ML20151T798

SE Related to NRC Bulletin 96-003,BWROG Topical Rept NEDO-32686, Util Resolution Guidance for ECCS Suction Strainer Blockage

ML20151T798
Person / Time
Issue date:	08/20/1998
From:	NRC (Affiliation Not Assigned)
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ML20151T788	List: ML20151T785 ML20151T798
References
PROJECT-691 IEB-96-003, IEB-96-3, NUDOCS 9809100159
Download: ML20151T798 (168)

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{{#Wiki_filter:. ~ . . ~ . . . -_ .. .. - . . _ - . - . _ - - . . - _ - - - - .- - - . . - . - . - . - . - . - - - - - - . . t August 20, 1998 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO NRC BULLETIN 96-03, BOILING WATER REACTOR OWNERS GROUP TOPICAL REPORT NEDO-32686,

                                                             " UTILITY RESOLUTION GUIDANCE FOR ECCS SUCTION STRAINER BLOCKAGE" (DOCKET NO. PROJ0691) a
                                                                           "~

9809100159 990903 PDR TOPRP EMV90 E 4 . . .C PDR ,

  ._ __ - ~_-._ _ _ _                                                   _ _ . _ . _ . _ . . _ . _ . . _ _ _ _ . _ . _ _ _ . ~                       _                                 _ _ . . _ .

t

,                     EXECUTIVE 

SUMMARY

. . . . . . .. . ..... .                                           .        .. .                    .                . ... .               ES-1             i ES.1 Selection of Breaks for Analysis .                             .             .           .               ....                .....          . ES-1               l ES.2 Generation of Insulation Debris by a Postulated Break                                                    ...... ......                          ES-2             !

ES.3 Other Sources of Drywell Debris . . . . . . . .. .... ... .. . . . ES-4 { ES.4' Transport of Drywell Debris to the Suppression Pool . . . . .. . ... ES-5 . ES.5 Suppression Pool Debris . . . . . . . . . . . . . . . . .. . ..... .. ES-6 , l ES.6 Suppression Pool Transport . . . . . . ... . . ... . . . . . . . . E S-6 ES.7 Head Loss Across the Strainer . ........ ..... . . ...... . ES-7 ES.8 Estimation of Available NPSH for ECCS Pumps . . . ... . . . . . . . . . E S-8 3 l ES.9 Other lssues . . . . . . . . . . . . . . . . . . . . . . . .. ...... ...... . . ES-9 l t

1.0 INTRODUCTION

. . . . .... ... . .. .......... ....................                                                                                        .1          !

1.1- Background . . . . . . . . . . . . . . . . . . . . . . . . . ... . .... . ..... .... 3 2.0 - DISCUSSION . . . . . . . . ... .. ...... ........ . .... .......... ... 8 f 3.0 URG GUIDANCE FOR DEMONSTRATING COMPLIANCE WITH 10 CFR 50.46 . . 10  ; 3.1 Evaluation of Resolution Options .. . . . .... . ... ... 10 i 3.2 Methodology For Sizing Passive ECCS Suction Strainers . . . . . . . . . . . . .18  ! 3.2.1 Sources of Drywell Insulation Debris . . . . . . . . . . . . . . . . . . . . . . . .18 . 3.2.1.1 Pipe Break Locations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18  ; 3.2.1.2 Zone of Influence . . . . . . . . . . . .. .... ... .. . 23 + 3.2.2 Sources of Other Drywell Debris . . . . . . .. . . ......... .29  ! 3.2.3 Drywell Debris Transport . ..... ... . . .. .. . ...... . 34 , 3.2.4 Suppression Pool Debris . . . . . . . ..... ... ..... .. . . 41 l 3.2.5 Suppression Pool Transport and Settling . . . ........... . . .42 l 3.2.6 Verification of Adequate ECCS Pump NPSH . . . . . . . . . . . . . . . ... 42  ;

3.3 Backflush . . . . . . .. ................ . . ........ . ..... . . . 46

                            . 3.4     Self-cleaning Strainers . . .............. ... ..... .... ...                                                                       ...        .47           ;

i 4.0 ADDITIONAL FEATURES THAT PROVIDE DEFENSE IN DEPTH .. . ........ . 48 i 5.0 CONSERVATISM . . . ..... ........ ..... . ...... ............. 49 5.1. ~ Selection of Break Locations . .................. .. .......... 49 i 5.2 Size of the ZOI . . . .......... ........ ... . . .. . .. .. .... 49 5.3 Debris Generation . . . . . . . . . . . . ...... . ....... . .......... 50 5.4 Drywell Debris Transport . . . . . . ... ....... ... . .. . . . . . . . . . 50 -

                             . 5.5   . Suppression Pool Transport . . . . . . .... . .... .......                                                             ... .             .     .51          ,

5.6 Head Loss and NPSH Margin . . . . . . . . . . . . . . . . . . . . . . . . . . .... 51 . r

                      .6.0     MISCELLANEOUS REVIEW COMMENTS ON BWROG GUIDANCE . . .                                                                               ....         .. 52-             ,

P 7.0 OVERALL CONCLUSIONS AND RECOMMENDATIONS . . . . . . . . . . .. ...... 53  !

8.0 REFERENCES

..... .                .. .......... ..                                  .. .................                                    .... 56                 i 9.0     LIST OF RELATED REPORTS AND DOCUMENTS IN THE NRC's PUBLIC                                                                                                           i
                              . DOCUMENT ROOM .. ................ .                                                     .. ... .....                             ...             .    .60          j I

P Y t C

1 1 Appendix A - Calculation to Check Estimates of Bulk Dynamic Pressures Computed by the B W R O G ..... ..... ... .... ... . .. .. . .. .., A-1 Appendix B - Analyses to Verify Values of P., for Selected Materials Reported by the BWROG and Suggestions for Development of Scaling Analyses . . . . . .. . . . B-1 Appendix C - Calculations to Examine the Accuracy of Reported Jet Volumes Bounded by

                         - Selected Load Isobars.-                             ..... . . . . ... . .. ..                      . .......               . ... ...             C-1 Appendix D - Calculations to Examine Zone of Influence Models Proposed for Two-Phase Jets . . . . . . . . . . . . . . ... .... . ........ ...                                            ...........                   . . . . . . . D-1 Appendix E - Calculation to Examine the URG Guidance on Thin-Bed Effect on Attemate Strainer Designs . . . . . . . . . ..... .. ... .                                           . ...... ........ ..                           .    . E-1 Appendix F - Mapping of the Zone of influence . . .                                       .. .... . ....... ...... ....                                 F-1 Appendix G - Calculations to Evaluate the URG Methods to Estimate the Quantity of Fines . .. . . . . . . . . . . .                   . . . . . . . . . . . . . . . . . . . . . . .          ....           . .. ..             . . G-1 Appendix H - Calculations to Examine the Accuracy of URG Drywell Debris Transport Factors . . . . . . . . . . . .                        ..       .. ....... ... .. ...... ......... . . .                                          H-1 Appendix l- Analyses to Examine the Accuracy and Applicability of ECCS Strainer Head Loss .... .... ...                                                ...     . ....... ..              ....         ..... ..                . . . 1-1 Appendir J - Calculations to Examine line Accuracy of URG Sludge Generation Fac! ors . . . J-1 Appendix K - Analyses to Examine the Accuracy of the URG Guidance for Primarily RMI Plants ! . .. . .. ...... ..                                        ....      ..... ...           ....... . .... .. ..                          . K-1 Appendix L - Staff Resolution of BWROG Comments on the Draft SER on the URG Dated December 31,1997 . . . .                                .... .... .......                   .     .................... . L-1

Executive Summary By letter dated November 20,1996, the Boiling Water Reactor Owners Group (BWROG) sutamitted for review by the U.S. Nuclear Regulatory Commission (NRC) a document entitled " Utility Resolution Guidance for ECCS Suction Strainer Blockage," NEDO-32686 (also known as the URG). The guidance provided in the URG can be divided broadly into the following areas: e selection of breaks for the analysis of strainer blockage e generation of insulation debris by a postulated break e drywell sources of debris other than insulation debris (e.g., concrete dust, paint chips etc.) e transport of debris from the break location in the drywell to the suppression pool e suppression pool debris (e.g., sludge and rust flakes) e transport of debris in the suppression pool and its accumulation on the strainer e head loss resulting from debris buildup for selected strainer geometries e guidance for estimating the available net positive suction head (NPSH) margin e other issues The following sections briefly describe the guidance provided in each of these areas of the URG, along with the related findings from the staff's evaluation. ES.1 Selection of Breaks for Analysis The primary system piping in a boiling-water reactor (BWR) varies in diameter from 3.81 centimeters (cm) to 60.96 cm (1.5 inches (in.) to 24 in.) or greater. Therefore, postulated breaks in the main steamlines, recirculation lines or feed water lines can be small, medium or large. Because it is difficult to analyze each postulated break, a criterion is needed to select the bounding breaks that maximize head loss across the pump suction strainers of the emergency core cooling system (ECCS). To address this need, Regulatory Guide 1.82, Rev.2, (Reference 5) states that as a minimum, licensees should consider the following postulated break locations: e breaks on the main steam, feedwater, and recirculation lines with the largest amount of potential debris within the expected zone of influence (ZOI) e large breaks with two or more different types of debris within the expected ZOI e breaks in areas with the most direct path between the drywell and wetwell e large and medium breaks with the largest potential debris-to-insulation ratio by weight The URG reiterates guidance from RG 1.82, Rev. 2 guidance; however, it also includes the following provisions: e Plants licensed in accordance with the NRC's Standard Review Plan (SRP) and Branch Technical Position (BTP) MEB 3-1 need not analyze all of the identified break locations. Instead, such plants may evaluate only those breaks that are most likely to occur. e Other plants may use the guidance from RG 1.82, or other guidance consistent with Title 10, Section 50.46, of the Code of Federa/ Regulations (10 CFR 50.46). However, licensees should exercise care to differentiate between pipe break locations used for ECCS evaluation and those that are in the plant's licensing bases. ES-1 1

l l 1 e Plants employing alternate strainer designs (i.e., strainers with large surface areas and cavities l to accommodate considerable quantities of debris without significant increase in head loss) need not analyze large and medium breaks with the largest potential debris-to-insulation ratio by weight. After reviewing the URG, the staff reached the following conclusions: e RG 1.82, Revision 2, provides the complete spectrum of breaks that should be analyzed to meet the intent of 10 CFR 50.46. The staff considers SRP Section 3.6.2 and BTP MEB 3-1 to be inappropriate for demonstrating compliance with 10 CFR 50.46. e Licensees may screen out large breaks with the highest particulate-to-fiber debris ratio by weight and MLOCAs in performing their plant-specific analyses,if their resolution includes both of the following:

1) Installation of a strainer similar to the stacked disk number 2, star strainer, or another geometrically similar strainer with deep crevices.

2) The licensee has adequate assurance from the strainer vendor that the screened out i breaks would not be more limiting in terms of head loss across the strainer. The vendor should have adequate test data to support screening of these breaks.

ES.2 Generation of Insulation Debris by a Postulated Break Postulated breaks in the primary piping would destroy insulation located in the region closely surrounding the separated broken ends because of the combined effects of blast wave and jet impingement. This zone of influence (ZOl) over which the destruction occurs strongly depends on the type of insulation and mode of encapsulation. In addition, the ZOI depends on the type of break (i.e., main steamline break, recirculationline break or feedwaterline break) as well as other l considerations, such as the extent of axial and radial separation of the broken ends.

URG Section 3.2.1.2, " Zone of influence" discusses the BWROG guidance related to mapping a I

ZOI around a postulated break location. The BWROG developed that guidance using experimente l data obtained from airjet impact testing (AJIT) and the results of the associated computationalfluid ' l dynamics (CFD) modeling. Specifically, the URG identifies four options (or methods) for determining the ZOI over which insulation would be damaged, although not all of the damaged insulation is in a readily transportable form. These methods are as follows: I L e Method 1 assumes that ZOI encompasses the entire drywell, and thus, all of the insulation l contained in the drywell would be damaged by the postulated break.

 . e Method 2 defines the following procedure for determining the zone of influence:

1) Assume that the break is a double-ended guillotine break (DEGB) with full separation resulting in continuous blowdown from both ends.

2) Determine the lowest dynamic pressure at which destruction would begin to occur for each

          , insulation material of interest. Estimate these destruction pressures after scaling the AJIT-measured values to the plant and taking into account that destruction pressure is inversely proportional to the target pipe diameter.
     - 3) For each insulation type, determine the ZOI by calculating the spatial volume enveloped by i            a specific damage pressure of interest for a jet expanding in free space, and mapping a ES-2 l

spherical zone of equal volume surrounding the break. The radius of the spherical zone is largest for the weakest insulation (i.e., lowest destruction pressure).

        ' 4) The ZOI for Method 2 is the largest volume sphere resulting from this analysis.

5) Determine the most limiting quantities of damaged debris by placing the ZOI at different locations in the drywell and estimating the volume of each type of insulation debris damaged by the jet. >

e Method 3 is similar to Method 2, except for the following differences:

1) Method 3 allows the licensee to take credit for break restraints and evaluate axial and radial offsets consistent with those restraints.

2) Method 3 allows the licensee to take credit for single-ended blowdown (e.g., steamline l break) i

3) Method 3 also allows the licensee to map different ZOls for different insulation materials.

e Method 4 allows the user to directly employ the results of CFD analyses in conjunction with } AJIT data to map the ZOI. However, the URG did not provide specific guidance regarding how j to apply the CFD tools. The staff has conducted several independent analyses to assess if the URG guidance is i appropriate and bounding. On the basis of these analyses, the staff concludes that Method 1 is clearly a bounding and conservative method for evaluating the 201 since it encompasses the entire drywell, and, therefore, bounds the amount of insulation debris that may be generated by the break. Method 2 uses the destruction pressure (P.), or the pressure at which destruction of insulation i I first occurs, to define a spherical ZOI around a given break. The staff believes that the spherical ZOls developed using Method 2 would be sufficiently large to envelop the entire zone over which destruction would actually. occur. This method is sufficiently conservative and, therefore, is l considered acceptable for use on insulations with low P values, However, for insulations with  ! high P. values, the staff recommends that licensees develop the ZOI on the basis of the " target area averaged pressures" (TAAP) instead of jet-center-line pressures. In addition, the staff  ; i believes that the spherical ZOI developed using Method 3 is acceptable, with the same comments presented for Method 2. The staff has concluded that the BWROG's basis for using the jet .. centerline pressure as the insulationt characteristic damage pressure (i.e., P.) is inadequately supported by analysis or data. The staff's review of the data and independent CFD calculations l lead to the conclusion that incipience of damage is more accurately characterized by TAAP or total l - I jet impingement load rather than local maximum pressure. However, because of the limited l number of insulations affected by this concem, the staff believes that this concem should be  ; addressed on a plant-specific basis. l I l The staff notes that the URG does not provide guidance regarding the types of analyses that licensees must undertake to determine the extent of axial and radial separations of the broken

   ; ends. Licensees desiring to take credit for limited separation of the broken ends due to pipe restraintsor single-ended blowdown should conduct supporting analyses. The staff expects that            e
   . these supporting analyses will be retained for possible future inspection.                              l Section 3.2.1.2 of the URG does not provide detailed guidance regarding Method 4. Therefore, the staff cannot accept Method 4 at this time. Licensees intending to use Method 4 should address        .

the staff's concems including validatation of the selected CFD code. l s ES-3 f i l e a a m ,a-=e . - * ->. -

ES.3 Other Sources of Drywell Debris

The URG provides guidance that individual utilities can use to identify other sources of debris in the drywell and to estimate the quantities of such debris that should be used in the ECCS strainer analysis. The URG also identifies the following other sources of debris

e Dirt / Dust: The URG suggests that licensees assume 150 lbm of dust / dirt for estimating the strainer head loss. This estimate is based on engineering judgement. e Other Transient Debris: The URG does not provide a specific value. Individual utilities should use their best judgement. e Rust from Unnainted Steel Surfaces: The URG recommends a value of 50 lbm on the basis of engineering judgement. e Particulate Debns The URG does not provide a specific value. Individual utilities should use their best judgement. e Paints /Coatinas: The URG recommends values of 47 lbm for inorganic zine coatings,85 lbm for inorganic zine top-coated with epoxy, and 71 lbm for 100% epoxy coating. These estimates are predicated on a study conducted by Bechtel Power Corporation. e Concrete- The URG does not provide a specificvalue. Individual utilities should use their best judgement. 'e Unaualified/ Indeterminate Paint /Coatinos: The URG does not provide a specific yaiue. Individual utilities should use their best judgement. As an alternative, the URG notes that licensees may remove the unqualified or indeterminate coatings, or attempt to qualify them through in situ qualification. The URG does not provide guidance regarding how licensees

   - should accomplish in situ qualification.

In addition, the URG cautions users that their foreign material exclusion (FME), housekeeping, and inspection programs must be adequate to ensure that the quantities of each of these types of , debris will not exceed the quantities assumed in the evaluation of ECCS strainer loading.  ! The staff compared the URG recommended values with the estimates previously developed as part I of the NRC sponsored study of a reference BWR 4 with a Mark I containment. The study was conducted by Science and Engincaring Associates, Inc. and the results are provided in NUREG/CR-6224, " Parametric Study of the Potential for BWR ECCS Strainer Blockage Due to LOCA Generated Debris," dated October 1995 (Reference 31). On the basis of this comparison, the staff found that most of the values suggested in the URG are about f.he same or larger than the corresponding NUREG/CR-6224 values. As a result, the staff cone:udes that use of the URG l values is acceptable; however, the staff notes that the NUREGICR-6224 study was conducted on  ! a reference Mark l containment. Because of the differences in plant design (e.g., size of , containment, NPSH margin, and so forth), the staff believes that some individual licensees may j wish to evaluate the applicabilityof the recommendationsof this section for their specific plant. The staff provided some suggestions on estimating the sources of dirt, dust and rust in the containment, i as well as paints /coatingsfor plants with unqualified or indeterminate coatings. These suggestions by the staff were provided for informationalpurposes and are not considered a requirementfor use of the URG suggested values. The staff notes that ti le sensitivity of the head loss calculations to these numbers may vary with the assumptions and the resolution option selected by each licensee. If the licensee is installing ES-4

a large passive strainer which is designed with very conservative assumptions relative to the . quantities of fibrous debris and sludge assumed to reach the strainer surface, the licensee may be able to demonstrate (by sensitivity analysis) that variations in the quantities of dirt, dust, rust flakes, etc. may not significantly affect the overall head loss across the strainer. If, however, the licensee attempts to justify their current strainer or to use assumptions that are as " realistic" as possible, the significance of the values determined in accordance with Section 3.2.2 of the URG escalates significantly. Consistent with the staff s guidance (discussed above), some licensees may also wish to evaluate the applicabilityof the conclusions of the Bechtel coatings report to their plant. Most importantly, the staff concludes that licensees should be cautioned to carefully evaluate the potential impact of unqualified and indeterminatecoatings on ECCS suction strainer head loss. If available, licensees are encouragedto use test data to supporttheir evaluation of coatings. It is the understanding of the staff that the BWROG is currently conducting a test program designed to evaluate the potential for coatings to become debris and transport to the suppression pool. However, if in doubt, assuming that.these coatings reach the strainer surface would clearly be the conservative measure. This would reduce the licensees' risk relative to the coatings issue, and could lead to additional margin in the strainer design if URG statements minimizing the potential impact of unqualified or indeterminate protective coatings are supported by the results of the staffs coatings review. ES.4 . Transport of Drywell Debris to the Suppression Pool Insulation debris is generated in the drywell and then transported to the suppression pool by the

  - reactor vessel blowdown and the various mechanisms that can wash debris down to the suppression pool. 'The guidance provided in RG 1.82, Revision 2, requires licensees to assume that all debris would be transported to the suppression pool.

Section 3.2.3 of the URG, entitled, "Drywell Debris Transport," documents BWROG guidance regarding various options for estimating the fraction of the damaged insulation (generated in the drywell) that will be transported to the suppression pool as a result of these mechanisms. The basis for the URG guidance for fibrous insulation is the following research conducted by the BWROG: e The damaged insulation was assumed to fall into three categories, including " fines", "large pieces," and " blankets." For each insulation, the BWROG used the AJIT data to derive the relative fractions of the insulation destroyed into each of these size categories (i.e., the size distribution factors). Specifically, the BWROG calculated these fractions as integral values avnraged over the entire ZOI. e The BWROG then estimated the fraction of the mass of " fines" that would be transported as

          .a result of blowdown and washdown following a main steamline break or a recirculation line break. These estimates are predicated on the results of small-scale testing undertaken by the BWROG. As a result, the URG recommends values of 1.0 for Mark I and Mark til containments. For Mark 11 containments, however, this fraction is 0.5 for steamline breaks and 0.56 recirculation line breaks.

e The BWROG identified floor gratings as the major locations for capture of "large pieces" and

            " blankets." On the basis of engineeringjudgment,the URG concludesthat 6.25% of the debris ES-5

i generated above the lowest grating would be transported to the suppression pool. The URG l also concludes that 78% of all debris generated below the lowest floor grating would be

transported to the suppression pool.

! l The URG provides similar guidance related to the transport of debris from reflective metallic insulation (RMI). Specifically, the URG divides the RMI debris into "small pieces (<6.0 in2) ", "large 2 i foils (>6.0 in )" and " intact assemblies." The BWROG again used AJIT data to derive the integrated size distribution fractions for the ZOI for each type of RMI On the basis of small scale transport testing, the URG guides licensees to assume that all of the small pieces would be transported to {

              . the suppression poolin Mark I and ill containments. For a Mark 11 containment, only 10% of the j               small pieces would be transported to the suppression pool in the event of a steamline break, while                   ,

l 5% would be transported in the event of a recirculation line break. ' i i The staff has previously communicated several concerns related to scaling small-scale transport test data to BWR conditions. In addition, the staff conducted a series of experiments to verify the j accuracy of guidance provided in the URG. The staff shared these results with the BWROG and ! individual utilities at appropriate forums. On the basis of these studies the staff reached the following conclusions:. l

• The URG guidance is non conservative for Mark 11 containments. The URG gives fractions for i j fine fibrous debris transport and RMI debris transport in Mark I and Mark lli containments, l assuming that 100% of the fine debris will transport to the suppression pool. The staff .

!~ concludes that the same transport factors should be used for Mark 11 containments. { 1 e For other containments, the URG guidance would yield conservative estimates for transport i

fractions.

ES.5 Suppression Pool Debris

! The focus of Section 3.2.4 of the URG, entitled " Suppression Pool Debris,"is on sources of debris  ;

!              which are present in the suppression pool before the occurrence of a LOCA. Both transient debris                    ;

]' and sludge are potentially present in the suppression pool at any given time. This section_of the 1 URG also reviews the LOCA-generated debris and transient debris, both of which were discussed { in earlier sections of the URG. The guidance was developed,in part, on the basis of an extensive BWROG survey of suppression pools of selected operating BWRs in the United States (Refs. 54 and 55). i ! The staff finds no deficiencies in the recommendations documented in the URG. The staff E reiterates the importance of the FME program to minimize the quantity of other potential debris. ES.6 Suppression Pool Transport The staff has extensively considered the transport of debris within the suppression pool. As part of NUREG/CR-6224 study Alden Research Laboratory conducted NRC-sponsored experiments to explore the transport of fibrous and RMI debris when subjected to chugging and post-chugging periods following a LOCA. The BWROG primarily relied on these experiments to develop the guidance documented in Section 3.2.5 of the URG, entitled " Suppression Pool Transport." ES-6 i

T

             ' The URG recommends that licensees not take credit for settling of debris in the pool during the high-energyphase of an accident during which the suppression pool undergoes thorough mixing.

The URG also recommends that licensees assume that all suppression pool debris will be resuspended during this phase. Finally, the URG gives the individuallicensees the option to l assume that there will.be no settling of debris in the pool even after the high-energy phase i terminates and the pool retums to quiescent conditions, or to determine settling rates using the methods described in Appendix B to NUREG/CR-6224. i The staff finds no deficiencies in the recommendations documented in the URG. However, the staff notes that Appendix B to NUREG/CR-6224 provides the required data only for selected types of insulation and particulates. Licensees using the methods descCbed in Appendix B to NUREG/CR-6224 for other types of insulation debris should be cautious about extrapolating the experimental data and models. ES.7 Head Loss Across the Strainer The BWROG devoted considerable resources to explore various generic designs for large passive strainers that can be used to replace the existing truncated cone strainers. The four designs , included are the 20-point star strainer, small stacked disk strainer,60-point star strainer, and large stacked. disk strainer. For each design, the BWROG obtained head loss data for various  ! combinations of fibrous insulation debris, sludge, recipe (paints + concrete chips), and RMI debris. The general characteristics (size, shape, etc.) of the debris used are consirtent with those used in the NUREG/CR-6224 study. The reader should also note that the NUREG/CR-6224 study selected these characteristes to maximize the resulting head loss. On the basis of the test data, the BWROG developed two correlational methods that can be used to estimate head loss across the strainers. The first method provides a non-dimensional head loss correlation that can be used to estimate l head loss across an alternate strainer design. The URG specified that this correlation is valid for - lower debris loadings. For higher debris loadings, the correlation is not applicable, and the URG recommends that licensees conduct strainer-specific testing. The second method provides a six-step process for estimating the strainer's RMI capacity and head loss across RMI debris beds. This method recognizes that RMI beds on strainers reach a saturati onthickness beyond which flow-induced drag forces are not large enough to retain the RMI pieces on the strainer surface. The URG specified this saturation thickness as a function of the type of RMI debris, and provided a correlation to estimate head loss across the RMI debris beds. [ For mixed beds (i.e., RMl+ fiber + particulate) the URG suggests that RMI does not contribute additionalhead loss in combination with other types of debris, and that it may actually reduce the head loss. On that basis, the URG states that head loss for mixed beds can be evaluated by ignoring RMI altogether and estimating the head loss resulting from other debris. The staff conducted several confirmatory calculations to validate the calculational procedutes provided in the URG and to examine the applicability of the calculational procedures to the actual , plant conditions. The staff has since shared the results of these analyses with the BWROG. On the basis of these analyses, the staff finds that the head loss correlation in the URG is unreliable ES-7 i

l l and incomplete for plant analyses and, therefore,is unacceptable. The staff strongly recommends that utilities use vendor-provided data to qualify strainer designs, rather than relying on the correlationsand calculationalproceduresspecifiedin the URG. In addition,the staff recommends that licensees' designs should be able to accommodate experimentaluncertainties associated with correlations and/or calculational methods developed by the vendors. The staff concludes that the BWROG generalized statement regarding the head loss of a fiber plus corrosion product debris bed bounding the head loss of a fiber, corrosion product and RMI debris , bed does not hold true in all situations. On the basis of the staff's analysis, the staff believes this issue should be resolved on a plant-specific basis. Licensees should ensure that their strainer vendor reviews the debris combinations of interest for their plant and ensures that the vendor data supports the head loss used in their plant-specific analysis. ES,8 Estimation of Available NPSH for ECCS Pumps Section 3.2.6 of the URG provides the BWROG guidance related to evaluating ECCS pump NPSH. The important points of this guidance are as follows: , e Licensees should not take credit for containment overpressure greater than atmospheric pressure in determining available NPSH, unless such credit is in conformance with the plant's existing licensing basis. e When evaluating available NPSH, licensees should consider a range of expected fluid temperatures unless the plant's licensing basis specifies the maximum expected fluid temperature. If specified, this temperature should be used unless plant's licensing basis is changed. The fluid temperature could affect both the avai.Y ble NPSH margin and the head loss across the strainer. e All strainers can be expected to be clean at the start of the postulated LOCA. It is not necessary to assume pre-existing blockage. e if ECCS blockage analysis uses reduced ECCS flow through the strainers in order to m.3et NPSH requirements, licensees should exercise care to ensure that changes in ECCS flow rat 0s are consistent with inputs and assumptions used in the evaluation model required by 10 CFR 50.46 to calculate ECCS cooling performance. Also, licensees should ensure that appropriate operating and emergency procedures are in place. e Licensees should carefully evaluate the applicability of head loss correlations before applying such correlations to estimate head loss across the strainers. e The ECCS strainer design should be consistent with the plant's limiting single-fai'ure assumptions. The staff finds no deficiencies in the recommendations presented in the URG. Licensees are strongly encouraged to design strainers with performance characteristics that increase the NPSH margin above the minimum required. Also, the reader should note that the staff is evaluating calculation of NPSH and plant licensing bases as part of its review of Generic Letter (GL) 97-04,

             " Assurance of Sufficient Net Positive Suction Head for Emergency Core Cooling and Containment Heat Removal Pumps."

ES-8

l ES.9 Other issues Section 3.1.3.4 of the URG discusses the nine " resolution options" available to licensees. f However, the staff notes that many of the " resolution options" are partial solutions which would still l likely require strainer replacement by the licensee. Specifically, Section 3.1.3.4 of the URG discusses the following resolution options: e "Further Refinement of Fixed Debris Source Terms " This option is simply a more detailed analysis of the containmentfor calculating the amount of debris that could reach the strainers in order to reduce the debris source term for sizing of the strainers, e " Replacement of Existing Strainers with Passive Strainers of Alternate Designs." This option would replace existing strainers with designs which have substantiallylower head loss with high debris loadings. Examples include the stacked disk and star strainer designs. e " Installation of Jacketing to Reduce the insulation Debris Source Term." This option would seek to minimize the amount of debris generated during an accident by covering it with a protective jacketing and/or banding. o "Reductionin Transient Debris Source Terms." This option would reduce debris source terms such as foreign material. To justify the reduction in transient debris, licensees may need to implement additional FME or housekeeping controls, or higher suppression pool cleaning frequency. e " Change Existing Licensing Basis." Examples of potentiallicensing basis changes include the use of a more realistic decay heat curve in lieu of the conservative curve used in the original licensing basis (i.e., American Nuclear Society (ANS) 5.1 versus May-Witt) and credit for containment overpressure in calculating available NPSH. Use of realistic decay heat curves would increase NPSH margin by reducing the calculated suppression pool temperatures following a LOCA. The BWROG does not recommend taking credit for containment overpressure for the calculation of NPSH margin.

          . ." Reanalysis of ECCS Suction Line Penetration Loads." It is recommended that this be done without reopening the licensing basis for containmentloads. This option seeks to maximize the size of the strainerthat can be put in the suppression pool by minimizing the structural impact of that strainer on the piping penetration to which it is connected. The URG does not provide any guidance on how licensees can accomplish this option. .Moreover, the BWROG does not recommend reopening the licensing basis for containment loads.

e " Partial Replacement of Fibrous insulation with RMI." Since RMI debris is less detrimental to strainer head loss than fibrous debris, this option seeks to minimize the amount of fibrous debris that may be generated during an accident. e "Use of a Strainer Backflush System." Should an ECCS suction strainer clog, this option would provide a method to clean the strainer by reversing water flow through the strainer. e " Installation of Self-Cleaning Strainers." This option would eliminate the need for detailed plant analysis by installing a strainer which would continually clean itself, effectively preventing clogging and subsequent loss of NPSH. The staffs has the following concems with these re olution options: e ' in discussing the resolution option on " Installation of Jacketing to Reduce the Insulation Debris Source Term" the URG states that, " Additional details on the use of jacketing is provided in Section 3.2.1." However, Section 3.2.1 does not provide guidance with regard to the types of ES-9 i

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1 bands to be used, construction of the bands, or instructions for mounting. In addition, the characterization of the effectiveness of insulation jacketing in this section is inconsistent with the AJIT test report. That report states "In the case of fibrous insulation materials, the use of jacketing as a means of reducing debris generation does not appear to be effective without the use of an additional banding material which better secures the jacketing to the insulation assembly and the pipe." Without further detailed information on how to apply this option, the benefits achieved, and the technical basis supporting the use of this measure, the staff is unable to determine the acceptability of this option.

• In discussing the resolution option on " Reduction in Transient Debris Source Terms," the URG discusses the crediting FME and housekeeping programs as a justification for reducing the amounts of transient debris assumed in a plant analysis. The staff has two concerns related to incorporatingthis option into a licensee's final resolution. First, if a licensee selects too low an amount of transient debris in their analysis, the potential exists for operability concems to be raised every time debris is found in the drywell, suppression pool, or wetwell. Second, if a licensee is considering increasing the amount of transient debris in sizing the new strainer, the staff believes that housekeeping or FME controls are not a substitute for periodic inspection and cleaning of the strainers or suppression pool. Given the numerous events reported over the last few years involving FME-related issues, the industry has not demonstrated that FME controls alone are effective in ensuring that materials are not left in the drywell, wetwell, or suppression pool. As such, the staff believes that licensees should conduct regularinspections of the suppression pool and ECCS suction strainers, and cleanings when necessary, during every refueling outage until ik,ensees demonstrate over time the ability to control foreign materials. The staff be!% irs it is more prudent to add margin when sizing strainers to account for the uncertainty ;n the effectiveness of housekeeping controls. This, in tum, will minimize the need for operability assessmentswhen small amounts of foreign material are found in the containment or suppression pool.

e The URG notas that part of a licensee's resolution to the strainer clogging issue could include a licensing basis change. The URG cites an example in which a licensee may wish to use a more realistic decay heat curve to reduce the calculated post-LOCA suppression pool temperatures. Specifically,the URG states that use of credit for containment overpressure is not recommended. The staff concurs that additional containment overpressure (other than an amount already approved by the staff for the existing licensing basis) should not be ueed as part of the resolution of this issue.

• The URG also discusses the potentialto reanalyze suction line penetrationloads. Specificaly, the URG states that it "may be possible to further increase the size of the attemate strainer design by reanalyzing ECCS suction penetration loads and suppression pool structural loads using more sophisticated techniques or by reducing conservatism in current design-basis calculations, but without reopening the licensing basis for containment loads." The staff has concems regarding this statement. Specifically,the hydrodynamicload programs for the Mark I, Mark ll, an't Niark lli programs were very specific in providing generic methodologies for calculating hydrodynamicloads. Each plant submitted a plant unique analysis report (PUAR) which provided the specific details of each plant's calculated hydrodynamicloads, including the methodology and coefficients used, etc. The approved methodologies had their basis in test data. The staff cautions licensees with regard to changing hydrodynamic load calculations without testing to demonstrate the validity of the revised calculations.

e The URG discusses the option of reducing the fibrous debris source term in the drywell by partially replacing fibrous insulation with RMI. The staff agrees that this is an appropriate option ES-10

for reducing the amount of fibrous debris which can be transported to the suppression pool; however, when using this option for a selected break, the licensee should reassess other breaks to ensure that the licensee has not changed which break is the most limiting in terms ! of NPSH margin. In addition,the licensee must now consider head loss in terms of combined l . fibrous /RMI debris beds. Although NRC Bulletin 96-03 allows the use of self-cleaning strainer designs as a resolution option, the BWROG recommends that licensees use a self-cleaning strainer only if resolution with a passive straineris not viable. The URG cites several concerns regarding the use of self-cleaning strainerdesigns. The staff finds that the URG provides comprehensive guidance on concerns to be addressed with an active strainer design. The staff notes no significant deficienciesin its review of this guidance. However, because of the concerns cited by the BWROG in the URG relative to the self-cleaning strainer, any licensee wishing to use an active strainer design as a resolution option should address the concerns stated in the URG. Although NRC Bulletin 96-03 allows backflushing as a potential resolution option, the BWROG recommends against use of the strainer backflush systems as a primary means of resolving the ECCS suction strainer clogging issue. The basic concern expressed by the BWROG is that backflushing will be needed early and frequently during the first 30 to 60 minutes of an accident. The BWROG considers backflushing more viable as a defense-in-depth measure only. Because of the reliance on operator action and mechanical systems, the staff concurs with the BWROG that backflushing is more effective as a defense-in-depth measure only. Section 3.3 of the URG provides guidance on the types of considerations a utility should address if designing a backflush system either as a primary means of mitigating an accident or as defense-in-depth measure only. The staff did not note any significant deficiencies in its review of this section. 1 ES-11

SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO NRC BULLETIN 96-03, BOILING WATER REACTOR OWNERS GROUP TOPICAL REPORT NEDO-32686,

       " UTILITY RESOLUTION GUIDANCE FOR ECCS SUCTION STRAINER BLOCKAGE" (DOCKET NO. PROJ0691)

1.0 INTRODUCTION

By letter dated November 20,1996, the Boiling Water Reactor Owners Group (BWROG) submitted for review by the U.S. Nuclear Regulatory Commission (NRC, the staff) a document entitled NEDO-32686, " Utility Resolution Guidance for ECCS Suction Strainer Blockage"(also known as the URG) (Ref 1) along with related technicalsupport documentation (Ref 2). Then, on November 25,1996, the BWROG submitted to the staff a facsimile containing additional information regarding the URG drywell transport methodology (Ref. 3). The purpose of the URG is to give boiling-water reactor (BWR) licensees guidance for complying with the requested achons of NRC Bulletin (NRCB) 96-03,

 " Potential Plugging of Emergency Core Cooling Suction Strainers by Debris"(Ref. 4). In particular, the URG focuses on providing detailed guidance for performing plant-specific analyses consistent with Regulatory Guide (RG) 1.82, Revision 2, " Water Sources for Long-Term Recirculation Cooling Following a Loss-of-CoolantAccident"(Ref. 5). NRCB 96-03 and RG 1.82, Revision 2, were issued by the staff to resolve a safety issue regarding the potentialfor clogging of emergency core cooling system (ECCS) suction strainers by debris during a loss-of-coolant accident (LOCA).

Prior to its submittalof November 20,1996, the BWROG had submitted eight draft sections of the URG in order to facilitate the staff's review of the final document. Specifically, the BWROG submitted four sections on March 31,1996 (Ref. 6), and four more on May 28,19PS (Ref. 7). By letters dated July 25,1996 (Ref. 8), and August 20,1996 (Ref. 9), the staff transmitted comments regarding the draft URG sections to the BWROG. The staff also discussed those comments with the BWROG in a meeting on August 19,1996. The results of the meeting are described in a meeting summary dated September 4,1996 (Ref.10). In addition, by facsimile dated December 23,1996, the staff transmitted a request for additional information (RAI) on the final URG to the BWROG (Ref.11). On January 13,1997, the BWROG provided the staff with survey results showing how many utilities intended to use the various options provided in the URG (Ref.12). The BWROG then provided their response to the staff's RAI on January 30,1997 (Ref.13). Additional supporting documentationwas provided to the staff by the BWROG in a letter September 19,1997 (Ref. 62). Before reviewing the URG, the staff closely followed the generic effort conducted by the BWROG l to resolve the issue regarding strainer clogging in the ECCS of BWRs. Throughoutthat monitoring, the staff continuously provided the BWROG with feedback. Then, in a letter dated June 13,1994 (Ref.14), the staff identified its initial concerns about the resolution being developed by the 1 l

            ' BWP,0G. The BWROG then began conducting testing to support their generic effort, and on August 9,1994, the BWROG forwarded to the staff a facsimile presenting a draft plan for testing the performance of alternate strainer designs (Ref.15). The staff responded with a letter dated September 12,1994, (Ref.16) containing comments on the proposed test program. By letter dated March 15,1995 (Ref.17), the BWROG submitted their final test plan to the staff. In RAI letters dated June 22,1995 (Ref.18), August 21,1995 (Ref.19) and April 22,1996 (Ref. 20), the staff identifiedits concems regarding the test program and the application of the test results. The staff transmitted additional concerns to the BWROG s 'a facsimile dated August 14,1995 (Ref. 21). The BWROG provided a written response to the RAI dated June 22,1995 by letter dated July 17,1995 (Ref. 22), and to the RAI from April 22,1996 by letter dateo Juiy 0,1996 (Ref. 23). The BWROG did not formally respond to the staff concerns from the RAI dated August 21,1995, although the staff concernswere discussedin meetings on May 31,1995; September 28-29,1995; April 4,1996; July 9-11,1996; and August 19,1996 (see meeting summaries and trip reports dated June 13,1995 (Ref. 24); October 6,1995 (Ref. 25); April 16,1996 (Ref. 26); July 25,1996 (Ref. 27); and September 4,1996 (Ref.10)). The BWROG also provided copies of their proposed test matrices in facsimiles dated June 23,1995 (Ref. 28), and June 30,1995 (Ref. 29).

In a letter dated December 31,1997, the staff issued a draft safety evaluation report (SER) on the URG to the BWROG (Ref. 63). The draft SER identified several areas where the staff did not agree with the conclusions stated in the URG (referred to as open issues in the staff's letter). It was requested that the BWROG review the draft SER and provide the staff with its response to any open issues identified in the draft SER. By letter dated March 13,1998, the BWROG provided its response to the draft SER (Ref. 64). Appendix L to this SER provides the BWROG's comments and the staff's resolution of those comments. The staff has since completed its review of the URG, the supporting documertation, the BWROG's comments and all relevant documents, and its conclusions are documented in this SER. In general, the staff found that portions of the URG are acceptable for use in conducting plant-specificanalyses to estimate combined debris loadings for sizing of ECCS suction strainers. However,the staff found that several portions of the URG are not acceptable because the methods lack sufficient guidance, supporting data, or analysis to justify their technical basis. This SER discusses each section of the URG, along with the basis for the staff's conclusions. Licensees desiring to use the portions of the URG not accepted by the staff should addressthe staff's concerns cited herein. In addition,the staff believes that several portions of the URG need additional clarification to minimize the potential for misinterpretation of the information provided. The staff has stated its position regarding these portions of the URG in the associated section of this SER. The staff closely reviewed the materials contained in the references cited above, as well as other pertinent references. In addition, the staff conducted independent confirmatory analyses to identify inadequaciesin the generic guidance provided in the URG, as well as inaccurate or unsubstantiated assumptions used to develop the stated guidance. This SER is intended to address each part of a plant-specific analysis. For this reason, the SER includes sections on each of the following topics: e' resolution options (Section 3.1) e pipe break locations (Section 3.2.1.1) 2

e debris generation /ZO! (Section 3.2.1.2) e. e other drywell debris sources (Section 3.2.2) e drywell debris transport (Section 3.2.3) e suppression pool debris (Section 3.2.4) e suppression pool transport and settling (Section 3.2.5) e net positive suction head (NPSH) including strainer head loss (Section 3.2.6) e backflush (Section 3.3) e self-cleaning strainers (Section 3.4) e conservatism (Section 5.0) o: general /overall URG comments These sections are also consistent with the sections of the URG on the same topics. In addition, Appendices A through K to this SER summarize the results of the confirmatory analyses performed j by the staff.

1.1 BACKGROUND

On July 28,1992, an event occurred at Barsebeck Unit 2, a Swedish BWR, which involved the  ; plugging of two containment vessel spray system (CVSS) suction strainers. The strainers were ' l plugged by mineral wool insulation that had been dislodged by steam from a pilot-operated relief valve that spuriously opened while the reactor was at 3100 kPa (435 psig]. Two of the three strainers on the suction side of the CVSS pumps that were in se'vice became partially plugged with mineralwool. Following an indication of high differential pressure across both suction strainers,70 minutes into the event, the operators shut down the CVSS pumps and backflushed the strainers. The Barsebeck event demonstrated that the potential exists for a pipe break to generate insulation debris and transport a sufficient amount of the debris to the suppression pool to clog the ECCS strainers. Similarly, on January 16 and April 14,'1993, two events involving the clogging of ECCS strainers occurred at the Perry Nuclear Power Plant, a domestic BWR. In the first Perry event, the suction strainers for the residual heat removal (RHR) pumps became clogged by debris in the suppression pool. The second Perry event involved the deposition of filter fibers on these strainers. The debris consisted of glass fibers from temporary drywell cooling unit filters that had been inadvertently dropped into the suppression pool, and corrosion products that had been filtered from the pool by the glass fibers which accumulated on the surfaces of the strainers. The Perry events demonstrated the deleterious effects on strainer pressure drop caused by the filtering of suppression pool particulates (corrosion products or " sludge") by fibrous materials adhering to the ECCS strainer l surfaces. This sludge is typically present in varying quantities in domestic BWRs, since it is ! generated.during normal operation. The amount of sludge present in the pool depends on the frequency of pool cleaning /desludgingconducted by the licensee. As a result, the BWROG and the NRC have conducted septerate test programs to quantify the sludge-related filtering effect. On the basis of these events, the NRC issued NRCB 93-02, " Debris Plugging of Emergency Core Cooling Suction Strainers" (NRCB 93-02), on May 11,1993 (Ref. 30). That bulletin requested licensees to remove from the containment fibrous air filters and other temporary sources of fibrous material,which were not designed to withstand a LOCA. In addition, NRCB 93-02 requested that i i 3 t

licensees take any immediate compensatory measures necessary to ensure the functional capability of the ECCS. Following these events, the staff performed calculations to assess the vulnerability of each domestic BWR. The results of these calculations showed that the potential existed for the ECCS pumps to lose NPSH margin as a result of clogging of the suction strainers by debris generated during a postulated LOCA. The staff then conducted a detailed study of a Reference BWR 4 plant with a Mark I containment. That study's results confirmed the results of the earlier staff calculations, and were published in NUREG/CR-6224, " Parametric Study of the Potential for BWR ECCS Strainer Blockage Due to LOCA Generated Debris," in October 1995 (Ref. 31). On January 26 and 27,1994, members of the NRC staff also attended a workshop in Stockholm, Sweden, which was sponsored by the Organisation for Economic Co-operation and Development / Nuclear Energy Agency (OECD/NEA), to discuss the Barsebeck event. At this workshop, representatives from other countries discussed actions taken or planned to prevent or mitigate the consequences of BWR strainer blockage. On the basis of the preliminary results of the staffs study, as reinforced by information learned at the OECD/NEA workshop, the staff issued NRCB 93-02, Supplement 1, " Debris Plugging of Emergency Core Cooling Suction Strainers," on February 18,1994 (Ref. 39). The purpose of this supplement was to request that BWR licensees take appropriateinterim actions to ensure the reliable operation of the ECCS following a LOCA so that the staff and industry would have sufficient time to develop a permanent resolution. In addition, the bulletin supplement apprised licensees of pressurized-waterreactors (PWRs) and BWRs of the latest information on the vulnerability of ECCS suction strainers in BWRs and containment sumps in PWRs to clogging during the recirculation phase of a LOCA. On September 11,1995 Limerick Unit 1 was being operated at 100-percent powe when control room personnel observed alarms and other indications that one safety relief valve (SRV) was open. The licensee implemented emergency proceduress Attempts by the reactor operators to close the valve were unsuccessful, and a manual reactor scram was initiated. Prior to the opening of the SRV, the licensee had been running the "A" loop of suppression pool cooling to remove heat being released into the pool by leaking SRVs. Shortly after the manual scram, and with the SRV still open, the "B" loop of suppression pool cooling was started. The reactor operators continued their attempts

                                                                                         ~

to close the SRV and reduce the cooldown rate of the reactor vessel. Approximately 30 minutes later, operators observed fluctuating motor current and flow on the "A" loop of suppression pool cooling Cavitationwas believed to be the cause, and the loop was secured. After it was checked, the "A" pump was successfully restarted and no further problems were observed. After the cooldown following the blowdown event, the licensee sent a diver into the Unit i suppression pool to inspect the condition of the strainers and the general cleanliness of the pool. The diver found that both suction strainers in the "A" loop of suppression pool cooling were found to be almost entirely covered with a thin " mat" of material, consisting mostly of fibers and sludge. The "B" loop suction strainers had a similar covering, but less of it. Analysis showed that the sludge primarily consisted ofiron oxides and the fibers were polymeric in nature. The source of the fibers was not positively identified, but the licensee has determined that the fibers did not originate within the suppression pool, and contained no trace of either fiberglass or asbestos. I I i l l

l l The Limerick event demonstrated the need to ensure adequate suppression pool cleanliness. In addition,it re-emphasized that materials other than fibrous insulation could also clog strainers. The staff notes that Perry's strainers were clogged by fibrous filter media. 1 In response to this event, the staff issued NRCB 95-02, " Unexpected Clogging of Residual Heat Removal (RHR) Pump Strainer While Operating in Suppression Pool Cooling Mode," on October 17,1995 (Ref. 40). The bulletin requested that licensees (1) assc 5s the operability of their ECCS l on the basis of the cleanliness of their suppression pool and ECCS strainers, (2) verify the  ! operabilityof the ECCS through an appropriate pump test and strainer inspection within 120 days from the date of the bulletin,(3) establish a pool cleaning program, (4) review their foreign material l exclusion (FME) practices and correct any identified weaknesses, and (5) implement any additional j l appropriate measures for ensuring the availability of the ECCS. Licensee responses to NRCB 93-02 and its supplement demonstrated that licensees had implemented appropriate interim measures to ensure adequate protection of public health and safety, and to allow continued operation until a final resolution to the strainer clogging issue could be achieved. NRCB 96-03 requested that licensees implement the final resolution to this issue. In responding to NRCB 93-02 and its supplement, licensees ensured that alternative water sources (both safety and nonsafety-related)to mitigate a strainer clogging event were available, emergency operating procedures (EOPs) provided adequate guidance for mitigating such an event, operators were adequately trained to recognize and mitigate a strainer clogging event, and loose and i temporary fibrous materials stored in containmentwere removed. Similarly, licensee responses to NRCB 95-02 showed that most licensees had recently cleaned their suppression pools, and that those who had not were scheduled to do so during the upcoming refueling outage. Moreover, a generic safety assessment conducted by the BWROG concluded that operators would have adequate time to use attemative water sources (25-35 minutes) after initial reflood of the reactor vessel. The staff also notes that the probability of the initiating event is low. For these reasons, the staff allowed BWR licensees to continue operation until they were able to fully implement their resolution to NRCB 96-03. Satisfactory resolution of NRCB 96-03 will ensure that the ECCS can perform its safety function and minirnize the need for operator action to mitigate a LOCA. The results of the staff study, documentedin NUREG/CR-6224, demonstrate that for the reference plant, there is a high probability that the available NPSH margin for the ECCS pumps will be i inadequate after a LOCA dislodges insulation and other debris which are then transported to the suction strainers. In addition, the study calculated that the loss of NPSH could occur less than 10 minutes into the event. The study also demonstrated that the adequacy of NPSH margin for an ECCS system is highly plant-specific because of the large variations in such plant characteristics as containmenttype, ECCS flow rates, insulation types, plant layout, plant cleantiness, and available l NPSH. l in addition, the Barsebeck event demonstrated that a pipe break can generate and transport l sufficient quantities of insulation and other debris to the suppression pool /ECCS strainers where l they can potentially cause the ECCS to lose NPSH. The Perry events further demonstrated that fibrous debris combined with corrosion products present in the suppression pool (sludge) can exacerbate the problem. This phenomenon was confirmed in the staff's study (described above). Alden Research Laboratory (ARL) in Holden, Massachusetts, further confirmed that the pressure drop across the strainer was greatly increased by the effect of fibrous debris on the strainer surface ^ 5 l l l l

  . - . . . - - - . - - - - . - - -                           . - . . - - . ~ - . - - - - - - -                      . -

i filtering sludge from the suppression pool water. The results of these tests are discussed in i

        ' NUREG/CR-6367, " Experimental Study of Head Loss and Filtration for LOCA Debris," dated December 1995 (Ref. 41). Additional NRC-sponsoredtesting conducted by ARL demonstrated that the energy conveyed to the suppression pool during the high-energy phase of a LOCA is sufficient to ensure that the fibrous debris and sludge are well mixed and evenly distributed in the suppression          ;

pool, and can remain suspended for a sufficiently long period to allow large quantities to be deposited onto the strainer surfaces. As a result, the staff has concluded that this problem is applicable to all domestic BWRs with pressure suppression types of containments. The basis for the staff's conclusionis as follows. There do not appear to be any features specific to a particular i plant, class of plants, or containment type that would mitigate or prevent the generation, transport to the suppression pool, or deposition on the ECCS strainers of sufficient material to clog the strainers, Parametric analyses performed in support of the NUREG/CR-6224 study, using parameterranges which bound most domestic BWRs, failed to identify parameter ranges that would prevent BWRs with other containment types from being susceptible to this problem. Notably, the , staff's study was conducted on a Mark I containment; Barsebeck, which is similar in design to a i Mark ll containment, experienced a strainer clogging event; and Perry, a Mark lli containment, also experienced a strainer clogging event. Title 10, Section 50.46 of the Code of Federal Regulations (10 CFR 50.46)(Ref. 42) requires that  ! licensees design their ECCS systems to meet five criteria, one of which is to provide long-term cooling capability following a successful system initiation for a sufficient duration so that the core , temperatureis maintained at an acceptablylow value and decay heat is removed for the extended period of time required by the long-lived radioactivity remaining in the core. The ECCS is designed  ; to meet this criterion, assuming the worst single failure. However, experience gained from operating  ; events and detailed analyses, as previously discussed, has demonstrated that excessive buildup i t of debris from thermal insulation, corrosion products, and other particulates on ECCS pump strainers is highly likely to occur. This creates the potential for a common-cause failure of the  ; ECCS, which could prevent the ECCS from providing long-term cooling following a LOCA. The staff has concluded, therefore, that licensees must resolve this issue in order to ensure compliance with , the regulations. RG 1.82, Revision 2, provides an acceptable method for ensuring compliance with 10 CFR 50.46. Thus, the BWROG wrote the URG to give licensees guidance for complying with  ; 10 CFR 50.46 in a manner consistent with the RG 1.82, Revision 2. Nonetheless,the staff recognizes that it is difficult to perform plant-specific analyses to resolve this (= issue because a substantialnumber of uncertainties are involved. Examples of these uncertainties  ! l i include the amount of debris generated by a pipe break for various types of insulation; the amount of debris transported to the suppression pool; the characteristics (e.g., size and shape) of debris  ! reaching the suppression pool; and head-loss correlations for various types of insulation combined with suppression pool corrosion products, paint chips, dirt, and other particulates. Many of these  ; uncertainties are plant-specific because of the differences in plant characteristics such as layout, insulation types, ECCS flow rates, containment types, cleanliness, and NPSH margin. l Consequently, testing and analyses were conducted by both the BWROG and the NRC to quantify l many of these uncertainties. . The staff closely followed the work of the BWROG to resolve this issue. The BWROG evaluated several potential solutions, and completed testing on three new strainer designs, including two passive strainer designs and one self-cleaning design. The BWROG effort was consistent with the 6

l options proposed in NRCB 96-03 for resolution of the potential ECCS strainer clogging issue. The BWROG then developed the URG to provide utilities with (1) guidance, including a calculational methodology, for plant-specific evaluation of the potential ECCS strainer clogging issue, (2) a standard, technically sound, industry approach for resolution of the issue, and (3) guidance that is .  ; consistent with the actions requested in NRCB 96-03 for demonstrating compliance with 10 CFR l 50.46. I Also, in NRCB 96-03, the staff noted that much of the effort and discussion on this issue has l focused on the threat caused by fibrous insulation. While the staff recognized that fibrous insulation represents the largest source of fibrous material in the containment, NRCB 96-03 reminded licenseesthat the events at both Perry and Limerickinvolved other sources of fibrous debris. Thus, j NRCB 96-03 cautioned licensees to focus their resolution for this issue on protecting the functional - capability of the ECCS from all potential strainer clogging mechanisms. ) l l l l I l 7 l l l

   ' 2.0      DISCUSSION The issue of potential strainer blockage is complex. Head loss across the suction strainers is a function not only of the amount of debris, but also of the types (e.g., fibrous insulation, paint, reflective metallicinsulation, dirt, corrosion products, etc.) and characteristics (size, shape, etc.) of the debris. This creates a challenge for the analyst to evaluate the worst case for potential strainer debris loadings. The analyst must a!so consider the potential for foreign material to be introduced during normal plant evolutions such as refueling and maintenance outages. In addition, the analyst must evaluate plant maintenance practices, including the maintenance of qualified coatings in the drywell and wetwell.

To simplify this process, RG 1.82, Revision 2, provided non-prescriptive guidance for performing a plant-specificanalysis (e.g., what should be considered, but not how to perform the calculations). To augment that guidance the BWROG developed the URG in order to give the individuallicensees additionaldetails on how to conduct the plant-specific analysis and provide a consistent response by the industry to NRCB 96-03. The URG is a comprehensive, but complex, document providing both general guidance conceming the various options available to resolve the issue, as well as detailed guidance for performing plant-specific analyses to estimate potential worst-case debris loadings on ECCS suction strainers during a LOCA. The document consists of one volume providing the analysis guidance (Ref.1) and three volumes of technical support documentation (Ref. 2). The technical support volumes include test reports and analyses that form the basis for the methodologies used to calculate strainer debris loadings and ECCS pump NPSH. Specifically, the URG provides methodologies for the following aspects of a plant-specific analysis: e estimating the amounts and types of debris that could be generated by a LOCA e estimating the amount of the debris that could be transported to the suppression pool L e estimating the amount of debris that could accumulate on the ECCS suction strainer surfaces e determining the head loss caused by the estimated debris accumulation e calculating the NPSH margin. Various plant-specific factors may affect the level of engineering effort and resources a given licensee may wish to devote to performing the analyses to ensure adequate sizing of its ECCS suction strainers. Flexibility in the generic guidance for performing these analyses is, therefore, desirable for licensees to accommodate the plant-specific design details affecting the necessary level of detail. For instance, some plants have more margin than others in the structural design for the ECCS suppression pool penetrations. When evaluating the loads (e.g., standard and l acceleration drag forces) that would be caused by bulk fluid motion across the strainer and its associated suction piping during a postulated transient or accident (i.e., hydrodynamic loads), a plant with more structuralmargin may be able to accommodate larger suction strainers without the significant structural modifications that a plant with a lesser margin might require. Therefore, the plant with more margin may opt to conduct a bounding analysis rather than expending engineering

   ~ resources in an unnecessarily detailed plant analysis, in order to give utilities this flexibility, the URG provides multiple methods for performing each part of the plant-specific analyses. This allows plants with more hydrodynamic load margin or more 8

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1 i l space for larger strainers in their suppression pool to use more conservative, or bounding, approaches which are less detailed and require less licensee resources to perform. Plants with less i margin or less space in the pool could opt for methodologieswhich result in lower calculated debris loadings, but require a higher level of licensee engineering effort. In providing flexibility, the BWROG opted not to link methodologies for calculating each part of a plant-specific analysis (e.g., a licensee may use Method 1 for estimating the amount of debris generated, but then use Method 3 for estimating the amount of debris transported from the drywell to the wetwell, etc.). Therefore, individual utilities have the flexibility to choose the methods they will use for each part of the analysis. This flexibility complicated the staff's review because it created 38 different ways a licensee could apply the URG guidance. Because of incomplete guidance and inadequate supporting documentation or analysis in several areas, the staff was unable to determine if all of the methodologies, or combinations of methodologies, were acceptable. To maximize efficiency of the review effort, the staff primarily focused on the guidance (or methods) that are reasonably well supported by data or analyses. Other methods, that lacked sufficient detail or technicaljustificationto permit staff review, were rejected. If individual licensees desire to use any portions of the URG (analytical or resolution options) that are rejected by the staff, they should resolve the staff's concems cited herein. l 1 I l l l 1 i 9 I

3.0 URG GUIDANCE FOR DEMONSTRATING COMPLIANCE WITH 10 CFR 50.46 in Sections 3.1 through 3.4 of the URG, the BWROG provides general guidance on plant "resolu"an options"and detailed guidance on plant-specific analysis methodologies. Section 3.1 provides an overview of the various resolution options available to licensees. Section 3.2 provides the detailed guidance on performing plant-specific analyses for sizing of passive ECCS suction strainers. Sections 3.3 and 3.4 provide additional detailed guidance on the two active resolution options which are specifically cited in NRCB 96-03 as potential ways to resolve the strainer clogging issue. 3.1 EVALUATION OF RESOLUTION OPTIONS This section of the URG gives utilities guidance for determining the level of detail they should use to analyze their plant and implement their resolution in response to NRCB 96-03. In this section, the BWROG also identifies key factors affecting the complexity and cost of evaluating strainer performance and implementing potential resolutions. This section also includes four flow diagrams (Figures 1 through 4), which display the process recommended by the BWROG for sizing ECCS suction strainers. Figure 1 provides an overview of the plant analysis process.- For plants that have more than a i minimal amount of fibrous insulation, the URG recommends that licensees size their strainers as large as possible without violating their penetration hydrodynamicload limits. Licensees should then evaluate the strainer performance with the calculated debris loading to ensure that it provides adequate performance for maintaining the ECCS pump NPSH margin. For plants with almost all reflective metallic insulation (RMI), Figure 1 provides two suggested methodologies:

1) Size the strainers on the basis of the head loss when the straineris loaded at the saturation level with RMI.

2) Size the strainer on the basis of E calculated expected debris loading.

For mostly RMI plants, Figure 1 does not recommend one sizing methodology over the other. L Figure 2 provides a flow diagram showing two methods for performing a plant evaluation to determine the amount of debris generated and transported to the suppression pool. (The diagram also referencesthe sections of the URG and RG 1.82, Revision 2, which relate to each step in the analysis). According to Figure 2, licensees would use the first method to specifically perform a detailed analysis of the zone of influence (ZOI) for a pipe break and to calculate the amount of insulation debris generated as a result. In parallel with this ZOI calculation, the analyst would evaluate non-insulation debris such as dirt, dust, rust, coatings, and so forth. These two calculatiors would then be input into the next part of the analysis shown in Figure 3. As an attemative to the detailed analysis, on Figure 2 shows a second method in which licensees would perform a simple bounding calculation assuming that all of the materials of interest are generated as debris and transported to the suppression pool. As with the first method shown in Figure 2, this method would provide the input into the next part of the analysis shown in Figure 3. Figure 3 provides the flow diagram for evaluating the amount of debris present in the suppression pool and calculating the total debris loading on the strainer, including the debris from the drywell. 10 l l

, The total debriu loading on the strainer then serves as one input to Figure 4, which illustrates the process for calculating the ECCS pump NPSH. Section 3.1 of the URG also gives additional guidance for estimating debris sources, establishing the current licensing basis, and evaluating resolution options. The URG categorizes debris sources as either fixed or transient. Specifically, fixed debris sources sre those which must be impacted by the LOCA break jet or blowdown forces to form debris that is transportable to the ECCS suction strainers. Examples of fixed debris sources include piping insulation and coatings. Transient debris sources are those which generally result from normal plant operations, and would be present in a transportableform prior to the postulated LOCA. Examples of transient debris sources include dirt, dust and any other loose materials present in the drywell or suppression chamber. Section 3.1 also points to some of the important licensing-basis assumptions that each utility must identify. These considerationsinclude containment overpressure and suppression pool temperatures assumed in the NPSH calculations, as well as pipe break locations. In addition, Section 3.1 includes an important recommendation,which is that licensees"should consider,if practicable, use of a strainer that results in acceptable ECCS pump NPSH without reliance on containment pressure." The staff notes that this statementis consistent with the recommendations of RG 1.1, " Net Positive Suction Head for Emergency Core Cooling and Containment Heat Removal System Pumps" (Ref. 57). In Section 3.1.2, the URG provides general guidance for plants with reflective metallic insulation (RMI). The BWROG notes that even plants with mostly RMI will have to demonstrate the adequacy of their strainers or implement an appropriate resolution. This statement reflects the results of testing which demonstrates that only a small amount of fiber combined with corrosion products can result in unacceptable head losses. The staff notes that the Perry and Limerick events also demonstrated this same conclusion. In Section 3.1.3, the URG provides guidance for plants with significant amounts of fibrous insulation in their containments. Specifically, the URG indicates that small amounts of fiber can lead to unacceptable head losses on ECCS systems employing the conical or cylindrical perforated plate strainers typically used by many BWRs prior to the issuance of NRCB 96-03. The BWROG recommends replacing existing strainers with one of the alternate designs tha.t have denanstrated better performance characteristics. The BWROG also recommends the use of the largest possible strainer, provided that the change would not alter the licensing basis for hydrodynamic loads. (The BWROG believes that staff review of new hydrodynamic load methodologies could delay final resolution of this issue.) The rest of Section 3.1.3 discusses various consideratiore that utilities

            ~ should keep in mind when considering their final resolution of this issue. These considerations include evaluating containment penetration load margins, plant physical constraints, and suction strainer type and size. Section 3.1.3.4 discusses the nine resolution options available to licensees, however, the staff notes that many of these options are only partial solutions and would still likely require strainer replacement by the licensee. The following discussion provides a brief overview of the resolution options discussed in URG section 3.1.3.4:

• The first option (Section 3,1.3.4.1) involves "further refinement of fixed debris source terms."

This option is simply a more detailed containment analysis intended to reduce the debris source term for sizing the strainers by calculating the amount of debris that could reach the strainers. A simplified calculation with bounding assumptions would more quickly provide an answer

requiring the least amount of engineering effort, but would tend to be very conservative. By 4

.                                                                                                                   11 i

i

contrast, the more refined analysis discussed in Section 3.1.3.4.1 would likely yield a lower debris source term, but would cost the licensee more in engineering time and effort. e The second option (Section 3.1.3.4.2) involves replacing the existing strainers with alternate passive designs such as the stacked disk or star strainer designs. The underlying rationale is to install a strainerthat has a higher capacity for debris capture. Specifically,the strainer would have a lower head loss when compared against the existing strainer for the same debris loading. This option is the same as resolution option 1 of NRCB 96-03 (Ref. 4). e The third option (Section 3.1.3.4.3) is to install jacketing to reduce the insulation debris source term, along with an appropriate attachment mechanism to hold the jacketing in place. The URG states that BWROG test data have shown that metal-jacketed insulation generates less debris than its unjacketed counterpartwhen exposed to a high pressurejet. The URG also states that use of the jacketing and attachment mechanism "will significantly reduce the amount of fibrous debris which can be transported to the suppression pool and contribute to strainer blockage." in addition, the URG notes that the manner in which the jacketing is attached is critical to its effectiveness. e The fourth option (Section 3.1.3.4.4) involves "reductionin transient debris source terms." The BWROG recommends this option if a licensee needs a small reduction in head loss to demonstrate an acceptable NPSH margin. To justify the reduction in transient debris, licensees may need to implement additional foreign material exclusion (FME) or housekeeping controls, or more frequent suppression pool cleaning. e The fifth option (Section 3.1.3.4.5) is to pursue a licensing basis change with the NRC. One f example cited as a potentiallicensing basis change is the use of a more realistic decay heat j curve in lieu of the conservative curve used in the originallicensing basis (i.e., American Nuclear Society 5.1 versus May-Witt). This, in turn, would improve the calculated NPSH margin by reducing the calculated suppression pool temperatures following a LOCA. The BWROG does not recommend crediting containment overpressure in calculating NPSH margins. r e The sixth option (Section 3.1.3.4.6)is to reevaluate ECCS suction line penetration loads without reopening the licensing basis for containment loads. The BWROG does not provide any guidance for how licensees can accomplish this option. Moreover, the BWROG does not recommend reopening the licensing basis for containment loads. e The seventh option (Section 3.1.3.4.7)is to partially replace fibrous insulation with RM1. For this option licensees would selectively replace fibrous insulation in the containment to reduce the amount of fibrous material that ultimately could be deposited on the ECCS suction strainers. The URG did not provide any further guidance fc,r how licensees could implement this option.

• The eighth option (Sections 3.1.3.4.8 and 3.3) is to install a backflush system. The BWROG does not recommend this option as a primary mitigating strategy because it would likely increase operator burden by requiring operator action early in the accident, and it would likely require repeated use within 30-60 minutes following the accident. Instead, the BWROG recommends this option as a defense-in-depth measure only.

12

e The ninth option (Sections 3.1.3.4.9 and 3.4) is to install self-cleaning strainers. The BWROG notes, however, that licensees would need to resolve significant design, qualification, and surveillanceissues before implementing this option. URG Section 3.4 provides further guidance on this option. Section 3.1.4 of the URG discusses other potential solutions that the BWROG has not yet fully evaluated. Consequently, licensees desiring to use these solutions would first be required to perform additional evaluation and testing. All of these potential solutions are altemate strainer designs which are either large-capacity passive strainers or strainers with a self-cleaning capability. Staff Evaluation for Section 3.1: Figure 1 of the URG provides guidance for plants with a

 " minimal" amount of fibrous insulation, but does not define what constitutes a minimal amount. In its response (Ref. 64) to the draft SER on the URG (Ref. 63), the BWROG clarified this point. It stated that less than a 0.32 cm (1/8 inch) coverage of the strainer surface by fibrous material is considered minimal. While the staff considers the definition provided by the BWROG to be acceptable, the staff notes that a licensee reviewing Figure 1 is likely in the process of defining the resolution path it intends to follow, and therefore, is unlikely to have performed sufficient analysis to determine if it could potentially entrain "minimar amounts of fibrous material on its strainer surface during an accident.

Figure 2 of the URG presents a discrepancy between Section 3.2.1.2.3.1 and the associated step in the flow diagram. The text in the diagram indicates that all of the materialof interest in performing a bounding analysis is assumed to be debris which is transported to the suppression pool. This clearly would be the most conservative method for calculating the amount of debris that could be transported to the suppression pool, and would eliminate the need for a detailed analysis. However, the staff notes that the flow diagram for this method cites Section 3.2.1.2.3.1 of the URG, which provides detailed guidance regarding Method 1 for calculating debris generation. The text of this section (page 37 of the URG) indicates that licensees may apply transport factors to the total amount of debris assumed in the drywell. It is not clear which is the intended URG recommendation for Method 1. It appears, however, that two methods are being combined into one. It would be clearer if they were separated. The bounding case would be to assume that all potential debris material in the containment is dislodged and transported to the suppression pool during a LOCA. A second method would be to assume that all of the material is generated as debris, but only a fraction of the total (predicted with the use of a transport factor) reaches the suppression pool. The staff's draft SER on the URG (Pef. 63) indicated that the BWROG should clarify the intent of the URG guidance. In its response (Ref. 64) to the draft SER, the BWROG clarified its intent for Method 1 in Figure 2 stating,"There are really two methods intended, either of which is acceptable. One method is to use a zone of influence that encompasses 100% of the material of interest in the drywell and 100% transport to the suppression pool. The second method is to take 100% of the material of interest in the drywell and then use the transport factors provided in the URG to determira the amount ofinsulationthat reaches the suppression pool." The staff concurs with the BWROG that both of these methods are acceptable. In Section 3.1.2 (page 14 of the URG), the BWROG states, "The head losses which resulted from the tests with combined RMI, fiber, and particulate debris were bounded by those seen in similar tests for the equivalent loading of fiber and particulate without RMI debris." This statement is not entirely correct. The staff evaluated the test data contained in Volume I of the URG Technical 13 i

l Support Documentation (Ref. 2) and concluded that the data do not support this conclusion under all cases. For example, test run number 15 was conducted with a 20-point star strainer at 9462 liters per minute (t/m) (2500 gallons per minute (GPM)) with 1.36 kilograms (kg) (3 pounds (Ibs)) of NUKON* insulation and 108.9 kg (240 lbs) of corrosion products. The resultant head loss across the strainer was 127 centimeters (cm) (50 inches (in.)) of water (H2 O). Test run number 33 was conducted with the same strainer at similar conditions and debris loadings except for the addition of 8.2 square meters (m2 )(88 square feet (ft2 )) of RMI debris. Test run number 33 resulted in a head loss across the strainer of 292 cm of H2 O (115 in. H2 O). The results of test run numbers J6 and J7 (with pump 2 mixing the tank for test run J7) present another example involving a truncated cone strainer at 18,924 t/m (5000 GPM), while test runs J23 and J24 present a similar example involving a 60-point star strainer. The NRC sponsored independent confirmatorytesting, conducted by ARL, with fiberglass insulation, corrosion products, and RMI. The results of these tests are documented in the ARL test report, entitled Head Loss of Reflective Metallic insulation Debris With and Without Fibrous insulation Debris and Sludge for BWR Suction Strainers," dated May 1996 (Ref. 43). After analyzing the results of these ARL tests, the URG and its supporting technical documentation (Refs.1 and 2), the BWROG response (Ref. 64) to the draft SER on the URG (Ref. 63), the staff concludes that the BWROG generalized statement regarding the head loss of a fiber plus corrosion products debris bed bounding the head loss of a fiber, corrosion product and RMI debris bed does not hold true in all situations, but can be generalized into three categories. First, in plants with minimal amounts of fibrous debris, the head loss of the RMI will tend to dominate. Second, in plants with more than minimal amounts of fibrous debris, but where RMI is the still the dominant debris source, the BWROG statementthat the head loss of the combined debris bed would be bounded by the head loss of just the fibrous debris and sludge tends to hold true. However, in the third case, if a licensw has large quantities of both fibrous debris and RMI which may reach the strainer surface durina an accident, the staff believes that the head loss would be additive. In other words, in this scenario, the head loss would be bounded by summing the numerical values of the head loss across the strainer with a fibrous debris / corrosion product debris bed only, and the head loss across the strainer for an RMI debris bed only (see Appendix K). However, further staff review of the URG led the staff to conclude that "the URG head loss correlation is unreliable and the guidance is inadequate to prevent inconsistent application of the correlation. On that basis that the staff I recommends that licensees employ vendor test data to demonstrate the head loss used to calculate the NPSH margin"(see section 3.2.6 of this SER). Because of the staff's conclusion on the URG head loss correlation,the staff believes this issue (head loss from combined fiber /RMI debris beds) should be resolved on a plant-specific basis. Licensees should ensure that their strainer vendor reviews the debris combinations of interest for their plant and ensures that the vendor's test data supports the head loss used in the licensee's plant-specific analysis. In the last paragraph on page 16 of the URG, the BWROG implies that utilities should take no action untilthe NRC completes its review of the URG. Although any change to that discussio,n would be made moot with the issuance of this SER, the staff emphasizes that licensees should take whatever action they can to resolve this issue as soon as possible. The staff encourages interim actions l which help to ensure the licensees' ability to mitigate a LOCA or a strainer clogging event until such time as the licensees are able to fully implement their final resolution for this issue. l 14 1 l 1

! l i I l Section 3.1.3.1 of the URG discusses the evaluation of containmentload penetration margins. The

URG states that a licensee's evaluation of containment penetration load margin should "also identify j

' any excess conservatism used in the existing structural analysis which could be reduced through the use of alternate analysis methods." The staff has concerns regarding this statement. I

Specifically, the hydrodynamic load programs for the Mark I, Mark ll, and Mark Ill programs were .

l very specific in providing generic methodologies for calculating hydrodynamic loads. Each plant l l submitted a plant unique analysis report (PUAR) for staff review and approval. These PUARs l F provided the specific details of each plant's calculated hydrodynamic loads, including the i methodology used and coefficients used, and so forth. The staff notes that part of the basis for j acceptance of these methodologies included supporting test data and conservative assumptions.  ! One main assumption was that the strainers were treated as solid cylinders since testing had not  ! l'; been performed to determine the drag coefficients for the perforated strainers. In essence, since the strainers are perforated, the' drag on a solid cylinder would bound the actual drag on the i perforated strainer. However, the staff's review of licensee responses to NRCB 96-03 has shown that many licensees are changing the coefficients used for calculating the standard and acceleration j F drag coefficients used in determining the hydrodynamicloads to take credit for the fact that their new  ; strainers are not solid cylinders. While the staff intuitively agrees that the perforated strainers have lower drag coefficients than similarly sized solid cylinders, the licensees have not demonstrated that ) the standard and acceleration drag coefficients of a perforated strainer can be accurately ) 2 determined by analysis alone. The staff cautions that licensees making changes to hydrodynamic

load calculation coefficients and/or methodologies should not do so without testing to demonstrate the validity of the revised calculations.

i in Section 3.1.3.4 and its subsections,the URG discusses nine " resolution options." Three of these

options are consistentwith the resolution options proposed in NRCB 96-03 (installation of attemate

} passive design strainers, self-cleaning strainers, or backflush); However, in the opinion of the staff, j the remainder are not

• resolution options." That is, none of the other six options are sufficient to l resolve this issue for any plant. On the basis of its current knowledge of existing plant strainer i designs and the deleterious phenomena that can affect head loss across the strainer and NPSH

_ margin, the staff does not believe that any BWR licensee can justify maintaining their existing

strainerdesign for resolution of the strainerclogging issue. Rather, the other six " resolution options" j discussed are better characterized as potentiallicensee actions, which could help licensees reduce j the size of the strainer needed to resolve the issue. However, the resolution options lack substantiad i detail regarding the technical basis for these options and the specific details concerning how to j~ apply each option. For this reason, a licensee should resolve the staff's concems regarding a given

option before using the option as a part of their resolution for the strainer clogging issue. The staffs ,

). specific concems related to the " resolution options" discussed in Section 3.1.3A are as follows: l

• In Section 3.1.3A.2 (page 20), the URG states that, "When properly applied, the results of the extensive testing conducted by the BWROG may be applied to strainers other than those tested by the BWROG." The staff finds that there is insufficientinformation regarding how to apply the BWROG test results to other strainers. In addition, the URG does not discuss the basis for this statement. Without further guidance and justification, the staff cannot consider this statement acceptable. For this reason, the staff recommends that licensees use vendor-specific data based on the plant-specific analyzed conditions as the basis for determining head loss across the strainer.

15

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• In Section 3.1.3.4.3 (page 20), the URG states that, " Additional details on the use of jacketing ,

is provided in Section 3.2.1." However, Section 3.2.1 does not provide any further guidarme other than information regarding debris generation. Section 3.2.1 also indicates the importance of banding to obtaining the desired effect of reducing debris generation; however, guidance regarding the types of bands to be used, construction of the bands (e.g., details as to size, thickness, material, weld versus riveted construction, etc.), and mounting instructions is not provided. Because of the lack of information as to how a plant is to apply this option, the staff is unable to reach any conclusion regarding the acceptability of this option. In addition, the characterizationof the effectiveness of insulationjacketing on this page is inconsistent with the test report from the BWROG air jet impact testing (AJIT) conducted at the Colorado Engineering Experimental Station, Inc. (CEESl). (The AJIT test report is included in Tab 3 of Volume il of the URG technical support documentation.) e in Section 5.1, " General Test Conclusions" (page 181), the AJIT report states, "In the case of fibrous insulation materials,the use of jacketing as a means of reducing debris generation does not appear to be effective without the use of an additional banding material which better secures the jacketing to the insulation assembly a.1d the pipe " However, the wording in Section 3.1.3.4.3(page 20) of the URG contradictsthe test conclusionby stating that " Testing performed by the BWROG (Reference 6) confirms that the fibrous insulation which is protected with metal jacketing is able to survive without producing debris at distances much closer to a pipe break than the same fibrous insulationwithoutjacketing." This statementis contrary to the test report conclusions in that it implies that jacketing by itself provides an improvement. The title of the section, " Installation of Jacketing to Reduce the insulation Debris Source Term," also implies thatjacketing by itself provides an additionaldegrm of reduction in debris generation. Without further detailed information on how to apply this option, the associated benefits to be achieved, and the technical basis supporting the use of this measure, the staff is unable to render a

         ' determination as to the acceptability of this option.

• In Section 3.1.3.4.4 (pages 20 and 21), the URG discusses the option of taking credit for FME and housekeeping programs as a justification for crediting lower amounts of transient debris in a plant analysis. The staff has two concerns related to incorporating this option into a licensee's >

final resolution. First,if a licensee selects too low an amount of transientdebris for its analysis, the potential exists for operability concems to surface anytime debris is found in the drywell, suppression pool, or wetwell. Second, if a licensee is considering an increase in transient debris in order to reduce the need for inspections,the staff believes that housekeeping or FME controis are not a substitute for periodicinspections of the drywell, strainers or suppression pool. Given < the numerous events reported over the last few years involving FME-related issues, the industry l has not demonstrated that FME controls alone are effective in ensuring that materials are not left in the drywell, wetwell, or suppression pool. Consequently,the staff believes that licensees should conduct regularinspections of the drywell, suppression pool and ECCS suction straines, and perform cleaning when necessary, during every refueling outage until the industry demonstrates over time the ability to control foreign materials. The staff believes adding margin when sizing strainers to account for the uncertainty in the effectiveness of housekeeping controls is a prudent measure. This, in turn, will minimize the need for detailed operability assessments when small amounts of foreign materials are found in the containment or suppression pool. 16 4

e in Section 3.1.3.4.5 (page 21), the URG notes that a part of a licensee's resolution to the strainer clogging issue could include a licensing basis change. The URG cites an example in which a licensee may wish to use a more realistic decay heat curve to reduce the calculated post-LOCA suppression pool temperatures. Specifically, the URG states that the BWROG does not recommend that licensees take credit for containment pressure greater than atmospheric pressure. When discussing the resolution of NPSH-related issues in a letter to the NRC's Executive Directorfor Operations (EDO) dated June 17,1997 (Ref. 44), the Advisory Committee on Reactor Safeguards (ACRS) explicitly stated, "We believe that allowing some level of containment; overpressure is not an acceptable corrective action because adequate overpressure may not be present when needed." The staff concurs that additionalcontainment overpressure (other than an amount already approved by the staff for the existing licensing basis) should not be used as part of the resolution of this issue. Moreover, the staffis evaluating its position regarding the use of containment overpressure in calculating NPSH margin as part of its review of Generic Letter (GL) 97-04, " Assurance of Sufficient Net Positive Suction Head for Emergency Core Cooling and Containment Heat Removal Pumps," dated October 7,1997 (Ref. 45).

I e In Section 3.1.3.4.6 (page 21), the URG discusses the potential to reanalyze suction line penetrationloads. Specifically, the URG states that it "may be possible to further increase the

size of the alternate strainer by reanalyzing ECCS suction penetration loads and suppression

pool structuralloads using more sophisticated techniques or through reduction of conservatism

in current design basis calculations, but without reopening the licensing basis for containment

loads." The staff's concems regarding Section 3.1.3.1, stated above, also apply to this section

! of the URG. e Section 3.1.3.4.7 of the URG indicates that an option for reducing the fibrous debris source term in the drywellis to partially replace fibrous insulation with RMI. The staff agrees that this is an appropriate option for reducing the amount of fibrous debris that can be transported to the i suppression pool; however, when using this option for a selected break,' licensees should i- reassess other breaks to ensure that the changes does not affect which break is the most

_ limiting'in terms of NPSH margin. In addition, licensees must consider head loss in terms of 3

combined fibrovs/RMI debris beds. (See the staff evaluation of Section 3.1.2 above.) I In Section 3.1.3.4.8 (page 22), the URG states that the BWROG does not recommend backflush l as a primary means of ensuring ECCS flow to the core. The basis for the BWROG's recommendationis that backflushing would place an unnecessary burden on operators early in an accident and would likely require repeated initiations during the accident. The staff concurs with the BWROG that backflush is a more viable option as a defense-in-depth measure. The staff also believes that, if used as a primary means of ensuring adequate ECCS flow, backflushing should be combined with the installation of a large-capacity passive strainer to maximize the amount of time before backflush initiation would be required. e In Section 3.1.3.4.9 of the URG, the BWROG discusses the use of self-cleaning strainers as a resolution option. See the staff evaluation of Section 3.4 of the URG for a discussion regarding the use of self-cleaning strainers as a resolution option. The staff also notes that a good practice would be to maintain defense-in-depth because of the uncertainties associated with any resolution to this issue. The staff strongly encourages the 17

i enhancement of alternate water sources (including maintenance of crossover valvss which conned I the ECCS to attemate water sources), operator training. and EOPs to ensure that operators can mitigate any situation involving loss of ECCS flow resulting from strainer clogging. In its letter to the ' EDO dated February 26,1996 (Ref. 46), the ACRS stated that a diverse means of providing emergency core cooling is desirable because of the difficulty in predicting with confidence the . amount of debris that would challenge the ECCS strainers. In its response to the ACRS dated March 22,1996 (Ref.47), the staff concurred with the ACRS comment and agreed to " place more 'l i emphasis on the need to improve,where appropriate,the procedures to better address core cooling i from attemative sources of water."

e 3.2 METHODOLOGY FOR SIZING PASSIVE ECCS SUCTION STRAINERS in Section 3.2 of the URG, the BWROG presents their analysis methods for performing a plant- l specificevaluationto size ECCS suction strainers. Each subsection presents a different part of the >

analysis including calculation of drywell debris sources, other sources of drywell debris, transport of drywell debris to the suppression pool, transport of debris within the suppression pool, head loss, and NPSH. ' i 3.2.1 Sources of DrywellInsulation Debris 4 This section of the URG discusses the methodologiesthat the BWROG recommends for calculating the amount of LOCA-generated debris from piping insulation. The guidance provided includes  : j

                  ' determining the break locations to be analyzed, the ZOI for the break jet, and the destruction factors for piping insulations typically used in domestic BWRs. Section 3.2.2 discusses other potential i

sources LOCA-generated debris.  :

                                                       ~

3.2.1.1 Pipe Break Locations Section 3.2.1.1 of the URG discusses the BWROG guidance related to selecting pipe break locations.The introduction to Section 3.2.1.1 discusses general considerations for the selection and summarizes important guidance provided in 10 CFR 50.46 (Ref. 42) and RG 1.82 (Ref. 5). In addition, this section includes guidance from Section 3.6.2 and Branch Technical Position (BTP) f' l MEB 3-1 of NUREG-0800," Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants," which is also known as the SRP (Ref. 48). The URG correctly states that 10 CFR 50.46 explicitly requires that "ECCS cooling performance l must be calculatedin accordance with an acceptable evaluation model and must be calculated for L a number of postulatedioss-of-coolant accidents of different sizes, locations, and other properties sufficient to provide assurance that the most severe postulated loss-of-coolant accidents are , i calculated." The staff believes a licensee evaluatingits compliancewith 10 CFR 50.46 should look to this statement for the criteria to be met when choosing the number and locations of the breaks  ! to be analyzed. The URG then provides a discourse conceming SRP Section 3.6.2 and BTP MEB 3-1. On page i 26, the URG quotes SRP Section 3.6.2 as stating, " Acceptable criteria to define postulated pipe rupture locations and configurationsinside containment are specified in Branch Technical Position i 18 l t

l l (BTP) MEB 3-1." The staff notes that this statementis taken completely out of context and, as such, does not accurately convey the position stated in the SRP Section 3.6.2, which is preceded in the SRP by the statement that " Specific criteria necessary to meet the relevant requirements of GDC 4 are as follows:" The URG then notes that NUREG-0897, Revision 1, " Containment Emergency Sump Performance" (Ref. 58), states that "SRP Section 3.6.2, ' Determination of Rupture Locations and Dynamic Effects l Associated with the Postulated Rupture of Piping,'should be used to identify potential break  ! locations." The URG then quotes BTP MEB 3-1, stating that " ..The rules of this position are intendedto utilize the available piping design information by postulating pipe ruptures at locations having relatively higher potentialfor failure, such that an adequate and practical level of protection , may be achieved." The BWROG includes these quotatinnsin the URG to establish a basis for using SRP Section 3.6.2 to define the pipe break locations that should be evaluated in order to demonstrate compliance with 10 CFR 50.46. In addition, Section 3.2.1.1.1 of the URG cites RG , 1.82, Revision 2, as a source of guidance for pipe break locations to be analyzed. Specifically, the URG quotes the following guidance from Section 2.3.1.5 of RG 1.82, Revision 2 ,

     "As a minimum, the following postulated break locations should be considered.                                   l l     e    Breaks on the main steam, feedwater, and recirculationlines with the largest amount of potential          I debris within the expected 201,                                                                           l e    Large breaks with two or more different types of debris within the expected ZOI, e    Breaks in areas with the most direct path between the drywell and wetwell, and e    Medium and large breaks with the largest potential particulate debris to insulation ratio by              !

weight." , 4 , I The BWROG does not consider the fourth criterion dealing with the largest particulate-to-insulation i ratio to be applicable for licensees using an altr, mate ctrainerdesign. Section 3.2.6.2.3 of the URG discusses the basis for this omission. l . After providing the above information as background, Section 3.2.1.1.2 of the URG presents the BWROG guidance for determining pipe break locations. Specifically, items 1,2, and 3 of this 4 section present attemative approaches for the selection of pipe break locations. (item i gives pipe . break selection criteria for three different licensing-basis situations. Item 1.a provides pipe break . location selection criteria for plants that were licensed with an MEB 3-1 analysis. Item 1.b provides pipe break location selection criteria for licensees who have not performed a stress analysis

 !   consistentwith MEB 3-1, but may desire to perform such an analysis. Item 1.c discusses the pipe break location selection criteria for licensees who have not identified pipe break locations using an approved stress analysis technique.) Item 4 cautions licensees about differentiating between pipe breaklocations used for ECCS evaluations and those which are in the plant licensing basis. Item 5 gives guidance regarding the treatment of pipe breaks inside the bio-shield walls.

Staff Evaluation for Section 3.2.1.1: In its evaluation, the staff compared the guidance provided in this section of the URG to the corresponding guidance provided in RG 1.82, applicable sections of the SRP, and with 10 CFR 50.46. 19

i in this section of the URG, the BWROG focuses on the postulated pipe break locations that the  ! licensee analyzes to demonstrate corr pliance General Design Criterion (GDC) 4, as presented in Appendx A to 10 CFR Part 50 (Ref. 42). GDC 4 requires that licensees must protect structures, systems and components (SSCs) important to safety from the dynamic effects (e.g., pipe whip,  ! direct steam jet impingement, etc.) and environmental effects (e.g., temperature, pressure,  ! radiologicaleffects) of postulated pipe ruptures. Consequently,GDC 4 imposes a requirement that  ; licensees must provide physical means (e.g., pipe restraints, physical barriers (walls), or physical f separation)to protect equipment important to safety from the effects of postulated pipe breaks and  ;

       . to ensure that those components are capable of performing their safety function (s) in a post-LOCA    !

environment. Because it is not practical to physically protect equipment in the containment from  ! every postulated LOCA, the staff concluded in SRP Section 3.6.2 that licensees could provide an l adequate and practical level of protection for compliance with GDC 4 by physically protecting l equipment important to safety from the postulated pipe breaks that have a relatively higher potential l for failure (e.g., postulated failures at high-stress and fatigue locations). As a result, when I demonetietinacomoliancewith GDC 4. licensees may analyze pipe breaks through the use of pipe stress analysis methodologiessimilarto that provided in BTP MEB 3-1 of SRP Section 3.6.2. The  ; staff, therefore, evaluates licensee's safety analysis reports against the requirements of SRP  ; Section 3.6.2 to " confirm that requirements for the protection of structures, systems, and components relied upon for safe reactor shutdown or to mitigate the consequences of a postulated  ; pipe rupture are met." Notably, the only acceptance criterion specified in SRP Section 3.6.2 is [ compliance with GDC 4. GDC 4, SRP Section 3.6.2, and BTP MEB 3-1 are not to be used for .

      - ECCS functionaldesign or compliancewith 10 CFR 50.46. The staff considers SRP Section 3.6.2 and BTP MEB 3-1 to be inappropriate for demonstrating compliance with 10 CFR 50.46.                    ,

The primary concem in the ECCS strainer clogging issue is the adequacy of ECCS strainer design l relative to ensuring that the ECCS can meet the cooling performance requirements of 10 CFR , 50.46. The staff notes that no concems have been identified during the resolution of this issue  ! l . relative to physically protecting the ECCS from the dynamic or environmental effects of a LOCA. l- In order to ensure adequate ECCS cooling capability,10 CFR 50.46 requires that ECCS cooling  ! I performance "must be calculated for a number of postulated loss-of-coolant accidents of different 'f sizes, locations, and other properties sufficient to provide assurance that the most severe postulated , loss-of-coolantaccidents are calculated." The staff notes that the worst breaks from the standpoint  ; of peak clad temperature may not be the worst from the standpoint of NPSH margin. As a result, i additional breaks may have to be evaluated. When evaluating ECCS performance for compliance ~ with 10 CFR 50.46, SRP Sections 6.3 and 15.6.5 are the appropriate sections of the SRP to consider. For instance, the review procedures of Section 15.6.5 specifically require reviewers to , ensure that "a variety of break locations and the complete spectrum of break sizes were analyzed." This is consistent with 10 CFR 50.46. , RG 1.82 provides the staff's position on what constitutes an appropriate spectrum of breaks to be , considered when evaluating the potential for strainer clogging. Specifically, Regulatory Position  ! 2.3.1.5 of RG 1.82 states, "As a minimum, the following postulated break locations should be considered: (a) Breaks on the main steam, feedwater, and recirculation lines with the largest i l amount of potential debris within the expected zone of influence,(b) Large breaks with two or more  ! l-different types of debris within the expected zone of influence, (c) Breaks in areas with the most  ; direct path between the drywell and wetwell, and (d) Medium and large breaks with the largest f f 20 , l

i

poteritialparticulate debris to insulation ratio by weight." The staff believes that the RG provides the complete scope of breaks needed to meet the intent of 10 CFR 50.46. Criterion 4 of Regulatory Position 2.3.1.5 of RG 1.82 states that one group of break locations a licensee should identify as a minimum are

• Medium and Large Breaks with largest potential particulatedebris to insulation ratio by weight." The reason these breaks should be considered is the " thin-bed effect," which has been observed by the BWROG and the staff in cylindrical and truncated cone strainer tests. Specifically, testing has shown that high head losses can occur on cylindrical or conical strainers with thin fiber beds and high concentrations of sludge. The reason for this observation is that thinner fibrous debris beds compress more tightly to the strainer surface.

When this occurs, the filtration efficiency (entrapment of particulates by the strainer and fibrous debris bed) increases resulting in a significantly higher head loss than in debris beds containing e significantly higher quantities of fibrous debris. In URG Sections 3.2.1.1.1 and 3.2.6.2.3, the BWROG states that they did not observe a thin-bed effect for attemate strainers; therefore, licensees who propose to use attemate strainers need not analyze medium or large breaks with the largest potential particulate-to-insulation debris ratio by weight.- The URG does not provide sufficient data to support this conclusion. There are three reasons for this. First, the data provided only apply to two specific types of alternate strainers (star and stacked-disk), and it is evident that not all licensees will limit their plants to using only these two attemate strainer designs. Second, other "altemate" strainer designs may not have the critical features that eliminate the " thin-bed effect." Third, even for the two types of attemate strainer designs that were tested, the data set is too limited to support such a broad conclusion. l l Because of these concerns, a confirmatory analysis was performed in support of this review. The staffs confirmatory analysis is documented in Appendix E. The staffs analysis does suggest that licensees may screen out medium LOCAs (MLOCAs) if they use the stacked disc strainer number i . 2, the star strainer, or another geometrically similar altemate strainer design that has deep cavities i sufficientto hold debris loadings consistent with a MLOCA for their plant. The basis for the staffs L conclusion is that the test data provided in the URG do demonstrate that with fiber loadings up to

            ' the equivalent amount to fill the crevices in the stacked disk strainer number 2, high head losses

! were not experienced even with high sludge-to-fibermass ratios. The amounts of debris that would

i. be required to completely fill the cavities between the disks in the stacked disk number 2 strainer would be approximately 0.28 cubic meters (m*) (10 cubic feet (ft')). This amount of fibrous debris is similar to the amount estimated for a MLOCA for the reference plant in NUREG/CR-6224 (Ref.

31).' For these types of strainer designs, the MLOCA does not appear to be the bounding break. However, the staff notes that its conclusion is founded on limited amounts of test data, estimates of debris loadings for the reference plant MLOCA only, and evaluation of two strainer designs only.  ; Consequently, the staff believes that licensees considering a resolution option using an altemate i strainer design may screen out MLOCAs from their plant-specific analysis if they ensure that the i vendor confirms that the thin-bed effect is not a problem for their plant-specific strainer application (i.e., the strainer design is such that lesser debris loadings could not result in higher head losses than those calculated for large break LOCAs). This can be done by evaluating the effect of varying debris loads through parametric analyses. Where possible, the staff believes that these analyses should be validated through comparison with applicable vendor test data. A second option would [ be to experimentally verify that the thin-bed effect is not an issue for the strainer design being

             ' considered using deb *ris quantities which approximate those for a MLOCA for a given plant.

21 , i ! I i i> )

Likewise, on the basis of the staffs review of several plant-specific submittals detailing licansres' design bases for estimating maximum debris loadings on their new strainer design (see Refs through 38), it appears unlikely in most cases that large LOCAs with the highest particulate to fib ratios by weight will be the limiting break in terms of creating the worst-case head loss across the strainers. Review of licensee submittals has shown that when using Method 1 or 2 for calculating the pipe break ZOl, the calculated amount of fibrous debris is sufficiently conservative to bound th T head losses in breaks with the highest ratio of particulates to fibrous debris by weight. However, the staff believes that in certain plant configurations,the potentialexists for debris beds with higher particulate-to-fiberratios to have the bounding head losses. One such case may be in plants with large quantities of both calcium silicate and fibrous insulation materials. The difference between th breaks with the largest amounts of fibrous debris and the breaks with the highest particulate to ' fibrous debris ratios may not be significantenough for the former to bound the latter. Consequently, as in the case with MLOCAs above, the staff believes that licensees considering a resolution option using an attemate strainer design may screen out large break LOCAs with the highest particulate-to-fiber debris ratio if they ensure that the vendor confirms that smaller breaks with higher particulate-to-fiber debris ratios do not result in higher head losses for their plant-specific strainer application. This can be done by evaluating the effect of varying debris loads through parametric analyses. However, the staff believes that vendors should have sufficienttest data to support these analyses. A second option would be to experimentallyverify that large breaks with the highest particulate-to-fibrous debris ratio are bounded by large breaks which generate higher fibrous debris loadings, but lower particulate-to-fibrous debris ratios. The staff notes that if the BWROG intends to include generic statements regarding all alternate strainerdesigns,it should support the guidance with additional data in one of two ways. First, the URG might cover a wider range of experimental parameters (e.g., fiber volume, sludge to fiber ratios, different strainer geometries, etc.) for all altemate designs that are actively considered by various individuallicensees. Altematively, the URG might demonstrate which parameters are key in strainer design to ensure that breaks with high particulate-to-fibrous debris ratios are not the bounding breaks for the strainer design under consideration. Conckmiens Rwdina Section 3.2.1.1: In summary, the staff reached the following conclusions e To be consistent with NRC requirements, the URG should give clear guidance that helps licensees select break sizes and locations that reasonably ensure acceptable ECCS performance under the most severe conditions. URG Section 3.2.1.1 largely, but not entirely, succeeds in meeting this objective. The staffs concem deals with the clarity of the guidance and the unnecessary focus on SRP Section 3.6.2. The staff concludes that it is inappropriate for the URG to cite SRP Section 3.6.2 as a basis for determining pipe break locations to demonstrate compliance with 10 CFR 50.46. There are two reasons for the staffs conclusion. First, SRP Section 3.6.2 does not provide guidance or acceptance criteria for demonstrating compliance with 10 CFR 50.46. Second, the BWROG has not demonstrated that break locations selected consistent with SRP Section 3.6.2 would bound the worst-case debris generation scenarios and, therefore, meet the intent of 10 CFR 50.46. e 10 CFR 50.46 and RG 1.82, Regulatory Position 2.3.1.5, give licensees adequate guidance regarding selection of pipe break locations for performing a plant-specific analysis relative to 22

l l debris generation. This guidance conciselyindicates where a licensee should focus its analytied efforts. Licensees may screen out targe breaks with the highest particulate-to-fiberdebris ratio by weight and MLOCAs in performing their plant-specific analyses, if their resolution includes both of the foilowing:

1) Installation of a strainer similar to the stacked disk number 2, star strainer, or another geometrically similar strainer with deep crevices.

2) The licensee has adequate assurance from the strainervendor that the screened out breaks would not be more limiting in terms of head loss across the strainer. The vendor should have adequate test data to support screening of these breaks.

In addition, the staff notes the following observations and guidelines:

• Each attemative evaluation method presented must reasonably ensure that licensees will suitably evaluate the most severe ECCS suction strainer debris loadings (from drywell insulation sources).

Bounding analyses, if used by licensees in lieu of specific pipe break location analyses, must address all debris species (from insulation sources) that would have been addressed by the specific pipe break location evaluations.

• The URG provides incomplete guidance regarding pipe breaks located inside the bio-shield wall.

The staff forwarded this position to the BWROG in Ref.11, The related BWROG response is  ! documentedin Ref.13. Citing utility responses documented in Ref.12, the BWROG argued in Ref.13 that breaks inside the bio-shield 'itall are not major contributors of debris. As a result, the BWROG does not believe that generic guidance is needed on this issue. However, the staff contended in its draft SER on the URG (Ref. 63) that additional guidance on the analytical considerations to be evaluated by licensees would be beneficial and consistent with the BWROG's stated goal of providing a consistent industry response to NRCB 96-03. In its response to the draft SER (Ref. 64), the BWROG stated,"The BWROG believes that the plant unique aspects of the amount and type of insulation inside the bio-shield will govem the most appropriate means of addressing this debris source. For many plants the amount of debris available inside the bio-shield is negligible relative to other debris sources and can be discounted. The BWROG recommends that this issue is best addressed on a plant-specific basis." On the basis of the staff's review of Ref. 64, the staff concludes that this issue should be addressed on a plant-specific basis. 3.2.1.2 Zone of influence URG Section 3.2.1.2, entitled " Zone of influence," documents the BWROG's guidance regarding various options for selecting a ZOI model that individual utilities can use to estimate the volume of debris generated by a postulated pipe break. The URG guidance provided in this section is predicated on the following supporting analyses which are included in the URG Technical Support Documentation (Ref. 2): 23

(1) "ZOI as Defined by Computational Fluid Dynamics," Revision 3, URG Technical Support i Documentation, Vol. II, Tab No.1, Continuum Dynamics Inc., Princeton, NJ. (2) " Air Jet impact Testing (AJIT) of Fibrous and Reflective Metal insulation," Revision A, URG Technical Support Documentation,Vol. II, Tab No. 3, Continuum Dynamics Inc., Princeton, NJ. (3) " Evaluation for Existence of Blast Waves Following Licensing Basis Double-Ended Guillotine Breaks," URG Technical Support Documentation,Vol. Ill, Tab No.13, General Electric Nuclear Energy, San Jose, CA. (4) " Total Pressure Topography and Zone of Destruction for Steam and Mixture Discharge from Ruptured Pipes," URG Technical Support Documentation,Vol. Ill, Tab No.14, General Electric Nuclear Energy, San Jose, CA. l- The staff reviewed URG section 3.2.1.2, along with the supporting analyses listed above, to assess the completeness and accuracy of the guidance provided. In addition, the staff compared the guidance provided in the URG to that provided in RG 1.82, Revision 2. l Section 3.2.1.2 of the URG provides four options (or methods) for selecting the ZOI over which LOCAjets would damage the insulation. Each method reduces the amount of conservatism relative to the previous method, but requires more rigorous analysis by the licensee. The method is , selected on the basis of licensee resources and the amount of conservatism the licensee desires to build into its strainer design. Method 1, the most conservative, bounds the ZOI by assuming that l it encompassesthe entire drywell. Methods 2 and 3 define a ZOI by determining the spatialvolume i enveloped by a specific damage pressure of interest for a jet expanding in free space and mapping

a spherical ZOI of equal volume surrounding the break. All of the insulation contained within that

! spherical volume is then assumed to be damaged'. Methods 2 and 3 have several important i differences, but they are essentially refinements that reduce the amount of conservatismintroduced ! by assumptions associated with Method 2. For example, Method 2 defines the ZOI by assuming full separation of both ends of a double-endedguillotine break (DEGB). In contrast, Method 3 allows the licensee to take credit for pipe restraints and to evaluate axial and radial offsets consistent with those restraints. Finally, Method 4 allows the user to defir,e the ZOI by directly employing the

i. results of computationel fluid dynamics (CFD) modeling.

The BWROG guidance allows flexibility for licensees to select a ZOI modeling option that best suits l their solution, and use it to construct the ZOI surrounding each break location selected for analysis. l All of the insulation contained in that ZOI is assumed to be " damaged." Licensees who do not wish to take credit for debris retention in the drywell can put all the " damaged" insulation into a single category and track it as it is transported to the ECCS strainer via the suppression pool model of interest. On the other hand, licensees wishing to take credit for debris retention in the drywell divide the total" damaged" insulation into two bins,1) debris generated above the lowest elevation grating, and 2) debris generated below the lowest elevation grating. Such a division is required to facilitate application of drywelltransport factors that are dependent on the location of insulation with respect to the lowest grating. However, URG Section 3.2.1.2 does not address the size distribution of the

     " damaged" debris. (Such information is provided in Section 3.2.3, "Drywell Debris Transport.")

l l l

      ' It is important to note that not all of the damaged insulation is assumed to be transponable.

24

l i ) ~ Staff Evaluation of Section 3.2.1.2 The staffs confirmatory analyses performed in support of its review of this section are documentedin appendices A, B, C, D, and F to this report. The staffs key conclusions from these confirmatory analyses are summarized as follows: e- The BWROG calculations in the URG underestimate the bulk dynamic pressures in Mark I containments by a factor of 10 at some locations. However, the staffs conclusion is that the bulk dynamic pressures would likely be insufficient to damage insulation materials such as those presently used in operationalBWRs, provided that the insulations are properly installed and well-

                                                                                                                                          ]

maintained. The tables in the URG for debris generation and transport assume that insulation ' is correctly installed and well-maintained. Licensees should ensure that the analysis reflects the actual plant conditions, in addition, the staff notes that in the BWROG's response to staff RAls (Ref.13) showed that the bulk dynamic pressures in Mark I and Mark lli containments could be 5-10 times higher than that calculated for a Mark 11 containment because of smaller containmert cross-sections. While this issue was resolved in Ref.13, the staff notes that the URG will not be updated again. Therefore, the staff wishes to note that this technical error still remains in j the URG. '

• The BWROG's basis for using the jet center line (JCL) pressure at the distance from the jet nozzle (UD) at which incipience of insulation damage was first observed in the AJITs as the insulation's characteristic damage pressure is inadequately supported by either analysis or experimental data. In the staffs opinion, the experimental evidence from the AJIT seems to contradict the JCL concept. Rather, the staffs review of the data leads to the conclusion that the incipience of damage is related to the total jet impingement load rather than the local maximum. This intuitively makes more sense in the staffs opinion, it does not seem logical that a peak pressure at one point on the insulation blanket would be responsible for destruction over the entire blanket where other portions are clearly exposed to lower pressures.

The staff also notes two additional concerns related to use of the JCL. First, the choice of the JCL to characterize damage raises questions related to scaling BWROG AJIT results to BWR drywells. Second, interpreting JCLs as the damage pressures, and subsequently using them in enveloping the volume over which debris damage occurs, may make the volume estimates for ZOI non-conservative. For all of the reasons discussed above, the staff conducted a confirmatory analysis (see Appendix B to this SER). On the basis of the staffs analysis, the staff believes that a target area averaged pressure (TAAP) or total jet impingement load are more technically correct bases for assessing potential damage. , The staffs concems over the use of JCL pressure can be characterized in the following way. The BWROG's logic of assuming that damage relates only to JCL pressure would lead to the conclusion that an insulation blanket that survived at 10 UD in the AJITs would also survive at 10 UD if the 7.6-cm (3-inch) nozzle is replaced by 30.5-cm (12-inch) nozzle. However, no basis exists for this conclusion. Similarly, there would be no need for the suggested correction formula (P = = Pi2d(12"+2t)/(D+2t))if damage relates only to the JCL (or altematelyto the maximum pressure an insulation blanket is subjected to). The BWROG's rationale is unclear for extrapolating AJIT experimental results to pipes of different diameters. The staff notes that this concem is only significant for insulations with high P. values. The further the jet impact is from the nozzle, the more closely JCL approaches TAAP and the choice 25

between the two metrics becomes inconsequential. As a result, thtre are only five types of insulationwhich are affected by this comment. The first two affected insulations are Darchem and Transco RMis. The staff notes, however, that the URG contains very conservative destruction and transportfractionsfor RMI debris (see Section 3.2.3 of this SER). These factors are used to calculate the amount of insulation in the ZOI that will be destroyed into a fine debris . and transported to the suppression pool. For RMI debris, the factor used for debris generation exceeded the maximum amount of debris observed during the AJIT by 500%. The staff believes that the conservative debris generation / transport assumptions of that part of the analysis outweigh the staffs JCL concem cited herein; therefore, this comment is not considered to be significant for RMI insulations. The second two affected insuletions are fibrous insulation that

are banded to reduce debris generation. Since banding hos not been accepted as a resolution option, the staff recommends that debris generation c'.sncems related to banded insulation be resolved on a plant-specific basis. The fifth affected lnsulation is calciurn silicate (Cal-Sil)which the staff notes should be treated as being eroded over time by the break jet. Use of the JCL to calculate the ZOl, in this case,is not applicable. The BWROG debris generation tests were of insufficientduration to show how Cal-Sit debris generation changes with time; however, Swedish testing (Ref. 67) has demonstratedthat Cal-S I and similar insulations erode over time. Because of the limited number of insulations affected by this staff concem, the staff believes that its concems regarding the use of JCL versus TAAo for ZO! calculations should be addressed on a plant-specific basis, e The BWROG's suggested correction formula is reasonable for scaling damage pressures measured in the AJIT facility for insulation blankets installed on 30.5-cm (12-in.) pipe to pipes of differentdiameters. The staff notes that this formula also supports a choice of a target area averaged pressure in place of the JCL suggested by the BWROG.

e The BWROG's estimates of volume of a freely expanding steam jet that is bounded by a pressure isobar of interest are conservative and well supported. Typically, the BWROG estimates of jet volumes are higher than or equal to ANSI /ANS 58.2 model estimates for both extremes (DEGB with full and limited separation). ' Therefore, the staff believes that the jet volumes listed in Table 1 of the URG are reasonable.

• The BWROG's suggested correction factors appear reasonable for scaling the jet volumes computed for steam breaks to recirculation breaks. Therefore, the staff believes that it is acceptable to use these correction factors to compute the jet volume bounded by a. pressure isobar of interest following a recirculation line creak.
• The BWROG choice of mapping a spherical ZOI with a volume equal to the volume of the double-ended conical ZOI for a freely expanding jet is unsupported either by analytical modeling or experimental evidence. The BWROG's rationale, however, appears logical (although qualitative). As a result, the staff conducted a confirmatory analysis using a limited CFD model to demonstrate the effect of the jet interaction with structures and piping in the drywell. This analysis demonstratedthe diffusion of the breakjet as it interactswith structure and piping. On the basis of this analysis, the staff concludesthat the spherical ZOls developed using Methods 2 or 3 in Section 3.2.1.2 of the URG are conservative and acceptable. The basis for the staffs conclusion is that the jet emanating from a broken pipe will lose energy and diffuse with distance and its interaction with surrounding pipes and structures, and the URG methodology does not 26 L

I

                                                                                   ,                                                                    \

accounifor this piping / structural interaction which conservatively increases the calculated size of the ZOI. (It will likely diffuse into a high-velocity flow within 5 -10 UD from the nozzle as it interacts with various structures.) The staff also notes that if the jet were not interacting with the surrounding structures (i.e., it was on a path that allowed free expansion), debris would not likely be generated. The staff concurs with the URG's recommended use of a sphericalmodel as the best means to account for the impact of drywell congestion, drywell structural interactions, and the dynamic effects of pipe separation.

   -*    The ZOls developed using Methods 1,2, and 3, and subsequently the volume of insulation assumed to be damaged snd available for drywell transport, are very large. For some insulations, the ZOI enveloped between a fourth to a third of the drywell. As an example, the ZOI computed for steel jacketed NUKON' using Method 2 is a spherical region approximately 11 break diameters (D) in radius, which is much larger than the volume of the ZOI calculated using CFD codes by the staff and the 7D sphere used in the NUREG/CR4224 study, as well as the NUREG-0897 guidance. The smallest 201 is greater than 10D in radius.

• The staff identified a concem related to the use of Method 3, which allows the licensee to

         " determine whether the break results in a single jet (such as a steamline break) or double jet (such as for a recirculationline break)." The staff points out that until the main steam isolation valves (MSlVs) close (about 0.3 - 0.5 s), fluid is expelled from both sides, although the jet may not be as energetic because of the effect cf the flow restrainer (i.e., choking occurs in the restrainer). Licensees should pay close attention to account for these phenomena if they wish to take credit for a single jet following a main steamline break (MSLB). The staff recommends that utilities not take credit for a singlejet in the case of a MSLB inside the containment. Since this is a design-basis accident (DBA), licensees' assumptions should be consistent with past design-basis scenarios in their Updated Final Safety Analysis Report (UFSAR).

• The staff notes that the experimental data for certain insulations is not very comprehensive, since testing was conducted for only a limited number of UD values. Specifically, the staff notes that in the AJIT, the BWROG did not adequately explore the exact location at which damage first occurs for certain types of insulation. For example, in the case of stainless steel Jacketed NUKON*, the AJIT test report documented damage at 50 UD with 12% of insulation destroyed into fines and 29% into larger pieces. But the BWROG has not explored damage beyond 50 UD. Similarly, in the case of unjacketed NUKON'significant damage occurred at 60 UD and no damage at 119 UD, but the BWROG did not report any data points in between. In view of this lack of data, some of the conclusions stated in URG become questionable, especially considering that the BWROG subsequently uses this damage-related information to estimate the fraction of fines generated. Another AJIT testing deficiency is that, for selected insulation blankets, the URG may overestimatethe JCL pressures at which damage was first noted, and this would lead to non-conservativeZOls. For exarnple,in the case of Diamond Power (DPSC)

Mirror Insulation with "Sure-Hold" bands, the URG reported a damage pressure of 190 psid. However, using the same experimental data and same NPARC computer code results (see URG Technical Support Documentation, Tab 1, page 18, Figure 9), the staffs confirmatory

       - analysis estimated the value to be 150 psid. The staff found several such discrepancies, as annotated in Table 1 of Appendix B to this report by an "". In all cases, the estimated damage pressures are lower than the URG values. The staff recommends the use of the values in Table 1 of Appendix B to this report for insulations annotated by an "", since these values are taken 27

directly from the BWROG's data. The data provided in the URG on page 46, Table 2 appears to be inaccurate and non-conservative With regard to the number of data points taken in the AJITs, the staff recognizesthat the BWROG's choice of limiting the number of air jet tests was resource related. However, un the basis of the conservative methods developed by the

         . BWROG for calculating the ZOI, the staff believes that the calculated ZOI will adequately bound any uncertainties related to minimal P , data for certain insulations, and as a result, the staff concludes that use of the P , values provided by the BWROG, as modified by Table 1 in Appendix B to this report is acceptable.

The strengths of URG Section 3.2.1.2 and the associated technical support documentation are as foliows: e The method used to develop the ZOI models is, for the most part, logical and supported by a large number of analytical and experimental studies. e The AJIT results provide valuable experimental data related to the destructive nature of expanding high-pressure jets. Such data were previously unavailable in the public domain, which limited the previous understanding of insulation destruction by high energy jets. e The URG reviews importart considerations of which licensees should be aware of in selecting a ZOI model and in tracking the damaged insulation. e The method for developing the size of the ZOI is conservative. The size and shape of the ZOI neglectthe effects of the breakjet interactionwith piping and structures. Piping and structures would tend to deflect the jet in different directions. For this reason, the shape of the ZOI would be more sphericalin shape than conical. As a result, the BWROG's choice of a spherical model for the ZOI appears logical. However, the interactions with piping and structures would cause the jet to lose energy and also shadcw other targets from the jet. The URG methodologies for determining the ZOI do not take credit for these conservative elements. The staff identified the following weakness in the technical support documentation for the URG: o The supporting documentation does not provide a scaling analysis justifying how the experimental damage generated by jets originating from a 7.6-cm (3-in.) diameter nozzle can > be sceled up to BWR drywells where the jet stagnation diameter is as large as 24 inches. Conclusions Regarding Section 3.2.1.2 Overall, the staff concludes that Method 1 is clearly a bounding and conservative method for evaluating the ZOI, since it encompasses the entire drywell, and therefore, bounds the amount of insulation debris that may be generated by the break. The staff also believesthat the sphericalZOls developed by using Methods 2 and 3 would be sufficiently large to envelop the entire zone over which destruction would actually occur. These two methods are thus sufficiently conservative to compensate for the weak.nesses noted above and, therefore, are considered acceptable for use on insulations with low P. values. However, for the insulations noted above with high P. values, the staff recommends that licensees address the staff's concems relative to calculation of the Z01 based on JCL on a plant-specific basis. l 28

                  .Section 3.2.1.2 of the URG does not provide detailed guidance regarding Method 4, which would
                 .. use an unnamed CFD code to determine the ZOI. Corisequently, the staff cannot accept Method

4. Any licensee desiring to use Method 4 should address the staffs concerns relative to the details of the analysis and how the code will be benchmarked. The staff believes that CFD codes are useful in obtaining insights, such as in the staff's evaluation of the interaction of a break jet with surroundhg piping and structures. The BWROG has not yet demonstrated, however, that a CFD code can accurately predict the specific ZOI for a pipe break or the amount of debris transport to the suppression pool. The purpose of Method 4 is to reduce the conservatism in the calculation of a 201. Because of the uncertainties involved in a LOCA and the plant-specific nature of debris generation and transportin a LOCA, the staff would require a much higher level of review in order to accept Method 4. However, the BWROG has not yet provided sufficient detail for the staff to reach any specific conclusions relative to the adequacy of using a CFD model for the purpose of 1

                 - determining the ZOI for a pipe break. As a result, the staff does not consider Method 4 acceptable l

without further detailed justification on a either a generic or plant-specific basis. 3.2.2 Sources of Other DryweH Debris Section 3.2.2 of the URG focuses on quantifying the sources of debris in the drywell other than pipe insulation. The introduction to this section reviews the relevant guidance provided in RG 1.82, Revision 2, and categorizes the other sources of drywell debris as transient, fixed, or latent debris. l Opecifically, the URG defines transient debris as non-permanent plant material brought into the i drywell, typically during an outage. Examples of transient debris include tools, rags, and temporary l filters. Fixed debris is part of the plant, and only becomes debris during a LOCA. Paints and l coatings which are delaminated from the coated surface by direct steam impingement from a pipe l break is an example of fixed debris. Latent debris appears after prolonged exposure to a LOCA environment, such as an unqualified coating whien is not directly impinged upon by the LOCA break l jet, but which subsequentlyfails as a result of prolonged exposure to the temperature, pressure, and radiation of the post-LOCA environment. l l The URG also cautions users that their FME, housekeeping, and inspection programs must be adequate to ensure that the quantities of each of these types of materials do not exceed the quantities assumed in the plant's evaluation of ECCS strainer loading. In developing the guidance for this section, the URG vsed the following supporting analyses from the Technical Support Documentation (Ref. 2): (1) " Performance of Containment Coatings During a Loss of Coolant Accident," Bechtel Power Corporation, Vol.111, Tab 12, of the URG Technical Support Documentation (Ref. 51).

                 - (2) "BWR Owners' Group Suppression Pool Sludge Generation Rate Data," BWROG, Vol. ll1, Tab 4, of the URG Technical Support Documentation.

The URG provides.the following recommendations for "other drywell debris sources" when l performing a plant-specific analysis for sizing the strainer: ( .e Dirt / Dust: The URG suggests that licensees assume a value of 150 lbm in the strainer head loss ! correlation. This value is founded on engineering judgement. The URG states that this value is believed to be conservative and considers concrete dust generated by break jet impingement ) on the containment boundaries. In addition, the URG states that, if licensees use a lower value, t 29 !' j . l

  -=           r     ,e

y _. ._ _ .. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ . _ _ _ _ _ _ ___ _ I they should documentthe basis for that value, including any programmatic controls that would help to maintairi the value within limits. I I e Other Transient Debris: The URG does not provide any specific values for other transient  ; debris. This judgment is left to the individual licensees, and should reflect their own baseline assumptions. The URG states that the' inspection frequency should be consistent with the i amount of NPSH margin, with smaller NPSH margins requiring (in the BWROG's opinion) l l greater inspection frequency.  ! e ' Rust from Unpainted Steel Surfaces: The URG recommends a value of 50 lbm, on the basis l l l l of engineeringjudgment. Again,the URG states that this value is believed to be conservative j and considers" unpainted steel surfaces in the drywell, the main vents /downcomers, and those ' in the suppression chamber above the pool level which may be swept as a result of LOCA- . induced swell." in addition, the URG states that, if licensees use a lower value, they should l document the basis for that value, including any programmatic controls that would help to j , i maintain the value within limits. e Particulate Debris Sources: The URG does not provide any specific guidance for particulate j i- debris sources, beyond cautioning licensees that other sources of fixed particulate debn,s may  ; l be present in the drywell on a plant-specific basis, j Paints / Coatings:On the basis of the Bechtelreport cited above (Ref. 51), the URG recommends  : l l that licensees assume specific

• bounding" values for coatings as available for transport to the

l.  !

l suppression pool. The recommended values are 47 lbm for inorganic zinc coatings, 85 lbm for inorganiczine topcoated with epoxy, and 71 lbm for 100% epoxy coating. These coatings are f assumed to be in the ZOI of the steam jet from the break. I e Concrete: The URG does not provide any specific recommendations other than a licensee l should evaluate the potentialfor concrete debris if the licensee is not using the value for dirt / dust l noted above. i I e Unqualified / Indeterminate Paint / Coatings: The URG does not provide any specific guidance l l other than a licensee should determine the quantity of such debris that can be available to l transport to the suppression pool. As an attemative,the URG notes that licensees may remove  : [ the unqualified or indeterminate coatings, or attempt to qualify them through in situ qualification l- However, the URG does not provide any guidance regarding how licensees can accomplish this j i in situ qualification. o Other Latent Material: The URG cautions licensees to consider the possibility that other latent k materials might become debris as a result of exposure to the LOCA environment. The kinds of l , 5 materials that might be of concem in this category include adhesive tags backed with an unqualified adhesive. l Staff Evaluation of Section 3.2.2: Although much of the guidance in this section is general, the  ; guidance appears adequate to caution licensees about considerations needed for an adequate l ECCS analysis. However, the staff believes that licensees should exercise caution in using the  ; j guidance in this section, especially when considering plant operation relative to strainer design. For 30 a

example, the URG states (on page 50) that " Licensees should recognize that the rigor of FME programs should be adequate to ensure that the transient debris source term used as a design input value in the strainer sizing calculationsis not exceeded. Consequently, licensees should consider i the trade-off between operationalflexibility and strainer size when establishing the values of drywell debris considered to be available for transport to the suppression pool." While this statement is accurate as far as the ECCS suction is concerned, it lays open a potentially larger problem with FME. FME is not solely an ECCS suction strainerissue. The FME problem also deals with materialsleft in piping systems and system components such as valves (See Refs. 49,50,59,60 and 61). Licensees should also consider other potential problems caused by poor or inadequate FME programs, not just the potential impact on suction strainers. The staff believes that FME  ! should always be maintained at the highest possible level when the potential exists to impact a safety system. Providing margin in strainer size to allow for breakdowns in FME controls is prudent to avoid operability concems; however, it in no way relieves the licensee of the responsibilities regarding foreign material control. As a result, the staff concludes that page 51 of the URG presents an unacceptable assertion in stating, " Note that where use of an adequately conservative value is assumed for a particular debris species (e.g., dirt / dust), periodic inspection are not necessary." In its response (Ref. 64) to the draft SER (Ref. 63) on the URG, the BWROG attempted to clarify this assertion by stating, "The BWROG notes that the intent of this URG statement is that inspections to quantify the amount of dirt / dust are not required. It was not intended to imply that general cleanliness inspections were not appropriate." The staff agrees with the BWROG's clarification. It is the staff's opinion that periodic cleanliness inspections are always necessary, regardless of any baseline assumptions used in the ECCS analysis. The interval between such inspections should only be adjusted on the basis of actual licensee performance, opportunity for introduction of additionaldebris, and the amount of conservv - min the base assumption. Similarly,the staff notes the same problem with the assertion on Pa;c a of the URG that "A larger NPSH margin should require less frequent inspection / audit than a smaller margin." NPSH margin is not the only characteristic of significance when evaluating inspection and maintenance intervals. If licensee performance does not demonstrate effective FME controls, inspection frequency must be increased in addition, the potential for introduction of debris since the last inspection should also be a consideration in determining inspection scope and interval. The principal strength of Section 3.2.2 is that it reviews important considerations of which licensees should be aware in assessing debris sources other than pipe insulation. It also provides some quantitative suggestions for the amounts of debris that may exist in drywells and suppression chambers. The discussions emphasize that FME, housekeeping, and inspection programs must be capable of keeping debris quantities within the limits assumed in the evaluation of the ECCS strainer loading from such debris. However, the staff believes that Section 3.2.2 has some technical shortcomings. First, some of the l guidance is too vague to be used in a consistent generic manner. Second, important assumptions regarding debris quantities are not supported by technical analysis or plant observation. While the staff does not believe these judgments are inappropriate, there is still concem regarding the lack of adequate justification for the recommended assumptions. On that basis, the staff offers the I following specific comments: 31 l

e Dirt / dust: The discussion in Section 3.2.2.1 states that only a small fraction of dirt / dust not , directly exposed to the'LOCA jet or impacted by break leakage flow would be expected to be l transported by the break flow or because of sprays if containment sprays are used. The  ; statement that only a small fraction might be transported to the suppression pool is not  ; supported by test data or actual observation. Licensees should also consider the fact that i steam / air velocities may be high throughout the drywell following a large-break LOCA. Also, steam condensation and run-off on structures could contribute to entraining dirt / dust in the j runoff; Once reaching the floor of the drywell, the turbulence in the water pool on the floor may be sufficient for the dirt to remain suspended and be transported to the suppression pool. (This  ! is especially likely in the case of a recirculationline break where water flowing out the break can provide a substantial amount of turbulence in the water pool on the drywell floor.) The staff , believes that conditions in the post-LOCA environment would be conducive to transport dirt / dust , to the suppression pool. The URG suggests a value of 150 lbm of dirt / dust as the value 'icensees l could use to ,

       " conservatively" address this type debris originating in both the drywell and suppression chamber areas above the suppression pool where dirt and dust could be entrained by pool swell.

4 The URG also states that this quantity includes concrete that would be eroded by the LOCA jet. , This quantity of 150 lbm is termed a judgment and is not supported by any analysis or - investigations. While the staff does not believe that use of the 150-Ibm assumption is , inappropriate,the staff does believe that some licensees may wish to conduct a more thorough l evaluation for applicability to their plant. The staff believes this could be done very easily l through sampling. It would be relatively straightforward for an individual licensee to take . samples of dirt and dust from drywell and suppression pool areas, determine the typical weight- j per-unit-area on collecting surfaces, and estimate a bounding value for all applicable surfaces. , An allowance would then have to be added for concrete dust generated by LOCA forces. The  ! current approach is simply a judgement, and as a result, some licensees may wish to ensure that it is conservative, in addition, licensees may wish to consider the potential impacts on the

• baseline assumption of containment size and the accumulation of additional dirt / dust over the l

l operating life of the plant. This method could also be used to estimate the amount of conservatism in the 150-lbm assumption for a given plant. The staffis not requiring that this  ; type of assessment be performed bylicensees. Rather, the staff is only noting that some i licensees may wish to perform this type of evaluation for their plant. For example, a licensee , l-with a small NPSH margin may wish to determine the amount of conservatism in their baseline j assumptions for other drywell debris sources. . e Rust Flake: The URG states that 50 lbm of rust flakes in the strainer head loss evaluation j

• conservatively" addresses the amount of rust that may be removed from unpainted steel i l surfaces and transported to the suppression pool. This URG-recommended assumption l- includes surfaces in the drywell, the vents /downcomers, and the suppression chamber above  !

the suppression pool. However, the URG does not document the basis for the 50-lbm  ! recommendation (other than engineering judgment). Again, as with the dirt / dust assumption  : discussed above, the staff does not believe that using the 50-lbm assumption is inappropriate. , However, the staff believes that an individual utility may wish to evaluate the applicability of this , value to their plant as was discussed above for the URG's recommended assumption for l dirt / dust. The staff believes that a licensee could develop a sound technical basis for the rust  ! flake assumption by sampling applicable drywell and suppression chamber areas and l l 32

l I conducting walkdowns to establish typical quantities of rust per unit area. (This information ! could be obtained and used to develop total plant estimates.) The URG also states that the BWROG expects that only a small fraction of the rust would become detached from steel surfaces during a LOCA event. However, the staff points out that this statementis unsupported by data or technical evaluations. As a result, the staff believes that some licensees may wish to more thoroughly evaluate applicability of this assumption to their plants, o Coatings: The URG provides estimates of the quantities of three types of qualified paints and I coating materials that may become debris as a result of LOCA jet impingement forces. The i , values presented in Table 3 (on page 58 of the URG) are predicated on a study performed by L Bechtel for the BWROG (Ref. 51) and apply to qualified coatings delaminated by direct jet impingement from a pipe break. The staff has not identified any concerns relative to the l conclusions presentedin Ref. 51. However,the staff notes that the issue of coatings and their

potentialimpact on the ECCS is an issue currently under staff review, and is the subject of GL l' 98-04,"Potentialfor Degradation of the Emergency Core Cooling System and the Containment Spray System After a Loss-of-CoolantAccident Because of Construction and Protective Coating l Deficienciesand Foreign Materialin Containment," dated July 14,1998 (Ref. 68). As a result, f

the conclusions presented in Ref. 51 are still under staff review. l By contrast, the guidance for unqualified coatings is incomplete and unsupported. For example, l - on page 61, the URG states, "After exposure to the LOCA environment, but only after containment pressure is reduced, there is a possibility that indeterminate / unqualified coatings may detach from the surface to which they were applied and become a debris source." The staff l- is particularly concerned because there is no basis for this statement and, in the staff's opinion, l it is entirelyinaccurate in fact, there is no evidence that indeterminate or unqualified coatings would be latent debris at all. For instance,if the coatings have lost adhesion over time because l of improper application or lack of qualification for the environment, there is no reason to assume that the turbulent environment of the reactor vessel blowdown could not cause the coating to detach and transport to the suppression pool. On page 62, the URG continues," Dependent on i several plant-specific factors, it may be possible to show that the failure of indetermhate/ unqualified coatings would not occur until late enough in the LOCA progression that there is no transport mechanism available to transport the failed coating from the drywell to the wetwell." However, the URG does not identify the " plant-specific factors" or discuss the basis for the statement. The staffis very concerned that this part of the URG greatly downplays the potential significance of unqualified / indeterminate coatings. i

                                      ~ While not providing explicit guidance, the URG as currently written tends to lead licensees away from accounting for this potential debris source by merely discussing why these coatings might         i not have an impact on the ECCS. In actuality, the potential significance of these coatings             I depends on the amount of such coatings in the containment, the licensee's NPSH margin, how well these coatings were applied, and the coating performance characteristics in both normal operation and LOCA environments. In light of recent events involving qualified coatings, as discussed in GL 98-04 (Ref. 68), and the lack of substantive technical basis for the BWROG             l I

guidance regarding unqualified and indeterminate coatings, the staff does not have enough information to evaluate the adequacy of the BWROG guidance. However, the staff considers it prudent to address unqualified / indeterminate coatings in the sizing of the new strainers installed in response to NRCB 96-03. This would help to avoid potential operability concerns ! l 33 1

• i and hardware modifications (e.g., resizing of the suction strainsrs) in tha future if clogging  ;

i concerns are raised as part of the staffs review of coatings-related issues. For the same j reason, licensees should consider the potentialimpact of " qualified" coatings that are improperly applied or maintained? Conclusions Regarding Section 3.2.2 The NRC devoted considerable effort to developing the NUREG/CR-6224 study (Ref. 31) and to conservatively estimate dirt / dust and rust debris. Where j l'  : . provided, the values suggested in the URG are about the same or larger than NUREG/CR-6224 values. As a result, the staff concludes that use of these values is acceptable; however, the staff 1- notes that the NUREG/CR-6224 study was conducted on a Reference Mark I containment. For this  ! i reason and the additionalreasons cited above, the staff believes that some licensees may wish to l

evaluate'the recommendations of this section for applicability to their plant. This is a sta# {

1 recommendationonly, andis not considereda requirementforacceptance of the URG by the i sta#. This concem is especially true for Mark Ill containments because they have larger concrete  ! areas, in addition, the potential for dirt / dust accumulation may be greater in the larger containments  ! !' i

       . if they have significantly larger areas of horizontal surfaces. The sensitivity of the head loss calculations to these numbers may vary with the assumptions and the resolution option selected by           l 4                                                                                                                    i the licensee. If a given licensee is installing a large passive strainerwhich reflects very conservative assumptions relative to the quantities of fibrous debris and sludge assumed to reach the strainer j         surface, then that licensee may be able to demonstrate by sensitivity analysis that variations in the      :
~

quantities of dirt, dust, rust flakes, and so forth may not significantly affect the overall head loss across the strainer. If, however, a_ licensee attempts to justify their current strainer, reduce the l amount of conservatism in the baseline URG methodologies, or use assumptions that are as  : j " realistic" as possible, then the significance of the values determined in accordance with Section  ; j 3.2.2 of the URG may escalate significantly.- i i i Consistent with the staff's guidance (discussed above), some licensees may wish to evaluate the  ! i applicability of the conclusions of the Bechtel coatings report to their plant. Most importantly, as l noted above, the staff concludes that licensees should be cautioned to carefully evaluate the  ; potentialimpact of unqualified and indeterminate coatings on ECCS suction strainer head loss. If . I available, licensees are encouraged to use test data to support their evaluation of coatings. It is the l

]

understanding of the staff that the BWROG is currently conducting a test program designed to evaluate the potential for coatings to become debris and transport to the suppression pool.  ; However, if in doubt, assuming that the coatings reach the strainer surface would clearly be the conservative measure. This would reduce the licensees' risk relative to the coatings issue, and  ; could lead to additional margin in the strainer design if URG statements minimizing the potential  ; impact of unqualified protective coatings are supported by the results of the staff's coatings review. , 3.2.3 Drywell Debris Transport j i Section 3.2.3 of the URG, entitled"Drywell Debris Transport," documents the BWROG's guidance f regarding various options for estimating the fraction of the damaged insulation (generated in the , drywell)that will be transported to the suppression pool as a result of the reactor vessel blowdown , and various mechanisms that can wash debris down to the suppression pool. The guidance l provided in this section is based on the following supporting analyses found in the URG Technical Support Documentation (Ref. 2):  ; 34 ;

1 (1) " Testing of Debris Transport Through Downcomers/ Vents into the Wetwell," Revision 1, URG l Technical Support Documentation, Vol. II, Tab 2, Continuum Dynamics, Inc., Princeton, NJ. (2) *BWR Drywell Floor Flow Modeling Following Pipe Break Loss-of-Coolant Accident," URG Technical Support Documentation, Vol.111, Tab 1, General Electric Nuclear Energy, San Jose, CA. (3) " Summary of Debris Washdown Experience," URG Technical Support Documentation, Vol. Ill, l Tab 17, BWROG. The staff reviewed the completeness and accuracy of the guidance in URG Section 3.2.3, as well as the associated supporting analyses, in addition, the staff evaluated this guidance against the guidance providedin RG 1.82, Revision 2 (i.e., transport fraction = 1), the results of the BWROG-sponsored research, and the results from the NRC-sponsored research conducted by Science and Engineering Associates, Inc. (SEA). This review revealed that the BWROG developed the following methodology to determine the  ! amount of debris transported from the drywell to the wetwell: I For each insulation type tested at the AJIT facility:

• The BWROG estimated the fractions of insulation contained in the ZOI that would be destroyed (destruction factor). The debris was then divided into three distinct size categories on the basis of the test data (" fines," "large pieces," and " blankets"). These fractions were calculated as '

i integral values applied over the entire ZOI volume for several insulation types making use of experimental data obtained from the AJIT. In addition, the URG estimates assume that, for , NUKON, all insulation contained within 3 UD of the break is destroyed into fines. In its response 1 (Ref. 64) to the drat SER (Ref. 63) on the URG, the BWROG provided further clarification on their methodology by stating that "100% destruction within 3 UD was assumed for all debris types." For " fines":

• The BWROG estimated the fraction of the mass of" fines"that would be transported as a result i of blowdown following a steamline break and a recirculation (water) line break. Different estimates were developed for Mark I,11, and til containments, on the basis of small-scale tests of downcomer geometries which were sponsored by BWROG and conducted by Continuum Dynamics, incorporated (CDI).
• The BWROG estimated the fraction of the mass of fines that would be transported as a result of washdown following a blowdown. For the recirculationline break, the ECCS runout flow was used as the basis, while spray flow was used as the basis for the steamline break. These estimates were founded on 1) small-scale experimentaldata from BWROG tests,2) washdown test data obtained from previous sources, and 3) one-dimensonal (1-D) and three-dimensional (3-D) modeling of water flow on the drywell floors. Different estimates were developed for Mark I, ll, and lli containments.

!

• The sum of these fractions (transport factor) provides the total fraction of fines transported to the suppression pool. Multiplicationof this transport factor by the estimated fraction of fines in l

35 I

 - .- . ..       -      -=      -..    - -.                  _.-.- _.-.--.                 -._           - _ - - ~._. -

t ' .the damagedinsulation provides a total mass of fines from the damaged insulation that would , !- be transpoded to the suppression pool by blowdown and washdown. l f For large pieces:  ; !' e No direct transport was assumed for the pieces located above thq lowest grating. The URG 2 considers that they can only be transported after erosion.  ! I e . The BWROG ectimated a fraction for "large pieces"' located below the lowest grating that would be transported during blowdcwn, and for the amount that would be eroded and transported l i l during the washdown phase that follows the reactor vessel blowdown. [ , For blankets: i e According to the BWROG, no transport is possible. The individual destruction and transport fractions were used to develop combined l j l destruction / transport factors for each insulation type as a function of the containment type and i l location of the debris. Tables 5 and 6 (on pages 83 and 84 of the URG), list these fractions for severalinsulations. To estimate the fraction of insulation debris (contained in the ZOI) reaching the suppression pool, i individual licensees may choose to use a drywell transport factor of 1.0, the value listed in the  ! Regulatory Guide 1.82, Revision 2 (Ref. 5), or the values listed in Tables 5 and 6 of the URG. For other drywelldebris,the URG recommends a drywell transport factor of 1.0. The URG ctates that . use of other transport values by licensees should be supported by an evaluation justifying their l bases. t Staff Evaluation of Section 3.2.3: In evaluating this section, the staff conducted a confirmatory  ; analysis (see Appendix H to this report), which yielded the following results: L Drywell To Suppression Pool Transport Factors:

i I

e The experimental data for drywell transport is dependent on the results of small-scale tests j e which have not been properly scaled. The staff forwarded its scaling concerns about the i BWROG testing at the time of theirinception by letter (Ref. 20). None of the staff's comments appearto have been resolved to date. In addition, the staff's analysis (See Appendix H to this report) suggests that the flow rates and duration simulated.in BWROG testing are not prototypical of conditions that exist in BWR drywells following a LOCA. For example, the flow velocities simulated in these tests are about 50% of the flow velocities expected following a . postulated 61-cm (24-inch) diameter steamline break. As a result, these tests may provide  ! erroneous estimates of drywell transport it was not clear to the staff in evaluating the BWROG , test program whether the test results would be reasonable, conservative, or non-conservative ,

                     - if scaled to a full-size plant. There is inadequate substantiation for the BWROG's claims that      l use of these test results would conservatively bound the drywell transport fraction.

36 j

 . -~     . . - . - . . .... - -- - - --- -                                - -.__ ---- --

e From the staffs research, the two primary keys to debris transport are debris size distribution and location. Testing conducted by the NRC in support of its confirmatory research in the area of debris transport has shown that floor gratings typically used in BWR plants are very effective at limiting transport of larger debris sizes. However, these gratings are not very effective at limiting transport of fine debris. The results of the staffs study and testing will be documented , in NUREG/CR-6369, "Drywell Debris Transport Study," which is scheduled to be published in i September 1998. The study's findings lead to the conclusion that calculation of fine debris is l criticalin evaluating the amount of debris that could ultimately transport to the suppression pool during a LOCA. In addition,it is also criticalto calculate the amount of debris generated below the lowest continuous grating in the drywell. e Another significantfinding is that the staff-sponsored tests of Mark 11 downcomer geometry did i l not identify any basis to conclude that the transport fraction for a Mark 11 containment would be ! different from that of a Mark I or Mark 111 containment. Therefore, the staff finds that the

transport fractions for Mark 11 containments listed on pages 75 and 80 of the URG are unacceptable. The URG also gives fractions (on the same pages) for fine fibrous debris i transport and RMI debris transportin Mark I and Mark lit containments assuming that 100% of l the fine debris will transport to the suppression pool.. These fractions are consistent with the staffs transport study and RG 1.82, Revision 2 (Ref. 5), and, therefore, are considered j acceptable. Moreover, the staff believes that these same fractions should also be used for Mark ll containments.

l e Page 76 of the URG provides guidance regarding the transport fractions to be used for large , fibrous debris (not whole or partial blankets which are considered unlikely to transport) ) generated below the lowest grating. Specifically,the values given are 70% for Mark I and Mark l l Ill containments and 30% for Mark ll containments. As noted above, the staffs confirmatory testing in support of its drywell transport study did not identify any basis for different transport l_ fractions for Mark 11 containments. Given the results of the drywell transport study, the staff l concludes that the transport fractions used should be the same for all three containment types. Similarly, pages 83 and 84 of the URG provide combined debris generation and transport factors  ! for various insulation type. Each factor is further divided into containment type and location of  ! the debris source (above and below the lowest grating in the drywell). On the basis of the staff-sponsored drywell debris transport study, the staff concludes that (1) the factors for Mark 11  ; containments are unacceptable,(2) the factors Mark I and Mark Ill containments are acceptable, and (3) the Mark I and Mark lli factors should also be applied to Mark ll containments. e . In the draft SER (Ref. 63) on the URG, the staff evaluation of the BWROG's guidance for assuming erosion of large fibrous debris concludes that the URG guidance is adequate given that the unthrottled ECCS flow does not continue for more than 3 hours. However, the staff stated that if the flow does continue for more than three hours, licensees should determine an appropriatefractionto assume. NRC-sponsored tests demonstrated that erosion of NUKON'

           -is linear, which would facilitate ease in scaling of NUKON erosion. The staff also noted that similar testing could be conducted for other insulation types, if necessary, to determine an appropriate fraction to assume for erosion. In its response (Ref 64) to the draft SER, the                   4 BWROG responded to this issue by stating "The staff concem discusses the erosion rate but does net consider the conservative position taken in the URG on the amount of insulation material that would be exposed to erosion... ..the URG assumes that 25% of fibrous "large 37 p         - . - - - .

j! , I l

                     ' debris"(i.e., not fines)is exposed to the eroding effects of the spill from the break. The BWROG l

believes that any concerns regarding the effect of erosion over periods greater than 3 hours are l more than offset by the conservative assumption on the amount of insulation and that adopting the staff position could result in additional operator burdens and would require a change to emergency operating procedures which would be inconsistent with their symptom-based design." On the basis of the BWROG's comments and further review of the level of conservatism in the URG analysis methodologies (see Section 5.0 of this SER), the staff concludes that the URG guidance on erosion of large fibrous debris from break flow is acceptable. Destruction Factors:

                  * ; The BWROG calculatedthe destructionfactors provided in the URG from the AJIT results. The  .

test results and associated data analysis are documented in Reference 52. The destruction  ; factors are derived on the basis of the calculation of q., which is defined as the fraction of debris  ; generated in a form that would have a low transport efficiency (e.g., large pieces or blankets). The BWROG conducted tests at several different distances from the jet nozzle (x/D) to' determine the pressure at which debris would be generated, the amount of debris generated, and the rough size distribution of the debris. The BWROG then calculated q, for each x/D test l result and integrated the values to give an average q, (q,4,,,,,)over the entire ZOI where damage would be expected to occur. For each insulation type and mode of encapsulation, the  ; URG thus provided a set of destruction factors in the URG that can be used to estimate the fraction of the insulation containedin the ZOI that would be destroyed into " fines." In principle. l i these values were derived on the. basis of the following methodology: (1) Full-scaleinsulation blankets were mounted on a target pipe located normal to the JCL. In ( [ i L almost all cases, the blankets were mounted such that the latches on the steel jacketing (if jacketing was used) were arranged to face the nozzle, while the seams in the blanket were i arranged to face away from the nozzle. This resulted in a conservative situation because  ! the protective steeljacket was quickly blown off, exposing the canvas-covered blanket to the jet. Meanwhile, because the blanket seam faced away from the nozzle, the blanket was  ; maintained in position for a longer duration. (2) After exposure to approximately 5 seconds of blowdown (although the valve was closed at j the 5 second mark, the blowdown continued for at least 3-4 more seconds), the amount of debris generated and the rough estimate of the debris size distribution was measured. l (3) The size and amount measurementswere carried out for different UD values. The fraction

• of debris not destroyed into fines (q ) was then plotted as a function of lJD and integrated over the entire ZOI to estimate the q,4,,,,, for that insulation and mode of encapsulation. l l

(4) To account for unforeseen phenomena, the q, numbers were further reduced by assuming , that all of the insulation contained in a spherical region within a radius of 3 pipe diameters 1 from the break would be destroyed into fines  ; i 38

L i e The staff reviewed this derivation process and its overall results. In addition, the staff conducted < both experimentaland analyticalstudies. On the basis of these studies, the staff concludes that

                      - The blar,ket arrangement used in the BWROG testing is highly conservative. In the

,. NRC-sponsored testing, the amount of debris generated was substantially less when the ! latches were arranged to face away from the nozzle or when the blanket seams were . l located facing the nozzle. In the former case, the steel jacket remained for longer duration l and protected the blanket. In the latter case, the blanket was stripped off the target in such

                         . a short time that very little damage was observed.

t

                      - The targets and structures located in the jet pathway would provide considerable protection
                                                                      ~

to the blankets. In the NRC-sponsored experiments, artificial means (high-strength steel bands) had to be used to hold the blankets in place to maximize debris generation. l Otherwise, no more than 25-30% of the insulation olankets were destroyed by the jets. l e The BWROG approach has the following conservatisms:

                     - Not all the targets in a BWR drywell are normal to the JCL. In fact, the stcffs survey suggests that a, majority of the piping (>65%) would be located parallel to the jet flow. In such a case, only a small portion of the blanket would te subjected to high dynamic pressures (unlike the BWROG experiments where most of the blanket was subjected to jet flow).
                     - Not all of the targets have steel jacket latches facing toward the nozzle and blanket seams facing away from the nozzle. The vendor survey indicates that no order is followed for installing the steeljackets or insulation blankets (although accessibility considerations often play a role).
                     - The blowdown does not continue at high pressures as tested in the BWROG studies.
                     - Finally,the structures offer considerable protection. The staff performed a CFD calculation to quantify the impact of structural impediments. This calculation'used more realistic structural elements to demonstrate how the jets are diffused by structures.

e On that basis, the staff concludes that the approach followed by the BWROG would yield conservative estimates for most insulations. This can be demonstrated by an analysis of steel-jacketed NUKON insulation, for which Method 2 yields a spherical ZOI approximately 11 pipe j diameters in radius. In the NUREG/CR-6224 reference plant, such a ZOI would include approximately25.5 m 8(900 ft') of insulation. Using an n, value of 0.78, this translatesinto fines of approximately 5.7 m8 (200 ft*). This value is slightly lower than the total volume of NUKON* insulation contained in a sphericalZOI with a radius of 7D in the reference plant used in the staff j study (NUREG/CR-6224). The CFD calculations conducted by the staff clearly demonstrate j that, given the structural congestion, high-velocity flows (sonic flows) do not continue beyond

                    - a spherical region with a radius of SD. Thus, the staff concludes that BWROG's suggested                              ;

numbers are probably conservative. However, the staffidentified a weakness in the URG data because the BWROG obtained q, values for several insulations on the basis of a very limited set of experimental data. (Examples are Temp-Mat, K-wool and some of the RMI.) In these 39

                              ,.                        ,                                               - ~ , . ,          -  - - , - - -

h cases, the BWROG used less than 5 data points to derive the r), values. The staff believes that the URG methods for determiningZOI (see Section 3.2.1.2 of this SER) and debris generation (noted above) are sufficiently conservative to outweigh the weakness identified regarding limited l data points for certain insulation types. Section 5.0 of this SER provides a more detailed

          ' discussion on the amount of conservatism in the URG analysis methodologies.

The staffs review identified the following strengths of this URG section: e The URG follows a logical path for conservativelyestimating the amount of insulation debris and the associated drywell transport factor. This path is somewhat similar to the one used in

          ~ NUREG/CR-6224 (Ref. 31) and in the staffs Drywell Debris Transport Study.                                                                l e    This section reviews important considerations of which licensees should be aware in estimating the drywell transport factor, e    The transport fractions for fibrous debris above the lowest grating (provided on pages 75 and 80 of the URG) for Mark I and Mark lli containments are considered to be conservative and appropriate for use.                                                                                                                     j
     -The major weakness of this URG section is that the test data from the BWROG-sponsored drywell transport tests were not obtained over the range of experimental variables that would support
     . scaling the data for full-size drywells. Similarly, the chosen experimental set-up does not scale appropriately to the BWR drywells.                                                                                                            ,

Conchmiens Reamrdina Section 3.2.3: In summary, the staff draws the following conclusions regarding URG Section 3.2.3: e .The staff finds that the transport fractions for Mark ll containments (listed on pages 75 and 80 of the URG) are unacceptable. The URG also gives fractions (on the same pages) for fine , fibrous debris transport and RMI debris transport in Mark I and Mark 111 containments, assuming that 100% of the fine debris will transport to the suppression pool. '.. 2'1 concludes that these values are acceptable and should also be used for Mark ll containments. Similarly, for the , combined debris generation and transport factors for various insulation types (pages 83 and 84 of the URG), the staff concludes that (1) the factors for Mark 11 containments are unacceptable, (2) the factors for Mark I and Mark lli containments are acceptable, and (3) the Mark I and Mark i lil factors should also be applied to Mark 11 containments. e = Page 76 of the URG presents guidance regarding transportfractions to be used for large fibrous j debris (not whole or partial blankets) generated below the lowest grating. Specifically, the values given are 70% for Mark I and Mark lli containments, and 30% for Mark 11 containments. ' The staff concludes that (1) Mark ll containments should use the same transport fraction as Mark I and Mark lil containments,(2) the BWROG provided insufficienttechnicaljustification for L assuming a transport fraction less than 100% for large debris generated below the lowest  ; drywell grating. However, the staff notes that the combined debris generation / transport factors t (pages 83 and 84 of the URG) conservatively bound these transport fractions, in its response (Ref. 64) to the draft SER (Ref. 63) on the URG, the BWROG noted "the BWROG approach is , to calculate a transport factor as a percentage of the inial debris while the staff approach is to 40 ' 1

l i' use a transport factor for transoortable debris. The BWROG notes that in the NRC Drywell Debris Transport Study, the NRC interpretation of the AJIT test report is that 40% of the NUKON* insulation within the ZOI is in the form of " canvassed debris"which is not transportable Hence, the NRC position is that the maximum amount of debris which can be transported to the suppression pool from the lower portion of the drywellis 60% of the initialinsulation within the  ; i 201, a lower number than the corresponding 78%" that would be predicted using the URG l combined debris generation / transport factors.- The staff concurs with the BWROG comment. e The staff believes that the URG provides adequate guidance for assuming erosion of large fibrous debris. e The approach followed by the BWROG for determining destruction factors would yield l conservative estimates for the insulations included in the URG and is, therefore, acceptable. The staff notes, however, that banding of insulation to reduce debris generation has not been accepted by the staff as a resolution option.

                                                                                                                   /

3.2.4 Suppression Pool Debris The focus of Section 3.2.4 of the URG,~ entitled " Suppression Pool Debris," is on sources of debris which are present in the suppression pool before the occurrence of a LOCA. Both transient debris and sludge are potentially present in the suppression pool at any given time. This section of the URG also reviews the LOCA-generated debris and transient debris, both of which were discussed

     'in earliersections of the URG. The guidance was developed, in part, on the basis of an extensive
     ' BWROG survey of suppression pools of selected operating BWRs in the United States (Refs. 54 and 55).

The BWROG survey showed that suppression pools can contain various types of debris unrelated ] to a LOCA. This debris would be transported to the ECCS suction strainers and could contribute to head loss across the strainer. Section 3.2.4 provides guidance related to identifying various sources of debris and important considerations that should be used to estimate the quantities of such debris. The URG identified the following sources of suppression pool debris: e fibrous debris entrained in the pool volume prior to a LOCA. l e non-fibrous debris entrained in the pool volume prior to a LOCA.  ; e the dirt / dust above the pool area which may be washed down during pool swell. j e other potential debris, such as operational debris and unqualified / indeterminate coatings. ' During its evaluation of the strainer clogging issue, the BWROG conducted a survey to estimate the quantities of sludge entrained in the suppression pools. On the basis of this survey, the BWROG recommended a sludge generation rate of 150 lbm per year. This sludge generation rate can be , coupled with frequency of pool cleaning to estimate the total quantity of sludge for use in the l analysis of ECCS strainer blockage. I l i 41 L l~

i l I j The URG does not specify generic estimates for any other types of debris. However, the URG does list the considerationsthat licensees should address while estimating the quantities of other debris to be used in the analysis of ECCS strainer blockage. The URG cautions licensees to recognize that the operability of the ECCS system may be challengedif the licensee cannot demonstrate that suppression pool debris source terms will be controlled at values less than assumed in the strainer sizing calculations. Staff Evaluation of Section 3.2.4: A single analysis was performed in support of this review. Its objective was to evaluate the adequacy of the BWROG recommended sludge volumes and their tractability. This analysis is documented in Appendix J. On the basis of that analysis, the staff concludes that the BWROG interpretation of survey information is acceptable and the URG guidance in this section is acceptable. 3.2.5 Suppression Pool Transport and Settling The BWROG recommended that licensees should not take credit for settling of debris in the pool l l during the high-energy phase where the pool undergoes chugging and/or condensation oscillations

The BWROG also recommended that all suppression pool debris should be assumed to be resuspended during this phase. Finally, the URG gives individual licensees an option to select no

! settling in the pool, even during later low-energy phase. or to estimate fraction settling making use of data and results from Appendix B to NUREG/CR-6224. Staff Evaluation of Section 3.2.5. The principal strength of URG Section 3.2.5 is that it reviews important considerations of which licensees should be aware in estimating the quantity of debris settlingin the pool. The staff did not identify any concerns related to this section, and therefore, it is acceptable. However, the staff notes that Appendix B to NUREG/CR-6224 provides the required ! data only for selected insulation and particulate types. Licensees using methods from Appendix B l to NUREG/CR-6224 for other types of insulation debris should exercise caution in extrapolating the ! experimental data and models. 3.2.6 Verification of Adequate ECCS Pump NPSH Section 3.2.6 presents the BWROG's guidance related to calculating strainer head losses and pump NPSH. This guidance is developed on the basis of the following report presented in the URG Technical Support Documentation (Ref. 2):

• CDI Report CDI-95-09, Revision 4, " Testing of Alternate Strainers with Insulation Fiber and Other Debris," Continuum Dynamics, Inc. (CDI), URG Technical Support Documentation,  ;

Volume I, Tab 2. This guidance specifically refers to Appendices A and B of that document for methodology and calculationalprocedures. ( Appendix A applies to passive strainer head loss predictionswith fibrous debris, while Appendix B applies to RMI debris.) The staff used the calculational procedures describedin Appendices A and B to assess the ability to predict the head losses associated with a number of the tests used to develop the procedures. The following discussion summarizes the staff's findings. 42

                                                     --                _ _ _ - -     _ _ _ _ _ _ _ _      a

URG Section 3.2.6.2.3 summarizes important guidance for applying Appendices A and B to CDI Report CDI-95-09. That technical support document describes the strainer head loss tests performed in develophg the calculational procedures presented in Appendices A and B, including the test facility, testing procedures, data reduction, and test results. The procedures in Appendices A and B are recommended for use by individual utilities to estimate head loss across the strainer as a function' of the flow velocity and the quantity and type of debris reaching the strainer. A dimension less head loss equation was provided for this estimate. Staff Evaluation of Section 3.2.6: The strainer head loss was predicted for a number of tests using the procedures outlined in Appendices A and B and compared with the corresponding experimentalhead losses.. The staff notes that the test results presented in CDI Report CDI-95-09 are the only data provided by the BWROG, and are for the stacked disk and star strainer types. The staff had two objectives in conducting its analysis. First, the staff sought to validate the calculational procedures by determining their ability to predict the test results from which the procedureswere developed. Second,the staff sought to evaluate the applicabilityof the procedures  ! to actual plant situations. This analysis is documented in Appendices I (fibrous debris) and K (for RMI debris) to this safety evaluation. In general, the results of the staff's analysis led to the conclusion that the approach outlined in Appendices A and B to CDI Report CDI-95-09 was unreliable and incomplete. l The URG contains valuable and useful data for predicting strainer head losses. However, the staff's i review revealed several concerns regarding the quality and applicability of these data.

      'e   The BWROG developed the URG model from test data where a true steady-state condition was not generally achieved. This implies that the debris loadings used in developing the model were

somewhat different than the actual loadings on the strainers.

e The BWROG developed the URG model for limited ranges of data (i.e., fiber, RMI and  ; particulate debris loadings, velocities, and strainer design), and using the model beyond these  ! limitations is especially risky because the models are non-mechanistic in nature, as illustrated by the following examples: l - The BWROG developed the model for lower debris loadings where the amount of fibrous debris was only large enough to fill the troughs in the strainer. Extending the correlation to 1 L higher loadings is inappropriate without additional substantive experimental or analytical

work. .

           - The BWROG primarily developed the model on the basis of NUKON' data. Its extension to other fibers is inappropriate without additional substantive experimental or analytical work.     !

i

           - The BWROG primarily developedits RMI saturation thickness guidance using star strainer                   !

r data, and an assumption that the debris bed would resemble a sphere. The URG does not } provide a basis for extension of this relationship to other strainer geometries. L

            - The BWROG RMI head loss correlations for the star and stacked disk strainers are based on data obtained for low debris loadings (insufficient volume of debris to fill the strainer

43 1

l l I

troughs). .The URG does not provide a basis for extrapolating the correlations to higher debris loadings. The staff believes that such an extrapolation will lead to non conservative head loss estimates.

      - The gravity head loss data for RMI was obtained for a chosen RMI debris size distribution.

Each utility must determine the applicability of the size distribution to their plant. For example,it is not likely that a plant having aluminum RMI would have the same RMI debris size distribution as a plant with stainless steel RMI. e The staff has shown that, in many cases, the URG model under predicts the experimental data used to develop the model; therefore, a licensee would need to review each head loss prediction in detail relative to the applicable data, to ensure a valid prediction. In addition, in many situations, such as the 60-point star strainer, a licensee would need to employ a significant safety factor in the prediction. e The BWROG used limited data (gravity head loss tests) to develop the " bump-up" factors used to account for miscellaneousdebris. In many situations,the bump-up factors have been shown-to severely over predict the head loss. While this over prediction is conservative, it can lead to severe design impacts, e Some of the head loss test runs (e.g., test run number J6) were conducted with thin fiber beds and large amounts of particulate debris. In these tests, the BWROG assumed that all particulate debris was captured by the debris bed, but this assumption is incorrect. The amount of particulate debris captured in the debris bed is unknown (i.e., underestimated). As a result, the use of these data to develop a correlation may under predict the impact of particulate debris and

     . lead to erroneous head loss predictions.

! e Two types of RMI debris were used in the URG strainer debris bed head loss tests (i.e., two l different size distributions of the 2.5 mil stainless steel foils), and each size distribution was used i over a different period of time. Thus, the tests for a specific strainer design are generally valid I only for one type and size distribution of RMI debris. For example, the stacked disk test l' (stacked-disk section of the self-cleaning strainer) only used the RMI debris obtained from l Diamond Power. Therefore, the URG model only applies to the stacked-disk strainer for this one type and size distribution of RMI debris. e The URG did not specify model validation, parameter sensitivity, or uncertainty analysis. This omission leaves open the question of whether a particularcombination of input parameters could cause the URG model to severely under predict head loss. I: On the Basis of this analysis, the staff has the following specific comments regarding this section of the URG: i e The staff is concerned that applying the URG strainer head loss model by blindly plugging l numbers into a cookbook step-by-step procedure as outlined in the report may lead to erroneous l head loss predictions. Rather, each prediction must be carefully anchored into head loss data l to ensure that it is both reasonable and conservative. The staff communicated this concern to the BWROG in Ref.11. However, the BWROG's response (Ref.13) did not address the overal 44

head loss prediction, instead relying on the accuracy of the bump-up factors. The staff, therefore, does not believe that the BWROG has resolved this concern. Moreover, the staff believes that resolution of this issue is vital to judging whether the BWROG correlation (if used by any licensee) is conservative, best-estimate, or under predicts. Resolution of this concern will also need to address the confidence level of the data (i.e., repeatability and uncertainties).

• The head loss predictions should use the same NUKON' debris properties that were employed in developing the URG model (i.e., densities and diameters) because the models are not sufficiently mechanistic to account for the effects of varying these properties. Also, the URG study used the fiber density of 38.4 kilograms per cubic meter (kg/m ) (2.4 pounds per cubic foot (Ibm /ft*)) which is the density generally assumed for the intact fiber insulation (sometimes referred to as the as-fabricated density). However, there are data showing that the density of actualdebris is considerably reduced by the destruction process. For example, fibrous debris used in tests conducted by Pennsylvania Power & Light Company (PP&L) at ARL had an actual density of 20.8 kg/m2 (1.3 lbm/ft ). By using this density rather than the as-fabricated density, )

the user would obtain a different fiber spacing distance, which would result in a different head i loss than if the user actually employed the as-fabricated density that is inherent in the non-mechanistic URG model. Since the basis for the URG correlation is not mechanistic and the procedure does not use more empirical parameters (rather, licensees are required to estimate more complex parameters),it is likely that use of the correlation by licensees will be inconsistent e The staff is concerned that applying the URG head loss prediction models to plant conditions that differ markedly from those conditions tested could lead to erroneous head loss predictions. Use of selected dimension less numbers creates the impression that the equation can be  ! generalized. However, the BWROG has not presented any analytical evidence to that effect.  ! As a result, licensees should carefully evaluate any extrapolations from the conditions tested. j At the inception of the alternate strainer test program, the staff cautioned the BWROG that its I approach for developing of a head loss correlation did not have a sound basis for extrapolating the correlation beyond the conditions for which it was developed. The BWROG responded that its testing was designed to be " functional" rather than a means for developing a correlation. However, the URG attempts to use the data compiled and correlation developed in a more l generalized form. For example, the data were obtained for conditions that simulate lower fiber loading on the strainers. The correlation should then be applicable, at best, to those conditions < However, the URG and its appendices do not state any such limitations. The staff therefore concludes that generalized use of the correlation beyond the original range of testing is unacceptable. e The experimentaldata, as well as the correlation presented for fibrous beds, were obtained for low-debris loading on the strainer surface. The staff has been unable to identify any rationale supporting use of the URG correlation for thick combination fibrous /particulatedebris beds, and it is the staffs opinion that the equation and procedures are not applicable for such beds. As a result, the staff recommends that licensees use vendor-specific test data demo ~nstrating the strainer head loss for various debris loadings up to and including the licensee's limiting debris load.

• The experimental data are neither complete nor supported by sufficient quantitative analytical reasoning to substantiate the URG statement that the thin-bed effect is not a concern for 45

I [

alternative strainers. The staffs analysis of the BWROG's data suggests that for the alternate i i strainer designs tested, small fiber loads coupled with large quantities of sludge will not result in very high pressure losses. In that context, it is reasonable to state that medium breaks will

.. not result in large head losses that are not bounded by large breaks, but a statement that no i ' thin-bed effect' was observed is incorrect. t 4

'     e    in calculating NPSH, licensees should ensure that their calculations are consistent with their

. licensing bases. For instance, no operator action is typically credited for the first 10 minutes [

during a postulated LOCA. Therefore, NPSH should be evaluated at runout flow until the plant's

licensing basis allows otherwise.

     .e    Reference 31 in the URG is considered an unacceptable methodology for determining the minimum NPSH for RMI debris beds. The staff finds that this methodologyincorrectly assumes that head loss across the strainer will be governed by laminar flow. While laminar flow is expected to be the case for fibrous debris beds, it would not be the case for RMI, where head loss will be dominated by turbulent flow. In the latter case, temperature correction is not necessary and, where used, will lead to non-conservative head loss estimates.

Conclusions Regarding Section 3.2.6 The staff concludes that the URG head loss correlation is unreliable and the guidance is inadequate to prevent inconsistent application of the correlation. 1 On that basis that the staff recommends that licensees employ vendor test data to demonstrate the head loss used to calculate the NPSH margin. The test data should include debris combinations  ; up to and including the worst-case debris loadings calculated for the plant. If a. scaled strainer model is used for conducting the head loss tests, the licensee should ensure that they have an  ; adequate technical basis for applying the vendor data to the full-size strainer.  ; 3.3 BACKFLUSH i

     .Section 3.3 of the URG provides the BWROG's guidance regarding backflushing of strainers. In                                                           j general, the URG guidance can be summarized as follows:

e The BWROG recommends against use of strainer backflush systems as a primary means of l resolving the ECCS strainer clogging issue, for the following reasons:

            - The time frame during which backflushing would be required is significantly less than 30 minutes. This places a hardship on the operators and raises human factors concerns.
            - For many plants, the BWROG anticipates that backflushing would need to be repeated                                                             j within 30 to 60 minutes. This may not be feasible, depending on the type of design used for                                    !

the backflush. e The BWROG also notes that the staff believes that backflushing, by itself, would probably not  ! be sufficientto resolve the issue. This is because the staff concurs with the issues cited by the BWROG above.  ;

                                                                                                                                                             )

46 [ i

e The BWROG believes that backflushing may be a viable defense-in-depth measure for plants with the necessary capability. Section 3.3 of the URG also gives a detailed list of design considerations for any licensee desiring to implement a backflush system. Staff Evaluation of Section 3.3: The staff reviewed the guidance provided in URG Section 3.3 and concludes that it completely discusses the types of considerations a licensee must address in implementing a backflush system. In addition, the staff agrees with the BWROG that backflushing is better used as a defense-in-depthmeasure (rather than the primary means of mitigating a LOCA). Therefore, the staff finds that the guidance presented in this section is acceptable. 3.4 SELF-CLEANING STRAINERS This section of the URG describes the design considerations that licensees must address in implementing a self-cleaning strainer design to resolve the strainer issue. In that context, this section correctly identifies some of the technical difficulties associated with developing an adequate self-cleaning strainer design to resolve the strainer issue: e optimizing the clean head loss and torque e startup of the plow which sweeps the strainer surface after debris has accumulated on the strainer surface during low-flow conditions e the effect of debris which gets chopped up by the plow on downstream ECCS components e surveillance / maintenance requirements Because of these issues, the BWROG recommends the use of this resolution option only if a passive strainer solution is not viable. Staff Evaluation of Section 3.4: The staff did not identify any deficienciesin this section. Because a self-cleaning strainerdesign relies on mechanical moving parts, the staff agrees with the BWROG that such a design is less desirable than a passive strainer for resolving the ECCS suction strainer issue.

                                                                                         /

(  ; 1 47

I 4.0 ADDITIONAL FEATURES THAT PROVIDE DEFENSE-IN-DEPTH

 -This section of the URG discusses the other plant features and operator training used to provide            ,
  ' defense-in-depth A key statementin this section relative to availabilityof alternativewater sources reads as follows:
       " System alignment to make use of alternate water sources may require manipulation of valves or other equipment that is infrequently _ operated. The valves and other equipment used _to provide altemate water sources for injection in support of the EOPs should be                  l l

considered for inclusionin the scope of the Maintenance Rule. It is expected that most if not all of the valves and other equipment will already be encompassed by the plant maintenanz l program. However, licensees should review the altemate water sources available as described in the plant EOPs ar.d ensure that all valves and other infrequently operated l equipment necessary to accomplish injection from these alternate water sources are . appropriately addressed by the plant maintenance program."  ! Staff Evaluation of Section 4.0: The staff did not identify any deficienciesin this section. The staff

 - concurs with the statement cited above relative to including alternate water source components in the scope of the maintenance program, and strongly encourages licensees to do so. This is an              ;

excellent way to ensure defense-in-depth by ensuring that altemative water sources are likely to be l available should they be called upon during an accident. 4 4 I I i l i i t 48

5.0 CONSERVATISM This section of the URG presents the BWROG's position on the degree of conservatism in the analyticalmethods described in Section 3.0. The staff has reviewed the BWROG's viewpoints on the conservatism contained in the URG methodologies and has reached the general conclusion that there are two types of conservatisms in the URG: voluntary and built-in. The first type is strictly voluntary on the part of the licensee. For example, a licensee may choose to not credit settling of debris in the suppression pool. This clearly would be the conservative approach to addressing settling. However, the licensee may also choose to allow credit for settling in its analysis. Credit for settling is nQ.t in itself "non-conservative;" however, such credit eliminates any conservatism added in using the "no credit for settling" option, and would be better characterized as a realistic or "best estimate" calculation. The staff believes that voluntary conservatism is a good practice and provides additional margin; however, voluntary conservatism is difficult to quantify since each licensee may do something different. For the purposes of discussing the amount of conservatism in the URG methodologies, the staff has focused its evaluation in this section on the built-in l conservatism that any licensee conforming with the URG will have automatically included in its analysis as a matter of following the minimum required URG guidelines. 1 Throughout the staff's evaluation of the URG, several areas have been identified in which the staff l believes that there is uncertainty as to whether a certain portion of the methodology is conservative, Examples of this are use of JCL to define P. for each insulation type; assumptions used for l dirt / dust, rust, and coating debris; and erosion of fibrous debris by break-water flow. The staff l believes that the built-in conservatism of the URG is adequate to overcome the uncertainties in these areas and gain a conservative result; however, if a licensee attempts to further reduce the conservatismin the analysis by using analytical methods not approved herein (e.g., use of a CFD code to determine the size and shape of the ZOI), the staff believes that the licensee should also address the uncertainties cited in this SER and demonstrate that the analysis retains sufficient conservatism to ensure that the results bound the worst-case scenario for debris blockage of the ECCS suction strainers. 5.1 Selection of Break Locations in Section 3.2.1.1 of this SER, the staff concluded that use of SRP Section 3.6.2 and BTP MEB 3-1 was unacceptable for demonstrating compliance with 10 CFR 50.46. In addition, the staff stated j that the guidance of RG 1.82 and 10 CFR 50.46 are adequate for determining pipe break locations  ; to be analyzed. The guidance of the regulatoryguide and the rule lead the analyst to evaluate the 1 bounding break with respect to debris generation and transport to the ECCS suction strainers. Although this guidance does not in itsd produce " conservatism" or " margin," selection of the bounding break for sizing of the strainers does enhance safety since a great majority of the breaks in a plant would result in the generation of significartly less debris and/or a lower head loss across the strainer than the bounding break. 5.2 Size of the ZOI The majority of the built-in conservatism in the BWROG's analytical methodologies lies in this part i of the analysis. In Section 3.2.1.2, the staff rejected the use of Method 4, which uses a CFD code 49

4 to define the ZOI, because the URG provided insufficient guidance on which codes to use, benchmarking the code, and so forth. ) Of the remaining methods, Method 3 has the least built-in conservatism of the three methods l' approved for calculating ZOls. The staff considers Method 3 to be conservative for two reasons.

                  ~.The primary reason is because the method does not account for the interaction of the break jet with 4

surrounding pipes and structures (see the, staff's analysis in Appendix F). This interaction would likely cause the jet to lose energy and, therefore, the actual ZO! during a LOCA would probably be smaller than the calculated. Second, although the use of a spherical ZOI appears to be a e reasonable approximation of a ZOI in a congested portion of the containment because of the jet ! interaction with structures and piping, it appears to be a somewhat conservative assumption. The analysis method in the URG (i.e., Methods 2 and 3) assumes that debris is generated equally throughout the ZOI. No credit is taken for shadowing of debris sources by piping and structures. As a result,' the assumption of a spherical ZOI in itself appears to add some conservatism to the analysis. Methods 1 and 2 represent additionallevels of voluntary conservatism.

                    ~ 5.3           Debris Generation This part of the analysis adds more conservatism in two ways. First, the debris generation tests j

were conducted in a manner to maximize the amount of debris generated -in particular, the amount of fine or transportable debris generated (see Section 5.4 on drywell debris transport to the l l suppression pool). This was done by orienting the air jet at a 90' angle to the target pipe and by orienting the seam in the insulation away from the jet to maximize exposure to the jet (i.e., residence time for the blanket in the jet flow), and hence, debris generation. Testing by both the BWROG and i the NRC demonstrated that this configuration maximized the amount of debris generated. In actual plants, insulation seams are randomly oriented, so it is highly unlikely that any one break would impact all targets so as to maximize the amount of fine debris generated. In addition, the URG - debris generation factors conservatively assume that all fibrous insulation within 3 (JD of the break is generated as fine debris. i I 5.4 Drywell Debris Transport in Section 3.2.3, the staff concluded that the transport fraction for fibrous debris in a Mark 11 containmentis unacceptable, and that Mark il containments should use the same transport fractions as Mark I and til containments. This means that all three containment types would assume 100% transport of fine fibrous debris from the drywell to the suppression pool. The staff considers this number a bounding number that does not necessarily add more conservatsm to the analysis. - The NRC-sponsored study on drywell debris transport (see NUREG/CR-6369) demonstrated that a very high percentage of fine debris will transport to the suppression pool. The study also showed that j transport of debris is both plant-specificand break-specific. Because a high percentage of fines will transport to the suppression pool and because of the uncertainty associated with trying to pick , maximum transport fraction, the staff believes that a 100% transport fraction is within the uncertainty of the calculation and, in itself, does not add significant conservatism. The staff does believe, j however, that the number is bounding. 50 l l 1

     ..   --       .      -      _ - - ._        ._         .- _ . - . - . - . - - - . ~ -                 .- - -

5.5 Suppression Pool Transport i The URG allows for settling of debris in the suppression pool after the high-energy phase of the accident. In the staff's opinion, assuming settling of debris in the suppression pool is a realistic l calculation,and does not add conservatism to the overall analysis, No settling should be assumed ) during the high-energy phases of the accident (i.e., blowdown, chugging, and condensation oscillations) because NRC-sponsored testing conducted at ARL has demonstrated that the suppression pool would be sufficiently turbulent during these phases of the accident to keep this i debris suspended in the pool. I 5.6 Head Loss and NPSH Margin The staff rejected the URG head loss correlation developed by the BWROG It is recommended that vendor data be used to conservatively bound the head loss across the strainers. The staff notes that certain licensing-basisassumptions can increase the conservative margin of the analysis. For instance, any containment pressure present during an accident over and above that which a licensee has credited in its licensing-basis represents additional conservative margin. Similarly, use of conservative decay heat curves that would maximize suppression pool temperature in performing an NPSH analysiswould add margin, as these curves would over-predictthe amount of decay heat added to the containment / suppression pool during an accident. Single failure criteria will also add conservative margin. Licensees with individual strainers on each pump suction would typically assume a loss of one ECCS train, maximizing the debris loading on the strainers for the other train and maximizing the head loss across the strainers. Similarly, a plant with a ring head suction (all pumps taking suction off the same strainers) would assume that all pumps are operating. This would maximize flow through the strainers and, as a result, the head loss across the strainers. i

 =

l I 4 I 51 l l

6.0 MISCELLANEOUS REVIEW COMMENTS ON BWROG GUIDANCE The staff has the following general comments regarding the URG.

• On page 1 of the URG, the BWROG states that the " probability of a DEGB in a BWR is extremely low (on the order of 1E-9 to 1E-12)". While the staff agrees qualitatively with the statement (i.e., that it is extremely low), it disagrees with the specific values cited in the URG.

Both the NUREG/CR-6224 study, as well as 90% of the individual plant examinations (IPEs), including BWR IPEs, estimated these numbers to be several orders of magnitude higher.

• The terms bounding and conservative are used frequently throughout the URG, but are not clearly defined anywhere in the document. In addition,where these terms are used in the body of the text, the BWROG did not always discuss the basis for stating that the individual method 7

describedis " bounding" or " conservative."The staff does not believe that such terms should be used to describe an assumption made strictly on engineering judgment unless BWROG can provide a technical basis for the statement. l i s l 52 l i

l 7.0 OVERALL CONCLUSIONS AND RECOMMENDATIONS The principal strength of the URG is that it reviews important considerations of which licensees should be aware in estimating the quantity of debris generated and transported through drywell and wetwellto the strainer, as well as the head loss resulting from the debris bed buildup. The overall framework suggested for ECCS suction strainer evaluation is very similar to that developed during the NUREG/CR-6224 study. Moreover, the BWROG obtained valuable data that were lacking at the time of NUREG/CR-6224 study, including data regarding generation and transport. In addition, some of the analyses conducted by BWROG are technically sound and well-founded on good engineering judgment. Nonetheless, the staff identified several identified instances in which the BWROG guidance wa: either unsubstantiated or developed using assumptions that lacked a sound analytical or experimental basis. In a few cases, the BWROG guidance can even be shown to result in erroneous estimates of the head loss, while in many cases their guidance could not be deemed either" conservative"or?non-conservative." This lack of confidence arose from the BWROG's use of inconsistent modeling assumptions or experimental data without sufficient technical justification for scaling to drywell operating conditions. The staff has found that the data can be interpreted and a basis established on which to conclude that the URG guidance is reasonable and/or " conservative " Where possible, the staff has proposed some alternativesthat licensees can use to improve their analyses. Licensees may wish to explore these altematives. The staff notes that the suggested attematives are a byproduct of the staff's review, not its objective. The following are the staff's key overall conclusions categorized by phenomena: e Selection of Breaks: Licensees should evaluate a sufficient number of breaks to ensure that the most limiting breaks are analyzed. Possible locations of the breaks should include pipe sections or welds in the area of the drywell where the highest density of fibrous insulation is installed. Breaks analyzed in support of strainer sizing should meet the requirements of 10 CFR 50.46 and, therefore, should not be limited to breaks analyzed for compliance with GDC 4 (i.e., MEB 3-1 break analysis). This will determine the limiting break relative to ensuring adequate ECCS NPSH margin. The staff also concludes that it is reasonable for licensees to screen out medium breaks in their strainer analysis if they plan to use alternative strainer designs with deep crevices for debris capture (such as stacked disk or star strainers), provided that the strainer vendor can provide adequate assurance that head losses from combinations of debris loadings up to those consistent with a large-break LOCA are bounded by the large-break LOCA rather than any smaller break. Licensees (or strainer vendors) should also have strainer test data to support this conclusion.

 - e Debris Generation: The staff's findings are summarized as follows:
       - The staffidentified errors in the P. factors provided in URG Table 1. The staff concludes that these values should be revised consistent with the values in Table B.1 of Appendix B to this SER. The staff's concems on the use of JCL versus TAAP for insulations having high Pm factors can be resolved on a plant-specify bat,;s.

53 L

    - The methodology used to develop _ destruction factors for calculations of fine debris is acceptable.
    - Methods 1 and 2 are reasonable and appear to provide conservative bounds for the volume of debris generated.
    - Method 3 should be applied with caution on a plant-specific basis, since it allows utilities to take credit for limited separation (restrained unrestrained and single-jet double jet).

Ucensees should consider that in the case of a main steamline break, flow would be from both ends of the pipe break until the MSIVs are closed.

    - The URG provided insufficient information regarding Method 4 for the staff to reach any conclusions conceming the proposed methodology; therefore, the staff concludes that Method 4 is unacceptable.
    - Damage to Calcium Silicate should be treated as erosion (as demonstrated by Swedish experiments).

o Other Sources of Debris: The staff concludes that the generic values provided in the URG for other sources of debris are acceptable. The staff provided guidance on methods licensees may use should they wish to evaluate these debris sources on a plant-specific basis. To avoid potential operability problems resulting from the ongoing NRC and industry efforts related to potential clogging of ECCS strainers by coating debris, the staff also suggests that licensees assume that all unqualified and indeterminate coatings are transported to the strainer surface, unless data is available supporting use of other assumptions. e Drywell Debris Transport: The staff has found no evidence that transport fractions for Mark 11 containments should be any different than for Mark I and Mark 111 containments; therefore, the staff concludes that the same transport fractions) should be used for all three containment types. The staff also concludes that the combined debris generation /transportfractions provided in the URG for Mark I and 111 containments (e.g., for RMI, fine fibrous debris, and large fibrous debris below the lowest grating in the drywell, and so forth) are acceptable for use in all three containment types. e Suppression Pool Transport The staff finds that this section is acceptable with no comments. e Head Loss: The staff's conclusions are summarized as follows:

     - The staff agrees with the BWROG that the " thin bed effects" are not likely to be an issue for the attemate strainer designs tested.
     - The generic applicability of the URG head loss correlationis not acceptable for the following reasons:

1)_ The correlations are based on data obtained for lower debris loadings than would be expected in many plants, and the correlations are not mechanistic to overcome this deficiency. 54

P

2) The RMI conclusions are specific to the strainer design tected and the type of RMI used in the test. No basis was provided for extrapolating to other RMI types and i strainer designs. >

3) The correlations are specific to the limited types of insulations tested. >

     - As a result of the staffs findings relative to the URG head loss correlation, the staff                 ,

recommends that licensees use test data to support the head loss used in their plant analysis.

     - The NPSH evaluation described in Volume il of the URG TechnicalSupport Documentatiort                   f Tab 15, is not acceptable since it only addresses viscous loss. For RMI, this would yield             i erroneous results.                                                                                    '

I- - The bump-up factors provide a " conservative means" for extending the fiber correlation to  ; other debris, but can create severe design impacts if used.

• Resolution Options:

     - Use of self-cleaning strainers is discouraged unless the licensee cannot reach adequate resolution with a passive strainer design.

l

     - Backflushing is recommended only as a defense-in-depth measure (rather than a primary method of mitigating a LOCA).

e Overall: The staffs overall conclusions are summarized as follows:

     - In general, the URG provides good guidance on how to evaluate the potential strainer clogging issue on a plant-specific basis, and provides acceptable methods for sizing of strainers. The staff has found certain portions of the URG unacceptablefor use by licensees due to inadequate guidance or insufficient technical justification. Where the staff has not accepted a portion of the URG, the staffs concerns have been noted in this SER. If a i          licensee desires to use a methodology or resolution option not accepted by the staff, they l          should resolve the staffs concerns identified in this SER.

l

     - In its response (Ref. 64) to the draft SER (Ref. 63),on the URG, the BWROG stated, "The BWROG requests that the staff considerissuing a supplementto NRCB 96-03 that provides                 j blanket schedule relief to the licensees in reaching final technical closure on NRCB 96-03 until an NRC-accepted methodologyis available that fully and completely addresses all the issues affecting the calculation of ECCS pump NPSH. The BWROG is not requesting blanket deferral for the installation of replacement strainers but only for final closure of the      I i

96-03 technicalresponse. Once the final NRC accepted methodologyis available, licensees l should be given adequate time to review their strainer designs, debris loading calculations, I l l and the need for any further actions (e.g., license changes for containment overpressure credit) before closure of NRCB 96-03 is required." In particular,the BWROG noted the fact i that the coatings issue is currently an open issue that could significantly impact the resolution of NRCB 96-03 for many licensees. The staff will consider issuing the requested deferralin a bulletin supplement. 55 l l l

i

8.0 REFERENCES

f i

1) NEDO-32686, Revision 0, " Utility Resolution Guidance for ECCS Suction Strainer Blockage,"

BWROG, November 1996. l l 2): " Technical Support Documentation Utility Resolution Guidance for ECCS Suction Strainer Blockage"(3 Volumes), BWROG, November 19%.

3) Facsimile Transmittalfrom T.A. Grean to R.B. Elliott," Summary Information Regarding URG  ;

Drywell Transport Methodology," November 25,1996.  ;

4) NRC Bulletin 96-03, " Potential Plugging of Emergency Core Cooling Suction Strainers by l Debris," May 6,1996.

5) Regulatory Guide 1.82, Revision 2, " Water Sources for Long-Term Recirculation Cooling l Following a Loss-of-Coolant Accident," May 1996. i

6) Draft Utility Resolution Guidance Document, Sections 3.1.4, "Backflush"; 3.2.1.1, " Postulated  !

Break Locations"; 3.2.2.2, " Suppression Pool Transport and Settling"; and 3.2.3.4, "ECCS  ! Pump NPSH Calculations," March 31,1996. . i 7); Draft Utility Resolution Guidance Document, Sections 3.1, " Evaluation of Resolution Options"; 3.2.2, "Other Drywell Debris Sources"; 3.2.4, " Suppression Pool Debris Sources"; l and 3.4 "Self-Cleaning Strainer," May 28,1996. *

8) Letter from C.H. Berlinger to R. Sgarro, " Comments on Draft Utility Resolution Guidance [

        ' Sections 3.1.4, 3.2.1.1, 3.2.2.2, and 3.2.3.4," July 25,1996.                                             !

9) Letter from C.H. Berlinger to R. Sgarro, " Comments on Draft Utility Resolution Guidance t Sections 3.1, 3.2.2, 3.2.4,' 3.4," August 20,1996 (Accession number 9608260002).  ;

10) Memorandum from R.B. Elliott to C.H. Berlinger, " Summary of August 19,1996, Meeting  ;

with the Boiling Water Reactor Owners Group (BWROG) to Discuss issues Related to the  ! Potential Loss of Emergency Core Cooling System (ECCS) Capability Due to Clogging of the Suction Strainors by Debris Generated During a Postulated Loss-of-Coolant Accident

                                                                                                                   'l (LOCA)," September 4,1996 (Accession number 9609100214).                  .

11) Facsimile Transmittal from M.L. Marshall, Jr., to T.A. Green, " Transmittal of NRC Staff's [

Initial Comments on URG," December 23,1996. l

12) Letterfrom T. A. Green to R. 8, Elliott," Preliminary Design Considerationsfor ECCS Suction . -)

Strainer Debris Loading and Head Loss," January 13,1997. i

 -13)    Letter from T.A. Green to R.B. Elliott, "BWR Owners Group Response to NRC Comments
                                                                                                                   .{

and Questions Regarding NEDO-32686, Revision 0, ' Utility Resolution Guidance for ECCS  ; Suction Strainer Blockage'," January 30,1997.  ! 14)- Letter from M.J. Virgilio to R. Pinelli (no subject line), June 13,1994 (Accession Number ' 9407010102). .

15) Facsimile transmittalfrom J.H. Munchausen to A.W. Serkiz, " Plan for Testing Pipe Insulation [

Debris Generation Due to Simulated Pipe Breaks," August 9,1994. i

16) Letter from G.M. Holahan to R. Pinelli (no subject line), September 12,1994.

17) Letter from T.A. Green to A.W. Serkiz, "BWR Owners' Group Program to Test Alternative ECCS Suction Strainers," March 15,1995.

18) Letterfrom M.D. Lynch to R. Sgarro, " Request for Additional Information (RAI) Regarding  !

the Strainer Test Program Being Conducted by the BWROG," June 22,1995 (Accession  ! Number 9507060112). .

19) Letter from M.D. Lynch to R. Sgarro, "Second Request for Additionallnformation Regarding l the Strainer Test Program Being Conducted by the BWROG (TAC No. M86925)," August  !

21,1995 (Accession Number 95082.0384). j 56 [ I

                                                                                                 }

l

20) Letter from C.H. Berlinger to R. Sgarro, " Request for Additional Information Regarding the Drywell Transport Program Being Conducted by the BWROG," dated April 22, 1996 (Accession Number 9608260002).

21) Facsimile Transmittal from M.L. Marshall, Jr.,lo A. Bilanin of Continuum Dynamics, Inc.,

    "Transmittalof Questions and Concerns Regarding the BWROG StrainerTests," August 14, 1995.

22) Letter from T.A. Green to R.B. Elliott, " Closure of BWR Owners Group Response to NRC

   ' Request for Additionallnformation Regarding the Strainer Test Program Being Conducted by the BWROG'," July 17,1995.

23) Letter from T.A. Green to R.B. Elliott, " Transmittal of BWR Owners Group ECCS Suction Strainer Committee Response to ' Request for Additimallniormaton Regarding the Drywell l

Transport Program Being conducted by the BWROG'," July 9,1996.

24) Memorandum from R.B. Elliott to C.H. Berhnger, " Summary of May 31,1995, Meeting with j the Boiling Water Reactor Owners Group (BWROG) to Discuss issues Related to the i Potential Loss of Emergency Core Cooling System (ECCS) Capability Due to Clogging of the Suction Strainers by Debris Generated During a Postulated Loss-of-Coolant Accident ,

(LOCA)," June 13,1995, l

25) Memorandum from M.L. Marshall, Jr., to C.Z. Serpan and C.H. Berlinger, " Trip Report and Meeting Summary of September 27 and 28,1995, Public Meeting with Boiling Water Reactor Owners Group in San Jose, CA Regarding the Resolution of the Boiling Water Reactor Suction Strainer Blockage issue," October 6,1995.

26) Memorandum from M.L. Marshall, Jr., to C.Z. Serpan and C.H. Berlinger," Summary of April 4,1996 Public Meeting Between the NRC Staff and BWROG Representatives to Discuss BWROG URG Document Conceming the BWR Suction Strainer Debris Blockage issue and the BWROG Planned Drywell Transport Test," April 16,1996.

27) Memorandum from M.L. Marshall, Jr., and R.B. Elliott to C.Z. Serpan and C.H. Berlinger,

• Trip Report July 9 through 11,1996: Observation of BWROG Air Jet Tests," July 25,1996 (Accession numbers 9608070185 and 9608120157).

28) Facsimile Transmittal from T.A. Green to R.B. Elliott, "BWROG ECCS Suction Strainer Committee Draft Test Matrices for Forthcoming Altemate Strainer Testing," June 23,1995.

29) Facsimile Transmittal from T.A. Green to R.B. Elliott, *BWROG ECCS Suction Strainer Committee Draft Test Matrices for Forthcoming Altemate Strainer Testing," June 30,1995.

30) NRC Bulletin 93-02," Debris Plugging of Emergency Core Cooling Suction Strainers," May 11,1993.

31) NUREG/CR-6224, Parametric Study of the Potentialfor BWR ECCS Strainer Blockage Due to LOCA Generated Debris," October 1995.

32) Letter from K.R. Jury (Carolina Power and Light Company) to the U.S. Nuclear Regulatory  ;

Commission, " Supplemental Response to NRC Bulletin 96-03, ' Potential Plugging of Emergency Core Cooling Suction Strainers by Debris in Boiling-Water Reactors'," June 5, 1997 (Accession Number 9706110277).

33) Letter from H.L. Sumner, Jr. (Southem Nuclear Operating Company), to the U.S. Nuclear Regulatory Commission.

• Proposed Criteria for ECCS Strainer Design," March 25,1997 (Accession Number 9704010557).

34) Letterfrom N.B. Le to H.L. Sumner, Jr., " Safety Evaluation Related to NRC Bulletin 96-03

   ' Potential Plugging of Emergency Core Coc. ling Suction Strainers by Debris in Boiling-Water Reactors'- Edwin 1. Hatch Nuclear Plant, Units 1 and 2," June 17,1997 (Accession Number 9706200164).

57

35) Letter from E.C. Simpson (Public Service Electric and Gas Company) to the U.S. Nuclear Regulatory Commission, " Proposed Resolution Approach - NRC Bulletin 96-03 Potential ,

Plugging of ECCS Suction Strainers by Debris," May 20,1997 (Accession Number  ! 9705290189).

36) Letter from D.H. Jaffe to L. Eliason," Safety Evaluation for Hope Creek Generating Station -

NRC Bulletin 96-03," October 31,1997 (Accession Number 9711180235).

37) Letter from G.A. Hunger, Jr. (PECO Energy) to the U.S. Nuclear Regulatory Commission,

      " Request for License Amendments Associated with ECCS Pump Suction Strainer Plant Modification," May 5,1997 (Accession Number 9705150005).

38) Memorandumfrom C.H. Berlingerto J.F. Stolz," Safety Evaluationfor Peach Bottom Atomic Power Station, Units 2 and 3, Relative to the Licensee's Response to NRC Bulletin 96-03,"

dated September 25,1997 (Accession Number 9710060349).

39) NRC Bulletin 93-02, Supplement 1, " Debris Plugging of Emergency Core Cooling Suction Strainers," February 18,1994.

40) NRC Bulletin 95-02," Unexpected Clogging of Residual Heat Removal (RHR) Pump Strainer While Operating in Suppression Pool Cooling Mode," October 17,1995.

41) NUREG/CR-6367,"ExperimentalStudy of Head Loss and Filtration for LOCA Debris," D.V.

Rao and F.J. Souto, December 1995.

42) Code of Federal Regulations, Title 10, Part 50, " Domestic Licensing of Production and Utilization Facilities".

43) ARL Test Report number 92-96/M787F," Head Loss of Reflective Metallic Insulation Debris with and without Fibrous Insulation Debris and Sludge for BWR Suction Strainers," Alan B.

Johnson, Mahadevan Padmanabhan, and George E. Hecker, May 1996.

44) Letter from R.L. Seale (Advisory Committee on Reactor Safeguards) to L.J. Callan (NRC Executive Director for Operations)," Proposed Final Generic Letter, ' Assurance of Sufficient Net Positive Suction Head for Emergency Core Cooling and Containment Heat Removal Pumps'," June 17,1997.

45) Generic Lettar 97-04, " Assurance of Sufficient Net Positive Suction Head for Emergency Core Cooling and Containment Heat Removal Pumps," October 7,1997.

46) Letter from T.S. Kress, PhD (Advisory Committee on Reactor Safeguards) to J.M. Taylor l (NRC Executive Director for Operations), " Proposed Final NRC Bulletin 96-XX, ' Potential

! Plugging of Emergency Core Cooling Suction Strainers by Debris in Boiling Water Reactors,' and an Associated Draft Revision 2 of Regulatory Guide 1.82, ' Water Sources for Long-Term Recirculation Cooling Following a Loss-of-Coolant Accident'," February 26,1996.

47) Letter from J.M. Taylor (NRC Executive Director for Operations) to T.S. Kress, PhD (Advisory Committee on Reactor Safeguards), " Proposed Final NRC Bulletin 96-XX,

     ' Potential Plugging of Emergency ^.; ore Cooling Suction Strainers by Debris in Boiling Water Reactors,'and an Associated Draft Revision 2 of Regulatory Guide 1.82, ' Water Sources for Long-Term Recirculation Cooling Following a Loss-of-Coolant Accident'," March 22,1996.

48) NUREG-0800, Revision 4, " Standard Review Plan," October 1985.

49) NRC Information Notice 94-57, " Debris in Containment and the Residual Heat Removal l System," August 12,1994.

50) NRC Information Notice 96-59, " Potential Degradation of Post Loss-of-Coolant Recirculation Capability as a Result of Debris," October 30,1996.

51) " Performance of Containment Coatings During a Loss of Coolant Accident," Bechtel l

Corporation, Volume lil, Tab 12, of the URG TechnicalSupport DocumentWion, November 10,1994. 58 l i

l l 1 52)- CDI Report 96-05, Revision 1, " Testing of Debris TransportThrough DowncomersNentsinto the Wetwell," Continuum Dynamics incorporated, URG Technical Support Documentation, 1 Volume ll, Tab No. 2 October 1996,. I

53) Not Used. '

54) BWROG Letter OG95-388-161, Attachment 4, "BWR Owners Group Suppression Pool Sludge Generation Rate Data," BWROG, June 1995.

55) BWROG Letter OG96-321-161, Attachment 2, " Suppression Pool Sludge Particle

                          ~

Distribution, Data - Average Distribution Calculation," September 1994. l

56) Not Used. '

i 57)' Regulatory Guide 1.1, " Net Positive Suction Head for Emergency Core Cooling and Containment Heat Removal System Pumps," November 2,1970. i

58) NUREG-0897, Revision 1, " Containment Emergency Sump Performance,"

59) NRC Information Notice 92-85, " Potential Failures of Emergency Core Cooling Systems )

Caused by foreign Material Blockage," December 23,1992.

60) NRC Information Notice 89-77, " Debris in Containment Emergency Sumps and Incorrect Screen Configurations," November 21,1989.

61) NRC Information Notice 88-87, " Pump Wear and Foreign Objects in Plant Piping Systems,"

November 16,1988.

62) Letter from T.A. Green to R.B. Elliott, "BWR Owners' Group Response to NRC Comments Regarding the Effect of RMI and Fiber Combination on Strainer Head Loss," September 19, 1997.

63) Letterfrom C.H. Berlinger to R. Sgarro," Draft Safety Evaluation Report of the Boiling Water Reactor Owners Group's Resolution Guidance for ECCS Suction Strainer Blockage,"

December 31,1997.

64) BWROG Letter BWROG-98004, from T.J. Rausch to the NRC, "BWR Owners' Group Comments Regarding NRC Draft Safety Evaluation Report of the BWR Owners' Group Utility Resolution Guidance for ECCS Strainer Blockage (NEDO-32686) dated December 31, 1997," March 13,1998.

65) BWROG Letter BWROG-94034,from L.A. England to A.C. Thadani, " Submittal of BWROG interim Safety Assessment and Operator Guidance in Response to NRC Bulletin 93-02, Supplement 1 (' Debris Plugging of Emergency Core Cooling Suction Strainers')," March 24,

     '1994.

66) BWROG Letter BWROG-94157, from R.A. Pinelli to A.C. Thadani, " Interim Report of the BWR Owners' Group ECCS Suction Strainer Committee, Dated December 1994," l December 15,1994.  !

'67) "Barsebeck 1 & 2, Oskarshamn 1 & 2, Ringhals 1. Report from Tests Concerning the Effect , of a Steam Jet on Caposillnsulation at Karlshamn, Carried Out Between April 22-23,1993 j and May 6,1993," Blomqvist and Dellby, SDC 93-1174.

68) GL 98-04, " Potential for Degradation of the Emergency Core Cooling System and the j Containment Spray System After a Loss-of-Coolant Accident Because of Construction and  ;

Protective Coating Deficiencies and Foreign Material in Containment," July 14,1998. l l 59 1

9.0 LIST OF RELATED REPORTS AND DOCUMENTSIN THE PUBLIC DOCUMENT ROOM The following table lists test reports and documents related to the ECCS strainer clogging issue that are available in the NRC's Public Document Room. Technical Documents in Public Document Room Document Accession Number 1 Zigler, G., et al., " Experimental Investigation of Head Loss and 9608050121 Sedimentation Characteristics of Reflective Metallic Insulation Debris," SEA NO. 95-970-01-A:2, Science and Engineering 9608050125 Associates, May 1996. 2 Murthy, P., Padmanabhan, M., and Hecker, G., " Tests of 9511010046 Par 1icle Settling Velocity in Still Water," Alden Research Laboratory, Inc., Holden, MA, June 1994. 3 Murthy, P., et al., " Head Loss of Fibrous NUKON Insulation 9511010046 Debris and Sludge for BWR Suction Strainers," 124-95/M787F, Alden Research Laboratory, h, ... Holden, MA, June 1995. _ 4 Johnson, A., Padmanabhan, M., and Hecker, G., "NUKON 9511010046 Insulation and Sludge Settling Following a LOCA in a BWR Suppression Pool," 114-95/M787F, Alden Research Laboratory, Inc., Holden, MA, June 1995. 5 Hoffmann, D. and Knapp, A., "RMI Debris Generation Testing: 9511010046 Pilot Test with a Target Bobbin of Diamond Power Panels," NT34/95/e32, Siemens AG, Karlstein, Germany, July 1995. 6 Memorandum from E. Cramer of SEA to M. Marshall of 9511010046 USNRC,

Subject:

Review of Existing Knowledge Base related to Generation of Iron Oxide Sludge in BWRs, September 21, 1994. 7 Memorandum from G. Zigter to A. Serkiz and M. Marshall of 9511010046 USNRC,

Subject:

RMI Debris Size Distribution, June 9,1995. 8 Video of RMI Debris Generation test in Karlstein, Germany. 9511010046 9 Williams, D., " Measurements on the Sink Rate and Submersion 9412080219 Time for Fibrous insulation," ITR-93-02N, Transco Products, May 22,1993. 9404070203 10 Williams, D., "The Effects of pH and Thermal Exposure on the 9412080219 Head Loss of Series A Shreds, NRC Guide 1.82,"ITR-92-3aN, Transco Products, May 18,1992. 9404070203 60

Technical Documents in Public Document Room Document Accession Number 11 Williams, D., " Experimental Measurements on the 9412080219 Characteristics of Flow Transport, Pressure Drop, and Jet impact on Thermal Insulation, NRC Guide 1.82," ITR-92-03N, 9404070203 Transco Products, May 18,1992. 12 Williams, D., " Postulations of the Range of Fibrous insulation 9412080219 Debris Size Generated by High Energy Jet impact," ITR 01N, Transco Products, April 16,1993. 9404070203 13 " Air Blast Destructive Testing of NUKON@ Insulation 9404070203 Simulation of a Pipe Break LOCA," Performance Contracting l Inc., October 1993. l 14 " Head Loss Tests with Blast Generated NUKON@ lnsulation 9404070 03 Debris, _ _.____" Performance Contracting, Inc., October 1993._ _ _ _ _ _ . . . . _ - . _ _ _ _ __ 15 "Karlshamn Tests 1992. Test Report. Steam Blast on insulated 9410130310 Objects," ABB Atom, RVE 92-205, November 30,1992. 16 "KKL - Specific ECCS Strainer Plugging Analysis According to 9410130310 Reg. Guide 1.82, Revision 1, for a Loss of Coolant Accident," KKL. 17 "The Marviken Full Scale Containment Experiment," 9410130310 ' MXA-4-206, September 1973. 18 "OECD/NEA Workshop on the Barsebeck Strainer incident in 9410130310 Stockholm January 26-27,1994 Do.umentation." 19 " Report Concerning the Quantity of Insulation Which Was Not 9410130310 Washed Down in Connection with the 314 Event," Sydkraft, PBM-9211-23, November 26,1992. 20 "Swedish N-Utilities Explain BWR Emergency Core Cooling 9410130310 Problem," ENS Nuc Net, News No 358/92, September 18, 1992. 21 Anderson, " Guaranteed Emergency Core and Containment 9410130310 Cooling - Laboratory Experiments with Insulation on Strainers," ABB Atom, RVD 92-193, December 1,1992. 22 Blomqvist and Dellby, "Barsebeck 1 & 2, Oskarshamn 1 & 2, 9410130310 Ringhals 1. Report from Tests Concerning the Effect of a Steam Jet on Caposil Insulation at Karlshamn, Carried Out l Between April 22-23,1993 and May 6,1993," SDC 93-1174. 61

Technical Documents in Public Document Room Document Accession Number 23 Bystedt, " Thermal Insulation on New Steam Generators and 9410130310 primary Pipes. Influence on Safety During Normal Operation and in the Case of Malfunction,"_ August 2,1989. 24 Fax 6n, "Barsebeck 1 and 2, Oskarshamn 1 and 2 - Strainers in 9410130310 System 322 and 323. Results from Blowdown Experiments in a Test Rig," ABB Atom, RVA 92-340, November 27,1992. 25 Fredell, "Karshamn Tests 1992. Steam Blast on Insulated 9410130310 Objects, Logbook," ABB Atom, RVE 92-202. _ _ _ _ _ .__ _ 26 Greis, " Pressure Drop in Connection with Fluid Flow Through 9410130310 Insulation Deposited on Strainers," ABB Atom, RPD 92-109, December 23,1992. 27 Hallst6m, " Guaranteed Emergency Core and Containment 9410130310 Cooling. Laboratory Experiments Concerning Insulation," ABB Atom, RVD 92_192, November 30,1992. 28 Henriksson,"Ringhals 1 - Pressure Drop on Screens from 9410130310 Thermal Insulation Debris," Vattenfall Utveckling AB, VU-S93:B6 March 30,1993. 29 Henriksson, "Ringhals 1 - Strainer System 322/322," Vattenfall 9410130310 Utveckling AB, VU-S92:56 December 18,1992. 30 Henriksson and Norling, "Barsebgck 1-2, Oskarshamn 1-2, 9410130310 Ringhals 1 - Filter Systems 322/323. Coverage and Back Rinsing Tests with Fiber Insulation and Newtherm, Scale 1:2. Status Report February 6,1993," Vattenfall Development Company, VU-S93:B14, June 22,1993. 31 Henriksson, "Barsebeck 1 and 2, Oskarshamn 1 and 2 - 9410130310 System 322/323 Testing of Permanent Strainers," Vattenfall Utveckling AB, VU-s93:B12, May 28,1993. 32 Hyverinen," Summary of STUK's Research Activities 9410130310 Concerning Strainer Clogging," STUK. 33 Molander, Arnesson, and Jansson," Steam Jet Dislodgement 9410130310 l Tests of Thermal Insulating Material," Studsvik Material, l M-93/24, March 1,1993. -- 1 34 Murthy and Hecker, " Head Loss with Blast Generated NUKON 9410130310 Insulation Debris Mixed with iron Oxide Particulates," ARL, April 1994. 62

i Technical Documents in Public Document Room Document Accession Number 35 Nystrom, " Evaluation of Transport Velocity for NUKON 9410130310 l Insulation Base Wool at Elevated Temperature and pH," ARL, l May 1991. l 36 Nystrom," Investigation of the Effect of pH on Head Loss of 9410130310 l NUKON Insulation Base Wool," ARL, April 1991. l 37 Nystrom, "Nukon Insulation Head Loss Tests," ARL, October 9410130310 1989. 38 Pennino and Hecker, " Head Loss Tests with Blast Generated 9410130310 l NUKON Insulation Debris," ARL, October 1993. 39 Perssson, " Downward Transport and Sedimentation of 9410130310 Insulation Material and the Build-Up of Pressure Loss in the Suction Filters," OKG, March 12,1992. 40 Steen and Dufva, " Review Report Concerning SKl's Handling of 9410130310 the So-Called Filter Affair." 41 Tarkpea and Arnesson," Steam Jet Dislodgement Tests of 9410130310 Thermal Insulating Material of Type Newtherm 1000 and Caposil HT1," Studsvik Material, M-93/41, April 7,1993. 42 Tarkpea and Arnesson," Steam Jet Dislodgement Tests of Two 9410130310 Thermal Insulating Materials," Studsvik Material, M-93/60, May 24,1993. 43 Wilde, " Strainer Test with Fiber Insulation and Reactor Tank 9410130310 Insulation, Results from the Small Model," Vattenfall Development Company, VU-S 93:B16, June 21,1993. 44 Voigt and Jerrebo," Testing of Strainer Performance in the 9410130310 Condensation Pool at Bvt 1," Sydkraft. 45 Wilhelmsson and Tinoco, "Forsmark 1 & 2 - Strainer System 9410130310 322/323," VU-S 93:B8. April 26,1993. Principal contributors: Rob Elliott, NRR Al Serkiz, RES Rich Lobel, NRR D.V. Rao, SEA /LANL Kerri Kavanagh, NRR Frank Sciacca, SEA Michael Marshall, RES Clint Shaffer, SEA l l 63

i Appendix A Calculation to Check Estimates of Bulk Dynamic Pressures Computed by the BWROG-

                                   ~

References:

A.1 URG, Section 3.2.1.2.3, Page 36, Line 1. A.2 Letter from D.V. Rao to M.L. Marshall, Jr.,

• Debris Drywell Transport Study, Draft Phase 1 Letter Report," SEA Letter 96-3105-010-A:2, September 27,1996.

                          . A.3              Letter from T.A. Green to R.B. Elliott, "BWR Owners Group Response to NRC Comments and Questions Regarding NEDO-32686, Revision 0, ' Utility Resolution Guidance for ECCS Suction Strainer Blockage'," January 30,1997.                                 '

Problem Definition: In Reference A.1, the URG includes the following statements:

                           -e        The bulk dynamic pressures in the drywell far from the break are lower than 0.02 psi.

l e The licensee need not worry about damage to insulation located outside the jet's ZOl. i The staff performed calculations to evaluate these URG conclusions. The assumptions used in performing these calculations are as follows: 1 e - LOCA Data:

                                     - Discharge from both ends of a pipe break will reach a maximum flow (M) of 8000 lbm/s, j                                             assuming a 24-inch DEGB with full separation (Ref. A.2). A higher flow rate is calculated if containment atmospheric pressure is considered.

i

                                     - Instantaneous containment pressure will be 15-40 psi. It takes several seconds for the containment pressure to buildup to 40 psi. The density of the steam and air mixture in the initial stages of accident (p) is 0.08 lbm/ft3 (Ref. A.2).

l e Geometrical Information: The staff compiled the following geometricalinformation for an average size Mark I containment (Ref. A.2). Realistic equipment congestion was then used to estimate flow velocities and dynamic pressures. Elevation Location Total Area (ft") Porosity Not Flow Area (ft')_ L Neck 750 0.8 > 600 l Upper Grating 1800 0.6 1080 l Lower Grating 1550 0.57 (=0.6) 930 e Velocity and Dynamic Pressure: Assuming that a quasi-steady state break flow occupies 100% of not flow area (A,..) available for flow, the estimated flow velocities (V.) and dynamic pressures (P. ) can be calculated as follows: V.=M/(pA,..) P.=M2/(2pA ,..g) l A-1 i r -- y --- - -w: w ,e

a

  )

On the basis of these assumptions, the estimated bulk dynamic pressures are as follows. Elevation LocatiGD Dynamic Pressure (psi) I Neck 0.24 Upper Grating 0.07 Lower Grating 0.10 These pressures are probably not large enough to inflict damage on properly installed jacketed fibrous insulation (such as those tested by the BWROG), Nevertheless, in the staff's opinion, these values are sufficiently large to inflict damage on improperly installed insulation (e.g., cut-to-fit partially exposed insulation blanket pieces some utilities may use to insulate hard-to-fit components such as valves) or insulation blankets that are not well maintained (e.g., partially torn insulation blankets that some utilities may not have replaced in the past). Note that in the event at Barsebeck, Unit 2, pressures in the same range generated substantial debris from aged unjacketed mineral wool blankets. ,

Conclusion:

. The BWROG underestimated bulk dynamic pressures for at least certain types of l containments (e.g., Mark 1). The staff is concemed that this error in the URG minimizes the

    - potential for debris generation in the regions far from the break. As a result, there is a lack of      i emphasis in the URG on the importance of proper installation and maintenance of insulation blankets (especially at hard to reach places). The staff cautions licensees to consider the potential for generation of miscellaneous fibrous debris attributable to these elevated dynamic pressures that exist far from the break. The staff notes that the BWROG addressed this                   l

l. comment in Reference A.3 above. The staff concludes that this response adequately . ,

addresses this issue. . s p I i [ t l l l A-2 l l

Appendix B , 1 Analyses to Verify Values of P , for Selected Materials Reported by the BWROG and Suggestions for Development of Scaling Analyses 1 References- I B.1 URG Section 3.2.1.2.3.2, Page 38, Line 13, and Page 46, Table 2. B.2 URG, Vol. II, Tab 3, CDI Report No. 95-06, " Air Jet Impact Testing of Fibrous and l Reflective Metallic Insulation," CDI, September 1996. B.3 URG, Vol. II, Tab 1, CDI Report No. 96-01, " Zone of Influence as Defined by Computational Fluid Dynamics, Revision 3," CDI, October 1996. B.4 Jet Model fromANSI/ANS-58.2, " Design Bas ls for Protection of Light Water Nuclear Power Pfar.ts Against Effects of Postulated Rupture," ANSI,1988. Problem Definition: In the URG, the BWROG provided a table of destruction pressures (P ) for selected insulation blankets (References B.1, 8.2, and B.3). This table, reproduced here for convenience, lists P , values for insulation blankets installed on 12-inch diameter piping. Material PuJpsi)_ l Darchem DARMET* , 190* Transco RMI 190* Jacketed NUKON* with "Sure-Hold" Bands , 190* Diamond Power MIRROR

• with "Sure-Hold" l 190*

Calcium Silicate with Aluminum Jacketing ' 160* K-Wool 40 Temp-Mat with Stainless Steel Wire Retainer  ; 17 Knaupf' 10 Jacketed NUKON* with Standard Bands 10 Unjacketed NUKON' 10 Koolphen-K' i 6 Diamond Power MIRROR

• with Standard Bands 4 l Min-K 4 in addition, for insulation types where the P , values are marked by '*' in the table above, the BWROG suggested that the P., values for other pipe sizes can be estimated using the following relationship:

P o, = Piz.,(12 inches /D) The BWROG derived the P., values listed in the table above as follows: l l e The AJITs were conducted at the CEESI facility using a 3-inch diameter jet nozzle and 12-inch diameter target pipe to determine the farthest location from a break at which a given insulation blanket will be damaged and dislodged from the brget pipe. The results of these B-1 i

tests are documented in Reference B.2. The location determined by the tests is defined as (UD)..

• The NPARC CFD calculations were used to determine J 3 JCL pressure associated with

        -(UD).. This pressure is listed in Reference B.1 as P..

• The correction formula listed above is suggested to scale CEESI results to different target pipe sizes.

The staff notes that URG did not address any scaling issues relative to the applicability of test data using a 3-inch diameter nozzle from the CEESI facility to en MSLB in a full-size plant. The staff and its contractor (Science and Engineering Associates, Inc. (SEA)) witnessed several of the BWROGs AJITs and carefully reviewed the documentation provided by the BWROG. The following paragraphs summarize the confirmatory analyses performed: o CEESI Test Facility and Experimental Procedure: The experimental program carried out at CEESI appeared reasonable and tractable according to the NRC's quality assurance (QA) program. The staff reviewed the experimental data provided in Reference B.2 to determine the maximum distance from the jet (UD) beyond which no noticeable damage was inflicted on the target. Column 4 of Table B-1 in this appendix lists these numbers. The staff made the following observations:

         - in the majority of the tests, the target consisted of a single piece of blanket (24-inches long) mounted on a 12-inch diameter target pipe. This allows for formation of a aga-prototvoscallow-pressure region on both ends of the insulation blanket leading to air flow from the high-pressure mid-region to both ends. Such an air flow would inflict more damage than would be expected in a BWR plant, where the insulation blankets are continuous.- As a result, the staff believes that the CEESI tests probably overestimate damage, especially in the case of fibrous insulation.
          - For some insulation types, the BWROG did not adequately explore the exact location at which damage first occurred. For example, in the case of stainless steet jacketed NUKON', the URG reports damage at 50 UD with 12% of insulation destroyed into fines and 29% into larger pieces. But the URG does not explore damage beyond 50 UD.

Similarly, in the case of unjacketed NUKON'significant damage occurred at 60 UD and no damage at 119 UD. No data points were reported in between. In view of such a lack

             - of data, some of the conclusions stated in URG become questionabk , especially
              . considering that this information is later used to estimate the fraction of insulation transported.

• BWROG Derivation of Damage Pressures: The BWROG employed the NPARC code results presented in Figure 9 on ppge 18 of Reference B.3 to estimate the JCL pressures corresponding to (UD).where damage was first recorded. These JCL pressures were then mterpreted by the BWROG as the damage pressures. On the basis of a detailed review, the staff has identified the following deficiencies in the methodology used by BWROG:

B-2

      - The URG may overestir.'. ate the JCL pressure at which damage first occurs. Although this is non-conservative, the staff considers this to be a minor deficiency because it was                   ,

only noted for selected insulation blankets. For example, in the case of DPSC mirror insulation with Gure-Hold bands, the URG reported a damage pressure of 190 psid. j The staff's contractor, SEA, used the same experimental data and NPARC code results l provided in Figure 9 of Reference B.3 to estimate this value to be 150 psid. Several l such discrepancies were found, and all of them are annotated in Table B-1 by '*'. In all  ! cases, SEA estimated damage pressures lower than the URG values. The staff ) recognizes that interpretation of experimental data is often subjective, and this may l explain these discrepancies. Nevertheless, tne staff recommends the use of the values i provided in column 4 of Table B-1 in this appendix. )

      - The staff's main concem relates to the simplifying assumption made by BWROG to equate the JCL pressure to the damage pressure. The rationale for such an assumption is unclear and not supported by experimental evidence documented in Reference B.2. In fact, this assumption is contrary to assumptions made in Appendix A, page 195 of Reference 8.2. An attemative would be to use jet impingement load (force) as a scalable variable for characterizing damage, at least in the case of selected insulations. The staff performed the following analyses to explore this altemative:

a) The CEESI experiments clearly suggest that, in the case of jacketed insulation, l damage occurs only after the outer casings on the insulation blankets (e.g., l stainless steel sheaths) are separated from the blanket. Usually, the outer casings i are secured by bands or latches of various types, ranging from simple latch and  ! strike devices to "Sure-Hold *" bends with modified "CamLoc'" strikes. The BWROG notes (on page 182 of Reference B.2) that a typical failure mode of these devices I involved deformation (or straightening) of the J-hook or destruction of the latch l mechanism. In both cases, separation of the outer casing occurs when the load on the insulation blanket exceeds the structural strengths of the bands. Since the latch l mechanisms or banding used were not typically located at the JCL in the AJITs, and , they were failing, the staff believes that the banding or latches were failing at a I pressure lower than the JCL. Consequently, the staff concludes that damage sbuld l be related to the total impingement force to which the blanket is subjected, rather l

                                                                                                                        ~

than the maximum pressure over a small localized region . The staff believes that the experimental evidence supports this in more cases than use of JCL pressures. In cases where the P.,,,is low, then use of the JCL pressure would not significantly impact the calculated ZOI since the average pressure applied on the target insulation would not be significantly different from the JCL pressure on the target, b) The difference in the choice of JCL pressure versus total force can be explained quantitatively by considering the radial distribution of pressures in an expanding jet illustrated in Figure B. I. As evidenced by this figure, at each L/D jet pressures are highest at the jet center-line and decrease rapidly with radial distance (R/D). For analysis purposes, Figure B.1 (of this appendix) uses a linear profile as suggested I

 ' For example. would a %-6nch diameter nozzle generate the same amount of debris as a 3-inch.

B-3

by the ANSI /ANS 58.2 Jet Model(Reference B.4)instead of a more realistic profile derived from more CFD calculations (e.g., Figure 11 of Reference B.3). Similar analyses may be conducted using more accurate radial profiles than those used in this study. Nevertheless, the net jet impingement load on the blanket is the sum of multiples of the local stagnation pressure in each radial zone and the area of that radial zone intersecting the blanket. As an alternative, one may choose to relate 4

                ' damage to target area averaged pressure (TAAP), which is essentially the ratio of jet .                                >

impingement load on the target to the target area. Figure B.2 (of this appendix) compares maximum (or JCL) pressures and TAAPs as a function of axial distance ' from the nozzle exit plane. A blanket length of 24-inches was assumed to estimate these TAAPs. From Figure B.2, it can be seen that at an UD of 10, the maximum pressure (or the JCL pressure) is 100 psid versus the TAAP of 40 psid, which is a large difference. - For a particular insulation, if the first reporteo d9 mage occurred at a UD of 10, the URG shows an estimated damage pressure of 100 psid instead of the more realistic damage pressure of 40 psid. This deficiencies could have considerable impact on the URG defined ZOI models for certain insulations having high P. values. This impact can be demonstrated by - considering pressure isobars in an expanding jet (see Figure B.3 of this appendix). As shown in this figure, the 100-psid isobar includes much lower volume than the , 40-psid isobar'. As a result, the volume of insulation destroyed would be higher if it  ; were estimated based on drywell volume bounded by a 40-psid isobar as compared  ; to that bounded by the 100-psid. - As noted above, the staff believes that this  ! comment is only significant for insulations with high P. values (e.g., where JCL , pressure is significantly higher than average pressure on the target). The staff also . l

               . notes that NPARC runs can be used effectively to provide a better estimate of target i                 area averaged damage pressures than those estimated in this calculation using a simplified 1-D jet expansion model. Because of the limited number of insulations                                         -

impacted, the staff believes this issue can be addressed on a plant-specific basis. The staff also recommends the use of the P. values listed in column 4 of Table B-1 herein. o t a For a nozzle size of 24-inches, the isobars in Figure B.3 very closely represent " target area averaged pressures

• at that location, assuming the target to be 24-inches long.

B-4

Table B-1 Results of CEESI Testing for Each Insulation Material. Insulation Material (L/D) Dest.3 URG JCL' Pressures Damage Estimated in Pressure Confirmatory (psi) Analysis Darchem DARMET* 5.0 190 190 Transco RMI

• 5.0 190 190 Jacketed NUKON' with Sure-Hold' Bands >11' 190 150*

DPSC MIRROR' with Sure-Hold

• Band 8.5 190 150*

Calcium Silicate with Aluminum Jacketing 7 160 150' K-Wool 15 40 < 40 Temp-Mat with stainless steel wire retainer 30 17 17 Knaupf' - 60 10 10 l Jacketed NUKON'with Standard Bands >50 , 10 - 6* Unjacketed NUKON' >60 ; < 119 10 ' 6* Koolphen-K' >80' > 6 4* DPSC MIRROR

• with Standard Bands .

99 4 4  ; Min-K i

                                                                                     >100'                  4                    <4              !

I ! e Scalability of Results to BWR Drywells: In the CEESI experiments, a 3-inch diameter nozzle was used to simulate a broken pipe, and a 12-inch diameter pipe was used to simulate a target pipe (Reference B.2). This raises the following concerns related to scalability of the experimental results:

               - How can damage pressures obtained for 12-inch target pipe be used to estimate damage pressures for a smaller or a larger pipe'? Since all insulation blankets are attached to pipes of different diameters by identical straps, their failure occurs at same target load irrespective of the target pipe diameter (i.e., one should look for load conservation). Therefore, the following equation holds:

l

          ' The maximum distance at which damage or dislodgment is reported for the insulation type of interest.

• The jet conter-line pressure corresponding to (UD) . The JCL pressure was extracted from the CFD results of Reference B.3.

8 Several ddferent types of Transco RMI insulation was tested. However, the results presented here are for TPI 0.024-inch sheath solid end (stainless steel) with latch and strike closures. According to the URG, this insulation appears to be the most commonly found Transco RMI in BWRs.

• Exact number not known since testing did not go beyond the values listed for which significant damage was evident.

B-5

t F8 .,= Fir,,, where, F ,,,= is the destruction load for a blanket installed on a pipe of diameter D F2, = is the destruction load calculated on the basis of CEESI experimental data for 12-inch pipe. The force-pressure relationship is: F8. = P ",,,

• A ,,

where, P ",,, = is averaged jet damage pressure (psi) 2 A y,= is area of jet-target interaction (in ), For target pipes fully immersed in the jet, it can be easily shown that A ,, = k(D+2t)L I where, k = a constant of proportionality D = Outer diameter of the target pipe (in) t = insulation blanket thickness (in) L = Length of the insulation blanket (in) Substituting these variables into the force conservation equation above yields the following: k*(D+2t)*L' P ",,, = k*(12"+2t)*L* P'2 ",,, or P ",,, = Pi2",,, *(12"+2t)/ (D+2t) A first-order approximation (within 125%) to the above equation is as follows: P ",,, = P'2.",,, *(12"/ D)

 - This is the correction formula suggested by the BWROG. The staff believes it is adequate and can be used for certain types of insulation (i.e., steel encapsulated insulations, RMI etc.).

B-6

f i

                             - How can damage pressures obtained using a 3-inch diameter nozzle be scaled for breaks associated with 22-inch diameter pipes or larger? This issue is pictorially illustrated in Figure B.4 (of this appendix) which shows that in CEESI testing, the blanket       ,

. is not completely encompassed by the high-pressure region of the expanding jet,  ;

L (especially for UD values less than 5). Evidence to that effect can be found in some of

the still pictures taken of damaged insulation cassettes (e.g., Figure 4-42 and Figure 4-l 43, Reference B.2) where damage occurred over a limited region. In BWRs, the broken l

pipes can be as large, if not larger than the target pipes. In such cases, high-pressure regions of the jet would completely encompass the insulation blanket, subjecting the entire front and side surfaces to high pressure. This raises questions related to scalability of CEESl results to BWRs. At least in part, this issue can be addressed if the 3 damage is thought to be proportional to the total load, as follows.  ! Consider that, in a BWR, a postulated LOCA involves a fully separated DEGB of a 24-inch MSLB. Now assume that an analyst is interested in quantifying the damage caused by the ensuing steam-jet impingement on a 24-inch diameter target pipe and ' located about 20 ft from the broken pipe (10 UD). As a first step, one can use the ANSI /ANS-58.2 model to predict total impingement load on a blanket located on that target pipe. For a blanket that is 24 inches long, this load is calculated to be l approximately 23,000 lbf, with an average pressure of approximately 40 psi (Note that j load is calculated assuming the medium to be steam). l Correspondingly, in CEESI air jet tests, the insulation blanket located on 12-inch target , pipe also located 10 D (or 30 inches) from the nozzle would be subjected to an average l- pressure of 40 psi (see Figure 2). The net force it is subjected to however is only , 11,520 lbf, not 23, 000 lbf computed for the BWR case above. As a result, licensees should exercise care to ensure that results from CEESI are not interpreted in terms of UD values, but instead in terms of the impingement load. l By contrast, in CEESl tests, an insulation blanket located on the same 12-inch target pipe but SD from the nozzle would be subjected to a total force of about 22,752 lbf. A case can be made that damage observed at 5 UD in CEESI air-tests is approximately equal to damage expected at 10 UD following a 24-inch MSLB.

• Fluid Medium of Experimentation: Air used in CEESI testing obviously has different ,

characteristics from high-temperature steam released following a LOCA. Once again, this difference can be accounted for if the analyst exercises care to think in terms of total load, not UD. Through NPARC results (see Figure 9, Ref. 3), the BWROG argued that air-based test results " conservatively bound" the damage expected in case of steam. The staff i concurs that compressed air can be used to create high-pressure fields at a given UD comparable to a steam jet of the same pressure. 1 B-7 l

i i i l i: i 1 i

                               ' ',           ' ' ,'/'

,f f.

                                                                         /
                                                                     '/, ' ///lf'         //l,/,,
                                                                                                       ',f//// l // //l
                                                                                 ~-

_ . ;.;/ -

'l .

4, ' /, . _ ;_ ; f:~, .

                                                                                                                                                                                      --l,.'
                                                                                                                                                                                         /.'k
                                                                                                                                                                          '                                        l 3
                                                                                                                                                                                         ':l l                         l                                                                                             _.
                                                                                                                                                                                        .l 1                                                                                                                                                                                             .
                                                                                                                                                                                     / /. ,

f . . . t Vozzle (O.D=3") 200 i l .

- 160 -

e I as Q- 1_ ANSI /ANS-58.2 Based

                                                                                                    ~

Axial Distance g  : - UD=3 A [ 80 - 1

                                                                                                                           .                                          ,                        -+- UD=5
                                                                      -{

g o

                                                                                                                                                                                               -G- UD=7
                                                                                                                                                                                               + UD=10 "e                 40
                                                                                                    ~
                                                                                                                                                                                               -*- UD=20 0       '''''''''''* - -                                                                ^
                                                                                                                                                                                                        ^

2 0 1 2 3 4 5 6 Normalized Radial Distance (R/D) Figure B.1. Radial Distribution of the Stagnation Pressure in the Jet. The actual pressure profile could be different from the linear profile assumed in the ANSI /ANS-58.2 Model. 9

                                                               .                                                        l 200
          ~
            =                                                      e Average Pressure Bleeket is Subjected i 160          -

Maximum Pressure Blanketis Subjected to ) Tu - O - i 120 - r ) E i s. 80 - e e e 40 5 0 0 ' ' ' O 2 4 6 8 10 12 14 16 18 20 Axial Distance from the Nozzle Exit (L/D) Figure 11.2. Comparison of Aserage (SEA Suggested) and Madmum (llWROG_URG) Pressures on a 24" long and 3" thick blanket installed on 12" target sersus its asial location. l 7 ANSI /ANS 58.2 Jet Model 6 'n

                                                                                                       ; A 'A'~#

_ Impingiment Pressure Isobars ' ' Q Steam from 1000 psi is' 5 -

                                                                      .        ;iA    A      A.A e        -

AA A A A g4 3

. . .,. g A. A A .A l

     $         :                      AA A j 3 F                          ,
                                         ,                ,      ,                    -       a     100 psid 2         i                                     .                                        o     40 psid
     - 2       -                    -    -                       -

1 m  : OOaa0 0^0D A Jet-Boundary 1 Da - 0- ' ' E======== 3 :: : 5 : : : : :: 0 5 10 15 20 Axial Distance (UD) Figure 11.3. Pressure Isobars for Steam Jet Expanding from a DEGB with Full Separation. Each Isobar Bounds the Volume of Jet in which Impingement Pressures are fligher than the Value Indicated in the Legend. i I

lRoizynj A. 3" Air Jet Impinging on a Target (Configuration used in CEESI tests) ,,

                                                 ,..****.*..**\ Jet Boundary
            .*.. ..                                          db Jet Center Line                     '.....,.,.;

l l

            .....,, -              lUD = 10 l 1

1 t ....,,**...,*...*** 1 B. 24" Pipe subjected to 24" DEGB Pipe. ** ... .,***- (BWR Drywell Case) . Figure 4. Schematic illustration of CEESI Testing Versus BWR Drywell Steam Jet 4 6 Impingement on Targets.

l l Appendix C Calculations to Examine the Accuracy of Reported Jet Volumes Bounded by Selected Load Isobars

References:

C.1 URG Section 3.2.1.2.3.2, Page 38, Line 13 and Page 46, Table 2. C.2 CDI Report No. 95-06, " Air Jet Impact Testing of Fibrous and Reflective Metallic insulation," URG Technical Support Documentation, Volume 11, Tab 3, C.3 CDI Report No. 96-01, " Zone of influence as Defined by Computational Fluid Dynamics," Revision 3, URG Technical Support Documentation, Volume ll, Tab 1. C.4 ANSI /ANS-58.2 Jet Model, " Design Basis for Protection of Light Water Nuclear Power Plants Against Effects of Postulated Rupture," ANSI,1988. C.5 EPRI NP-4362, "Two Phase Jet Modeling and Data Comparison," Electric Power Research Institute,1986. Problem Definition: In References C.1 and C.3, the BWROG reported volumes of jet regions enveloped by selected isobars (2,4,6,10,17,40,160, and 190 psid). inese volumes were computed as a function of radial and axial offsets. The calculations used the NPARC computer code with thermodynamic properties of steam. The staff performed calculations to evaluate the adequacy of the BWROG estimates using the ANSl/ANS-58.2 model (Reference C.4). These calculations are confirmatory and intended as a check of the BWROG calculations presented in Reference C.2. The staff believes that the NPARC computer code used in the URG to model steamline breaks is a more capable method  ! to model steam jets than the' ANSI /ANS-58.2 model. However, the ANSI /ANS-58.2 model has been thoroughly benchmarked with experimental data, and its accuracy (and limitations) are  ; well established (Reference C.5). Furthermore, the ANSI /ANS-58.2 model also provides a ' good bounding estimate for recirculation line breaks which cannot be modeled with single-phase CFD codes such as NPARC. Volumes of Jet with Pressurer Higher than a Prescribed Damage Pressure: Figure C.1 of this appendix presents impinge.aent load isobars for a postulated DEGB with full separation in main steamline and recirculation line breaks. Figure C.2 of this appendix presents similar plots for a DEGB with limited separation (no radial separation and an axial separation of 0.25D). These isobars were drawn on the basis of the model presented in ANSI /ANS-58.2. Careful examination of these figures reveals the following trends:

• The jets originating from MSLBs tend to remain focused around the JCLs for longer distances. For example, JCL pressure is higher than 1.5 bars (or 22 psid) at distances beyond 20 L/D. Note also that this value compares favorably with NPARC results for total pressure plotted in Figure 9 of Reference C 3. On the other hand, the radial extent to which the 22-psid isobar spreads is about 3D.

C-1 m .. .

l

   . e . The jets originating from recirculation line breaks diffuse to low pressures more rapidly than      ;

those from MSLBs. For example, in the case of a recirculation line break, the 22-psid ] isobar extends only up to about 7 L/D, instead of 20 L/D in the case of an MSLB. i e . The main s'teamline results (especially JCL pressures) are in reasonable agreement with , the NPARC results documented in Reference C.2. 1 The following conclusions can be drawn regarding breaks with limited separation: e Thn MSLBs once again remain focused and go far beyond recirculation breaks of similar I magnitude. I e In general, the jet expansion from a limited separation break is more modest in extent than a full separation. l The staff calculated the jet volumes enveloped by each isobar. Figure C.3 of this appendix  ; presents these estimates for the following cases: , e a postulated MSLB as predicted by ANSI /ANS-58.2 model j e a postulated recirculation line break as predicted by the ANSl/ANS-58.2 model (Note that these values are applicable only to the sub-cooled blowdown phase.) , e the volume of a postulated spherical model (such as that used in NUREG/CR-6224), with increments in radius from 3UD to 15 UD .l

   'e    a postulated MSLB aa predicted by NPARC in the URG (Table 1, Page 46, of Reference C.1).

e a postulated recirculation line break as predicted by NPARC in the URG (Table 1, Page 47, Note 5, Reference C.1). The comparison presented in Figure C.3 suggests the following conclusions: e ' For impingement pressures larger than 40 psid, the volumes enveloped by the jet predicted in the URG are more conservative than the ANS!/ANS 58.2 predictions. As explained in - Reference C.3, this is expected since the ANSI / ANS-58.2 model does not include shock dynamics and radial pressure distributions mechanistically. This comparison presents a - good check of URG calculations.  ; e For impinge nent pressures between 25 and 4 psid, URG results and NPARC results are l Very close to each other. Once again, this comparison represents a good check for URG calculations. e At pressures below 4 psid, the URG volumes are lower than the ANSI Model by up to a  ! factor of 4. This result is not surprising because neither model is very effective at these low t C-2 i

 . _ . . -    __ .        __    . _-.       . . _ , _ . ~ . . _ _ _ _       _ _ . . _ _ _ _ . . _ _ _ . _ . _ _ . _   . . _ _ _

f pressures. The staff notes that very few insulation types are significantly damaged at these low pressures. e The multiplication factors provided for recirculation breaks appear to perform reasonably well for all pressures.

e. Overall, it appears that a 17-psid isobar bounds a volume equal to that of a sphere with a radius equal to 7 UD. Similarly, a SUD sphere was found to adequately bound the isobars with pressures larger than 150 psid.

Figure C.4 of this appendix presents a similar comparison for DEGB with no radial separation and an axial separation of 0.25 D. Once again, good agreement was observed between the ANSl/ANS 58.2 results and NPARC results at low pressures, while at high pressures, the NPARC results were conservative.

           . As a result of the~se comparisons, the staff concludes that the URG-predicted volumes are l             conservative or reasonable in the pressure ranges of interest, depending on the impingement l             load. Their use, if properly justified, is acceptable.                                                             '

t P l l l I i i . C-3

7 00 6 00 5 00 p 4 00 3 00 2 00 -- - - - - 1.00 - 0 00 0 00 2.00 4 00 6 00 8 00 10 00 12 00 14 00 16 00 18 00 20 00 LD

                                     -G-Boundary -O-P=7 5 + P=2 5 -O-P=1.5 lA. Main Steam Line Break. Full Separation l 12 00 10 00 8 00 h 600 4 00       g 2 00 -

0 00 -- ========== N -- 0 00 5 00 10 00 15 00 20 00 25 00 LO Bounday -O- P=7 5 P=2 5 -O- P=1.5 lB. Recirculation Line Break. Full Separation. Sub-cooled blowdown l Figure C.I. Jet Impingement Loads Computed Using ANSI /ANS 58.2 Model for DEGB with Full Separation. u

1 1 I lI 1 i i A. Main Steam Line Break  ! (0.25 D Separation) l n-- - - _ 5.------ - . . .

     ~ ; s:                                                                               . _ _ _

s DEC

         , 0C.
                                                               .....................-_._.                                   j
                                  =      :=       2=          a=    =   ,=    -;           .:     ,=          _: .;         ,

A LD) f l

                                  -*- s e *v -o- P 7 5 -e- e .2 5 --o - e , 5 1

B. Recirculation Line Break S i. .v (0.25 D Separation) 450 M l I 4 00 35; in N 250 -

c g 1

5:

=- O l n h h I

       --                    w'%_ t   -----

et _ . .

= :n  := )=  :=  != s= n  != , cc , :- ,

P LD)

                                   + B o TriL/ -O- P 27 5 -e- p .: 5 --CF- P = : 5                                           '

1 i Figure C.2. Jet Impingement Loads Computed Using ANSI /ANS 58.2 Model for DEGil with Limited Separation. I l l l l l l

10" 5 Steam Break ANSI Steam Dreak. URG 15UD Recire Break . ANSI Al Recirc Break.URG E g 5 Spherical Model 10L/D 3 li 10 *

 -                                                                                                                                                   7UD   l t,                                                                                                                     yo . u s L                  .                                 .          nl ti HiHIHI i,,                l . I H i H Isil Eli RIl FIllli ril 190 I I" l F I F        160                                    40                                    25                           17     6         2 Isobar Pressure (psid)

Figure C.3. Jet Impingement Load Isobar volumes for Fully Separated Steam Line and Recirculation Line Breaks. Bases: ANSI /ANS 58.2 and NPARC/URG l 10" E Steam Break- ANSI E Steam Break.URG Spherical Model l 190 160 40 25 17 6 2 Isobar Pressure (bar) Figure C.4. jet Impingement Load Isobar Volumes for Limited Separation Steam Line Breaks. Bases: ANSI /ANS 58.2 and NPARC/URG

Appendix D Calculations to Examine Zone of Influence Models Proposed for Two Phase Jets

References:

D.1 URG Section 3.2.1.2.3.2, Page 46, Table 2, and Page 47, Note 5. D.2 CDI report No. 96-01, "ZOI as Defined by Computational Fluid Dynamics," Revision 3, URG Technical Support Documentation, Volume 11, Tab 1. D.3 GE Report DRF A74-00004," Total Pressure Topography and Zone of Destruction for Steam and Mixture Discharge from Ruptured Pipes," URG Technical Support Documentation, Volume Ill, Tab 14, September 1996. D.4 Jet Model from ANSI /ANS-58.2, " Design Basis for Protection of Light Water Nuclear Power Plants Against Effects of Postulated Rupture," ANSI,1988. D.5 EPRI NP-4362, "Two Phase Jet Modeling and Data Comparison," Electric Power Research Institute,1986. D.6 NUREG/CR-2913, "Two Phase Jet Loads," Sandia National Laboratories,1983. D.7 SEA 96-3105-010-A:2, " Debris Drywell Transport Study," Draft Phase 1 Letter Report, September,1996. Problem Definition: In Reference D.1, the BWROG proposed the following correction factors to account for reduction in jet volumes corresponding to the recirculation line break, as a function of the target load: Insulation Destruction i Correction Factor for Pressure _(psi) Recirc. Line Break 0-20 1.0 20-30 , 0.9 30-40 l 0.8 40-50 ' O.7 50-60 O.5

                                 >60                           0.4 The basis for developing this table is documented in References D.2 and D.3. The staff performed the following calculations to evaluate the appropriateness of these factors. The ANSl/ANS 58.2 model(Reference D.4) was again used as a basis for the calculations. The l

results are as follows. Jet Volumes Corresponding to Subcooled Water Discharge: Immediately following a LOCA, subcooled water exits the break and expands into the containment. Past computer runs using the RELAP code (Reference D.7) suggest that subcooled blowdown occurs over a period of 5-10 seconds, during which exit quality of the break jet increases from 0 to 0.02 while the vessel pressure decreases from 1000 to 700 psi. Figures C.1 and C.2 in Appendix C of this SER show expanding jet isobars for flashing subcooled water discharged during this initial stage of a postulated DEGB in a recirculation line. Figures C.3 and C.4 from that appendix compare the volumes of jet bounded by each impingement load isobar for steam and recirculation line breaks with URG predictions provided in Reference C.1. Reference C.1 D-1 l

l l predictions are derived from the information presented in the table above. As shown in these l figures, during subcooled water blowdown, the corresponding jets tend to be less energetic. For recirculation line break jets, the staff's confirmatory analysis estimated volume ratios l consistent with the fractions listed above. On that basis, the staff concludes that the values presented in Appendix A to Reference D.3, j

 " Volume of Influence for Saturated Steam Versus Saturated Water," Revision B, are reasonable. The staff also notes that past debris generation data reported by European                    l investigators also supports this finding.

Jet Volumes Corresponding to Two-Phase Mixtures: After initial blowdown, the exit quality l increases steadily; thereafter, the blowdown at the exit plane consists of two-phase mixtures (Reference D.7). Jet impingement loads associated with st.ch flows were experimentally measured in the Marveklan tests (Reference D.5). Moody has proposed a scaling scheme which justifies the use of this Marvekian test data to BWRs. The scaling criterion is acceptable, and as such that data has been widely used for similar purposes before (e.g., References D.5 and D.6). However, the URG does not explain in a tractable manner how the Marvekian test data are used to corroborate the correction factor table presented above. As a result, the f; following analysis was performed. 5 The pressures reported in the Marvekian tests can be tabulated as shown in Table D-1. A plot  ! of JCL pressures (in column 9) versus UD is presented in Figure D.1 for three types of l blowdowns: subcooled liquid, steam / liquid mixture, and steam. A review of Figure D.1 j suggests the following: e Stagnation pressures near the nozzle would be higher for subcooled breaks over a narrow ' radial range. e Far from the nozzle, for UD > 4, the stagnation pressure is higher for steamline breaks as compared to both subcooled and saturated liquid breaks. f e However, mixture and steamline breaks look somewhat similar thereafter. t These trends are well established and have been explained using the K-FIX code in Reference i D.5, and using the CSQ code in Reference D.6. Therefore, Figure D.1 can be used to conclude [ that mixture blowdown at a given stagnation pressure is no more severe than steam blowdown l l from the same stagnation pressure. Coupled with the fact that actual vessel stagnation pressure falls to about 700 psia before the onset of two-phase mixtures, this finding was used [ j to compute the load isobars for mixture jet expansion during blowdown. Figure D.2 illustrates  ! the isobars. Comparison of isobars presented in Figure D.2 with those presented in Figure C.1 would clearly establish that pressures associated with two-phase blowdown are considerably lower than steam blowdown. [ l i Further calculations were performed to corroborate the correction factors listed above. These ' calculations support the conclusion that the correction factors cited above from the URG do . conservatively bound the jet volumes. Therefore, the staff concludes that use of these l L correction factors is ' acceptable. l l l D-2 f l t

t l f Table D-1 A Summary of Marveklan Test Data for Blowdown Test UD Time _ Thermodynamic. . Vessel Pressure JCL Ratio of (s) Descrpt. AT ('C) Range Average _(MPa) JCl/ Stag..

 ~TO~ ~ ~ ~ ~1.2   0-29     Subcool   OT23   4.3-3.1         3!7      3.7          1       !
                , 29-45     Mixture x > 0.10 3.1-2.5        2.8       1.12      0.4 52-55      Steam   x = 1.0 1.5-1.1          1.3    0.78       0.6 8       2       O! 55 i Subcool    0-23   4.3-3.2       3.75      1.875      6!s 25-44 , siixture
                                                 ~               ~                ~~

x > 0.10 f2 2.9 3T05 OTs1 0.2 49T55 , Steam

                                               ~

x = 1.d 2 0-1.1 1.5s 0.4ss OT3~ 7 4 0-25 Subcool 0-23 4.4-3.2 3.8 0.38 0.1  ; 25-43 Mixture x > 0.10 3.2-2.8 3 0.375 0.125 48 Steam x = 1.0 2.1-1.1 1.6 0.28 0.175 l I D-3 l l

Analysis of Marvekian Data

                 ).

BWROG/URG I $ Subcooled

$ Mixture m 0.8 .- saturated (U .

(4 . Q. 0.6 .- 3 - g a  : 7 0.4 _ - + - 0.2 ? + o

O O ~ ' ' ' '''''''''''''''

1 1.5 2 2.5 3 3.5 4 UD Ratio l

           'fC
            .                                               ,ee  a

• l  ::: - -

                                          < ::   u:
                                                    ,=======,=
                                                      .:.: n::

_ _ a;

c 18:: :c::

l Lt ( l .

                                 + E rndr/ -O- P =' S -G- P = 2 5 -O _P ='_5_

Figure D.2. Jet Impingement Load Isobars for Two-Phase Mixture Jets that Result During Late Stages of a Recirculation Break LOCA. l l

l Appendix E Calculation to Examine the URG Guidance on Thin-Bed Effect on Alternate Strainer Designs

References:

E.1 URG, Section 3.1.3, Page 16, Line 7. l E.2 URG, Section 3.2.1.1.1, Page 28, Line 12. E.3 URG, Section 3.2.G.2.3, Page 117, Line 24. E.4 Appendix l to CDI Report 95-09, " Testing of Alternate Strainers with Insulation Fiber and Other Debris," CDI, URG Technical Support Documentation, Volume 1, Tab 2. Problem Definition: In References E.1, E.2, and E.3, the URG presents the following statements: e The thin-bed effect is an issue for semi-conical strainers, but not for stacked disc strainers or any other " alternate strainers."

• Therefore, licensees that propose to use attemate strainer designs need not analyze medium LOCAs, because they are not limiting relative to debris generation and transport.

As a result, the staff performed a series of data comparison analyses to evaluate the l completeness and accuracy of the URG statements regarding thin-bed effects. Results: The ability of thin fiber beds to trigger large pressure drops when combined with particulates (e.g., corrosion products, dirt, etc.) has been demonstrated by both the Perry and Limerick events. Studies by the NRC, European regulatory agencies and the BWROG have , focused on characterizing the thin-bed effect. Figure E.1 provides a sketch of the " thin-bed effect" as it relates to head loss across the strainer. As shown in this figure, at very low thicknesses (<1/8") the strainer surface is partially covered by fibrous shreds. Corresponding to this situation, the head loss across the strainer is low. With a slight increase in the thickness, the strainer is more uniformly occupied and starts to filter out some of the particulate debris passing through the debris bed. However, as experimentally evidenced, these beds break down or undergo reconfiguration under the influence of the larger head losses caused by the particulate filtration (See NUREG/CR-6224, Appendix-E). This trend continues until the bed gains the strength necessary to sustain head losses. Thereafter, the head loss increases rapidly as the thin fiber bed continues to filter out a large fraction of the particulate debris. The resulting debris is characterized by a very dense, relatively impervious, particulate bed formed by a relatively small number of fibers. At higher fibrous debris bed thicknesses, this trend reverses because the debris bed starts to become more porous. The thin-bed effect has been widely observed for flat-plate, cylindrical, and semi-conical (truncated cone) strainers. Table E-1 shows the URG data for semi-conical strainers demonstrating the effectiveness of thin-beds to introduce large head losses. As can be readily seen from this table, high head losses across the strainer are possible at very low insulation

loading when coupled with large corrosion product (sludge) mass. These data confirm the high l_ head losses reported ;n the Limerick and Perry events.

E-1

l l Proving existence or non-existence of a thin-bed effect in stacked-disk strainers is more ! complex. Figure E.2 illustrates the debris bed buildup on a stacked disc strainer surface. When the cavities of the strainer are partially filled, a substantial portion of the strainer surface is still open for particulate flow without being filtered. For these situations, the BWROG experimental data (see Table E-2) have shown that the thin-bed effect is not an issue. Even for the case when the cavities are nearly full, there has not been a drastic increase in head loss, in spite of large sludge-to-fiber mass ratios. However, this does not absolutely rule out occurrence of the thin-bed effect in stage 3 of Figure E.2. The BWROG has not reported any experimental data l supporting their conclusion of "no thin-bed effect* during this stage, as all of the reported data in the URG apply to stages 1 and 2 of Figure E.2. Although Test P5 provides data for the case l when the insulation goes beyond the cavities, it is one single data point and corresponds to a rather thick insulation layer (3-inch theoretical thickness). Table E-1 Experimental Head Loss Data for Truncated Cones Test ID . Insulation Mass Bed Thickness. Sludge Mass Head Loss Mass . Ratio

                                                                       +

(Ibm) (inch) {lbm) (in H2 O_)_ 6 0.5 ' O.14 500 1000 425 7 1 0.28

                                                 ~

60 60 385 8 3 . 0 83 16 5 >500 Strainer Surfa_ce Area = 18_ sq. ft_ Strainer Flow Rate = 5000 GPM Table E-2 BWROG Head Loss Data for Stacked-Disk Strainer. l Test ID Strainer Type Cavity . insulation % Cavity i Sludge : Head Volume i Mass ; Occupied i Mass l Loss j (ft3) (Ibm) > jlbm) ' (in H O)_ 2 l , 21 . Stacked-Disk #1 ! 3.53 1 11.8 180 23 _ 22 Stacked-Disk #14 3.5_3 3

• 35.4 I 180 6_5 3.53 3 35.4 240 72

        ~22       ' Stacked-Disk #11 250 22" Stacked-Disk #1 i           3.53           4        47.2          240    '

23 Stacked-Disk #1i 3.53 6 > 70.8 240 350 P2 . Stacked-Disk #2' 10 17 70.8 85 7 P3 Stacked-Disk #2' 10 ' 25 104.2 100 10 P4 Stacked-Disk #2- 10 3 12.5 100 0 P5 Stacked-Disk #2 10 50 208.3 100 28 in P5 the insulation goes beyond the cavities. The rest of the insulation forms apniform laver 3-inch thickness. The staff performed additional exploratory calculations to evaluate the question of whether licensees who propose to use an alternate strainer designs (e.g., stacked-disk strainer) should E-2

analyze MLOCAsc Calculations performed for NUREG/CR-6224 for an MLOCA postulated in the reference plant (BWR 4, Mark 1) with an assumed drywell transport factor of 1.0 for transportable debris, resulted in an insulation debris volume on the strainer of 24 ft' (or a mass ' of 10 lbm). The BWROG data clearly suggest that both stacked-disk number (no.) 1 and , stacked-disk no. 2 can accommodate such debris loads with sludge-to-fiber m' ass ratios of up to I 30 without a noticeable increase in head loss (see data for Test P4). Therefore, the staff believes that MLOCAs can be screened out if stacked-disk strainers are used. j On the basis of the above analyses, the staff draws the following conclusions:  : e The BWROG claim that thin-bed is not observed in alternate strainers is not adequately

    . substantiated. The reported data apply to two strainer designs (stacked-disk and star). In addition, the data address a narrow range of experimental parameters.

e The existing data, however, suggest that licensees may screen out MLOCAs if they use stacked-disk strainer no. 2, star strainers, or other such strainers with large cavity (crevice) capacities for debris buildup (which prevent even debris bed buildup across the strainer surface at low fibrous debris loads) provided that the strainer vendor can demonstrate that debris loadings lower than the bounding large break LOCAs (e.g., loadings consistent with a spectrum of breaks from MLOCAs to large LOCAs) would not be limiting in terms of head loss across the strainer. Strainer vendors should have adequate test data to support this assurance. I i f E-3 I

      , --  .s,-r ~ ,- w- -

w ,-w - - . - - . , , ,v--- - ww,-e

l 2 At very low thickness, beds are non-uniform. Umited filtration. Small head loss. l C Slight increase in thickness initially filters large fraction. But, they reconfgure due to increased head loss. 11; if M-studge = 150 lbm A 8 ,

                                                                                /

k. ,..

                                                        * !,                                  M-studge = 100 lbm                           /
                                                                                                                              /
                                                                          /                                          '
                                                                         /                                     /

i

                                                                        /                         -

g / [ y ,-( M-sludge = 50 lbm pata trend n obeemdin flat-piste strainers.

                                                               \      '
                                                                        ,#                                                     - WR       Datn !
                                                               \M                    Amount of Fiberto PooW Figure E-1. Thin Bed Effect: Description a

4 , Figure E-2. Description of Debris Buildup on Stacked Disc Strainers

• ___ l Lnw Loading Moderate Loading High Loading to. u.ai. : i l l l

,__ y 1[iltration Coefficiept l %ders= Lead 63 ,

                                   . /    '

ei,  ! f' :  : 4 4urface Area for Deposition ~ 1 f' l l

                        ,'         l      l                                                    s                                                                                      s      !

n,o t s, Fiber Volume t

i Appendix F

Mapping of the Zone ofinfluence l

l

References:

F.1 URG, Section 3.2.1.3.2, " Method 2 - Target Based Analysis Using Limiting Size Zones of influence." F.2 CDI Report No. 96-06, " Air Jet impact Testing of Fibrous and Reflective Metallic Insulation," URG Technical Support Documentation, Volume 11, Tab 3. Problem Definition: In Reference F.1, the URG stated that:

• A spherical 201 should be used to define the geometrical region over which damage to the insulation blankets would occur.

e For fibrous insulation (e.g.,NUKON'), this region is as large as 10 break-diameters in radius. Neither of these assumptions were fully substantiated by the BWROG. Furthermore, the BWROG stated that these assumptions would yield conservative estimates of the ZOI since the assumptions ignore the presence of pipes and other structuralimpediments. A series of computational fluid dynamic simulations of the jet expansion with and without structures were conducted to verify the adequacy of the BWROG recommendations. Methodology: In the URG, information is provided related to experiments that were conducted to d5termine the failure pressure for NUKON* insulation cassettes; both encapsulated and non-encapsulated. These experiments reveal that damage is possible when the local total pressure exceeds 10 psi. Considering that downstream of shock-front, total pressure is made up entirely of the dynamic pressure, the local flow velocity that would be capable of inflicting damage can be calculated as follows: Pm = % p V2 fg, Where, p = gas (air) density at near-atmospheric conditions that exist downstream of shock (Ib/ft3) V = gas velocity (ft/s) g, = conversion factor (32.12 lbf/lbm) After appropriate unit conversions, the velocity corresponding to damage pressure is 2 V = (10)(32.12)(144)(2)/(0.067) 7 The density was derived from the CFD calculations conducted as part of this study. This took into account the combined l effects of lower than atmosphenc pressures and temperatures in the jet. I F-1

1 l

V=1175 ft/s (cr 358 m/s) l I Thus, damage is possible whenever the jet velocity exceeds 1175 ft/s, although, more conservatively, damage can be assumed for velocities in excess of 985 ft/s (300 m/s). j 1 1 The general method followed by the staff in this calculation is- 1 e CFD calculations were conducted to examine velocity fields in a freely expanding jet. These calculations were used to provide a reference case and also to compare the results with the BWROG results in References G.1 and G.2. e Using the CFD calculations, the impact of adding structures in the pathway of the jet

were examined, up to the congestion levels typical of BWR drywells.

Results and Discussions Calculation no.1:^ Define the spherical region dimensions in the ZOI as recommended by the BWROG7 Egr Steel Jacketed NUKON': P. for NUKON'in Table 2 of the URG = 10 psi Extract A from Table 1 of the URG (as predicted by step #3): A = 4708 Volume of the ZOl; V = 4708 DS %. D = 24 in. (or 2 ft.) V = 37,664 ft S; which is about 25% of the drywell volume. In terms of equivalent sphere: RS = % (4708*6/n)DS; R= 10.4 D The radius of the spherical region is 10.4 times the diameter of the break. These are large ! spheres compared to NUREG/CR-6224 and any other volumes previously used. This is l used as the reference case forjudging the conservative nature of BWROG recommendations. l Calculation no. 2: Check the adequacy of the pressure fields for freely expandingjet predicted using the BWROG methodology? To examine this, the air jet originating from a 8-in (20-cm) diameter nozzle was allowed to expand freely into a 160-in (400 cm) diameter cylinder (20D),160-in (400 cm) in length l (20D). The inlet to the nozzle was air at a pressure of 600 psi and sonic velocity (965 ft/s or 300 m/s). The expanded jet flow fields are calculated using the following computational details: AR = 3 cm; AZ = 2.5 cm; A0 = 45*

• Typical time step = 10~5 to 2.5x 10-5 seconds (lower time step initially)

Typical Execution time = 12-14 hrs CPU for 0.15 seconds of real time AR. AZ. and 60_ radial. axial and angular nodal lengths used in the discretization. F-2

 - . . - ~ . . . - - - - - - _ - - - - - . - -                                                             .-- - - .. - - - . - - - - ..
                          ' The results of the CFD simulations are illustrated in Figure 2a of this appendix. As shown in this figure, freely expanding Jets resemble semi-conical regions as described in NUREG-0897. The static pressure approaches atmospheric pressure within 1-2 break diameters and remains steady thereafter. The local fluid velocity increases initially reaching values as high as 2790 ft/s (850 m/s). However, this reduces to slightly above 985 ft/s (300 m/s) at a distance of above 10D and remains fairly constant up to and well beyond 20D. This confirms the behavior described in the URG. Thus, it is likely that high flow velocities would be maintained at very long distances for a freely expanding jet. Figure 2b of this appendix shows flow velocity isomers for a freely expanding Jet. The dynamic pressures calculated in the present study are slightly below those in Figure 9 of Reference 2.
                          ' Calculation no. 3: Examine the impact of adding a simple structure such as a grating in the Jet path?

l_' l To examine the impact of a single grating-like structure, a baffle plate is artificially introduced into the calculation domain. The structure was denoted to be with an area blockage of 20%, and pressur9 drop characteristics given by e AP = 0.125 (pV2fg,) This case is shown in Figure 3a of this appendix, with the predicted flow fields shown in l Figure 3b of this appendix. As shown here, the presence of a single grating can l considerably alter the flow fields, such that flow velocities downstream of the grating are l reduced well below the 985 ft/s (300 m/s) necessary to inflict damage. Thus, gratings can provide considerable " shadowing" effect. However, it is not clear, if the gratings can withstand such loads. (Note that gratings are not load-qualified structures.) Calculations no. 4: Examine the impact of pipes and I-beams arranged in a manner similar to those commonly encountered in BWR drywells? To examine this issue a total of five structures were introduced in the pathway of the expanding jet. ~ As shown Figure 4a of this appendix, these structures include:

• A 8-in (20-m) diameter pipe located in the centerline of the break jet to simulate the I effect of the other end of the broken pipe.

!- e Three pipes, each 20 cm in diameter and located in the pathway of the jet, considerably offset from the JCL. l e ~ One pipe anchored on an I-beam; the pipe is 8-in (20-cm) in diameter and I-beam is 8-in (20-cm) in height. At any given axiallocation, flow area averaged blockage is les.s than 40%. The degree of l- . congestion is consistent with the values identified from a survey of BWR drywells. To

                                 - The value of momentum loss coefhcient (0.125) was calculated from hand-calculations using approximations. This value, if at
                                 . all, under predicts pressure drop and is, thus, conservative.

!- F-3 I 1 i-

minimize computational effort, the pipes were not modeled in detail". The results of the , CFD simulation are shown in Figure 4b of this appendix. As shown in this figure, higher  ; than 985 ft/s (300 m/s) velocities were observed at distances close to the break opening. However, farther from the break, flow velocities decreased considerably. Resulting

• velocities are well below the velocities required to inflict damage to the insulation blankets.

To further confirm this finding, the following variations were added: l

• A cavity was added to create a narrow region that closely resembles the neck region of l' the drywell. This case was created to analyze breaks postulated in the neck region of the drywell. (See Figures 4.c and 4.d of this appendix) e The boundary conditions were altered to simulate Mark 11 drywells. (See Figure 4.e of .

this appendix) in all these cases, pipes and l-beams were found to have resulted in dispersal of the air jet over a substantially larger cross-section. The resulting flow velocities outside a spherical  ; region 7D in radius were considerably lower than the 985 ft/s (300 m/s). t

Conclusions:

A series of CFD simulations were carried out to examine the impact of . drywell structures on the ZOI. It is not the intent of these calculations to address this issue comprehensively, instead, the focus had been to obtain order of magnitude estimates of jet dispersion when subjected to drywell structures. The results of the calculations described above should not be interpreted as "best-estimate" predictions. They were conducted for . i insights only. These calculations suggest that use of a spherical ZOI is appropriate, since it tends to better approximate the jet expansion in a congested drywell volume. They suggest that l presence of structures, such as pipes, I-beams and gratings would disperse the jet. As a result, the jet velocities outside the spherical ZOI with a radius of 7D are lower than those required to inflict damage to the insulation blankets. Thus, use of a 10D sphere by the BWROG (as shown in calculation no.1 above) in the sample problem is considered l

                                                                                                                  ~

conservative and appears reasonable. i lt should also be recognized that conclusions reached are subjected to the following assumptions: i e Levels of congestion (" piping forest") is limited to a narrow region closer to the break.  ! Addition of structures beyond this region would further reduce velocities. e The structures were not modeled exactly using CAD drawings of the plants. i D I l

           "   An additions Mutation suggested that this is not a rnajor issue.

l o  : l F-4  ! l 4

 . . - ,             . - - , - - , . . - - _ . . , , , . ~ , - - . ,   -m,      . , .. _ ,

1 I 1 i l. a i 1 ' i i . N ' t .. i l

                                    *                \

I l . . i e t. i . l 1

                                                                                                      ~
                                                                                                                                          )

1 !- Mgure 2a. Velocity Melds in a Freely expanding jet. [The Nozzle diameter is 20 cm. The volume of the computational area: 400 cm Diameter Cylinder,400 cm in length. The time step 104seconds. Reponed flow fields are for a quasi-steady state. These are the flow fields most likely encountered in the BWROG Experiments at CEESI; High velocities far from the nozzle exit]. i i I 1 i L ,

l l l

g. ~ ;

l

                                    \
                                                                                                         .r.
                                       \                                                 ..
                                        \

t. s

                                                \

Figure 2b. Velocity contours in a freely expanding jet. [The associated dynamic 2 pressum can be calculated as P - % pV /ge. At a velocity of 380 m/s, the dynamic pressure is 10 psi; which is the damage pr- ure for NUKON. This calculation confirms that for distances beyond 20 D, the velocita . within the jet would be fairly uniform, it covers the blanket completely, and pressures exceed 10 psid.]

7.-_-.- E i i i l l l l i 2 ( , i i 1 i I I i t l I l 1 t I l l k ! Figure 3a. Geometry used to simulate the effect of a single grating on the expansion of a airjet. The piping region was not used in these calculations. The Baffle Plate Approximation was used to simulate the floor grating. The baffle plate was assumed to < have a blockage of 20% and a non-linear head loss coefficient of 0.125. The coefficient was chosen conservatively based on measured experimental data as well as hand calculations. i O m,. -- nn, , , , . . , -_ -.,, - - - .. - .. .-- , ., , . ,, . _ . -- , ,

l l l

                                                                                                         .~

c [

                                                              'f%  '
                                                                                               -            \
                   -            t>ys; ,~. x                                           -
                                ;).?.e'.::. ,; .;;.  .
                                ..; ,.l. *':ns; _ ;            e
                                                                           \
                                }t h

h. e h.?;f L (' ;tyt.;w, .

• pe N

                                ,..               :n 8 p.s      _[.          h.

ff. _ ?:f :; , t

                                \ py ;

ccy : ...

                                  'f V l

. p . .. . . -

                                    'g,g? -' y ..

9 Figure 3b. Flow velocity fields and contours high lighting the impact of adding a baffle plate in the jet expansion pathway. As shown here, the flow velocities downstream of the baffle plate are less than 300 m/s. The velocities upstream are super-sonic. The jet is wider. Comparison with Figure 2a would reveal that a single grating can substantially alterjet expansion, both upstream and downstream of the grating. l l l l

4 i i 4 l l I l l l i i i suma } i

                                                        \I
                                                         ;-.      1 3

y. I \ i . i 1

                                                                \                       ,

l i \ . . i i 1 . i - i ! Figure 4a. A geometry used to study the impact of structural Impediments to jet

expansion. A total of five structures were added. The maximum blockage was 40%.

! These structures were assumed to have symmetry around jet center line. The flow outlet was assumed to be on the sides, to simulate a Mark I geometry. l l 1 I 4 i i I i . 4 ) i i l t i 1 i

t> rev 1 4

- .' s e

l 4 Figure 4b. Flow fields corresponding to geometrical case shown in Mgure 4a. As shown here, local flow velocities much lower than 300 m/s characterize majority of the flow area. High flow velocities are confined to the ' piping forest' region. There also, some of the stmetures are not subject to high flow velocities, because of ' shadowing' effect. l I

i. . _ .

i 1 i t i 1 5, 1 i i 1 1 .... i F i ! U ! E wu l @ ! 00, $Q { 6S i E 4

                                   >y    .    ..

p !$h .. 4 }

                                   , p.:D...f;
                                             . .fft.

h  :/ i , g.._,pt?.i. c . p; . _ r 1 CA ;?m ^ , e -; 1 i i Figure 4c. The geometrical configuration used to simulate a postulated break in the neck region of a Mark I BWR containment. An axial cavity was added to the geometrical arrangement shown in Figure 4a to simulate the ' narrow' neck region. Otherwise, the geometrical arrangement is essentially same as Figure 4a.

s l ! 1 8 l l l b

                                   ,5 l                        is i

1 a i - i Figure 4d. Flow fields corresponding to geometrical case shown in Figure 4c. The flow outlet in this case is through the sides to simulate a Mark I drywell. Break is in the neck region. l 4 ?

.J . .a n .y L. 1

                                                                                            . ., .c -fl* ,y                                                                               i h_,
                                                                                            . e.e

1. cq#.:.n

                                                                                                    .           x

_i;. - - f ;h 4 l

                                                                                                 ^':
                                                                                                   ..,.:..:                                                                               l l

l l l Figure de. Flow Delds corresponding to geometrical case shown in Figure 4c. The How outlet in this case is through the end to simulate a Mark II drywell. 4 i i E 4

.i 4

4 -5

     .-..y.---.w.                       ,            ., , , . . _ _ , _ _ - . . - - -

                                                                                                           *,Ed.35 2wea AL1 sum   &4-w                                                                                                                                            t i

Appendix G Calculations to Evaluate the URG Methods to Estimate the Quantity of Fines References G.1 URG, Table 4, Page 71. G.2 CDI Report 96-05, " Testing of Debris Transport through Downcomers/ Vents into the Wetwell," URG Technical Support Documentation, Volume ll, Tab 2. G.3 WBE Report No. 796-001, " Evaluation for Existence of Blast Waves Following Licensing Basis Double Ended Guillotine Pipe Breaks," Science and Engineering Associates, Inc.,1996.

    - G.4         CDI Report 96-06, " Air Jet impact Testing of Fibrous and Reflective Metallic Insulation," URG Technical Support Documentation, Volume 11, Tab 3.

G.5 Appendix-B to this SER, " Analyses to Verify Values of P for Selected Materials Reported by BWROG and Suggestions for Development of Scaling Analyses," 1998. Problem Definition: In Reference G.1, the BWROG recommended a set of " destruction factors" that can be used by licensees to estimate the volume of fine debris generated by a postulated LOCA. - These destruction factors were derived based on the experimental data obtained at the AJIT, and were provided for each insulation as a volume averaged quantity to facilitate ease of use by licensees. A series of analyses were conducted to examine the acceptability of the recommended values, with particular emphasis on determining whether or not the destruction factors would result in either " conservative" or " reasonable" estimates for the quantity of fines produced. The focus of the analyses was the production of fines from NUKON' blankets, although the conclusions reached are considered valid for other insulation types also. The staff's confirmatory analyses consisted of the following steps:

• Analysis of BWROG experimental data and comparison with NRC-sponsored test data.
• Analysis of effects from other phenomena (e.g.: jet deflection by various structures).

Analysis of Air Jet impact Testing (AJIT) Data on Size Distribution: Table G.1 presents percentage of fines generated (by mass) for NUKON* blankets as a function of the target . distance from the jet nozzle (UD), blanket jacket status and blanket seam arrangement. The fraction of insulation not destroyed, termed as rk by the BWROG, is plotted in Figure G.1 (of this appendix) as a function of UD for NUKON*. This figure is identical to Figure G.1 of  :

Appendix E in Reference G.2, with the exception that an additional data point obtained for

[ NUKON* with Sure-Hold bands is included. Also shown in the figure is the linear fit for the data proposed by the BWROG. A close examination of the data reveals that: 4

• lrrespective of the type of encapsulation, the fraction of the fines contained in the debris is only a function of the distance from the jet nozzle as long as the jet is energetic enough to peel off insulation immediately upon impingement. For example, insulation with no jacket at SUD resulted in the same debris fraction as that which was covered 1- with stainless steeljacketing secured on the target pipe by "Sure-Hold' bands.

i . G-1 4

  -      --,.      .     --      - -      -     - - - - - . , - ,   ,                                                           r

e The fraction of fines is a strong function of the location of the blanket seam with respect to the jet nozzle. One data point obtained for seam arrangement described as 3 o' clock (i.e., the seam directly in front of the nozzle) yielded the largest ris or, the least number of fines. I e The BWROG's linear regression is a poor fit for the data, and fails to explain all the trends. The data suggest that the fraction of fines initially increases as a function of UD from the jet nozzle until reaching a maxim'm at 30 UD. The amount of fines decreases thereafter as a function of UD. 5 Table G-1 AJIT Experimental Data for NUKON' Blankets. 1 [ Fines (%) is percentage of fines by mass. 9, of Reference G.2 is 100-Fines (%)] Test Jacketed , Seam i L/D Fines rio Blankets l  ! (%) i [Ref. G.2] I

        ~5-2           No        ,

9 l 5 25.4 - 74.6 48.8 Y. "Sure-Hold" ' 9k  ! 7 22.0 78.0 70.0

        ~31-1 3-1 i   Y. Standard i         9k   !     20      46.3  i    53.7     i      0.0
        ~5-1 i         No         i     3k         20       7.1   t   92.9     ,

35.6 5-3 ! No ' 9k i 30 60.0

                                                              ~

40.0 31.3

         ~2-1 i   Y. Standard       ,    9    !    50      25.3   .

74.7  ; 32.6

         ~3-2 i   Y. Standard ;         9k    i 50~

11.9 88.1 59.1 T-6 No j 9k 1 50 28.0 7 270 3_3.5 No 9k { 60.5 6.3 4 93.7 l 30.3 _5-5 ! i No 9k i 80_ 2.0 98.0  ; 92.0 _6-2 <  ! _6-1 ' No t 9k  ! 115.5 ' O.0 l 100.0 i 10_0.0 5-4 No 9k 119 0.0 100.0 100.0 Comparison with NRC Sponsored Testing: As part of its drywell debris transport study, the NRC conducted a series of debris generation / transport tests at the same CEESI facility that was used by the BWROG for the AJIT. Although the intent of the NRC tests was not to generate data regarding debris generation, a by-product of these tests included insights into debris generation. The exploratory tests employed a 3.75-in (9.5-cm) diameter nozzle, instead of the 3-in (7.6-cm) diameter nozzle used in the AJIT tests described above. The following findings of NRC tests are in qualitative agreement with the AJIT test data:

• The direction of seam with respect to the jet is the key factor that determines the quantity of fines generated by a break jet, if the seams are directly facing the jet, then the blanket tended to be blown away, and suffer only limited destruction. Very little fine debris were generated. This confirms the results of the data in BWROG test 5-1. The BWROG conducted most of its tests with the seam in the 9 o' clock position maximizing potential debris generation. Thus, the data are conservative.

G-2

l e Only rarely did the quantity of debris generated exceeded 50% of the target insulation, irreapective of where the blanket is placed (i.e., UD value) and its seam alignment.  ; Additional banding (which is non-prototypical) and end plates were required to keep the l blanket in place in order to generate fines in excess of 50%, in spite of these j engineered features, the maximum fraction of blanket destroyed into fines is 60%. l Thus, a value of 50% forms a realistic upper bound for the destruction factor for typical insulation mounting configurations used by BWR licensees. It is very unlikely that higher l than 50% is possible. ) l e The destruction factors (or the percentage of fines) vary considerably with distance from i the jet nozzle. Increasing the UD initially increased the destruction factors, until they . l reached a maximum. Thereafter, they decreased with distance. This is consistent with the data plotted in Figure G.1. Although a. linear fit of the data is an easy solution, it is not consistent with the trends L exhibited by the data. The data exhibit the following three distinct characteristics: l

e Minimum Fine Debris Generation Reached at 0 UD

As can be seen from Figure G.1

                               -(of this appendix), riereaches a maximum of 80% as UD approaches zero. This implies that about 20% of the debris would be fines. However, the staff believes that this result I                                 can be attributed to the 3-in (7.6-cm) diameter nozzle size used in the AJIT. Initially, for UD < 10, air jets from the nozzle tend to remain focused. For a blanket located at 5 UD, Figure G.2 (of this appendix) illustrates the radial pressure distribution of the exposed target blanket [ References G.3, G.4, and G.5]L in addition, Figure G.3 of this appendix [ Reference G.7] illustrates the peak and average pressures on the target                             1 blanket.1 The average pressure suggests that the blanket remains on the target pipe

only for a short interval. During this short time, destruction occurs in the localized region of the blanket which is subjected to high pressures. As evident from Figure G.2, high pressures (> 50 psi) are confined to a circular area in the middle of the blanket that is approximately 2.5-3.0 nozzle diameters (D=.) in radius. If one were to postulate that l all the insulation contained in this high pressure area would be pulverized into fines, the l = fraction of blanket destroyed into fines can be calculated as

! Fines (%) = 1-r1. = (Area over which high pressure jet impinges)/(total blanket surface area) l where, l l l Total Blanket Surface Area = n(D, + t ).L. ) Area over which high pressure jet impinges = n(2.5D..)' l D, = Diameter of the target pipe (12 in.) l p -t = blanket thickness (3 in.)

j. L = Length of the blanket (24 in.)

D%, = Nozzle Diameter (3 in.) l After substituting all the values, the total fraction of insulation in fines can be estimated ) to be about 16-22.5% (depending on the choice of 2.5D., or 3.0D=.). L G-3

  - .-. i
                                          --        -     -~ _             .    -    ._                            _._        . - .   ._ _ .-

t At 20 UD, it can be shown that the predicted percentage of Fines using the same formulae above would be close to 50%, because the jet area envelopes the entire front surface of the blanket. l L The implication of this analysis is that the 20% minimum value for fine debris generation l at 5 UD is a reflection of the 3-in (7.6-cm) diameter nozzle used in these tests. If in the ! AJIT tests, the nozzle diameter had been increased, the percentage of fines produced would probably increase over this region. This was observed in the NRC tests where a ( 3.75-in (9.5-cm) diameter nozzle was used. e ' Maximum Reached At 30 UD: As can be seen from Figure G.3 (of this appendix), the average pressure on the target blanket decreases with distance from the jet nozzle, l

reaching about 15 psig at 30 UD. As UD increases, the time the blanket would spend l on the target pipe before being blown off by the jet (blanket residence time), which is inversely proportional to the average pressure, increases steadily. Larger residence .

times would imply that there is more time for the high pressure to penetrate the blanket l and cause damage to the blanket. Apparently, at a point where a combination of peak

pressure greater than 17 psid and an approximate average pressure of 13 psid occur, l the target blanket destruction reaches a maximum. This suggests that if the target blanket is exposed to an average pressure of approximately 17 psid, maximum target blanket destruction is possible. In addition, this destruction may result in debris i

L ' generation which is about 60% fine debris. Note: the 60% fine debris generation is only ! slightly larger than 50% (the fraction of insulation that is actually exposed to the jet with the remaining 50% being shadowed by the target pipe). e Decrease in Fines (%) at UDs > 30: As the target distance from the jet nozzle increases l beyond 30 UD, the peak and average pressures the target is exposed to decreases. L Although the residence time for the target insulation blanket also increases with distance , from the jet nozzle, beyond 30 UD the lower the destructive force of the jet leads to less debris generation. Ultimately, a point is reached where the peak pressure cannot penetrate the outer jacketing, preventing the jet from damaging the insulation. As the peak and average pressures continue to reduce, therefore, the fraction of fines also decreases. r Conclusions of the Comparison: Analysis of the experimental data and its comparison with NRC sponsored test data suggests that use of a linear fit to derive volume averaged destruction factors does not properly scale the experimental data to drywell conditions. 1 l' Nevertheless, the method employed has the following conservatisms": l e . All the data included in the analysis was obtained for a condition in which blanket seams are arranged in the 9 o'clock position. NRC-sponsored testing found that seam position alone can significantly impact debris generation, and the 9 o' clock position maximizes generation of fines. i i

           "     It should be noted that the BWROG incorporated the blast effects by assurning that all the debris located in a spherical zone 3 nozzle-diameters in radius would all be destroyed into fines.

• G-4 i

l , e The method completely ignores the impact of targets present in the path of an [ expanding jet. Quantification of Conservatisms in the BWROG Recommended Values: In order to evaluate the magnitude of conservatism involved in the BWROG recommended values for debris generation, a series of calculations were performed using the NUREG/CR-6224 (SER Reference 31) reference plant as the basis for the case study. In the reference plant, NUKON'is used as the insulation on all primary piping. The ZOI computed for that plant (also see Appendix F to this SER) using Method 2 of the URG is a spherical region 10.2 break diameters (D) in radius. For a recirculation line break postulated in the most congested region of the drywell, the l total quantity of insulation contained in a 10.2 D sphere is approximately 750 ft . The , volume averaged destruction factor suggested by the BWROG for NUKON'is 0.23. Total l quantity of fines generated is 172 ft'. t An alternative method for calculating the debris generated would be to assume that : e 100% of the insulation would be destroyed in a spherical region 3D in radius due to the blast effects from the postulated double-ended guillotine break. This conservatively-bounds the possible effects of the blast wave. As discussed in Refere~nce G.3, the blast effects would most likely be bounded by a spherical zone 3D in radius. For the l reference plant the volume of debris contained in a 3D sphere is 35 ft'. l e 50% of the insulation would be destroyed between 3D and the outer boundary where the dynamic pressures fall well below 10 psi. As discussed in Appendix F, due to the ' presence of structures, the dynamic pressures subside considerably within the 7D sphere. For the reference plant, the quantity of insulation contained between 3D and 7D is 191 ft 8. Using a destruction factor of 0.5, the quantity of fines can be estimated as 95.5 ft . , The total quantity of fines generated would be 130 ft8 . This value is about the same order of magnitude as that recommended by the BWROG. The latter number still has the following conservatisms: e It does not take into consideration the orientation of the seam with respect to the jet direction." e it does not give credit for less than 50% damage observed at lower impingement pressures. Based on this analysis, it is concluded that destruction factor recommended by the BWROG would result in reasonable estimates for the fines.

 "    Discussions with the in'sulation vendors and contractors suggest that no particular arrangement is followed to ahgn the seams in a particular onentation. They are randomly arranged with respect any postulated break.

I G-5

1 100 ~ 1 Y l e 80

                                                       -"'-9...

g BWROG Fit 60 -

                                                                                                 \
                                                     ~

e

~ /. in all cases encapsulations were blown of

                                                                                                    }

40 - i f immediately. Debris from jet on Nukon

                                                                                                     \              \
                                                                                                      \ ,../'                                                                                                No Jacket; 9 0" Clock 9      CC ineket; 9 0 Clock 20 7                                                                                                                                                           y noa,cg,,;3 o."cioeg
                                                  .                                                                                                                                                  $ Sure-Hold; 9 O" Clock 0

0 20 40 60 80 100 120 Target Length to Diameter Ratio (UD) Figure G.I. Dependence of q on L/D Observed in AJIT [Ref. G.6]

                  ;V, ::
                                               ..                      n.
                                             '? '..
                                                                                                                                                 ~
                                                                      ,',../ .

1

                  ,i s                                       . ' . - . . -                                    s
                  .: -                                                            z.                             .                                                                                 .,-
                                                                                                                                                                                                 -                                                              1
                                                                                                                                                                                        ,- .       7,
                                                                                                                                                                                     '~ ' : ',

s'; ',:', I

                  +;' ', .    ,
                                                                   ,l Q l'                                                  . ,.l:,j'; b '., , j, l , : ;;,; 3 '%

5 a _ 160 h

                                                                               ,E                            (                          ,.                                                     ANSI /ANS-58.2 Based 10           h                                                                                              Axial Distance
                                                                               $ 3,                             :                                                                                              - UD=3 5 6;'
                                                                              ~~                     80 1_                                                                                                     + UD=5 nm                               -

9 UD=7 o"

                                                                              "E                                                                                                                               - T- UD=10 40 1                                                                                                      - Ar- UD=20 r __ ,

0 ''''* N ' ^

                                                                                                                                                                                                                                        ^

0 1 2 3 4 5 6 Normalized Radial Distance (R/D) Figure G.2. Radial Distribution of the Staunation Pressure in the jet. The Actual Pressure Pronle Could be Different from the I.inear ProGle Assumed in the ANSI /ANS-M.2.\lodel.

1 i 100 \ - 80 -

     $ 60      -            -
                                        .'5%;\g a

g , e Percentage of Blanket into Fines e -

s. Percentage of Blanket in the Jet Area into Fines o e.

G .~

    ' 40 _
                                                         "~:-
                                     ,/                                     ....
             .                    5                                                    "~ -
                                                                                                   . - . . . . . . o 20 --                     -l-                   -

1.

                           /e               .e 0 ._ "               '                   '      '             '             '    '           

O 10 20 30 40 50 60 70 80 Jet Average Pressure (psi) Figure G.3. Percentage of Blanket and Blanket in the Jet Area Destroyed into Fines as a Function of Jet Pressure. Analysis of AJIT Data [Ref. G.6]. s

i 1 i V Appendix H Calculations to Examine the Accuracy of URG Drywell Debris Transport Factors  !

References:

i H.1 URG, Page 75. I H.2 CDI Report No 96-05, " Testing of Debris Transport through DowncomersNents into the Wetwell," URG Technical Support Documentation, Volume 11, Tab 2, November,1996. H.3 SEA 96-3105-010-A:2, "Drywell Debris Transport Study, Phase l Draft Letter Report," Science and Engineering Associates, Inc., September 27,1996. HA Letter from C.H. Berlinger to T.A. Green, "Second Transmittal of NUREG/CR-6369, 'Drywell Debris Transport Study'," dated April 8,1998. Problem Definition: The URG guidance assumes that only 50% of the fines would be transported to the suppression pool for a Mark 11 containment during steam blowdown. In addition, the URG provides transport fractions for Mark I and Mark lli containments. The

   - transport factors for Mark l's and ll's were founded on the results of small-scale tests of downcomer/ vent geometries. The Mark lil factors were predicated on the more limiting conclusions drawn for Mark l containments. The staff performed the following analyses and experiments to evaluate the URG guidance:

e The staff sponsored four tests simulating steam flow in the lower region of the drywell of a Mark II. The tests simulated Mark ll geometry where steam flow would enter the downcomers. o Calculations were performed to estimate the steam velocities in the BWROG-sponsored testing documented in Reference H.2. e The staff conducted a detailed drywell debris transport study (DDTS), which included testing and analysis to determine the key factors that affect debris transport from the drywell to the wetwell. The staff's findings are summarized in the following paragraphs: . Confirmatory Experiments: The NRC sponsored experiments, both separate effects tests

   - and integrated tests, to examine the impact of vent / floor arrangement on the transport of debris. In both cases, the vents were designed to simulate Mark ll containment flows as close as possible, both at the vent entrance as well as at distances sufficiently farther from the entrance. (CFD and MELCOR results were used to design the vent geometry.) Tunnel approach velocities were close to 25 ft/s (7.8 m/s) and vent velocities close to 150 ft/s (46.6 m/m). These tests (Reference HA) yielded the following results:                                    )

e . The total insulation captured as a percentage of insulation arriving at the vent is 8-13% I for classes 2-6.' Classes 2 and 6 are markedly larger than the insulation shreds used in H-1 l l l l

I the BWROG tests. In that sense, these values are expected to be larger than what would be anticipated for smaller debris. I The capture percentage increases to 35% for classes 6+. Note that 6+ debris are l typically larger than clearances in the gratings. For such debris, gratings are found to have a more significant impact on limiting debris transport. Large debris were deposited i on the back wall equivalent to Mark 11 floor, On the basis of these results, the staff concludes that an inadequate basis exists for the 50% credit for Mark 11 containments recommended by BWROG in the URG. Scaling Uncertainties Associated with BWROG Testing: In the BWROG-sponsored steam tests conducted by CDI (Reference H.2), the blowdown was typically 2.45 seconds from a 0.25" orifice. Flows scaled according to the vent /downcomer flows are equivalent to those from a 17 inch diameter pipe break. In addition, the same flows scaled from the barrel diameter of the test facility to full scale are equivalent to a 12-14 inch pipe break LOCA. Thus, the velocities used are 50-60% lower than the velocities anticipated in the containment following a main steamline or recirculation line break LOCA. As calculated in Reference H.3, debris settling velocities are strong functions of the fluid velocity. No scaling rationale was provided in Reference H.2 as to how such a set of experiments can be extrapolated to BWR containments. Comparison with the Guidance Provided in the URG: The major finding of the BWROG experimental program was that Mark ll vents can retain up to 50% of the debris during both main steamline and recirculation line breaks. The NRC sponosored specific experiments to evaluate this as part of the DDTS. These experiments were conducted at con 6tions deemed to be typical of an MSLB. The data from the NRC-sponsored testing conducted in support of the DDTS study suggest that wet vent entrances do capture small debris. However, capture fractions are no more than 15% for small pieces, with the majority of that debris deposited on the floor. This value is much lower than the 50% proposed by the BWROG. Furthermore, it is likely that the ECCS flow from the break (in the case of a recirculation line break) would likely resuspend the majority of this debris and transport it to the vents. On the basis of these results, the staff concludes that the URG guidance is nonconservative for a MARK 11 containments. For other containments, the URG guidance on page 75 of the URG is consistent with the upper-bound estimates of the DDTS, and consistently higher than the study's center estimate. While applying the URG suggested transport factors, licensees should take care to ensure that the underlying assumptions are consistent with the particular plant being analyzed. In particular, the following considerations should be addressed:

• All testing done by NRC and BWROG employed 4-in x 1-in x %-in floor gratings. All of the results (e.g., capture efficiencies) were derived assuming that the grating occupies 100% of the cross-section with no chance for debris to bypass them. By contrast, if the utility identifies large discontinuities or gaps in gratings that would allow a fraction of the debris to pass through, the utility may wish to revise the transport factors accordingly.

H-2

f e implicitly, both studies assumed that unthrottled ECCS conditions exist for a maximum of 3 hours following a recirculation line break, if unthrottled ECCS operation is expected ' for more than 3 hours, the licensee may wish to revise the washdown fractions accordingly. NRC sponsored test results in Reference H.4 could be used to scale the l washdown factor up.

Conclusions:

The staff concludes that the BWROG provided transport fractions for Mark 11 containments (on page 75 of the URG) are not adequately supported. Mark 11 containments should use fractions similar to Mark I containments. However, the fractions provided for Mark I and ill containments for the transport of fines are acceptable.  : I s I 1 r i H-3 l

1 l l Appendix 1 Analyses to Examine the Accuracy and Applicability of ECCS Strainer Head Loss

References:

1.1 CDI Report No. 95-09, " Testing of Alternate Strainers with Insulation Fiber and Other Debris," URG Technical Support Documentation, Volume I, Tab 2. l.2 NUREG/CR-6370, " BLOCKAGE User's Manual," December 1996. l.3 NUREG/CR-6224, " Parametric Study of the Potential for BWR ECCS Cmer Blockage Due to LOCA Generated Debris," October 1995. Problem Definition: As part of the URG Technical Documentation, the BWROG provided the results of its head loss testing program conducted by the Electric Power Research Institute (EPRI) at the EPRI Non Destructive Examination (NDE) test facility in Charlotte, NC, as well as descriptions of the various cookbook approaches that can be used to estimate head loss induced by alternate and truncated cone strainers. This analysis was conducted to verify the adet,Jacy of the proposed head toss estimation approaches. Results of the Review: The staff has reviewed, and performed computations, to determine if the URG-proposed approach provides reasonable estimates of strainer head loss. Specifically, the staff applied the URG models to simulate the experimental data for a l number of the tests for which data were included in the report. Time-dependent behavior was simulated by incorporating the URG models into a modified version of BLOCKAGE 2.5. The debris bed head losses predicted by the URG models for selected test runs were compared to the experimental values in Tables C-1 and C-2 (Reference 1.1) for fiber / particulate and RMI beds, respectively. Test runs were selected that indicated the head losses were approaching a steady-state value. The staff notes that one important criticism of the URG tests is that reasonable steady-state conditions were not achieved in a significant number of the test runs. This is important because the amount of debris on the strainer was deduced by taking the known quantities of debris introduced into the water tank and assuming that essentially all of the debris was deposited onto the strainer when steady-state head loss was achieved. Therefore, the debris bed composition was relatively unknown during transient conditions. It is believed that pool turbulence was sufficiently high to prevent debris from settling to the bottom of the tank. The results of four time-dependent simulations (for Tests PS, J28R,4, and J6, respectively) are shown in Figures 1 through 4 of this appendix. These results lead to the following conclusions. Stacked-Disk (PCI) Prototype No. 2 Strainer: Fiber / particulate simulations were performed for Tests P3, PS, and P8 for a range of flow rates, as shown in Table C-1 of Reference 1.1. The URG model appears to yield reasonable or conservative predictions of strainer debris bed head loss for the ranges of conditions tested, as follows: e fiber loadings range to 50 lbs. e corrosion products to fiber mass ratios to 10 e approach velocities to 0.5 fps (on the basis of the circumscribed area) 1-1

e no miscellaneous debris Note that head loss will be over predicted when the strainer surface area is not completely covered (as was obviously the case in Test P4), and miscellaneous debris was not considered in testing this type of strainer. There was insufficient data (see Table 6-5, URG Technical Support Documentation, Volume 1) to determine with certainty that the strainer area was completely covered for the simulated test runs; however, it is likely that the coverage was complete, or nearly complete, since the average fiber debris bed thickness across the entire strainer area was 0.74,1.5, and 0.30 inches for Tests P3, P5, and P8, respectively. The time-dependent debris head loss for Test P5 predicted by the URG modelis shown in . Figure 1 compared to the head loss predicted by the NUREG/CR-6224 correlation and to the experimental test data. The strainer flow rate in the test was nominally 5000 GPM; however, it was varied from 2500 to 10000 GPM starting at about 70 minutes (see test data on Page C-102 of URG Technical Support Documentation, Volume I, Tab 2). The URG model did a good job of predicting the test. It over predicted early in time because of incomplete coverage of the strainer. Apparently, debris on the strainer shifted as a result of varying the flow rate because the head loss associated with 5000 GPM was less after the 5000 GPM flow was resumed than before the flow rate was varied. The shifting of debris by varying the flow rate was, of course, not predicted by the models. The NUREG/CR-6224 correlation did not perform well when attempting to predict Test PS, as its predicted head loss at 5000 GPM was only about a third of the experimental head loss. Its poor performance is attributed to the fact that it was developed for a strainer with a uniform debris bed thickness and a uniform approach velocity, as would be expected for the truncated cone strainers. For stacked-disk and star strainers, the debris is apparently driven preferentially into their crevices resulting in distinctly non-uniform debris distributions and approach velocities. The NUREG/CR-6224 correlation may either require modification or the development of appropriate input guidance for it to be reliably applied to these non-uniform strainers. Apparently, the only stacked-disk strainer design tested with RMI debris was the stacked-disk portion of the self-cleaning strainer (SCS-SDP). One of these tests, Test A1, was simulated over a range of strainer flow rates as shown in Table C-1 of Reference 1.1. In all simulations performed for this strainer, the URG models conservatively over predicted the debris bed head losses by more than 100%. Stacked-Disk (PCI) Prototype No.1 Strainer: Fiber / particulate simulations were performed for Tests 20 and 22 at three flow rates, as shown in Table C-1 (Reference 1.1). These results are similar to those for stacked-disk number 2; however, there was less test data to examine as reflected in the URG plot for non-dimensional head loss for the first prototype (see Figure 6-8, Page 70, Reference 1.1). This curve was drawn with very limited data resulting in a straight line fit, which does not seem likely to be the case. 60-Point Star Strainer: The URG model generally under predicted the 60-point star strainer by 20 to 30%, as shown in Table 1, whenever the strainer surface area was 1-2

completely covered. (Coverage was determined by comparing the calculated nondimensional thickness associated with each debris loading with the required minimum  ; nondimensional thickness reported.) The URG model over predicted two tests, J22 and J23, because the strainers were not completely covered. The ranges of conditions tested include: e fiber loadings range to 25 lbs. e sludge-to-fiber debris mass ratios up to 25 e approach velocities to 0.5 fps (based on the circumscribed area) e either zero or " full recipe" (see Reference 1.1) miscellaneous debris Note that miscellaneous debris increases the experimental head losses for tests J28R and J23 by 24% and 116%, respectively and the URG model bump-up factors appeared to compensate appropriately. Figure 2 of this appendix shows the time-dependent debris head loas for test J28R predicted by the URG model versus the head loss predicted by the NUREG/CR-6224 correlation, and the experimental test data. The strainer flow rate in the test was nominally 5000 GPM; however, it was varied from 2500 to 5000 GPM starting around the 40-minute point in the test. (See test data on Page C-188 of Reference 1.1.) The URG model under predicted the test by 20 to 25% throughout the test. The NUREG/CR-6224 correlation did not perform well when attempting to predict test J28R, as its predicted head loss at 5000 GPM was only about 15% of the experimental head loss. Again, the NUREG/CR-6224 correlation's poor performance must be attributed to the fact that it was developed for a j strainer with a uniform debris bed thickness and a uniform approach velocity, which is  ; clearly not the case with this strainer design. 1 l The URG model could be used to predict fiber / particulate debris bed strainer head losses j for the 60-point star strainer if a reasonable safety factor is applied to compensate for the l relatively uniform underpredictions shown herein, and provided that the conditions of the l calculations are within the ranges of conditions listed above. l The 60-point star strainer was tested with RMI debris and one of these tests, J20, was simulated with the URG model for a range of flow rates shown in Table C-1 (Reference 1.1). ) In all of these simulations, the URG models over predicted the debris bed head losses by 15 to 40%. , 20-Point Star Strainer: Fewer test runs were simulated for the 20-point star strainer than for the 60-point star strainer, and all of the simulations except one over predicted the experimental head loss. Test run 11, which had fiber debris but no particulate, was under predicted by 47%. Two of the over predictions resulted from incomplete coverage on the strainer. The test run involving Kaowool rather than NUKON' was extremely over predicted by a factor of 259 which appears to be related to the fMeness of its fibers (~2.5 microns in diameter) relative to the NUKON' fibers (~7.1 microns) for which the model was developed. In fact, all of the test runs checked involving Kaowool were way over predicted (i.e., by factors of 46,259, and 14 for test runs J12,35, and J30, respectively). It is likely that the 1-3 i

validity of the URG model as applied to the 20-Point Star strainer is similar to its validity as applied the 60-Point Star strainer; however, the uncertainty is higher. Truncated Cone Strainer: The URG model is less reliable for simulating test runs using the truncated cone strainer design, which tend toward lower-fiber loadings with higher particulate-to-fiber mass ratios. Three of the simulated runs (6,7. J6) had incomplete coverage of the strainer, and two of the runs (6, J6) had mass ratios larger than the upper limit of 120 for which the model was developed (see Figure 6-6, Page 68, Reference 1.1). Using the URG model beyond this upper limit of 120 is non-conservative because the head loss beyond this limit increases by some unknown amount. The primary reason that the URG model over predicted Run J6 was an excessively large and unrealistic bump-up Factor of 4.2. The bump-up factor accounts for the head loss contribution of the miscellaneous debris where the head loss without miscellaneous debris is multiplied by the bump-up factor to get the total head loss. The reason the bump-up factor is so large is the URG assumption that the fiber-to-particulate mass ratio used in calculating the bump-up factor must be limited to 4, whereas the actual mass ratio for this test was 360. This means that the misce llaneous debris contribution over powers the equation. This assumption was designed to guarantee that the head loss predictions would be conservative, but under certain conditions, it can render the URG model unusable. The time-dependent head loss for Run 4 was predicted using both the URG model and the NUPEG/CR-6224 correlation as shown in Figure 3 of this appendix. In this situation, the NUREGICR-6224 correlation does an excellent job, whereas the URG model over predicts the head loss by about 40% It was not surprising that the NUREG/CR-6224 correlation performed well for this test run because the correlation was specifically developed for the truncated cone strainer. Note that in Run 4, the strainer was completely covered with fiber debris and there was no particulate debris. Another test, Run J6, was also simulated but with distinctly different results. In the J6 simulation, the NUREG/CR-6224 (Standard Simulation) grossly over predicted the head loss, as shown in Figure 4 of this appendix, whereas the URG model simply over predicted the head loss by a factor of about 2. The reason that the NUREG/CR-6244 correlation performed so poorly was that BLOCKAGE predicted that most of the particulate debris was on the strainer, when in reality, it most certainly was not. A second simulation (realistic simulation) where only about 5% of the particulate debris was allowed to accumulate on the strainer shows a much better agreement with the experiment. If all of the 180 lbs. of corrosion products were deposited onto this 18-ft2 strainer, the entire surface area would have been covered with sludge to a depth of 1.8 inches, whereas the thickness of fiber debris (uncompressed) was only 0.15 inches; that is, it is highly unlikely that this thin layer of fibers could hold that much sludge in place and, if it did, the head loss would have been l excessive as predicted by the NUREG/CR-6224 correlation (standard). The conclusion l must be that the fiber bed became saturated with particulate debris, thereafter as much particulate passed through the fiber as was deposited onto the fibers. The NUREG/CR-6224 " realistic simulation" is considered the correct simulation of the experiment. Therefore, it must be further concluded that in at least one of the URG experiments, the I-4 l

1 assumption that nearly all of the debris added to the system will be located on the strainer when the head loss approaches steady state is in error. Using the URG model to simulate the truncated cone strainer given the test conditions for which the URG model was developed has been shown to be unreliable.

== Conclusions:== When used in the cookbook approach outlined in Appendices A and B of Reference 1.1, the URG model is generally unreliable and incomplete for the following reasons: e The URG model was developed for limited ranges of data (i.e., fiber and particulate debris loadings, velocities, and strainer design). Using the model beyond these limitations is especially risky because the models are non-mechanistic in nature. e in many cases, the URG model has been shown to under predict the experimental data used to develop the model; therefore, each head loss prediction should be reviewed in detail relative to the applicable data to ensure a valid prediction, in many situations, such as the 60-Point Star strainer, a significant safety factor should be factored into the prediction.

• The bump-up factor used to account for the miscellaneous debris was developed with limited data (gravity head loss tests). In many situations, the bump-up factor has been shown to severely over predict the head loss. While this over prediction is conservative, it can render the use of the model impractical, especially with plants having low NPSH margins.

e Some of the test runs (e.g., J6) simply overpowered a thin layer of fibers with massive amounts of particulate debris so that the strainer debris apparently become saturated with particulate. Thus, the actual particulate debris loading on the strainer which was used to develop the model was not known. Instead, the total system inventory was assumed to be deposited onto the strainer when it likely was not.

• Debris such as duct tape, tie wraps, and plastic tags included in the recipe of miscellaneous debris was not included in the modeling effort. It is possible that this debris had only a minor impact on the overall head loss, but the report did not discuss ,

this issue or what quantities of these debris types would be needed to significantly affect I head loss. i l e Extending the URG model to other types of debris, such as Kaowool rather than NUKON', could be risky because the URG model was essentially developed for the NUKON* fibers. This review showed that the URG model tended to seriously over predict the head loss associated with test runs using the Kaowool. First of all, the over prediction may render the URG model unusable for predicting head loss associated with Kaowool. Secondly, the URG model could seriously under predict the head loss for some other type of fiber (i.e., in the opposite direction from the Kaowool). This could be the case for a fiber wi+h thicker strands than NUKON' l-5

e The same NUKON' debris properties should be used as were employed in developing the URG model(i.e., densities and diameters). The fiber density of 2.4 lbm/ft' used in the URG study is the number generally assumed for the intact fiber insulation (sometimes referred to as the as-fabricated density), but there are data showing that the-density of actual debris is considerably reduced by the destruction process. For example, fibrous debris used in the PP&L-sponsored tests conducted at ARL had an , actual density of 1.3 lbm/ft'. Employing this density rather than the as-fabricated l density, the user would obtain a different fiber spacing distance, which would result in a different head loss than if the user actually used the as-fabricated density that is inherent in the non-mechanistic URG model. e All of the test runs were conducted using a mass of corrosion products with the same representative size distribution (i.e.,83,11, and 6% for size ranges represented by 2.5, 7.5, and 42.5 microns, respectively), and the URG model has not been validated for alternative size distributions. For example, one plant (designated as Plant J in URG Volume Ill) found that 27% of its particles were in the 10-75 micron range compared to the 6% of the representative study. It is likely that had the size distribution of Plant J been used in Run J6 rather than the representative distribution, the head loss would have been greater simply because fewer of the particles would have passed through the fiber bed than was apparent from the simulations performed for this review. In addition, the NUREG/CR-6224 head loss correlation has shown that the head loss is a function of the particulate-specific surface area, which is in turn a function of the particle diameters. e Two types of RMI debris were used in the URG strainer debris bed head loss tests. Specifically, these include two different size distributions of the 2.5-mil stainless steel foils, and each size distribution was used over a different period of time. Thus, the tests for a specific strainer design are generally valid for only one type and size distribution of RMI debris. For example, the stacked-disk tests (stacked-disk section of the self-cleaning strainer) only used the RMI debris obtained from Diamond Power since all of these tests were conducted in August 1995. Therefore, the URG model, as it applies to the stacked-disk strainer, was developed only for this one type and size distribution of RMI debris. Furthermore, it must be assumed that the self-cleaning strainer is representative of stacked-disk strainers in general, since sufficient dimensions were not provided to determine if the size of the disks were the same as the two PCI prototypes (i.e., the spacing between the disks could well impact RMI debris loading). e The URG model was developed from test data where a true steady-state condition was not generally achieved, implying the debris loadings used in the model development were somewhat different than the actual loadings on the strainers. e The URG report did not provide model validation, parameter sensitivity, or uncertainty analysis leaving open the question of whether or not a particular combination of input parameters could cause the URG model to seriously under predict head loss. In conclusion, the URG model must be used with care, not blindly plugging numbers into a cookbook step-by-step procedure as outlined in the report. Rather, each head loss prediction must be anchored into head loss data to ensure that it is reasonable and I-6

_. . . .= .-. . ~ _ _ . ._ - . . . . . . . . _ - . - . _ . ~ . - - ~ _ = - - - - . ....... _ l conservative. For all of the reasons cited above, the staff recommends that vendor-specific i test data be used to demonstrate the head loss assumed in a licensee's NPSH calculations. l l 1 l n b i 1 1 1 l I l I' l t i e

'f 5

t l-7 4 2-

16 , , , , , , , , , , i i Experimental 14 - URG Model - NJREG/CR-6224

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                                                                                                     *a E          PCI-2 Strainer

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  -     10  -
                                                                                                  -M                           -

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s O ' ' ' ' ' ' ' O 1 2 3 4 5 6 Time (103sec) Figure 1: Debris Bed Head Loss for Run PS

20 , , , , , , . . . Exporimentof -- 18 - URG Model NJREG/CR-6224 m 16 - u 5y 14 - 60 Point Star Strainer ' ',,.'..,(  ;  ; f'1 _.l_- 25 lbs. NUKON ,

                                                                                                                                                                                                    ,. '                   i.                    i 12                               -        100 lbs. Par-Ic ulat e                                                                                                  ,-                              !                    !      ;

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40  ; , , , , , , i i Expe-imental i s 35 - NJREG/CR-6224 ,e 1

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400 , , , , , , , , > i * ' ' i > Experimen tal 350 - URG Model / - NUREG-Recdis tic / m NUREG-S tandard / t 300 -

 %                                                                                                             f y            Trurcated Cano
               .5 lbs. NUKON                                                                               7 v

C 250 - 18 0 Lhs. Particulate  ! _ E

s 25% Recipe /

M 200 - E f - u_ l 3 150 - 7 - 5 .5 / r 100 - O

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                                    /
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0 ' ' t - ' ' ' = = ' ' ' ' ' O.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4 0 Time (103sec) Figure 4: Debris Bed Head Loss for Run J6

Appendix J Calculations to Examine the Accuracy of URG Sludge Generation Factors

References:

J.1 URG, Section 3.2.4.3. J.2 BWROG Letter OG94-661-161, "BWR Owner's Group ECCS Suction Strainer Committee Suppression Pool Sludge Particle Size Distribution," URG Technical Support Documentation, Volume lil, Tab 2, September 13,1994. J.3 Attachment 2 to BWROG Letter OG96-321-161, " Suppression Pool Sludge Particle Distribution Data - Average Distribution Calculation," URG Technical Support Documentation, Volume Ill, Tab 3. J.4 BWROG Letter OG95-388-161, Attachment 4, "BWR Owners Group Suppression Pool Sludge Generation Rate Data," URG Technical Support Documentation, Volume Ill, Tab 4. Problem Definition: In the URG, the BWROG provided guidance regarding the quantity of suppression pool corrosion products (sludge) that should be used in utility analysis of strainer blockage. A value of 300 lbm/ year was recommended as the sludge generation rate, in lieu of establishing plant-specific sludge generation rates. The basis for the generation rate and characterization were provided in References J.2 and J.3, which the staff evaluated to determine the adequacy of the basis for the BWROG's conclusion. Results and Discussions: The BWROG's survey information is provided in Figure J.1 of this appendix, which shows that in all of the plants but one (Mark I, ll and lil), generation rates are far less than 200 lbm/yr. From the NUREG/CR-6224 study, the staff is aware that the reference plant estimates were very conservative and were derived on the basis of wet sludge mass (not the dried sludge). Based on this, the staff concludes that the BWROG-recommended value of 300 lbm/ year is reasonable and sufficiently conservative. Also, the URG provides comprehensive guidance for those utilities that do not wish to use the value j of 300 lbm/yr. l 1 J-1 l

1400 'Very Conservative Mass of S!udge in The Bounding Pool at Time of Survey 1200 - i > Sludge Generation Rate 1000

                                                                                                        - Sludge Mass of 450 lbm 800 -                                                                                                     is used in the Base Case 600 +

e + +- e +

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        ~s-s           =. =<

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                                                      .! ;E .! ~!              7 s+ !,s si 11 if is E:

e  ; == 3; er .); ilas;11 si 4~E 12s 4 2 er 2  ;; i: .:: i: ce c: -; et cr 5- 5-  ?! (1 2- i- jE I: I it !! 11 lt it 3 3

                                                                                         ;           5     :-        ;

Figure J.1. Sludge inventory and Sludge Generation Rate for Selected Plants l l l l i i

l I l Appendix K Analyses to Examine the Accuracy of URG Guidance for Primarily RMI Plants l

Reference:

K.1 URG K.2 CDI Report No. 95-06, " Air Jet impact Testing of Fibrous and Reflective Metallic Insulation," URG Technical Support Documentation Volume ll, Tab 3,. l K.3 CDI Report No. 95-09, " Testing of Alternate Strainers with Insulation and Fiber  ! Debris," URG Technical Support Documentation Volume I, Tab #2,. K.4 Letter from C.H. Berlinger to T.A. Green, "Second Transmittal of NUREG/CR-6369, I

           'Drywell Debris Transport Study'," dated April 8,1998.

K.5 ARL Report entitled, " Head Loss of Reflective Metallic Insulation Debris With and { Without Fibrous insulation Debris and Sludge for BWR Suction Strainers," April ' 19%. Problem Definition: In the URG, the BWROG also provided guidance for use by plants l primarily having RMI insulation. This guidance included methods developed by the BWROG to estimate:

• The quantity of RMI debris generated by a postulated LOCA (i.e., destruction factots).

e The fraction of that debris that would be transported to the suppression pool (i.e., drywell transport factors). e The total quantity of RMI debris that could accumulate on the strainers, o The resulting head loss. Various analyses were conducted, as documented in this appendix, to evaluate whether the BWROG guidance represents a adequate basis for strainer design. This appendix summarizes the important findings of the review effort. Finally, the last section of this report provides a brief discussion of insights gained from the LaSalle RMI test report, provided to staff for review in l June 1998. Guidance on the Zone of influence: As indicated previously in this SER, the staff has l concluded that URG methods 1,2 and 3 (Pages 37 through 42, Reference K.1) are  ; I acceptable for calculating the debris generation ZOI from a pipe break. The staff believes that these methods would provide conservative estimates for the ZOI, and hence, the quantity of debris generated. However, some plants may not use ZOI calculations; instead , focusing on estimating head loss on the basis of determining a " saturation thickness" of RMI l debris that could get on the strainer surface. This " saturation thickness" is essentially the maximum amount of RMI debris that could physically accumulate on the strainer before the approach velocity would be too small to entrain more debris on the strainer surface. l Guidance on the Drywell Debris Transport Factors: The URG used experimental data to suggest that no more than 50% of the RMI contained in the ZOI gets destroyed into pieces that can be categoriz'ed as transportable. Therefore, the maximum volume of debris that K-1 l I l

can be transported to suppression pool is 50% of the total RMI contained in the ZOI. A

 - close review of BWROG AJIT test data indicates that use of 50% would result in a conservative estimate for the quantity of transportable RMI debris.

The BWROG relied on experimental data from CDI small-scale transport tests to derive the following drywell transport factors (Reference K.2): I Table K-1 Factors for combined generation and transport of RMI. Containment Type M5LB Recirc. Break Mark l 0.5 0.5 Mark ll 0.05 0.03 , Mark lil 0.5 0.5 For Mark I and ill containments, the URG concludes that nearly all of the transportable RMI i debris would be transported to the suppression pool. 'In the case of Mark II, the URG concludes , that the downceiner arrangement would " capture" nearly 90% of the debris approaching them.  !

                                                                                                                            +

On this basis, the BWROG recommended a drywell transport factor of 0.05 for an MSLB, and 0.03 for a recirculation line break. It is the staff's opinion that the BWROG recommended drywell transport factors for Mark 11 containment are non-conservative, because: e: The CD1 experiments were not properly scaled. In the CDI facility, steam breaks were simulated using blowdown from a 0.25-in (0.64-cm) orifice that typically lasted for 2.45 seconds. The intent of the CDI tests is to achieve the flow velocities at the entrance of the downcomer that are fairly representative of a real scale BWR Due to experimental  ; limitations, the actual flow velocities at the downcomer entrance are approximately less than . half the flow velocity following a postulated DEGB. In the bulk of the barrel, where the majority of the debris settling was observed, the flow velocity is less than a quarter of the flow velocity expected in a real Mark 11 containment following a DEGB. Thus, the flow -i velocities simulated in the tests are extremely low compared to the real case. Therefore, ' debris settling noted in the CDI tests may not be representative of reality. In the staff's opinion, the results are most likely non conservative, e The RMI debris used are stainless steel foils. All the tests were conducted using stainless steel RMI foils that are 0.0025 inch" in thickness (Diamond Power Mirror

• insulation). The staff believes that direct application of these data to lighter debris such as aluminum RMI would likely result in non-conservative transport factors.

o ' Qualitatively, ARL's experimental data do not support low transport factors for Mark II. At  : ARL [Ref. K.4), a facility was built which more closely simulated flow velocities throughout the test section (in the barrel, at the entrance and in the down comer). This facility was used to measure transportability of various size fibrous shreds. For fibrous debris. this facility has shown that Mark 11 downcomers do not pt==ans any special characteristics that would result in high capture fractions. Although no tests were carried out to study capture of RMI pieces  ; r 13 The actual thickness may be substantially different from the nominal thickness of 2.5 mil. K-2 .

by the Mark ll downcomer, selected fiber tests can provide some insights. In those fiber  ; tests, very little capture was observed for small and medium fibrous debris that possessed - weight and gravitational settling velocities close to those of aluminum'5 Similarly, the capture efficiency was less than 40% for larger debris that are rnore representative of l stainless steel debris, ' Given these findings, the staff believes that the URG transport factors for RMI debris are non- l i conservative for Mark ll containments. (Note that a similar conclusion was reached for fibrous debris.) Individual plants that do not intend address RMI issues using the saturation thickness

         . approach should use same transport factors for Mark ll as for Mark I and Mark lli, unless the utility has datalevidenu that support the use of another factor.

Guidance on Pure RMI Head Loss: Appendix B of Reference K.3 provides guidance for determining head loss due to accumulation of RMI debris on the strainer surface. This guidance directs the analyst to take the following steps: e Estimate the maximum thickness of the debris layer on the strainer surface.

• Establish the relationship between the debris layer thickness and the foil surface area.
• Determine the head loss resulting from the accumulation of the maximum RMI layer on the strainer surface.

               - Capacity to retain RM/: RMI pieces approaching the strainer surface would become                                                   i attached to the strainer surface only if the drag on the debris due to flow is larger than the sum of gravitational forces and the turbulence drag. Otherwise, the RMI peces would be dislodged from the strainer and will not considerably contribute toward head loss. As shown in Table K-2 below, the BWROG experiments have shown that 0.0025-                                             ;

inch thick stainless steel RMI debris are no longer retained on the strainer surface when the local approach velocity based on circumscribed area is less than or equal to 0.2 ft/s. Table K-2 BWROG Experimental Data Establishing Point Where RMI No Longer Attaches to Strainer Surfaces

            . Geometry / Test ID                       Flow (GPM)                                     Flow Area                Velocity (ft/s)

Truncated Cone /T7 1600 18 ft2 l 0.2 ft/s and T8 i  !

            ~60 point star /A4                                1250                           14.52 (22 x 0.66) ft2 ' '            O.2 ft/s The value of 0.2 ft/s shown in the table above is approximately equal to half the gravitational settling velocity for 2.5-mil stainless steel RMI pieces (see Table 6-7 of Reference K.3). On this
         ~ basis, the BWROG hypothesizes that RMI debris do not attach to the strainer surface if the local flow velocity is less than half the settling velocity of the RMI debris. In the URG, the BWftOG suggests settling velocities listed in Table 6-7 be used in conjunction with Equation 6-9 to i'

Because capture is driven by the weight of the debris and the flow velocity. The measured settling velocity of small and medium debris in still water is close to 0.15-0.20 ft/s (see Reference K.4) as compared to the settling velocity of 1.5 mil-thick aluminum debris which is 0.25 ft/s (see Table B-1 of Reference K.3). The measured settling velocity of class 6+ size fibrous debris is approximately 0.37 ft/s which is comparable to the measured

               - settling velocity of 0.4 ft/s for 0.0025-inch stainless steel foil debns.

K-3

v

    ' estimate the. maximum thickness of the RMI layer. Equation 6-9 is produced here for                                              ,

convenience:

                                                                                                                                       ~

ts = (DU4)" [(2U/U,)"- 1) (K.1)

          - Where, D L = L the outer diameter of the strainer L . = .the length of the strainer U= the approach velocity.on based on the circumscribed area of the strainer U, - = the settling velocity of the RMI being analy::ed The experimental evidence as well as theoretical reasoning would clearly lead to the conclusion
    ' that RMI debris buildup would reach a " saturation point" or a maximum, beyond which local flow velocaties would not induce sufficient drag to overcome forces imposed primarily by turbulence and secondarily by gravity. Whether or not the hypothesis that was being advanced by -

BWROG (specifically, Uw $ U/2) to describe this equilibrium is accurate by itself is debatable. For example, one could argue that maximum thickness would be strongly dependent on both

     - the residual turbulence and the shape and size of the debris, not just the shape and size of the debris as assumed by the BWROG. However, the staff has accepted the BWROG hypothesis.

The rationale for staff acceptance is two-fold: , l e it was staffs belief that turbulence levels in the EPRI tank are equal to or less than those f expected in the BWR suppression pool during the high and intermediate energy phases of l- , ! pool dynamics. Typically, high and intermediate energy phases only last few minutes ' following a large break LOCA. After that point, low energy recirculating water flow pattems ' exist in the suppression flow. Such flow conditions would allow for RMI debris fragments to ' settle down quickly (within 2 minutes for 2.5-mil SS RMI as demonstrated by ARL testing). On the other hand, the BWROG saturation thickness hypothesis is implicitly based on the assumption that higher energy turbulence would be present to enable debris accumulation l until saturation conditions are reached Thus, the saturation thickness hypothesis is l considered to be conservative. e . To confirm this conclusion, the' staff conducted a senes of calculations aimed to determine maximum credible RMI debris loads on suction strainers following a LOCA. These calculations employed the BLOCKAGE computer code and applied ARL test data i. l conservatively. For a generic BWR suppression pool, the BLOCKAGE analyses led to the l conclusion that debris loads estimated using BWROG hypothesis were always larger than ' maximum credible loads expected on the strainer following a large break LOCA. l The conclusions presented above were based on assumptions that are supported by NRC/ARL

      . experimental data. Although NRC/ARL data were obtained for 2.5-mil SS RMI, theoretical analyses were used to extrapolate the data to 1.5-mil aluminum RMI and 6-mil aluminum RMl".

L Furthermore, the BLOCKAGE analyses assume a generic BWR suppression pool response as described in NUREG/CR-6224, Appendix-B.

        " Table 1 of Appendix-D tg Reference K.2 suggests that US BWRs primarily employ three types of RMI on piping and

) components: 2.5-mil SS,6-mil Al and 1.5-mil A1. ! K-4 L i

. Individual utilities that plan to use the saturation thickness approach should ensure that the assumptions made by the BWROG in deriving Equation 6-9 are applicable to the strainer they propose to install, especially in conjunction with the type of RMI. This caution is intended to focus attention on the BWROG assumption that debris would be deposited spherically on the strainer surface. This assumption formed the basis for Equation 6-9 of Reference K.3 (reproduced above as equation K.1).- Neither the pictorial evidence nor any analytical reasoning was provided in support of such an assumption. Some of the pictoriv evidence suggest that debris accumulation resembles in some cases more of a cylinder (or a distorted cone) than a sphere. Equation 6-9 of Reference K.3 does not reflect this finding and can be proven to be non-conservative for certain designs (e.g., long strainers (e.g., where strainer length is much greater than strainer diameter), odd shaped strainers and for strainers which are closer to the torus wall). To demonstrate that point, consider a strainer on which debris deposition is expected to resemble a cylinder (e.g., long cylindrical strainers). For such a strainer, a more appropriate equation to calculate to is: t = D(1+D/(4L))/2 ((2U)/U,-1) (K.2) Where, D = the strainer circumscribed diameter (ft) ) L = the length of the strainer (ft) U = .the approach velocity (ft/s) calculated on circumscribed strainer area t = . the maximum thickness of the debris layer (ft) While this equation is also not exact (because it assumes the debris deposition on the strainer to be semi-cylindrical), it is more representative of reality. For long strainers (e.g., girder-to- , girder strainers) or for strainers in which both ends are blocked, the above equation further reduces to: t = D/2 [(2U)/U - 1] (K.2a) 1 In both equations, U = Q/(A + A ) Where, A. = the circumscribed area per the URG definition (nDL) Aw= the end area of the strainer (n/4 D2); if blocked by wall or support plates Aw is equal to 0 . Note that equation K.2 and K.2a are substantially different from Equation 6-9 of Ref. 3. The difference is attributable to the fact that Equation K.2 is derived assuming that debris layer builds up cylindrically, where as Equation 6-9 assumes a spherical deposition. To quantify this difference, consider a case in which a utility proposes to use a cylindrical strainer 4 ft - long and 3 ft in diameter. The utility has stainless steel RMI with a settling velocity of 0.4 ft/s. Finally, the net ECCS flow through the strainer is 7500 GPM. For such a case, if an K-5 l

o analyst estimates the maximum debris layer thickness, Equation 6-9 predicts the maximum thickness to be 0.843 ft, where as Equation K.2 predicts this value to be 1.534 ft; a difference of 8.3-inches. Several such cases can be created to demonstrate that Equation 6-9 of Reference K.3 for i: certain cases can yield non-conservative results. On this basis, the staff concludes the i following:

• Universal use of Equation 6-9 (or for that matter K.2) would not accurately predict saturation thicknesses and can be non-conservative for selected strainer geometrical configurations. The staff suggests that each utility may wish to derive an appropriate

       . equation that is best suitable for their strainer configuration.

e However, this does not negate applicability of saturation thickness hypothesis proposed L by the BWROG. Instead, it is intended to alert utilities that more appropriate equations can be derived to suit a particular strainer type and design. Determination of Theoretical Thickness: An attemative to determining the maximum capacity of a strainer is the theoretical thickness of the RMI bed formed on the strainer surface. Depending on the size and shape of the RMI debris, for a given foil area (or foil mass) the actual volume occupied by the debris can vary widely. A measure of porosity or

   " packing density" was represented by an empirical parameter K,in Reference K.3. The exact definition of K,is:

Vau, = K, A. (K.3) Where, 2 Au = the RMI foil surface area (ft ) Vaui = the actual volume occupied by the RMI (ft*)

            ' K, ' = the empirical constant usually measured from experiments (ft)

The staff measured K, values for stainless steel RMI fragments of various sizes. The measured K, values varied widely with the size of the debris fragments. As shown in Table 1 of Reference K.5, for an RMI mass distribution of 0.81 grams per cubic cm (g/cc), the actual bed thickness measured in the experiments varied between 1 and 2.5 inches (2.5 and 6.4 cm) as debris fragment sizes were varied from %-inch (0.64-cm) to 4-inch (10.2-cm). ' Qualitative observations by the staff suggest that "the smaller sized RMI debris would form stiffer beds with lower void fractions originally (i.e., before being subjected to water flow) than the larger sized RMI debris." However, the difference in head loss between the two cases indicates little effect of RMI debris size on head loss. Typically, at lower velocities (U < 0.75 ft/s) the smaller debris resulted in a head loss that is 10-20% higher than the larger debris. At higher velocities, this trend reverses. In all cases, the observed differences are within the estimated experimental uncertainties. The following K, values were derived based on experimental measurements for the stainless steel RMI debris used in NRC-sponsored testing at ARL: K-6

i Table K-2 K, Values Derived From ARL Test Results i Debris Type Original Bed l

                          % to %-inch                      0.007 1 0.002                                    1 1 and 2 inch                     0.008 1 0.003 2 and 4 inch                     0.013 1 0.004                                    :
                          %,1, 2 and 4 inch                0.009 1 0.003 The majority of NRC te' sting was done using the last combination (i.e., M,1, 2 and 4 inch).                i Some of the debris were provided to the BWROG for their testing. (The exact size                            l L distribution of the debris provided to the BWROG is unknown.) For those pieces, the BWROG measured a value of 0.015 for K, as shown in Table 6-8 of Reference K.3. While                        i the absolute value is higher than the values given above, it is possible that the BWROG may have measured it for larger pieces. The staff notes, however, that the experimental                     ,

uncertainties in both cases could be large enough to preclude a definitive conclusion. 1 i Upon further review, the staff finds that the values provided in Table 6-8 of Reference K.3 l are slightly higher than corresponding NRC measurements. The staff notes that the NRC l measurements were made after the debris was subjected to small amounts of flow required j to configure the bed, while the BWROG measured dry samples dropped randomly into a - pipe. Furthermore, the BWROG's values are representative of a size distribution of RMI debris used in the BWROG's tests. If a particular utility believes that the size of RMI debris expected to reach the strainer is different from that used by BWROG, the utility should measure the appropriate value for use in its plant specific analysis. Settling Velocities: Another important factor relating to estimation of saturation thickness is settling velocity of the debris. Settling velocities reported in Table 6-7 of Reference K.3 are slightly higher than those measured in NRC-sponsored testing at ARL. Table K-3 Settling Velocities of RMI Materials Measured in NRC-Sponsored Tests at ARL Debris Type NRC Data BWROG Data

              % to %-inch                  0.39 0.07 1 and 2 inch                 0.40 0.07              0.47 2 and 4 inch                 0.45 0.07 -
              %,1,2 and 4 inch             0.40 0.07 These values are within 20-25% of the BWROG's reported results. Once again, it is possible that BWROG's values are representative of the size distribution of debris selected for testing.~ If a particular utility believes that the size of RMI debris expected to reach the strainer is different from that used by BWROG, the utility should measure an appropriate                    !

value for use in its plant-specific analysis. Head Loss across RMI beds: The BWROG provided the following generalized equation to l predict head loss across RMI debris: K-7 l 1

                                                                                                            ]

AH = K, U2 tnw (or) AH = K, Ki U2 AJA, (KA) Where, AH = the head loss (ft-water) U = the approach velocity (ft/s) calculated based on the circumscribed strainer area taw = the larger of theoretical thickness and maximum thickness (ft) 2 K, = the frictionalloss coefficient (ft'/s ) K, = the empirical constant previously discussed above (ft) 2 Au = the foil surface area (ft ) 2 A, = the circumscribed area of the strainer (ft ) The K, values were given in Table B-3 of Reference K.3 for different materials and different strainer geometries. The staff observed the following:

• On the basis of the gravity head loss test data, the BWROG derived a K, value of 5.1 for the NRC's stainless steel RMI on flat plate strainers. As noted above, a K, value of 0.014 was measured in NRC-sponsored test of stainless steel RMI debris provided to the BWROG. This would result in the following equation, normalized to foil area:

AH = 0.0714 U2 AdA, (K.5) This equation did fit a sizable number of the NRC data points obtained for 2.5-mil stainless steel RMI debris beds. However, several NRC data points (especially those where bed compression and debris size is an issue) were above Equation K.5. De following equation was found to bound NRC data reasonably well: AH = 0.108 U2 AJA, (K.Sa) f Equation K.5a also takes into consideration factors such as experimental uncertainties and repeatability. Although the difference between K.5 and K.5a is considerable (up to 30%), it is well within the experimental uncertainty of both experiments. In view of this, the staff believes that the uncertainties in any of the correlations should be identified and addressed in calculations by the individual utilities. This comment is particularly important for plants with small NPSH l margin to start with. Because of the uncertainty associated with the head loss correlations provided in the URG, the staff recommends that utilities use vendor test data to support the head loss used in their NPSH calculations.

i.

• In addition to gravity head loss tests, the BWROG conducted a series of semi-scale strainer l tests. In these tests, the debris used was made of 2.5-mil SS RMI foils manufactured by CDI. One of the strainers used in the study is a truncated cone strainer. For that strainer, the BWROG reported experimental data for several RMI debris loadings. Table K-4 of this appendix summarizes these data along with the Test ID. Also shown on Table K-4 are the head loss values predicted using Equation K.5a. Clearly, the head loss can be explained rather well by this correlation. However, this analysis shows two apparent errors in the URG. First, the data plotted in the URG for the truncated cone should plateau out around K-8 l

                  -.                       .-           ...     .      .    -      -    .~               . - .-

l l 12 not 25 as shown in the figure. Secondly, Table 6-11 in the URG suggests that the head 1 loss for truncated cone should be predicted by AH = 0.35 U2 A /A, (i.e, K,=0.014 and K,=25) (K.6) This equation over predicts head loss from tests T3, T4, T5 and T6 considerably. In view of this, it is concluded that BWROG conclusions related to truncated cone are wrong, albeit they are very conservative. Table K 4 Comparison of Equation K.5a Predictions with Head Loss Measured for Truncated Cone Strainers

Test ID Flow Head Loss RMI Eqn. K.5a 1

T4 7500 15 180 15.5 5000 8 180 6.9 2500 1 180 1.7 T5 7500 27 360 31.1 5000 13 360 13.8 2500 3 360 3.5 T6 7500 38 500 43.2 l 5000 17 500 19.2 l 2 2500 4 500 4.8 T3 7500 10 120 10.4 5000 5 120 4.6 2500 1 120 1.2 The BWROG's conclusions related to the stacked-disk and star strainers are incomplete and l cannot be accepted for debris loads beyond which they were tested. The primary reason for this conclusion is that the BWROG test data were obtained for RMI debris loads that are substantially lower than those required to fill up the gaps and result in thick beds. Also, the , correlations developed by the BWROG do not possess basic parameters that allow them to be j extended to higher debris loadings. For example, all the stacked-disk strainer data were obtained for an RMI debris loading lower than 210 ft2 . It would take in excess of 1500 ft2 of RMI to fill up the gap volume and start building a layer outside the gap. In conclusion, the head loss for RMI debris beds should be based on individual plant (or  ; vendor) experirnental data. Although the BWROG obtained valuable experimental data, its ) applicability is limited to truncated cone strainers. For truncated cone strainers also, a more appropriate correlation is Equation K.Sa which was found to adequately predict experimental data from the following sources:

• NRC/ARL experimental data obtained using a mixture of RMI debris generated by steam blast tests, e CDI gravity head loss test data using the same insulation.

K-9

I .* CDI test data obtained using 2.5-mil stainless steel RMI debris manually generated by CDI. . i Finally, CDI gravity head loss test data suggest that manually generated RMI debris would  ; result in higher head loss than air blast generated debris. This fact could not be fully  ; substantiated. Further research in this area is required before reaching such a conclusion. Head Loss for Mixed Beds: In the URG (Section 3.1.2, page 14), it is stated that "the i head losses which resulted from the tests with combined RMI, fiber, and particulate debris were bounded by those seen in similar tests for the equivalent loading of fiber and particulate without RMI debris." In a meeting with the BWROG on February 9,1998, the , staff and the BWROG modified this position as follows: "The head losses which result from combined RMI, fiber, and particulate debris can be bounded by the higher of RMI only bed or fiber and particulate bed." i The staff conducted a series of tests to investigate head loss resulting from RMI and fibrous debris accumulation on the strainer. The BWROG also conducted similar tests. In both , cases, the data clearly suggest that in most cases, the revised position is accurate (Speedically, ' the head loss for mixed beds is bounded by higher of RMI or fiber plus sludge correlations.) This conclusion is clearly true when the bed is made of a large quantity of RMI and trace , quantities of fiber (e.g., saturation thickness of RMI and 0.5 lbm of NUKON*). This conclusion is  : i also true when the bed is mainly made of fibrous debris, with trace quantities of RMI. However in the intermediate range there is potential that mixed bed head loss would exceed individual ' contribution of the debris constituents. A more appropriate method for this region is to add the i contribution of individual constituents to estimate the total head loss. An attemative would be for 'j the individual utilities to obtain experimental data in support the head loss used in their NPSH analysis. . Impact of LaSalle Strainer Test Data: Commonwealth Edison Company (CECO) issued a , report documenting experimental findings related to 1.5-mil aluminum (AI) RMI (used at LaSalle  ; County Stetion, Units 1 and 2) debris accumulation on the stacked <$isk strainer design being used at LaSalle. In the report, CECO states that "These conditions are directly relevant to the LaSalle replacemnet strainers and are not necessarily representative of conditions for other l BWRs. Direct extrapolation of these results to other foil types and/or strainer approach  ! I velocities is not recommended " The staff concurs with this statement. However, the staff reviewed this report to determine if the data from the report would revise any of the staff's  : findings stated in this SER or any of its appendices. On the basis of this review, the staff  ! concludes that none of the its previous conclusions would be changed by the information r contained in the CECO report. The basis for this conclusion is as follows: e Equation K.2 suggests that saturation thickness for 1.5-mil Al RMI debris (U,=0.2 ft/s) is a function of velocity. At a strainer flow of 4000 GPM, the expected saturation loading would correspond to a bed thickness between 4 and 5 ft (depending on assumptions related to bed ' buildup). The equivalent foil area is about 20,000 fta. LaSalle conducted its tests with RMI loadings up to 2250 ft . Neither Equation K.2 above nor the BWROG equation predicts saturation at the LaSalle test conditions. Equation K.2 suggests that debris should fall off the strainer due to gravitational settling at a flow of about 1000 GPM. The LaSalle report ., K-10 r

confirms this finding, although debris detachment appears to be more gradual than predicted by Equation K.2 o The head loss obtained in Tests 3 and 4 in the CECO report are readily predicted using a modified form of Equation K.5a. These predictions for 2250 ft2 of 1.5-mil Al RMI would have been 40,23 and 10 inches of water respectively, corresponding to strainer flow rates of 4000,3000, and 2000 GPM. These results compare well with the experimental data for Test 4. e The CECO data also does not negate the conclusion that mixed bed head loss can be estimated as a sum of constituent contributions. Instead, it supports this conclusion. The CECO report postulates that the increase in head loss for the comL'.2d debris bed (fiber plus RMI) is due to " synergistic effects" of RMI and fibers. The staffs review suggests that another plausible reason for the observed behavior relates to the location of fibrous debris in Test 5 (fiber plus RMI) versus Test 1 (fiber only). In Test 1, the fibrous debris was subjected to very low velocities in the proximity of 0.18 ft/s. In Test 5, due to the presence of RMI, the fibrous debris would now accumulate on the circumscribed surface. As a result, the fibrous debris in Test 5 would be subjected to a velocity in excess of 0.4 ft/s, approximately 2.2 times larger than Test 1. Consequently, higher head losses are expected in Test 5 than a simple sum of Test 1 and Test 4. On the basis of this assumption, the staffs calculates head losses far in excess of 100 inches at a strainer flow rate of 4000 GPM. This is consistent with the experimental data. At 2000 GPM, the NRC model would have resulted in a head loss estimate of approximately 50 inches-water as opposed to the measured value of 58 inches Clearly, the report sheds light on head loss for RMI debris beds other than 2.5-mil stainless steel in conjunction with stacked-disk strainers. The report raises severalissues that should be addressed on a plant-specific basis. It also provides valuable data. However, it does not negate any conclusions stated in this SER or any of its appendices.

 ' Overall

Conclusions:

On the basis of the its review, the staff reached the following conclusions: e The URG guidance related to debris generation and zone ofinfluence are reasonable and would most likely yield conservative estimates for the quantity of debris generated. , e The URG guidance on transportability of debris in Mark I and lli containments are reasonable and consistent with NRC analyses. For Mark 11, the staff disagrees with the URG recommendations and concludes that Mark ll containments should use the same transport factors as Mark I and Mark 111 containments. e The URG guidance on saturation thickness is reasonable. However, individual utilities should separately determine the applicability of URG Equation 6-9 to the specific strainer

       ~ designs being considered.

l { K-11

e The URG guidance on settling velocities and 'K,' values are slightly higher than those measured by USNRC for the same debris. However, these differences are attributable to experimental uncertainties and would not likely significantly alter the final strainer design. e The URG guidance on head loss for special strainer designs (e.g., stacked-disk strainers) is incomplete, having been developed based on head loss data obtained for thin beds of RMI. The staff recommends that vendor-specific data be used in the plant-specific NPSH analyses.

• The URG conclusion related to head loss in mixed beds (specifically, RMI plus fiber and sludge) is not considered acceptable and is modified as follows: "The head losses which result from combined RMI, fiber, and particulate debris can be bounded by the higher of RMI only bed or fiber and particulate bed." As modified, the staff considers this assumption reasonable for two extremes: a) where debris is primarily made of RMI, with trace quantities of fiber, and b) where debris is primarily made of fiber, with trace quantities of RMI. For the intermediate conditions, the URG conclusions could not be substantiated. A more appropriate method for this region is to add the contribution of individual constituents to estimate the total head loss. Another acceptable option is for the individual utilities to obtain experimental data to support the head loss used in their NPSH analysis.

l K-12 i

Appendix L Staff Resolution of BWROG Comments on the Draft SER on the URG Dated December 31,1997 By letter dated December 31,1997, the staff transmitted the draft SER on the URG to the BWROG. The BWROG provided its response in a letter dated March 13,1998, Table L-1 provides a summary of the BWROG comments and the staff's resolution of i those comments. Table L-1 Summary of BWROG Comments on the Draft SER on the URG Com. Draft Draft SER issue Description BWROG Response Proposed Staff Resolution No. SER Ref. I C*aisounced conservatisme: The approach adopted by The sWROG recommende that the SER communeceio en especteson The staff beneves that th.re is sufficient conservatism in Overan 1 the staff in rowtowing the URG results in comments on each that Mceneses will apply Individual poreone of the IJRG wtth a petmery the URG - 1 _ - _ which the staff finds acceptable to i area where, M severe 3 cases, the staff idenefles a more focus on the overall conserveesm of their plent-specific application nf snow certsen portions to be used in spMe of technicet c- ._J.__. appention then the method provkled in the the URG in determining strainer head lose and the resultlne ECCS conceme cited in the SER. The staff SER has been revised l UptG. AppMcogon of the more c.._..R applicagon pump NPSH mergin. The BWROG ogrees that sech licensee should to include e discussion on thee conservatism in SER section i suggested by the etsff M each and every eres een result in evoluets its use of the URG to ensure that the plant-spec IIc 5.0. However, the staff stMI found many resolution options en overeN c_ . thet le so greet for some plants that oppilcagon of the guldence provides en overall conserveeve approach (such as bending) unacceptable due to the lack of sufficient  ! It could require a pesolve strainer of e etze that It could only eneusing the now strainers comply wfth the ., .. _ _ ._ _ of guldence, supporting date, or adequate technical be installed by re-opening the contelnment goede snelysis, 10CFR90.dt. y__-^

                                                                                                                                                                                                                                                -       Licensees doeletng to use portions of the URG or through renonce on contelnment overpressure (not                                                                                                                                              which the staff has rejected wlN son need to resolve the currently credited) when calculeeng NPSH. Ir the draft SER                                               The BWROG urgos the staff to include e discussion recogntring the                       stofre concoms.

the etsff dose not provide a perspecilve on how the overen overeS consenregam of the URG epproach in onsor to menemize the conservesem of the URG methodology will be considered burden on both the staff and licensees in performing plant specific when evolusting the acceptabHity of any Individuel poreon reviews, of the snelysle. 0**'I **** r**='m 8d" ret in caosure of ivice es4; The oWROG requeste that the staff consider iseutne e s- . , :io The staff wesi consider ine n.ed followins for a burieten 2 OveraH NRCS M43 that provides bienhet schedule rollet to the Heentees in e. _ fonowing the cornpledon of its review of the a reasonese: The leeuse idenOfled in the draft SER and the pustble actions which may be required once the staff reaching finst technical closure on NetC8 9643 untM en NRC-eccepted URG. completes their review of 1) the comenge leeue (draft methodology la avellable that fully and completely addresses all the l I Genortc Letter 97-XX), and 2) the NPSe4 Z... lesves ofpoeting the calculaeon of ECCS pump NPSH. The BWROG le e provided in response to Generic Letter 9744, war ukety not requesene blenket deferret for the instensson of , --- impact the closure of Ilconsee rocoonees to NRC8 9643. etrainers but only for Anet closure of the 9843 technical response These lesues, bened on our elecoselone on February 6, are Once the final NRC occepted methodology is eveNeblo, Ncensees should be given odoquete ame to review their strainer d=40ns, debrte  ! not curroney projected by the NRC to be fuNy resolved prior to the heuence of the SER on the URG. loeding calculations, and the need for any further actions (o e, neense thenges for conteinenent overpressure credit) before closure of NRC8 9643 le required- , On 8* **'*". "d h*=*c'en: N' Ins em 2m putac The sWRm ben == w bec=== of ew wchnical mapauny ed ow Thutan concurs M R woukHw approprien to share 3 OveraH meceng to discuss the draft SER the staff Indicated that on- demonstrated high knowledge level of the NRR t _ _ 6 staff future inspeceon guldence with the utliities since it would site reviews would be conducted by NRR headquarters staff involved with thle leeue, it is appropriate for the headquarters etsff to , Garfy define staff espectations releeve to 9643 for e email number of plants. The need for or machenism conduct the inittel on40te reviews. The BWROG le interested in how resolutions. The stem win attempt to do so es soon as the  ; for accompNehing on.elte reviews endfor inspections for thle broad and complex knowledge beoe will be translated into future guldence hoe been developed other plante le undecided pending the outcome of the Inteel inspeceon guldence. Accordingly,the BWROG requests the on-stte rewtowe. Opportunky to review and cornment on proposed NRC Inspection piene and modutos that would be used to guide inspection activities j subsequent to the on-este reviews. I

Com. Draft Draft SER l=ue Description BWROG Response - Proposed Staff Restlution No. SER

        ' Ref.-

use.ne.e ed empo muna =m =cemed = = no reuse mmme==r-o.nem..es,se n seeden m oo-emes.mo ame ine e. reed wem me nos 4 mepptc sie responese provedad hereen to usoir spaceIIc comunenes est recennnendemons niede hessen. Housever, tre several cases, Page 2 ucensees esenne = me en pav:me et me una not eneviouse reemusen speans. we how ausented a coerer where me annos a comument m inconomesa ene me name eccepend by me seen ehemed escrees the concerne clied poentipecene vueponese are appropreses. u herther inconnemen le purpees et me uno which is to ensure a unwonn Industry 2ndj huseen in peone.epoeme outmasses? required, me seen is segueseed to eserwy me noeure or such reopense to NnCS e843. When no gmeence or menknee hifenneson. guldence is provided In Wie URG. Wie Interpreeselon et hour

                  *mnce me *R *cnod ame== een and a,,ormie                                                                                               a nnpos m em e, son is ion up n s. nievasues Page 8,                                                                                                                                          uceneese. The sten cannot, mereforo decerniene w safety
                  & -am on seeny at me 'resceumon opeone,' these were concerem anse sput of me kiiptenweisemen of opthuis riot 1st1    periwany conessered unaccepeshi s memout seamens revisised esenhoe necepeance of this mustoo comment supperung jusencemen or techmem doesne beene proviend womed huper seen necepance or opeone which were not by a sh:enese or me annos. w endesteuse neeneses emeere rewtowed and wouw sneelsed liceneses as to the scope of to niche use of any portiene (enseyeces or resseumon sie esofra UnG revleur. Thorofore, no chanee wise he smede optione) et sie UfeG Wiet are not accepend by Wie sesR. Wiey meiouw reseeve me seafre conceme cease eiereen in a plant-                                                                             to the SEft in response to mes conunent unesse has
                                       -                                                                                                                 sumetert informession to reach a conceussen a ghren pormon specenc -

of the UnG. h 8 08 8""d8 ** wy su una rose nr. uu mmneh emmes is inenamel m mere ====t um = me son-m ; a m pese 5 Page '*d=8 wheim F*'""my meant "m*ensm"er: a*mou*n*es"et nerous miem'emen. es imeare any enmyme worm is eene. The esmenon 11,1st1 provised my me annoo on pose ,tr a rewnne to cren, of "StafI h"8 *" **c***'"u"n'o*e*n*m** ueensee apper ine sw ha""a e pient a ** *'a not newe Evaluati me een,deon on ,ogo ur. Two m so,,,se,ha ,,en,g,wi,r i,ut to an me seen men ves met om eennWon is --- and has On" revloed the SER acconfengly l une rimochen nimen't ehkh WIR Ted in Ihaude a h ganoG ogem em en amucien med to etww. The m . h mW ogem set meer mmod m accepubk, mi em 6 Page reamy suo messesse intoneed, espier of which In P. one SER ties been upalated accorqfingey Soundne Assumamen en Osbres

11. last enemod is no use a eene of minuance met encompeesse sees or m.

y assense et inewest in me erywon and toes tronoport to me suppremeten peos. Tim escend momed is a tone sees of W. meeense Continu of niessuet in om airywen and men use the trenoport sectore pnevleed ed on in sw uno to essermere me emment et ineusemen met reaches s. Page 12 nas need iese snouw me Added to need Lees === rimer + prein esincusseens inurtne the aserse putiesc meetine it opp ore that the 77e sten concurs with the ownos comment and hee 7 page partcussese: DenC poenson es that the UnG _ ^ eiet sesW conceme are focused on Wie UptG eteenment east Hher + rowteed the SER booed on the SwnoG Information and the 12,2nd need im h,m nom , near + permeussess is neuneed my permeussess mounes en head i.e som ner.c + pensevenese e nem veevne of hnewreview my e men. head seen hem aber + paracussess is hicorrect. HetC wones and met me sesN heNeves more are poesneeNy cases where sw UltG g mesmem may sim me vaw. m ownos conema ihm nr c== wem nem head i ee seesd o n -+ pwecome head sees. estraniety emeN flhorleadings, Wie M + nhor + porticulmass head Ises mer escoed met ser smer peus penseussene memous neu. The enenne et me uno sessement wee met for cases where the emer peus paracueen head losses escoed or are comperehte to Wie head Ioeses for 14W slone, see semmon of IIMt to tie flhor peus pertetsames had seussys remune in a escrease in strainer heed toes. TNs posMon to supponed by the enftoo som esse tese 00 er4te.tet). The euwtos beneves that INe losese can he most reedNy addressed on & plantepecNic bases by having the Heenose escure the stroener verumor revleuse the doente of inserest to the parecuter peant and connem that me heed lose from smer + paracusesse + nem does not onceed that of fmer

                                                                               + penscussese. NINe .,,. -- " . cannot be provided, appropnose
                                                                               -.          _ meses on piantepoeme consesono shoued be mese to account for the increcee in the need lose asevend to sw nen.

L Com. Draft-' Draft SER issue Description. BWROG Response Proposed Staff Resolution No. SER Ref.- i g page stomodenses Leeds: -The === cessene met neeneses The owRoo nemene met ses m a piant-specac issue end is ometse The e== conews met hydrodyn.mc i.ees mum no meheng changes to hyendynende tend celeulmoon me scope odernesed in sie UptG. The URG notes met me need to resolved on a plantepoclRe bests; however, the stafra 13,1st comacene, eneer =mheemogme eheum not so .neww conomer hydrosyr nc seems min dose na asempt = semese caiseen een ,emmise a a a e,,,op,ime cei, son to aceneses 1,last meeng 's 8"sene*=*e ** se'8"r ** dee8 esp'apae's ==*e8 8er po'*ennmg hy*oernemac se=8 - '~'-=-as conomering changes to mee neeneing mems emeutssons j calcutagene.- as veces Iseues are not reteese to sereiner posfonnance por so. The sesN esos not consteer wise to tse en open leave, noris - this consteered the 9eru,n for eserosekig plant-opecffic  ! e The enstoo ---- ^: met enemos rotseed to hyeodynende Icede hymodynende load concens he resolved on a vendor and plantepocNic beels. , I# g g 8pn tegen et MWIDG Test Data to omer Obeiner Deelene The SwRoG to not euere of any scenese West ineenes to Innessi e strainer of a eseign beood solely on sie 34WRoG test does. The leo change required 13,3rd no,',d sesRme to e,,,, Rnds swRoo sist store to insi,RIetent me,esuns = anw sonne,Infonnesen

                                                                           -                  es  to co,icwe aim aceneses mious use n, seer e, seat este swRoo                                                                                                                               ;

j ,*por mes reason, to ster r=*====ade meet - _ use -with me Scenses*e snelysed conelsons es the beels for vender specIAc slate beood on sie IIconese's enelysed doesmdning head lose screes the sereiner conensono en see bests for esW hood lose acrose g me oesnw.-  ; t Page un w eendmasJacemeno: o= = um ince or heonnesen Tim swRoG nam em udenus= = == un wpchoeng and w menconmsms em me _ my me swRoo e 10 es to hour a plant is to appey this speen, see sesN ts unette tending is prowleed in URG volume n Teh 3, page 1g5-1g3, peregraph to unaccepeates nn e- a hupstes that the etse has { 13,4th .o ,sech .sy conch,mmi,ege,eng een o,een. wi someon, s.t.t. esproved om opmen her use, veien in rect, insumeient j vie cherectoriescon of sie -- ^^ of hieusemen guheence mes been provised *y the sustoo por ate use, or jachseng on eue ,ege is - -  : nh v met re, ort The swRoo _ met mese n.  : which winne a creet var men avmw. in someon, insancum one mists t COfttiftU pJrTr' - without furmer esemand Ingennesen on how to henanggecheting In onger to meninetes efetwee generemon should have supporung its use. For instance, detets genwesen toets I apply men opman and om eseecesand benegas echtsved, and evemenes appropresse ^- - ^ ^ _ on hour me URG does wee were not conducted from dNporont target to jet neute ed On [ me octance mese suppermig me use w ens monome, um appeed wuch suppat me mehnice neon sw such emme. engwe or wem nrying nume ro of menes, engin at mend y Page 15 ene ,e ,,n,,,o e ,,,m,e e .am,,,nnesen se to v. inamnemon, or,,,,,emon of - ou,dence is nm , oc, r a i ty of aus e, eon.- provised on ehemen conceveten owneona, amannonce L and , --^ . requireniones, minhuunt or critical

                                                                                                                                                                                        --                                         I mounung regisirennents, sec. Use et this opean wMhout -      f further detofted rewtow by the ster le not conskforod        {

accepteldo. The ster hee, however, proviesel more estall in the SER releeve to concerne that nood to tse addressed i seiould sits be en option a Heensee wenhos to pursue. The I staff notes sist sie pages cited by the WWWROG provide [ conchimm rasen to meeng of h.uisson wim t=neng. i but no generte suksence on how to appey me date.  ? f I i I f t i L-3  ; i

Com. ' Draft - Draft SER lasue Description BWROG Response- Proposed Staff Resolution SER- i No. - Ref. - . _ The ownOo mennes met scenseen have temen sign = cent sense to The ownOs hem groupes neo arguments togemer =sdeh do pew casanene riemmense me eten bonnes met <egaw y page inspecWone of the suppw.en pool and ECCS et,ttlet - huprove suppreeston poet cemenunees in scopense to SuNeens g342 not necesserey go togemer enhough they are cleerty . i and eg4n. The SwROo reco n o,.de met neenoese enou,e est ,esoted. nio,ecueno and timennige e,e t ,o esencey 14,2nd sand,,or, and esse,d ,e umn necesse,y, enoued no - amnesent iseuse. inspeceans are survemences necessary to i conducted every seuenne outage une sceneses have _ t sect ==peone made for denete source tonne in eineng the streiners are g demonstrated over une me enmiy to contros foreign eispropetete given me peontepecmc oceans taken to remove and ensure operatuRy of the ECCS. The stoR boNovos that centret fossign meteriale. One hoy element le me planned freepsoney inspectone of See suppreselon poet and ECCS suction i snetortels." strainere neuer to conducted every rehseIIng outage unal of poolinspection and cemening Housever,Wie SwHOG tollowee Wiet requirtng oillicanoese to perfenn W and cleanings every the Ilconose has elemonstrated that a longer Interval is . renseens outage adde en unnecessary burden to plants which have appropriate. In no case does the etsN beneve that me  ! taken elentpcent actions to control foreign meteriale, or which have Intervel should to estendeel tesyond every other refueling , used wry conservative soeumpeone in otrainer design. outage. OperehlINy of me ECCS sauet be vertfled on a regular tests. As w15e all espoty system servoittences,it ' unset be done regardless of sie liconose's glootpr: ar neeneing bases soeuripeone to ensure met they are operating utWeln sielrlicensing or sloolgn beets, and are In I compuence wem the reguissons. Since these inspeceone l can be conducted wnh remote cameros or with a diver, the y staff does sect feel West any unnecessary bungen has been , piece on licenosos with this . . -_ The ster points i L eut Wiet wletout inspectione. Wie operetsipty of the ECCS cannot be -M densoneensted isntN called upon to portona les ere oty function. Ellminetton of inspecdone by e Econese woestd sleo tend to estabiloh a culture where the hnportance of uneintelning pool cleenNness would be

                                                                                                                                                                                                                       -- , - . This couhllead to retemation of FRAE vigHence Ipy IIconeses workers The etsfra alreft SER on cleonings only stated that they              f should be conclutted when necessary. The stoR afoes not               r tielleve that any isnneccesary Insrden hee been placed on             r IIconeses wIth this . A ._ N Inspections asetermine                   !

that Wie Hconese is et rtok of esconding Me Ilconsing or [ atoeign tiente alue to foreogre motorialin the suppreselon ' -) pool, then the pool should be cleaned prior to etertup. t Common sense says that cleaning of suppreselon pools on i e regular beate le a good practice to avoid poesneel I prohlome secocleted mmh elatuts (e g., minemtring the potendel for porticulates or slutfge to cause woor on pump j lieerings, etc4 The sten has ensured that les position is cleerty stated in  ! the SEft. - [ t I i f I I i t 4 i e L-4 i L a m,-..-y,.s.ca,_c - - - , &~ ,,m,.-.,m--, . ,r.e ..r.w.,,-.y..y - ,- - . - . . . - .n--.----%, ..-,.-. v-..-# y . , - -w.-. .. , . - - ,. , ,, , . , - , . - .. .~- . , , . - - - - - - - . , , - -

t Com. Draft Draft SER issue Description BWROG Response Proposed Staff Restlution No. SER Ref. ,

                      .g    pggg     Conthunent Overerseews: "The samt concwe met edemonet                        .:overpreneurs (other then me N BWnOG , _ _            _:_ met, W precocem, planto not creet conceinment overpressure in the resciugen of this issue. However, The smR concwe wie me BWnOG comment, hower, no change to me sEn is needed apocNiceny in response to thee 14,3rd amount abeedy a,,n d by me seen for me eximeng                                                             me uno noise met in some com vermus pienteme factere my                             commene.

j IIconoing beste) should not be used me part of the resciunon make it e=-= y to credit containment overpressure. The BWnOG of this soeue. The snow to ovesumeng to posecon on use of . - -  ? _ met Rconoese intoneng to mehe e thenge to their COnting overpressure in concusseng espsH mergen se Nconsing beste relouve to cremeng conteenment evequesours should ed Oft ' part of sie restow of(GL g744) ,," perform the appropriate snelysee to f __ the minimum enount or - __ x. -_ _ . avanebie. These snelysee Page 15 shoum he so,o,mm, eut,n,ined ,or stor ,evies, and e,,,o,et The sWnOs notes met me more u._-. .__. ; me regubu=nte = n om esses oe meno et innuence, doente generemen, ,ansport, and heed too. 6. the more Nhesy that some ^^-_ - _wie nood to creet containement overpreneure in order to meet sto requirements of Busistin 9843. Encessive cm__. ehousd be avoissed. Page 8hea*= sucem pmesse Loser m uno agg== Tm w mmimr m sw hyeodynmie inede imue. sa me== = imm sa son mpon= to inni no. s. 13 use a more see m acesse mennegues or reducson in no. g. 15,2nd c_ - ce cm.nt demon besse emco wunout j reopening the lh.ensing boole for containment loads. "The stafre concerne reganging secuen 3.1.3.1 are stoesd above and appey to ede necean ce me una moo. tuno necean 3.1.3.4.s, page 213 The ownOo concure. w change needed. 14 Page "l'_**veivets hower, when using ter were case

                                                                         == opean   ser when         a emeted                     chenmina break, em inemeson 15,3rd     neennes m.oum go boca and ,eemos ou,or b,sene to y       ename met me neenm he not change em tween wmch is me most undeng in tenne or wpsu mergin.-

DWeet-Dum: "h mR soongly acamen sw h BWnOG undemneng e mm tegunge = met denuhtepe N stow conews and has revlowed the SER to ensure 15 Page _ _ _ 2 of motornese water sources (Inciuding t,ut riot e , _ ,- -__ The BWnOG consistency in the longerege reiseve to where it is meidng

1. en "ence _. _

15, last _ _ _ . . ___ or e,oseover ,simi, o,e,eme omning, and ,ee_ met e. enn use ionguage in sie sEn mm cieerty .- : _ or .nc, . , _ u v.reue requirements _ from that of encouragemente end as in the case cited here by the BWNtOG. j emergency opereeng processures to enowe eget operatore _ octuel, , con sniegato any estuogon irevoiving loom of ECCs fkav due prussent oceans and suggested evaluation approaches. Doing so COfttinU to strainer clogging _.the stem concurred wouh the Acas wouid avoid confusion wnh actues . , - _..:. ed On comment and agreed to piece more empheme on me need to imenm wh= eppmerisse, em pacedu.se to bener Page 16 m,,,,,ees co,, co,,,,,, ,n,,,, en,,,,me sowces e, wher.- uw or uEs 3 t ser secuen w arum Laceem w be we nom vor == or umyon, ownOs aceme eww typiceny choem m en nam em n knows e aume era ace no who 16 Page 16 not to use the RIES 3-1 approach and Instood used en approoch that ettempted to use RIEB 31 breake without conalderation of Evolueeed DrU conoksere stoes breaks that woukt reeuit in the menemum detwte other non4BES 31 pipe break location . The staff e m m eon.

                                                                                                                                                                                                                                          ' He pomeon met ow use of MEB 31 for mis Page                                                                                                                                                                                                            ..

oppucation is 1 , , ,,' ate, and more importantly, - 18,2nd com,setwyunnec ,y, I r L-5

Com. Draft. Draft SER b ue Description BWROG Response Proposed Staff Resciutisn No. SER Ref. The swRoG recommende met mee i eue can be most reedny The one conews however. L shouw notsc - n q7 p g, Tmn med eneet - useum LocAs: me stat bonnes met aconnese considering a soluson option meing en efternate addressed on a plant epoclRc boots by having me licensee mesure that out KoCA. wittout - from me strainer vendor 18, last me strener nneer rwswa me debris comunemons of inemme to he met h=se dobre somenge couid not mun in more ammng e,einer design enound es,sem.ntesy we,wy to,onewe i perticular plant and conRrm that the heed lose from the meeknum head lose acrose the strainer. The vendor should have j using esteeng vendor or BWItoG date) that the then-bed susncient date to support its posinon. The stsW has revised i ' sWects to not en locus for Wie strainer design being detwte loseng bounds thet of looser detsrte loads. The dobrts combination reculeng in the highest strainer head lose for the the SER to make this poestion more cesor, l COntinu conoksered usina detres euentiges which ero cone Mont wigt e EocA for meer meant otherwese,the seconoce espected flow rete should tie used in me NPSH ceiculomon for the e On should consider See ROCA when performing Wielr plant eCCS pumps. This con be accompilehod try parametric vertenon of Page 20 ,nei, e ,,enned _ _ r,,me acenese wouw not me doute ioede when ,e,,o,m n, need iose ca,cuissons. Tme need to ennsyne moeum LOCAs wie me sergest polonees approach to recommended beccues et avoids me bunsen of espacepy perecuente detwee to ineuseman reso by weight" osebnemng the nyected zon. detwee generemon and transport resmung from asLOCAs whee seu amouring me most umiens need ueensees may screen out RoCAs in pereorming their toes case le considered plantepeeme enseyees w mey intend to Instou a strainer p09' olmner to sie elected met riumtser, stor strainer, or another The SwROG believes that the stected assok strainer eseigns typiceNy beng instomed as re,iecem.nie hoe sumenner deep cewc met 21,2nd geometriceny simmer seener wnh deep emicos eumenne IALoCAs can be screened out of consisteretton. to hold testwte loemngs coneletent wMh e ISLOCA for their < 1 plant.- The owRoG recommende met mm issue be reeceved in me some way The ow concurs; however, neensen shoute not sc=n p.g, Lerne Locae wem tthment Paracueen to ribrous oebets by . qg Welsfit "Thorsters, the eten concludes that seconeses se Item No.17. out these tweeks without assurance from the strainer i 20,1st1 shouw een evmumm mese LoCas wem em mghese vendor vet nigher wudge to atier rocos couid not enun in ~f more hmieng fieed loss across the strainer. The vendor i pareculets to fitwoue debris ratioe by wooght to ensure that those breche t00 not become more Ilmtling in tonne of head should have sufMclent date to support its posftlon.. The i lose Wien me tweeks that produce me highest volume of staff has revised the SER to make this position more clear. abrous assbets." , A88megn swivenon memodo: -each manwsw Tiw swRm caeurs provided such efternettve evoluetto.1 methods igCFR93.48 to e part of e6 Mcensee's Ilconsing bases. This  ; 19 Page evaluegon momed presented must provisto rossonable oro consistent w0th the plant Ilconsing tseele. rule is the Insels for the staffs comrnent No change to the  : 21,4th ,. met ino most seve,o eCCs euction e=siner SER ro<iulred i detute seemage them dry n insulemon weremi he 1 suhebsy weiusted."  ; 5 T' owRm conews. Noce.ng m tvimt 20 Page 8'"a8ena Aa8a" ~**""*"8 "dr'" """8 br acenesse in new of specme pipe bruen iocamon samyses. 21,5th need t add,ues na detwm specme twom hieuseson sources) g wuch han not been e dreened by me specme pipe tweek i noceeon evoluseone.- areene inside blowied: -The uRG guidance on pipe The swRoG t= nom niet em piant unique =pects of me emew and The sten conc = met mes pert of ew encyce is punt- ! Page 21 breaks inside sie bioghield wen la incomplete. Woo sten type of Insulation insiste sie tuto4hleid wiu govern t*:a most specific. The staff wee recommeneng that the BWROG  ; f 21,6th - approprism meene of addmaing mis debris source. For many pients provide guidence on what shouis be considered in i , benevos met odemons gumenee on me eneyecal conehterations to lie evaluated by the liconese would be me amount of eletwte evenable inside to bio-shiehl le negligible evaluating detwte sources within the bio-shleid w N and l j benencial and consistent w8ti the SwROG*e stated goal of rotative to other detuto sources and con be escounted. The BWROG their potoneelimpact on NPSH. The staff win Mow this to l I provieng a conetstent industry response to NRCS ge43.* recommende that this issue is best ashiressed on a plent-specmc be etkheesed on a plant. specific basis, but cautions that n [ l beste. sound technicet bests for the Mconsee's resolution of this l part of the enetysis should be estabHshed and maintained. The SER has been revloed accorengly.  ! (  ! l I l L-6 i m - ,m - _ - . _ . . . _ _ . , , . _ . . . _ _

                                                                           - -.                      .~             - . , _ .       .                 _ ~ ,                 ,   -             , . , _ . . .        .             __             ,

Com. Draft Draft SER is:ue Description BWROG Response Proposed Staff Resolution No. SER Ref. 22 Page 23 But Denomic P'vesure: "N ""08 c8'cu'**** A* "**8 by ** ene, me amoG prwrtousey seermee em issue bi w seen wen chenee sw seR se not raiuire a chenee to em

                              . hun synenec prenewee in enortI                respones to NRC RAI. A revleton of the UptG is not enecipeese.         UltG but isNI sel noes the techneemt error in the ustG. Yne g9     __

_ try a sector or to se some sacemens However, ster weg eleo noes me BWRoG response to ster quessono sw essere ennsysis ese- that the busk eynemic Further, the swfioG noise that even it the buen dynamic pressure on the URG where this i eve orteinewy resoeveis. preneure issues Ilhely be Inousnclent to elemeye aneulselon sufRelent to remiove insulellon, no knpoct en the streiner pectormance motortels such as vices presenWy uses in opereelenal woute be espected given that loose insuiselon woulti come off as erste, w the ineuessone are property ineeense one wes. ressehrosy ineset beenkees which,in actoreence wem em leftC DrywoM

              ..._. _. _ uceneses eheues ensure met me ense ees       r to    Detwee Transport study, are not tren portsbes reRecove of me actuel peant condesone. In semeen, the                                                                   .

URG caecedesione ser bulk eynomic preneure in e IIert I conesirement should be W to be __ .;weeh the evntoG e response to same RAes en Reference 12.- L-7

Cum. Draft Draft SER imus Descriptian - BWROG Respon00 Proposed Staff Rmlutian No. SER Ref. Page 23, Jet cawrene Prenare (Jcts wweve Teram Arw Anremed Sugg=eng mm urget me awraged prmum (TAAP) may to a enn in the staff's draft SER,it is demonstrated how TAAP 23 Presouro (TAAPI: *The staff beneves that a target ares technicaNy correct basis for eseessing potengel damage to insulaeon explains the BWROG's AJIT toot date. In the BWROG gg averaged pressure or jet " , , 2 load are more presupposes one _ .___ '_ the feMure mechanisme of vertous response quoted here, meltjustification does not explain technicaNy correct besos for essessing potoneel damage. If insuesson types subjected to impingement by a LOCA jet. It is not their test dets. For example, for NUKON, debrts genersoon thee approach is not taken, the WWftOG should provide a otprious that an impacting jet, which has a emenor someter than the Increases wtth distance from the jet nozzle up to 30 tJD tsetter resonale for eclecting the local jet contorene target deemeter le not more doctruceve then a jet which le very wide (whHe the jet is getting larger, JCL pressure is geteng pressure et the UD location where incipient damage was compared to the target diameter. This is because the smeMer jet may emenor and velocityhnomentum is geteng smaller), and first observed as the _ __ _. property that uniquely not remain attached alsout the target, and may redirect the momentum then decreases beyond that If the smaner jet has more controis insulaeon damage." of the incoming flow at right angles to the flow direction. The larger destructive power as the SWROG cleams It may, then why ja on uw omer hand prwumabey emeins seached, and ** muteng don debem generemon go up n esence Inc== nom PaE 23' "The WWROG should develop a logical resonale which drag forces could be less than that resulting from the smaller deemster the tpreek, and then go slown after 30 UD7 At 30 tJD, a 4Iil1 would also resolva the staff a concern (descritged in jet. G^,,- _ . ,, the situason le technically complex, and in light of simple calculation demonstrates that this is the i Continue Appenden B) reiseve to applying the BWROG serjet impact me appelcedon _. ^ . .. , the jet contorene stagnetton preneure approximato destance at which the jet enerely engulfs the aseng mula = fun eine SWR drywon. - wee chmen as ow n=ete = tiuanery me ineumoon duenceon meget. in edemon,em percenage oninn genmad quais t d on pressure. If one considers the fact that in a drywell where an piping is the amount of target bee,1het which is exposed to the jet. Page 24 "The NRC concludu met om JCL approach would resuM in randomly odonted, the average target would be oriented 45 degrees to AdmMeedy. em BWROG k rWordng to two effent stre Jets Page 25, a smanraol forineusesons wMh a higher P., (l.e., the jet contorene, use of jet centerNne stagnoson pressure, as the at the some UD, but the point stMt holds true. The BWROG DARMO, wMh Camloc eemn and leechu, Transco Rul, measum insuladon duencoon pronum h my conumen. dem shows ed a largerjet wMh ins vWocMy and 5th1 Jacketed NUKON with Sure-Hold Bonde.D6emond Power _-- is creating more debris. The NRC also saw this IIerror with Sure-Hold sends, and catsu with Aluminum The WWROG beneves that, without a commensurate Increses in safety in the Drywon Dobrts Transport Study, where a 3.75 inch Jocheeng) than would a TAAP teased analysts. The effect of beneftt,the added comptently of the TAAP modelis not justified and nozzle cteerty generated more debris than a 3 inch diameter JCL vs TAAP would tue mentmal on other :.- . types that imposing It as a . , ' _ _ ;would cause unneccesary notate et the same tJD. (those w4th a lower P.,,)." reonelysts. Further, se noted previously, the BWROG beNeves that the overeN conservatism in the various phases of the analysis is adequate However, upon further review, the staff no longer views this to address any concerns that may artse regarding the acceptabHtty of comment as being a significant concern because it only "Th'** '** "wmode (zOs uomods 2 a 3) are men a perecuser area. The sWROG mcommends that om staff approve me invo4vn a MmMod sutset of Insutocon typn. The are Page 26' sufficiently c ..-. ..a to componeste for weaknesses JCL modet for use on all Inoutadon types tested by the BWROG. 3rd 1 ,ot,e,,o ,and m . ,o,e consed.dacce, eb,tne esseneeNy

m. comment. five n,et types of Insulaeon

                                                                                                                                                                                                                                                                                                                                                                                                            ,, o,,  chem ,nd which are,,,,.

7,,nsco affected,by s ,on, staff for use on ineuteson wtth low P., values. For as a licensee is sizing their strainer based on saturation lasulaeone noted above w0th high P ,,vetues,the staff loading of RAIt dobrls or using the debris recommends met the 208 be developed based on the generationttransport factoes cited in the URG, this comment

• target area averaged pressures" Instood of JCL is inconsequential due to the level of conservaesm in the pressurse." analysis, in the staffs opinion, the conservative generation and transport assumptions outweigh the concern stated in this open item. The second two insulations are banded to reduce dobrts genersoon. Since the staff has not yet accepted beneng as a resolut60n option, the staff recomtnends that related debris generaeon concerns for banded Insulations be addressed on a plant-spec!fic basts.

In comment 27, the staff points out that Cal _SH should be treeted as eroding aver eme. BWROG debris generation tests were of short duration. The staff has agreed to allow this to be addressed on a plant-specific bests. The staff notes that the BWROG*s response to the draft SER did not explain why JCL is an appropriate metric. Stanie versuer " - - ^ ^ Flcm from a Stoem Une Broek: The SWROG recommends that licensees be given the opeon to As stated in the draft SER, this was a staff recommendation 24 Page 25, "The staff recommends that utpitles not take credit for a demonstrate on a plant 4pecific bests that the ZOI for o steem line only. It was also stated in the same paragraph that if single-singie jet in the case of a main steem Mne break inside break to less then that caused by assuming doubleended flow from ended flow was assumed by the licensee, they should Continue containment

• the breek. Alterneuvely, licensees may conservatively assume accourt for the offects of double-ended flow up to the time da"ew*nded now. em mSws cion. The staff s comments do not preclude the d on recom... made by the SWROG, so no change is p 90 g required.

L-8

e Com. Draft Draft SER lacue Description BWROG Response Proposed Staff Resolution No. SER Ref. 25- Page N, une hieummen osenween one uwns for sosse Tsie swmos recosmondemon m. eneri me overen 1 -- or g Insulatene: *As e resuM, me ster beNovos West ugNue. m soon coricure wesi me ownco cornmerit evid ties Wie snelyele prevleuely discussed, that the ster should not impose rewteed the SEn to include e discueston on the lieving wiseertete where Wie does eso limleed should conduct requiremente for odegenet isogne of noseertels por should Wesy admoonas essene 8er mese **eeresse unsees they one a _ In Wie LNto analysts _-^ _._. Seesten hupose a bonnene approach on moes meeorisse where there is unned roeponse to euwtoo conument t. toundene approach to those meenrieler does. 26 Page 26, Zo' thmed N A**mmbb: "As a "e"M "e*od 4 m not m ownos concum. e_ __ accepeesse by the seest weehout further deemsted No esense emiuimd g9 Newacemen on a paent-opecmc besse? C0fttinue d on Page 27 27 Page 47, ommene a casa shoued be Tressed as arosson -ommese ourtne sw nie une on assee.mo seen reised concerne about om 7t= eens concure and hee added more deteN to the

                                                     'g           to catetum escaso should be tree'ess as crosion es               lhuisted numtierof SUWmOG tests of ceiciuni eHiceae insulseson,          description eri the SER.

demonstrated by Sweesh soportmenes. Table 2 should be poselbee vertellone in remune entong different types of calcium emcees bt8Het revised to efeer Wie failure criterton " Oneulmuon and the o85ect of aging on the P of the insulellout i Due to these Iseuse. Wie WWuftOG recommends shot licensees with calcium sulceas Insulation resolve them on a plantepectAc beste. 23 Page 29, Perseec hisescueno are fossesserv- As a resuet. the sees The ovvnoo noes inet the Ineont ce ihes usto essesment is that no change required. h SwROG's etertftcetion has been con edere sw sonowing _  : on pees at of ww uno to inspecuene ac euenser em amount ce ervdust ere noe required. a 1st1 he unece penble.1eoes met where use et en edegumessy was not intended to iniperthat seneret cimenenses inspeceone were noemd in me SER. conserveehm vehse m ensamed ser a paracuter debres not appr+petees. , opecise (e.e, dh*ductl. pertoec inspeceans em not necessary

• M le wie etsfre opinion met periodic

                                                                      ,         ere sheers necessary roomreses of any tieseline soeumpesons used in the ECCS enalysis. The Ineorval between such inspectione should only be adjusted tissed on actual Hesnese y^ . _ __-- and Sie amount of e_..__.          he the bene assumpliert" L-9                                                                                                                                                                                                                                                  I

Com. Draft Draft SER lanue Description BWROG Response Proposed Staff R colution No. SER Ref. Assure UftG Guidance le Assecalde to Your plant "The The WWYtOG rec _ _ that as part of me overaN ovaluedon of 9pe The staff concurs wnh me SWROG es long as the bultt4n 29 Page 29, losues retoed try Bulleen 9643, each Rcenese should queINeuvely conservenom in the calculaeon doecribed in SER section staff notes that10ceneses should make every effort to ensure that the guklance in Section of 3.2.2, or any other conokser whether the generic guldence contained M the UptG is 5.0 is retained. It further analyste rennement is performed section of the URG, le appucable to their pient before appropriate for meer peent it should not tee necessary for Ilconeses to try a licensee, then the staff does not agree with the Impeemeneng that guedence on their plant" conduct asetaned quantneuve evaluasons to jusefy NRC-accepted BWYtOG comment because me numbers for dirt, dust, rust. values in the URG te e, onwdust, rust nakes, sludge distreuson, egel etc, used in me anasysis by scensees are based on t.lconesse may elect to use different values then those provkled in the engheoring judgement The staffs acceptance is also URG and, where lose c_._, . _ _ _ than me approved URG vehses, bened on engineering Juegement Since the staff considers > ehould alocument an adequate bests for the values veed, those ,-- - a to be acceptable,the staff has removed the . , .;to assoas the appHcabtNty for each plant However, he staff still bellowes that certain Mcensees may stfit wteh to be prudent and perform an ,

                                                                                                                                                                        . to ensure that the rumbers in the URG represent c .          .__. _ numbers, and that they wouki not tekely to euceed those values durMg normal operanon. The           ;

i staff hee pointed cut in its safety evaluenon simple ' methods that can be used to ensure that tne

• numbers used are approprtete on a plant-specific basis.

The stafr bouevos that this would be a prudent practice by liconeses regenfloss of whether they are refining their analysis or not These methods are simple estimanons, and  ! wouki not constitute a significant burden on the licensee. The staff also pointo out that the resures of any qualitadve

                                                                                                                                                           .._             performed by a Mcensee could focus the licensee on areas that requhe further detailed analysis. An example may tuo that a ucensee assessing their quanfled comengs slotermining that the cond9 tion of their quellfled comenge (e e., bustering, poenne during normat opersoon) le such that they now must make a detailed assessment to determine the impact of the coating condition on their analysis.

. . .. . . . the staff beneves that any values less conserveuve then the URG vetues to be used by any licensee should be bened on tietailed technical analysis, not qusHtative assessments or engineering judgements.

L-10

Com. Draft Draft SER l=ue Descripti2n Es - AOG Response Proposed Staff Restlution  ! No. SER - Ref. - + 30 - Page 30, fee mm. obwount Wahm Itat Adeousashr summerted "N The WWROG understeneng of mio language le met me stH considore see stee response to BWROG comment 29. sten bemoves a woute be prudent ser venues to verwy sus 1se em vesue to em acceptete. - number Wirough eennpling. R wouhl be reistively I straighWorward 9er sie WWROG or an Individualliconese to Furmer, the BWROG believes that this leave le adequately addressed totus semiples of dirt and eluet from the tirywou and given Sto roc _ _ _ _ an item 1 for each licenses to conshfor the suppreeston pool ernes, testermine typiced weightp-unit overaN { ..;.m of their eyelustion end, as deserttled in item 29, aree en conecting sentoces, anel calculate a bounding vehse the appropriateness of the URG guedence to their plant. The BWROG 'i for all appelcable surfaces. An snowance woestd have to be tiellovse that there le negNgible safety benent to be schlowed tpy  : aseded for concreto dust generated by LOCA forces. be - regulrtne Der encouraging) that each licensee empeecstly vertry itis ashfluon, _ _ . _ should be givers to c -

                                                                                                                                                                                             ^

value and met the redledon esposure recolved in acc _ -" n. ette, and Wie potengel for additonet clert anel dust would not lie justlRed. accumusemon over me opereene ufo of the pient WhNe me

• sten does not hollove that use of the UftG 100 Itun assumpeon to Inappropriate, Wie sten eloos believe Wiet it i would be prudent for indhredual Mconese to conduct a more  !

Page 32, ,,,ugn _ - - > 1st1 , -considersbee one wee devoted to em deveiopment of om B8UftEGdCR4224 (flef 31) study to develop -_ _ i-^ _ esametes of dersduet and rust. where provided, the vesues suggested in the UltG are atuout the some w larger then MullEGdCR4224 values. As a result, the eten concludes  ; that use of these values le acceptable, however, the staW notes that me NUREGdCR4224 study wee conductosi on a roterance beenk I concelnment. For then reason and the . , askilsonal ressene cited alpovo, the ster bonswee it would  ! tuo pruelent for Inephrkluel liconecos to evaluete the , recommendedene of this secton for apre emuty to their , plant?  ! Page 30, 80 'ba. Rat Flek* vasuo nest Adeemetesv susserted: -This see me oWROG response to comn=nt So. The sWRoG see sten response to ownOG comnwn 29. i 31 presents the same concem to the ster for this suggeeWon unclerstanding of this language le that the ste ts conoletors the 50 Itwn. gg so for the direfust vehse noted above. Again, the staff veine to tw acceptable and that vertRea6cn le not e , , . beneves that e sound technteel Insels could be eleveloped tsy l se .ipang =cr e e-ma= orywen and suppression chamber [ areas combined wesi wendowns to estebuen typical y guaneese of rust per uret eree. As wie me dort and dust t

              ,                                                                         mocus. con noted abow, em soon does not bemove met use                                                                                                                                                                                                                                                                                                                [

of.co m me assum on is bia, pro,risto -  : t coeunes besected hv me LOCA Jet Seu en Oson leen ,as WWROG notes that because me ster seu hee thle leeue usuler Tim staff wtM consider an entnolon for comonstrating 32 Page 31, g *The sten has not teenWRed any current conceme retaeve to rewtow, many Ucensees may not be atste to reach a conctunion on compHence with 9643 based 0:', coatings reisted losues. the c-- _ in ftsterence 51 (Sachtet floport). However, whether or not the repiscement strainere util setlefy the . m . _ _ However, the licensees should proceed with instattation of , 4 the staff poents out that die leeus of coolings anel their of Duneen 9643. The inspect on the schealute for closure of the the hardware [ potengel inipact on the ECCs le en leeus cusveney UrNier Sulleen 9643 response le discussed in further deteH In stem No. 2.  ; sissf review, and le me sublect of a generic letter espected i to be leeusal in earty 1998. As a result, the of  ! Reserence si em een under seen review.- Page 32 su oWstOG roepense to hem No. 29. see sten response to sWROG comment 29

                                                                                        -e n          : wnh == steers guidance abow,It woved esso 2W                                                    em prudent for neonesee to evesuste the -_-.--f                                                  _ of the Bechtel comunge report to ensure =rame*Ilty of those concluetone to meer piant?                                                                                                                                                                                                                                                                                                                                             p L-11                                                                                                                                                                                                                                                                                                                                                                                                                                                  L
    -- - _ _ _ _ _ _                        _ _ _ _ _ __ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _                                                     _ . . _ _ _ _ . _ _ _ _ _ _ _ _ - _ _ _                                                                       ___________-.                   _ _ _ _ _ _ _ _ _ _ _ _                _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ - . _ _ _ _                                           _____       o

L Com. Draft Draft SER I cue Description BWROG Response Proposed Staff Resolution' t No. SER' t

                  ' Ref.

The ISIC DIsserese met Useuspeed Cessnee are a Lesent See BUUROG Roeponse to Nom No. 32. As acted above, the seer wee conswer esteneng the 33 Page 31, enemine ser esmonstrosing compnence with TERCE es.43 ombate Beause: -The sesR es parecueerey concemed y9 because Store le no heels ser Wile semesment, one in Wie The SuWROG hee undereston a tossing progrese ser unqueIIIIed unell the cogenge leeue le secopved ' sesfre opinion, R lo enmely inaccurses. In fact, Geore le ne comunge. The toeOng ens ===acamaad enelysse wW be used to addreen evesence that - - ' or ungamened comunes wouw sw eenceme ressed by the seeN. This Is e esperses eNert that wm not - to essent estres et esL mo more to no reason to moeune he ederessed ley me URG. West see turtulent environntent of sie reacter vessel tegnesem couw not cause me comune to entsch and Page 31, iron pertmumappe essen pom? I -en usht et recent sensemed comune evenne and me lack at subesensve tecennical hoods ser Wie WWUROG guedence t reserene unquesmes and ine eensenses comense,me seen does not have enough Inconneson to ovelueen see eseguacy me - - , Page 32, 3rd1 "s" h"P* ann"r " nand ***** '" "a" **n*'"*" ** liconeses should be causened to cerehsily evolueen Wie poennee8 hupact of unquesmos one inesiennensee comunes on ECCS sucWon sereiner hoes toes. N in aleubt, esseneng the comense reach the seresner serence wouht cenere r to the conserveeve seenwo. Then wouw proutse me ucensee l wem tese reek rWeehw to sw comunes issue one coued imod to admoonet mergen in sereiner emeten N URG - which menemene the poesness impact et unqueense ., pressenve comenge are supperend by the voeules of me esefre comune reveaw? Come6 to ineusemen oseewceen ew mine a up: hi sommon. sees esmrueven a s uo wee soeuned vor en eserm types. Tem emR nmse mm accepeamm. :: dose not apper to to true 34 Page 33 su uRG menwme moun= out er m se inneson vor Re, howwer 5th1 conomined suNhtn 3 UD of Wie Iweek to controyed into nnes, a le not eteer, however, that men - r -ani wee mese ser all debris types? Page 35, osenina In Lauset Loves acessnes: -Large eserm severend To ruosa see tenue, me suwtos recommenes met om sten conswer eased on om empre evaluamon of the buHt.in conserveWsm 35 stove Wie lowest greeng shouse not he descounted N the - Wie overall conservenom in Wie WWWROG epproach as being municionGy In sie URG sneshodologies, the staff has removed thle - g sowest noor groene is noe - - or hee outeenneet c_ z _ to odereas mes concern. The evntOG noese that there requiremwnt from ew URG.  ! openings in it arough which server emeres couw tronoport. are mulupse invece of greense and other steeructone which wouhl In this case, en approprisen frecean at large deerts tvem esso be enecevo se prevenung the transport of dearte but they are not , abow me greene shouw to conessered me transporestse - creened in um enesynes- t if Sie above approach se riot =dapand Wie suff should ciertfy what consmunes subseenessopenenes andaspyropstees frecean et eerse eserie es mese tonne couw toed to inconeeseent reeuteeory

                                                                                                     '""'prenson.

I L-12

Com. Draft Draft SER issue Description BWROG Response Proposed Staff Resolution No. SER Ref. Page 35, merk N Treneemt veeuse Not Accostaba. -Therehwo,me Tfw besse for me etsfre current posioon not to accept the tronoport A copy of the NUREG was forwensed to the svWtOG on 36 stoff finde the tronoport fractions for Mark N containmente values for Mort N*e le the roeuhe of testing conducted by the NRC. Apr# 18,1998. The staff is weMing on any further commente y listed on pages 75 and 30 of the URG to be unacceptabte These teste are documented in NUREG4Ris300 which has not yet from the WWROG that results from their review. Fractione are meno given on the same pages for fine fibroue . been puhetehed. The etsff completed these teste in the first half of detwte tronoport and RtIt detwts tronoport in 80erk re and 1997 and made a presentation of the reeutte in July 1997. The Mrs. The values esven for mark rs and Nro assume that svWtOG hee previously requested a draft of me NUREG so es to be 100% of the fine detute will tronoport to the suppreselon abes to rewtow the deemste of the test setup, paramotors and pool. The staff beneves that mese some freceone should procedures. The staff has stated that they cannot teksee the NUREG also be used for Nort fre. unell final puhelcation. The BWROG requeste the -m _._..:^, to defer their response to this leeue untN the NUREG to mado eveNebte. Upon receipt, we w31 evoluete the impact of the test differences between the SWROG ecated teste and the NRC teste on me outcome of sw results. Page 35, iso % Tewooort of Lawne oebfie fem = the Lowest Granna- Thh heue wee dhcumd whh Sw stem and molved at t.m Fetwuery The staff concure with the BVWtOG comment and has 37 "The stoR conchsdes that enoufHctent tecfmicaljueWAcetion 9th mooting. In summary,me SWROG approach le to cattutete a mMifted the SER accordingly i g has been provided for assuring a ; , ' fractkm less tronoport factor as a percentage of the jgW detwte while the staff then 100% for large detwte generated below the lowest approach to to une e transport factor for transoortable detwto. The Regarding the evWtOG's second comment, regarding the drywatt grating." SWItOG notes that in the NRC Drywell Detwts Transport Study, the overen conservatism in the analysis methods in the URG, NRC Interpretuson of the AJIT test rer9 to that 40% of the NUMON see the staffs respones to BWROG comment no.1. Inoutellen wethen the 201 le in the hW V *canvessed detwto" which to not tronoportmus. Hence, the NRC postoon is that the maximum amount of debets which can be e _ , _.^. ^ to the suppreselon pool from the lower porWon of the drywon to 90% of the Inittelinsuleeon within the ZOt, a lower number than me corresponding 70% of the URG. This provkles further ovkfence that the recommended values in the URG support the avWtOG postuon that the overall .-. _^^.. . _ le sufRcloney c_ ._ _ t Page 36, Erosion from Unthrottled ECCS Flow *1f N does conunue The staff concern discusses the eroelon rate but does not conalder The staff concure with the BWetOG comment and has 38 for more then three hours, then the Neenese should the cm._:. _ position taken In the URG on the amount of revloed the SER accordentl y However, the staff takes gg decennene en appropriate frecean to aoeume. Eroelon of inouemeen matorted that would be esposed to erosion. Following the excepdon to the absolute language in the BWROG . NUMON was shown to be Inneer In the NRC teste, so scaling tweek, the fitwove detwie generated will be distributed over the comment WhNe it is unlikely in the stafre opinion that 25% of orgelon of NUMON can be performed sooty. SimWor containment and only a emell fraction will come to root wtthin striking or snore of the insulation detwts may land where it well be toseng could be conducted for other insulation types,If distance of spill fWwn the breelt A portson of that which does reelde in eroded by tweek flow,it cannot be said that the caly necessary, to elotermine en appropriate frecilon to assume the spIII area will be pushed askfe try the flowing water as It oplashes poestbie scenerlo is that "only a smaN fractior, wl.H come to _ l for erosion.* onto the drywell floor. Therefore, only a eman frecuon of the targe rest within strthing distance of splN from the break. A  ! fiber detwts is subjected to weeh down erosion. Despite this, the URG portion of that wHI be pushed aside by the flowing assumes that 29% of fitwous "large detwte" (La., not finee) is exposed wator_Therefore, only a small fraction of the large ffber i to the oroding effects of the spMI from the twealt The BWROG detwts le subjected to wash down erosion." In fact, AJIT beNoves that any concerne regertNng the effect of erosion over toegng and NRC testing showed that grodngs in the tweak portodo greater then 3 hours are more then offset Ipy the c1__ . :.; jet flow stream could filter and retain large detwts. For a assumption on the amount of insuleWon that adoptin0 the staff tweek in a vertically oriented pipe (such as a rectre line), position could result in addleonel operator bunions and would require then,It is possetdo to accumulate a significant amount of t a change to emergency opereeng procedures which woukt be detwee below the break. Inconsistent wtth their s,.

                                                                                                                                               ,                         2 deelget.

The WWROG e - _.C that erosion vehses conste*snt with those in . the URG (e.g.,8.26% for HUMON fiber,29% for MenK occj tse ' eccepted and that a ame dependent factor not be Introduced. L-13 l

_u __, q s _a__< ,,.s, - - - - - - - - - - - - - - - , - - ~ - - - - - - - - - - - . , - - - - , - - - - - , - ,- -,-----,-,-------------------~-----------------------------~-----------------m----- - - - - - - , ~ - - - - - - -

                                                                                                                                                                                                                                                                                                                                                                                                                                        ----------ww--------------- - - - - - -

Com. Draft . Draft SER 12:ue Description BWROG Response Proposed Staff Resolution No. SER Ref. The URG methodoiogy seawne 1oos nnes (nber) wNhtn 3 pipe See ster response to BWWtOG comment no.1. Smed on [ Page 38, New osser---vehwe No ded ser some - 39 "However, the sten teentNted that N values were obtained tNometere. Where test date wee Nndted for some metertele, the Sw ovensR conserwegem, me sten Rnds this accepte4de- e for severos housesons bened on a wry undted set of evWtoG used curve shapes that were coneestent wah materiale for emportmental date. Esemples are Temp-aset, K. wool and which several date points outsted. The volume everaged destruction i 5 some of the Rett. Therefore, the etse suggests that factor le not algnflicency effected by the curve shape. licensees with these ineutettone determine N.weluso se SpNous: Based on the overallc- ^^ - in the 201 methodology,the , BWWIOG r that the guhlence in the URG be accepted and Assume that en the insulation contained in 30 met me liconeses not be required to adopt the opproach suggested by 1. spherical region becemos destroyed into fines, the staff in the draft SER. and

2. Assume that root of the insuloson would be I destroyed such that local N.le equel to the lowoot N.wegue measumd in the exportments."

AN SUWt Mcmwen Intend to use es heed lose model provided by me The stow concurs. No change required < Page 42, WWROG Hud Lou Mohl N UnroNebb and IncomeleW- ' 40 Use of cookbook procedure may leed to erroneous heed eseected strainer vender which le specNIc to the reptocement strainer. ( gg loss c. - -. The staff does not beneve their provtous C-- ,, the leave le moot and furmor response le not provkled comment on this topic hee been resolved. The BWWIOG does note that liceneses shouh, be seneleve to the , leeues releod by me staff regarding heed lose correlatione and shouhl eseurs that,where appReeben, mese issues are adequateer addressed by the stralner vendor. veriosonin Fiber Donelty: NUKON Hber density se See roeponse to item 40. The WWWt0G eleo notes that mese, not No change required 41 Page 42, h2 **" "' (*"'*"'#3"**"**d"**I~'3 **"'"'#**"'"'*d'""***'*****""*"* i Nunn"nend sw s'WWto"G modet does not address which couhlleed to inconsistent resulte. Su emponu to hwn ao. No change required. Page 42, undted AssucebiNew of some: Appe r ing om swRoo had 42 loss predicnan modet to plant conditions that differ g3 markedly from tooted conditione couhllead to erroneous l heed loss prodletions. These IlmeteWonc should be cteerty stated. , F No change roquared.  ; Heed Lon asoder not Asencebw to Thica ese: The test see respone to tism 4o. 43 Page 43, were beoed onloor debrte losiings on . dato and c-. _ g4 the stralner surface. The ststre opinion is that the equeMon and me procedures are not oppNcalde to thick cor ibinetton ftbrousiporticulate tietwie beds. *As e result, the tAnff recommende that ^^- - - - utillas vendor specific test dote dee -- _ __ _ . the stralner heed lose for vertous debrie ios.Ings u, to erni miudir.g me .cenese s iimi., debris Boed." dato is neerer complete Su response to hun 40. No change required. i Page 43, Thin. bed Efhct "The ' 44 n F WM l suppormd by sufRclent _--.-__ analyWeel ltem $ reasoning to supportthe URG statomontthat he thin. bod [ { effectle not a concern for eNernate strainers. itle reasonstdo to state that medium brooks will not result kt large heed looses that are not bounded by large tweeks, but ' e-  : met no 'then. bed sanct' wee observed is incorrect." f

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L-14

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Com. Draft Draft SER issue Description BWROG Response Proposed Staff Resolution No. SER: Ref. Page 43, 1!!e Licensino Basis for Operator Actons: "in calculadng The BWROG concurs. No change requimd. 45 NPSH, itcensees should ensure that their calculadons are m6 cons;sterc Wth their licensing basis. For instance, typicany, no operator action is credited for the first to minutes during a postulated LOCA. Therefore, NPSH should be evaluated at runout flow until the plant licensing basis allows otherwise." Page 43, Temocrature cormeson is unece eeabn :e Reference at in From the discussions dudng the meenne on 244e,it was learned that The staff has clattfled the SER. 46 the URG (CD1 Memo 98-t3 Effect of Temperature on NPSH the staff postion is that the temperature correction .. 4'Q, is 7 Including Strainer Head Loss)is considered es en not oppilcable to RMI debrts beds. The BWROG concurs that R is not unaccepuble methodology by the staff for determining applicable to RMI beds but that the URG methodology is appilcable to minimum NPSH. The staff finds this methodology fiber beds. unacceptable because it incorrectfy assumes that head loss across the strainer wlit be governed by laminar flow." Page 41, Particulate Mass Not Accuratefv Accounted forin the See response to trem 40. No change required. 47 D"tsiennon ceiam l Item 5 Page Submit Anatysn for P*oe Senerstionmnde Ended The BWROG recommends that the staff revise this position and not The staff concurs and has revtsed the SER accordingfy. 48 ewown: vensen desiring to take cmdtt for amned mquim that neensus sutunn supparung snafysn for sp. uparam ES-3' separation of the broken ends due to pipe restraints or or single ended blowdown for staff review pdor to their use. Instead, laSt single ended blowdown should conduct supporting licensee should assure these analyses are evaliable for review during SentenC analyses and submit them for further review before tholt inspectiort. use." 49 L-15 l _ _ _ _ _ _ _ _ _ _ .}}