ML20206S661
| ML20206S661 | |
| Person / Time | |
|---|---|
| Issue date: | 01/11/1999 |
| From: | Advisory Committee on Reactor Safeguards |
| To: | Advisory Committee on Reactor Safeguards |
| References | |
| ACRS-3138, NUDOCS 9905210193 | |
| Download: ML20206S661 (11) | |
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UL RX CERTIFIED BY:
Date issued: 1/11/99 Graham B. Wa'lis - 1/25/99 ADVISORY COMMITTEE ON REACTOR SAFEGUARDS i
THERMAL HYDRAULIC PHENOMENA SUBCOMMITTEE MEETING MINUTES T/H CODE ACTIVITIES / NRC T/H RESEARCH STATUS DECEMBER 16-17,1998 ROCKVILLE, MARYLAND INTRODUCTION:
The ACRS Subcommittee on Thermal Hydraulic Phenomena held a meeting on December 15-16,1998, with representatives of the Westinghouse Electric Company
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(Westinghouse), the Electric Power Research Institute (EPRI), and the NRC Staff. The l
purpose of this meeting was for the Subcommittee to discuss: the application of the 3
Westinghouse Electric Company's WCOBRA/ TRAC best-estimate large-break LOCA code to Westinghouse plants with upper plenum injection (UPI); the NRC Thermal-Hydraulic Code Review Action Plan; the RETRAN-3D transient analysis code; and, the status of the NRC thermal-hydraulic research program. The entire meeting was open to the public. Mr. A. Singh was the cognizant ACRS staff engineer and Designated Federal Official for this meeting. There were no written comments or requests for time to make oral statements received from members of the public. The meeting was convened by the Subcommittee Chairman at 8:30 am, December 16,1998, recessed at 6:55 pm that day, reconvened at 8:30 am, December 17,1998 and adjourned at 3:30 pm that day.
ATTENDEES ACRS Members /ACRS Consultants:
G. Wallis, Chairman V. Schrock, Consultant T. Kress, Member N. Zuber, Consultant M. Fontana, Member A. Singh, DFO Westinghouse:
Electric Power Research Institute:
M. Nissley L.Agee S. Dederer M. Paulson (CSAI-Consultant)
K.Takeuchi J. Hoss o\\ '
r@ap\\
NRC Staff
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R. Caruso (NRR)
F. Eltawila (RES)
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R. Landry (NRR)
D. Ebert (RES)
DESIGNATED ORIGINAL N
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38 PDR Cmetified I!y
T/H Phen. Sub. Mtg. 12/16-17/98 Minutes J. Staudenmeier (NRR)
B. Gitnick (Scientech - Consultant)
N. Lauben (RES)
There were approximately 10-15 other members of the public in attendance during this meeting. A listing of those attendees who registered is available in the ACRS office files.
Public participation during this meeting was limited to the presentations by the above named industry representatives.
The presentation slides and handouts used during the meeting are attached to the Office Copy of these Minutes. The presentations to the Subcommittee are summarized below.
CHAIRMAN'S COMMENTS G. Wallis, Subcommittee Chairman, convened the meeting; he had no opening comments.
EXTENSION OF BEST-ESTIMATE LOCA METHODOLOGY TO PWRs WITH UPI Introductory Remarks Mr. M. Nissley, Westinghouse, introduced discussion on the application of the Westinghouse best-estimate (BE) large-break (LB) LOCA methodology to PWR plants which utilize UPl. This is an extension of the same LBLOCA methodology, previously approved for use on Westinghouse 3-and 4-loop plants, using the WCOBRA/ TRAC code.
For today's discussions, Westinghouse would focus on the changes made to WCOBRATTRAC to accommodate modeling of UPI versus cold-leg injection. The status of documentation supporting this work, as well as application of the Code Scaling, Applicability, and Uncertainty methodology to same was briefly reviewed.
Technical Presentations Representatives of Westinghouse provided presentations on the following topics:
- Description of UPI Plant Geometry
- Phenomena identification and Ranking Table Results for UPI Phenomena e Details of the WCOBRA/ TRAC UPI Code Physics
. Code Validation / Sensitivity of Consequences to UPI Model e Concluding Remarks
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T/H Phen. Sub. Mtg. 12/16-17/98 Minutes Westinghouse noted that use of UPI required additional, and more detailed, modeling to better evaluate the UP injection. The PIRT noted above, shows such UPI phenomena as entrainment/de-entrainment, phase separation and CCF draln/ fallback are ranked higher for UPI plants. The physical models for the key UPI phenomena were discussed, including the modeling of CCFL (counter current flow limit), and interfacial vapor condensation. Finally, results of the. code predictions to relevant test data (e.g., GE Subcooled CCFL tests, Cylindrical Core Test Facility UPI tests and UPTF tests) were discussed. Westinghouse showed conclusions that: the UPI BE methodology conforms to the Code Scaling, Applicability, and Uncertainty process, key phenomena unique to UPI do not impact the overall ECC results, and, the overall uncertainty methodology remains intact.
NRR Presentation Mr. F. Orr, NRR, discussed the status of NRR's review of the application of the Westinghouse BE LBLOCA methodology to UPI plants. The scope of review, key technical issues, schedule for completion of review and conclusions were noted. NRR has found the Westinghouse application acceptable and plans to issue a Safety Evaluation Report to this effect in February 1999.
Subcommittee Comments /Concems 1.
Mr. Schrock expressed concem that Westinghouse is using a split-break model, absent any verification by test data.
2.-
Westinghouse was unable to adequately explain the modeling detail shown for the flow of UPI water down into the low-power core channels.
3.
In response to questions from Dr. Zuber, Westinghouse noted that they had not exercised their CCFL model against test data that is prototypic of the UPI plant upper plenum geometrical configuration.
4.
Professor Schrock noted that the Westinghouse code calculation is showing evidence of hysteresis, which indicates a significant error in the coding.
5.
In response to Subcommittee questions, Mr. Orr (NRR) said that NRR required Westinghouse to range the key UPI models to ensure their adequacy.
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TM Phen. Sub. Mtg. 12/16-17/98 Minutes OVERVIEW OF RES THERMAL-HYDRAULIC RESEARCH ACTIVITIES Introduction 4
Mr. F. Eltawila, RES, provided an overview of the RES activities in the area of thermal-hydraulics. Issues discussed included: FY-99 resources, relationship of research to agency needs, goals, measures of success for the present program, TM Five-Year Plan, and accomplishments in past year. Key points noted included:
For FY-99 the TM program has lost $2M and 6 FTEs. This shortfall will result in e
schedule slippages. ACRS should comment on this loss of research capability in the area of thermal-hydraulics.
Applying risk-informed principles in regulatory matters will result in use of best-e estimate TM codes to assess safety margins.
RES is developing a T/H code for accident and transient analyses for operating e
LWRs and advanced passive reactors, with coupling to such codes as: 3-D reactor kinetics, containment, severe accident, fuel and computational fluid dynamics (CFD).
The Five Year Plan will focus on a rod bundle heat transfer program and e
development and verification of CFD models/ codes.
Work completed in the past year included coupling neutronic and TM code capability, program elements for code consolidation, progress on development of a graphical user interface (SNAP), and installation of new components in the TRAC-M code.
Technical Presentations Representatives of NRC-RES provided presentations on the following topics:
Development of Symbolic Nuclear Analysis Package (SNAP) Preprocessor for graphical user interface (GUI) capability Coupled thermal-hydraulic / 3D neutronic codes e
Code Consolidation Example: BWR Jet Pump Model e
Code Consolidation Example: Interfacial Drag Package o
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T/H Phen. Sub. Mtg. 12/16-17/98 Minutes These presentations focused on the work accomplished by RES over the last year related to the code consolidation effort. Specifically, the SNAP program involves development of a GUI for the RELAPS and TRAC-M (Modem) codes. The SNAP for RELAPS is undergoing beta testing; the TRAC-M SNAP is scheduled to be ready for beta testing at the end of FY-99. RES provided a demonstration of the SNAP GUI capability to the Subcommittee. Likewise, RES has coupled the 3D neutron kinetics code PARCS (Purdue Advanced Reactor Core Simulator) to both RELAP5 and TRAC-M. Finally, details of the code consolidation process were discussed and two example projects reviewed: (1) recovery of jet pump modeling capability in the TRAC-M code, and (2) modularization of TRAC-M via the interfacial drag model.
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Subcommittee Comments /Concems 1.
Dr. Wallis suggested that NRC take the lead in development of best-estimate T/H codes / analytical tools in order to spur their use by the industry.
2.
In response to Dr. Kress, Mr. Eltawila noted that NRR has not expressed support for such work as the coupling of the 3-D neutronic capability to the T/H codes. He indicated that the ACRS should comment on this matter, if the Committee sees a need for continued T/H research capability at NRC.
3.
In response from Dr. Zuber, Mr. Eltawila indicated that NRR has endorsed the use of the TRAC-M code, pursuant to RES's Code Consolidation Plan.
4.
Dr. Zuber said he would provide RES with references for relevant two-phase test data that can be applied to verification of the TRAC jet pump model.
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In response to comments from Dr. Wallis, Mr. Kelly noted that he has discovered many examples of undocumented features, errors, and deliberate modifications existing in the TRAC code. He said that this aques for a through validation of these codes. Mr. Kelly said he is documentiniall the code anomalies he discovers as well.
RETRAN-3D TRANSIENT ANALYSIS CODE Introduction Mr. L. Agee (EPRI) provided an overview of the RETRAN-3D code. Items discussed included background, code features and capabilities, summary of verification and
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validation and assessment activities, code applications, design review and conclusions.
RETRAN is based on the RELAP4 code, and 3D represents the third major version. The code is designed for analysis of Chapter 15 transients (excluding Appendix K LOCA m
T/H Phen. Sub. Mtg.
6-12/16-17/98 Minutes analysis) and plant events, as well as evaluation of evolving safety issues. EPRI maintains that the latest version of the code (3-D, MOD 2) has been extensively assessed via separate-and system-effects analyses. The code is compliant with the quality assurance standards of Appendix B to 10 CFR Part 50.
I Technical Presentation Details of the features and maintenance of RETRAN-3D were discussed by Mr. M.
Paulson (CSI, Inc.). Mr. Paulson detailed: the evolution of the RETRAN code versions, the features of RETRAN-3D - including the verification and assessment performed, the licensee / organizations planning to/using the code, and the maintenance activities (including the procedure for performing code maintenance (error correction, addition of code revisions, code testing, etc.)). Examples of the results of assessment analysis for modeling of PWRs were also discussed.
NRR Presentation Results of the NRR RETRAN-3D acceptance review were provided by Mr. R. Landry.
NRR, as part of its revised code review process, performed a review of the documentation submitted in support of the RETRAN-3D code review. Details of the review scope, i
content, and status were noted. NRR issued a letter of acceptance, dated December 4, 1998, stating that the staff finds the EPRI code documentation (NP-7450: "RETRAN-3D -
A Program for Transient Thermal-Hydraulic Analysis of Complex Fluid Flow Systems")
acceptable to permit formal review. Mr. Landry also noted that the current schedule milestones call for the next meeting of the T/H Phenomena Subcommittee to be held in March 1999 to continue review of this matter.
Subcommittee Comments / Concerns 1.
In response to Dr. Kress, Mr. Agee said that EPRI has not performed a formal assessment of the uncertainties associated with the code calculational results.
2.
Dr. Zuber observed that the drift flux model used in RETRAN cannot model the phenomena of CCFL for plate geometries.
3.
Mr. Schrock cautioned EPRI that its non-condensible model may not be adequate to model situations where upflow is the dominant phenomena.
4.
Dr. Zuber raised a concem with the slip models used in the code. Dr. Wallis indicated that the Subcommittee would pursue this matter during a future meeting.
Similarly, issues were raised regarding modeling thermodynamic nonequilibrium applications.
T/H Phon. Sub. Mtg. 12/16-17/98 Minutes 5.
In response to Subcommittee questions, EPRI noted that the "-3D" version of RETRAN was assessed against comparison calculations using the "-02" version of the code. This was done with the utility customers in mind, who already have a considerable investment in the "-02" code version.
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Dr. Wallis said that the Subcommittee's review of the "-3D" version of RETRAN will focus on the changes made to the code from the "-02" version, including the addition of new models/ correlations, and the associated verification / validation
. performed.
PEVELOPMENT OF THERMAL-HYDRAULIC CODE REVIEW GUIDANCE Summarv of Presentations Representatives of NRR provided presentations on the program underway to develop guidance to support the staffs review of thermal-hydraulic codes. The need for this guidance grew out of issues associated with the Lessons Learned from the Maine Yankee Independent Safety Assessment and concems expressed by the ACRS during its review of the Westinghouse AP600 Test and Analysis Program.
Mr J. Staudenmeier discussed the development of code guidance arising from the Maine Yankee IST and the specifics of the proposed Standard Review Plan (SRP) section. NRR noted that the IST identified problems with the adequacy of code documentation, asses'sment, and inconsistencies in the staffs code review process. To address this, the NRR staff is developing a SRP section as well as a Standard Format and Content Guide / Regulatory Gulve.' Details of the SRP content, scope, and organization were noted.
Mr. N. Lauben (RES) discussed the development of a proposed Standard Format and Content Guide / Regulatory Guide (RG) related to transient and accident analysis. Key points noted were:
The RG will address analysis methods for all Chapter 15 transients and accidents.
The concept of an " acceptable evaluation model" (EM) as cited in Appendix K of 10 CFR 50.46 will be applied.
I The EM development and assessment process should be PIRT based.
e EM validation by organizations other than those responsible for the plant-specific i
analysis will be carefully controlled.
T/H Phen. Sub. Mtg.
8-12/16-17/98
- Minutes Review of the draft SRP Section and proposed RG by the Subcommittee is proposed in July 1999.
Mr. R. Caruso discussed the specifics of the interim code review process, which is proceeding in tandem with development of the code review guidance. Mr. Caruso made the point that as a result of recent events, participation of the ACRS, the sensitivity of code reviewers to the need for improved documentation, etc., the reviews of new T/H codes (WCOBRA/ TRAC small-break LOCA, RETRAN, S-RELAP5) will not be compromised.
Subcommittee Cbmments and Concems 1.
In response to Dr. Zuber, NRR noted that all relevant T/H test data for code validation will be stored in-house by RES in a T/H code Data Bank.
2.
Dr. Wallis noted that NRR will need to decide on its standards for code review as part of the exercise in developing the review guidance.
3.
Drs. Wallis and Zuber advocated use of best-estimate codes combined with uncertainty evaluations for those parts of the analysis where data / correlations are lacking.
4.
Mr. Schrock urged the staff to consider inserting guidance that encourages use of peer-reviewed test data existing in the literature, rather than the current practice of relying largely on NRC-generated test data for code validation.
5.
In response to Dr. Zuber, NRR noted that they will be obtaining a functioning copy of the codes under review to check the code's fidelity.
6.
Regarding development of the proposed Regulatory Guide for generic transient and accident analysis methods, Dr. Wallis recommended that the language in the guide not be equivocal-in order to ensure meaningful compliance with the basic principles specified.
1 7.
In response to Dr. Kress, Mr. Lauben indicated that a set of Appendices would
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accompany the guide to address key phenomena, assessment, uncertainty, etc.,
unique to each class of events.
8.
Regarding the need to perform code sensitivity studies of anticipated operational occurrences, Dr. Kress indicated that the staff needs to determine what its objectives are here, and not necessarily rely on the industry's economic motivation to avoid such events.
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T/H Phon. Sub. Mtg. 12/16-17/98 Minutes Prior to adjoumment, Mr. Landry suggested that the next meeting of the Subcommittee to continue review of the RETRAN code be scheduled for late-March 1999.
SUBCOMMITTEE CAUCUS Westinghouse UPI Best-Estimate Methodology Dr. Zuber-Approves use of the BE methodology in general. However, in this case the Westinghouse presentation was not convincing given the lack of adequate modeling of the CCFL and condensation phenomena. Suggested use of a CCFL correlation verifed against test data.
Professor Schrock - The information presented at this meeting does not justify NRR's position that additional modeling is not needed for WCOBRA/ TRAC to successfully model the UPI plants.
j Dr. Kress - Agree with above comments. Doesn't believe that the argument was made for the spilt break being the limiting case. Suggest that Westinghouse perform calculations to test for the limiting case here by varying the exit temperature of the fluid, as well as perform similar calculations for the other breaks considered.
Dr. Fontana - Believes that Westinghouse has a viable case but needs to enhance its organization, presentation and documentation to demonstrate it conclusively.
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Dr. Wallis - A more convincing case needs to be made for this matter, if ACRS endorsement is sought.
RES Thermal-Hydraulic Research Activities Dr. Zuber-Work on the TRAC-M code is of high quality. Urge RES to make the code modular. Questions the need for additional experimental data on reflood.
Professor Schrock - Consolidation program appears excellent. Suggest that RES identify models/ correlations that need to be replaced or deleted in the TRAC-M code.
RES indicated that this work will be performed beginning next year, subsequent to completion of the consolidation effort.
Dr. Kress - Kudos to the staff-the code consolidation work represents one of the better 1
research programs. Raised the issue of ensuring adequate funding to see this work to completion. Dr. Zuber made the point that use of best-estimate codes is worth a lot of money to the nuclear industry.
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T/H Phen. Sub. Mtg. 12/16-17/98 Minutes Dr. Fontana - No comments Dr. Wallis - Information provided by RES will be helpful for the Committee's annual report to the Commission, now in preparation.
RETRAN-3D Transient Code The sense of the Subcommittee was that EPRI had made an excellent start in supporting the staff's review of this code.
Development of Thermal-Hydraulic Code Review Guidance Dr. Wallis commented that the development of T/H code review guidance is an excellent opportunity to make a significant improvement with regard to the future use of accident and transient codes.
BACKGROUND MATERIAL PROVIDED TO THE SUBCOMMITTEE PRIOR TO THIS MEETING Memorandum dated December 1,1998 from P. Boehnett, ACRS, to Thermal Hydraulic Phenomena Subcommittee including the following material:
e Letter from H. A. Stepp, Westinghouse Electric Co. to NRC,
Subject:
Comparison of Best-Estimate LOCA Methodologies for Westinghouse PWRs with Upper Plenum injection and Cold Leg injection, dated August 6,1998 (contains proprietary material) e Westinghouse topical report: Application of Best Estimate Large Break LOCA Methodology to Westinghouse PWRs with Upper Plenum injection, WCAP-14449-P, S.1. Dederer, et al., August 1995 (proprietary) e Letter to P. Boehnert, ACRS, from H. Stepp, Westinghouse,
Subject:
Information Regarding the December 10 Meeting with the ACRS Thermal-Hydraulic Phenomena Subcommittee, dated December 2,1998 Excerpts from Sections 3,4, and 5, of WCAP-12945-P-A: Code Qualification e
Document for Best-Estimate LOCA Analysis, S. Bajorek, et al., March 1998 e
Draft Technical Evaluation Report: Application of Best Estimate Large Break LOCA Methodology to Westinghouse PWRs Wdh Upper Plenum injection, INEEUEXT-98-00802, C.P. Fineman, September 1998
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T/H Phen. Sub. Mtg. 12/16-17/98 Minutes.
Information on NRC RES Thermal-Hydraulic Research Program: (1) Excerpt from e
NUREG-1635 Vol 1:" Review and Evaluation of the Nuclear Regulatory Commission Safety Research Program", on T/H Research Needs, dated June 1998, (2) Memorandum to T. Collins, NRR from F. Eltawila, RES,
Subject:
Some Perspectives on Thermal-Hydraulics, dated June 3,1998, (3) Note to P. Boehnert, ACRS, from F. Eltawila, RES,
Subject:
Progress on Code Consolidation Activities, dated November 2,1998 NOTE:
Additional details of this meeting can be obtained from a transcript of this meeting available in the NRC Public Document Room,2120 L Street, Washington, D.C. 20006, (202) 634-3274, or can be purchased from Ann Riley & Associates, LTD.,1250 l Street, Suite 300, Washington, D.C.
20005,(202) 842-0034.
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