NUREG/CR-6369, Vol. 2 

SEA 97-3105-A: 15

Drywell Debris Transport

Study: Experimental Work 

Final Report 

Science and Engineering Associates, Inc. 

U.S. Nuclear Regulatory Commission 

Office of Nuclear Regulatory Research 

Washington, DC 20555-0001
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NUREG/CR-6369, Vol. 2 

SEA 97-3105-A:15 

Drywell Debris Transport 

Study: Experimental Work 

Final Report 

Manuscript Completed: February 1998 

Date Published: September 1999 

Prepared by 

D. V. Rao, C. Shaffer, B. Carpenter/SEA 

D. Cremer, I Brideau/SEA 

G. Hecker, M. Padmanabhan, P. Stacey/ARL 

Science and Engineering Associates, Inc. 

6100 Uptown Blvd. NE 

Albuquerque, NM 87110 

Subcontractor: 

Alden Research Laboratory 

30 Shrewsbury Street 

Holden, MA 01520 

Prepared for 

Division of Engineering Technology 

Office of Nuclear Regulatory Research 

U.S. Nuclear Regulatory Commission 

Washington, DC 20555-0001 

NRC Job Code W6325
NUREG/CR-6369, Vol. 2, has been 

reproduced from the best available copy.
Abstract

This report describes three test programs undertaken as part of the DDTS to provide basic understanding regarding transport 

of insulation fragments in the drywell following a postulated LOCA. The first two tests focused on transport of debris by 

blowdown flow. They obtained data related to (a) inertial capture of insulation debris on typical BWR drywell structures 

while they are transported across the structures by the steam flow; and (b) degradation of large insulation pieces captured on 

floor gratings when exposed to high velocity steam flow with suspended droplets. These tests clearly established that wet 

floor gratings would capture significantly more debris than any other BWR drywell structures (e.g., pipes, I-beams and 

vents). The capture efficiency of all structures was found to be a strong function of debris size and structural wetness, but a 

weak function of flow velocity and local flow patterns. Floor gratings possess 100% capture efficiency for insulation pieces 

larger than 6"x4". These large pieces do not degrade or are not forced through the grating clearances (1.5"x4") when 

subjected to high velocity droplet flow, even though the differential pressure across them is as high as 1 psid. 

The third test program addressed the issue of washdown of debris previously captured on floor gratings by break over flow 

or containment spray flow during ECCS recirculation phase. These tests concluded that majority of the small debris pieces 

captured on various structures would be washed down by break flow or spray flow. On the other hand, erosion is the only 

available mechanism by which large pieces deposited on the floor gratings would be transported. In three hours, as much as 

25% of the larger pieces can be eroded and transported to the suppression pool.

ini NUREG/CR-6369
Contents 

Page 

Abstract . iii 

Executive Summ ary ................................................................................ xiii 

A cknowledgm ents .................................................................................. xv 

A cronym s ........................................................................................ xvi 

1 Introduction ................................................................................... 1-1 

1.1 Background and Objectives ................................................................. 1-1 

1.2 Program O verview ........................................................................ 1-1 

1.3 R eferences .............................................................................. 1-4 

2 Separate Effects Test Program to Evaluate Inertial Debris Capture on BWR Drywell Structures ................. 2-1 

2.1 Phenomena Selected for Study ............................................................... 2-1 

2.2 Test Facility ............................................................................. 2-1 

2.2.1 Flow Tunnel ...................................................................... 2-1 

2.2.2 Insulation Injection ................................................................ 2-4 

2.2.3 Geometry of Objects Tested ......................................................... 2-4 

2.2.4 Insulation Debris Generation ......................................................... 2-4 

2.3 Test Plan and Procedure .................................................................... 2-9 

2.3.1 Test M atrix ....................................................................... 2-9 

2.3.2 Test Procedure .................................................................... 2-9 

2.4 Results .......................................................................... 2-11 

2.4.1 Gravitational Settling .............................................................. 2-20 

2.4.2 Effect of Obstructions Tested Individually ............................................. 2-20 

2.4.3 Effect of Approach Velocity ........................................................ 2-20 

2.4.4 Effect of Surface W etness .......................................................... 2-25 

2.4.5 Effect of Debris Size (Class of Insulation Debris) ....................................... 2-25 

2.4.6 Effect of Debris Loading ........................................................... 2-25 

2.4.7 Effect of Structural Combinations .................................................... 2-26 

2.4.8 Vent Cover Testing ............................................................... 2-30 

2.4.9 Upstream and Downstream Gratings .................................................. 2-30 

2.4.10 Grating Debris Degradation Tests .................................................... 2-32 

2.4.11 Overall Evaluation of Application of Results ........................................... 2-37 

2.5 Conclusions ............................................................................ 2-37 

2.6 References ............................................................................. 2-38 

v NUREG/CR-6369
Contents (Continued) 

Page 

3 Integrated Effects Test Program to Evaluate Inertial Debris Capture on BWR Drywell 

Stru ctures ...................................................................... ............ 3-1 

3.1 B ackground and Objectives ................................................................. 3-1 

3.1.1 O bjectives and Scope ............................................................... 3-1 

3.2 Program Elem ent ......................................................................... 3-2 

3.2.1 D evelopm ental Tests ............................................................... 3-2 

3.2.2 Production Tests ................................................................... 3-2 

3.2.3 D ata A nalyses .................................................................... 3-2 

3.3 Test Facility D escription ................................................................... 3-3 

3.3.1 A ir Blast Test Cham bers ............................................................ 3-3 

3.3.2 Structural Test Section .............................................................. 3-3 

3.3.3 Test Instrum entation ............................................................... 3-5 

3.4 Scaling Considerations ................................................................... 3-5 

3.5 D evelopm ental Tests ..................................................................... 3-13 

3.5.1 Test M atrix for the Developmental Tests ............................................... 3-13 

3.5.2 Flow Velocity M apping ............................................................ 3-14 

3.5.2.1 N ozzle D ischarge ........................................................ 3-14 

3.5.2.2 Pitot Tube Perform ance ................................................... 3-14 

3.5.2.3 Characteristic Bulk Flow Velocities .......................................... 3-15 

3.5.2.4 Adequacy of Flow Fields Relative to Debris Transport Objectives .................. 3-19 

3.5.3 Initial Debris Generation and Transport Characteristics ................................... 3-19 

3.5.3.1 D ebris G eneration ....................................................... 3-19 

3.5.3.2 Jet D uration ............................................................ 3-19 

3.5.3.3 Surface W etting ......................................................... 3-19 

3.5.4 Facility Modification and Test Procedure Development ................................... 3-19 

3.6 Production Tests ......................................................................... 3-20 

3.6.1 Test M atrix for the Production Tests .................................................. 3-20 

3.6.2 Description of Target Insulation Blankets .............................................. 3-20 

3.6.3 Testing Procedures ................................................................ 3-20 

3.6.4 Data Collection Procedures ......................................................... 3-22 

3.6.4.1 Debris Collection Locations ................................................ 3-22 

3.6.4.2 Debris Classifications ..................................................... 3-22 

3.6.4.3 Photographic D ata ....................................................... 3-27 

NUREG/CR-6369 vi
Contents (Continued) 

Page 

3.6.5 Drying and W eighing Debris ........................................................ 3-32 

3.7 Debris Transport and Capture Test Results .................................................... 3-33 

3.7.1 Definitions of Debris Transport and Capture Fractions .................................... 3-33 

3.7.2 Data Reduction Procedure .......................................................... 3-34 

3.7.3 Estimate of Non-Recovered Mass Distribution .......................................... 3-34 

3.7.4 Estim ate of Canvas Cover W eight .................................................... 3-35 

3.7.5 Error A nalysis ................................................................... 3-35 

3.7.5.1 Source of Experim ental Error .............................................. 3-35 

3.7.5.2 Bounding Experimental Error .............................................. 3-37 

3.7.6 T est R esults ..................................................................... 3-38 

3.7.6.1 Transport of Small Sized Debris ............................................ 3-38 

3.7.6.2 Transport of Large and Medium Sized Debris .................................. 3-45 

3-8 R eferences ............................................................................. 3-50 

4 Separate Effects Test Program to Evaluate Washdown of Insulation Debris by ECCS Flow .................... 4-1 

4.1 Introduction ............................................................................ 4-1 

4.1.1 B ackground ...................................................................... 4-1 

4.1.2 O bjectives and Scope ............................................................... 4-1 

4.2 T est Facility ............................................................................. 4-1 

4.2.1 T est Setup ........................................................................ 4-1 

4.2.2 D ebris M aterials ................................................................... 4-3 

4.3 Test Plan and Test Procedure ................................................................ 4-4 

4.3.1 T est M atrix ....................................................................... 4-4 

4.3.2 Test Proceudre .................................................................... 4-5 

4.4 T est R esults ............................................................................. 4-5 

4.4.1 Confirm atory Tests ................................................................ 4-5 

4.4.2 Erosion Tests ..................................................................... 4-9 

4.4.2.1 Effect of Flow Rate (Break versus Spray) ..................................... 4-10 

4.4.2.2 Effect of Duration Erosion ................................................. 4-10 

4.4.2.3 Effect of Bed Thickness (or initial mass) ...................................... 4-10 

4.4.2.4 Effect of Debris Size and Structure on Erosion ................................. 4-10 

4.4.2.5 Experimental Data Repeatability ............................................ 4-10 

vii NUREG/CR-6369
Contents (Continued) 

Page 

4.5 Sum m ary and Conclusions ................................................................. 4-13 

4-6 R eferences ............................................................................. 4-13 

5 C onclusions ................................................................................... 5-1 

5.1 A ir B orne Transport ....................................................................... 5-1 

5.2 Transport During Long-Term ECCS Recirculation ............................................... 5-1 

NUREG/CR-6369 viii
Figures 

Page 

I-1 Potential debris transport pathways studied .................................................. 1-2 

1-2 Debris sizes and distributions used in study .................................................. 1-3 

2-1 General arrangement of test tunnel .......................................................... 2-2 

2-2 Test tunnel components showing test sections and filter box ..................................... 2-3 

2-3 Non-dimensional velocity distribution in large test tunnel with final flow conditioner ................ 2-5 

2-4 Head loss across flow conditioner versus average velocity in large (4ft x 4 ft) test 

Section .............................................................................. 2-6 

2-5 D ebris injection system .................................................................. 2-7 

2-6 Pre-injection sizes of shredded nukon fibrous insulation debris shown on a 2" x 2" grid ............... 2-8 

2-7 Comparison of debris capture from A) test 6, and B) test 8 ..................................... 2-21 

2-8 Debris capture on the 2-ft diameter pipe; 50 ft/sec, Class 2 to 4 debris, 

and 6.3 -gm/ftf approach concentration ..................................................... 2-22 

2-9 Debris capture on single grating at 50 ft/sec ................................................. 2-23 

2-10 Arrangement and debris capture with two gratings; 50 ft/sec, Class 2 to 4 ......................... 2-24 

2-11 Debris capture on grating test; 50 ft/s, Class 2 to 6+ debris, and 12.5 gin/ft2 

approach concentration (test 25) .......................................................... 2-27 2-12 Combined m ember layouts .............................................................. 2-28 

2-13 Debris capture on test combination 3; 50 ft/sec, Class 2 to 4 debris, and 6.3 gm/ft2 

approach concentration (test 16) .......................................................... 2-29 

2-14 Simulated M ark II vent geometry ......................................................... 2-31 

2-15 Effects of approach concentration and velocity on debris retention at gratings ...................... 2-33 

2-16 Effects of blockage of gratings on tunnel velocity and pressure drop through debris ................. 2-34 

2-17 Insulation blockage with 5-1/2" thick pieces held in place on floor grating 

Prior to starting the blower .............................................................. 2-35 

2-18 Results of blockage tests with 1A"-thick insulation pieces: 40% initial blocked area ................. 2-36 

2-19 Debris blockage after test; 140 ft/s and 60 sec water spray on 100% blockage 

using 1/8" insulation layer .............................................................. 2-37 

3-1 CEESI outside calibration facility .......................................................... 3-3 

3-2 CEESI facility structure dimensions ........................................................ 3-4 

3-3 Schem atic of structural test section ......................................................... 3-4 

3-4 Frontal view of a structural test section ..................................................... 3-6 

3-5 CEESI debris transport instrumentation ..................................................... 3-6 

3-6 Typical CFD calculated flow patterns near jet nozzle and target ................................... 3-9 

3-7 Typical CFD calculated flow patterns in structural test section .................................. 3-10 

3-8 Typical nozzle pressure history ................................................. ......... 3-15 

3-9 Typical pitot tube response .............................................................. 3-16 

3-10 Out-of-range pitot tube response ......................................................... 3-17 

3-11 Plugged pitot tube response ............................................................. 3-17 

3-12 Comparison of measured and predicted bulk flow velocities .................................... 3-18 

3-13 Target blanket installation ............................................................... 3-21 

3-14 Sampling of small pieces of debris ........................................................ 3-24 

3-15 Sampling of medium pieces of debris ...................................................... 3-24 

3-16 Sampling of large pieces of debris ........................................................ 3-25 

3-17 Sample of agglomerate debris ............................................................ 3-25 

3-18 Comparison of debris samples ........................................................... 3-26

ix NUREG/CR-6369
Figures (Continued)

Page 

3-19 Sampling of shredded canvas debris ....................................................... 3-26 

3-20 Large section of canvas on continuous grating (Test H6) ....................................... 3-28 

3-21 Typical debris deposition on split grating (Test H1R) ......................................... 3-28 

3-22 Typical debris deposition on split grating (Test H2) .......................................... 3-29 

3-23 Typical debris deposition on V-grating (Test H2) ............................................ 3-29 

3-24 Debris deposition on a dry split grating (Test H7) ............................................ 3-30 

3-25 Deposition in auxiliary tank at bend (Test H2) ............................................... 3-30 

3-26 W ater film on horizontal I-beam (Test H I) ................................................. 3-31 

3-27 View of exhaust screen in auxiliary tank (Test H I R) .......................................... 3-31 

3-28 View of panel blocking of diffuser section behind nozzle (Test H7) .............................. 3-32 

3-29 Distribution of non-recovered insulation mass ............................................... 3-36 

3-30 Overall Transport of small debris through test facility ......................................... 3-39 

3-31 Capture of small debris by I-beams and pipes ............................................... 3-41 

3-32 Capture of small debris by V-grating ...................................................... 3-43 

3-33 Capture of small debris by split grating .................................................... 3-44 

3-34 Capture of small debris by continuous grating ............................................... 3-47 

3-35 Capture of small debris by auxiliary tank bend .............................................. 3-48 

3-36 Demonstration of CEESI test repeatability .................................................. 3-49 

4-1 Photograph of the washdown experimental wet-up ............................................ 4-2 

4-2 Schematic representation of the washdown test setup .......................................... 4-2 

4-3 Erosion of medium size debris manually cut from original blankets by 

B reak flow (Test #1) .................................................................... 4-7 

4-4 Erosion of small air jet generated debris by spray flow (Test 13) ................................. 4-8 

4-5 Eroded pieces filtered by coarse debris catcher (Test 2) ......................................... 4-9 

4-6 Effects of duration of Erosion on the percentage of initial blanket eroded .......................... 4-12

NUREG/CR-6369 X
Tables 

Page 

E-1 Debris capture efficiencies ............................................................... Xiv 

2-1 Debris capture testing matrix for completed tests ............................................. 2-10 

2-2 Results of BW R drywell capture tests ..................................................... 2-12 

2-3 Effect of debris size ................................................................... 2-26 

3-1 Typical BW R drywell surface areas ....................................................... 3-12 

3-2 Summary of CEESI facility scaling to Mark I drywell ......................................... 3-12 

3-3 Test matrix for the developmental tests .................................................... 3-14 

3-4 Pitot tubes/transducer ranges of performance ................................................ 3-16 

3-5 Measured characteristic bulk flow velocities ................................................ 3-18 

3-6 Test matrix for the production tests ....................................................... 3-21 

3-7 Insulation debris sizes .................................................................. 3-23 

3-8 Comparable ARL I-beam and pipe debris capture data ........................................ 3-42 

3-9 Modified ARL I-beam/pipe debris capture data .............................................. 3-42 

3-10 Comparable ARL capture data for gratings ................................................. 3-46 

3-11 Test m atrix for the repeatability tests ...................................................... 3-49 

4-1 Experim ental uncertainties ............................................................... 4-4 

4-2 Test matrix for SEA washdown experiments ................................................. 4-6 

4-3 Results of washdown erosion test program .................................................. 4-11 

4-4 Effect of flow rate (i.e., break versus spray) on erosion of debris ................................ 4-12 

4-5 Effect of debris size and structure on erosion ................................................ 4-12 

4-6 Effect of debris size, debris loading (i.e., thickness) and test duration on erosion .................... 4-13 

5-1 Capture fractions recommended for estimating drywell transport fractions during 

Blow down (short-term ) .................................................................. 5-2

xi NUREG/CR-6369
Executive Summary

A postulated LOCA in a BWR whose primary piping is 

insulated with fibrous insulation will generate fibrous 

debris in a region close to the broken pipe. These 

insulation fragments, ranging in size from small 

fragments to partially damaged blankets, will be entrained 

by the ensuing steam flow and carried through the 

drywell to the suppression pool. However, the drywell is 

congested with numerous structural elements (e.g., pipes, 

gratings, I-beams and vents) that could impede such 

transport. The debris particles are expected to impact 

these structural elements, which are expected to be wet as 

a result of steam condensation and droplet deposition. It 

was not known if such a particle upon impact will be 

captured on the structural surface or will be sheared off 

by the high flow velocity (25-150 ft/s). It was also 

unknown whether the captured debris would be retained 

on the structures in spite of short-term (= I minute) 

exposure to high steam flow during the remaining 

blowdown or long-term exposure (15-180 minutes) to 

water from break overflow or containment spray flow. 

Three experiments were designed and conducted as part 

of the DDTS to provide basic understanding and insights 

related to short-term and long-term fibrous debris 

transport in the BWR drywells. The first two experiments 

focused on studying inertial capture of fibrous debris on 

typical drywell structures during airborne transport. The 

third experiment studied washdown of debris previously 

deposited on various drywell structures by break overflow 

and containment sprays. 

A series of separate effects tests were conducted at ARL 

to obtain a basic understanding of fibrous insulation 

capture on typical BWR drywell structures due to inertial 

capture. Using an air flow tunnel with water spray 

nozzles, these tests studied debris capture as influenced 

by size of debris particles, mass loading of debris 

(grr/ftl), shape and orientation of individual structures, 

congestion of structures, structural wetness, and gas fluid 

velocity. Low gas velocity tests, between 25 and 50 ft/s, 

were conducted using the full 4 ft by 4 ft cross-sectional 

area of the tunnel, and a smaller test section insert (2 ft by 

2ft) was used to achieve velocities as high as 150 ft/s. 

Mechanically shredded and pre-weighed fibrous debris of 

different sizes was injected into flow stream using a 

debris injection gun. The debris capture fraction for each 

structure was estimated as the ratio of the debris deposited 

on the structure to the quantity of debris approaching that 

structure. The major findings of the study were that 

gratings captured more debris than any other drywell 

structures, that surface wetness strongly influenced debris 

capture, and that capture on vent plates and vent entrance

is moderate. 

While the ARL separate effects tests provided valuable 

data, the tests had notable limitations of relatively light 

debris loading on the structures compared to expected 

BWR conditions, modest assortment of debris sizes and 

non-prototypical congestion of structures. Also, the test 

data was obtained for simplified flow fields (plug flow 

approaching the structures). Application of such a data to 

BWR drywells would have required detailed 

understanding of the local flow fields in each region of 

the containment. These limitations prompted additional 

experiments of a more integrated nature. The principle 

objectives of these tests were two-fold: (1) to provide 

debris capture fractions for each structure that could be 

compared to ARL tests to quantify impact (if any) of the 

three dimensional flow patterns that are more typical of 

BWR drywells, and (2) to provide integrated data that 

could be used to benchmark analytical models and 

methods that are ultimately used to predict debris 

transport within a BWR drywell. 

These integrated debris transport tests were carried out at 

the CEESI air blast facility by SEA. The test method 

selected was debris generation and subsequent transport 

by a dispersing 1100-psi air jet through a tunnel with 

structural characteristics scaled to a BWR drywell. The 

tunnel was 70 feet long and 10 ft in diameter. It was 

equipped with water fog-sprays to uniformly wet the 

structures with warm water and space heaters to pre-heat 

the structures and tunnel atmosphere. The debris were 

generated by jet impingement on an aged insulation 

blanket constrained on both sides to maximize debris 

generation. The debris was then carried by the airflow 

over 20-ft long structural congestion, a 900 bend, and a 

Mark I vent entrance, all of which were pre-wet fed by 

warm water to simulate surface wetness. The structural 

arrangement was designed to be representative of a BWR 

drywell based upon a survey of Mark I and Mark II 

containments. The design of the test section and the 

nozzle arrangement was based on computational fluid 

dynamics simulation of the drywell as well as that of the 

test facility. The tests demonstrated the ability of 

structural components to capture debris. The average 

overall transport fraction for small debris in the CEESI 

facility was 33% of the total debris generated. Once 

again gratings were found to be the most effective debris 

catcher. The average fraction of debris captured by each 

test structural component are given in Table E- 1. The 

capture fractions were found to be relatively independent 

of the debris mass loading (lbm/ft2) impacting the

xiii NUREG/CR-6369
structures, at least within the range of interest to BWR 

drywells. The debris capture data are consistent with 

ARL test data indicating that the finer aspects of the local 

flow fields (e.g., eddies and wake) do not significantly 

influence debris capture. 

The ARL and CEESI tests clearly established that a 

fraction of the small and large debris would be deposited 

as they are transported through the drywell during 

blowdown. Likely locations for the deposition are floor 

gratings located at different elevations. These pieces 

would then be subjected to remaining blowdown flow, 

which consists mainly of steam intermixed with water 

droplets, and washdown water flow. Short-term erosion 

or detachment of these pieces from the location where 

they were originally deposited was studied using the ARL 

test facility. In these tests, 6" by 6" pieces (1/4"-thick) 

were mounted on a grating normal to the flow direction 

and were exposed to airflow at a velocity of 150 ft/s and 

water drop quality as high as 10%. Under these 

conditions, the pressure drop across the pieces was as 

high as 0.5 psi. No noticeable degradation in the pieces 

was observed and nearly 100% of the debris was located 

at the original location where they were deposited by 

inertial capture.

Long-term erosion and relocation caused by water flows 

was studied at an SEA test facility. In these tests, debris 

of various sizes were placed on gratings and pipes and 

subjected to water flow typical of containment spray 

nozzles and break overflow. The structures were 

assembled in a 2-ft by 2-ft test section with clear glass to 

visualize test progression. The debris used were primarily 

generated by air jets, although a few large pieces of 

manually cut pieces were used in selected tests. The 

testing established that both containment sprays and break 

overflow are capable of washing down small debris 

deposited on various drywell structures during blowdown. 

The larger pieces do not undergo instantaneous 

degradation when subjected to water flow as high as 50 

GPM/ft2 ; instead, they erode continuously with time. Rate 

of erosion is negligible for containment sprays, but can be 

as high as 25% for break overflows, assuming continuous 

operation for three hours. 

The results of the experiments were used in conjunction 

with analytical models and engineering judgement to 

obtain drywell transport fractions. Analyses of the 

experimental results also were used to identify important 

plant features that control debris transport in the drywell.

Table E-1. Debris capture efficiencies.

NUREG/CR-6369

Structure Type Capture Fraction Capture Fraction 

Small Debris Large Debris 

I-beams and Pipes arranged to prototypical congestion 

over a debris path length of 20 ft 9% =0% 

Gratings 

V shaped grating (at an angle with flow) 28% 

Other grating (normal to bulk flow) 24% 100% 

900 bend in the flow 17% (None tested) 

Mark I Vent Entrance < 10% (None tested) 

Mark II Vent Entrance 15% (None-tested)

xiv
Acknowledgements

The authors would like to acknowledge contributions of Mr. Michael Marshall, Mr. Robert Elliott, and Mr. Aleck Serkiz of 

US Nuclear Regulatory Commission for their enthusiasm and unwavering support to the experimental program. Review 

comments provided by the Phenomena Identification and Ranking Table (PIRT) panel members, Drs. Gary Wilson, Lothar 

Wolf, Brent Boyack, Ken Williams and Mark Leonard was instrumental in the design and conduct of the experiments. 

Numerous individuals have contributed towards completion of this study. At SEA Mr. Kirk Weingardt, Ms. Kami Burr and 

Mr. Jerry Stockton played a key role conducting the experiments as well as during the data analysis. At CEESI, Mr. Roger Shaffer and Mr. Walt Seidel played a key role in preparing the experimental facility for testing. 

The ARL staff performed excellently to design and conduct the separate effects experiments on-time and within budget. Their contribution is especially impressive and has made this test program a pleasure to coordinate. 

Finally, SEA would like to recognize Mr. Bruce Alpha and Mr. Edward Wolbert of Transco Products, Inc. for their support of the experimental program. All of the target insulation blankets used in the integrated effects test were manufactured 

specifically for these tests and provided by Transco.

XV NUREG/CR-6369, Sup. 1
Acronyms

ARL Alden Research Laboratory Inc. 

BWR Boiling water reactor 

BWROG Boiling Water Reactor's Owners Group 

CEESI Colorado Engineering Experiment Station 

DDTS Drywell debris transport study 

ECCS Emergency core cooling system 

LOCA Loss of cooling accident 

MSLB Main steam line break 

PVC Polyvinyl chloride 

SEA Science and Engineering Associates, Inc.

NUREG/CR-6369 xvi
1. Introduction

1.1 Background and Objectives 

A LOCA in a BWR would generate piping insulation 

debris, ranging in size from small fibrous insulation pieces 

to partially torn insulation blankets. These debris would 

be transported from the drywell (where they are 

generated) to the suppression pool by the high velocity 

steam flow during blowdown. During their transport, 

there is a potential that some of these debris may be 

captured by inertial or other means on various drywell 

structures (e.g., pipes, gratings, I-beams and cable 

conduits), whose surfaces are expected to be wet due to 

steam condensation and droplet deposition. Following 

blowdown, debris transport can also occur during long

term ECCS recirculation mode when water is introduced 

into drywell as a result of break overflow or containment 

spray operation. As this water cascades down various 

structures, it may erode and wash down some of the debris 

previously deposited during blowdown phase, and deposit 

them on the drywell floor where they would be subjected 

to pool dynamics. Figure 1-1 illustrates these potential 

debris transport pathways. 

Tests were conducted as part of the DDTS to obtain 

experimental data related to: (a) debris capture on various 

drywell structures due to inertial impact while they are 

transported by steam-gas flow during blowdown and (b) 

washdown and erosion of such captured debris by water 

flow during long-term ECCS Recirculation phase. The 

overall objectives of the test program were to obtain 

experimental data that could be used in conjunction with 

analytical models to predict transport of debris in BWR 

drywells and to draw insights related to controlling 

phenomena and plant features that influence debris 

transport. 

1.2 Program Overview 

Three different test programs were undertaken to compile 

the required experimental program. All these tests studied 

transport of low-density fiberglass insulation commonly 

used in US nuclear power plants. All tests were 

conducted at ambient temperatures. Air-was used to 

simulate steam in the inertial capture tests. Figure 1-1 

illustrates the transport pathway studied in each test 

program.

The first series of tests, conducted at ARL, are separate 

effects tests, in that they were designed to provide basic 

understanding of the phenomena that control inertial 

capture of fibrous debris pieces of different sizes on 

typical drywell structures. Air was used to simulate steam 

and water sprays were used to wet the structural surfaces. 

These tests employed a 4-ft x 4-ft test section through 

which ambient air was forced by a blower. Insulation 

debris were transported by that airflow across the real size 

drywell structural elements, where a fraction of them were 

deposited due to inertial impaction. Associated inertial 

capture efficiencies were measured for typical drywell 

structures (I-beams, pipes, and floor gratings of various 

sizes and orientations, and vent assemblies) as a function 

of airflow velocity (over a range of 25-150 ft/s), surface 

wetness and debris size. The debris used in these tests 

were produced by mechanical shredding of the aged 

insulation blanket, using procedures previously 

established as part of NUREG/CR-6224 study [Refs. 1.1 

and 1.2]. Figure 1-2 compares the size distribution of 

debris used in these tests with the debris size descriptions 

provided in NUREGICR-6224 and the nomenclature used 

by the BWROG [Refs. 1.2 and 1.3]. Section 2 provides a 

description of these tests and the results of the test 

program. 

The second series of tests were conducted at CEESI to 

determine inertial capture efficiency of drywell structures 

assembled to prototypical congestion levels'. In these 

tests ambient temperature 1100-psi air jets were used to 

generate insulation debris and transport them over the 

structural assembly whose surfaces were pre-wet by warm 

water sprays. The transport velocities varied between 25

fts/s and 50-ft/s, which were determined to be prototypical 

transport velocities in the lower regions of the drywell 

following a MSLB. Transport efficiencies were measured 

as a function of debris size and structural surface wetness. 

Figure 1-2 compares size distribution of debris used in 

these tests, with those used in other tests [Refs. 1.2 and 

1.3]. A complete description of these tests, the scaling 

rationale used in their design and the experimental data 

are presented in Section 3. 

The final series of tests were conducted at SEA to obtain 

experimental data related to erosion and washdown of 

insulation debris previously deposited on various

1 Prototypical congestion levels were determined from a 

BWROG survey of Mark I and Mark II drywells.

1-1 NUREG/CR-6369
Introduction

Advected Long-Term

Figure 1-1. Potential debris transport pathways studied.

NUREG/CR-6369 1-2
Introduction

ARL Separate 1 2 3 4 5 6 

CEESI Integrated [Small 

Santa Fe Washdown Fines Small 

BWROG AJIT Fines 

PP&L Flume lA

Medium Large Canvas 

I M ie diu m 11 La rg e IH IIHII l Dfll lll Irllh I J1II I III 1I IIJ.II 

1Large Canvas 

g llI~ llllEllllfrrflllJIIIIll flItl lllfll Eflfllllllllll IH I

Figure 1-2. Debris sizes and distrubitions used in study.

1-3 NUREG/CR-6369
Introduction

structures when subjected to break overflow or 

containment spray flow. In these experiments, insulation 

debris fragments placed on various structures (e.g., 

gratings and pipes) were subjected to water flow scaled to 

be representative of containment sprays and break 

overflow. The fraction of debris transported due to a 

combination of washdown and erosion phenomena was 

measured as a function of debris size and time. Figure 1-2 

compares the size distribution of debris used in these tests, 

with those used in other tests [Refs. 1.2 and 1.3]. 

Section 4 provides further details on test description, test 

procedures, and test results. 

Section 5 discussed overall findings of the experimental 

study and their recommended usage. This section also 

provides a comparison of the data with that obtained from 

previous experiments (e.g., BWROG test program).

The results from these tests were used to quantify 

appropriate logic tree branches as described in the main 

body of this report. 

1.3 References 

1.1 D. V. Rao and F. Souto, "Experimental Study of 

Head Loss and Filtration for LOCA Debris," 

NUREG/CR-637, Science and Engineering 

Associates, Inc., 1996. 

1.2 G. Zigler, et al., "Parametric Study of the Potential 

for BWR ECCS Strainer Blockage Due to LOCA

Generated Debris, NUREG/CR-6224, Science and 

Engineering Associates, Inc., 1994. 

1.3 Boiling Water Reactors Owners' Group, "Utility 

Resolution Guidance for ECCS Suction Strainer 

Blockage," NEDO-32686, 1996.

NUREG/CR-6369 1-4
2. Separate Effects Test Program to Evaluate Inertial 

Debris Capture on BWR Drywell Structures

2.1 Phenomena Selected for Study 

The objective of these tests was to provide a basic 

understanding related to inertial capture of small 

insulation debris generated by a postulated MSLB. Past 

analyses and bench-top experiments have shown that 

debris generated by MSLB tend to be mostly dry with 

traces of wetness on the surface [Ref. 2.1]. Furthermore, 

it is estimated that these debris possess enough inertia to 

impact objects located in their pathway. It is also known 

that the structures would be wet due to a combination of 

steam condensation on their relatively cool surfaces and 

deposition of water droplets resulting from jet expansion. 

[Ref. 1.2] However, it was not known if surface forces 

introduced by surface wetness would be sufficient to 

capture the debris. These tests were designed to provide 

the necessary insights regarding the importance of inertial 

capture on various drywell structures. 

A secondary objective of these tests was to study possible 

degradation and erosion mechanisms for large pieces 

during blowdown. Large pieces (typically larger than 6" x 4") are expected to be captured on the floor gratings 

whose clearances are 1" x 3". Such pieces would then be 

exposed to high velocity steam flow intermixed with water 

droplets for about a minute. A series of tests were 

conducted to study potential for degradation of the 

insulation pieces under these conditions. 

The parameters selected for study were: flow velocity, 

surface wetness, structure type, debris size and debris 

loading. Flow velocity was varied between 24-150 ft/s to 

be representative of flow velocities in various regions of 

the drywell. Experiments were conducted using small 

debris, categorized according to NUREG/CR-6224 

nomenclature (see Figure 1-2). The structures simulated 

included: I-beams, piping of various diameters, gratings, 

and Mark II vents. Finally, the wetness was varied 

qualitatively between dry to draining water film 

conditions.' The debris loading, expressed as 

concentration of debris per unit cross-sectional area 

approaching the structures, was varied over a narrow 

range of 6.3 to 12.5 g/ft2 .

2.2 Test Facility 

2.2.1 Flow Tunnel 

Components of the test air tunnel are shown in Figure 2-1. 

To avoid recirculation of the debris, the tunnel had a once 

through flow system, with the blower at the upstream end 

and an air filtering plenum downstream of the test section. 

The tunnel was constructed using full panels of medium 

density overlay plywood with an external wood stud 

framework, such that the inside cross section dimension 

was 4 ft x 4 ft. Steel strapping was used to prevent seams 

from opening up when the tunnel was pressurized by the 

blower. To achieve a uniform velocity distribution, a 

combination of perforated plates and a honeycomb 

structure was used. The head loss across this flow 

conditioning device was calibrated with respect to 

measured tunnel velocities and this correlation was later 

used to set the test velocities. 

Two ranges of test velocities could be established based 

on the cross sectional area of the test section. Relatively 

low speed tests, up to 50 ft per second, were conducted 

using the full 4 ft x 4 ft area of the tunnel. A smaller 2 ftx 

2 ft test section was inserted within the large test section 

to achieve velocities up to 150 ft per second. As shown in 

Figure 2-2A, the large test section was 8 ft long, as 

defined by the length of the acrylic viewing panels on the 

ceiling and one side, whereas the smaller high velocity test 

section was 5 ft long and fit within the larger test section. 

About 2 ft downstream of the test section(s), the 4ft x 4ft 

tunnel section entered an 8ft x 8ft, 16 ft long filter box 

shown in Figure 2-2B. The roof and rear wall were 

covered with two inch rubberized "hog hair" filter media. 

After the hog hair became clogged with insulation debris, 

the filter media was replaced with corrugated paper filter 

panels. 

A flow conditioning structure was installed just 

downstream of the blower, and this conditioner consisted 

of two 40% open perforated plates, spaced 4 inches apart, 

upstream of an 81 cell, 2 ft long, plywood honeycomb

' Surface wetness was not quantified in terms of water 

film thickness.

2-1 NUREG/CR-6369
Debris Capture

FILLER B OX

34 Fr

8.75 FT FROM 

SPRAY INJECTION TO 

TEST SECTION 

K

15.5 FT FROM INSi 

INJECTION GUNS 

TEST SECTION

TEST SECTION 

WINDOW (8FF)

40% PERF PLATE AND 

HONEYCOMB FLOW 

STRAIGHTENER 

LATION 

TO

I, I. I . 4,"

li II il II

250 HIP 

AXIAL-CENTRIFUGAL 

BLOWER

11 ----------- - ---- U

/ / / ft / f/f / I1/ / I I" / / f/I I /I f/I f//"I f /1II//I/I /fI

ELEVATION

Figure 2-1. General arrangement of test tunnel.

NUREG/CR-6369

/ !/ /

I:

2-2

1 I I-K] ýý
Debris Capture

A) SHOWING THE SMALLER 2 FT X 2 FT TEST SECTION MOUNTED 

INSIDE THE 4 FT X 4 FT SECTION; BLOWER IS FAR RIGHT

B) FILTER BOX; FLOW EXITS THROUGH TOP AND REAR PANELS 

Figure 2-2. Test tunnel components showing test sections and filter box.

2-3 NUREG/CR-6369
Debris Capture

honeycomb structure (which can be seen in Figure 2-5B). 

Figure 2-3 shows the velocity distribution at the test 

section with the conditioner in place, indicating that 

essentially all velocities were within about ±10% of the 

average. 

To provide a non-intrusive means to set the tunnel 

velocity using an air-over-water U-tube manometer, the 

head loss across the flow conditioner was calibrated to 

velocity measurements taken in the tunnel over a range of 

blower speeds. The resulting relationship for the large 

test section is shown in Figure 2-4. 

2.2.2 Insulation Injection 

The fibrous insulation debris was introduced within the 

tunnel by pressurizing sections of four inch PVC pipes 

capped at one end and with a rupture disk at the discharge end. A schematic of the debris injection system is shown 

in Figure 2-5. The pipe sections were suspended from the 

tunnel ceiling downstream of the flow conditioning 

structure and filled with preshredded insulation. Air was 

pumped into the capped end of the pipe sections until the 

rupture disk failed, and the jet of escaping air dispersed 

the insulation debris. Adequate insulation dispersal and 

complete discharge of debris required the rupture disk to 

burst at an appropriate pressure. Through 

experimentation with different rupture disk materials from 

metals to paper, a single sheet of 3M brand overhead 

transparency plastic material produced a rupture disk 

which reliably burst at 50 to 52 psi. In addition, this 

material did not disintegrate and contaminate the 

insulation upon rupture, but rather, consistently split into 

three to four flower-like petals. The position of the 

injection pipes was selected by preliminary testing to 

produce a relatively uniform pattern of debris on a fine 

screen placed across the test section. 

2.2.3 Geometry of Objects Tested 

Two categories of obstructions were tested, referred to in 

this report as single member tests and combined member 

tests. Single member tests involved mounting up to two 

objects of the same type (identical cross section) side by side within the test tunnel, both similarly aligned to the 

flow. In cases where the projected or frontal area of the 

test member was small, for example, I-beams with the web 

parallel to the flow, two identical pieces were mounted to 

increase the material capture and the accuracy of weighing 

the dried material.

Combined member tests included mounting several shapes 

with different orientations or more than one of a common 

member section, each aligned differently to the flow. By 

design, the arrangement of individual members in each 

combination was related to the single member tests, so 

that debris capture on individual components used in 

combinations could be compared to the capture k'hen 

tested alone. Effects of member proximity, wake effects, 

and shielding could thereby be evaluated. 

The surface finish of the test obstructions varied from 

slightly rusted (not flaking) for the I-beam sections to 

newly painted for the 1 ft and 2 ft pipes. The floor grating 

was galvanized steel which made the surface rough and 

purposely non-skid. 

2.2.4 Insulation Debris Generation 

The fibrous insulation debris was generated from heat 

treated NUKON base wool blankets. The blankets were 

cut up manually and then subjected to a leaf shredder 

following a prescribed procedure (Ref. 2-2) to produce the 

desired fragment sizes. A classification of debris sizes 

(Ref. 2-3) was used to grade and separate the insulation 

debris into two groups, Classes 3 & 4 and Classes 5 & 6. 

Debris sizes larger than Class 6 are termed in this report 

as Class 6+ and mainly included fragments 3 to 4" in size, 

obtained manually by pulling pieces from a NUKON 

blanket. As further fragmentation of debris was caused by 

the injection system in the facility, the originally 

introduced Classes 3 & 4 resulted in debris of Classes 2 

through 4, while the original Classes 5 & 6 debris was 

further fragmented to give a size range of Classes 2 

through 6. Further fragmentation of the larger pieces 

(Class 6+) was relatively negligible and is neglected. 

Figure 2-6 shows the pre-injection appearance of the 

debris comprising Classes 2 through 4, 2 through 6, and 2 

through 6+. 

Taking into account some additional fragmentation by the 

injection system, tests covered four different mixes of 

fragment sizes, as follows: 

1. Classes 2 through 4 (injection pipes loaded with 

Classes 3 and 4). 

2. Classes 2 through 6 (injection pipes loaded mostly 

with Classes 5 and 5; but also with some Classes 3 

and 4).

NUREG/CR-6369 2-4
Debris Capture

VEL DISTRIBUTION AT THE TEST SECTION 

VIEW: LOOKING UPSTREAM AVG V=36 FT/S

48 

44

40 

36 

32 

, 28 

S24 

20 

16 

12 

8 

44

0 1 1 1 1 1 1 ! 1 ! i 1 1 1 i ! ! i 1 i i ! i 

0 4 8 12 16 20 24 28 32 36 40 44 48 

INCHES 

NOTE: VALUES ARE LOCAL VELOCITIES DIVIDED BY AVERAGE VELOCITY 

Figure 2-3. Non-dimensional velocity distribution in large test tunnel with final flow conditioner.

NUREG/CR-6369

I1.00 0.94 0.94 0.96 1.03 1.07 1.07 0.88 

1.04 1.04 1.03 1.07 1.13 1.14 1.10 0.91 

1.06 1.08 1.04 1.01 1.06 1.05 1.02 0.83 

0.96 1.06 0.97 0.94 0.93 1.00 1.01 0.85 

0.94 1.02 1.00 0.94 0.93 0.99 1.03 0.92 

0.94 1.03 1.03 0.99 0.97 0.96 1.10 0.94 

0.97 1.06 1.09 1.07 1.03 1.03 1.09 0.95 

1.00 1.04 1.07 1.02 0.94 0.89 0.94 0.89

2-5
Debris Capture

60 + 5 ....... ............................... .. .... ............................... i .......................

-- --- ------

.............. ........... !........

S4 0 ........................... ... • ......................... .....,.'........................... ... ............................ •................................; ............................... .............................. 

53 0 ....... 

30 

t ~V = CIIE: 

C = 58.5 

S2 0 .................................. ............... E - 0 . 2 . ...................... ........................ ....... ..................... ...... ................ 

1 0 ............................. .............................. .............................. ............................... ............................... ................................ :................................. 

oDTAD 

0 11 1--!111 -+++ 11 +-H-i-l- ! 1 1 ! 1 ! 1 1 1 -+1- iII + I 1 1 1 H 

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 

HEADLOSS: U-Tube Reading (H), ft 

Figure 2-4. Head loss across flow conditioner versus average velocity in large (4ft x 4 ft) test section.

NUREG/CR-6369 2-6
Debris Capture

TUNNEL FLOW

COMPRESSED 

AIR SOURCE

" • 4V PVC PIPE 

-RUPTURE DISK C 4LA ED BETWEEN FLANGES

A) SIDE VIEW OF In=ECrION PIPE

B) LOOKING UPSTREAM AT DEBRIS INJECTION PIPES, WATER SPRAY 

NOZZLES ON SIDE WALLS AND HONEYCOMB FLOW CONDITIONER 

Figure 2-5. Debris injection system

2-7 NUREG/CR-6369.
Debris Capture

Figure 2-6. Pre-injection sizes of shredded NUKON fibrous insulation debris shown on a 2" x 2" grid.

NUREG/CR-63 69

I

2-8
Debris Capture

3. Classes 2 through 6+ (injection pipes loaded with 

Classes 3 & 4, 5 & 6, and 6+ using the same weight 

from each group, and 

4. Class 6+ only. 

2.3 Test Plan and Procedure 

2.3.1 Test Matrix 

A test matrix (see Table 2-1) was developed to evaluate 

the effect of the following variables on debris capture:

a. 

b. 

C. 

d. 

e. 

f.

Gas velocity 

Wetness of structure surfaces 

Debris size 

Structure geometry 

Structure orientation to the flow direction 

Flow through a typical BWR Mark II vent opening

As shown in Table 2-1, 44 tests were conducted in total, 

including 4 repeat tests. Tests requiring gas velocities of 

50 ft/s or less were conducted with the larger 4 ft x 4 ft 

duct section, while the higher velocity tests were 

conducted with the 2 ft x 2 ft duct section. Tests 1 

through 22 covered various drywell structures, such as 

pipes, I-beams, and gratings, and were all conducted for 

an injected debris weight of about 100 gm. A few tests to 

ascertain the effects of debris size (Classes 2 to 4 versus 2 

to 6) and wetness of structure surfaces were also included 

among these tests. The structures were tested individually 

(single member tests) in Tests 1 through 13 and 19 

through 21, while Tests 14 through 18 and Test 22 were 

with combinations of structures (combined member tests). 

Tests 1 through 18 and Test 22 were conducted with an 

approach air velocity of 50 ft/s, while Tests 19 through 21 

were conducted with 25 ft/s velocity. 

BWR drywells typically have two floor gratings 

significant distances apart relative to the grating thickness 

and, hence, tests were conducted with two gratings placed 

at a distance of 4 ft apart in the test facility to examine the 

relative debris capture at an upstream and downstream 

grating. Tests 23 through 26 and 31 through 34 were 

formulated to test the two grating arrangement for 

different approach velocities, debris masses 

(concentration) and sizes. 

Tests 27 through 30 were conducted with a typical Mark 

II vent geometry to ascertain debris capture on the vent 

cover or on the floor, as influenced by surface wetness 

and debris size. Since gravity had only a minor influence

on fibrous debris transport and capture (i.e., the fibrous 

debris fall velocity is low compared to the gas flow 

velocity), the vent was oriented horizontally for testing 

convenience. These tests were conducted with an 

approach velocity of 25 ft/s in the 4 ft x 4 ft test section, 

which resulted in a vent velocity of about 185 ft/s. With 

the higher system losses generated by the vent, hikher 

flows were not tested due to blower capacity limitations. 

Additional single grating tests to cover a range of 

velocities and debris masses resulted in Tests 35 through 

38. Tests 39 and 40 were included to evaluate debris 

capture on solid objects at higher velocities of 100 to 150 

ft/s, but with the same debris concentrations as the 

previous tests at 50 ft/s. Tests IR, 2R, 20R and 29R were 

repeats of Tests 1, 2, 20, and 29, respectively. 

Tests 41 through 44 were conducted to investigate the 

potential for insulation debris to degrade or disintegrate 

when subjected to a wet high velocity gas flow. These 

tests were conducted in the small (high velocity) test 

section using 1/8" to 1a" thin layers of rough-cut 

(approximately 6" x 6") insulation pieces placed on a 

single floor grating. 

2.3.2 Test Procedure 

The following lists the step by step test procedure. Tests 

that required variations to the procedure are noted on an 

individual basis in Section 2.4. 

a. The desired test structures were installed in the test 

section of the air tunnel. 

b. Both injection pipes were filled with the selected 

pre-weighed mass of insulation debris (maximum of 

50 gm/pipe at a time). 

c. The desired air velocity was set by measuring the 

head loss across the flow conditioner and adjusting 

the blower speed. 

d. Video cameras to record debris capture were turned 

on. 

e. The surfaces of the objects were wetted by turning the 

sprays on for the selected duration. 

f. Within a maximum of 10 seconds after stopping the 

water sprays, the first debris injection pipe disk was 

ruptured and the second disk rupture occurred about 

10 seconds later.

2-9 NUREG/CR-6369
Debris Capture

Table 2-1. Debris capture testing matrix for completed tests. 

Test Obstruction description Prewet Air velocity Approximate Weight of 

No. time in conduit debris size injected 

(sec) (ftMs) (type) insul. 

(gml 

1 2ft dia pipe parallel to flow 10 50 2 to 4 100 

2 2 ft dia pipe @ 90 deg. to flow 10 50 2 to 4 100 

3 1 ft dia pipe @ 90 deg to flow 10 50 2 to 4 100 

4 (1) grating @ 26 deg. to flow 10 50 2 to 4 82 

5 (1) grating @ 45 deg. to flow 10 50 2 to 4 87 

6 (2) 10 x 4 I-beam flange to flow 10 50 2 to 4 100 

7 (2) 10 x 4 I-beam web to flow 0 50 2 to 4 100 

8 (2) 10 x 4 I-beam web to flow 10 50 2 to 4 100 

9 (2) 10 x 4 I-beam web to flow 30 50 2 to 4 100 

10 2 ft dia pipe @ 90 deg. to flow 0 50 2 to4 100 

11 (2) 10 x 4 I-beam web to flow 10 2 to 4 100 

12 (1) grating @ 90 deg. to flow 10 50 2 to 4 100 

13 (1) grating @ 90 deg. to flow 10 50 2 to 6 100 

14 combination #1 10 50 2 to 4 100 

15 combination #2 10 50 2 to 4 100 

16 combination #3 10 50 2 to 4 100 

17 combination #3 30 50 2 to 4 100 

18 combination #3 30 50 2 to 6 100 

19 1 ft dia pipe @ 90 deg. to flow 10 25 2 to 4 100 

20 (2) 10 x 4 I-beam flange to flow 10 25 2 to 4 100 

21 (2) 10 x 4 I-beam web to flow 10 25 2 to 4 100 

22 combination #3 30 50 2 to 4 100 

23 (2) grating 90 deg. to flow 10 50 2 to 4 100 

24 (2) grating 90 deg. to flow 10 50 2 to 4 200 

25 (2) grating 90 deg. to flow 10 50 2 to 4 200 

26 (2) grating 90 deg. to flow 0 50 2 to 4 100 

27 vent with cover 0 25 2 to 4 100 

28 vent with cover 10 25 2 to 4 100 

29 vent with cover 10 25 2 to 6 100 

30 vent with cover 10 25 6+ 100 

31 (2) grating 90 deg. to flow 10 100 2 to 6+ 50 

32 (2) grating 90 deg. to flow 10 140 2 to 6+ 50 

33 (2) grating 90 deg. to flow 10 100 2 to 6+ 100 

34 (2) grating 90 deg. to flow 10 140 2 to 6+ 100 

35 (1) grating 90 deg. to flow 10 132 2 to 4 50 

36 (1) gating 90 deg., to flow 10 100 2 to 4 25 

37 (1) grating 90 deg. to flow 10 100 2 to 4 100 

38 (1) grating 90 deg. to flow 10 150 2 to 4 100

NUREG/CR-6369 2-10
Debris Capture

Table 2-1. Debris capture testing matrix for completed tests (continued).

Test Obstruction description Prewet Air velocity Approximate Weight of 

No. time in conduit debris size injected 

(sec) fIts) (type) insul. 

(gin) 

39 (1) 10 x 4 I-beam flange to flow 10 100 2to4 25 

40 (1) 10 x 4 I-beam web to flow 10 100 2 to 4 25 

IR repeat of test 1 10 50 2 to 4 100 

20R repeat of test 20 10 25 2 to 4 100 

29R vent with cover 10 25 2 to 6 100 

2R repeat of test 2 10 50 2 to 4 100 

41 debris on grating 60 134 1⁄2" thick 42 

42 debris on grating 60 126 1⁄2/2" thick 42 

43 debris on grating 60 138 1/4" thick 36 

44 debris on grating 60 130 1/8" thick 100

g. The blower speed was ramped down to bring the air 

flow to zero in approximately 30 seconds. 

h. Video cameras were turned off. 

I. Black and white photographs were taken of the test 

obstructions with captured insulation. 

j. The captured debris on each surface of the objects 

and the walls and floor was separately collected, 

dried and weighed. 

k. The percent of debris captured was calculated. 

Percent Capture was determined as follows: 

1. The injection system produced a uniform cross

sectional distribution of insulation debris approaching 

the test objects. Based on the test tunnel cross 

sectional area and the total weight of the injected 

insulation, an approaching insulation concentration, 

grn/ft2 , (weight per area) was calculated. 

2. The frontal, or projected, area of the test objects was 

calculated.

3. The maximum theoretical capture amount per test 

object was determined by multiplying the projected 

area of the object from item 2 by the approaching 

total debris concentration from item 1. 

4. The Percent Captured was determined by dividing the 

dry weight of the insulation actually collected from 

the obstruction(s) by the maximumtal theoretical 

amount from item 3, multiplied by 100 to convert to a 

percent. 

2.4 Results 

The test results are summarized in Table 2-2. 

Photographs of debris capture for all tests were taken, and 

selected photographs are included in this section for 

discussion of basic phenomena. Conforming to the 

objectives of the tests, the effects of each test variable on 

debris capture are discussed separately based on the test 

data. Using the major findings, an overall evaluation of 

the application of these results to quantifying debris 

capture in a BWR drywell following a LOCA is also 

provided.

2-11 NUREG/CR-6369
Debris Capture

Table 2-2. Results of BWR drywell capture tests.

OBSTRUCTION 

DESCRIPTION

2ft dia pipe parallel to flow 

repeat of test 1 

2ft dia pipe (@ 90 deg. to flow 

repeat of test 2 

1 ft dia pipe (a 90 deg. to flow 

grating @ 26 deg. to flow+ 

grating (a 45 deg. to flow+ 

(2) 10x4 I-beam flange to flow 

(2) 10x4 I-beam web to flow 

(2) 10x4 I-beam web to flow 

(2) 1 Ox4 I-beam web to flow 

2ft dia pipe (a 90 deg. to flow 

(2) 10x4 I-beam web to flow 

grating @ 90 deg. to flow+ 

gating @) 90 deg. to flow+ 

combination # 1 

total of vertical beams 

total of horizontal beams 

total of combination #1

PREWET 

TIME 

SEC 

10 

10 

10 

10 

10 

10 

10 

10 

0 

10 

30 

0 

10 

10 

10 

10

PROJECTED 

AREA OF OBSTN. 

sQ-Fr 

3.1 

3.1 

8.0 

8.0 

4.0 

16.0 

16.0 

2.7 

6.7 

6.7 

6.7 

8.0 

6.7 

16.0 

16.0

PERCENT 

OF AREA 

OBSTRUCTED 

20 

20 

50 

50 

25 

100 

100 

17 

42 

42 

42 

50 

42 

100 

100

AIR VELOCITY 

IN CONDUIT 

Fr/S 

50 

50 

50 

50 

50 

50 

50 

50 

50 

50 

50 

50 

50 

50 

50 

50

APPROXIMATE 

DEBRIS SIZE 

(TYPE) 

2 to 4 

2 to 4 

2 to 4 

2 to 4 

2 to 4 

2 to 4 

2 to 4 

2 to 4 

2 to 4 

2 to 4 

2 to 4 

2 to 4 

2 to 6 

2 to 4 

2 to 6 

2 to 4

WEIGHT OF 

INJECTED INSUL. 

10n 

100 

100 

100 

100 

82 

87 

100 

100 

100 

100 

100 

100 

100 

100

WEIGHT OF 

CAPTURED INSUL 

gsn 

3.6 

3.7 

4.2 

4.8 

1.1 

12.0 

14.6 

2.0 

0.0 

9.6 

13.1 

0.0 

2.7 

16.2 

26.7

1 

IR 

2 

2R 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14

PERCENT** 

INSUL. CAPTURED 

ON OBSTRUCTION(S) 

18 

19 

8 

10 

4 

15 

17 

12 

0 

23 

31 

0 

6 

16 

27

2.7 17 100 1.8 11 

6.7 42 98 4.3 11 

8.2 51 100 6.1 12

+ Grating approximately 75% open area ** Compared to the maximum possible capture amount; using the 

projected area of the obstruction and a uniform insulation distribution. Percent 

capture for individual componants in the combination tests is based on the available 

approaching weight of insulation: injected weight minus any material captured on upstream components.

NUREG/CR-6369

TEST #

2-12

26.7 27
Debris Capture

Table 2-2. Results of BWR drywell capture tests (continued).

OBSTRUCTION 

D.t"21CPPT'TA-N

PREWET 

TIME

PROJECTED 

AREA OF OBSTN.

PERCENT 

OF AREA n'VlOTDT T71TV T%

AIR VELOCITY 

IN CONDUIT

APPROXIMATE 

DEBRIS SIZE

WEIGHT OF 

INJECTED INSUL.

WEIGHT OF 

CAPTURED INSUL

PERCENT** 

INSUL. CAPTURED

S........... .X-t"• vo x.k . r 110 LA z IQ onIg ,. ON OBSTRUCTION(SL 

15 combination #2 10 50 2 to 4 

total of upstream 10" pipe 3.3 21 100 2 10 

total of vertical beams 2.7 17 98 2 12 

total of horizontal beams 6.7 42 96 1 2 

total of downstream 12" pipe 4.0 25 95 1 4 

total of combination #2 9.9 62 100 7.4 12 

16 combination #3 10 50 2 to 4 

total of upstream 12" pipe 4.0 25 100 2 8 

total of upper beam 3.3 21 98 5 24 

total of lower beam 1.3 8 93 1 13 

total of grating+ 16.0 100 92 9 10 

total of combination #3 8.6 100 100 16.1 16 

17 combination #3 30 50 2 to 4

total of upstream 12" pipe 

total of upper beam 

total of lower beam 

total of grating+ 

total of combination #3

4.0 25 0)7

97

91

100

I O0)

91

07

4.0 97

4

91 none

97 20

12

8S A 100

+ Grating approximately 75% open area 

Compared to the maximum possible capture amount; using the 

projected area of the obstruction and a uniform insulation distribution. Percent 

capture for individual componants in the combination tests is based on the available 

approaching weight of insulation: injected weight minus any material captured on upstream components.

NUREG/CR-6369

8

9

non•

10

9_

0

IR 1

2-13

91 13

TEST #

3.3

1.3

16.0

8.6

21
Debris Capture

Table 2-2. Results of BWR drywell capture tests (continued).

OBSTRUCTION 

DESCRIPTION

PREWET 

TIME 

SEc

PROJECTED 

AREA OF OBSTN. 

RO.PT

PERCENT 

OF AREA O"1RTP! TC.t•Tln

AIR VELOCITY 

IN CONDUIT 

1T/n

. . .. 9M ON OIS T U C IO N (S) 18 combination #3 30 50 2 to 6 

total of upstream 12" pipe 4.0 25 100 2 8 

total of upper beam 3.3 21 98 6 29 

total of lower beam 1.3 8 92 2 26 

total of grating+ 16.0 100 90 13 14 

total of combination #3 8.6 100 100 22.4 22 

19 1 ft dia pipe @ 90 deg. to flow 10 4.0 25 25 2to4 100 1.2 5 

20 (2) 10x4 I-beam flange to flow 10 2.7 17 25 2 to 4 100 1.6 10 

20R repeat of test 20 10 2.7 17 25 2 to 4 100 1.4 8 

21 (2) 10x4 I-beam web toflow 10 6.7 42 25 2 to 4 100 4.3 10 

22 combination #3 30 50 2to4 

total of upstream 12" pipe 4.0 25 100 2.1 8 total of upper beam 3.3 21 98 3.9 19 

total of lower beam 1.3 8 94 1 13 

total of grating+ 16.0 100 93 7.7 8 

total of combination #3 8.6 100 100 14.7 15 

23 (2) grating 90 deg to flow+ 10 16.0 50 2 to 4 100

APPROXIMATE 

DEBRIS SIZE {TDr•

WEIGHT OF 

INJECTED INSUL.

WEIGHT OF PERCENT" 

CAPTURED INSUL. INSUL CAPTURED

total on upstream grate

total on dowr 

total for test:

100

nstream grate 100

23 I O0(

100 173't1

83 106 V

23 100 in

+ Grating approximately 75% open area 

Compared to the maximum possible capture amount; using the 

projected area of the obstruction and a uniform insulation distribution. Percent 

capture for individual componants in the combination tests is based on the available 

approaching weight of insulation: injected weight minus any material captured on upstream components.

NUREG/CR-6369

17•

106

"17 0

17

I I

,)Q

2-14

TEST #

100

83

1 OI3
Debris Capture

Table 2-2. Results of BWR drywell capture tests (continued).

DES'-VTv-"QW SEC Sn-FT OBSTRUCTED FT/S rrYPEN

OBSTRUCTION

PREWET 

TIME 

errt

PROJECTED 

AREA OF OBSTN. 

.flj3.w

PERCENT 

OF AREA A"P:ITP T TCTW 1"

AIR VELOCITY 

IN CONDUIT

APPROXIMATE 

DEBRIS SIZE 

(TVPP.•

WEIGHT OF 

INJECTED INSUL. 

gm

WEIGHT OF 

CAPTURED INSUL 

2m

PERCENT" 

INSUL. CAPTURED 

ON OBSTRUCTION(S)

24 (2) grating 90 deg to flow+ 10 16.0 50 2 to 4 200 

total on upstream grate 100 200 38.2 19 

total on downstream grate 100 162 21.5 13 

total for test 24 100 200 59.7 30 

25 (2) grating 90 deg to flow+ 10 16.0 50 2 to 6+ 200 

total on upstream grate 100 200 96.5 48 

total on downstream grate 100 104 11.2 11 

total for test 25 100 200 107.7 54 

26 (2) grating 90 deg to flow+ 0 16.0 50 2 to 4 100 

total on upstream grate 100 100 9 9 

total on downstream grate 100 91 5.9 6 

total for test 26 100 100 14.9 15

+ Grating approximately 75%0 open area 

** Compared to the maximum possible capture amount; using the 

projected area of the obstruction and a uniform insulation distribution. Percent 

capture for individual componants in the combination tests is based on the available 

approaching weight of insulation: injected weight minus any material captured on upstream components.

NUREG/CR-6369

TEST #

2-15
Debris Capture

Table 2-2. Results of BWR drywell capture tests (continued).

OBSTRUCTION 

DESCRIPTION

PREWET PROJECTED 

TIME AREA OF OBSTN. 

SEC SQ-FT

PERCENT 

OF AREA 

OBSTRUCTED

AIR VELOCITY 

IN CONDUIT 

FT/S

APPROXIMATE 

DEBRIS SIZE 

(TYPE)

WEIGHT OF WEIGHT OF 

INJECTED INSUL. CAPTURED INSUL. 

grn wm

PERCENT** 

INSUL. CAPTURED 

ON OBSTRUCTION(S)

27 vent with cover++ 0 3.4 21 25 2 to 4 100 0 none 

28 vent with cover 10 3.4 21 25 2 to 4 100 

tunnel floor u/s of cover 1.6 

tunnel floor d/s of cover 7 

face of cover 21 98 2.1 10 

back of cover 0 

tunnel walls d/s of cover 3.7 

outside of pipe 2.4 

tunnel back wall 5.3 

total for test 28++ 100 88 9.8 11 

29 vent with cover 10 3.4 21 25 2 to 6 50 

tunnel floor u/s of cover 0 

tunnel floor d/s of cover 4.7 

face of cover 21 50 0.8 8 

back of cover 0 

tunnel walls d/s of cover 0 

outside of pipe 1.3 

tunnel back wall 3.9 

total for test 29++ 100 45 6 13

+ Grating approximately 75% open area 

"Compared to the maximum possible capture amount; using the 

projected area of the obstruction and a uniform insulation distribution. Percent 

capture for individual componants in the combination tests is based on the available 

approaching weight of insulation: injected weight minus any material captured on upstream components. 

++ Percent captured was calculated using only the material collected from the vent cover, pipe and back wall. 

NUREG/CR-6369 2-16

TEST #

FI
Debris Capture

Table 2-2. Results of BWR drywell capture tests (continued).

TEST~~ iiOBTRCTO An,,.~~~~~~ t1aattu V Au.. L!-r 1 rOI l

OBSTRUCTION 

nl7QI' ID'PNM

PREWET 

TIME 

917f,

PROJECTED 

AREA OF OBSTN.

PERCENT 

OF AREA (%fl TT5 T TI"rV7%

AIR VELOCITY 

IN CONDUIT

APPROXIMATE 

DEBRIS SIZE

WEIGHT OF WEIGHT OF 

INJECTED INSUL. CAPTURED INSUL. 

0m Rm

PERCENT" 

INSUL CAPTURED ON OFITRI TCTTAN/(,fl

29R vent with cover 10 3.4 21 25 2 to 6 100 

tunnel floor u/s of cover 1.6 

tunnel floor d/s of cover 8.4 

face of cover 21 98 4.1 20 

back of cover 0 

tunnel walls d/s of cover 0 

outside of pipe 0 

tunnel back wall 7.2 

total for test 29R--+ 100 90 11.3 13 

30 vent with cover 10 3.4 21 25 6+ 100

tunnel floor u/s of cover 

tunnel floor d/s of cover

2.1

face of cover 21 98 8.3 40 

back of cover 0 

tunnel walls d/s of cover 0 

outside of pipe 2.4 

tunnel back wall 20.1 

total for test 30++ 100 89 30.8 35

+ Grating approximately 75% open area 

Compared to the maximum possible capture amount; using the 

projected area of the obstruction and a uniform insulation distribution. Percent 

capture for individual componants in the combination tests is based on the available 

approaching weight of insulation: injected weight minus any material captured on upstream components. 

++ Percent captured was calculated using only the material collected from the vent cover, pipe and back wall.

2-17 NUREG/CR-6369.

O ... ..... Tr-TQW .. uq

2.1 

RR

TEST #
Debris Capture

OBSTRUCTION 

fVr 'OD-rA.

PREWET 

TIME

PR 

AREA

Table 2-2. Results of BWR drywell capture tests (continued). 

OJECTED PERCENT AIR VELOCITY APPROXIMATE WEIG 

OF OBSTN. OF AREA IN CONDUIT DEBRIS SIZE INJECT]

HT OF WEIGHT OF 

D INSUL CAPTURED INSUL

PERCENT** 

INSUL CAPTURED A ioor-, % una I KUOBS RUT- ITI (TYPE) gm 9m ON OBSTUCTION(S) 

31 (2) grating 90 deg to flow + 10 4.0 100 100 2 to 6+ 50 

upstream grate 4.0 100 50 12.8 26 

downstream grate 4.0 100 37 6.2 17 

total for test 31 100 50 19 38 

32 (2) grating 90 deg to flow + 10 4.0 100 140 2to6+ 50 

upstream grate 100 50 19.7 39 

downstream grate 100 30 3.6 12 

total for test 32 100 50 23.3 47 

33 (2) grating 90 deg to flow + 10 4.0 100 100 2 to 6+ 100 

upstream grate 100 100 29 29 

downstream grate 100 71 12.2 17 

total for test 33 100 100 41.2 41 

34 (2) grating 90 deg to flow + 10 4.0 100 140 2 to 6+ 100 

upstream grate 100 100 23 23 

downstream grate 100 77 9.4 12 

total for test 34 100 100 32.4 32 

35 (1) grating 90 deg to flow + 10 16.0 100 132 2to4 50 3 6 

36 (1) grating 90 deg to flow + 10 16.0 100 100 2 to 4 25 1.7 7 

37 (1) grating 90 deg to flow + 10 16.0 100 100 2 to 4 100 7.6 8 

38 (1) grating 90 deg to flow + 10 16.0 100 150 2 to 4 100 7 7 

39 (1) 10x4 I-beam flange to flow 10 16.0 100 100 2 to 4 25 0.1 0 

40 (1) 10x4 I-beam web to flow 10 16.0 100 95 2 to 4 25 3.7 15

+ Grating approximately 75% open area 

** Compared to the maximum possible capture amount; using the 

projected area of the obstruction and a uniform insulation distribution. Percent 

capture for individual componants in the combination tests is based on the available 

approaching weight of insulation: injected weight minus any material captured on upstream components. 

NUREG/CR-6369 2-18

TEST #
Debris Capture

Table 2-2. Results of BWR drywell capture tests (continued).

OBSTRUCTION 

IDg~rnIPTIAn

TOTAL 

WETTING PROJECTED 

TIME AREA OF OBSTN. 

QC _ll

PERCENT 

OF AREA 

nuviDVTyS T'"r%

AIR VELOCITY 

IN CONDUIT 

Uricw

APPROXIMATE 

DEBRIS SIZE rr1.nrl•

PRETEST 

WEIGHT OF 

INSUL

POST TEST 

WEIGHT OF 

INSUL.

TUNNEL PRESSURE 

DROP THROUGH 

DEBRIS

.. Cj- , t.,,:,a.,, .ro L. a r, n Rom wig 

41 (1) grating 90 deg to flow++ 60 1.7 42 134 1/2" thick 35 35 0.43 

with (5) pieces of debris 

42 (1) grating 90 deg to flow++ 60 1.7 42 126 1/2" thick 32 32 0.43 

with (5) pieces of debris 

43 (1) Eating 90 deg to flow++ 60 1.4 36 138 1/4" thick 16 15 0.41 

with (5) pieces of debris 

44 (1) grating 90 deg to flow++ 60 4.0 100 130 1/8" thick 30 30 0.45 

with (1) piece of debris 

++ Debris degradation test. Debris was placed in grating prior to starting the blower 

The injection guns were not used for this test.

NUREG/CR-6369

TEST ft

2-19
Debris Capture

2.4.1 Gravitational Settling 

The horizontal arrangement of the test facility simplified 

its construction and testing (compared to a vertical tunnel) 

but, the arrangement created the potential for gravitational 

settling, i.e., debris might settle and be captured on the 

tunnel floor upstream of the test obstruction(s). 

To reduce the potential for capture on the tunnel floor, the 

water spray nozzles and debris injection pipes were 

positioned to minimize floor wetness and the amount of 

insulation injected upstream on the tunnel floor while 

maintaining an adequate distribution of both at the test 

section. 

The effects of settling in the tunnel were found to be 

negligible for all of the test obstructions except the 

simulated Mark II vent geometry. With the vent 

geometry coupled with larger debris, some debris settled 

to the floor and to a lesser extent. As discussed in Section 

2.4.8, because the tunnel surfaces did not simulate actual 

boundaries, the material attributed to gravitational settling 

was not included in the calculation of debris retention. 

2.4.2 Effect of Obstructions 

Tested Individually 

Test obstructions were classified as "solid" or "screen" 

objects. Flow went around solid objects, such as pipe and 

beam sections, whereas flow could pass through floor 

grating. Testing of individual objects involved mounting 

one or two of the same shapes in the tunnel. When two 

objects were used, the arrangement was such that both 

were in the same cross-sectional plane and neither was in 

the wake of the other. 

Of the solid objects, an I-beam oriented with the web 

perpendicular to the flow, Test 8, produced the highest 

percent capture, 23% (percent capture was defined in 

Section 3.2 above). The same I-beam, oriented with the 

flanges perpendicular to the flow, i.e., the web parallel to 

the flow (Test 6), captured approximately half that 

amount. Post-test photos of these two tests are shown in 

Figure 2-7. 

A 2-ft diameter pipe was tested parallel and perpendicular 

to the flow, with a hemispherical cap attached to the 

upstream end for the parallel-to-flow tests. In this 

parallel-to-flow configuration, the percent capture was

18% and 19% for Test 1 and 1R (a repeat test). When 

this pipe was oriented perpendicular to the flow, the 

percent captured reduced to 8% and 10% for Test 2 and 

2R (a repeat test). Figure 2-8 shows photographs of 

typical capture on a 2-ft diameter pipe. 

The floor grating was commercially available grating 

which consisted of 1" x 1/4" steel bars, 1" on center, 

supported by welded perpendicular rods every 4 inches. 

The whole grating was galvanized by dipping which 

produced a rough non-skid surface. The rough surface 

can be seen in Figure 18B. As oriented in the test tunnel, 

the open area was approximately 75%. 

The floor grating produced the highest capture (mass) of 

the individual members tested. From Test 12, 16% (16 

gm) of the approaching weight of Class 2 to 4 debris was 

retained on a single 4 ft x 4 ft panel of grating, see Figure 

2-9A. With debris Class 2 to 6, the retention increased to 

27% (27 gin), as shown in Figure 2-9B for Test 13. 

For calculating percent capture on the grating, whether 

alone or in Combinations, 16 ft2 (the total tunnel section 

area) was used for the projected area, which (by the 

definition in Section 3.2) means that the grating is 

exposed to 100% of the approaching debris. This method 

produces a low apparent percent retention on the grating, 

as compared to only using the solid portion of the grating. 

2.4.3 Effect of Approach Velocity 

The air velocity for the majority of the tests was 50 ft/sec. 

The floor grating and I-beam obstructions were also 

tested at velocities up to 140 ft/sec using the smaller test 

section inserted into the basic test tunnel (see Figure 2-3). 

With prewetting, 50 ft/sec through the floor grating with 

Class 2 to 4 insulation debris, Tests 12 and 23 (upstream 

grating) produced an average capture of 17%. The 

approach debris concentration for these tests was 6.3 

gm/ft2 (100 gm injected) and Figure 2-10 shows the 

debris capture for Test 23. Using the same approach 

concentration but at a velocity of 100 ft/sec (Test 36), the 

percent capture reduced to 7%. A similar reduction in 

capture occurred for a higher approach concentration 

(12.5 gm/ftf); Test 24 at 50 ft/sec produced 19% capture 

compared to Test 35 at 132 ft/sec which produced 6% 

capture. These results indicate that for the smaller (2 to 

4) class debris, the higher velocity appears to force the 

debris through the grate to reduce the capture percentage.

NUREG/CR-6369 2-20
Debris Capture

A) I-BEAMS MOUNTED FLANGE TO FLOW

B) I-BEAMS MOUNTED WEB TO FLOW

Figure 2-7. Comparison of debris capture from A) test 6, and B) test 8.

2-21 NUREG/CR-6369
Debris Capture

A) VIEW THROUGH TEST SECTION WINDOW

B) VIEW FROM INSIDE THE TEST TUNNEL

Figure 2-8. Debris capture on the 2-ft diameter pipe; 50 ftlsec, class 2 to 4 debris, 

and 6.3 gm/ft2 approach concentration.

NUREG/CR-6369 2-22
Debris Capture

A) CLASS 2 TO 4 DEBRIS (TEST 12)

B) CLASS 2 TO 6 DEBRIS (TEST 13)

Figure 2-9. Debris capture on single grating at 50/ft sec.

2-23 NUREG/CR-6369

tZmanaw.
Debris Capture

/

0

a

a

0

WIDTH = 4 FT 

7Z/// Z/

D/S GRATING

U/S GRATING

0

0

0

I . /

4 FT

FLOW

-, -,.----,----.------------------------------------- I I V

4 FT 

A) GRATING ARRANGEMENT

B) DEBRIS CAPTURE IN TEST 23 

Figure 2-10. Arrangement and debris capture with two gratings; 50 ft/sec, class 2 to 4.

NUREG/CR-6369 2-24

/
Debris Capture

the upstream grate at 50 ft/sec, see Figure 2-11. When the 

velocity was increased to 100 ft/sec with other variables 

held constant (Test 31), the percent capture reduced to 

26% for the upstream grate. But, when the velocity was 

increased to 140 ft/sec (Test 32), the percent capture on 

the upstream grate increased again to 39%. This percent 

capture is still lower, however, than the 48% measured at 

50 ft/sec. The approach concentration was increased to 

25 gm/ft2 for Tests 33 and 34 with velocities of 100 and 

140 ft/sec, respectively. The upstream grate percent 

capture for these two tests was 29 and 23, which agree 

with the results of Test 31 and support the trend that 

higher flow velocity reduces the capture potential of the 

floor grating. 

The I-beam was tested with the web parallel to the flow 

(Test 39) and with the web perpendicular to the flow (Test 

40) with velocities of 100 and 95 ft/sec, respectively. The 

insulation debris approach concentration and prewet times 

for these tests was identical to Tests 6 and 8, which had a 

flow velocity of 50 ft/sec. At 50 ft/sec, the upstream 

flange surface produced 12% capture, while at 100 ft/sec, 

the material captured on the same surface was 

immeasurable. From Test 8, with 50 ft/sec, the web of the 

beam produced 23% capture, which reduced to 15% when 

the velocity was increased to 95 ft/sec in Test 40. 

In general, therefore, increasing the approach velocity 

above 50 ft/sec resulted in a decrease in the material 

captured. 

2.4.4 Effect of Surface Wetness 

Except for the floor grating, all of the obstructions 

required some prewetting for debris capture to occur. 

With no prewetting, Tests 7, 10, and 27 (see Table 2-2), 

an I-beam, pipe section, and vent cover, respectively 

produced no debris capture. Video documentation clearly 

shows debris impacting, but not adhering to the dry 

surfaces of these objects. 

The majority of tests were conducted with a 10 second 

prewet time, although several tests were repeated with a 

30 second prewet and this resulted in higher capture 

percentages; e.g., Test 9 was a repeat of an I-beam 

oriented with the web perpendicular to the flow. Test 8 of 

this geometry produced a capture of 23% with a 10 

second prewet; with the 30-second prewet time of Test 9, 

the capture increased to 31%. 

With combined obstruction geometries, the increased 

prewet time did not show the same trend. With a 10

second prewet time, Combination #3, (Test 16) shown in 

Figures 2-12 and 2-13, produced an overall 16% capture. 

When repeated with a 30-second prewet time in Tests 17 

and 22, the overall capture was approximately the same, 

19% and 15%, respectively. 

Floor grating was tested in single panels, in dual panels, 

and in combination with other members. Tests with 

debris Class 2 to 4 showed that a single grate spanning the 

entire tunnel section (Test 12) produced a 16% debris 

capture. For the same test conditions with two parallel 

grates (Test 23), the upstream grate captured 17%. The 

performance of the downstream grate will be discussed in 

Section 4.9 below. The percent captured on the upstream 

grate reduced to 9% when there was no prewetting (Test 

26). Because there was still 9% capture without 

prewetting, the grating material was less dependent on 

surface wetness compared to the solid objects, which did 

not capture any debris without prewetting. 

2.4.5 Effect of Debris Size 

(Class of Insulation Debris) 

Three ranges of debris size were tested, Classes 2 to 4, 2 

to 6, and 2 to 6+. The following summary, drawn from 

Table 2-2, compares pairs of tests in which the only 

difference between the two tests in a pair was the 

insulation debris size (Class): 

With the exception of Test 11, tests repeated with larger 

insulation debris produced higher capture percentages. The 

most dramatic increase was between the upstream grate of 

Test 33 and that of Test 37, both with a flow velocity of 100 

ft/sec; the retention percentage increased by a factor of 3, 

from 8% to 29% with the larger debris size. 

2.4.6 Effect of Debris Loading 

The concentration of insulation debris per cross-sectional 

area approaching the obstructions, also referred to as 

debris loading, could be varied by adjusting the weight of 

insulation placed into the injection pipes. The maximum 

weight of insulation debris per pipe was 50 gin; in the 4 ft 

x 4 ft test section, this produced a 6.3 gm/ft2 

concentration. To inject more debris for a test required 

reloading the pipes, and this was accomplished by 

reducing the blower speed to a value that retained all 

captured material while allowing a technician to enter the 

tunnel. The blower was then adjusted back up to speed 

and the test continued. The water spray system was not 

used for the second injection to prevent captured material 

from the first injection from being washed off. For the

2-25 NUREG/CR-6369
Debris Capture

Table 2-3. Effect of debris size.

higher velocity tests which used the smaller test section, 

the injection pipes were operated with a lower mass of 

insulation debris to yield the same (or desired) 

concentration. For example, to produce a 6.3 gm/ft2 

concentration in the 2 ft x 2 ft high speed section, one 

injection pipe was loaded with 25 gm of debris, whereas 

100 gm was used for the 4 ft x 4 ft cross-section. 

Presumably, one effect of increasing the debris approach 

concentration is that the retention would increase towards 

a saturation point where material being striped off equals 

that being retained. Another possibility, especially 

applicable to the grating, is that higher approach 

concentrations might result in bridging of debris over the 

grate openings and, thus, produce a more effective 

screening device. 

A configuration with two panels of floor grating, shown in 

Figure 2-10, was tested at high and low air speeds with 

different masses of injection debris. At 50 ft/sec, a 

comparison of Tests 23 and 24 indicated no appreciable 

change in total retention percentage when the approach 

concentration was increased from 6.3 gm/ft2 to 12.5 

gm/ft2 ; the percentage capture varied from 28% to 30%. 

Similar results were obtained from Tests 31 and 33 with 

this configuration at 100 ft/sec, the total percent capture 

varied from 38% to 41%, respectively, when the approach 

concentration was increased from 12.5 gm/ft2 to 25 gm/ft2 . 

An identical increase in approach concentration at 

140 ft/sec reduced the total percent capture from 47% to 

32% for Tests 32 and 34, respectively.

The results of these tests indicate that the effects of 

varying the approach concentration produced no 

appreciable change in retention on the floor grating. 

2.4.7 Effect of Structural Combinations 

Three configurations of combined obstructions (Figure 2

12) were tested. The method for determining the percent 

capture on downstream members in the combined 

structures accounted for insulation debris that was 

captured by upstream members. The first step was to 

separate the overall layout into a series of "planes" normal 

to the oncoming flow. For example, Combinations 1 

consisted of two planes; the first being the two vertical 

beams, and the other, the two horizontal beams. 

Similarly, for Combination 3, the pipe and beams form the 

upstream plane, while the floor grating was the second 

plane. By the same method, Combination 2 was divided 

into four planes. If, for example, the members in the 

farthest upstream plane of obstructions retained 4 gm, the 

caldulated approach concentration for the next 

downstream plane of members was adjusted to reflect the 

reduced weight of available debris. 

Combination 1, shown in Figure 2-12, consisted of four 

10 x 4 inch I-beams. The upstream vertical beams were 

oriented with the web parallel to the flow. The remaining 

two horizontal beams were located so as to be in the wake 

of the upstream beams and the downstream beams were 

oriented with the flanges parallel to the flow.

NUREG/CR-63692

Obstruction description Debris class Percent capture Test no. 

(2) 10 x 4 I-beam web to flow 2 to 4 23 8 

(2) 10 x 4 I-beam web to flow 2 to 6 6 11 

Grating 90 deg to flow 2 to 4 6 12 

Grating 90 deg to flow 2 to 6 27 13 

Combination #3 2 to 4 16 16 

Combination #3 2 to 6 22 18 

(2) Grating 90 deg to flow 2 to 4 30 24 

(2) Grating 90 deg to flow 2 to 6+ 54 25 

(1) Grating 90 deg to flow 2 to 4 8 37 

(2) Grating 90 deg to flow 2 to 6+ 29 33 

*Upstream grate

2-26
Debris Capture

A) VIEW OF UPSTREAM GRATING

B) BACK SIDE OF UPSTREAM GRATING SHOWING 

DEBRIS FORCED THROUGH THE BARS 

Figure 2-11. Debris capture on grating test; 50 ft/s, class 2 to 6+ debris, and 

12.5 gm/ft2 approach concentration (test 25).

2-27 NUREG/CR-6369
Debris Capture

/

16 {--.--

16 

16

/

(2) 16"o.c. ,0x4I-bems 

a FLOW 

Total of 

(4) 0x4 I-bcams

ElI /

IlOin diameter 

FLOW

32

Configuration #1 with 

(1) iOinpipe 

(I) 12in pipe

/ /7/ / / / /7//

PROJECTED AREA- 8.2 SQ-Fr

PROHECTED AREA. 9.9 SQ-FT

CONFIGURATION 2

CONFIGURATION 3

SIDE VIEW OF COMPONENT ARRANGEMENT FOR 

COMBINED MEMBER TESTING

PROJECTED AREA. 8.6 SQ-Fr 

(WITHOUT GRATING) 

VIEW LOOKING 

DOWNSTREAM

Figure 2-12. Combined member layouts

NUREG/CR-6369

/ 7/ 7 / 7 /7/ 

CONFIGURATION 1

2I 

1II

I -I

'N

¢ • r . ¢ ¢ ( ¢ ( (

2-28
Debris Capture

A) VIEW THROUGH TEST SECTION WINDOW

B) VIEW FROM INSIDE THE TEST TUNNEL 

Figure 2-13. Debris capture on test combination 3, 50 ft/sec, class 2 to 4 debris, and 

6.3 gm/ft2 approach concentration (test 16).

2-29 NUREG/CR-6369
Debris Capture

Combination 1 was tested with Class 2 to 4 insulation at a 

velocity of 50 ft/sec (Test 14). The individual capture 

percentage for both upstream and downstream beams 

captured was 11%. The 11% retention on the upstream 

beams in Combination 1 agree well with those of Test 6 

(at 12%) which indicates, as expected, that the 

downstream members in do not effect the retention 

performance of the upstream members. The upstream 

members, though, clearly reduced the retention found on 

the downstream beams. The beam orientation in Test 8 as 

identical to the downstream members in Combination 1. 

Test 8 produced a 23% capture compared to the 11% on 

the downstream beams in Test 14. Apparently, the debris 

retention ability of the beams is reduced when they are 

located in the turbulence of the wake region behind 

upstream members. 

Combination I was modified by the addition of two 10

inch pipes to form Combination 2, as shown in Figure 2

12. Comparing the performance of individual members in 

Combination 2 (Test 15), as described above for 

Combination 1, the retention on downstream members 

was lower by approximately 50% than comparative tests 

with individual members. The upstream 10" diameter 

pipe in Test 15 retained 10%, which is an increase when 

compared to the 4% found when a 12" pipe was tested 

alone (Test 3). However, the results of Test 3 are suspect 

because tests with 12" diameter pipe in an upstream 

location, Tests 16, 17, and 18 produced 8% capture, 

similar to the 10% capture of Test 15 with a 10 inch pipe. 

Combination 3 incorporated the pipe section, two 

orientations of the 10 x 4 inch beam, and the floor grating 

as shown in Figure 2-12. The pipe and beams forming the 

upstream members produced retention percentages similar 

to those from the independent obstruction tests. The 

retention on the downstream grating reflected the effects 

of being in the wake of the upstream members; from Test 

12, the percent capture on the single floor grating was 

16%, whereas the grate in Combination 3 retained 10% 

and 13% from Tests 16 and 17, respectively (for Test 17, 

the prewet time was 30 seconds but, as discussed in 

Section 4.4, debris retention on the grate was not strongly 

dependent on the extent of prewetting). Figure 2-13 

shows the debris capture for Test 16 with Combination 3. 

2.4.8 Vent Cover Testing 

The general arrangement of the tested single Mark H- vent 

entrance is shown in Figure 2-14A; although the vent pipe

was installed horizontally in the test tunnel, as shown in 

Figure 2-14B. The approach velocity in the 4 ft x 4 ft 

section (simulating the drywell area per vent) was 25 

ft/sec, which produced approximately 180 ft/sec in the 

downstream vent pipe. Even higher velocities occur at the 

vent entrance due to flow contractions. The vent surfaces, 

including the underside of the cover and inside the pipe, 

were pre-wetted by water spray nozzles positioned around 

and in the vent structure. Several size classes of fibrous 

debris were tested; Classes 2 to 4, 2 to 6, and 6+, each 

with an approach concentration of 6.3 gm/ft2 . The percent 

capture for the vent geometry was calculated by using 

only material collected from the vent cover, pipe and back 

wall of the test tunnel (the back wall representing the 

drywell floor). Some debris was collected from the tunnel 

side walls and floor, but because these surfaces were not 

simulating actual boundaries, material collected from 

these surfaces was subtracted from the total mass injected 

upstream before calculating the percent retention on other 

surfaces. 

With no prewetting (Test 27), no insulation debris was 

captured on the vent entrance. With a 10 second prewet 

(Test 28) and Class 2 to 4 insulation, the capture was 

11%, of which 5.3 gm or 54% by weight was collected 

from the back wall of the tunnel (which simulated the 

drywell floor). For Test 29, the injected approach 

concentration was 3.1 gm/ft2 which produced a 13% 

capture of which, 65% by weight was from the back wall 

of the tunnel. The same retention was found when the 

approach concentration was increased to 6.3 gm/ft2 for 

Test 29R, with 64%, by weight, collected from the back 

wall. Test 30 with class 6+ insulation produced 35% 

capture, with 65% by weight collected from the back wall. 

2.4.9 Upstream and Downstream Gratings 

Floor grating was found to retain the highest weight of 

insulation debris and, as described in Section 4.4, the dry 

floor grate did capture debris (unlike all other tested 

obstructions which captured no debris without 

prewetting). Also, as will be discussed further below, 

floor gratings alone captured nearly the same amount of 

debris as the total amount retained by floor gratings with 

other obstructions. For these reasons, the test program 

focus shifted toward investigating floor grating in 

different flow velocities with a range of debris size 

(classes), using both individual gratings and two gratings 

spaced several feet apart.

NTJREG/CR-6369 2-30
Debris Capture

Solid Deflector Plate

Support Bars (8)

A) DIMENSIONED SKETCH OF VENT 

(INCHES PROTOTYPE)

B) VENT AS INSTALLED IN TEST SECTION 

SHOWING DEBRIS CAPTURE IN TEST 29R 

Figure 2-14. Simulated Mark H vent geometry.

2-31 NUREG/CR-6369
Debris Capture

Early tests with a single grating at an angle to the flow 

with Class 2 to 4 debris; Tests 4 and 5, and perpendicular 

to the flow; Test 12, all produced 15% to 17% capture. 

Larger debris (Class 2 to 6) increased retention to 27% in 

Test 13. 

A second panel of grating was installed 4 ft downstream 

from the first panel (see Figure 1 A) to determine the 

retention characteristics of the second &rating. With Class 

2 to 4 debris and 50 ft/sec flow velocity and no prewet 

(Test 26), the overall (total) capture for both gratings was 

15%. The upstream grate retained 9%, compared to 15% 

to 17% for tests described above with a 10 second prewet 

time. With a 10 second prewet time (Test 23), the overall 

capture was 28%. The upstream grate retained 17%, 

which agrees with previous single grate tests described 

above, and the downstream grate retained 13%, indicating 

a slight reduction in capture; possibly due to the fact that 

the first grate filters the larger pieces so that the debris 

approaching the second grate is composed of smaller, and 

more difficult to retain, debris sizes. 

The injected concentration was doubled for Test 24, by injecting 200 gm of Class 2 to 4 insulation, and the overall 

capture was 30%, with 19% and 13% retained on the 

upstream and downstream grating, respectively. As the 

retention values did not appreciably increase with the 

higher injection weight (for Class 2 to 4 debris), the 

percent capture is not cumulative, i.e., a "saturation point" 

is reached, after which additional fibrous debris of this 

size passes through the grate. 

Tests with dual gratings showed a substantial capture (up 

to 50% with larger size debris) on the upstream grating, 

but less capture (about 10% to 13%) in the downstream 

grating. Apparently, the upstream grating filters out the 

larger debris, and the remaining smaller debris can pass through the downstream grating. Plots of percent capture 

on gratings against tunnel velocity are given in Figure 2

15, comparing the capture on upstream and downstream 

gratings for various debris sizes. Generally, larger size 

debris and lower velocities resulted in more capture at the 

upstream grating, see Figure 2-15A. Photographs in 

Figures 2-10 and 2-11 also show this trend. For the 

downstream grating, no such trends are indicated, see 

Figure 2-15B. There was no consistent effect of debris 

concentration for either grating. 

2.4.10 Grating Debris Degradation Tests 

Additional tests were conducted with grating to 

investigate the potential for captured insulation debris to

degrade or disintegrate when subjected to a wet, high 

velocity flow. First, tests were conducted in the small 

(high velocity) test section to establish a relationship 

between tunnel velocity and insulation-blocked area on 

the floor grating. Up to five roughly 6" x 6" pieces of 

NUKON insulation were distributed on a single panel of 

floor grating to vary the open area of the grate from 50% 

to 80%. With no prewetting, the tunnel velocity and 

pressure we ri,, rdcd as the open area was decreased 

using 1/2" and 14" thin debris pieces. The resulting 

relationships between blockage area, velocity, and 

pressure are shown in Figure 2-16. From these results, a 

blockage of approximately 40% was chosen for the 

degradation testing. 

Five 1/2" thin pieces of fibrous insulation debris were 

arranged on the floor grating as shown in Figure 2-17. 

This thickness was manually prepared by pealing off the 

appropriate layer from the standard 2" to 3" thick batts. 

Before the blower was turned on, the pieces were held in 

place by a layer of hardware cloth that was hinged at the 

bottom of the tunnel. When the air flow was sufficient to 

hold the debris against the grating, the hardware cloth was 

pivoted away from the grate and secured to the tunnel 

floor. The flow was adjusted, tunnel velocity and pressure 

were recorded, and the water spray system was turned on. 

The blower and spray system were both turned off after 

the spray had run for 60 seconds. The test procedure was 

repeated with 1/4" and 1/8" thin pieces of insulation 

debris. 

No apparent breakdown of either the 1/2" or 1/4" 

insulation debris was seen, although the pieces -bowed 

between the grating bars, Figure 2-18A, and the edges of 

the insulation pieces wrapped back around the grate bars 

to flap behind the grate, as shown in Figure 2-18B. The 

insulation was pushed back between the grate bars, but 

neither thickness tested showed signs of "blowing 

through." The pre- and post test weights of the insulation, 

shown in Table 2-2, confirm the observation that 

negligible debris was lost, i.e., no material was broken off 

and swept away from the sample pieces. 

Based on the above results, a test with 100% blockage 

using a 1/8" thin layer of NUKON debris was conducted 

to determine if degradation would occur with this 

extremely thin layer. With 100% blockage using a 1/8" 

layer, the tunnel velocity was 130 ft/sec. After the 60

second air flow with water spray, several areas were found 

to have broken through and wrapped back around the 

grating bars as shown in Figure 2-19. However, the post

test dry weighing showed only negligible debris had been 

lost.

NUREG/CR-6369 2-32
50

Debris Capture

80 100 120 

Tunnel Velocity, ft/s 

Injection Concentrations

140

0 6.3 g'sqft 0 12.5 g/sqft L 25 g/sqft 

A) UPSTREAM GRATING

60 80 100 120 140 

Tunnel Velocity, fts 

Injection Concentrations

160

0 6.3 g/sqft 0 12.5 g/sqft & 25 g/sqft 

B) DOWNSTREAM GRATING. 

Figure 2-15. Effects of approach concentration and velocity on debris retention at gratings.

NUREG/CR-6369

02to6+ 

CLASS2TO6+ 02to6+ 

"Tto 6+ 

"V"2 to 6 

CLASS 2TO6 02,T6O L2 to 6+ 

02 o4 

SCLASS 2 TO 4 

_2104 

210o4 --------------------------------- _________ to_ 4 t2 2o04 .2o

(D 

0 

0 

020 

oJ 

10

n

40 60

50 

040 

30 

10 

0

40 160

J

2-33
Debris Capture

150 

148 

U 

w 146 

S144 

"142 

140 

138 

136

5 10 15 20 25 30 35 

PERCENT AREA BLOCKED

o 1/2" Debris 

, 0.44 

S0.43 ............ 

S0.42 

S0.4 

0 0.39........ 

© 0.38 

0.38 .............. 

S0.37 

S0.36 2

0 1/4" Debris - 1/2" (Linear Fit) ........ 1/4" (Linear Fit)

5 10 15 20 25 30 35 

PERCENT AREA BLOCKED

0 1/2" Debris 0 1/4" Debris - 1/2" (Linear Fit) ....... 1/4" (Linear Fit)

Figure 2-16. Effects of blockage of gratings on tunnel velocity and pressure drop through debris.

NUREGICR-6369

40 45

40 45

2-34
Debris Capture

Figure 2-17. Insulation blockage with 5-1/2"-thick pieces held in place on 

floor grating prior to starting the blower.

2-35 NUREG/CR-6369
Debris Capture

A) INSULATION BOWED BETWEEN THE GRATING BARS

B) VIEW FROM DOWNSTREAM; THE INSULATION EDGES 

WRAPPED AROUND AND THROUGH THE BARS 

Figure 2-18. Results of blockage tests with 1

/2"-thick insulation pieces: 40% initial blocked area.

NUREG/CR-6369 2-36
Debris Capture

Figure 2-19. Debris blockage after test; 140 ft/s and 60 sec water spray on 

100% blockage using 1/8" insulation layer.

Overall, these blockage tests indicate that at gas velocities 

up to 140 ft/sec, thin pieces of fibrous insulation do not 

further disintegrate after being captured on the floor 

grating. 

2.4.11 Overall Evaluation of Application 

of Results 

A major finding of the tests is that gratings captured 

significantly more debris by weight than any other objects 

tested. For example, the combination of objects in Test 

17 showed that out of 100 gm of injected insulation 

debris, the grating captured 12 gm, while all other objects 

together collected only 6 gin. Also, comparing test data 

for a grating only with a combination of objects upstream 

of a grating (other test parameters identical), i.e., 

comparing Test 12 with Test 16, it is evident that the total 

capture for the combination of grating with upstream 

objects was essentially equal to the capture on a single 

grating only. This suggests that for debris capture 

evaluation, A first-order approximation could be to ignore 

all objects upstream and between gratings, and consider 

all deposition to be simulated by only the gratings. This 

would be a maj or simplification of the drywell debris 

capture evaluation, considering the numerous structures, 

their orientations and the complex flow patterns in an 

actual plant. 

The above simplification is valid if the gratings cover the 

entire flow area, thereby forcing the flow to pass through 

the gratings without bypassing them. Also, it may be 

noted that the debris size plays a role in the amount of

capture on the first grating, with higher capture of larger 

debris. Hence, some knowledge of actual debris sizes will 

help refine the evaluation. Test results showed a 

relatively small effect of velocity on debris capture on the 

first grating, although somewhat higher deposition 

occurred at lower velocities (see Figure 2-15). 

Larger size but relatively thin insulation debris sheets (6" 

x 6" or larger) captured at gratings were found to be 

retained without further disintegration, even with 

approach gas velocities as high as 140 ft/sec. 

2.5 Conclusions 

The following conclusions are based on the test results, as 

summarized in Table 2-2, for fibrous insulation debris: 

i. Gratings captured more fibrous insulation debris 

compared to other structural components. For 

example, the downstream grating in combined 

member Tests 16 through 18 captured more debris 

than all the other upstream obstructions combined, 

and the grating in Test 17 collected two-thirds of the 

total captured by this combination of obstructions. 

ii. Under identical conditions of surface wetness, gas 

velocity, debris size and debris mass, a single 

grating captured as much debris as structural 

members combined with a downstream grating. 

Hence, one can approximate the total capture by 

neglecting upstream objects and considering only 

the downstream grating.

2-37 NUREG/CR-6369
Debris Capture

iii. Wetness has a clear influence on debris capture for 

objects like pipes and beams; when dry, these 

surfaces did not capture any debris. Floor grating 

capture was less sensitive to wetness. 

iv. Dual gratings showed substantial capture (averaging 

about 25%) on the upstream grating, see Figure 2

15A, but less capture (about 12%) on the downstream 

grating, see Figure 2-15B. Generally, larger size 

debris and lower velocities resulted in more capture at 

the upstream grating, up to about 40%. For the 

downstream grating, no trends with initial upstream 

debris size or gas velocity was indicated, see Figure 

2-15B. 

v. Mark II vents with wetted surfaces showed debris 

capture on the cover plate and the simulated drywell 

floor totalling about 12%. The largest size debris 

tested, Class 6+, resulted in a total capture of 35%. 

No capture occurred on the downstream side of the 

cover nor inside the vent, even when prewetted. 

vi. Negligible break up or disintegration of insulation 

debris captured on the grating was found when 1/8" 

to 1/2" thin pieces of insulation sheets (about 6" x 6") 

were subjected up to 140 ft/sec of approaching gas 

velocity.

vii Gravitational settling, i.e., loss of fibrous debris by 

capture on the tunnel floor, was negligible for all 

tests except the MARK II vent geometry. Material 

attributed to settling during the vent tests was not 

included in the calculation of percent capture. 

2.6 References 

2.1 D. V. Rao, et al., "Drywell Debris Transport Study: 

Draft Phase I Letter Report," SEA 96-3105-010

A:2, Science and Engineering, 1996. 

2.2 Murthy, P., Padmanabhan, M., Weber, F.J., and 

Hecker, G.E., "Head Loss of Fibrous Nukon 

Insulation Debris and Sludge for BWR Suction 

Strainers," ARL Report No. 124-95/M787F, June 

1995. 

2.3 Zigler, G. et al. "Parametric Study of the Potential 

for BWR ECCS Strainer Blockage Due to LOCA 

Generated Debris," NUREG/CR-6224, Prepared by 

Science and Engineering Associates, Inc. for the 

U.S. Nuclear Regulatory Commission, August 

1994.

NUREG/CR-6369 2-38
3. Integrated Effects Test Program to Evaluate Inertial Debris Capture on 

BWR Drywell Structures

3.1 Background and Objectives 

The separate effects tests described in Section 2 provided 

valuable data regarding inertial capture on BWR drywell 

structures. Those tests had notable limitations: 

1. The debris loadings were light. The gun arrangement 

chosen for injection of the debris limited the amount 

of debris that could be introduced into the flow. The 

maximum debris loading achieved in the tests is 

2 Ibm/100 ft2 compared to 2-10 lbm/ 100 ft' expected 

in the BWR plants. It was not clear if the findings of 

separate effects test regarding effectiveness of grating 

would be applicable to BWR plants. 

2. Modest assortment of debris sizes. Separate effects 

tests were done using debris that were generally 

classified as small [see Figure 1-2]. No data were 

obtained on inertial capture of larger debris. 

3. One dimensional flow fields. Debris were carried to 

the structural elements by a flow that is best 

described as plug flow. Direct application of such 

data to BWR plants is questionable. 

4. Non-prototypical congestion of structures. 

Experiments have shown that structural congestion 

can significantly influence capture. However, 

prototypical congestion levels could not be 

reproduced in the test facility. 

These limitations prompted experiments of a more 

integrated nature. 

The integrated effects tests, reported herein, were 

designed to study debris transport under integrated and 

prototypical BWR drywell conditions following a 

postulated MSLB LOCA. These integrated debris 

transport tests were carried out by SEA for the NRC at 

the CEESI. Hereafter, these tests are referred to as the 

CEESI debris transport tests. 

3.1.1 Objectives and Scope 

The primary test objective was to gain insights into the 

transport of fibrous debris by means of small-scale 

experiments and to determine fibrous debris transport 

fractions under prototypical BWR drywell conditions

following a postulated MSLB for use in analytical 

models. The test method selected to accomplish this 

objective was debris generation and subsequent transport 

by a dispersing air jet through a facility with 

characteristics somewhat similar to a BWR drywell.. The 

principal test results were debris capture fractions for the 

various structural components. 

The main steam lines in BWRs exit the reactor vessel at 

relatively high elevations within the containment drywell 

and drop downward before penetrating the containment at 

about the mid-height level. Insulation debris generated at 

these higher elevations will be transported to the lower 

regions of the containment by the steam flow by reactor 

vessel depressurization. As the debris travels downward, 

it will contact drywell structures and equipment (e.g., 

gratings, beams, pipes, pumps, valves, ducts, and other 

structural supports). Some portion of the debris 

interacting with a structural component will be captured 

(stick) by that component. Other debris will pass through 

the downcomer vents into the suppression pool. 

Prototypical operating conditions considered included 

flow velocities, surface wetness, debris transport path 

lengths, and congestion and type of structures along the 

debris transport pathway. The structural components 

placed in the transport pathway inside the test chamber 

included gratings, pipes, and I-beams. In addition, the 

debris transport pathway passed through a 900 bend. The 

diameter of the test chamber was approximately 10 ft and 

the total transport path length was approximately 70 ft. 

Bulk flow velocities entering the area containing the 

congestion of structural components generally ranged 

from 25 to 50 ft/sec. Because surface wetness of the 

structures was found in the ARL debris capture tests to 

strongly influence debris capture, and because structural 

surfaces with a BWR drywell following a LOCA would 

be expected to rapidly wet with steam condensate, the 

surfaces in the CEESI debris transport tests were 

artificially wet with a misting system prior to initiating 

each test. Insulation debris was maintained dry unless the 

debris picked up moisture upon interaction with a 

structural surface. 

Insulation blankets were mounted and restrained to 

maximize the destruction of the blanket, i.e., generate the 

largest possible concentrations of debris passing through 

the congestion of structures. This was accomplished by 

restraining the blanket in front of the jet for as long as

3-1 NTJREG/CR-6369.
possible. Obtaining data regarding debris generation, 

specifically the size distribution of the debris, was not an 

objective of this experiment. 

The debris transport and capture data obtained from the 

CEESI tests was intended to serve as a means for 

benchmarking analytical methods and models applied to 

predicting debris transport within a BWR drywell. The 

CEESI test data was correlated with data from the ARL 

separate effects debris capture tests to provide a 

consistent data set. During the design of the experiment, 

scaling analysis determined the appropriate level of 

congestion for the structural components so that the 

congestion was somewhat typical of a BWR drywell. 

Further, one-dimensional jet expansion calculations and 

two- and three-dimensional CFD simulations determined 

the appropriate nozzle diameter of the air jet to obtain 

expected prototypical drywell bulk flow velocities. 

3.2. Program Elements 

The CEESI test program advanced in the following four 

steps:

1. 

2. 

3. 

4.

Test development analyses and experimental design 

Developmental tests, 

Production tests, and 

Data analyses.

3.2.1 Developmental Tests 

Seven baseline tests were conducted to determine: 

"• The adequacy of the selected jet nozzle diameters to 

provide the desired bulk flow velocities, "* The duration of the air jet needed to complete debris 

transport, "* Optimal insulation mounting and location for 

maximum debris generation, 

"* Optimal test procedures such as prewetting structures 

using the misting system, and 

"* Optimal procedures for collecting and classifying 

debris 

These development tests were instrumented with Pitot 

tubes connected to transducers to monitor and map flow 

distributions before the flow entered the congested test 

section. The measured flows (reported in Section 3.5) 

agreed well with the predicted flow velocities. 

Approximately 10 to 12 second of air jet duration was 

needed to complete debris generation and transport. For 

maximum debris generation, the insulation blankets 

needed to be steel banded and supported at both ends to 

hold the blanket in position longer for more complete

destruction. Experience gained with these tests was 

applied to developing the operating procedures for the 

production tests and four of the seven tests provided 

useful debris transport and capture data. 

3.2.2 Production Tests 

Additional modifications were made to the facility prior 

to conducting the production tests. These modifications 

were: 

" End restraints were installed on both ends of the 

insulation blanket to keep the blanket in the path of 

the air jet, thereby maximizing debris generation (note 

that this method of mounting the blanket is not 

prototypical of BWRs; therefore, debris generation 

results may not be valid for debris generation models), 

"* Additional misters were installed to more uniformly 

wet the structures. 

"* The Pitot tubes which sustained significant damage in 

the developmental tests were removed. 

Using test procedures developed from experience gained 

conducting the developmental tests, ten production tests 

were conducted. The test parameters varied during the 

tests included the distance between the target insulation 

blanket and the air jet nozzle, the jet nozzle diameter, and 

the jet duration time. Debris was collected and bagged by 

location and type for subsequent drying and weighting 

which provided the primary data for computing the 

transport fractions for the CEESI test facility and the 

capture fractions for the structural components. Test 

repeatability was shown. Video and still pictures 

provided visual data for drawing insights into the 

transport processes. 

3.2.3 Data Analyses 

The data analysis first focused on accounting for the final 

distribution of the mass of the original blanket which was 

weighted prior to each test. The final distribution of mass 

not recovered from the test was estimated based on 

observations by the test personnel. (It was not practical to 

collect much of the very fine debris, such as individual 

fibers, deposited on the structures and walls. In fact, 

much of this fine debris was expelled from the test 

chamber through screens installed at the exits from the 

test chambers to catch debris.) The debris mass not 

recovered following the tests was found to dominate 

experimental error and the estimate of its final location 

distribution was used to formulate an error analysis. 

Debris transport and capture fractions were then 

calculated from the final mass distributions and the 

capture fractions correlated with the data from the ARL 

separate effects tests.

NUREG/CR-6369 3-2
Integrated Effects

3.3. Test Facility Description 

The CEESI is located outside Nunn, Colorado 

approximately 100 miles north of Denver at a converted 

decommissioned Atlas missile site. The site was 

converted in 1965 to a commercial air and water 

calibration facility. The station compressed air facilities 

can store as much as 11,000 ft3 of air at 2500 psia. The 

debris transport tests were conducted in the CEESI 

Outside Calibration Facility shown in Figure 3-1. 

3.3.1 Air Blast Test Chambers 

The main test chamber consists of a horizontal large 

diameter cylinder that was approximately 93 ftin length 

and 9.4 ft in diameter (inner). A 32-ft long auxiliary 

chamber of the same diameter was attached with a 

flanged collar at the exit end of the main chamber in a 

horizontal "L" configuration. The flow area of the 

flanged collar (7.2 ft inside diameter) was about 60% of 

the flow area of the test chambers. A conical diffuser 

section was attached to the upstream end of the main 

chamber (behind the air jet nozzle) but this conical 

section was nearly completely blocked (a small section at 

the center was blocked by a screen) such that only a small 

fraction (order of 5-10%) of the air exited the test 

chamber in the reverse direction. Exhaust air flows 

exiting the far end of the auxiliary chamber were filtered 

by a reinforced perforated steel plate (1/8 inch mesh) that 

covered that opening. Target

insulation blankets were mounted on a 12.75 inch outer 

diameter pipe that extended across the main test chamber 

at mid height and was positioned directly in front of the 

air jet nozzle. The target pipe was secured to rails on 

either side of the test chamber which extended 

horizontally 30 ft from the jet nozzle. A burst disk 

mounted upstream of the nozzle in the air supply line 

ruptured after system pressure of approximately 1000 

psig was applied across the disk. Figure 3-2 shows the 

test chambers drawn to scale. 

3.3.2 Structural Test Section 

The structural test section contained an assemblage of 

structural components (e.g., gratings, pipes, and I-beams) 

designed to simulate a prototypical section of a BWR 

drywell. A survey was conducted of typical structures 

that exist in Mark I and Mark II containments and their 

respective surface areas prior to designing the structural 

test section. The design generally focused on maintaining 

the same surface to volume ratios as found in the BWR 

containments. To the extent practical, the structures were 

oriented in a manner analogous to the orientations found 

in the actual plant conditions. A comparison of the 

CEESI geometry with a Mark I is discussed further in 

Section 3.4 

The structural components of the structural test section 

are shown schematically in Figure 3-3. All I- and all 

pipes were 10 inches in diameter. I-beams were oriented 

with their web into the direction of air flow. Starting 

from the

Figure 3-1. CEESI outside calibration facility.

3-3 NUREG/CR-6369
CEESI Facility Structure Measurements

E

Figure 3-2. CEESI facility structure dimensions.

Irl"

U1. IV. V. 'A. 

Figure 3-3. Schematic of structural test section.

NUREG/CR-6369. 3-4
Integrated Effects

front (flow entrance) of the structural test section, the test 

section contains the following structural subassemblies: 

"• A continuous grating with two vertically oriented 

pipes directly behind, 

"• I-beams with a full length beam oriented vertically 

and a half beam oriented horizontally, 

"* I-beams with a full length beam oriented 450 from 

vertical, 

"• Horizontally oriented pipe with a half I-beam 

oriented vertically, 

• Pipe oriented 450 from vertical, 

• V shaped grating, 

• Two half-section gratings separated axially by 22 

inches, referred as the split grating. 

The gratings of the V-grating were at an angle of 

approximately 560 to the axis of the main test chamber 

and the V-grating did not obstruct the entire flow, i.e., 

portions of the air passed over the top, under the bottom, 

and around the sides without passing through the grating. 

The V-grating was 5 ft wide at its widest and it obstructed 

about 57% of the total test chamber flow area. All 

gratings were manufactured from 1/8-inch steel bars. The 

dimensions of a 'grating cell', defined by the spacing 

between the bars was 3.75 inches by 1 inch. 

Most of the structural test assembly can be seen in the 

photo shown in Figure 3-4 taken from just behind the 

continuous grating. Note that the pipes and I-beams look 

somewhat like a large pinwheel. A warm water high 

pressure (150 psi) misting system, constructed from PVC 

pipe, was installed in the structural test section to wet the 

structural assemblies. 

3.3.3 Test Instrumentation 

Test instrumentation for the CEESI debris transport tests 

consisted of pressure sensors with transducers in the air 

jet supply line to monitor nozzle air flow, Pitot tubes with 

transducers in the approach to the structural test section to 

measure flow velocities, and video cameras to record the 

motion of debris particles. Locations of the 

instrumentation are shown Figure 3-5. Other non

instrumentation data consisted of still pictures taken 

before and after each test and the collection of debris by 

location and classification from both test chambers. 

Nozzle Air Flow. The pressure history of the jet nozzle 

was measured and recorded for each test by pressure

sensors with transducers in the air jet supply line. The 

actual jet duration time for each test was determined from 

this pressure history. A sample pressure trace is shown in 

Section 3.5. 

PitotTubhe. Pitot tubes connected to transducers were 

mounted in the approach to the structural test section to 

measure flow velocities. The axial and radial locations of 

each Pitot tube are shown in Figure 3-5. Two of the Pitot 

tubes were located axially in front of the other six tubes 

which were arranged in the same axial plane. The Pitot 

tubes were only used in the developmental tests. Since 

the tubes sustained substantial damage during the 

developmental tests and the test flow velocities were 

adequately characteristic during these tests, the tubes 

were removed prior to the production tests. 

Video Cameras. Video cameras were mounted in the test 

chambers to record the motion of debris particles as the 

particles moved through the chambers. Only one camera 

was installed for the developmental tests and it was 

located behind the jet nozzle looking past the target 

mount and downrange towards the structural test section. 

Two additional cameras were mounted for the production 

tests. The first of these was mounted at the far end of the 

main test chamber looking back towards the structural test 

section so it could record the motion of debris exiting the 

split grating. The second of these additional cameras was 

mounted in the auxiliary test chamber near the joining 

flange collar looking towards the exhaust screen at the far 

end so it could record the motion of debris as the debris 

passes through the 90' bend upon entering the auxiliary 

test chamber. 

3.4 Scaling Considerations 

The CEESI experiments were designed to focus primarily 

on capture of steam-bome debris on various drywell 

structures following a postulated double-ended guillotine 

break in a main steam line in the mid region of the 

drywell. The rationale for that selection and the 

supporting calculations are documented in Ref. 3-5. This 

section discusses how the experimental parameters used 

in CEESI experiments scale to the conditions expected to 

exist in the BWR drywell following a LOCA. The 

controlling parameters are: working fluid, flow velocity 

and flow patterns, debris size/characteristics, debris 

wetness, drywell surface wetness and structures/obstacles 

followed by how they are simulated in the CEESI tests.

3-5 NUREG/CR-6369
Figure 3-4. Frontal view of a structural test section.

Exhaust Screen

Location of Pitot Tubes with Respect to the Horizontal

Location of Pitot Tubes with Respect to the Vertical 

Figure 3-5. CEESI debris transport instrumentation.

NUREG/CR-6369 3-6
Integrated Effects

Finally, the effect of expected distortions on the 

experimental results was noted. 

Working Fluid Choice- In the bulk of a BWR drywell 

following a MSLB, the debris would be entrained and 

transported by steam at a temperature of 260 TF and a 

pressure of 40 psia(Ref. 3-5). Past calculations have 

shown that fine water droplets (1-10 microns in diameter) 

are suspended in a steam continuum (void fraction zl.0) 

at low equilibrium qualities (=0.1). 

In CEESI experiments air (typically 50OF at stagnation 

condition and 14 psia) was chosen as the working fluid. 

This known deviation from prototypical conditions could 

have the following macro- and micro- scale effects: 

1. Usage of air instead of condensing steam (or mist 

flow) eliminates possibility of debris capture by 

diffusiophoresis. For the debris size of interest, the 

capture driven by diffusiophoresis (capture velocity 

=0.01 m/s) is negligible compared to inertial capture 

(Stokes number >> 1) [Ref. 3.5] 

2. Expansion of air from its stagnation conditions will 

result in overcooling in the jet pathway. Past 

calculations suggest that the resulting temperature 

can be as low as 5OF, corresponding to a stagnation 

temperature of 50 TF. If proper precautions are not 

taken, water may freeze and eliminate surface 

wetness which is vital for capture'. To avoid this 

possibility, the drywell interior was pre-heated before 

every test to up to 75 OF. Also warm water (> 100 *F 

@ 150 psia) was injected into the flow stream to wet 

the structures. A simple heat balance was conducted 

to ensure that freezing would not occur. Visual 

inspection after conclusion of each test revealed no 

evidence of freezing. The debris can be clearly seen 

to be attached to structures by a thin water film. 

3. Stokes number (Stk) is inversely proportional to the 

gas media kinematic viscosity, therefore usage of 

colder air instead of steam results in lower Stokes 

numbers. At the range of Stk being examined (i.e., 

2.5-6.5), this effect on Stk is negligible. 

It is difficult to exactly quantify the impact of each of 

these effects on the capture efficiency measured from 

these tests. Qualitatively, however, it is clear that these 

effects possess the potential to lower capture efficiency 

I Debris are held on structures by water surface tension as 

demonstrated by the fact that dry debris do not stick to surfaces (see 

Section 2).

and thus maximize transportability of debris. No 

corrections were made to account for this known 

deviation from prototypicality. 

Flow velocity, and flow patterns: A series of 

computational fluid dynamics (CFD) calculations were 

performed using commercially available CFD codes to 

draw inferences regarding steam flow patterns that exist 

in the drywell following a postulated large break LOCA 

(Refs. 3-5, 3-9, and 3-10). The scope of these 

calculations varied from 1-D scoping calculations that 

estimated cross-sectional area averaged fluid velocities 

.assuming plug flow to refined CFD calculations on jet 

deflection by structural elements. Based on these 

calculations it was concluded that steam flow velocities in 

the close proximity of the break tend to be near-sonic or 

super sonic. The extent of this region depends on the 

break orientation and the structural congestion close to 

the break. Sufficiently far from the break (L/D > 10) the 

jets will dissipate into pressure-driven flows with 

velocities in the range of 30-50 ft/s, with an average of 

about 45 ft/s. In the drywell floor region these velocities 

may be even lower, close to 30 ft/s. The bulk flow can be 

approximated as being parallel to the drywell walls, 

where as the localized flow patterns differ considerably 

within the containment depending on the pipe break 

location, and structural arrangements. CEESI 

experiments were designed to measure capture efficiency 

at velocities that are typical of lower parts of the 

containment where bulk flow velocities are typically less 

than 45 ft/s. 

To simulate these flow conditions in CEESI experiments, 

efforts were made to ensure that nozzle size and flow 

would be sufficient to induce bulk flow > 45 ft/s, and that 

flow as it is entering the piping region of the test section 

would be nearly axial. Selected calculations were used to 

design the test section. In addition, the test section was 

instrumented to confirm that actual flow in the test section 

is according to the calculations. In the first calculation a 

1 -D choked-flow model was employed to determine the 

flow rate through the nozzle at the exit plane. These 

calculations suggested that a 3.75-inch diameter nozzle 

(nominally 4 inch nozzle) would be required to establish 

desired bulk flow velocity of 45 ft/s (corresponding mass 

flow through the nozzle is about 300 lbm/s). On the other 

hand, a 3-inch diameter nozzle would be sufficient to 

establish a flow velocity of 30 ft/s. The mass balance on 

the high pressure storage tank2 was used to confirnm that

2 The storage tank pressure was measured before and after each test. 

The mass balance was then used to estimate the mass of air discharged.

3-7 NUREG/CR-6369
the actual bulk flow through the test section is equal to or 

greater than the flow rate predicted by the 1 -D model. 

During the design process, a CFD calculation was run to 

examine flow fields that would result from a 4-inch 

diameter (at the stagnation point) jet on the target pipe. 

Examples of these CFD calculations are presented in 

Figures 3-6 and 3-7. Figure 3-6 shows the flows near the 

jet nozzle as velocity vectors overlaid onto the fluid 

temperatures (variations in color). The simulated jet is in 

the lower left corner and the simulated target pipe is 

shown at mid level. Figure 3-7 shows the flows and 

temperatures further downstream in the region of the 

structural test section. The flow pattern, of course, 

changed with the axial position of the target but the flow 

patterns through the structural test section remained 

relatively uniform. The actual flow patterns may differ 

slightly from the CFD code predictions, because of the 

underlying modeling assumptions. For example, space 

behind the nozzle was not modeled to minimize the 

calculational nodes. Similarly, the first grating was 

assumed to be a baffle plate with a non-linear pressure 

drop coefficient of 5 and the presence of various 

structures in the piping region was ignored. More refined 

CFD analyses were determined to be cost-prohibitive. 

To map actual flow patterns, the experiments relied on 

two sets of measurements. The test section was 

instrumented with fast-responding Pitot-tubes to monitor 

axial velocities of flows entering the structural test 

section. A total of three tests were run with the sole 

purpose of mapping out the flow patterns. No effort was 

made to map out flow patterns within the piping regions. 

These measurements exhibited some dependence of flow 

velocity on the radial and angular position with respect to 

the center-line (see Section 3.5.2.3). In addition, the test 

section was equipped with three video cameras which 

were used to monitor movement of small debris. The 

debris pieces (especially the small debris) served as 

tracers illuminating three-dimensional flow patterns. 

These video pictures indicated that bulk flow moved 

consistently in the forward direction (with respect to the 

nozzle exit plane), but that there exists a 3-D movement 

of the flow. Flow patterns within the structural test 

section appeared to be simple; no eddies were 

discovered. A strong eddy was noted to exist behind the 

nozzle, which was capable of entraining a fraction of the 

debris and

trapping the debris behind the jet. The data reduction 

procedures corrected the test results for the debris 

deposited behind the jet. 

Based on these analyses and measurements, it was 

concluded that at a nozzle diameter of 3.75-inch, bulk 

flow velocity in the test section would vary between 38 

and 60 ft/s, depending on the radial location and axial 

plane. These velocities are typical of expected flow 

velocities in the majority of drywells. A comparison of 

present experimental results with the results of the 

separate effects tests3 indicates that presence of three

dimensional flow patterns has little effect on the debris 

capture. 

Debris Size and Debris Characteristics Debris generation 

experiments conducted by past experimenters have shown 

that generated fibrous debris would range in size from 

individual fibers to partially destroyed blankets. 

Transportable debris can be adequately categorized with 

three general size groups: small, medium and large. The 

small pieces are best described as loosely attached fibers 

with no structure left over from the original blanket. The 

medium pieces tend to possess some of the original 

blanket structure at the middle, but appears beaten-up on 

the outside. The large pieces on the other hand are torn 

pieces of the original blanket. Their composition is likely 

to vary with the location and orientation of the target pipe 

with respect to the nozzle. 

The CEESI experimental facility was best suited for 

producing such a wide range of debris and simultaneously 

introducing them into the flow stream in a prototypical 

manner. The following sections provide a pictorial 

description of the actual debris generated and used in the 

present experiments. Visual inspection of these debris 

suggests that debris used in the CEESI tests are consistent 

with photographs and videos published by past 

investigators. 

Debris Wetness The debris generation experiments have 

also shown that steam generated debris are nearly dry 

(with some moisture on the outside). Two bench-top 

experiments were conducted as part of this study, to 

confirm that debris subjected to steam remain mostly dry. 

In the first experiment, a steam jet from industrial steam 

boiler (150 psi) was used to generate small pieces from an 

intact blanket. Visual inspection of the pieces suggested 

that the outer surface gets wet. In the second experiment,

3 In the separate effects tests diffusers were used to straighten the flow 

and ensure that flow closely resembles plug flow as confirmed by tracer 

visualization of the flow fields.

NUREG/CR-6369 3-8
Integrated Effects

temperature 

( - = 7.21E+02)

fluid

94 

66

0.0

I 

r

I .805

FLO W-3D® t=.4921 y=2.172E+00 (ix=2 to 14 kz=2 to 19) 

16:43:00 12- 2-1996tvwk hydr3d: version 7.0.1 

CEES 4" Nozzle: 3D, 16" Pipe at 40" Downstream 

Figure 3-6. Typical CFD calculated flow patterns near jet nozzle and target.

WIN32 1996

NUREG/CR-6369

and vectors 

235 

207 

179 

151 

i i122

2.0291 

z

-. 1000

1-

3-9
Integrated Effects

fluid temperature and vectors

( -- = 9.78E+00) 

15.0676 4 4 # i # 4 4

Z 

I .79 12

0.0 0.77 

r

293.1 

290.6 

288.0 

285.4 

282.9 

280.3

277.7

1.54

FLOW.3D® 

16:43:00 

CEES 4"

t=.4921 y=2.172E+00 (ix=2 to 25 kz=69 to 80) 12- 2-1996tvwk hydr3d: version 7.0.1 WIN32 1996 

Nozzle: 3D, 16" Pipe at 40" Downstream

Figure 3-7. Typical CFD calculated flow patterns in structural test section.

NUREG/CR-6369 3-10
Integrated Effects

previously destroyed blanket pieces were exposed 

continually to steam flow with suspended water droplets. 

After a minute of exposure, the debris mass increased by 

no more than 10%, indicating negligible wetting. 

No efforts were made to simulate debris wetness. This is 

a known deviation from the prototypical conditions. Its 

effect is likely to minimize debris capture on various 

structures, and thus maximize debris transport. 

Structural Surface Wetness Structural surfaces would be 

wet as a result of: a) deposition of fine water droplets 

produced during isentropic expansion of steam jets in the 

containment and b) condensation of steam. Actual water 

layer thickness on a given structure most likely varies 

with time. Past scoping calculations and MELCOR 

calculations suggest that steam condensation alone can 

produce water layer thickness as high as 200 microns 

with in 1 second. The scoping calculations also suggest 

that water droplets produced by isentropic expansion 

would be about 10-50 microns in diameter and would 

possess sufficiently large stokes number to impact various 

structures located in the bulk flow. Together, it is very 

likely that all structural surfaces would be wet, with 

thickness sufficient to drain (or be re-entrained by steam 

flow) within the first two seconds. 

Procedures for wetting structures located in the CEESI 

facility were developed based on several exploratory tests 

in which fine misters positioned at different locations 

were used over selected intervals. Sprays were added as 

needed to ensure that all structures were evenly wetted. 

Typically sprays were run several minutes before each 

test to ensure that a liquid layer builds up to sufficient 

thickness to drain under gravity. After approximately 5 

minutes of spraying, the liquid film on the structures 

attained a steady state. Rough measurements 4 of liquid 

layer thickness suggest that it is a strong function of the 

structural orientation and structural geometry. For 

example on the horizontal section of a I-beam the layer 

thickness is typically about 0.5 mm, on the other hand 

layer thickness on the vertical surface of the I-beam is 

much less (z 0.1 mm). It is important to note that 

observed deposition profile exhibited little or no 

dependence on the initial layer thickness. For example, 

on an I-beam, the majority of the deposition occurred on 

the vertical surface which was perpendicular to the bulk 

flow direction, but is lowest where film is thicker.

Geometri Scaling A comprehensive survey of drywell 

structures (Ref 3-5) was undertaken to identify types of 

structures present in a drywell and the levels of 

congestion. Typical piping runs were found to vary 

between 6-inch and 28-inch, while the I-beams varied 

from 6" wide to 12" wide. The surface area for each 

structural class are shown in Table 3-1. This table did not 

include structures that are judged to be plant specific or 

those that vary widely from plant to plant. As evident 

from this table, the average surface to volume ratio of the 

structures in the drywell is about 1 ft/ft, although it 

varies from 1.3 ft/ff in the lower regions of the drywell 

to 0.4 ft/ft2 in the upper part of the neck. All the 

structural elements with a characteristic diameter larger 

than 12"are laid-out vertical or horizontal (e.g., steam 

lines and grating I-beams) and together they contribute to 

about 0.6 ft2/f. The remaining structures (conduits and 

instrument tubes) were designed to fit the space and 

contribute up to a surface to volume ratio of 0.4 ft2 

Pictures of the drywell at different elevations, together 

with Table 3-1, were used to design the CEESI test 

geometrical configuration. The intent was to initially 

assemble the major structures up to a congestion level of 

0.66 W/ft/ over 25-ft long test section. If considerable 

capture is observed, then increase the congestion to 1.3 by 

adding miscellaneous structures to study its impact on 

capture efficiency. Initial structures consisted of 12" 

diameter pipes arranged perpendicular or parallel to the 

flow direction and 12" wide I-beams with webs facing the 

flow. In addition, actual size gratings employed in the 

plant as floor gratings were also used in the CEESI 

facility. As little capture was noted during the 

developmental tests that no additional structures were 

added prior to the production tests. 

The congestion levels employed in these tests was 

approximately the same as the congestion expected in the 

regions between the first and second gratings. Measured 

capture efficiency is therefore typical of that estimated in 

the mid-region of the drywell. Usage of this capture 

efficiency for the area below the lowest grating would 

maximize potential for transport (which is conservative). 

The scaling of the CEESI facility to a Mark I drywell is 

summarized in Table 3-2. 

Geometrical Orientationr The CFD calculations indicated 

that primary flow direction in the Mark I and II 

containments would be vertical. The orientation chosen 

in

4 Choice of not using accurate water film thickness is based on insights 

gained from ARL experiments which suggested that for layer thickness 

higher than 100 rm debris capture is only weakly dependent on the 

surface wetness.

3-11 NUREG/CR-6369
Integrated Effects

Table 3 -1. Typical BWR drywell surface areas. 

Mark I Mark II 

Fraction Fraction 

Type of structure Area of total Area of total (ftr2) (fte) 

Containment structures 38,600 0.260 43,420 0.229 

Pipes and conduits 66,290 0.448 66,290 0.350 

Valves and equipment 8,510 0.057 8,510 0.045 

Gratings 18,330 0.124 54,990 0.290 

Ductwork 9,850 0.067 9,850 0.052 

Miscellaneous 6,500 0.044 6,500 0.034 

Total 148,100 1.000 189,500 1.000

Table 3-2. Summary of CEESI facility scaling to Mark I drywell. 

Parameter Parameter value Scale 

BWR Mark I CEESI 

Nominal MSL break size 22 inch 4 inch 5.5 to 1 

Lower grating cross-sectional area 2,000 ft 70 f12 29 to 1 

Predicted bulk flow velocity at grating <50 ft/sec <50 ft/sec 1 to 1 

Containment volume upstream of final grating 130,000 f-t 4,200 fte 30 to 1 

Containment volume upstream of downcomers 170,000 ft' 7,700 ft' 22 to I 

Post-blowdown atmosphere turnover time 4 seconds 2 seconds 2 to 1 

Surface-to-volume ratios* 

Pipes and I-beams 0.45 0.47 1 to 1 

Gratings 0.12 0.13 1 to 1 

Walls and miscellaneous 0.43 0.40 1 to 1 

*Over a 10-ft long section

NUREG/CR-63693 3-12
Integrated Effects

the CEESI experiments is horizontal. This deviation 

raised the following concerns: 

1. As debris transports from the target to the structures, 

it may separate from the flow and stratify towards the 

lower regions of the test section. Such stratification 

would skew the final results. Theoretically it is 

known to occur if the gravitational settling velocity 

of the debris class is equal to or higher than the bulk 

flow velocity and the flow turbulent velocity. For the 

present conditions of interest, the gravitational 

settling velocity for the debris was measured to range 

between 0.75 - 5 ft/s (small to large) while the bulk 

flow velocity is in excess of 45 ft/s and estimated 

turbulence velocity is in excess of 7 ft/s. 

Corresponding to such conditions, gravitational 

settling is expected to be minimal. An experiment 

was conducted at ARL to confirm these calculations, 

where debris varying in size from small to medium 

was injected into the flow and was captured down 

stream using a mesh screen. At a bulk velocity of 30 

ft/s, debris were uniformly distributed across the flow 

cross-section, confirming that no stratification is 

expected for flow velocities larger than 30 ft/s. 

2. Inertial impaction potential may vary as a result of 

gravity vector orientation. Typically this effect is 

evaluated by the ratio of Stokes number to Froude 

number (which translates into a ratio of gravitational 

settling velocity to flow velocity). If the ratio is 

much smaller than unity, the flow is commonly 

believed to be dominated by inertial forces and its 

direction on particle deposition is negligible. For the 

present experiment, this ratio varies between 0.03 

and 0.15 depending on the debris size. 

Based on these analyses it was concluded that this noted 

deviation has negligible effect on the measured capture 

cross-sections. 

3.5 Developmental Tests 

Seven developmental tests were conducted to determine 

adequacy of the experimental design to achieve the test 

objectives and to develop optimal test procedures to get 

the most out of the production tests to follow. The bulk 

flow velocities entering the structural test section were 

measured and compared with velocity predicted by design 

analyses. 

Experience was gained in prewetting structural surfaces 

prior to initiating the test and in collecting and classifying

debris. Debris generation and transport within the CEESI 

facility were examined. 

3.5.1 Test Matrix for the Developmental 

Tests 

The test parameters varied included the nozzle diameter, 

the jet duration length, the distance between the jet nozzle 

and the target insulation blanket, the blanket manufacture, 

the method of restraining the blankets, and the method of 

wetting the structures. The test conditions for each of the 

seven developmental tests are shown in Table 3-3. 

The first three tests focused on mapping test chamber 

flow velocities and the last four tests focused on 

characterizing the debris generation and transport. Target 

insulation blankets were not installed on instrumentation 

tests I-1, and 1-2 so that debris would not interfere with 

the instrumentation (the target pipe mount was however 

in place in front of the jet to disperse the jet flow). 

Because the flow velocities were reasonably well mapped 

during the first two tests, the decision was made during 

testing to install a target insulation blanket on the third 

instrumentation test. 

All developmental tests used the nominal 4 inch nozzle 

except Test W- 1 which used the nominal 3 inch nozzle 

(actual diameters were slightly smaller than nominal 

diameters). The focus was on the 4-inch nozzle because 

this nozzle provided higher test chamber bulk flow 

velocities (more prototypical) than the 3 inch nozzle. 

Data collected during the production tests using the 3 inch 

nozzle provided debris transport data at an alternative 

bulk flow velocity. The jet duration time, i.e., the length 

of time air was supplied to the nozzle, of 5 seconds was 

adequate for the instrumentation tests but was found 

inadequate for complete debris transport. 

The distance between the jet nozzle and the insulation 

blanket was varied because it affected the level of 

destruction of the blanket and consequently the quantity 

of debris generated. The distances shown in Table 3-3 

were measured from the nozzle to the front face of the 

blanket. This distance is also expressed in the multiple of 

the nominal jet diameter, i.e., L/D, to accommodate 

debris destruction models based on this ratio.

3-13 NUREG/CR-6369
Integrated Effects

Table 3-3. Test Matrix for the developmental tests. 

Test Nozzle Air Jet Target position Blanket description Structure diameter duration wetness 

No. ID Distance L/D Make Length Restraints 

(inch) (second) (inch) (ft) 

Instrumentation tests 

1 1-I 4 5 56 14 None N/A N/A Dry 2 1-2 4 5 40 10 None N/A N/A Dry 3 1-3 4 5 40 10 Transco 3 None Partial 

Debris characterization tests 

4 W-1 3 5 36 12 Transco 3 SS Bands (3) Wet 

5 W-2 4 12 48 12 PCI 1.5 SS Bands (2) Wet 

6 W-3 4 12 48 12 Transco 3 SS Bands (3) Wet 

7 W-4 4 12 100 25 Transco 3 SS Bands (3) Partial

The insulation blankets used were manufactured by was 

provided by Performance Contracting, Inc. (PCI). The 

Transco blankets were 3 ft in length compared to 1.5 ft 

for the PCI blanket. Stainless steel bands (either 2 or 3) 

were placed around the blanket to hold the blanket in 

place but the blankets were not encapsulated by a metal 

jacket. 

Surfaces in the structural test section were wetted for the 

debris characterization tests because surface wetness is 

both prototypical and has been shown to strongly influence debris capture. In Tests W-l, W-2, and W-3, 

the structures were sprayed using the installed misting 

system prior the initiating each test. In Tests 1-3 and W-4, 

the misting system was not activated but the surfaces 

were prewet with a water hose prior to the test. The 

hosing method of wetting surfaces was found to leave the 

surface only partially wet because the water tended to 

drain off of the surfaces before the tests could be 

conducted. 

3.5.2 Flow Velocity Mapping 

The development tests were instrumented with Pitot tubes 

connected to transducers to monitor and map flow 

distributions before the flow entered the congested test 

section. The locations of the Pitot tubes were shown in 

Figure 3-5.

3.5.2.1 Nozzle Discharge 

The air discharge was monitored and recorded, as 

discussed in Section 3.3, by pressure sensors equipped 

with transducers in the jet air jet supply. One sensor was 

located in the air supply tank and the second sensor was 

located upstream of the nozzle. A typical nozzle pressure 

history is shown in Figure 3-8. 

The jet duration time specified for each test was 

approximated with a countdown by the facility operators 

at CEESI and the actual jet duration time verified for each 

test from the recorded pressure once the supply valve was 

closed. The actual jet duration time shown in Figure 3-8 

was about 12.5 seconds where the test specification called 

for 12 seconds but the jet air flow continued until about 

14 seconds. 

3.5.2.2 Pitot Tube Performance 

The Pitot tubes/transducers used were not designed to 

measure initial shock flow but quasi-steady flow 

following the flow shock that follows the rupture of the 

rupture disk. The response time of the Pitot 

tube/transducers to changes in flow velocity was about 

0.05 to 0.1 seconds. The response time for the data 

acquisition system was.

NUREG/CR-6369 3-14
Integrated Effects

10.000 20.000

Time (seconds) 

Figure 3-8. Typical nozzle pressure history.

0.05 seconds. The Pitot tubes were not protected from the 

impact of insulation debris, and were therefore susceptible 

to plugging 

The data acquisition had a total of 16 channels available 

for data collection and each Pitot tube required two 

channels, therefore Pitot tubes were mounted in eight 

locations designated as P1, P2, P3, P4, P5, P6, P7, and 

P8, as shown in Figure 3-5. No data, however, is 

available for Pitot tube P3. The measurement ranges for 

the Pitot tubes are listed in Table 3-4. 

Processing the Pitot tube data was accomplished by 

smoothing the fluctuations with a moving average 

technique, as illustrated by the typical Pitot tube response 

shown in Figure 3-9 for Pitot tube P6 during Test 1-2. 

The moving average technique simply projected the next 

value based on the average of the preceding 25 values. A 

singular value representing a characteristic velocity was 

then estimated for each valid Pitot tube response. 

Many of the Pitot tube responses were invalidated either 

due to the response being out-of-range for that instrument 

or due to an erratic response. Each Pitot tube response 

was reviewed to ensure that the response was within the 

measurement range of the instrument. Figure 3-10 shows 

that the response of Pitot tube P1 during Test I-1 ranged

between 5 and 15 ft/sec whereas the instrument range was 

67 to 133 ft/sec, therefore, this data was out-of-range and 

not considered valid (this Pitot tube was subsequently 

replaced with a lower ranged tube). Other Pitot tubes 

responses were invalidated when their responses became 

erratic due to obstructions of insulation debris or to water 

intrusion into its transducer, such as, the response shown 

in Figure 3-11. 

3.5.2.3 Characteristic Bulk Flow Velocities 

The bulk flow velocities measured for the 4 inch jet 

nozzle ranged from about 35 to 60 ft/sec. Only two valid 

velocity measurements were obtained for the nominal 3 

inch nozzle (Test W-l) and these velocities were 28 and 

30 ft/sec. The measured flow velocities are tabulated in 

Table 3-5. The transducers for Pitot tubes P4, P5, and P8 

performed poorly following the first test, Test I-1, most 

likely due to water intrusion into the transducer. 

As shown in Figure 3-12, the measured bulk flow 

velocities compared favorable with the velocities 

predicted from the one-dimensional jet expansion 

calculations that were modeled assuming isentropic flow 

through a nozzle. The predicted flow velocities were 

about 30 and 45 ft/sec for the 3 and 4 inch nozzles, 

respectively.

NUREG/CR-6369

2000 

1500 

1000 -

-50&8t

00"% 

CL 

%t00 

W90

3-15

L 
Integrated Effects

Table 3-4. Pitot tubes/transducer ranges of performance. 

Pitot tube Transducer Minimum Maximum 

location rating flow flow 

velocity velocity 

(In-H20) (ft/sec) (ft/sec) 

P1* 0 to 5.0 67 133 

0 to 2.5 47 105 

P2 0 to 2.5 47 105 

P4 0 to 1.0 30 67 

P5 0 to 1.0 30 67 

P6 0 to 1.0 30 67 

P7 0 to 1.0 30 67 

P8 0 to 2.5 47 105 

Tube ranging to 5.0 in-H 20 was replaced with lower 

range tube after Test I-1. The upper range after Test I

1 was 2.5-H20. 

Instr. Test #2, Pitot Tube #6

5 10

-Air Velocity (ft./min.) 

-25 per. Mov. Avg. (Air 

Velocity (ft./min.))

15 20 25

Time (s)

Figure 3-9. Typical pitot tube response.

NUREG/CR-6369

.4

4

o 

0m

6000 

5000 

4000 

3000 

2000 

1000 

0 

-1000

!

3-16
Integrated Effects

Instr. Test #1, Pitot Tube #1

- Air Velocity (ft./min.) 

-25 per. Mov. Avg. (Air 

Velocity (ft./min.))

6000 

5000 

"* 4000 

g 3000 

2000 

"8 1000 

0 

-1000 

-2000

15 20 25

Time (s)

Time (s)

Figure 3-11. Plugged pitot tube response..

NUREG/CR-6369

5 10

7000 

6000

a) 

E 

0

5000 

4000 

3000 

2000 

1000

Figure 3-10. 

Out-of-range 

pitot tube 

response.

0 

-1000

W

I

3-17
Integrated Effects

Table 3-5: Measured characteristic bulk flow velocities.

CEESI Bulk Flow Velocities

-A ! A _ 

SPredi ted by Mode s 

0

0.0 '01 

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

EHI

* 1-2 

A 1-3 

0 W-1

1.0

Normalized Radial Location (R/Ro)

Figure 3-12. Comparison of measured and predicted bulk flow velocities.

NUREG/CR-6369

Test ID Flow velocity at pitot tube location Pn 

P1 P2 P4 P5 P6 P7 P8 

(ft/sec) (ftlsec) (ft/sec) (ft/sec) (ft/sec) (ft/sec) (ftlsec) 

I-1 Invalid 37 45 52 47 42 57 

1-2 38 43 Invalid Invalid 45 40 Invalid 

1-3 37 0 Invalid Invalid 42 40 Invalid 

W-1 Invalid Invalid Invalid Invalid 28 30 Invalid 

W-2 37 42 Invalid Invalid Invalid Invalid Invalid 

W-3 37 41 Invalid Invalid 42 40 Invalid 

W-4 Invalid Invalid Invalid Invalid Invalid Invalid Invalid

80.0 

70.0 

60.0 

50.0 

• 40.0 U 

S30.0 

20.0 

10.0

3-18
Integrated Effects

3.5.2.4 Adequacy of Flow Fields Relative to 

Debris Transport Objectives 

The jet nozzles (i.e., 3 and 4 inch nominal diameters) 

selected for these tests appeared adequate to complete the 

objectives of these tests but the faster flows of the 4-inch 

nozzle was deem more appropriate. Therefore, most of 

the production tests employed the 4-inch nozzle. 

Flow velocity measurements illustrated that the focused 

jet flow was sufficiently dispersed or disrupted by the 

target mount to achieve a reasonably uniform flow 

through the structural test section. A review of the video 

cameras footage showed extremely turbulent mixing of 

debris in the target region of the test chamber. Still 

photos of the structures showing the captured debris 

further support a relatively uniform mixing of the debris. 

A small portion of the air flow, less than 5% of the total 

flow, exited the test chamber through a small screened 

opening behind the jet. This reverse air flow and its 

associated debris transported were factored into the debris 

transport analyses. 

3.5.3 Initial Debris Generation and 

Transport Characteristics 

3.5.3.1 Debris Generation 

Four developmental tests were conducted using Transco 

blankets consisted of fiberglass insulation encased in a 

tough canvas bag designed to wrap around the pipe. Each 

Transco blanket was 3 ft long and approximately 3 inches 

thick. The blankets were held in place by canvas straps 

and on most tests were further supported by stainless steel 

bands. The blanket was arranged so that seams did not 

face directly into the air jet. One test, Test W-2 was 

conducted with a 1.5 ft long PCI blanket but only an 

insignificant amount of debris was generated because the 

short blanket was ripped from the pipe mount relatively 

intact. In the other tests, the blankets remained more than 

50% intact indicating the need for a modification to the 

blanket mount to enhance debris generation in the 

production tests to meet the test objective of predicting 

debris capture under relatively high loading conditions. 

Four of the seven developmental tests provided useful 

debris transport and capture data and those results are 

presented in Section 3.7.

3.5.3.2 Jet Duration 

Minimizing air usage was critical to keeping tests costs 

within budget, but to obtain valid debris transport results, 

the air jet must flow long enough for the debris generation 

process to complete and the resulting debris to either 

deposit on a structure or pass through the test chamber. 

Determining the time required to flush the system was one 

objective of the developmental tests. Post test 

observations of debris deposits, Tests 1-3 and W- 1, where 

the jet duration time was only 5 seconds indicated that 5 

seconds was not enough time for complete debris 

transport. The other tests that used 12 seconds of air 

appeared adequate. It was determined that the production 

tests would use at least 10 seconds for 4 inch nozzle tests 

and 12 seconds for 3 inch nozzle tests. Note that the 

flushing time for a 3 inch nozzle test was longer than for a 

4 inch nozzle test because the flows were slower. This 

issue was further evaluated in the production tests. 

3.5.3.3 Surface Wetting 

Two methods for prewetting the surfaces of the test 

structures prior to the activating the air jet and 

subsequently destroying the blanket were tested. One 

method was to simply spray the structures with a water 

hose until the surfaces were thoroughly wet and the other 

was to spray the surfaces using the PCV pipe misters 

installed inside the test chamber. The hosing method was 

found inadequate because the water tended to drain from 

the surfaces before the test could be conducted whereas 

the misting system was operated until the test was 

completed. The misting system was operated long 

(approximately 10 minutes) enough to form a draining 

water layer. Draining water formed small pools on the 

chamber floor prior to flowing out through small drain 

holes. Structure wetness was verified by the test operators 

upon reentry into the chamber following the test. 

3.5.4 Facility Modification and Test 

Procedure Development 

Assessing the data from the developmental tests indicated 

a need for some addition but relatively minor 

modifications to the CEESI facility. The following 

modifications were made prior to performing the 

production tests:

3-19 NUREG/CR-6369
Integrated Effects

1. The special end supports were installed on the 

target mount pipe to prevent the blanket from 

moving axially along the pipe and out of the path 

of the jet flow. Holding the insulation target in 

place longer enhanced the destruction of the 

blanket, thereby increasing the mass of debris 

available for transport through the structural test 

section. 

2. The spray misting system was enhanced to more 

uniformly wet the structures in the structural test 

section. 

3. To accommodate the extreme winter conditions at 

the facility, heaters were purchased to heat the test 

chamber interior to a temperature >70 F to prevent 

the extreme exterior cold from affecting test 

results, 

4. A second and a third video camera were installed 

to film debris transport at two alternate locations. 

Experience gained with these tests was applied to 

developing the operating procedures for the production 

tests. 

3.6. Production Tests 

Ten production tests were conducted to produce data for 

the calculation of insulation debris transport and capture 

fractions. This section describes the tests conducted, test 

procedures, data collection procedures, photographic 

results, and the subsequent drying and weighting 

procedures. The data reduction and tests results are 

discussed in Section 3.7. 

3.6.1 Test Matrix for the Production Tests 

The test parameters varied included the nozzle diameter, 

the jet duration length, whether or not the surfaces were 

wet, and the distance between the jet nozzle. The test 

conditions for each of the ten production tests are shown 

in Table 3-6. 

These tests focused on the 4 inch nominal jet nozzle 

because of the faster bulk flow velocities resulting from 

the larger nozzle. Two tests, Li and L2, were conducted 

.with the 3 inch nozzle to test for differences in debris 

capture characteristics associated with the slower flow 

velocities. 

The tests specifications called for an air blast duration 

time of 10 seconds for the 4 inch nozzle tests, except for 

Test H2 which was specified as 15 seconds, and 12

duration times listed in Table 3-6, however tended to be 

seconds for the 3 inch nozzle tests. The actual recorded 

somewhat longer the test specifications. Based on post

test observations, the air jet duration times were in all tests 

deemed long enough to flush the airborne debris from the 

test chambers. 

The structures in the structural test section were wet by 

the spray misting system in all tests, except Test H7 which 

was conducted dry. Test H7 was conducted dry to 

illustrate the pronounced influence that surface moisture 

had on debris capture. 

The distance of the target from the jet (i.e., the distance 

from the nozzle to the front face of the blanket) was 

varied to ensure at least one test with maximum possible 

debris generation and to vary the density of debris passing 

through the structural test section. Tests conducted with 

an L/D in the neighborhood of 30 were found to 

completely or nearly completely totally destroy the 

blanket restrained as it was in these tests. 

Test HIR was designed to repeat test HI as closely as 

possible to show test repeatability. As it turned out, Tests 

Hi, H1R, H2, and H3 were all close enough in test 

conditions to demonstrate repeatability (shown in Section 

3-7). 

3.6.2 Description of Target Insulation 

Blankets 

All of the target insulation blankets used in the production 

tests were manufactured by Transco specifically for these 

tests. Transco blankets consisted of fiberglass insulation 

encased in a tough canvas bag designed to wrap around a 

pipe. Each Transco blanket was 3 ft long and 

approximately 3 inches thick. The blankets were held in 

place by canvas straps. The blankets were further 

supported by 3 stainless steel bands and 2 end supports to 

prevent axial movement along the pipe mount. The 

Transco blankets each had 2 seams, i.e., each blanket was 

formed from 2 half sections, which were arranged so that 

the seams were at the top and at the bottom and did not 

directly face the nozzle. The target blanket for Test H1R 

as mounted for testing is shown in Figure 3-13. 

3.6.3 Testing Procedures 

The following test procedure was followed as closely as 

practical for all of the production tests.

NUREG/CR-6369 3 -20
Integrated Effects

Table 3-6. Test matrix for the production tests. 

Test Nozzle Air jet Structure Target position 

diameter duration wetness 

No. ID - IDistance [ L/D 

(inch) (second) (inch) 

1 HI 4 13 Wet 120 30 

2 HIR 4 13 Wet 120 30 

3 H2 4 15 Wet 120 30 

4 H3 4 14 Wet 80 20 

5 H4 4 13 Wet 160 40 

6 H5 4 14 Wet 200 50 

7 H6 4 14 Wet 40 10 

8 H7 4 16 Wet 120 30 

9 Li 3 17 Wet 80 27 

10 L2 3 24 Wet 84 28

Figure 3-13. Target blanket installation.

3-21 NUREG/CR-6369
Integrated Effects

1. Record test parameters. 

2. Clean test chamber of debris and unneeded 

equipment. 

3. Warm test chamber using propane heaters as 

needed. 

4. Weigh and mount insulation blanket on target 

mount. 

5. Record test chamber interior temperature. 

6. Setup and activate all three video =aneras and 

check lighting. 

7. Clear chambers of personnel and secure screen 

door. 

8. Open wooden cover plate on the blocked-off 

diffuser end of the main test chamber. 

9. Turn on misters and spray structures for 

approximately 10 minutes. 

10. Open the air supply and pressurize air jet rupture 

disk. 

11. Turn off air supply to jet nozzle after specified air 

jet duration. 

12. Turn off misters immediately afterwards to avoid 

washing captured debris off of the structures. 

13. Close the cover to the diffuser section. 

14. Wait 2 minutes before entering test chambers. 

15. T urn off video cameras. 

16. Take still pictures of test chamber interior showing 

blanket destruction and debris capture. 

17. Collect debris per debris collection procedures. 

18. Record observations and deviations from standard 

test procedures. 

19. Obtain test pressure history from CEESI data 

acquisition system. 

3.6.4 Data Collection Procedures 

Debris transport data consisted of collecting as much of 

the insulation debris as reasonably practical and 

photographing the interior structures and spaces. A 

portion of the debris in each test was not recovered, 

referred to herein as non-recoverable debris (NR). The 

majority of the NR debris included fine debris blown out 

of the test chambers through the exhaust screens and fine 

debris deposited on walls and structures that was simply 

too small to collect from a practical consideration. 

3.6.4.1 Debris Collection Locations 

Determining debris transport and capture fractions 

required knowing where the debris resided immediately 

following completion of the test, therefore debris was 

collected from discrete sections of the test chambers or 

from specific structures. Twelve specific locations were 

predetermined to accomplish this task. Debris collected at

these locations was bagged separately by its location and 

by its classification that is described in the next section. 

The 12 locations were: 

1. On the screen door at the far end of the auxiliary test 

chamber where the exhaust air exited from the 

chamber. 

2. The remainder of the auxiliary chamber. 

3. The section of the main chamber between the split 

grating and the collar joining the main and auxiliary 

chambers. 

4. On the split gratings. 

5. On the V-grating. 

6. The section of the main chamber between the 

continuous grating (first grating) and the split 

7. The structural components of the structural test 

assembly. 

8. The continuous grating. 

9. The main chamber between the target mount and the 

continuous grating. 

10. The main chamber behind the target mount 

including the inside surface of the panel blocking 

flow through the diffuser section. 

11. The target mount itself. 

12. Behind the panel blocking the diffuser section 

including a small amount sometimes found on the 

concrete pad outside of the test chamber. 

3.6.4.2 Debris Classifications 

Insulation debris consisted of pieces of bare fiberglass 

insulation of various sizes, pieces of shredded canvas, 

agglomerated pieces containing both insulation and 

canvas, and large sections of the canvas cover that 

remained relatively intact and sometimes contained 

substantial quantities of insulation. The bare insulation 

pieces were divided into 3 general size groups, i.e., large, 

medium, and small. Their characteristics are provided in 

Table 3-7. It was reasonably assumed that all of the NR 

debris was small debris since virtually all the large and 

medium debris was collectable. 

In the collection process, debris was bagged by seven 

classifications at each location. These seven 

classifications were: 

A. Canvassed insulation consisting of large sections of 

canvas covers encapsulating insulation (protected 

insulation). 

B. Insulation attached to Class A debris but extruding 

from the canvas (unprotected insulation). 

C. Large pieces of exposed insulation. 

D. Medium pieces of exposed insulation.

NUREG/CR-6369 3 -22
Integrated Effects

Table 3-7. Insulation debris sizes.

E. 

F. 

G.

Small pieces of exposed insulation. 

Pieces of shredded canvas without insulation. 

Agglomerated debris consisting of a tangled mix of 

canvas and insulation.

The target blankets during the production tests were 

generally completely or nearly completely destroyed by 

the air blast and the destruction was similar from one test 

to another. Usually one relatively large section of canvas 

was found on the floor near the target or hanging on the 

continuous grating and this section of canvas sometimes 

contained substantial insulation, up to 45% (Test H5) of 

the total. Other times this canvas section was empty. 

Insulation found inside of the canvas would be trapped by 

any grating and would then be expected to be protected 

from subsequent erosion by washdown flows in a BWR 

drywell. This insulation was classified as Class A upon 

collection. However, any insulation attached to this large 

section of canvas but hanging out of the canvas would not 

be protected from washdown erosion but would still be 

trapped by any grating. This insulation was collected 

separately and classified as Class B but as it turned out, 

there was very little Class B debris (< 3%). 

All debris transporting to the far end of the test chamber, 

i.e., exhaust screen, was small debris. The large pieces 

were stopped by the continuous (first) grating 

encountered. The medium sized debris making it through 

the continuous grating was usually stopped by the next 

grating encountered but none of the medium was found at 

the exhaust screen. Only a relatively small quantities of 

medium debris were generated and the quantities were not 

sufficient to evaluate debris capture fractions.

The debris collection process was rather thorough in order 

to anticipate any type of debris generated and its 

subsequent transport. However as it turned out, the debris 

transport in the CEESI tests was focused almost entirely 

upon the transport of small pieces of debris. 

Several photographs were taken of debris samples during 

the process of drying and weighing the collected debris. A 

typical piece of small debris might measure 3 inch in 

length and 1 inch in diameter and its density likely 

significantly reduced from its originally density. A 

sample of small debris is shown in Figure 3-14. 

Medium and large debris, as shown in Figure 3-15 and 3

16, respectively, generally had the appearance of intact 

insulation. The original insulation was formed in layers 

and these layers tended to separate during the destruction 

process. Large and medium debris tended to still show 

this layered structure. 

Figure 3-17 shows a sample of the agglomerated debris. 

This sample consisted mostly of a wad of canvas strings 

with small bits of entangled insulation. 

The large, medium, small, and agglomerate samples 

shown in Figure 3-14 through 3-17 are compared in 

Figure 3-18 so that their relative sizes can be put into 

prospective. The samples were, moving clockwise from 

the upper left comer, large, small, agglomerate, and 

medium. 

To help visualize the destructive process of the air blast, a 

sampling of canvas shreds is shown in Figure 3-19. The 

metal piece in the photo was the blankets identification 

tag.

NUREG/CR-6369

Debris Relative size Description 

classification 

Large > hand size Large pieces were too large to pass through a grating and therefore were 

all located either upstream of the continuous grating or behind the target 

mount. 

Medium > grating cell but < hand size Medium pieces sometimes were forced through a grating, although they 

were generally larger than a grating cell. 

Small < grating cell Small pieces would generally pass through a grating cell unless the piece 

was to inertially impact on a grating bar. Small debris included fine 

particles such as individual fibers that could also pass through the catch 

screen of the exhaust flow.

3-23
Integrated Effects

Figure 3-14. Sampling of small pieces of debris.

Figure 3-15. Sampling of medium pieces of debris.

NUREG/CR-6369 3-24
Integrated Effects

Figure 3-16. Sampling of large pieces of debris.

Figure 3-17. Sample of agglomerate debris.

3-25 NUREGICR-6369
Integrated Effects

Figure 3-18. Comparison of debris samples.

Figure 3-19. Sampling of shredded canvas debris.

NUREG/CR-6369 3-26
Integrated Effects

3.6.4.3 Photographic Data 

Upon reentering the test chamber following each test, the 

test engineer photographed features of the test for later 

analysis. These visual experimental results helped greatly 

in understanding and documenting the debris transport 

process. A sampling of the photos are presented here. 

Figure 3-20 shows the front side of the continuous grating 

following Test H6. The target in Test H6 was placed 

relatively close to the nozzle (L/D of 10) and the large 

section of blanket shown hanging from the continuous 

grating held about 42% of the total insulation. Also seen 

in this figure is a section of the PCV misting system 

(upper left) and the two vertical pipes located directly 

behind the continuous grating. 

The dominant debris deposition process was inertial 

deposition which is clearly shown in Figures 3-21 through 

3-23. In Figure 3-21, which shows a portion of the split 

grating following Test HIR, fine debris is seen captured 

somewhat uniformly on the front surfaces of the bars. 

Figure 3-22 shows a larger portion of the split grating 

following Test H2. Larger pieces of small debris looking 

somewhat like "cotton balls" are shown. All of this debris 

was small enough to pass through the grating, which this 

size of debris did when it did not impact the bars. Note 

that there is no medium or large debris present in these 

pictures. Figure 3-23 shows similar deposition on the V

grating. 

The deposition shown in the preceding three photos was 

deposition onto wet gratings. Test H7 was conducted dry 

to specifically illustrate the effect of wetness on debris 

capture. A portion of the split grating for Test H7 is 

shown in Figure 3-24. Only a few small "cotton ball 

sized" pieces were captured by the grating. Note the total 

lack of fines that were shown so clearly for deposition of a 

wet grating in the preceding photos. 

Dry surface behavior was also evident in Figure 3-20 that 

showed the continuous grating following Test H6. As it 

turned out, the misting system did not wet the continuous 

grating as planned, most likely because a slight draft in the 

test chamber after the diffuser cover was opened caused 

the mist to drift downrange from the target. However, a 

side benefit of the drifting mist was the wetting of the 

auxiliary chamber wall where the flow makes its 90' bend. 

A view within the auxiliary tank that includes the wall 

impacted by the bending flow is shown in Figure 3-25. As

shown in the figure, substantial small debris was inertially 

captured at the bend. Nearly all of the debris collection in 

the auxiliary tank, except for the debris on the exhaust 

screen, was found at the bend. 

Although surface wetness had a profound affect on the 

ability of a surface to capture debris, quantifying the 

wetness of the surfaces was not practical for these tests. 

The tests have clearly shown that wet surfaces tend to 

hold onto debris while dry surfaces do not. The tests also 

indicate that partial wetness, somewhere between wet and 

dry, will capture with an effectiveness somewhere 

between wet and dry capture effectiveness and this is 

demonstrated in results presented in Section 3-7. A brief 

attempt was made to photograph surface wetness to 

roughly quantify the wetness of these tests. The best of 

those photos is shown in Figure 3-26. The water film on a 

horizontal I-beam was compared to the thickness of a coin 

(quarter). This film appears to be about 0.5 mm. (500 

microns) thick. The film thickness on the vertical I-beam 

surfaces was obviously considerable thinner than on the 

horizontal surface. A general observation regarding 

surface wetness was that even a thin film, such as formed 

on the vertical surfaces of the grating bars, was sufficient 

to capture significant quantities of fine debris. 

A view of the auxiliary tank exhaust screen from the 

inside following Test HiR is shown in Figure 3-27. The 

pattern of debris deposits on the screen from filtering the 

exhaust air flow shows the debris preferentially deposited 

on the outer portion of the screen probably was the result 

of the flow structure after the flow made the 900 bend. 

The video cameras indicated a spiral type of motion down 

the auxiliary tank. 

A view of panel blocking of diffuser section behind nozzle 

following Test H7 is seen in Figure 3-28. The blocking 

panel was constructed of plywood with a narrow screen 

section in the middle. The photo shows some small debris 

that was filtered from air escaping the test chamber 

through the diffuser section. A small amount of air also 

escaped through the narrow gap between the panel and the 

test chamber walls resulting in a small quantity of debris 

behind the panel in some tests. 

3.6.4.4 Video Cameras 

Video footage was taken of each test by each of three 

video cameras. This footage was of limited value but 

some debris transport trends were observed. These trends 

are discussed here.

3-27 NUREG/CR-6369
Integrated Effects

Figure 3-20. Large section of canvas on continuous grating (Test H6).

Figure 3-21. Typical debris deposition on split grating (Test HIR).

NUREG/CR-6369 3-28
Integrated Effects

Figure 3-22. Typical debris deposition on split grating (Test H2).

Figure 3-23. Typical debris deposition on V-grating (Test H2).

3-29 NUREG/CR-6369,
Integrated Effects

Figure 3-24. Debris deposition on a dry split grating (Test H7).

Figure 3-25. Deposition in auxiliary tank at bend (TestH2).

NUREG/CR-6369 3-30
Integrated Effects

Figure 3-26. Water film on horizontal I-beam (Test HI).

Figure 3-27. View of exhaust screen in auxiliary tank (Test H1R).

3-31 NUREG/CR-6369
Integrated Effects

Figure 3-28. View of panel blocking of diffuser section behind nozzle (Test H7).

Video Camera 1 The first camera was mounted behind 

the jet nozzle facing downrange past the target to the 

structural test section. It was intended that this camera 

film the destruction off the target blanket but field of view 

so quickly filled with whirling debris that little could be 

seen. This camera observed very turbulent debris 

transport that showed some spiral flow behavior across its 

field of view. 

Video Camera 2 The second camera was mounted at the 

far end of the main test chamber facing uprange toward 

the structural test section. This camera filmed small 

debris after the debris passed through the split grating on 

its way to the auxiliary tank. The debris looked similar to 

large snowflakes coming at the windshield of a moving 

car. 

Video Camera 3 The third camera was mounted in the 

entrance end auxiliary test chamber facing the exhaust 

screen. This camera filmed the debris as it made the 90' 

bend turn upon entering the auxiliary tank. This debris 

was generally propelled towards the opposite auxiliary 

tank wall where the non-deposited debris tended to curl

upwards in the beginning of a spiral flow pattern as the 

debris was then propelled towards the exhaust screen. 

Prior to the onset of the jet flow, the mist from the PCV 

spray system could be seen drifting into the auxiliary tank 

where it wetted the opposite wall where deposition was 

observed. Note that a spray system was not installed in 

the auxiliary chamber. 

3.6.5 Drying and Weighing Debris 

The insulation and canvas debris collected following each 

test and was placed in plastic bags and labeled with the 

test identification, collection location, and debris 

classification. The processing of all this debris starting 

with verifying that bags had been properly classified. 

Most of the debris absorbed water from the surfaces or 

from the floors of the test chambers. 

The moisture levels of the debris ranged from dry to 

extremely wet and the debris had to be dried before 

weighing. A variety of methods were tried including

NUREG/CR-6369 3-32
Integrated Effects

wringing excess water from the debris, heating the debris 

in an oven, and simply spreading the debris out on 

tablesand allowing the moisture to evaporate. The oven 

worked best but it could only accommodate a small 

quantity of debris at a time. The best procedure seem to 

be to wring out the excess moisture, spread the debris and 

allow it dry in a heated room for a few days, and then 

finishing the process by placing debris that had not dried 

sufficiently in the oven. The debris was dried until any 

remaining moisture would not significantly impact the test 

results. 

Prior to weighing the debris, the canvas was separated 

from the insulation. The canvas for each test was weighed 

collectively rather than by location. Each bag of 

insulation was weighed separately and recorded. As a 

quality assurance measure, the debris for the entire test 

(contained in one large trash bag) was weighed and 

recorded, plastic bags included. Then, the weights of the 

individual bags were summed along with a reasonable 

estimate for the plastic bags and then compared to the 

total weight. The weighing process continued until all 

mass was accounted within an error margin of less than 

2%. 

The test results now consisted of tables of debris masses 

arranged by collection location and debris classification. 

These tables were then used to calculate debris transport 

and capture fractions which is the subject of Section 3-7. 

3.7 Debris Transport and Capture 

Test Results 

Debris transport and capture in these tests conducted at 

CEESI focused on the small debris which consisted of 

debris generally smaller than the cell size of a grating (see 

Section 3.6.4.2 for debris size classifications). Relatively 

intact sections of blanket, large sections of canvas, and 

large pieces of insulation were always stopped by the first 

grating encountered. Although a substantial fraction of 

the medium debris, which was generally larger than a 

grating cell size, was forced through the first grating 

encountered and then stopped by a subsequent grating, 

there was not enough of the medium debris generated to 

justify calculating debris transport data. All debris found 

at the exhaust screen was small debris. Therefore, this 

section focused on small debris transport. 

Small debris was found to readily transport at the CEESI 

test flow velocities which were designed to be 

prototypical of the bulk of the BWR drywell following a

MSLB. Significant gravitational settling was not 

observed, i.e., flow turbulence kept debris churning until 

completion of the air blast, even in the more quiescent 

places such as end space in the auxiliary tank (opposite 

the exhaust end). The dominant debris capture 

mechanism was clearly inertial deposition which was 

strongly influenced by surface wetness. 

Debris transport fractions and debris capture fractions 

were computed from the collected debris weight tables. 

3.7.1 Definitions of Debris Transport and 

Capture Fractions 

The transport fraction as applied to the CEESI tests 

defined the fraction of debris entering the congested 

structural test section that subsequently transported to the 

exhaust screen at the end of the auxiliary test chamber. 

Note the structural test section was design to simulate the 

structural congestion of a portion of a BWR drywell. The 

transport fractions presented herein were calculated using 

the following equations. 

F, Mlscreen +Mhat 

M(3-1)

where 

F1

the transport fraction 

the mass deposited on the exhaust screen of the 

auxiliary tank 

Mexhaust 

the mass passing through the exhaust to the outside 

Mcont 

the mass approaching the continuous grating

(3-2) M str 

M~str + M bypass

NUREG/CR-6369 3-33
Integrated Effects

where

F• 

M.st Mbypa

= the capture fraction 

= the mass deposited on the structure 

= the mass passing by or through the 

structure.

Debris transport and capture fractions presented herein 

were plotted as a function of debris loading. Debris 

loading as used herein is defined as the total time

integrated one-dimensional mass flux of debris 

approaching a particular structure. This included both 

debris captured by that structure as well as debris 

bypassing that structure. The units used herein are Ibm 

per 100 f

2 of test chamber cross sectional area. 

3.7.2 Data Reduction Procedure 

Starting with the tables of debris masses correlated by 

collection location and debris classification, the debris 

transport and capture fractions were calculated using the 

following data reduction procedure 

"* The initial mass of the canvas cover was estimated and 

subtracted from the initial weight of the blanket 

(blankets was weighed prior to testing) to obtain an 

estimate of the initial insulation mass. 

"* Total mass of non-recovered debris was calculated as 

the difference between initial insulation mass and the 

total mass of debris recovered. 

"* A best estimate distribution for the final location of the 

non-recovered mass was estimated (see next section). 

"• The estimate of non-recovered mass was added to the 

recovered mass to obtain a complete mass balance. 

"* The transport and capture fractions were calculated per 

the above equations. 

The error analysis, discussed in Section 3.7.4, shows that 

the distribution of the non-recovered mass dominated the 

overall experimental error. The distribution of the non

recovered then became the corner stone of the error 

analysis. 

The computations were programmed into an EXCEL 

spreadsheet to facilitate the data reduction procedure. 

3.7.3 Estimate of Non-Recovered Mass 

Distribution 

A distribution showing where the non-recovered debris 

mass was likely to have been was estimated based on the 

observations of the test engineer. These observations

"* All non-recovered mass safely assumed to be small 

debris. 

"* Substantial debris was lost from test chambers - Substantial amount of fine debris seen passing 

through auxiliary tank exhaust screen 

(documented in video footage). 

- Substantial amount of fine debris seen passing 

through auxiliary tank exhaust screen 

(documented in video footage). - Small quantities of debris collected in diffuser 

section and behind blockage panel and some 

even collected on concrete pad outside diffuser 

nozzle entrance. - Test chambers had a number of small orifices 

such as the floor drain holes where some 

debris could have been lost. - In Test H7, a cover plate blocking a man hole 

on top of the auxiliary tank was blown off 

allowing considerable debris to be blown out. 

* Substantial debris was deposited within the test 

chamber but was not collected, primarily because it 

was too small. 

Post-test washdown of the test chambers showed 

accumulation of fines in the washdown flows. 

Considerably more of the washdown fines were found in 

the main tank than in the auxiliary tank. 

Washdown fines in the main tank were found 

predominantly near the structural assemblies. 

Washdown fines in the auxiliary chamber were found 

predominantly near the exhaust screen. 

These general observations were compiled using the logic 

chart shown in Figure 3-29 to form a plausible best 

estimate distribution of where the non-recovered mass 

resided. The first decision in the logic chart was the 

fraction of the non-recovered mass that was retained 

within the test chambers. Observation suggested that half 

or a little more than half remained in the chambers. The 

best estimate engineering judgment was that 60% 

remained within the chambers leaving 40% to be expelled. 

Of the expelled debris, 20% was judged to leave through 

the blocked off diffuser section behind the nozzle. An 

estimate of flow resistances suggested that only about 5% 

of the air flow went in this direction but this air would

NUREG/CR-6369

included:

3-34
Integrated Effects

have had a higher density of debris since it was closer to 

the target. Therefore, 20% was deemed a reasonable 

estimate. The next logic question in the chart was how 

much of the non-recoverable mass was deposited in the 

main chamber. Observations suggested that the dominant 

amount was in the main chamber and the engineering 

judgment was 75% in the main chamber leaving 25% for 

the auxiliary tank. 

Most of the debris mass in the washdown flow was found 

near the structural test section and likely consisted of fine 

debris actually captured by the structures but too fine to 

collect. Sixty percent of this debris was distributed among 

the structural components based on their relative 

efficiency of capturing debris and the other 40% was 

applied to the chamber itself with half placed before the 

test section and half after the test section. In the auxiliary 

tank, more of the washdown debris was found near the 

exhaust screen, therefore, based on engineering judgment 

it was assumed that two-thirds of the debris was fine 

debris washed off of the screen. 

These engineering judgments resulted in the plausible best 

estimate shown at the right in Figure 3-29. It was 

recognized that this process was not very exact but it 

provided a reasonable method of proceeding. Best 

estimate debris transport fractions and capture fractions 

could then be calculated. The uncertainty of the method 

provided the basis for the error analysis which put error 

bars on the reported data herein. 

3.7.4 Estimate of Canvas Cover Weight 

Each insulation blanket was weighed prior to mounting 

the blanket in the test chamber. Because the insulation 

was sewn into the canvas cover, it was not possible to 

weight just the insulation. Therefore, the weight of the 

canvas cover including its attaching hooks, bands, and 

name tag had to be estimated. The blanket manufactures, 

Transco, were consulted and they indicated that weight 

would vary slightly from blanket to blanket but that the 

weight was likely a few ounces over 5 lbm for each 

blanket. Upon destruction by the air blast, some lost of 

canvas mass in the form of fine debris was expected. The 

total weight of canvas debris recovered after each test 

approached 5 Ibm. Subsequently, a nominal weight of 5 

Ibm was assumed for the total weight of the canvas cover 

including its attachments for each test. Any data

reduction error introduced into the results from using this 

assumption was deemed minimal. Note that 

approximately 37% of the total blanket weight was in the 

canvas cover. 

3.7.5 Error Analysis 

The error analysis consisted of identifying the sources of 

error associated with conducting the CEESI tests, 

determining which sources dominated the experimental 

error, and then quantifying the dominant sources. 

3.7.5.1 Source of Experimental Error 

The sources of experimental error, i.e., means by which an 

error could have been introduced into the experimental 

data, can be grouped into three categories. These 

categories are the conditions of the tests, the collection of 

the insulation debris, and the post-test processing of the 

debris. 

3.7.5.1.1 Test Conditions 

Any departure from specified test conditions had the 

potential of affecting the results of the experiment. 

Departures from specified test conditions noted during the 

experiment included: 

"* Non-uniformity in the insulation blankets, "• Uniformity in surface wetness, 

"* Integrity of the test chamber, and 

"* Air temperature. 

The destruction of the target blanket likely varied 

somewhat from blanket to blanket. For example, the 

blanket in Test HIR was completely destroyed in that no 

insulation remained within the canvas cover, whereas in 

Test HI about 22% of the insulation remained in a large 

section of the canvas. Test HIR was intended to repeat 

Test Hi, i.e., identical test specifications. Minor 

variations existed in the construction of the blankets, as 

evidenced by the variation in their weights which ranged 

from 13 to 14 lbm (13.5 " 4%). The impact of blanket 

non-uniformity was a variation in the quantity of debris 

generated and as will be demonstrated in the presentation 

of the results did not significantly affect the debris 

transport and capture fractions.

NUREG/CR-6369 3-35
Integrated Effects

Figure 3-29. Distribution of non-recovered insulation mass.

Since surface wetness had a dominant influence on the 

ability of a structure to hold onto captured debris, non

uniformity in surface wetness was expected to affect the 

debris capture results. Two methods of wetting the 

structures was tested during the developmental tests, i.e., 

spraying the structures with a water hose prior to initiating 

the test and misting the structures for about 10 minutes 

prior to and during the test. The hose spraying method 

was rejected because the water tended to drain from the 

structures letting the surfaces dry before tests could be 

conducted leaving the surface only partial wet. The mist 

from the misting system, used during the production tests, 

was found to drift downrange leaving the continuous 

grating (first grating) relatively dry. Further, the misting 

time varied from test to test because the time required to 

setup and conduct the air burst varied. The tests show that 

surface wetness tends to reach an asymptote where

additional wetness does not increase the effectiveness of 

the structure to capture debris. The major impact of these 

variations in surface wetness was 1) the continuous 

grating behaved like a dry structure and two of the 

developmental tests shows capture results somewhere 

between wet and dry behavior. It is likely that some 

variation in the capture results can be attributed to 

variation in surface wetness. 

The integrity of the test chamber was compromised in one 

test, Test H7, when a hatch cover was blown out causing a 

substantial loss of insulation debris. Since Test H7 was 

conducted dry, considerably more debris collected on the 

exhaust screen at the end of the auxiliary tank than 

collected during the other tests. This greater mass of 

debris caused a larger back pressure in the auxiliary tank 

which over pressurized the hatch. This problem, of

NUREG/CR-6369

Non-Recovered Debris Retained First Second Path Fraction 

Distribution Distribution 

Best Estimate 

Vessel Before 1 0.090 

0.20 

Continuous Grating 2 0.000 

0.00 

Beams 0.045 

Main Vessel 0.10 

0.75 V-Grating 0.090 

0.20 

Split Grating 0.135 

In-Vessel 0.30 

0.60 Vessel After 6 0.090 

0.20 

Total Screen 0.100 

1.00 Auxili Vessel 0.67 

Bend 8 0.050 

Downstream 9 0.320 

Expelled 0.80 

0.40 Upstream 10 0.080 

0.20

3-36
Integrated Effects

course, only affected Test H7 and did so by increasing the 

uncertainty in its capture fractions. 

The test chamber were preheated with propane heaters to 

about 70 'F prior to conducting each test. However, due 

to sometimes extreme winter conditions, the chamber air 

temperatures could not be controlled with a high degree 

accuracy. The primary concern was to prevent freezing of 

water sprayed onto the structures which would certainly 

have invalidated the data. Freezing was definitely 

prevented and the fluctuations in air temperature that did 

occur were not expected to significantly affect the quality 

of the data. 

3.7.5.1.2 Debris Collection 

Incomplete or inaccurate collection of the insulation 

debris was a primary source of experimental error in the 

CEESI tests. Insulation debris was widely dispersed 

throughout the test chambers from one end to the other. 

Collection problems included: 

• Debris lost from the test chambers, 

* Debris relocation prior to collection, 

"* Incomplete debris collection within the test chambers, 

and 

"* Bagging errors. 

Substantial debris was lost from the test chambers through 

the exhaust screens in the form of very fine debris and this 

debris certainly could not be retrieved once blown out into 

the open environment beyond the screens. This fine 

particle debris, as observed and recorded with a video 

camera, appeared as an opaque brown cloud extending 10 

to 20 ft from the exhaust screen and lasting several 

seconds. 

Captured debris may have relocated following a test 

before it could be collected. In particular, debris could 

have fallen off of a structure where it was captured so that 

it was collected as floor debris which of course would 

reduce the resulting capture fraction for that structure. 

Personnel were instructed to exercise all care practical to 

not facilitate relocation of debris and it is believed that 

little actual relocation occurred. 

It was not feasible to collect all of the really fine debris 

such as the individual fibers that was found coating wet 

surfaces. Even the task of collecting all of the smaller 

pieces was a formidable one. Visual observations during 

the post-test washdown of the test chamber indicated that

a substantial amount of fine debris was deposited on the 

interior surfaces. 

The possibility that a bag of debris was mislabeled was 

minimized by checking the inventory during post-test 

processing with the inventory taken immediately 

following the test and further checking the inventory with 

known locations where debris should have been taken. 

Further, the contents of the bags were check to ensure that 

the debris was categorized correctly. Experimental error 

of this type was minimized. 

3.7.5.1.3 Post-Test Processing of Debris 

Following completion of the tests, the debris was dried 

and weighted by location and classification. Possible post

test debris processing errors included: 

"* Incomplete separation of canvas and insulation, "* Incomplete drying of the debris, and 

"• Inaccurate weighing. 

Insulation debris and canvas debris were usually 

intermixed and intertwined. While large pieces of canvas 

debris were easily separated from the insulation, much of 

the canvas debris consisted of individual threads of canvas 

and it was not practical to separate all the threads from the 

insulation. Conversely, canvas pieces usually had small 

bits of insulation adhering to them. Incomplete separate 

of debris was not deemed to have a significant impact on 

the transport results. 

Any moisture left in the debris upon weighing, minor 

dampness, would introduce error into the test results. The 

drying process was continued until any remaining 

moisture was deemed unimportant. 

Debris weighing errors were minimized by performing a 

mass balance, i.e., the weight of all of the debris from one 

test was compared to the total of the weights of individual 

bags (including the plastic bags). This process continued 

until these two weights were within 2% (usually less) of 

each other. Therefore, errors associated with debris 

weighing were not considered to be a primary source of 

experimental error. 

3.7.5.2 Bounding Experimental Error 

Debris collection errors were found to dominate over the 

post-test processing errors. Variations in test conditions 

were not amenable to bounding the magnitude of the error 

but were reflected in the data scatter. The post-test

3-37 NUREG/CR-6369
Integrated Effects

processing errors were estimated to be on the order of 1 to 

2%. Thus, the mass of debris not recovered during the 

debris collection process dominated the overall errors 

(order of 15 to 25%) associated with the experimental 

results. Therefore, the error analysis focused on the non

recovered mass. 

The method described in Section 3.7.3 was used to bound 

the experimental error associated with the non-recovered 

mass. The logic chart illustrating this method, shown in 

Figure 3-29, was also employed in the error analysis. 

The dominant uncertainty in the non-recoverable mass 

distribution logic chart was the fraction of non-recovered 

mass lost from the test chambers. The more non

recovered mass that was lost through the exhaust screen at 

the end of the auxiliary tank, the smaller would be the 

calculated debris capture fractions. Conversely, the more 

mass retained within the test chambers, particularly if the 

mass was on the structures, then the larger the calculated 

capture fractions. 

Using the logic chart and taking the fraction of debris 

expelled from one extreme to the other extreme (all or 

nothing) would certainly bound the error associated with 

the non-recovered mass. However, the extreme conditions 

of zero and one were deemed excessive because 

substantial mass was known to be expelled and substantial 

mass was known to be retained. The error bounds shown 

in the result plots in the next section were determined by 

assuming first that 90% of the non-recovered mass was 

lost from the system to obtain one bound and then 

assuming 10% to get the other bound. These bound are 

likely overly conservative in estimating the errors 

associated with the non-recovered mass and therefore 

should reasonably compensate for not considering all of 

the other smaller sources of error. 

The error bounds were expanded for two tests where 

special debris collection problems were encountered. In 

Test H7, as previously noted, a hatch cover was blown off 

thereby greatly increasing the lost of debris mass from the 

test chamber (approximately 53% of the total insulation 

mass). For Test H7, the logic chart was modified to add 

an addition path for debris to leave the test chambers and 

it was assumed that 70% of the expelled mass left through 

the blown hatch. 

During post-test processing of Test L 1, it was apparent 

that all of the debris from the preceding test, Test H6, had 

not been collected because the total quantity of Test Li 

debris exceeded its initial insulation mass. The data from 

Test LI was salvaged by comparing its masses with those 

of other tests to determine likely locations containing

extra mass, and then adjusting the mass table accordingly 

to obtain best estimate results. Engineering judgment was 

used to expand the error bounds for Test Li sufficiently to 

ensure that the bounds enclosed the true experimental 

result. The end result was larger error bounds for Tests 

H6 and Li. 

3.7.6 Test Results 

Generated debris was classified in three size groups, 

small, medium, and large. Only the small debris was 

amenable to the development of debris capture fractions 

and therefore will be discussed first. The medium and 

large sized debris are then briefly discussed. 

3.7.6.1 Transport of Small Sized Debris 

Small insulation debris consisted of insulation smaller 

than the approximate size of a typical grating cell. This 

debris included fine particles such as individual fibers but 

did not include small pieces of insulation attached to 

canvas that effectively transported as medium or large 

debris. The small debris test results for the CEESI debris 

transport tests are shown in the following series of figures. 

Overall Transport in CEESI Facility The overall transport 

of debris in the CEESI test chamber is shown in Figure 3

30 as the fraction of the small debris entering the 

structural test section at the continuous grating that 

subsequently transported through the structural test 

section into the auxiliary tank and onto the exhaust screen. 

These transport fractions are shown as a function of the 

debris loading entering the structural test section, i.e., the 

time-integrated mass flux of debris impacting the 

continuous grating in units of Ibm per 100 ft2 of chamber 

cross-sectional area (the cross-sectional area of the 

chambers was 69.6 ft2). 

A transport fraction is shown in Figure 3-30 for each of 

the tests where significant debris was generated. Tests 

using the 4 inch nozzle are shown with a circular point 

and those with using the 3 inch nozzle with a square point. 

Tests where the structural surfaces were wet are shown as 

solid points, whereas dry and only partially wet tests are 

shown as non-solid points. The points are shown with the 

error bounds discussed above indicated as error bars. 

Since Test H7 was conducted dry, its transport fraction 

was nearly one (shown in the upper right hand comer). 

Tests 13 and W4, shown as the two non-solid circles in the 

upper left comer, were conducted with the structures only 

partially wet because these tests were wet using the water 

hose method which proved inadequate. The

NUREG/CR-6369 3-38
Inegrated Effects

I I I I I I I

I -

Debris Deposited Behind Target (10-15%) 

Not Considered in Transport Fraction )

0

)

F

4T

0

- OVERALL TRANSPORT

a

I I I I

4 6 8 10

Debris Loading Entering Structures (lb/lO0 ft2) 

Figure 3-30. Overall transport of small debris through test facility.

NUREG/CR-6369

100 

90 

80

0 CEESI(4 in) - Wet 

0 CEESI(4 in) - Dry/Partial Wet 

I CEESI(3 in) - Wet 

Mean for CEESI Wet . Tests

(

70 

60 

50 

40 

30

0 

la- cri 

IU,

20 

10 

0

0 2

I

(

I I i II I

3-39

. .. O.. .. .. .. ..
Integrated Effects

developmental tests, shown as the four left most data 

points had lower debris loadings because the target 

blankets were not adequately restrained to maximize 

debris generation. The effect of surface wetting on debris 

transport is clearly shown in Figure 3-30, i.e., wet 

structures capture debris while dry do not and partially 

wet surfaces perform somewhere in between wet and dry 

behavior. The mean value of all the wet tests was 33%. 

Note that the transport does not appear to be a function of 

the debris loading, at least for the loading ranges studied. 

The error margins tended to be smaller for the tests with 

higher debris loadings because there was more debris 

mass generated and the fraction of debris not recovered 

tended to be lower. 

I-Beam and Pipe Structures The fraction of debris 

captured while passing through the I-beam and pipe 

assemblies is shown in Figure 3-31 as a function of the 

debris entering these assemblies. The mean value for the 

wet tests was 9.3%. The CEESI results for debris capture 

by I-beams and pipes were compared to the results from 

the ARL separate effects tests. Adjusted test data for 

eight ARL separate effects tests are also shown in Figure 

3-31. The ARL data applicable to this comparison was 

reproduced in Table 3-8. 

The ARL data was adjusted because the ARL capture 

fractions applied to individual beams or pipes, whereas, 

the CEESI capture fractions applied to the combines 

structural assemblies. The cross-section areas of the 

beams and pipes, as viewed by the approaching debris, 

expressed in the fraction of the test chamber cross

sectional area were approximately 50% for the I-beams 

and 20% for the pipes. 

Little debris was observed captured on the pipes in CEESI 

and the ARL capture fraction for a 12 inch pipe (note that 

CEESI pipes were 10 inch in diameter) in a 50 ft/sec air 

flow was only 4%. With 20% of the test chamber cross

sectional areas obstructed by pipes which capture 4% of 

debris traveling within this 20% area, then only about 1% 

(0.2 X 0.04 = 0.008) of the debris passing through the 

structural test section would be expected to be captured by 

the pipes. 

Since the I-beams obstructed 50% of the test chamber 

area, the ARL capture fraction for I-beams was adapted to 

CEESI by simply dividing the ARL number by 2. The 

total expected capture fraction for the combined CEESI 

structural test section based on the ARL data was one-half 

the ARL number for I-beams plus 1% to account for 

pipes. The ARL capture fractions adapted to the CEESI

structures are shown in Table 3-9 as well as being plotted 

in Figure 3-31. 

The ARL data in Figure 3-31 was focused at one 

relatively light debris loading at about 1.4 Ibm/100ft2 

which was an artifact of the limitations of that experiment. 

Thus, this figure clearly demonstrates one of the primary 

objectives of the CEESI tests, i.e., to obtains debris 

capture data at higher debris loadings more prototypical of 

accident conditions postulated for a BWR drywell. 

Postulated BWR debris loadings could extend to even 

higher levels than the CEESI experiment. The quantities 

of debris under study in NUREG/CR-6224 peaked at 

about 111 ft3

, which would correspond to a CEESI debris 

loading of about 11 lbm/1n00ft2 if uniformly distributed 

over a 2500 ft2 drywell grating. Therefore, the CEESI 

debris loading agreed well with the debris generation 

quantities understudy in NUREG/CR-6224. Research 

performed after the NUREG/CR-6224 study by the BWR 

Owners Group contains much more conservative debris 

generation quantities which could result in debris loadings 

several times the maximum loading generated in the 

CEESI tests. Although the I-beam capture fractions 

shown in Figure 3-31 do not indicate a dependency upon 

debris loading, care should be taken in extrapolating 

beyond the CEESI debris loadings. 

In Figure 3-31, the range in the ARL capture fractions 

generally encompasses the CEESI data. The variation in 

the ARL capture fractions was due primarily to variations 

in wetting (10 or 30 seconds of sprays) and debris size 

(either 2-to-4 or 2-to-6). Larger debris captured better 

than small debris and wetter surfaces captured better than 

dryer surfaces. The wetness was not quantified in either 

experiment but was deemed based on visual observation 

to be generally comparable. The CEESI debris size 

distribution from the air blast destruction of a blanket was 

generally broader than the ARL debris which was 

artificially created. All in all, the capture results for the 

two experiments are in good agreement. 

Gratings The fractions of debris captured while passing 

through a grating are shown in Figures 3-32 and 3-33 for 

the V-grating and the split grating, respectively. The 

debris loadings in these figures are the mass flux of debris 

impacting that particular structure. The mean values for 

the wet tests were 28% and 24%, respectively. The results 

for the two gratings are very similar in terms of their 

debris capture per unit surface area as shown in the 

figures. The V-grating, however, only obstructed 57% of 

the entire cross-section of the test chamber which was 

factored into Figure 3-32.

NUREG/CR-6369 3-40
Integrated Effects

I I

I-BEAMS AND PIPES

ARL Capture Data 

Projected Area of 

Projected Area of

Adapted to CEESI Geometry 

I-Beams Was 50% of Total Area. 

Pipes Was 20% of Total Area.

L.I I

2 4 6 8

Debris Loading (Ibm/100 ft2) 

Figure 3-31. Capture of small debris by I-beams and pipes.

NUREG/CR-6369

100 

90 

80 

70

* CEESI(4 in) - Wet 

0 CEESI(4 in) - Dry/Partial Wet 

N CEESI(3 in) - Wet 

A ARL - I-Beams 

......... Mean for CEESI Wet Tests

U, 

0 

L_ 

,--

60 

50 

40 

30 

20 

10 

0

0 10

3-41
Integrated Effects

Table 3-8. Comparable ARL I-beam and pipe debris capture data.

Table 3-9. Modified ARL I-beam/pipe debris capture data. 

Test Indiviual I-beam Capture fraction 

ID capture fraction modified to CEESI 

geometry 

___(%) (%) 

8 23 12 

9 31 16 

14 11 6 

16 24 13 

17 20 11 

18 29 15 

21 10 6 

22 19 10

NUREG/CR-6369

Test ID Prewet Flow Debris size Debris loading ARL capture 

time velocity on structure fraction 

(sec) (ft/sec) (lbm/100fte) (%) 

Pipes (12 inch) 

3 10 50 2 to 4 1.38 4 

19 10 25 2 to 4 1.38 5 

I-beams (10 inch) 

8 10 50 2 to 4 1.38 23 

9 30 50 2 to 4 1.38 31 

12* 10 50 2 to 4 1.35 11 

16* 10 50 2 to 4 1.35 24 

17* 30 50 2 to 4 1.34 20 

18* 30 50 2 to 4 1.35 29 

21 10 25 2 to 4 1.38 10 

22* 30 50 2 to 4 1.35 19 

*I-beamr in a combination arrangement

3-42
Integrated Effects

I 100 I

90 

80 

70

a

S...L.....

,A

A

2 4 6 8

Debris Loading (Ibm/100 ff2) 

Figure 3-32. Capture of small debris by V-grating. 

3-43

NUREG/CR-6369

* CEESI(4 in) - Wet 

V-GRATING 0 CEESI(4 in) - Dry/i 

E CEESI(3 in) - Wet 

A ARL - Wet 

16 ARL - Dry 

......... Mean for CEESI WE 

Capture Data Adjusted for Projected Area 

V-Grating Projected Area Was 57% of Total Area.

I I I I

-QU,

Partial Wet 

f Tests

60 

50 

40 

30 

20 

10 

0

0

I' I I L I I I %IJ

10

I ...... t ......... t .....................

I | | | i i
Integrated Effects 

100 

90 

80 

70

0~ 

-o 

U,

60 

50 

40 

30 

9n

10 

0

SPLIT GRATING

.. .... ... -A

0 2

Debris Loading (Ibm/100 ft2) 

Figure 3-33. Capture of small debris by split grating.

NUREG/CR-6369

I I III 

0 CEESI(4 in) - Wet 

o CEESI(4 in) - Dry/Partial Wet 

0 CEESI(3 in) - Wet 

A ARL - Wet 

Ax ARL -Dry 

......... Mean for CEESI Wet Tests

I

A

4 6

'I

8 10

, I IIII -

I I

II | | |

3 -44

S. .. .. .... .. .......
Integrated Effects

Again, the CEESI test data was compared with applicable 

ARL separate effects test data, as shown in Figures 3-32 

and 3-33. The ARL data applicable to this comparison 

was reproduced in Table 3-10. While certainly 

comparable, the ARL data tended to be somewhat lower 

than the CEESI data. The highest ARL capture fraction of 

27% was for a test with larger debris (2-to-6) and with the 

longer 30 second wetting time. One significant difference 

between the CEESI and ARL debris was that the CEESI 

debris included a considerable mount of fine particles, 

whereas the ARL debris did not. The importance of 

capture of these fine particles by gratings is clearly shown 

in Figure 3-21, which shows a consistent layer of fine 

debris on the front surfaces of the grating. The relatively 

effective capture of this fine debris in the CEESI tests was 

likely responsible for the somewhat higher capture 

fractions seen in the CEESI tests. 

The first grating that the debris encountered was the 

grating referred to as the continuous grating. It was 

intended that this grating provide debris capture data at a 

relatively higher debris loading since it was the first 

grating encountered. However, as it turned out, this 

grating remained dry or nearly dry due to an air draft 

moving downrange that caused the water mist to bypass 

wetting the continuous grating. Therefore, little debris 

was actually captured by the continuous grating. The 

debris capture results for this grating, shown in Figure 3

34, are presented to further show the contrast between 

debris capture by a wet grating (V-grating or split grating) 

and a dry grating. In Figure 3-34, virtually no small 

debris was captured on the continuous grating in many of 

the tests. These data points are shown as non-solid circles 

at the bottom of the plot. Other tests showed a small 

amount of small debris capture but substantially less than 

found on the V and split gratings. This was likely due to 

some moisture on the continuous grating but much less 

than complete wetness. Note the complete lack of fine 

debris capture in Figure 3-20. 

Bends in the Flow Path When the blast air flow entered 

the auxiliary test chamber from the main chamber, the 

flow had to make a 90' bend where the chamber wall had 

been wetted by mist drifting with the slight air draft 

through the chambers. A substantial amount of debris was 

deposited at this bend and this deposition expressed as a 

capture fraction is shown in Figure 3-35 as a function of 

the debris passing through the collar to the auxiliary 

chamber in term of mass flux based on the cross-sectional 

area of the chambers, not the collar. The mean value for 

the wet tests was 17%. Note that the cross-sectional area 

of the collar was about 60% of the main chamber area and

that the mean capture fraction based on the collar cross

sectional area would be about 28%. 

Test Repeatability One measure of the quality of any 

experimental result is whether or not the test result could 

be repeated. As it turned out, four of the CEESI tests 

were very similar. Test HiR was intended to be a repeat 

of Test Hi. The test conditions for these tests are 

repeated in Table 3-11. The blankets in Tests HiR, H2, 

and H3 were considered completely destroyed, i.e., 100% 

of insulation turned into debris. Test HI was considered 

about 78% destroyed since 22% of its insulation remained 

within the canvas cover. The transport and capture of 

small debris for these four tests are compared in Figure 3

36. The data clearly illustrates test repeatability. 

3.7.6.2 Transport of Large and Medium Sized Debris 

The majority of the debris generated in the CEESI tests 

(not including insulation still encased in canvas) was 

classified as small debris, however, each test had some 

large and medium sized debris. Typically, a few percent 

of the insulation was classified as large debris and a few 

percent as medium debris. Some general statements can 

be made regarding the transport of large and medium 

debris but there was not sufficient quantities of the debris 

to determine capture fractions for the structures. 

The large debris (i.e., debris somewhat loosely sized as 

larger than a hand) was found stopped by the first grating 

encountered. No large debris was found beyond the 

continuous grating in any of the tests implying a grating 

capture fraction of one. The large debris was all 

contained in the section of the main chamber bounded by 

the panel blocking off the diffuser section behind the jet 

nozzle and the continuous grating. Within this space, the 

large debris generally churned with the highly turbulent 

flows until the air blast ceased. Following the air blast, 

the large debris was recovered from both in front of the jet 

and behind the jet with no clear preference as to which 

way. In Test HiR, for example, 94% of the large debris 

was found behind the jet but in Test H2, 93% was found 

in from of the jet. In conclusion, the large debris 

appeared to easily transport with the depressurization 

flows and relatively thoroughly mix due to the turbulence 

but was readily contained by a grating. 

Some medium debris (i.e., debris somewhat loosely sized 

as smaller than a hand but larger than the cell of a grating) 

was forced through the cells of the continuous grating, 

however, there was not a statistically sufficient quantity of

3-45 NUREG/CR-6369
Integrated Effects

Table 3-10. Comparable ARL capture data for gratings. 

Test LD* Prewet Flow Debris Debris ARL 

time velocity size loading on capture 

structure fracture 

(sec) (ft/sec) _bm/100ft 2

) (%) 

4 10 50 2to4 1.13 15 

5 10 50 2 to 4 1.20 17 

12 10 50 2 to 4 1.38 16 

13 30 50 2 to 4 1.38 27 

23-1 10 50 2 to 4 1.38 17 

23-2 1.14 13 

24-1 10 50 2 to 4 2.76 19 

24-2 2.23 13 

26-1 Dry 50 2 to 4 1.38 9 

26-2 1.25 6 

*Tests 23, 24, and 226 each had two gratings.

NUREG/CR-6369 3-46
Integrated Effects

Integrated Effects

I I I I I I

CONTINUOUS GRATING

100 

90 

80 

70

Note: Wetness on this Grating Uncertain 

in CEESI Tests. Data Strongly Indicates 

Dry or Only Slightly Moist Surfaces

A

A

0 . N

N

60 

50 

40 

30 

20 

10 

0

2 4 6

Debris Loading (Ibm/100 ft2) 

Figure 3-34. Capture of small debris by continuous grating

NUREG/CR-6369

0 CEESI(4 in) - Partial Wet 

o CEESI(4 in) - Dry 

N CEESI(3 in) - Partial Wet 

A ARL - Wet 

A ARL - Dry

CL 

0~ 

C.V) 

LSp 0 I I I• I -- 1 E- I

A

0 8 10

I

I | i A 0

3 -47
Integrated Effects

100 

90 

80 

70

I I 

AUXILIARY 

TANK BEND 

* .*{

2

.........

4 6 8

Debris Loading (Ibm/100 ft2) 

Figure 3-35. Capture of small debris by auxiliary tank bend.

NUREG/CR-6369

T

I I I I | 

* CEESI(4 in) - Wet 

o CEESI(4 in) - Dry/Partial Wet 

E CEESI(3 in) - Wet 

......... Mean for CEESI Wet Tests

a,> 

=1

C--) 

L.. 

-Q 

aJ

60 

50 

40 

30 

20 

10 

0

0 10

V E

i XL a

i

I I I I a ;K" ,

3-48
Integrated Effects

Capture and Transport of Small Debris

50.00% 

40.00% 

30.00% 

20.00% 

10.00% 

0.00%

Continuous Structural 

Grating Asserrblies

V-Grating Split Grating Auxiliary Tank 

Bend

Figure 3-36. Demonstration of CEESI test repeatability. 

Table 3-11. Test Matrix for the repeatability tests. 

Test Nozzle Air jet Structure Target position 

diameter duration wetness 

No ID Distance L/D 

(inch) (sec) (inch) 

1 H1 4 13 Wet 120 30 

2 HIR 4 13 Wet 120 30 

3 H2 4 15 Wet 120 30 

4 H3 4 14 Wet 80 20

NUREG/CR-6369.

Overall 

Transport

3-49
Integrated Effects

the medium debris. The total quantity of debris generated 

was only a few tenths of a pound. When capture fractions 

were calculated using the method employed for the small 

debris, the capture fraction for the continuous grating 

varied from zero to 50% and for subsequent gratings, the 

capture fraction varied from near zero to 100%. In 

general, medium sized pieces of debris forced through the 

first grating were stopped by the second grating 

encountered. I-beams and pipes did not appear to capture 

any medium sized debris. No medium debris transported 

to the exhaust screen and in only one test, Test H7 

conducted dry, was any medium debris collected in the 

auxiliary tank. Therefore, there was no data produced 

regarding the capture of medium debris at a bend in the 

flow. In conclusion, medium debris mixes well in flow 

turbulence and readily transport in open spaces, but will 

be heavily captured by gratings. 

3.8 References 

3-1 "Parametric Study of the Potential for BWR ECCS 

Strainer Blockage Due to LOCA Generated 

Debris," G. Zigler, J. Brideau, D. V. Rao, C. 

Shaffer, F. Souto, and W. Thomas, NUREG/CR

6224 Science and Engineering Associates, Inc., 

SEA93-554-06-A:1, October 1995. 

3-2 "Potential Plugging of Emergency Core Cooling 

Suction Strainers by Debris in Boiling Water 

Reactors," NRC Bulletin 96-03. 

3-3. "Water Sources for Long-Term Recirculation 

Cooling Following a Loss-of-Coolant-Accident," 

Regulatory Guide 1.82, Revision 2 May 1996. 

3-4. "BWR Drywell Debris Transport Phenomena 

Identification and Ranking Tables (PIRT)," Gary 

E. Wilson, Brent Boyack, Mark Leonard, Ken 

Williams, and Lothar Wolf, Letter Report to 

USNRC, Initial Issue, June 28, 1996.

3-5. "Drywell Debris Transport Study," D. V. Rao, F. 

Sciacca, C. Shaffer, F. Souto, and G. Zigler, Draft 

Phase 1 Letter Report to the NRC, SEA 96-3105

010-A:2, September 27, 1996. 

3-6. "MELCOR 1.8.0: A Computer Code for Nuclear 

Reactor Severe Accident Source Term and Risk 

Assessment Analyses," R. M. Summers, R. K. Cole, 

Jr., E. A. Boucheron, M.K. Carmel, S. E. Dingman, 

and J. E. Kelly, NUREG/CR-5531, SAND90-0364, 

SNL, January 1991. 

3-7. "Experimental Evaluation of Internal Debris Capture 

on BWR Drywell Structures Following a LOCA,"" 

P. S. Stacy, M. Padmanabhan, and G. E. Hecker, 85

97/M787F, April 1997. 

3-8. "BWR Drywell Debris Transport PIRT Review of 

SEA Experimental Plan," Gary E. Wilson, Brent 

Boyack, Mark Leonard, Ken Williams, and Lothar 

Wolf, Letter Report to USNRC, Initial Issue, 

November 15, 1996. 

3-9. "Simulation of BWR Drywell Flow Behavior in 

Response to a Recirculation-Line LOCA Using a 

Computational Fluid Dynamics (CFD) Code," Ken 

Williams, Flow Simulation Services, Inc., Letter 

Report to USNRC, FSS Report RX-96-05, 

November 1996 

3-10. "Drywell Transport Study Supplemental Report: 

Analytical Studies," D. V. Rao and C. Shaffer, 

NUREG/CR-6369, Supplement, Science and 

Engineering Associates, Inc., SEA 97-3105-A: 16, 

September 1997.

NUREG/CR-6369 3-50
4. Separate Effects Test Program to Evaluate Washdown 

of Insulation Debris by ECCS Flow

4.1 Introduction 

4.1.1 Background 

As discussed in the previous sections, the floor gratings 

employed in the BWR drywells provide the largest 

potential for capture and retention of insulation pieces as 

they are being transported during blowdown. Nearly all 

the debris pieces that are considerably larger than the 

floor-grating clearance (4"xl.5") are likely to be captured 

by the grating and a significant fraction of the pieces 

smaller than 4"xl.5" would be captured by the grating. 

Therefore, it can be postulated that at the end of 

blowdown the floor gratings would accumulate 

considerable quantities of insulation debris. For some 

plants, the volume of debris trapped on the gratings at the 

end of blowdown may be as high as 400 ft3

. This 

insulation debris would then be subjected to water flows 

that can result from break overflow (primarily in the case 

of a recirculation line break) or containment sprays turned 

on to cool the drywell atmosphere. A fraction of the 

debris may be washed down to the drywell floor as a 

result of exposure to water flow. Presently very limited 

experimental data is available to quantify the transport 

fraction associated with this phase of the accident, which 

has the potential to be a dominant contributor, especially 

considering that large quantities of debris are exposed to 

continuous water flow for extended periods of time. 

Two tests were conducted by the BWROG (TR25 and 

TR3 1) to study the potential for erosion and/or transport 

of large and small insulation debris by washdown [Ref. 4

11. In these tests, a large piece of insulation (6"x3"x2") 

was placed on a full-scale grating at the start of the test. 

The piece was initially subjected to blowdown flow (for a 

period of 15 seconds) which consisted of steam in case of 

TR25 and a two-phase mixture in case of TR3 1. Erosion 

of less than 2% was observed in case of steam blowdown, 

while close to 20% of the piece was eroded by the 

mixture. The left over piece was then subjected to water 

flow that varied with time, increasing from an initial value 

of 1 GPM/ft2 to 12 GPM/ft2 . In TR25 the piece was 

exposed to water flow for a total of 30 minutes, while in 

TR3 1 it was subjected to water flow for 75 minutes. 

Based on these two tests, the BWROG concluded that: 

Most of the small debris (< grating size) would be 

washed down with very small quantities of water flow 

irrespective of where they were located originally, 

and

About 20% of the large piece will be eroded and 

transported to the drywell floor in the form of small 

clumps [Ref. 4.1 ]. Washdown reaches an 

asymptotic behavior with erosion leveling off after 

about 15 minutes of continuous exposure to water. 

These results were then used by BWROG to develop 

guidance related to a drywell debris transport fraction 

Their conclusions were not based on a defensible rationale 

given that: a) the duration of testing and test flow rates are 

not typical of those expected in BWRs following a LOCA 

(e.g., tests were conducted using a maximum of 60 GPM 

flow spread evenly over 5 ft2 of grating), and b) the 

conclusions were drawn based on two tests in which 

several variables were simultaneously varied in a non

prototypical manner; their data did not appear to support 

their conclusions (e.g., in TR31 less than 10% of NUKON 

brick appeared to have been eroded by water flow in 

contrast to 25% recommended by BWROG). Finally, the 

BWROG tests did not provide any insights into the type 

and size of pieces generated by erosion and their 

transportability. 

To overcome this lack of data, SEA conducted a series of 

tests under sponsorship of the NRC. 

4.1.2 Objectives and Scope 

The primary objective of SEA testing was to obtain 

experimental data that could be used to estimate what 

fraction of insulation initially captured by floor gratings 

would be eroded and transported by water flow during the 

washdown phase. The secondary objective was to 

confirm the conclusions stated by BWROG and their 

usage in developing the guidance presented in Reference 

4.1. Tests were conducted with water at room 

temperature using insulation pieces generated by air-jet 

from aged Thermal Wrap"- insulation blankets. Both 

debris sizes and water flow rates were varied to simulate 

washdown of small debris by containment sprays as well 

as erosion and transport of large debris by break flow. 

4.2 Test Facility 

4.2.1 Test Setup 

The tests were performed at the SEA Santa Fe facility. 

Figure 4-1 is a photograph of the test set up and 

Figure 4-2 is a schematic of the test facility. A 400 gallon

4-1 NUREG/CR-6369
Washdown of Insulation Debris

Figure 4-1. Photograph of the washdown experimental set-up. 

Experiments were conducted at SEA-Santa Fe.

Flow Meter

Grating with 1. x 4 Section

Figure 4-2. Schematic representation of the washdown test setup.

NUREG/CR-6369. 4-2
Washdown of Insulation Debris

tank was used as the water reservoir for recirculation 

purposes. To avoid recirculating debris pieces along with 

the flow, two filters were placed in the tank. The first 

filter, a debris catcher, was positioned right below the test 

section to trap large pieces. The second filter was fitted to 

the pump section to filter out finer debris. 

Aluminum grating with dimensions identical to those of 

the steel grating in BWR drywells was placed across the 

top of the tank. The test section, 2-ft x 2-ft in cross

section and 5-ft long, was placed on top of the grating. 

The entire section was fabricated using 0.50" thick clear 

polycarbonate, which allowed visual observation of the 

tests. Three 2-in. diameter plexiglass pipes were used 

across the inside of the box to simulate pipes in the actual 

reactor containment and break-up the jet in a prototypical 

fashion. 

A 250 GPM centrifugal pump was used to inject water 

into the test section through a 4" diameter PVC pipe. In 

tests simulating break flow, the water was allowed to flow 

directly from the PVC outlet. In tests simulating spray

induced washdown, a removable spray head (2-ft x 2-ft in 

cross-section with a hole size of 1/8") was attached to 

PVC outlet. The desired flow rates were achieved by 

properly throttling the control valve located downstream 

of the pump. Calibrated flow meters were used to monitor 

the flow. Two different flow meters had to be used due to 

the large difference in flow rate requirements between 

break flow and spray flow. 

Water from the pump outlet was allowed to fall under 

gravity to impact the mock-up pipes which broke the jet 

and spread the water flow across the test section fairly 

uniformly. The cascading flow was then allowed to 

impinge on the debris layer placed on the grating at the 

start of each test. Under gravity, the water was allowed 

to washdown to the bottom of the test section and then 

into the storage tank. 

4.2.2 Debris Materials 

The insulation material used was heat treated Thermal 

WrapT, which is a low density fiber glass marketed by 

Transco Products, Inc. (TPI). Four sizes of debris were 

used in the tests. These sizes were selected to represent a 

wide range of debris sizes expected to be generated 

following a LOCA. The CEESI air blast test results were 

used to select the debris size and characteristics, as 

described below.

Fine (F): 

Finely destroyed insulation pieces that can be best 

characterized as loosely attached individual fibers less 

than an inch long. Typically such fines were found 

attached to wet surfaces, such as pipes and grating. These 

debris were obtained directly from blast-jet experiments 

conducted previously by SEA (see Section 3). These 

materials were used in two tests (C-2 and C-4). 

Small (S): 

The Insulation debris of a light, loose, and well-aerated 

texture with an average density lower than 0.25 Ibm/ft3 

usually consisting of loose clusters of individual fibers. 

Typically these pieces were about 1.5" in size and 

possessed little of the original structure or the chemical 

binding. In CEESI tests, they were found to have been 

attached to the wet gratings. These debris were obtained 

directly from blast-jet experiments conducted previously 

by SEA (see Section 3). These debris were mainly used in 

spray tests. 

Medium-J (M-J): 

Insulation debris pre-torn from the blanket by an air-jet 

impingement. These pieces keep some of the original 

structures in the inner regions, while they look torn-down 

or loose on the outside. Typically these pieces are about 

6"x4" in dimension. In CEESI tests they were found to 

have been attached to the wet or dry gratings. These 

debris were obtained directly from blast-jet experiments 

conducted previously by SEA (see Section 3). Very few 

pieces that can be characterized as M-J were obtained 

from SEA testing. As a result only two tests were 

conducted using this type of debris. 

Medium-O (M-O): 

Same geometric as above, but the pieces were produced 

by cutting the intact insulation into small pieces. These 

pieces were primarily used in break flow tests as a 

substitute to jet generated debris, because only limited 

quantity of jet generated debris were available for testing. 

These pieces possess same density as as-fabricated 

blankets. 

Large (L): 

The SEA Air-Jet tests have clearly demonstrated that large 

pieces produced from jet impingement tend to retain most 

of their original structure. As a result, large cut-out pieces 

of as-manufactured blanket were used. These blanket 

pieces ranged in size from 10"x 10" to 18" x 18" 

depending on the availability of insulation.

4-3 NUREG/CR-6369
Washdown of Insulation Debris

4.3 Test Plan and Test Procedure 

4.3.1 Text Matrix 

Table 4-I presents the test matrix. The testing proceeded 

in two steps: a) confirmatory tests and b) erosion tests. 

The confirmatory tests consisted of five tests designed to 

confirm some of the observations reported by BWROG 

[Ref. 4.1]. Then 21 erosion tests were conducted to 

quantify erosion as a function of flow rate and debris size. 

Selection of test parameters varied in these tests is based 

on the rationale described below. 

Table 4-1. Experimental uncertainties. 

Experimental Measurement Estimated 

parameter unit uncertainty 

Flow Rate GPM ±10% 

(Break Flow) 

Flow GPM ±15% 

Spray Flow) 

Insulation gm +3 gms 

Mass 

Moisture in gmn May have con

Dried tributed toward 

Insulation lowered estimates 

of erosion rate by 

up to 10%. 

Duration of min +1 min 

Exposure 

1. Flow rate into the test section. A control valve 

located downstream of the pump was used to control 

the flow rate. A flow meter located downstream of 

the control valve was used to monitor flow rate; flow 

meters were calibrated. Two flow rates were selected 

for experimentation. A flow rate of 175 GPM (or 

approx. 45 GPM/ft2-grating) was selected to be 

representative of break flow. On the other hand, a 

flow rate of 20 GPM (or approx. 5 GPM/ft2 -grating) 

sprayed by 1/8" nozzles was used to simulate the 

containment spray flow. The following rationale was 

used to derive the flow rates:

Break Flow 

" Estimated flow area at the lower grating in a BWR: 

2000 ft2 for Mark I, 4500 ft2 for Mark II. Assuming 

that water trickles down to a quarter of the 

containment, the flow cross-sectional area is 500 ft2 

for a Mark I. 

" Estimated ECCS flow rate: 25,000 GPM (+15 % 

depending on the plant power level). Probably real 

flow rates would be much lower given that 25000 

GPM is the design flow at a head of 150 ft-water. 

During recirculation, flow would most likely be 

around 17500 GPM. 

"• Estimated Flow Rate in a Mark I BWR is 50 

GPM/ft2

. Credible Flow Rate = 35 GPM/ft2 . "• Maximum Flow Rate scaled to the test section: 50 

gpm/ft2 x 4 ft2 = 200 GPM. Credible Flow Rate = 

140 GPM.. 

"* Corresponding Velocity: 0. 14 ft/s. 

"• Simulated Flow Rate: 175 GPM. 

Spray Flow 

Estimated flow area at the lower grating in a BWR: 

2000 ft2 for Mark I, 4500 ft2 for Mark II. 

Containment sprays cover entire containment. 

"• Estimated spray flow rate: 7500 GPM 

"• Flowrate in a real BWR is 4.7 GPM/ft2 " 

"• Flowrate scaled to the test section: 4.7 GPM/ft2 x 4 

ft' = 18.75 gpm. " Corresponding Velocity Velocity: 0.0104 ft/s (Note 

velocities are very low. Not much erosion possibly) " Simulated Flow Rate: 20 GPM 

2. Debris layer weight (or theoretical thickness) and 

debris size. Debris was weighed before each test. 

Also debris was manually cut into desired size 

pieces (if needed). The test facility can handle 

pieces as large as 1.5-ft x 1.5-ft. Sizes were as 

described in Section 4.2.2. Debris layer theoretical 

thickness were varied from 1⁄4" to 2" which 

corresponds to mass loading of 5 lb/100-ft2-grating 

to 40 lb/100-ft2-grating. This falls well within the 

expected volume of insulation trapped on the grating 

which varies from 50 ft3 (or 120 lbm) to 400 ft3 (960 

Ibm).

NUREG/CR-6369 4-4
Washdown of Insulation Debris

3. Duration of Exposure. Duration of exposure was 

monitored manually. All spray experiments were 

carried out for 30 minutes, which was estimated to be 

the maximum credible time sprays would be operated 

following a LOCA (Emergency Operating Procedures 

call for operation of sprays for 3 to 4 times following 

a LOCA, about 10 minutes each time). The break 

flow experiments were carried out for up to 3 hours, 

which was estimated to be the maximum credible 

time for continuous operation of ECCS at full flow. 

It is very likely that operators will throttle the ECCS 

within the first hour after LOCA. 

4. Mode of water iniection (spray vs. break). Tests 

addressed both spray and break flow induced erosion. 

No other processes of washdown (e.g., condensate 

drainage) were studied. 

4.3.2 Test Procedure 

The following step-by-step test procedure was followed 

during every test: 

• At the beginning of every day, wash and fill the 

storage tank with water. 

* Cut and weigh debris required for test according to 

the test matrix. 

* Select spray or break flow type. If spray is selected, 

then install spray header. 

"* Carefully place debris pieces of pre-determined size 

and weight on the grating. 

"• Close the valve and turn on the pump, taking suction 

from the fine-mesh filtered intake. 

° Slowly open the valve until desired flow is achieved. 

• Let the water flow continue for the duration called for 

in the test matrix. 

• Turn off the pump. 

• Collect left-over debris on the grating, oven dry it 

until it is completely dry. 

* Collect the debris on the filter screen under the grate. 

Also dry and weigh it for the purpose of mass 

balance. 

4.3.3 Experimental Uncertainties 

The following uncertainties in the experimental 

measurements are estimated based on calibration and 

repeated measurements. 

4.4 Test Results 

A total of 26 tests were conducted (see Table 4-1). In 

each test, a pre-determ-ined quantity of insulation debris

was placed on the grating and then subjected to spray or 

break flow for a period of up to 3 hours. At the end of the 

test, pieces left-over on the grating were collected and 

dried. Mass eroded and percentage eroded were estimated 

from the mass difference between the initial and final 

mass on grating. Table 4-2 presents the results for each 

test. Figures 4-3 and 4-4 illustrate examples of debris 

before and after being subjected to washdown in Tests E-1 

and E-13, respectively. Figure 4-5 shows eroded pieces 

trapped on the debris catcher (Test E-l). In Test E-1 

medium pieces of debris cut from original blankets were 

subjected to break flow washdown for a period of 30 

minutes. As shown in Figure 4-3, erosion occurred fairly 

uniformly, thus suggesting that all pieces were subjected 

to similar water flows irrespective of their location. Even 

at the end of the test, the original blanket structure is 

visible in the non-eroded portion, suggesting that the 

erosion process consists of peeling off layers from the top. 

Visual observation suggests that erosion occurs 

continuously with time. Note also that eroded pieces are 

typically very small and can be best characterized as fines. 

These pieces tended to remain suspended in the 400

gallon water tank under minimal turbulence conditions. 

In Test E-13 Small (S) pieces of CEESI air-blast 

generated debris were subjected to spray flow for a period 

of 30 minutes. As shown in Figure 4-4, spray flow 

washed down most of the loosely attached clumps and 

clumps that possess some of the original structure 

survived. Visual observations suggest that the majority of 

the washdown occurred within the first 15 minutes. 

4.4.1 Confirmatory Tests 

The objective of the confirmatory tests was to verify the 

following conclusions stated by the BWROG [Ref. 4.1]: 

1. Little or no erosion is possible for insulation pieces 

covered in canvas when subjected to washdown flow 

resulting either from break overflow or containment 

spray. 

2. Most of the Small debris pieces will be washed 

down by water within first 10-15 minutes after 

which washdown reaches an asymptote. 

3. Large pieces will not be forced through the grating 

even at high flows. They will remain on the grating 

and may erode with time. Erosion also exhibits an 

asymptotic behavior. 

Test C-1 was designed to address the issue related to 

erosion of insulation covered in the original canvas cloth 

in which it is packed. A piece of partially torn Thermal 

Wrap blanket generated from CEESI Air Blast tests was 

cut into 10" x 10" x 3" piece and placed in the center of

4-5 NUREG/CR-6369
Washdown of Insulation Debris

Table 4-2. Test matrix for SEA washdown experiments.

Test ID Flow/Test configuration Insulation debris characteristics Quantity of insulation 

Size Size 

Type Flow Duration category physical Canvas Mass Theo. Thick 

(GPM) (W) (gms) (in) 

C-1 Break 175 30 M(O) 6" x 4" Y 196 0.5 

C-2 Break 175 30 S+F 1.5" x 1.5" N 200 0.5 

C-3 Spray 20 30 F <1.5" x 1.5" N 185 0.5 

C-4 Spray 20 30 F <1.5" x 1.5" N 184 0.5 

C-5 Break 175 30 M(O) 6" x 4" x 1/4" N Not Measured 0.5 

E-1 Break 175 30 M(O) 6" x 4" N 196 0.5 

E-2 Break 175 30 M(O) 6" x 4" N 362 1.0 

E-3 Break 175 15 L >10" x 10" N 360 1.0 

E-4 Break 175 180 L >10" x 10" N 362 1.0 

E-5 Break 175 30 L >10" x 10" N 366 1.0 

E-6 Break 175 60 L >10" x 10" N 370 1.0 

E-7 Break 175 30 M(O) 6" x 4" N 180 0.5 

E-8 Break 175 30 <M(O) 6" x 4" N 194 0.5 

E-9 Break 175 30 S(O) 1.5" x 1.5" N 185 0.5 

E-10 Break 175 30 L >10" x 10" N 720 2.0 

E-11 Spray 20 30 M(J) 6" x 4" N 184 0.5 

E-12 Spray 20 30 S(J) 1.5" x 1.5" N 364 1.0 

E-13 Spray 20 30 S(J) 1.5" x 1.5" N 96 0.25 

E-14 Spray 20 30 S(J) 1.5" x 1.5" N 187 0.5 

E-15 Spray 20 30 L >10" x 10" N 368 1.0 

E-16 Spray 20 30 <M(O) 6" x 4" N 186 0.5 

E-17 Spray 20 30 S(J) 1.5" x 1.5" N 368 1.0 

E-18 Spray 20 60 M(O) 6" x 4" N 187 0.5 

E-19 Spray 20 30 S(J) 1.5" x 1.5" N 715 2.0 

E-20 Break 175 120 L >10" X 10" N 362 1.0 

E-21 Break 175 30 M(J) 6" x 4" N 720 2.0

NUREG/CR-6369 4-6
Washdown of Insulation Debris

A. Before exposure to break flow.

B. After exposure to break flow. 

Figure 4-3. Erosion of medium size debris manually cut from original blankets by break flow (test 1).

4-7 NUREG/CR-6369
Washdown of Insulation Debris

A. Before exposure to spray flow.

B. After erosion by 30 muniutes of spray flow. 

Figure 4-4. Erosion of small air jet generated debris by spray flow (test 13).

NUREG/CR-6369 4-8
Washdown of Insulation Debris

Figure 4-5. Eroded pieces filtered by coarse debris catcher (test 2).

the grate. Visually it can be seen that the piece consisted 

of several small holes and worn out canvas outer clothing. 

After 30 minutes of continuous exposure to 175 GPM 

flow, visual observations exhibited no noticeable erosion 

of the pieces. Visual observations also suggest that water 

flows around the blanket, but not through the blanket 

which would be required to inflict damage. No attempt 

was made to dry the insulation pieces and perform a mass 

balance. 

Tests C-2, C-3 and C-4 were designed to address the 

second issue, involving, washdown of small pieces of 

debris attached to various structures during blowdown. 

Photographs from the CEESI tests clearly suggest that 

debris are loosely attached to the surface of interdicting 

structures due to surface wetness. They also tended to be 

fairly dry on the outside and wet closer to the structural 

surface. To simulate this, dry pieces of insulation debris 

that can be characterized as Fines (see Section 4.2.2) were 

manually dropped on the pre-wet grating and pipes. 

These structures were then subjected to water flow. Test 

C-2 simulated break flow, where as Tests C-3 and C-4 

simulated spray flow. Test C-5 is a repeat of C-2, except 

for the fact that pieces are slightly larger. In all cases, the 

insulation was completely washed down within the first 5 

minutes. No pieces were left behind on the grating, either 

during spray flow or during break flow 

Test C-5 was designed to determine if a large piece is 

susceptible to being broken down and forced through the 

grating in a short period of time. A single dry piece of 

insulation blanket, 6"x4"xl/2" in size, was placed in the 

middle of the grating and was subjected to break flow of

45 GPM/ft2 . The insulation piece survived approximately 

45 minutes of continuous flow, although continuous 

erosion was noted. 

Based on this testing it is concluded that: 

1. Partially torn insulation blankets covered with the 

original canvas clothing are unlikely to be eroded by 

water flow during washdown. This confirms the 

BWROG stated conclusion. 

2. Fines attached to various wet structures during 

blowdown as a result of inertial impaction will be 

washed down by the water flow, irrespective of 

whether the flow is induced by break overflow or 

containment sprays. Also, small pieces deposited on 

the gratings will be washed down completely in the 

case of break flow. In both cases, transport is 

complete within few minutes. No conclusions can 

be drawn related to washdown by condensate 

drainage 

3. Pieces sufficiently larger than the grating (classified 

as M-O, M-J and L in Section 4.2.2) possess 

sufficient structure and are not susceptible to being 

forced through the grating clearances in a short 

period of time. Erosion (if any) occurs over a longer 

period of time. It does not reach an asympotic 

behavior. 

4.4.2 Erosion Tests 

A total of 21 erosion tests were conducted with the 

objective of estimating the mass fraction of the insulation

4-9 NUREG/CR-6369
Washdown of Insulation Debris

fragments that would be eroded when exposed to 

break/spray flow for a pre-determined period of time. In 

all these tests debris fragments of pre-determined size and 

weight were placed uniformly on the grating and were 

exposed to break and spray flow. Almost all of the break 

flow tests were conducted using relatively large debris 

retaining the original blanket structure as previous tests 

have shown that small pieces with no original structure 

do not survive under break flow. The fraction eroded was 

estimated from the difference in mass between debris 

placed on the grate and debris that remained on the 

grating after drying. Table 4-3 presents the results. 

4.4.2.1 Effect of Flow Rate (Break versus Spray) 

Table 4-4 presents a test-by-test comparison of 

washdown fractions as a function of test debris size. As 

shown in this table, under similar test conditions break 

flows erode a larger fraction of debris than spray flow. 

Such a dependence is expected considering that break 

flows discharge considerably larger flow. 

4.4.2.2 Effect of Duration Erosion 

The effect of time on erosion by break flow was explored 

in tests E-3, E-4, E-5, E-6 and E-20. Results of these 

tests are presented in Figure 4-6 as a function of time. 

From this figure it can be clearly seen that erosion is a 

linearly increasing function of time, at least over the first 

three hours. The error bars on the graph represent 

estimated experimental uncertainty. The spread in the 

data is due to variability in debris bed formation. 

The effect of time on erosion was not explored in the case 

of sprays because erosion was found to be minimal 

(except for small and medium pieces). 

4.4.2.3 Effect of Bed Thickness (or initial mass) 

Theoretical thickness of the bed is a measure of debris 

loading on the grating (lbm/ft2 ). It is computed as:

T, = Ml(p'Ag)

where: 

T, 

M 

Ag 

P

(4-1)

= theoretical thickness (ft) 

mass of insulation (lbm) 

= cross-section Area of the Grating (ft2) 

- as-fabricated density of insulation (2.4 

lbm/fe)

theoretical thickness for medium size debris pieces with 

original structure (M-O) by break flow. As evident from 

Table 4-2, the fraction eroded is inversely proportional to 

the bed theoretical thickness. On the other hand, the 

quantity of insulation eroded is approximately the same in 

both cases. This suggests a constant rate erosion in the 

case of large and medium pieces that retain the majority 

of the original blanket structure. 

Tests E-12, E-13, E-14 and E-19 examined erosion of air

blast generated debris by spray washdown. As evident 

from Table 4-2, no noticeable dependence existed 

between theoretical thickness and percentage eroded. 

This is consistent with the visual observation that loosely 

attached parts of the debris were quickly eroded by the 

sprays (visual observation suggests that it occurred within 

the first 15 minutes). The left over debris pieces retained 

some of the original structure and were not eroded by 

spray. 

4.4.2.4 Effect of Debris Size and Structure on Erosion 

Tables 4-5 compares erosion of Medium and Small pieces 

cut manually from the original blanket with those 

generated by air jet. As evident from this table, the 

potential for erosion is smaller for pieces that possess 

some of the original structure.' 

Table 4-6 compares erosion potential as a function of 

debris size. Data suggest that in the case of debris pieces 

that possess original blanket structure, mass eroded is 

independent of debris size, but is only dependent on time 

(somewhat weakly dependent on theoretical thickness). 

To illustrate this trend, in Table 4-5 rate of erosion (mass 

eroded per hour per 100-fte) is presented as a function of 

debris size and theoretical thickness. As evident from 

this table for break flow, the erosion rate is fairly 

independent of size and thickness and can be bounded by 

a value 3.0 lbm/100-ft2

-gratingihr. 

4.4.2.5 Experimental Data Repeatability 

Data repeatability can be best judged by comparing 

results of similar or identical tests. As shown in Table 4

3, Test E-7 is an exact repeat of Test E-l and Test E-17 is 

an exact repeat of Test E-12. In both cases, the fraction 

eroded was found to be within +10% of each other. In 

reviewing the data it should be noted that all 

measurements are associated with experimental

Tests E-1 and E-2 measured erosion as a function of Manually cut pieces possess strong structure that is typical of original 

pieces.

NUREG/CR-63694 4-10
Washdown of Insulation Debris

Table 4-3. Results of washdown erosion test program. 

Debris 

Test Flow size Theo. Initial Final Mass 

ID type Duration type Thick. mass mass eroded Percent Comments 

(min) (In) (gm) (gm) (gm) (%) 

C-1 Break 30 M(O) 0.5 Not Meas. Not Meas. Not Meas. Not Meas. Visually, erosion is insignificant. 

C-2 Break 30 S+F 0.5 200 0 175 100 All the insulation was forced through the grating. 

C-3 Spray 30 F 0.25 100 0 20 100 Same as above. Insulation only fines. 

C-4 Spray 30 F 0.25 100 0 20 100 Same as above. Insulation only fines. 

C-5 Break 30 M(O) 0.5 Not Meas. Not Meas. Not Meas. Not Meas. Erosion was evident. No large-scale break through. 

E-1 Break 30 M(O) 0.5 196 172 24 12 All pieces aged. Manually cut from Original blanket. 

E-2 Break 30 M(O) 1.0 362 341 21 6 All pieces aged. Manually cut from Original blanket. 

E-3 Break 15 L 1.0 360 355 5 1.4 All pieces aged. Manually cut from Original blanket. 

E-4 Break 180 L 1.0 362 264 98 27 All pieces aged. Manually cut from Original blanket. 

E-5 Break 30 L 1.0 366 343 23 6 All pieces aged. Manually cut from Original blanket. 

E-6 Break 60 L 1.0 370 353 18 5 All-pieces aged. Manually cut from Original blanket. 

E-7 Break 30 M(O) 0.5 180 160 20 11 All pieces aged. Manually cut from Original blanket. 

E-8 Break 30 <M(O) 0.5 194 171 23 12 All pieces aged. Manually cut from Original blanket. 

E-9 Break 30 <(O) 0.5 185 133 52 28 All pieces aged. Manually cut from Original blanket. 

E-10 Break 30 L 2.0 720 Test aborted. Noticed build-up of a water layer on debris. 

"E-1 1 Spray 30 M(J) 0.5 184 152 32 17 Debris generated from CEESI Experiments [Ref. 2]. 

E-12 Spray 30 S(J) 1.0 364 214 151 41 Debris generated from CEESI Experiments [Ref. 2]. 

E-13 Spray 30 S(J) 0.25 96 51 45 47 Debris generated from CEESI Experiments [Ref. 2]. 

E-14 Spray 30 S(J) 0.5 187 107 80 43 Debris generated from CEESI Experiments [Ref. 2]. 

E-15 Spray 30 L 1.0 368 368 <1 <1 Debris generated from CEESI Experiments [Ref. 2]. 

E-16 Spray 30 <M(O) 0.5 186 182 4 2 All pieces aged. Manually cut from Original blanket. 

E-17 Spray 30 S(J) 1.0 368 230 138 38 Debris generated from CEESI Experiments [Ref. 2]. 

E-18 Spray 60 L 0.5 187 185 <2 <1 All pieces aged. Manually cut from Original blanket. 

E-19 Spray 30 M(J) 2.0 715 481 235 33 Debris generated from CEESI Experiments [Ref. 2]. 

E-20 Break 120 L 1.0 362 300 62 17 All pieces aged. Manually cut from Original blanket. 

E-21 Break 30 M(J) 2.0 720 375 345 48 Debris generated from CEESI Experiments [Ref. 2].

4-11 NUREG/CR-6369,
Washdown of Insulation Debris 

Table 4-4. Effect of flow rate (i.e., break versus spray) on erosion of debris.

No. Test conditions Break flow Spray flow 

Size Duration % Erosion Test ID % Erosion Test ID 

I L 30m 6 E-5 <1 E-15 

2 M(O) 30 m 6 E-2 <1 E-18 

3 M(J) 30 m 48 E-21 18 E-11

30 L

Test Conditiors: 

:Size: Large E-4 -c> 

25 ------ :Ticknesa 1- ---- ---- Flow: B.-eak 

i I I 20 ------- -- - --.......-- -- I ------

UJW• • E-20 

0 15 - ------ -- .. -.. - -- .. -.- . .. . . ----- ------ .... .------- ... ... 

4) 

0. 

0 20 40 60 s0 100 120 140 160 180 

Erosion Time (in) 

Figure 4-6. Effects of duration of erosion on the percentage of initial blanket eroded. 

Table 4-5. Effect of debris size and structure on erosion.

NUREG/CR-6369

Debris size Test condition Air-jet generated Manually cut pieces 

Flow type Duration Erosion (%) Test Erosion (%) Test 

M Break 30 48 E-21 12 E-1 

S Break 30 100 C-2 28 E-9 

M Spray 30 17 E-11 <1 E-18

4-12
Washdown of Insulation Debris

Table 4-6. Effect of debris size, debris loading (i.e., thickness) and test duration on erosion. 

Test Test Description Erosion data Erosion data 

ID 

Theoretical Debris Mass Percentage of lb/100 

thick. (In) size type Duration eroded initial mass ft2

/hr 

(m) (gm) 

E-1 0.5 M(O) 30 24 ± 3 12 2.7 ± 0.33 

E-2 1.0 M(O) 30 21 ± 3 6 2.4 ± 0.33 

E-3 1.0 L 15 5 ± 3 1.4 1.2 ± 0.75 

E-4 1.0 L 180 98 ± 3 27 1.8 ± 0.1 

E-5 1.0 L 30 23 ± 3 6 2.7 ± 0.33 

E-6 1.0 L 60 18 ± 3 5 1.2 ± 0.2 

E-7 0.5 M(O) 60 20 ± 3 11 2.4 ± 0.33 

E-8 0.5 <M(O) 30 23 ± 3 12 2.7 ± 0.33 

E-20 1.0 L 12 62_±3 17 1.8_±0.1

uncertainties which are estimated and presented in Section 

4.3.3. 

4.5 Summary and Conclusions 

A total of 26 washdown tests were conducted to quantify 

the potential for erosion of insulation debris fragments 

captured on grating as they are subjected to water flow 

resulting from break overflow and/or from containment 

sprays. The tests employed several debris fragment sizes 

and two flow rates. Based on these tests the following 

conclusions can be drawn: 

1. All finer debris that are smaller than the grating, 

but are captured on grating as a result of inertial 

capture would be washed down when subjected to 

break and/or containment sprays. A transport 

factor of 1.0 should be assigned for such fragments. 

2. A significant fraction of the medium pieces 

(generated by jet impact on insulation blanket) 

would be eroded and transported to the drywell 

pool. A transport factor of 1.0 is recommended in 

the case of break overflow (e.g., following a 

recirculation line break); on the other hand, for 

sprays a transport factor of 0.5 appears reasonable. 

3. Erosion of larger pieces is dependent both on time 

and flow rate. At very small flow rates that are

typical of containment sprays, erosion of large debris 

pieces is negligible, especially considering that 

containment sprays are only operated intermittently. At 

larger flow rates typical of break flow, erosion can be 

large. For such conditions an erosion rate of 3.0 lbm/100

ftE/hr is recommended. For the assumed base case scenario 

(i.e., debris is uniformly distributed on the grating at the 

end of blowdown, break flow cascades and spreads evenly 

over a quarter of the grating, and break flow occurs 

unthrottled for a period of 3 hrs following a LOCA after 

which the break is isolated and/or throttled), the erosion 

can be as high as 25% of the large pieces that are 

separated from the canvas during their generation. For 

shorter or longer duration, the quantity eroded can be 

estimated using an erosion rate of 3.0 lbm/100-ft2/hr. 

4. The secondary debris generated from erosion of 

large pieces tends to be very small pieces that are 

likely to remain suspended in a pool of water with 

minimal turbulence. Visual observations suggest 

that they tend to be very small loosely attached 

clumps of individual fibers. 

4.6 References 

4.1 Boiling Water Reactor Owners' Group, "Utility 

Resolution guidance for ECCS Suction Strainer 

Blockage," NEDO-32686, Rev. 1, 1996.

4-13 NUREG/CR-6369
5. Conclusions

5.1 Air Borne Transport 

The conclusions of the study related to short-term (or 

blowdown) transport can be summarized as follows: 

1. Inertial capture is an important mechanism for 

removal of debris from flow stream provided the 

drywell structures are wet. Gravitational settling, 

other mechanism studied in the test program was 

negligible except for large-canvassed pieces. 

2. Surface wetness has a clear influence on the 

capture of small debris by various drywell 

structures; when dry, these structures did not 

capture any small debris. For large debris 

structural wetness has negligible effect. 

3. Capture efficiency of individual structural elements 

decreases when they are grouped with other 

structures, except for gratings whose capture 

efficiency did not change. Video images of debris 

transport clearly demonstrate that due to wake 

effects created by the first layer of structures debris 

particles transport around the structures located 

downstream of them. 

4. Gratings captured more fibrous debris than any 

other structural components, individually or 

together with other structures. Under identical 

conditions of surface wetness, gas velocity, debris 

size and debris mass, a single grating captured as 

much debris as structural members assembled to 

typical BWR congestion levels over a 20-ft length. 

5. Bulk flow velocity appears to have little impact on 

capture efficiency, at least within the range tested 

(25-150 ft/s). Similarly, three-dimensional local 

flow patterns appear to have an insignificant effect 

on capture efficiency as demonstrated by good 

agreement between CEESI and ARL experimental 

data for gratings and structural combinations. Note 

that ARL tests employed flow control devices to 

straighten the flow before it approached the test 

objects, where as in CEESI a complex three

dimensional flow transported the debris over the 

test objects. 

6. Mark I and Mark II vents with wetted surfaces can 

be effective at capturing larger debris. However,

their capture efficiency for small debris is typically in the 

range of 12%. 

7. Degradation of large pieces deposited on gratings by 

inertial capture is negligible when exposed to the 

remaining blowdown flow that follows. In the tests, 

negligible break up or disintegration of insulation 

debris captured on the grating was found when 1/8" 

to 1⁄2" thin pieces of insulation were subjected to up 

to 140 ft/s of approaching air velocity. The pressure 

drops resulting from the flow were as high as 0.5 

psi. 

Capture efficiencies recommended for use to estimate 

drywell transport fractions during blowdown are provided 

in Table 5-1. While applying the transport fractions care 

should be taken to ensure that: 

The capture efficiency should be applied to only that 

fraction of the debris that is expected to be 

transported across the structural group during 

blowdown. 

Appropriate capture efficiency should be selected 

after determining the surface wetness of the 

structures. 

5.2 Transport During Long-Term 

ECCS Recirculation 

The following conclusions related to long-term transport 

can be drawn from the experimental data: 

1. Small debris deposited on the surface of the 

structural elements can be easily washed down by 

containment sprays or break overflow. Recapture of 

these pieces on any of the structures located down 

stream is unlikely. 

2. Large pieces do not undergo instantaneous 

degradation even when they are subjected to water 

flows as high as 50 GPM/ft2 which is representative 

of break overflow. Instead they undergo continuous 

erosion at a rate of 3 lbm/100-ft2

/hr. Erosion of large 

pieces by spray flow is negligible. 

3. No erosion was observed in the case of large pieces 

covered with canvas lining covering them. It is 

unlikely that such pieces would be transported 

during washdown by water flows.

5-1 NUREG/CR-6369
Conclusions

Table 5-1. Capture Fractions Recommended for estimating dryweH transport 

fractions during blowdown (short-term).

See size definition plotted in Figure 1-2 for CEESI Tests. Small and Large correspond to photographs 3.6-2 and 3.6-4. .Lower bound refers to the minimum capture observed in the experiments (after accounting for experimental uncertainty) for 

the conditions specified in the table. .Best estimate represents the average capture fraction measured for the conditions specific in the table. " Dry refers to when the surface of the structure is dry or partially dry. Other models should be used to determine if a 

particular structure is expected to be dry or wet in the BWR drywell during blowdown. 

12. Beyond a minimum structural wetness capture is negligibly effected by wetness. Other models should be used to determine 

if a particular structure is expected to be dry or wet in the BWR drywell during blowdown.

NUREG/CR-6369

Debris size' Wetness Recommended capture fraction Rationale 

Lower bound9 I Best estimate'" 

Floor Grating (4" x 1.5" clearance) 

Small Dry11 0% 0% See Figures 3.7-4 and 3.7-6. 

Wet 15% 25% See Figures 2.7-4 and 3.7-6. 

Large Dry 100% 100% See Section 3.7.6.2 

Wet 100% 100% See Section 3.7.6.2 

Congested Structures (prototypical of BWR drywells) 

Small Dry 0% 0% See Figure 3.7-3 

Wet 0% 10% See Figure 3.7-3 for best estimate. Engr. Judgement for Lower bound 

Large Dry 0% 0% CEESI tests showed no evidence of deposition. 

Wet 0% 0% 

Mark 11 Vent Entrance 

Small Dry 0% 0% 

Wet 5% 10% 

Large Dry 5% 10% 

Wet 10% 35% 

Mark I Vent Entrance 

Small Dry 0% 0% 

Wet 1% 5%

5-2
NRC FORM 335 U.S. NUCLEAR REGULATORY COMMISSION 1. REPORT NUMBER (2-89) (Assigned by NRC, Add Vol., Supp., Rev., NRcM 1102, BIBLIOGRAPHIC SHEET and Addendum Numbers, if any.) 

3201.,3202 BBIGAHCDATASHE 

(See instructions on the reverse) NUREG/CR-6369, Vol. 2 

2. TITLE AND SUBTITLE SEA 97-3105-A: 15 

Drywell Debris Transport Study: Experimental Work 3. DATE REPORT PUBLISHED 

MONTH I YEAR 

September 1999 

4. FIN OR GRANT NUMBER 

W6325 

5. AUTHOR(S) 6. TYPE OF REPORT 

D.V. Rao, C. Shaffer, B. Carpenter, D. Cremer, and J. Brideau Final 

7. PERIOD COVERED (Inclusive Dates) 

8. PERFORMING ORGANIZATION -NAME AND ADDRESS (If NRC, provide Division, Office or Region, U.S. Nuclear Regulatory Commission, and mailing address; if contractor, provide name and mailing address.) 

Science and Engineering Associates, Inc. Subcontractor: 

6100 Uptown Blvd. NE .' AAlden Research Laboratory 6100querque, U NM Bl. N30 Shrewsbury Street 

Albuquerque, NM 87110Holden, MA 01520

9. SPONSORING ORGANIZATION - NAME AND ADDRESS (If NRC, type Same as above. if contractor, provide NRC Division, Office orRegion, U.S. Nuclear Regulatory Commission, 

and mailing address.)

Division of Engineering Technology 

Officeof Nuclear Regulatory Research 

U.S. Nuclear Regulatory Commission 

Washington, DC 20555-0001

10. SUPPLEMENTARY NOTES 

M. Marshall, NRC Project Manager

11. ABSTRACT (200 words or less)

This report describes three test programs undertaken as part of the DDTS to pro vide basic understanding regarding transport of insulation fragments in the drywell following a postulated LOCA. The first two tests focused on transport of debris by blowdown flow. They obtained data related to (a) inertial capture of insulatio n debris on typical BWR drywell structures while 

they are transported across the structures by the steam flow; and (b) degradati on of large insulation pieces captured on floor 

gratings when exposed to high velocity steam flow with suspended droplets. The se tests clearly established that wet floor 

gratings would capture significantly more debris than any other BWR drywell str uctures (e.g., pipes, I-beams and vents). The 

capture efficiency of all structures was found to be a strong function of debri s size and structural wetness, but a weak function 

of flow velocity and local flow patterns. Floor gratings possess 100% capture efficiency for insulation pieces larger than 6"x4". 

These large pieces do not degrade or are not forced through the grating clearan ces (1.5"x4") when subjected to high velocity droplet flow, even though the differential pressure across them is as high as I psid. 

The third test program addressed the issue of washdown of debris previously cap tured on floor gratings by break over flow or containment spray flow during ECCS recirculation phase. These tests concluded that majority of the small debris pieces captured on various structures would be washed down by break flow or spray flow. On the other hand, erosion is the only available mechanism by which large pieces deposited on the floor gratings would be transported. In three hours, as much as 25% of the larger pieces can be eroded and transported to the suppression pool.

12. KEY WORDS/DESCRI PTORS (List words or phrases that will assist researchers in locating the report.) 13. AVAILABI'ITY STATEMENT 

BWR Suction Strainers unlimited 

Drywell Debris Transport 14. SECURITY CLASSIFICATION 

Transport Experiment (This Page) 

unclassified 

(This Report) 

unclassified 

15. NUMBER OF PAGES 

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