PK 

T4-2 H PK 

T4-3 M PK 

T4-4 H PK 

T4-5 L I changed initial ranking from high to low 

based on email received from Chen

K 

T4-6 H K 

T4-7 L PK 

T4-8 L PK 
H-15

T4-9 L PK 

T4-10 M PK 

T4-11 L PK 

T4-12 M PK 

T4-13 M PK 

T4-14 L PK 

T4-15 L UK 

T4-16 L UK 

T4-17 L UK 

T4-18 M PK 
H-16

T4-19 L UK 

T4-20 L PK 

T4-21 L UK 

T4-22 L UK 

T4-23 M PK 

T4-24 L PK 

T4-25 L too low a residence around the sump 

screen

UK 

T4-26 L UK 

T4-27 L PK 

T4-28 M PK 
H-17

T4-29 M PK 

T4-30 L UK 

T4-31 L PK 

T4-32 M K 

T4-33 M K 

T4-34 L PK 

T4-35 L K 

T4-36 M This ranking was changed based on 

following email: "As discussed today, 

the [containment pool] pH could change 

between 9 and 4.5 which is significant to 

warrant a High [ranking]. As the chance 

of getting to pH=4.5 is little, I can live 

with a rating of Medium but not less."

PK 

T4-37 L PK 
H-18

T4-38 L UK 

T4-39 H amorphous silica particles can enhance 

sump screen plugging

PK 

T4-40 M PK 

T4-41 M PK 
H-19

Table H-4: Delegard T4 Ranking Summary

Issue 

Number

Importance 

(H, M, L)

Rationale Knowledg

e (K, PK, 

UK)

Rationale

T4-1 L Little condensate flow and little 

corrosion observed in ICET.

K ICET showed little corrosion attack in 

condensing region.

T4-2 L Anticipate low lead corrosion rate in the 

system. 

PK Some scoping tests would aid in 

determining severity of this 

phenomenon.[1]

T4-3 M The effect of galvanic couples was not 

examined but could be strong, 

especially for aluminum.

UK See T2-22. 1

T4-4 L ICET and other testing showed little iron 

corrosion. However, effects of high and 

low temperature surfaces need to be 

studied (see T3-20 to -26).

PK Studied in ICET and other testing. 1

T4-5 M Though relatively important, this 

situation has already been examined in 

ICET and other testing.

PK Studied in ICET and other testing. 1

T4-6 M Though relatively important, this 

situation has already been examined in 

ICET and other testing.

PK Studied in ICET and other testing. 1

T4-7 M Though relatively important, this 

situation has already been examined in 

ICET and other testing.

PK Studied in ICET and other testing. 1

T4-8 M Though relatively important, this 

situation has already been examined in 

ICET and other testing.

PK Studied in ICET and other testing. 1
H-20

T4-9 M Though relatively important, this 

situation has already been examined in 

ICET and other testing.

PK Studied in ICET and other testing. 1

T4-10 M Though relatively important, this 

situation has already been examined in 

ICET and other testing.

PK Studied in ICET and other testing. 1

T4-11 M Though relatively important, this 

situation has already been examined in 

ICET and other testing.

PK Studied in ICET and other testing. 1

T4-12 M Though relatively important, this 

situation has already been examined in 

ICET and other testing.

PK Studied in ICET and other testing. 1

T4-13 M Though relatively important, this 

situation has already been examined in 

ICET and other testing.

PK Studied in ICET and other testing. 1

T4-14 L The materials in the seal table appear to 

be similar to materials in other areas 

exposed to the coolant. The seal table 

area also seems to be in a relatively 

stagnant location and, being removed 

from the flow currents, might not 

contribute significantly to the solute or 

suspended solids burden.

PK Assessment by reactor engineer 

needed to validate bases of judgment 

that seal table materials influence is of 

low importance.

T4-15 M The effects of thermolysis and radiolysis 

on the bisco seals should be assessed 

with those of the organic materials 

(paints, plastics).

UK See T2-24 and T3-29.

T4-16 H The flotation phenomenon has the 

potential to motivate a lot of solids to the 

sump screen.

UK This mechanism looks like froth flotation 

used in ore beneficiation.
H-21

T4-17 H Similar to T2-24 and T3-29. UK See T2-24 and T3-29.

T4-18 M See T1-7. Effects of oil not studied; oil 

may accrete small solids and drift 

downstream to span matted fibers at 

sump screen.

PK Effects of oil to accrete finely particulate 

solids under this system not known but 

example exists in oil spills from oil 

tankers onto beaches.

T4-19 ? Any consideration of biofilms must first 

evaluate the potential for biota to 

survive in ~0.2 molar boron. Note that 

borates are used as algaecides.

UK The essentially steady presence of 

~2000 ppm boron (about 0.2 moles per 

liter) is ensured by the injection of the 

emergency core cooling water about 20-

30 minutes post-LOCA. T4-20 ? UK

T4-21 ? UK

T4-22 ? UK

T4-23 L The ~100 ppm chloride seemingly had 

little effect on the solids loading. 

However, other radiolytic effects on the 

electrical insulation may have larger 

effects on the solids behavior (see T2-

24, T3-5, and T3-29, for example).

K Tested in ICET and other experiments.

T4-24 M This is addressed in T1-1. PK Crud releases observed during reactor 

shut-down and spent fuel storage.

T4-25 M This is addressed in T3-16. UK Testing of the effects of high radiation 

fields needed for sump screen beds. 

Effects expected to be higher for the 

organic materials.
H-22

T4-26 M The effects of radiolysis on the 

inorganic components are expected to 

be lower than those of the organic 

materials.

UK Testing is necessary as suggested in T2-

20 and T3-6.

T4-27 ? See T4-19 through T4-22 for 

speculation on the detrimental effects of 

borate on biota. Radiolysis would 

decrease the potential for biofilms 

further.

UK The essentially steady presence of 

~2000 ppm boron (about 0.2 moles per 

liter) is ensured by the injection of the 

emergency core cooling water about 20-

30 minutes post-LOCA.

T4-28 M Similar to T4-26. UK Testing is necessary.

T4-29 M Oxidizing conditions imposed by high 

dose radiolysis of chloride brines to 

form hypochlorite; low chloride in ECCS 

may not be sufficient to form 

hypochlorite.

PK Tests of aluminum in waters containing 

100 ppm chloride and 100 ppm H2O2

showed no enhanced corrosion at 

~92°C.

T4-30 M Agglomeration could enhance sump 

screen blockage

UK Testing is necessary.

T4-31 M See T2-8. K See T2-8.

T4-32 H For pump seal and erosion issues, see 

T3-19.

UK See T3-19.

T4-33 H UK
H-23

T4-34 L Contributions of solutes from secondary 

cooling likely to be very low. Secondary 

coolant leakage only can dilute solids 

and solutes concentrations.

K If anything, serves to dilute solids and 

solutes concentrations.

T4-35 H See T3-20. UK See T3-20.

T4-36 L The quantity of dissolved aluminum is 

already low at pH 10; pH decrease will 

have little additional effect. Differences 

in metal solubility represent little 

difference in the total solids loading in 

the suspended solids budget.

K Aluminum, zinc, and lead are the only 

amphoteric metals in the system (iron, 

zirconium, copper are not amphoteric).

T4-37 H See T3-27. UK See T3-27.

T4-38 H UK

T4-39 H The continued dissolution of Cal-Sil 

followed by the precipitation of 

amorphous silica will occur. The 

precipitating silica can span over the 

solids bed on the sump screen.

PK This effect is amenable to investigation 

through the parametric studies 

suggested for T4-3 to T4-13

T4-40 H PK
H-24

T4-41 L The incremental addition of solids 

scoured from surfaces after the first day 

is expected to be small unless large, 

dense, and abrasive pieces (e.g., UO2

fuel bits) are added to the system. Most 

solids found in ICET were finely 

particulate (e.g., aluminum hydroxide, 

tobermorite) and/or softer than metal 

(e.g., fiberglass).

PK Corrosion/erosion testing may help 

confirm the effects of scouring.

[1] Note that the parametric small-scale testing may provide a better overall assessment of the chemical interactions suggested in 

phenomena T4-2 through T4-13. The testing would study the effects, on the solids listed in phenomena T4-2 through T4-13 plus CalSil and concrete, of solution composition including pH and dissolved phosphate and borate. Cal-Sil is a special case in that it 

contributes significant calcium and silicate to the solution and also affects the pH. The testing would examine the formation of solid 

phases and the rates of material corrosion in the various systems.
H-25

Table H-5: Litman T4 Ranking Summary

Issue 

Number

Importance 

(H, M, L)

Rationale Knowledg

e (K, PK, 

UK)

Rationale

T4-1 L Subsequent to spray termination the 

contribution to recirculation water 

dissolved/precipitated materials from 

unsubmerged components will be 

minimal. It will be limited by the rate of 

condensation that should be a small 

factor during this time period.

PK Without the presence of containment 

spray there is no driving force to remove 

precipitated materials from 

unsubmerged surfaces.

T4-2 M Most lead shielding n containment will 

be covered with plastic coatings. The 

overall dissolution of lead should only 

result in concentrations on the order of 

ppb to small ppm range. However, lead 

is known to induce cracking in stainless 

steel components.

PK This is a long term effect which is 

minimized by the low potential 

concentration of lead and the neutral pH 

conditions.. 

T4-3 M All containment-building components 

are grounded using either copper or 

aluminum grounding straps. These are 

generally uncoated and found at the 

bottom of containment; thus they will be 

submerged.

PK Precipitated materials may actually be 

‘attracted’ to these grounding materials 

coating them, and inhibiting the 

dissolution of copper. However, this 

has not been effectively tested. Some 

ICET results indicate that this is 

potentially true.

T4-4 H The inhibition of carbon steel corrosion 

by boric acid occurs in combination with 

other corrosion control agents under 

specific concentration ranges. The 

combination of soluble and insoluble 

ionic materials in the recirculated water 

will be more suited towards corrosion 

rather than inhibition.

K PWR operating history with carbon steel 

and mild steel corrosion with boric acid.
H-26

T4-5 L During this time period the water level in 

containment should remain fairly 

constant. Equilibrium between 

dissolved and precipitated species will 

be reached.

PK Results of ICET indicate that within 

about 10-20 days the equilibrium 

condition would be reached for 

dissolution of materials.

T4-6 L During this time period the water level in 

containment should remain fairly 

constant. Equilibrium between 

dissolved and precipitated species will 

be reached.

PK Results of ICET indicate that within 

about 10-20 days the equilibrium 

condition would be reached for 

dissolution of materials.

T4-7 M Equilibrium conditions should be 

established. The maximum amount of 

materials to be leached ant precipitated 

should have already occurred by day 15.

PK Results of ICET programs demonstrate 

the equilibrium is eventually 

established.

T4-8 M This particular material may continue to 

contribute in the longer term due to 

radiolytic effects on fiberglass insulation. 

This is not true with other species.

K Insoluble silicates, silicon dioxide and 

other silicon compounds are subject to 

radiolytic dissolution (PWR spent fuel 

pool silica issues).

T4-9 L After several days settling of precipitates 

will most likely coat many metallic 

surfaces causing them to react more 

slowly with the bulk water.

PK Results of ICET programs with these 

material coupons show minimum 

dissolution after initial periods of 

exposure.

T4-10 L After several days settling of precipitates 

will most likely coat many metallic 

surfaces causing them to react more 

slowly with the bulk water.

PK Results of ICET programs with these 

material coupons show minimum 

dissolution after initial periods of 

exposure.

T4-11 L This effect would have already occurred. PK ICET coupon tests.

T4-12 L After several days settling of precipitates 

will most likely coat many metallic 

surfaces causing them to react more 

slowly with the bulk water.

PK Results of ICET programs with these 

material coupons show minimum 

dissolution after initial periods of 

exposure.
H-27

T4-13 L Amount of coating is limited. Amount 

submerged my be a significant portion 

or that available. Changed ranking from 

M/L to L based on following email: 

"Initially I denoted this as “L?”. Digby 

had rated this as “H”. Based on the time 

frame, the pH of the solution and the 

limit on the amount of zinc that can be in 

containment, this should definitively be 

an L. The zinc that dissolves or leaches 

from the metallic surface or primers 

would almost immediately be 

precipitated as the hydroxide. In the 

quiescent flow of the containment this 

material would form a protective barrier, 

inhibiting additional dissolution of zinc."

UK Zinc based coatings have not been 

tested in this environment. It is 

unknown what effect radiolysis will 

have.

T4-14 L The seal table is in a low flow area, and 

most likely sill not significantly contribute 

to dissolved materials. May be a source 

of non-metallics.

UK Each plant will have varying designs for 

this part of plant. Would need more 

information for all plants to determine 

long range effects.

T4-15 L These fire barrier materials are also 

significantly ‘waterproof’. They are 

organic polymers formed using a 

metallic (proprietary) catalyst.

UK Specific testing would have to be 

performed to ascertain the contribution 

from these materials in the post-LOCA 

environment.

T4-16 L Materials of low enough density to float 

would most likely be ground up in pump 

impellers without causing significant 

pump damage.

PK These materials would generally be soft 

and not contribute to component wear.

T4-17 M Only if various metallic based coatings 

are present

PK Plant design dependent.
H-28

T4-18 M Any small leaks of pump oils or raw 

water systems in containment will 

provide additional materials for 

precipitation and bacterial growth.

PK Several plants have raw water systems 

in containment. All plants have RCP oil 

and other small pump oil reservoirs that 

could add to organic loading. Long term 

corrosion of these components could 

lead to loss of materials from these 

systems.

T4-19 M Containment buildings contain bacteria 

and algae from exchange with outside 

air during normal operation. Raw water 

leaks and foot traffic prior to event will 

also contribute to bacterial/spore 

loading.

PK PWR experience has generally shown 

that biofilms are detrimental to plant 

components. With no controls on 

biofilm growth, under deposit corrosion 

is very likely. This will lead to SCC and 

pitting corrosion.

T4-20 M Containment buildings contain bacteria 

and algae from exchange with outside 

air during normal operation. Raw water 

leaks and foot traffic prior to event will 

also contribute to bacterial/spore 

loading.

PK PWR experience has generally shown 

that biofilms are detrimental to plant 

components. With no controls on 

biofilm growth, under deposit corrosion 

is very likely. This will lead to SCC and 

pitting corrosion.

T4-21 M Depends on the type of bacteria and the 

oxygen supply available in containment .

UK It is not clear how long the oxygen 

supply in containment will last with large 

scale corrosion taking effect.
H-29

T4-22 H Debris beds will provide a ‘nesting’ 

location for bacteria and spores. Any 

organic materials (food source) will likely 

be trapped there. 

Additional rationale received in email: 

Containment buildings are routinely 

exposed to outside air during refueling 

outages. The large refueling hatch is 

open and the containment building is 

operated under a negative pressure 

(this ensures no gaseous or particulate 

releases). Refueling outages are 

routinely scheduled for spring and fall, 

the two times of the year when there is 

the greatest amount of fungal and 

bacterial spores in the air, not to 

mention pollen. These materials will get 

sucked into the containment building. 

Under normal operating conditions 

these generally do not create a problem, 

but following a LOCA where debris gets 

concentrated, the food source for these 

microbes will be in close contact with 

them. The biological products from 

growth are polysaccharides that are 

sticky, tenacious materials. These 

compounds are known to cause fouling 

in other systems in power plants, 

especially on stainless steel surfaces. 

They initially lead to reduction in heat 

transfer capability, but eventually cause 

pitting and under deposit corrosion, 

leading to component failures. 

Conditions in containment are rife for 

their evolution and production. Their 

growth starts almost immediately but left 

unchecked increases exponentially and 

within 15 days may create significant c

hallenges to both heat transfer and f

low.

I think that this should be rated ‘high’ in 

this time frame

PK Industry experience in these areas is 

rare, however this has occurred in raw 

water systems on traveling screens.
H-30

T4-23 L The breakdown of cable insulating 

materials would slow down at this point

PK Long term tests of the effects of 

radiation to the cable coatings in this 

liquid environment would need to be 

done to confirm this.

T4-24 M The CRUD layer on the fuel surface will 

begin to spall as a result of changing 

fuel centerline temperature (loss of 

decay heat effect).

K This effect can be easily observed in 

the SFP of nuclear power facilities with 

older fuel assemblies.

T4-25 M As more debris accumulates the 

possibility to concentrate radionuclides 

by coprecipitation increases. Any 

observed radiolytic effects will also 

increase.

PK Effects will depend on the material on 

the debris bed. Testing of specific 

materials would me necessary to 

determine the overall effect.

T4-26 L During this time period, the general 

radiolytic effects should have reached 

equilibrium (except in those areas where 

radionuclides will accumulate see T4-

25)

UK Specific testing would need to be done.

T4-27 L Bacteria and algae are much more 

resistant to the effects of radiolysis than 

other materials.

PK Significant events at PWRs where oil 

spills in SFPs have lead to growths of 

biofilms and algae even in the presence 

of high exposure from spent fuel.

T4-28 M These effects will reach equilibrium. 

The build up of hydrogen will continue 

but would be mitigated through the use 

of hydrogen recombiners.

PK Plant design. Need tests on radiolytic 

effects to solidify this factor.

T4-29 L The concentration of chlorides will 

generally be low. Formation of 

hypochlorite will occur but at low 

concentrations so as not to cause 

significant oxidizing effects.

PK Limited chloride source term.

T4-30 M The presence of ionizing radiation in 

solution will increase net ‘charge’ in 

solution favoring agglomeration of 

suspended materials.

PK Flocculating agents work better at 

higher ionic strengths
H-31

T4-31 M Air exchange would be minimized 

following a LOCA in order to reduce 

radioactive emissions. Thus a minimal 

amount of CO2 would be introduced into 

containment.

K With containment spray off and minimal 

make up water the source of carbon 

dioxide would most likely be depleted 

with the first day.

T4-32 M During this time period the continued 

presence of two phase flow through the 

pumps will have some effects on 

metallic erosion.

PK These pumps are designed as “pure” 

water pumps.

T4-33 M During this time period the continued 

presence of two phase flow through the 

pumps will have some effects on 

metallic erosion.

PK These pumps are designed as “pure” 

water pumps.

T4-34 M RHR heat exchangers are cooled wither 

by raw water or component cooling 

systems.

K The cleanliness levels of the systems 

that may leak into the RCS is not the 

same as the RCS and containment. 

This will contribute contaminants that 

will have various effects.

T4-35 H Precipitate formation due to temperature 

drops will also trap other soluble 

materials. Any particulates that normally 

would pass through the HX will also be 

trapped by precipitate.

K Long-term operation of plant heat 

exchangers has shown that debris can 

bridge multiple tubes and lead to 

reduced flow. This is documented in 

PWR databases for heat exchanger 

maintenance.

T4-36 L The changes in pH expected this long 

after the event are very small.

K The pH function will be unaffected due 

to the large buffering capacity after the 

leaching of materials with the buffering 

agent.

T4-37 L/M This can be mitigated by plant operators 

because reversal of flow can be 

performed on a routine basis.

K Plant design characteristics allow for 

the change of flow from hot leg to cold 

leg based on core cooling needs.

T4-38 M As the fuel continues to cool spallation 

from the surfaces will continue.

K SFP bottom deposits confirm that this 

happens routinely as fuel cools down 

over months of storage.
H-32

T4-39 L It is unlikely that amorphous SIO2 will 

exist due to radiolytic effects.

K Silica compounds in water are know to 

decompose to yield soluble silicates in 

the presence of a strong radiation field.

T4-40 M As precipitates become denser their 

transportability will decrease.

K Precipitates settle better after aging and 

increasing in density.

T4-41 L The Low flow conditions that exist would 

not be significant ot cause general 

scouring.

PK Plant specific design features.
H-33

Table H-6: MacDonald T4 Ranking Summary

Issue 

Number

Importance 

(H, M, L)

Rationale Knowledg

e (K, PK, 

UK)

Rationale

T4-1 L Corrosion of unsubmerged material due 

to condensation may contribute to the 

transfer of material into the containment 

pool. Initial rankings changed due to 

following email, rankings indicated 

separately: Please find attached a table 

with my re-assessments of some 

originally "high" ratings of issues. On 

examining these issues again, it was 

evident that I did not fully recognize the 

impact of:

1. Time of exposure after the initial 

LOCA.

2. The amount of the specific material in 

the containment (e.g., zinc).

My re-assessments also reflect the 

results of continuing radiolysis 

modeling, albeit with less-than-optimal 

codes that have been jerry-rigged from 

our reactor modeling work. 

Nevertheless, if the fields are as high as 

Bob indicates, the eventual production 

of nitric acid, in addition to the elevation 

of the redox potential, becomes a 

critical issue.

K This is essentially an “atmospheric 

corrosion” problem, which has been 

extensively studied in corrosion science.

T4-2 H Corrosion of submerged material due to 

condensation may contribute to the 

transfer of material into the containment 

pool.

K The corrosion of materials has been 

extensively studied and the rate of 

production of corrosion products can be 

predicted, in many cases.
H-34

T4-3 M Copper, which is present in 

containment, may corrode to produce 

corrosion products that will contribute 

significantly to the inventory of solid 

products.

UK Copper corrodes only under oxidizing 

conditions. The environment that will 

exist post-LOCA is probably reducing in 

nature, due to the presence of 

hydrogen, but this issue must be 

resolved by modeling.

T4-4 L The corrosion of iron is inhibited by 

borate ion and this will lead to a lower 

inventory of iron corrosion products than 

otherwise would be the case.

K There is little evidence that borate ion 

significantly inhibits the general 

corrosion of iron; recent evidence 

suggests that it does inhibit localized 

corrosion (e.g., pitting).

T4-5 M The corrosion of aluminum is inhibited 

by corrosion products and other 

material precipitated on the metal 

surface.

PK The corrosion of Al is well understood 

and under some circumstances the 

corrosion rate is reduced by deposits. 

Prediction of the precise conditions is 

problematic.

T4-6 M Possibility of the corrosion of aluminum 

being catalyzed by the corrosion 

products of other metals.

K The corrosion of Al is catalyzed by Cu 

that forms by a displacement reaction 

on the Al surface. This is a wellunderstood phenomenon.
H-35

T4-7 L Dissolution of fiberglass contributes 

products to the solid inventory in the 

pool, based upon the ICET test plan. 

Initial rankings changed due to following 

email, rankings indicated separately: 

Please find attached a table with my reassessments of some originally "high" 

ratings of issues. On examining these 

issues again, it was evident that I did 

not fully recognize the impact of:

1. Time of exposure after the initial 

LOCA.

2. The amount of the specific material in 

the containment (e.g., zinc).

My re-assessments also reflect the 

results of continuing radiolysis 

modeling, albeit with less-than-optimal 

codes that have been jerry-rigged from 

our reactor modeling work. 

Nevertheless, if the fields are as high as 

Bob indicates, the eventual production 

of nitric acid, in addition to the elevation 

of the redox potential, becomes a 

critical issue.

K Has been demonstrated by the ICET.

T4-8 M Leaching of fiberglass produces 

products that inhibit metal corrosion.

PK Possible, but to my knowledge not firmly 

established.
H-36

T4-9 L Zn passivation in galvanized steel leads 

to enhanced corrosion of iron. Initial 

rankings changed due to following 

email, rankings indicated separately: 

Please find attached a table with my reassessments of some originally "high" 

ratings of issues. On examining these 

issues again, it was evident that I did 

not fully recognize the impact of:

1. Time of exposure after the initial 

LOCA.

2. The amount of the specific material in 

the containment (e.g., zinc).

My re-assessments also reflect the 

results of continuing radiolysis 

modeling, albeit with less-than-optimal 

codes that have been jerry-rigged from 

our reactor modeling work. 

Nevertheless, if the fields are as high as 

Bob indicates, the eventual production 

of nitric acid, in addition to the elevation 

of the redox potential, becomes a 

critical issue.

K This has been demonstrated 

experimentally.
H-37

T4-10 L Zn corrosion products contribute to 

solids loading. Initial rankings 

changed due to following email, 

rankings indicated separately: Please 

find attached a table with my reassessments of some originally "high" 

ratings of issues. On examining these 

issues again, it was evident that I did 

not fully recognize the impact of:

1. Time of exposure after the initial 

LOCA.

2. The amount of the specific material in 

the containment (e.g., zinc).

My re-assessments also reflect the 

results of continuing radiolysis 

modeling, albeit with less-than-optimal 

codes that have been jerry-rigged from 

our reactor modeling work. 

Nevertheless, if the fields are as high as 

Bob indicates, the eventual production 

of nitric acid, in addition to the elevation 

of the redox potential, becomes a 

critical issue.

K Zn corrodes to form solid corrosion 

products that will contribute to the solids 

inventory in the containment pool.
H-38

T4-11 L ZnO or Zn(OH)2 may precipitate with 

other species to form solid corrosion 

products. Initial rankings changed 

due to following email, rankings 

indicated separately: Please find 

attached a table with my reassessments of some originally "high" 

ratings of issues. On examining these 

issues again, it was evident that I did 

not fully recognize the impact of:

1. Time of exposure after the initial 

LOCA.

2. The amount of the specific material in 

the containment (e.g., zinc).

My re-assessments also reflect the 

results of continuing radiolysis 

modeling, albeit with less-than-optimal 

codes that have been jerry-rigged from 

our reactor modeling work. 

Nevertheless, if the fields are as high as 

Bob indicates, the eventual production 

of nitric acid, in addition to the elevation 

of the redox potential, becomes a 

critical issue.

PK Co-precipitation has been demonstrated 

experimentally, although the 

phenomenon cannot be predicted from 

first principles or quantitatively.
H-39

T4-12 L Zinc oxide and hydroxide dissolves at 

pH > PZC to form zincate ion (ZnO2

2-). 

Initial rankings changed due to following 

email, rankings indicated separately: 

Please find attached a table with my reassessments of some originally "high" 

ratings of issues. On examining these 

issues again, it was evident that I did 

not fully recognize the impact of:

1. Time of exposure after the initial 

LOCA.

2. The amount of the specific material in 

the containment (e.g., zinc).

My re-assessments also reflect the 

results of continuing radiolysis 

modeling, albeit with less-than-optimal 

codes that have been jerry-rigged from 

our reactor modeling work. 

Nevertheless, if the fields are as high as 

Bob indicates, the eventual production 

of nitric acid, in addition to the elevation 

of the redox potential, becomes a 

critical issue.

K The conditions under which dissolution 

occurs are well characterized 

experimentally and thermodynamically.
H-40

T4-13 L Destruction of Zn-based coatings will 

contribute to the inventory of corrosion 

products, including zinc species in the 

solution. Initial rankings changed due 

to following email, rankings indicated 

separately: Please find attached a table 

with my re-assessments of some 

originally "high" ratings of issues. On 

examining these issues again, it was 

evident that I did not fully recognize the 

impact of:

1. Time of exposure after the initial 

LOCA.

2. The amount of the specific material in 

the containment (e.g., zinc).

My re-assessments also reflect the 

results of continuing radiolysis 

modeling, albeit with less-than-optimal 

codes that have been jerry-rigged from 

our reactor modeling work. 

Nevertheless, if the fields are as high as 

Bob indicates, the eventual production 

of nitric acid, in addition to the elevation 

of the redox potential, becomes a 

critical issue.

PK While this true, the rate with which Zn 

dissolution products accumulate from 

coatings cannot be predicted 

quantitatively. The formation of zinc 

carbonates, hydroxides, and 

phosphates can be predicted 

thermodynamically.

T4-14 Do not understand the term “seal 

table”)?

 
H-41

T4-15 L Fire barriers containing silicon-based 

materials might become a significant 

source of solid products. Initial 

rankings changed due to following 

email, rankings indicated separately: 

Please find attached a table with my reassessments of some originally "high" 

ratings of issues. On examining these 

issues again, it was evident that I did 

not fully recognize the impact of:

1. Time of exposure after the initial 

LOCA.

2. The amount of the specific material in 

the containment (e.g., zinc).

My re-assessments also reflect the 

results of continuing radiolysis 

modeling, albeit with less-than-optimal 

codes that have been jerry-rigged from 

our reactor modeling work. 

Nevertheless, if the fields are as high as 

Bob indicates, the eventual production 

of nitric acid, in addition to the elevation 

of the redox potential, becomes a 

critical issue.

PK Dissolution phenomenon are 

characterized empirically, but insufficient 

data are available for predicting the 

accumulation of products.

T4-16 M Organic material could increase the 

buoyancy of debris, thereby aiding its 

transport.

K The floatation of minerals is a much 

understood phenomenon in the mining 

industry.

T4-17 H Leaching of submerged coatings could 

contribute species to the containment 

pool, including Pb from Pb-based 

paints.

PK The general principles of leaching are 

understood from the mining industry, but 

the rates cannot be predicted 

quantitatively at the current time.
H-42

T4-18 H RCP oil is stored in tanks in 

containment. The failure of these tanks 

would contribute significantly to the 

inventory of foreign material in the 

containment pool.

PK Since the oil is a liquid, it is difficult to 

predict exactly the consequences of the 

rupture of an oil storage tank.

T4-19 L Biofilms that may form on metal 

surfaces could lead to the production of 

acids and hence increase metal 

corrosion rates.

PK The time frame is too short for this to be 

a serious issue. Also, oxidizing 

bacteria, which might produce organic 

acids, would be inhibited if reducing 

conditions exist within containment. 

Finally, the buffer capacity of the coolant 

should overwhelm any organic acid 

formed.

T4-20 L General corrosion enhanced under 

reducing conditions by SRBs (sulfate 

reducing bacteria).

PK The time frame is too short for this to be 

a serious issue.

T4-21 M SRBs might cause hydrogen 

embrittlement in submerged 

components.

PK Occurs only on iron and carbon steels, 

but the time is too short for this to be a 

significant issue.

T4-22 M Bacteria grow in pre-existing debris 

beds and contribute to screen clogging.

PK Again, the time frame is too short for this 

to be a serious issue.

T4-23 M Chlorides form via the radiolytic 

breakdown of cable insulation.

K The rate of radiolytic degradation of 

many insulation materials is well-known 

and it is possible to estimate the 

chloride release rate if the ionizing 

radiation dose rate is known. Unless 

the dose rates are very high, the release 

rate is expected to be low and of little 

consequence compared with other 

sources. See T3-5.
H-43

T4-24 M Oxide spalling off reactor fuel due to the 

high temperature gradient across the 

cladding wall. Initial rankings 

changed due to following email, 

rankings indicated separately: Please 

find attached a table with my reassessments of some originally "high" 

ratings of issues. On examining these 

issues again, it was evident that I did 

not fully recognize the impact of:

1. Time of exposure after the initial 

LOCA.

2. The amount of the specific material in 

the containment (e.g., zinc).

My re-assessments also reflect the 

results of continuing radiolysis 

modeling, albeit with less-than-optimal 

codes that have been jerry-rigged from 

our reactor modeling work. 

Nevertheless, if the fields are as high as 

Bob indicates, the eventual production 

of nitric acid, in addition to the elevation 

of the redox potential, becomes a 

critical issue.

K This phenomenon can be predicted, in 

principle, from a thermal stress analysis. 

Sufficient spalling may compromise the 

integrity of the cladding, thereby 

increasing the risk of fission product 

release.

T4-25 H Radio nuclides transported into the 

debris bed will alter the local chemical 

conditions.

K See xxxx

T4-26 H Radiolysis results in changes in 

oxidation states of materials and 

determines the reaction products 

formed.

K See xxxx
H-44

T4-27 M Radiolysis inhibits the formation of 

biofilms. Initial rankings changed due 

to following email, rankings indicated 

separately: Please find attached a table 

with my re-assessments of some 

originally "high" ratings of issues. On 

examining these issues again, it was 

evident that I did not fully recognize the 

impact of:

1. Time of exposure after the initial 

LOCA.

2. The amount of the specific material in 

the containment (e.g., zinc).

My re-assessments also reflect the 

results of continuing radiolysis 

modeling, albeit with less-than-optimal 

codes that have been jerry-rigged from 

our reactor modeling work. 

Nevertheless, if the fields are as high as 

Bob indicates, the eventual production 

of nitric acid, in addition to the elevation 

of the redox potential, becomes a 

critical issue.

PK This is true at high dose rates, but may 

not be so at low dose rates.

T4-28 H Radiolysis causes changes in the redox 

potential in the debris bed and the 

containment pool.

K This effect can be predicted using 

radiolysis models for water and the 

mixed potential model.

T4-29 H Radiolysis of chloride-containing water 

produces HClO (hypochlorous acid), 

which enhances the corrosion rates of 

metals and alloys.

K This effect can be predicted using 

radiolysis models for water and the 

mixed potential model.

T4-30 L Radiolysis enhances the agglomeration 

of chemical species.

UK Reviewer is unaware of this effect.
H-45

T4-31 L Radiolysis may convert CO2 into 

carbonates.

UK Since the oxidation state of carbon in 

CO2 and CO32- is the same (+4), it is 

difficult to see how radiolysis can 

convert one into the other.

T4-32 H Erosion-corrosion of pump components 

due to particulates in the water.

K This is a well established phenomenon 

that could easily lead to degradation of 

pump performance.

T4-33 M Pump seal degradation might contribute 

to debris inventory. Potential amount of 

debris is probably small compared with 

that from other sources.

K This is a well established phenomenon 

that could easily lead to degradation of 

pump performance.

T4-34 L Failure of steam generator may allow 

contamination of the containment pool 

with secondary side coolant. The 

chemistry of the secondary coolant is 

such that the impact would be minor 

and may even be beneficial.

K The chemistry of the secondary coolant 

is well-defined and its impact on the 

containment pool chemistry is readily 

predicted.

T4-35 M Precipitation of solids in the heat 

exchanger may reduce the efficiency of 

heat transfer. This is potentially 

important, in terms of heat removal from 

the core, but in the event of a LOCA the 

majority of the heat will be removed by 

coolant flowing from the break.

PK Precipitation can be predicted 

qualitatively and possibly semiquantitatively if the chemistry is welldefined. Recirculated containment pool 

water may make this prediction difficult.

T4-36 M Drop in pH of evolving containment pool 

water may cause the precipitation of 

aluminum (and other metal) hydroxides. 

It is not clear what process could cause 

such a drop in the face of the high 

buffer capacity.

UK The process causing the reduction in pH 

would need to be first identified.
H-46

T4-37 H Precipitation of solids in the core could 

impede heat transfer from the fuel and 

lead to overheating of the fuel, 

ultimately resulting in fuel cladding 

failure and the release of fission 

products.

PK Precipitation can be predicted 

qualitatively and possibly semiquantitatively if the chemistry is welldefined. Recirculated containment pool 

water may make this prediction difficult.

T4-38 H Spalling could lead to cladding failure 

and the release of fission products to 

containment.

K The oxidation and spalling of zirconium 

alloys is well characterized and, if the 

chemistry of the environment can be 

defined, the phenomenon can be 

predicted.

T4-39 L Amorphous silica forms on the surfaces 

of precipitates and makes less likely 

their transport to the sumo screen. I do 

not see the chemical basis for this 

postulate.

UK The process responsible for the 

proposed effect would need to be first 

identified.

T4-40 M Co-precipitation and ripening would 

produce larger precipitates that are less 

likely to be transported to the screens. 

That may be correct, but the larger size 

might greatly increase the probability of 

entrapment of those particles that are 

transported to the screens.

PK The effect of size on the tendency of 

particles to settle, be transported, and to 

be trapped can be predicted if the flow 

field can be defined to characterize the 

hydrodynamic forces involved.
H-47

T4-41 M Turbulent flow, particularly under 

impingement conditions, may cause the 

rapid loss of material from a surface and 

hence contribute to the debris inventory 

in the pool. Initial rankings changed 

due to following email, rankings 

indicated separately: Please find 

attached a table with my reassessments of some originally "high" 

ratings of issues. On examining these 

issues again, it was evident that I did 

not fully recognize the impact of:

1. Time of exposure after the initial 

LOCA.

2. The amount of the specific material in 

the containment (e.g., zinc).

My re-assessments also reflect the 

results of continuing radiolysis 

modeling, albeit with less-than-optimal 

codes that have been jerry-rigged from 

our reactor modeling work. 

Nevertheless, if the fields are as high as 

Bob indicates, the eventual production 

of nitric acid, in addition to the elevation 

of the redox potential, becomes a 

critical issue.

K Erosion-corrosion, scouring, and 

impingement attack are well defined and 

this phenomenon could, in principle, be 

defined with sufficient accuracy for the 

present purposes.
APPENDIX I

PIRT Panelist Evaluation of T5 Phenomena:

ECCS Recirculation from 15 Days until 30 Days into 

LOCA
I-2

Table I-1: ECCS Recirculation (15 days to 30 days)a,b

Issue 

Number

Phenomena Description Implications

T5-1 Organic 

radiolysis

Radiolysis of organics leads 

to carbonate formation 

1. Create nucleation sites for 

species precipitation

2. scavenge dissolved Ca to 

impede formation of other 

compounds

3. Additional solid species 

contribution which leads to 

degraded system 

performance (head loss, 

etc.) a Sump pool temperatures are expected to range between 40 – 60C during this time period.

b Phenomena listed in earlier time periods (i.e., T1, T2, T3, T4) may continue to be active or 

important during this time.
Table I-2: Apps T5 Ranking Summary

Issue 

Number

Importance 

(H, M, L)

Rationale Knowledg

e (K, PK, 

UK)

Rationale

T5-1 L Amount of organics likely to be small in 

relation to other debris and reactants.

UK Further study required to quantify 

effects.
I-4

Table I-3: Chen T5 Ranking Summary

Issue 

Number

Importance 

(H, M, L)

Rationale Knowledg

e (K, PK, 

UK)

Rationale

T5-1 No 

comment

 No 

comment
I-5

Table I-4: Delegard T5 Ranking Summary

Issue 

Number

Importance 

(H, M, L)

Rationale Knowledg

e (K, PK, 

UK)

Rationale

T5-1 M Radiolysis of organic materials likely to 

lead to other products before carbonate.

PK Testing of radiolysis of organic materials 

has not been done for the post-LOCA 

system.
I-6

Table I-5: Litman T5 Ranking Summary

Issue 

Number

Importance 

(H, M, L)

Rationale Knowledg

e (K, PK, 

UK)

Rationale

T5-1 L Unless there is a significant introduction 

of organic materials after the initial 

event this will not be significant term.

PK This is dependent upon ingress of oils 

(degraded pumps),or biologicals (raw 

water leaks).
I-7

Table I-6: MacDonald T5 Ranking Summary

Issue 

Number

Importance 

(H, M, L)

Rationale Knowledg

e (K, PK, 

UK)

Rationale

T5-1 M Radiolysis of organic material leads to 

carbonate formation and ultimately to 

the precipitation of calcium carbonate, 

which contributes to the solid inventory 

in the pool. This is possible, but 

whether carbonate forms will depend 

upon the redox potential. Initial 

rankings changed due to following 

email, rankings indicated separately: 

Please find attached a table with my reassessments of some originally "high" 

ratings of issues. On examining these 

issues again, it was evident that I did 

not fully recognize the impact of:

1. Time of exposure after the initial 

LOCA.

2. The amount of the specific material in 

the containment (e.g., zinc).

My re-assessments also reflect the 

results of continuing radiolysis 

modeling, albeit with less-than-optimal 

codes that have been jerry-rigged from 

our reactor modeling work. 

Nevertheless, if the fields are as high as 

Bob indicates, the eventual production 

of nitric acid, in addition to the elevation 

of the redox potential, becomes a critical 

issue.

PK The radiolysis of water is fairly welldefined, but the redox conditions 

necessary for the formation of 

carbonate is not.