ML20198A023
| ML20198A023 | |
| Person / Time | |
|---|---|
| Site: | 05200003 |
| Issue date: | 12/18/1997 |
| From: | Huffman W NRC (Affiliation Not Assigned) |
| To: | Liparulo N WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP. |
| References | |
| NUDOCS 9801050272 | |
| Download: ML20198A023 (5) | |
Text
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December 18, 1997 l
Mr. Nicholas J. Uparuto, Manager Nuclear Safety and Regulatory Analysis Nuclear and Advanced Technology Division Westinghouse Electric Corporation P.O. Box 355 Pittsburgh, PA 15230
SUBJECT:
OMEN ITEMS ASSOCLATED WITH THE AP600 SAFETY EVALUxTION REPORT (SER) ON THE APPLICABILITY OF WCOBRATTRAC FOR ANALYSES OF AP600 LARGE BREAK LOSS-OF COOLANT ACCIDENTS (LBLOCA)
Dear Mr. Liparuto:
The Reactor Systems Branch of the U.S. Nuclear Regulatory Commission has provided a draft SER input to the Standardization Project Directorate on the applicability of the WCOBRA/ TRAC computer code for analyses of LBLOCAs, GER Chapter 21. The input has open items which include code application and methodology restrictions. These open items have been extracted from the SER and designated as final safety evaluation report open iteins and are provided in the enclosure to this letter.
If you have any questions regarding this matter, you may contact me at (301) 4151141.
Sincerely, 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 gg gg
Enclosure:
As stated cc w/ encl: See next page
. plSTRIBUTION:
g(-0) i Docket File PDST R/F TQuay PUBLIC TKenyon WHuffman JSebrosky DScaletti JNWilson ACRS (11)
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g Llois,0 8 E23 RCaruso,0-8 E23 TColline,0-8 E23 SNewberry,0-8 E2 GHolahan,0-8 E2 DOCUMENT NAME: A:WCTLBLOCA.OI To receive a copy of this document, Indicate in the box: "C" = Copy without attachment / enclosure "E" = Copy with attachment / enclosure "N" = No copy OFFICE PM:PDST:DRPM BC:SRXB:DSSA N
D:PDST:DRPM l NAME WCHuffrha,0r '.g__
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12/17/97 12/t4 /97 OFFICIAL RECORD COPY l
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Mr. Nicholas J. Liparuto Docket No. 52 003 Westinghouse Electric Corporation AP600 cc.
Mr. B. A. McIntyre Mr. Russ Bell Advanced Plant Safety & Licensir.g Senior Project Manager, Programs Westinghouse Electric Corporation Nuclear Energy institute Energy Systems Business Unit 1776 i Street, NW P.O. Box 355 Suite 300 Pittsburgh, PA 15230 Washington, DC 20006 3706 Ms. Cindy L. Haag Ms. Lynn Connor Advanced Plant Safety & Licensing Doc Search Associates Westinghouse Electric Corporadon Post Office Box 34 Energy Systems Business Unit Cabin John, MD 20818 Box 355 Pittsburgh, PA 15230 Dr. Craig D. Sawyer, Manager Advanced Reactor Programs Mr. Sterting Franks GE Nuclear Energy U.S. Department of Energy 175 Curtner Avenue, MC-754 NE 50 San Jose, CA 95125 19901 Germantown Road Germantown, MD 20874 Mr. Robert H. Buchholz GE Nuclear Energy Mr. Frank A. Ross 175 Curtner Avenue, MC 781 U.S. Department of Energy, NE-42 San Jose, CA 95125 Office of LWR Safety and Technology 19901 Germantown Road Darton Z. Cowan, Esq.
Germantown, MD 20874 Eckert Seamans Cherin & Mellott 600 Grant Street 42nd Floor Mr. Charies Thompson, Nuclear Engineer Pittsburgh, PA 15219 AP600 Certification NE 50 Mr. Ed Rodwell, Manager 19901 Germantown Road PWR De*ign Certification Germantown, MD 20874 Electric Power Research Institute
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. c-OPEN ITEMS (INCLUDING CODE APPLICATION AND METHODOLOGY RESTRICTIONS)
ASSOCIATED WITH THE APPLICABILITY OF WCOBRA/ TRAC FOR ANALYSES OF AP600 LARGE BREAK LOSS-OF. COOLANT ACCIDENTS, FSER CHAPTER 21 440.738F The best estimate AP800 LDLOCA methodology submittal by Westinghouse was reviewed to.
determine its ss;": we with 10 CFR 50.46 and compatibility with NRC guidance in Regulatory Guide (RO) 1.157 and the Code Scaling, Applicability, and Unoortainty (CSAU) methodology.
l Based on the review of the information provided by Wes'inghouse in WCAP 14171 P and responses to NRC questions, the staff requests that restrictions on the methodology and l
application of WCCBRA/ TRAC to AP600 be clearty documented in both WCAP 14171 P and the i
AP600 SSAR.
The anolication restrictions irsalude:
Use of WCOBRA/ TRAC for analyzing the AP600 during long term cooling is being 1,.
addressed separately. AP600 use and application of WCOBRA/ TRAC, por the methodo -
logy documented in WCAP 14171 P, should tw restricted to the initial phase of the
- LBLOCA (i.e., the time at which the core is quenched).
l 2.
Application of the Westinghouse methodology and WCOBRA/ TRAC to small break LOCA was not considered in the staffs review and should not be permitted.
3.
Based on National Research Universal (NRU) reactor assessment results, there is some
, uncertainty in the transient rod intomal pressure (RIP) calculation that will effect the burst temperature criterion in WCOBRA/ TRAC analyses. The spproved methodology review found Westinghouse's uncertainty inethodology adequately accounts for the uncertainty in j
transient RIP for local effects. However, Westinghouse also calculates hot assembly (HA) rod burst in the full WCOBRATTRAC analyses called for in its methodology. In Westing-house letter to the NRC, " Docketing of Supplemental information Related to WCAP-12g45 P," NSA sal g6156, dated April 30, igw6, (List II, item 2), Westinghouse commit-ted that if WCOBRA/ TRAC calculates a HA rod reflood PCT greater than 1600'F but not i
rod burst, the initial RIP in the WCOBRA/ TRAC HA rod would be increased until burst is
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calculated and the moro limiting of the burst and non-burst cases would be chosen. This is needed to adequately account for transient RIP uncertainties and their effect on rod burst in the WCOBRA/ TRAC runs.
4.
In the Code Qualification Document (CQD), page 7 24, Westinghouse stated the fuel pellet thermal expansion model in MATPRO 11, Revision 1, used in WCOBRA/ TRAC was almplified by omitting the corrections for mixed oxide (Pu), in Westinghouse letter to the NRC, " Docketing of Supplemental Information Related to WCAP 12g45-P,"
NSA sal g6156, dated April 30,' igg 6, (List II, item 6), Westinghouse committed to -
resubmitting the relevant WCOBRA/ TRAC mMels for NRC review if the code will be used to analyze US licensed plants with mixed oxides. Westinghouse should formalize this commitment.
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2-l 5.
In the approved uncertainty methodology, a number of assumptions for distributions were supported using plant-specific data. In Westinghouse letter to the NRC, "Docke'ing of Supplemental in'ormation Related to WCAP 12945-P," NSA sal 96156, dated April 30, 1996, Attachment 5, and Westinghouse letter to the NRC," Docketing of Supplemental Information Related to WCAP 12945-P," NSA sal 96167, dated May 9,1993, Attach-monts 1 and 2, Westinghouse agreed to verify the following assumptions on a plant-specific basis; a.
The process used to accc unt for the response surface uncertainty assumes the data points are normally distriL ted, with constant variahca, around a straight line. The normality must be checked for each phase of the accident for each plant.
b.
HOTSPOT PCTs are normally distributed. This must be checked at each point where the HOTSPOT PCT is varied in a Monte Cario sample: the points used to build the response surface for the HOTSPOT standard deviation (c p) and the validation
- points, c.
Response surface for 0,p is accurate or conservative. This should be checked t,y comparing the response surface estimate with the Monte Carlo standard devidon at each validation point. The response surface method should not severely underesti-mate any standard deviation.
6.
The distributions corresponding to WCOBRA/ TRAC uncertainty based on experiments (ca) and the' uncertainty due to experimental data scatter (cy will be checked for normality if the code is modified or the assesstrent data base changes. See Westing-house letter to the NRC," Docketing of SupplementalInformation Related to WCAP-12945 P," NSA sal 96-156, dated April 30,1996, (List lli, item 2).
7.
Westinghouse letter to the NRC," Docketing of Supplementa:Information Related to WCAP 12945 P," NSA sal-96156, dated April 30,1996, (List 11, item 10 and Attach-ment 4), Westinghouse committed to use a multiplier to account for rod to rod radiation effects in the heat transfer multiplier data base.
8.
Westinghouse response in its letter to the NRC, "Open issues and Confirmatory items Related to the Review of WCAP 12945 P," NSA sal 96-028, dated January 26,1996, (Attachment 5), derived the expressions for the shear stress to the wall and to the vapor shown in CQD Eqns. 6-120 and 6121. Westinghouse concluded that the wall shear stress equr. tion used the incorrect friction factor. To assess the effect, Westinghouse reev.aluated FLECHT SEASET Test 31805 with a corrected version of WCOBRATTRAC.
There was little impact on the PCT, and the results from the corrected code version had slightly later quench times. Westinghouse concluded the effect was small, and the NRC agreed. Therefore, Westinghouse proposed that the error be tracked and corrected when other changes to the code are required. Westinghouse should formally document the commitment to make this change for the AP600 applications.
I
3-The methodoloov rectictions include:
9.
Approval of Westinghouse's methodology depends on the time step sizes used to show small mass and energy errors and used in PWR time step convergence studies (see Volume 4, question 50, Westinghouse letter to C. P. Fineman, INEL, NTD NSA-MYY 9515, dated May 12,1995). If the time step sizes used in the methodol-ogy change, Westinghouse should justify similar results are obtained with the new time step scheme.
10.
In Westinghouse letter to the NRC, ' Docketing of Supplemental Information Related to WCAP 12945-P." NSA sal 96156, dated April 30,1996, (Ust II, item 6), Westinghouse committed to not changing the value and range of the broken loop cold leg noz.zio loss coefficient for plant specific applications. Also, the values developed aply only to LBLOCA before core quench.
11.
If the 1 percent core wide oxidation limit is exceeded with the base methodology, Westing.
house committed in Westinghouse letter to the NRC, " Docketing of Supplemental Informa-tion Related to WCAP 12945-P," NSA sal 96156, dated April 30,1996, (List Ill, item 5), to identify, in the appropriate licensing submittal or the engineering report, whic.h of the options described in its response to Volume 2, question 62, (Westinghouse letter to the NRC," Docketing of SupplementalInformation Related to WCAP 12945 P,"
NSA sal 96-156, dated April 30,1996-Attachment 12), were used to bring the calculated core wide oxidation below the 1 percent limit by reducing the margin in the calculated results.
440.739F in the review of the approved methodology, Westinghouse provided a detailed evaluation of compensating errors in WCOBRA/ TRAC as applied to three and four loop plants. In generfJ, the staff considers that evaluation applicable to the AP600 analysis because of; (a) the si'ailarity of the AP600 and three-and four loop plant LBLOCA responses; (b) the AP600 specific assessments for DVI showed that WCOBRA/ TRAC gave conservative estimates of ECC bypass and core cooling; and (c) while AP600 has better blowdown cooling than three and four loop plants, the global model run matrix ranges the calculated blowdown PCT and cooling. However, Westinghouse needs to supply data and/or analysis to support the above arguments. Alter-nately, Westinghouse could clarify and justify how it addresses the issue of compensating errors in the AP600 LBLOCA best estimate methodology.
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