ML20129G980

Summary of 961015 Telcon W/Util to Discuss thermal-hydraulic Uncertainty RAI Responses.Questions on RAI Responses,Summary of W Responses & Update to Open Item Tracking Sys Based on Results of Telcon Encl

ML20129G980
Person / Time
Site:	05200003
Issue date:	10/28/1996
From:	Huffman W NRC (Affiliation Not Assigned)
To:	NRC (Affiliation Not Assigned)
References
NUDOCS 9610300301
Download: ML20129G980 (8)

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• October 28, 1996 APPLICANT: Westinghouse Electric Corporati'.

PROJECT: AP600

SUBJECT:

AP600 TELEPHONE CONFERENCE TO DISCUSS THERMAL-HYDRAULIC UNCER-TAINTY REQUEST FOR ADDITIONAL INFORMATION (RAI) RESPONSES The subject telecon was held on October 15, 1996, between representatives of Westinghouse Electric Corporation and the Nuclear Regulatory Commission (NRC) staff. The purpose of the teleconference was to address questions the staff had on RAI responses provided by Westinghouse letter NSD-NRC-96-4808, dated August 30, 1996. Attachment 1 is the list of individual participating in the telechone conference. .

Attachment 2 contains the questions the staff had on the RAI' responses.

Attachment 3 is a summary of the Westinghouse responses to these questions.'

Attachment 4 is an update to the open item tracking system based on the results of the telecon.

original signed by:

William C. Huffman, Project Manager Standardization Project Directorate Division of Reactor Program Management Office of Nuclear Reactor Regulation Docket No.52-003 Attachments: As stated cc w/ attachments:

See next page DISTRIBUTION w/ attachments:

Docket File PDST R/F TQuay PUBLIC DTJackson WHuffman TKenyon JSebrosky WDean, 0-17 G21 Alevin, 0-8 E23 TCollins, 0-8 E23 DISTRIBUTION w/o attachments:

FMiraglia/AThadani, 0-12 G18 RZimmerman, 0-12 G18 EJordan, T-4 D18 g ti DMatthews JMoore, 0-15 B18 g DOCUMENT NAME: A:10-15-TH. TLC (91 AP600 DISK) *E' = Copy with attachment / enclosure "N* = No copy T3 reenive a copy of thee doewnent, Indicate in the boa: "C* = Copy without attachment / enclosure 0FFICE PM:PDST:DRPM I SC:SRXB;B R D:PDST:DRPM l NAME WHuffman:sg M W Alevinl yf/ T TRQuay4 Wi DATE 10/.Td96 ~10/37/9 F ) 10/9y/96

/ OFFICIAL RECORD COPY 9610300301 961028 PDR ADOCK 05200003 A PDR

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Westinghouse Electric Corporation Docket No.52-003 cc: Mr. Nicholas J. Liparulo, Manager Mr. Frank A. Ross Nuclear Safety and Regulatory Analysis U.S. Department of Energy, NE-42 Nuclear and Advanced Technology Division Office of LWR Safety and Technology Westinghouse Electric Corporation 19901 Germantown Road i P.O. Box 355 Germantown, MD 20874 ,

i Pittsburgh, PA 15230 l Mr. Ronald Simard, Director Mr. B. A. McIntyre Advanced Reactor Program j Advanced Plant Safety & Licensing Nuclear Energy Institute i Westinghouse Electric Corporation 1776 Eye Street, N.W. I Energy Systems Business Unit Suite 300

, Box 355 Washington, DC 20006-3706 Pittsburgh, PA 15230 Ms. Lynn Connor Mr. John C. Butler Doc-Search Associates Advanced Plant Safety & Licensing Post Office Box 34 4

Westinghouse Electric Corporation Cabin John, MD 20818 Energy Systems Business Unit Box 355 Mr. James E. Quinn, Projects Manager Pittsburgh, PA 15230 LMR and SBWR Programs GE n, clear Energy Mr. M. D. Beaumont 175 Curtner Avenue, M/C 165 Nuclear and Advanced Technology Division San Jose, CA 95125

. Westinghouse Electric Corporation l One Montrose Metro Mr. Robert H. Buchholz I

11921 Rockville Pike GE Nuclear Energy Suite 350 175 Curtner Avenue, MC-781 l Rockville, MD 20852 San Jose, CA 95125 1

Mr. Sterling Franks Barton Z. Cowan, Esq.

i U.S. Department of Energy Eckert Seamans Cherin & Mellott NE-50 600 Grant Street 42nd Floor 19901 Germantown Road Pittsburgh, PA 15219 i Germantown, MD 20874 Mr. Ed R6 dwell, Manager Mr. S. M. Modro PWR Desig' Certification Nuclear Systems Analysis Technologies Electric fewer Research Institute Lockheed Idaho Technologies Company 3412 Hillview Avenue Post Office Box 1625 Palo Alto, CA 94303 Idaho Falls, ID 83415 Mr. Charles Thompson, Nuclear Engineer AP600 Certification NE-50 19901 Germantown Road Germantown, MD 20874

WESTINGHOUSE /NRC AP600 THERMAL-HYDRAULIC UNCERTAINTY RAI RESPONSE QUESTIONS l l TELECONFERENCE PARTICIPANTS OCTOBER 15, 1996 H&ME ORGANIZATION l Larry Hochreiter WESTINGHOUSE l Debra Ohkawa WESTINGHOUSE  ;

Cindy Haag WESTINGHOUSE l Alan Levin NRC Bill Huffman NRC J

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j Staff telecon questions on Westinghouse RAI responses provided by Westinghouse

letter NSD-NRC-96-4808- 1 1

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B81 492.15 Please provide a quantitative estimate of what Westinghouse

considers " ample margin" to the PCT limit as discussed in this response. l Regarding the response to how margins will be reflected in j the overall baseline PRA, Westinghouse has indicated that .

i scenarics which have less than 1 percent impact on the I j focused PRA will not be considered. Although this may be 4

justifiable for the focused PRA, scenarios that are less than 1 percent of the focused PRA frequencies are of the same order of magnitude as the baseline PRA and would appear i to potentially impact the baseline results. Please provide additional information on this.

492.21 The response to this question did not specifically address the staff's concerns. It is understood that during steam cooling conditions there is relatively little difference in the results if either " good" or " poor" heat transfer is assumed. The staff is more interested in the heat transfer during the transition from covered to uncovered and the return to covered. For those sequences in which the core uncovers but " damage" is not predicted because the core recovers before PCT exceeds whatever cutoff is established (to account for " adequate margin), the timing and modeling of the transition from nucleate boiling to steam cooling and vice-versa may have a significant effect on the predicted peak temperature. It is for this reason that it would appear that core heat transfer should be a high-importance phenomenon (it is tied to some extent to calculation of the two-phase level, as well). The transition of most interest is probably from uncovered to rewetted. It is assumed that dryout is modelled as essentially concurrent with reaching a void fraction of I at a particular level (though that may not actually be the physical case). However, depending on the rod surface temperature when the mixture level recovers,

" quenching" may well not coincide with the mixture level reaching a given elevation. If there is a delay between i

recovery and rewet, the calculation of film boiling heat i transfer and the transition to nucleate boiling is impor-tant.

492.23 The staff's question regarding this RAI response is how one differentiates between the importance of one source of ECC injection and another in terms of its PIRT ranking. West- l inghouse did not address this aspect in the response. i l

Attachment 2

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In addition, the response states that there "is no modelling consideration of whether RNS prevents ADS-4 actuation." It 1

" was the staff's understanding that if RNS was available in a '

baseline PRA LOCA event tree, it affected the consideration j of whether ADS-4 was needed--i.e., failure of ADS-4 would j not need to be considered in the event tree. Please provide additional information on the role of RNS in the baseline j PRA.

J i 492.24 The response to this RAI does not clarify how Westinghouse j- will treat the discharge coefficient for breaks that are

!. near or equal to the pipe diameter in question. Specifical- l

! ly, for full diameter breaks (or equivalent), how would '

l Westinghouse establish the break coefficient impact without l varying it explicitly. The staff has seen analysis results

from Westinghouse that appeared to indicate that relatively 1 i small changes in this parameter could cause significant

! changes in calculated peak temperatures (although it was not clear why that should have been the case). The RAI response j i does not provide a convincing argument that the break dis- '

! charge coefficient should not be an important parameter in j the PIRT. Westinghouse should be prepared to explain the i

values of discharge coefficients used in the T-H analyses  ;

j and why they are conservative. 1 l 492.25 Please provide some elaboration on this response. For in-  ;

i stance, if both NOTRUMP and MAAP show the same " trend" of  !

i decreasing core mixture level, but NOTRUMP uncovers and MAAP i i does not, is that "okay" or "not okay?" Further, the second l part of the answer seems in part to contradict the first, or at least, they do not appear entirely consistent. For the first paragraph, if differences in the trend are, in fact, caused by a "well-defined deficiency in MAAP4" does this ,

mean that the comparison is "okay?" (That's what the sen- 1 tence seems to say.) If there is a "well-defined deficiency l in MAAP4," wouldn't this be a case where (in para. 2) "phe-  !

nomena are encountered that are beyond the capability of '

MAAP4?" (i.e., doesn't a deficiency imply a situation beyond the capability of the code?)

492.30 The staff notes that one aspect of a SGTR that distinguishes it from a SBLOCA scenario is the potential for containment bypass. Westinghouse should address this difference when it prepares the pertinent documentation the discusses SGTRs and SBLOCAs

RAI# Subject October 15 Telecon Discussion 492.15 Provide a quantitative estimate of what Westinghouse " Ample margin" is based on expecting calculated PCTs to be in the range considers " ample margin" to the PCT limit as discussed of 1200* to 1800 F, which is below the temperature of significant zirc in this response oxidation.

Regarding the response to how margins will be reflected Wesunghouse will address the impact on the Baseline PRA, as well as the in the overall baseline PRA, Westinghouse has indicated Focused PRA, if the MAAP4 benchmarking identifies issues that switch that scenarios which have less than 1% impact on the scenarios from successful core coohng to failure. The reference to the focused PRA will not be considered. Although this may letter that discusses the T/H uncertainty resolution process is to indicate be justifiable for the focused PRA, scenarios that are less that that process is a subset of (it will " supplement") the assessment; the than 1% of the focused PRA frequencies are of the same T/H uncertainty resolution is not the entirety of the assessment mentioned order of magnitude as the basehne PRA and would in the RAI response.

appear to potentially impact the laseline results. Please provide additional inforination on this.

492.21 Why is the core heat transfer not ranked "high" or Discussion centered on the predicted PCT dependency on the two-phase "important" in the PIRT? 'the staff is more interested in mixture level. Westinghouse agreed to search through our existmg LOCA the heat transfer during the transition from covered to documentation to find support for position that the ranking of the two-uncovered and the return to covered. phase mixture level is sufficient, and the effect of the core heat transfer on PCF is small.

492.23 The staff's question regarding this RAI response is how The issue is why the CMT temperature is not ranked as high importance one differentiates between the importance of one source on the PIRT, while the IRWST temperature is. The CMT operates at high of ECC injection and another in terms of its PIRT enough pressures that the CMT water injecting will be significantly ranking. subcooled. By contrast, the IRWST injects at low pressures, and relatively small changes in the temperature can affect the subcooling. It was also noted that while CMT temperature is not identified as "high importance," it is identified as an area of "high interest" because it is unique to AP600. Therefore, CMT temperature is a parameter that will be examined in the benchmarking.

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L NRC's October 10,1996 Comments on MAAP4 and T/H Uncertainty RAI Responses RAI# Subject October 15 Telecon Discussion 492.23 (Cont) ne response states that there "is no malelling There is a difference between saying that RNS prevents ADS-4 actuanon  !

consideration of whether RNS prevents ADS-4 and whether ADS-4 actuation is needed for RNS. ADS-4 is not needed to actuation." It was the staff's understanding that if RNS lower the RCS pressure to achieve RNS injectum Therefore, ADS-4 is was available in a baseline PRA LOCA event tree, it not a decision point on event paths that have successful RNS. Questions affected the consideration of whether ADS-4 was that do not differentiate between successful core cooling and core damage  !

needed . are not asked on the event trees. It was also noted that if the ADS-4 question is not asked on an event tree, that does not mean that its actuation has been prevented; it only means that it was not credited.

i During the discussion, another issue on a potential adverse interaction was identified by the NRC. However, the issue has already been transmitted ,

via an RAI, and will be addressed through that pathway.

492.24 The RAI response does not provide a convincing The discussion started with Westinghouse re-iterating the position that argument that the break discharge coefficient should not analyzing a range of break sizes addresses the issue.

be an important parameter in the PIRT. Westinghouse  ;

should be prepared to explain the values of discharge The dialogne turned to a discussion of a broader issue of whether the r coefficients used in the T-H analyses and why they are uncertainties of all the high importance items in the PIRT are going to be conservative, sulatantiated as being bounded. It was agreed between Westinghouse and the NRC that we need further discussion on this broader issue.  !

492.25 ne questions are on the interpretation of trends in the Westinghouse and the NRC agreed that we will need to see the results of ctwnparison of MAAP4 and NOTRUMP, and what is the benchmarking to be sure that we agree on the interpretation of trends, meant by code deficiencies. and whether differences are significant. The NRC noted that the key to this issue is the last statement of the RAI response: "This will be judged based on whether wrong conclusions would be drawn if analysis results j were available from MAAP4 only."

492.30 The staff notes that one aspect of a SGTR that Westinghouse agrees with the comment, and wiu include this issue within j distinguishes it frtun a SBLOCA scenario is the potential documentation.

for contamment bypass.

i 4 OPEN ITEM TRACKING SYSTEM STATUS

RAI NUMBER NRC STATUS DESCRIPTION OF RERAINING ACTION 492.15 RESOLVED NONE 492.16 RESOLVED NONE 492.17 RESOLVED NONE

492.18 RESOLVED NONE i 492.19 RESOLVED NONE 492.20 RESOLVED NONE 492.21 ACTION W Westinghouse agreed to find additional support for its position on the PIRT ranking of two-phase mix-ture level and its affect on core heat transfer.

492.23 RESOLVLD NONE 492.24 ACTION U Westinghouse and the staff need to have further ACTION N discussions on how high importance items in the PIRT will be substantiated as bounded.

492.25 ACTION W Resolution pending results of MAAP4 benchmarking effort. 1 492.26 RESOLVED NONE 492.27 RESOLVED NONE l 492.28 RESOLVED NONE 492.29 RESOLVE 0 NONE 492.30 ACTION W Westinghouse to address the difference between l SBLOCAs and SGTRs in terms of the potential for containment bypass in the final T-H uncertainty i documentation.

492.31 RESOLVE 0 l

NONE l

492.32 RESOLVED NONE l

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