ML20139A285

Forwards RAI Re PRA Review for AP600.Portions of Info Submitted in June 1992 Application for Design Certification Requested to Be Exempt from Public Disclosure.Staff Will Withhold Requested Info for 30 Calendar Days from Ltr Date

ML20139A285
Person / Time
Site:	05200003
Issue date:	03/17/1997
From:	Joseph Sebrosky NRC (Affiliation Not Assigned)
To:	Liparulo N WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP.
References
NUDOCS 9704250185
Download: ML20139A285 (5)

Text

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flarch 17, 1997

! Mr. Nicholas J. Liparulo, Manager l Nuclear Safety and Regulatory Analysis Nuclear and Advanced Technology Division Westinghouse Electric Corporation P.O. Box 355 Pittsburgh, PA 15230-

SUBJECT:

' FOLLOWON QUESTIONS REGARDING THE PROBABILISTIC RISK ASSESSMENT (PRA)

FOR'THE AP600'

Dear Mr. Liparulo:

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As a result of its r'eview of the June 1992 appitcation for design certifica-tion of the AP600,sthe staff-has. determined that it needs additional informa-tion. Specifically, the; enclosure to this' letter contains requests for '

additional 1.nformation concerning,the AP600 PRA.-

p You have requested that" portions' of; the iriformation s'ubmitted in the June 1992, appication for design certification be exempt from mandatory public disclosure. . While thet staff _ has not completed its review of your request in accordance with the requirements'of 10 CFR 2.790, that portion of the submitted information is being withheld from public disclosure pending the staff's final determination. lThe staff concludes that these followon ques- ,

tions do not contain those portions of the information for which exemption is sought. However, the staff will withhold this letter from public disclosure for 30 calendar days from the date of this letter to allow Westinghouse the opportunity to verify the staff's conclusions. If, after that time, you do not request that all or portions of the information in the enclosures be withheld from public disclosure in accordance with 10 CFR 2.790, this letter ,

will be placed in the Nuclear Regulatory Commission Public Document Room. 4 If you have any questions regarding this matter, you may contact me at (301) 415-1132.

Sincerely, original signed by:

Joseph M. Sebrosky, Project Manager Standardization Project Directorate Division of Reactor Program Management Office of Nuclear Reactor Regulation Docket No.52-003.

Enclosure:

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DATE 03/r2/97 // 03]t4 /9V 03/[1/97 '

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Mr. Nicholas J. Liparulo Docket No.52-003 Westinghouse Electric Corporation AP600 cc: Mr. B. A. McIntyre Ms. Cindy L. Haag Advanced Plant Safety & Licensing Advanced Plant Safety & Licensing Westinghouse Electric Corporation Westinghouse Electric Corporation Energy Systems Business Unit Energy Systems Business Unit 1 P.O. Box 355 Box 355  !

Pittsburgh, PA 15230 Pittsburgh, PA 15230 Mr. M. D. Beaumont Mr. S. M. Modro Nuclear and Advanced Technology Division Nuclear Systems Analysis Technologies Westinghouse Electric Corporation Lockheed Idaho Technologies Company One Montrose Metro Post Office Box 1625 11921 Rockville Pike Idaho Falls, ID 83415 Suite 350 Rockville, MD 20852 Enclosure to be distributed to the following addressees after the result of the proprietary evaluation is received from Westinghouse:

Mr. Ronald Simard, Director Ms. Lynn Connor Advanced Reactor Programs DOC-Search Associates Nuclear Energy Institute Post Office Box 34 1776 Eye Street, N.W. Cabin John, MD 20818 Suite 300 Washington, DC 20006-3706 Mr. Robert H. Buchholz GE Nuclear Energy Mr. James E. Quinn, Projects Manager 175 Curtner Avenue, MC-781 LMR and SBWR Programs San Jose, CA 95125 GE Nuclear Energy 175 Curtner Avenue, M/C 165 Mr. Sterling Franks San Jose, CA 95125 U.S. Department of Energy NE-50 Barton Z. Cowan, Esq. 19901 Germantown Road ,

Eckert Seamans Cherin & Mellott Germantown, MD 20874 600 Grant Street 42nd Floor Pittsburgh, PA 15219 Mr. Charles Thompson, Nuclear Engineer AP600 Certification Mr. Frank A. Ross NE-50 U.S. Department of Energy, NE-42 19901 Germantown Road Office of LWR Safety and Technology Germantown, MD 20874 19901 Germantown Road Germantown, MD 20874 Mr. Ed Rodwell, Manager PWR Design Certification Electric Power Research Institute 3412 Hillview Avenue Palo Alto, CA 94303 1

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DISTRIBUTION Letter to Mr.' Nicholas J. Linarulo. Dated: March 17. 1997

-* Docket File

• Enclosure to be held for 30 days

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• 1 AP600 PRA REVIEW 2

REQUEST FOR ADDITIONAL INFORMATION 1

RAI 720.384 and 720.385 are Related to DSER Open Item 19.1.3.1-2 720.384 The staff has asked Westinghouse (RAls #2808 and #3258 in 0ITS and I i

during the June 25, 1996, meeting) to explain how the contri- I butions of spurious ADS valve actuations to the various LOCA 1 i

initiating event frequencies were calculated. Westinghouse responded by (1) summarily describing a general approach for calculating the frequency of spurious actuation of ADS valves due to faults in I&C systems and (2) indicating that the requested l l information is provided in Chapters 3 and 26. However, the staff

are still unable to find in the PRA adequate documentation ex-plaining how the reported contributions to LOCA initiating event

frequencies (i.e., 1.8E-8/yr to the intermediate LOCA, 1.1E-8/yr l

to the medium LOCA and 5.4E-5/yr to the large LOCA) were derived.

• Please explain. Also, please list the reason (s) the frequency of

' spurious actuation (by PMS or DAS) of two stage #4 ADS squib valves (which according to the criteria reported in Table 3-2 of PRA contributes to a large LOCA) is much higher than the frequency of spurious actuation of only one stage #4 squib valve (which contributes to the medium LOCA initiating event frequency).

720.385 In addition to I&C faults, electrical faults (e.g., hot shorts in cables somewhere between a protection logic cabinet and the operator of a squib valve) can cause spurious operation of squib valves. EPRI's Utility Requirements Document (pages A.A-12 and A.A-19; Revision 5.6) recommends a spurious actuation failure rate for explosive (squib) valves of 4E-7/hr. Please explain why this failure mechanism was not considered in the AP600 PRA.

RAI Related to DSER Open Items 19.1.3.1-4 and 19.1.3.1-6 720.386 Westinghouse responded to the staff's m gnd follow-on RAls (720.329 and 720.330), regarding DSER Open Items 19.1.3.1-4 and  ;

19.1.3.1-6, by stating that post-24 hour risk is not significant without providing adequate supporting documentation. The staff had asked Westinghouse to identify accident sequences that require  :

long-term cooling, the actions needed to be performed by the l operators and the systems that must be available to per form these actions (including operational requirements).

Westinghouse states that risk associated with long-term cooling is

, not any different for AP600 than it is for operating reactors and that such risk has been addressed and accepted by the staff.

Westinghouse's argument, however, is not consistent with the staff's position as documented in NUREG-1242 (NRC Review of EPRI's ALWR Utility Requirements Document, Vol. 2, Pt. 1, pages 1A.2-4 Enclosure

i and 1A.2-5) or with the industry's position as documented in Section 2.10 (Revision 4) of EPRI's Utility Requirement Document (URD). EPRI's URD states that " mission time is only for calcula-tion of equipment unreliabilities: actions that must be taken beyond 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> (e.g., changes in system alignment or replenish-ment of water sources) shall be considered explicitly." In response to comments from the staff, EPRI supplemented Sec-tion 2.10 in Revision 4 to require that (1) actions that must be i taken beyond 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> be considered explicitly and (2) sensitivity of the results to selection of mission times be evaluated for systems that provide long-term core cooling and containment heat removal .

i For an appropriate response, Westinghouse will need to address l previous RAls related to long-term cooling by (1) identifying and I categorizing accident sequences which require long-term cooling, '

(2) assessing the frequency of each accident sequence category requiring long-term cooling (i.e., before long-term cooling failure probabilities are considered), (3) identifying and charac-terizing (for each of the accident sequence categories) the operator actions that need to be performed and the systems that must be available to perform these functions, and (4) identifying j insights and potential operational requirements. Long-term I cooling is an important part of PRA insights and should be ad-

, dressed in both the baseline and the focused PRA.

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