ML20206S336

Summary of 980611-12 Open ACRS Thermal Hydraulic & Severe Accident Phenomena Subcommittee Meeting in Rockville,Md Re Continuance of Review of Results of W Test & Analysis Program in Support of AP600 Design Certification

ML20206S336
Person / Time
Site:	05200003
Issue date:	06/22/1998
From:	Advisory Committee on Reactor Safeguards
To:	Advisory Committee on Reactor Safeguards
References
ACRS-3114, NUDOCS 9905210100
Download: ML20206S336 (10)

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Date Issued: 6/22/98 T. S.

Kress - 7/8/98

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ADVISORY COMMITTEE ON REACTOR SAFEGUARDS THERMAL HYDRAULIC AND SEVERE ACCIDENT PHENOMENA SUBCOMMITTEE SUBCOMMITTEE MEETING MINUTES WESTINGHOUSE AP600 TEST AND ANALYSIS PROGRAM JUNE 11-12, 1998 ROCKVILLE, MARYLAND INTRODHETTON:

The ACRS Subcommittee on Thermal Hydraulic Phenomena held a meeting on June 11-12.

1998 with representatives of the Westinghouse Electric Corporation and the NRC Staff. The purpose of this meeting was for the Subcommittee to continue its review of the results of the Westinghouse test and analysis Program (TAP) being conducted in support of the AP600 design certification. During this meeting, the Subcommittee reviewed the issues and concerns pertaining to the AP600 Passive Containment Cooling (PCS) System that were cited in the Committee's February 19, 1998 interim report on the AP600 design certification review. The meeting was open to the public for a total time of 14 hours1.62037e-4 days <br />0.00389 hours <br />2.314815e-5 weeks <br />5.327e-6 months <br />, 22 minutes. Mr. P. Boehnert 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, June 11, 1998. recessed at 5:50 pm that day, reconvened at 8:30 am on June 12, 1998, and adjourned at 2:02 pm that day.

ATTFNDFF9 ACRR Momhpre/ACR9 Cnnsultant5:

T. Kress Chairman I. Catton, Consultant D. Fontana. Member V. Schrock. Consultant R. Seale. Member N. Zuber. Consultant P. Boehnert. DF0 3

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J. Woodcock J. Gresham W. Brown B. McIntyre p N 'il'n Princinal NRC sneakprt:

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E. Throm (NRR)

N. Lauben (RES)

J. Kudrick (NRR)

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2 6/11-12. 1998 There were 5-10 members of the public in attendance at 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 and NRC 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 sumarized below.

INTR 0ntirTORY PRFRFNTATTnNR - OPFN RFRRTON Chairman *< Cnmments 1

T. Kress. Subcommittee Chairman, convened the meeting at 8:30 am and introduced the Westinghouse representatives present to begin their presentations.

UFRTINI,HntlRF PRFEFNTATIONE l

Westinghouse provided presentations on the following items:

A top level overview of the licensing basis documents supporting the design basis accident analyses for the PCS and key results of the PCS scaling report Resolution for the following 10 issues that were cited in the ACRS February

19. 1998 Interim Report on the AP600 design certification review:

ISSUES IDENTIFIED IN ACRS FEBRUARY 19. 1998 LETTER PERTAINING TO WESTINGHOUSE TEST AND ANALYSIS PROGRAM:

J AP600 PASSIVE CONTAINMENT COOLING SYSTEMS 1)

Justification for Use of Incorrect Expression in Rate-of-Pressure-Change Equation (Equation 34. WCAP-14845. Revision 2).

2)

Justification for Inappropriate Cancellation of Partial Derivative Function to Arrive at Equation 34 3)

Re-evaluation of Derivation and Quantification of Scaling Pi Groups Resulting from Correction of Equation 34 r.

4)

Justification for Use of Well-Mixed Assumption in WG0THIC Code for Calculation of Containment Behavior 5)

Justification for Use of Steady-State Testing in LST to Validate Transient Heat Transfer Correlations in WG0THIC 6)

Justification for Normalization of Rate-of-Pressure Change Term in Equation 34 l

7)

Technical Basis for Treatment of Cooled Containment Boundary Laminar l

Sublayer in WG0THIC 8)

Validation Basis for Assuming Low Elevation for MSLB I

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3 6/11-12,1998 l

9)

Justification for Appropriate Margin in Calculated Peak Containment Pressure 10)

Quantification of Impact of Incorrect Addition and Removal of Mass and Energy During the LST on Usefulness of this Data for Validation of WG0THIC i

Westinghouse made presentations on the issues noted above. All presentations were made in open session.

j With regard to the scaling analysis. Westinghouse noted the following key points:

Due to the significant scaling distortions that exist, the large Scale Test (LST) facility is not used as an system-level representation of an AP600 pressure transient.

Steady-state LST data were used to validate mass and energy transport rate equations for the same, and this data, together with ranged boundary conditions and other SET data, were used to validate certain WG0THIC code models.

As a result of the limitations of the PCS test database noted above.

Westinghouse used a conservative evaluation model approach for the licensing i

of the PCS.

RilREOMMITTFF COMMFNTS AND CONEFRNR During discussions of the ~10 Questions' noted above, the Subcommittee noted the following comments and concerns:

Th' Subconrnittee indicated that Westinghouse needed to make a clear case to demonstrate that its code modeling is conservative. Dr. Catton opined th'at the containment will survive a design basis accident. The problem is that the case for ensuring that the 45 psig design limit will not be exceeded has not yet been made.

3 Professor Schrock raised the issue of the poor quality of the Westinghouse documentation and the lack of clear presentation of its test / analysis results for this matter.

Drs. Catton and Kress noted that Westinghouse has, in effect, rationalized poor modeling of the containment by use of conservatism. Westinghouse should have used a best-estimate approach. Dr. Zuber suggested that Westinghouse provide a listing of the conservatisms used and the impact of each conservative assumption on peak containment pressure; i.e., provide a sensitivity study.

(Note: B. McIntyre provided information relative to i

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4 6/11-12 l'998 3

sensitivity analyses performed by Westinghouse, which included peak pressure results for the nominal input case. Substantial margin in peak containment pressure is shown - Figures 1-2.)

ACR9 CON 9ttiTANT PRF9FNTATION ACRS Consultant Dr. N. Zuber made a brief presentation that focused on his concerns relative to the PCS. His key points were:

He is grateful that Westinghouse has finally acknowledged the limitations of the LST facility.

Based on the EH calculations, it is clear from the analyses performed by C.

Kampe of NRR. using the CONTAIN code, that all three heat removal mechanisms j

(absorption in containment interior, heat transfer through the containment shell, and, external water coverage) are required to prevent the design pressure from being exceeded.

I No transient data are available for validation of the (lumped parameter)

GOTHIC code. Lumped parameter codes cannot adequately model the dominant T/H processes that govern the internal pressure seen.

The central question becomes: how can Westinghouse demonstrate adequate containment integrity for the design basis accidents?

i NRC STAFF PRF9FNTATIONS Mr. N. Lauben (RES) provided the results of AP600 containment pressure analysis that he performed for a large-break LOCA case using the RELAP5/ MOD 3 code. An integrated model was used to allow a best-estimate calculation of the mass and energy flow rates between the RCS and containment. The results of the calculations (Figure 3) show a significant degree of margin exists before the peak containment pressure is exceeded. This is largely due to the use of a highly conservative mass and energy release assumed in the evaluation model case as calculated with the WG0THIC code.

Messrs. E. Throm (NRR) and L. Wulff (U Md.) discussed the results of NRR's review of 3

the acceptability of the AP600 PCS. Mr. Throm summarized the scope, content and results of NRR's review effort. In summary. NRR has concluded that the Westinghouse WGOTHIC code combined with the AP600 evaluation model methodology can be used to demonstrate that the AP600 PCS meets the requirements of the applicable General Design Criteria. and is acceptable.

Dr. L. Wulff (NRR Consultant) discussed his evaluation of the international containment testing database, with regard to the AP600 containment analyses.

In particular, he reviewed the results of applicable tests conducted at the German HDR test facility. Some of these tests were prototypic to the AP600 PCS as water was

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5 6/11-12. 1998 sprayed externally on the containment dome. The test results show that the external spray eliminates concerns with regard to stratification and results in efficient mixing of the internal containment atmosphere. Dr. Wulff also noted that the conservative mass and energy release assumed by Westinghouse in its EM analyses

" swamps" any other uncertainties relative to the calculation of peak containment pressure.

During the above presentations. Mr. Schrock requested the details associated with the mass and energy analysis used for input to the calculation of containment pressure response for the DBAs. Dr. Catton suggested that NRR incorporate the analysis performed by Mr. Lauben into its evaluation of the acceptability of the PCS.

)

RIIRC0te4TTTFF CAllCll9 The following points were noted during the Subcommittee's caucus:

Dr. Kress requested written reports from the Consultants.

l Dr. Catton noted that the evaluation model approach used by Westinghouse is truly conservative. in large part, due to the excess mass and energy assumed i.

for the release from the RCS. He said that Westinghouse doesn't address the l

stratification issue - but that phenomenon is overwhelmed by the other l

conservatisms. NRR's review of the HDR test results and Mr. Lauben's analysis l

shown today bring it all together for him on this matter.

Professor Schrock said he would reflect on the information provided before sending his report. He expressed concern with the focus on code results to the exclusion of test data as it resulted in a lot of nonproductive exchanges.

Finally, he asked that Westinghouse provide details of the assumptions used in its blowdown analysis.

I Dr. Zuber thanked Westinghouse for acknowledging the limitations of the LST facility with regard to a lack of adequate scaling. He questioned why Westinghouse did not. long ago, detail the conservatisms in its evaluation model approach. The conservative mass and energy input used for the peak l,

pressure calculation carries the day for this issue.

Dr. Zuber also asked to see the blowdown analysis details. He also asked if Mr. Lauben could provide an analysis of peak containment pressure for the i

AP600 for the case of a dry containment exterior (i.e., adiabatic cooling).

WF9TINCsH0llRF F01IOW-ON ACTTONS Westinghouse committed to providing the following material to the ACRS by June 26, 1998:

n T/H,rhen.,Sub. Mtg.

6 6/11-12, 1998 1.

Brief written replies to the ten ACRS issues cited in its February 19, 1998 AP600 Interim Letter, and discussed at this Meeting. The information requested by Professor Schrock relative to the mass and energy input to the containment calculations will be included in these replies.

2.

The conservatisms used in the PCS Evaluation Model will be documented and provided to the Subcommittee.

RACKGR0llND MATFRTAI PROVTOF0 TO THF E!!RriM4TTTFF PRIOR TO THIS MFFTING 1.

ACRS Letter to L. Joseph Callan. ED0 : " Interim Letter on the Safety Aspects of the Westinghouse Electric Company Application for Certification of the AP600 Plant Design". dated February D.1998.

2.

Memorandum dated February 27, 1998, transmitting page changes for WCAP-14807:

"NOTRUMP Final-Validation Report for AP600" Volumes 1 and 2. to update the WCAP to Revision 4.

3.

Memorandum, dated March 13. 1998, transmitting errata pages to WCAP-14807 Revision 4.

4.

Set of page changes to WCAP-14727: " Scaling and PIRT Closure Report". Volumes 1 and 2. to update the report to Revision 2.

5.

Memorandum, dated March 2.1998, transmitting additional material for incorporation into WCAP-14727. Revision 2.

6.

WCAP-14305. Revision 2: "AP600 Test Program ADS Phase B1 Test Analysis Report".

7 WCAP-14171. Revision 2: "WCOBRA/ TRAC Applicability to AP600 Large-Break Loss-of-Coolant Accident".

8.

Memo. B. McIntyre. Westinghouse, to R. Seale. ACRS. transmitting "Roadmap" 4

titled. " Westinghouse Response to ACRS Concerns" dated April 20, 1998.

l s-l 9.

Letter. Westinghouse Electric Company, to NRC. " Revised Response to FSER Open l

Item 440.796F. Part E. on the NOTRUMP Final Validation Report, dated April.28.

1998.

10.

WCAP-14305. Revision 3. "AP600 Test Program. ADS Phase B1 Test Analysis Report".

11.

WCOBRA/ TRAC OSU Long-Term Cooling Final Validation Report". WCAP-14776.

Revision 4.

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.6/11-12, 1998 12.

NRC Letter. T. Essig, NRR. to N. Liparulo, Westinghouse

• Documentation of Topical Report WCAP-12945(P). ' Westinghouse Code Qualification' Document for Best Estimate Loss of Coolant' Analysis.*(TAC No. M83964)" dated April 9, 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 I Street. Suite 300. Washington. D.C. 20005. (202).842-0034.

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10-2 Table 101 Nominal Inputs and Correlations Sensitivity Results

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LOCA GENSTITVII1ES Case Case Description Blowdown Post-Blowdown Pressure at Pressure Peak 24 Hours (psig)

Pressure (psig)

(Psig)

AP600 Evaluation Model 34.4 43.9 18.9 1

Heat & Mass Transfer 34.4 42.5 16.8 Multipliers on the Contamment Shell 2

Nommal Initial and Ambient 33 3 39.8 11.0 Conditions (plus case 1) 3 Nonunal Chme Material 33 3 39.0 10.4 Properties (plus Cases 1,2) 4 Nommal Steel-to-Concrete Gap 33 3 38.8 10.4 Thickness (plus Cases 1,2,3) 5 Nommal External Annulus Loss 33 3 38.7 10.2 Coefficients (plus Cases 1,2,3, 4) 6 Condensation on Dead-Ended 33 3 36.7 10.1 Compartment Heat Sinks Considered (plus Cases 1,2,3,4, 5) 7 Nommal Mass and Energy 32.4 30.6 9.2 Releases (plus Cases 1,2,3,4,5, 6) 1 Total Conservatism Represented 2.0 13.3 9.7 by Above Assumptions for j

LOCA Transient MSLB SENSITIVIIY Case Case Description Peak Pressure (psig)

Evaluation Model 44 8 s

8 Nommal Inputs and Correlations 39.9 with Conservative Mass and Energy Releases and Stratification Bias Conservatism Shown 4.9 l

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