ML20199F318

Forwards Request for Addl Info Re June 1992 Application for Design Certification of AP600 in Area of PRA Analysis for Shutdown Conditions

ML20199F318
Person / Time
Site:	05200003
Issue date:	12/18/1997
From:	Joseph Sebrosky NRC (Affiliation Not Assigned)
To:	Liparulo N WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP.
References
NUDOCS 9802030132
Download: ML20199F318 (5)

Text

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Decemberf18,1l99'//^

Mr. Nicholas J. Liparulo, Manager

- Nuclear Safety and Regulatory Analysis Nuclear and Advanced Technology Division Westinghouse Electric Corporation-P.O. Box 355 -

Pittsburgh, PA 15230 -

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SUBJECT:

REQUEST FOR ADDITIONAL INFORMATION 'RAl) REGARDING THE LEVEL 2 PROBASILISTIC RISK A83E88 MENT ANAu(SIS FOR SHUTDOWN CONDITIONS-

Dear Mr. Liparulo:

)

^

- As a result of its review of the June 19g2, application for design certification of the AP600, the -

staff has determined that it needs adCtional information. The subject RAls can be found in the -

enclosure to this letter L You have, requested that portions of the information submitted in the June 1992, application for design certification be e?empt from mandatory public disclosure, While the 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. The staff concludes that these follow on questions do not contain those

' portiona of the information for which exemption is sought = However, the staff will withhold this -

~ letter frora public disclosure for 30 calendar days from the date of this letter to allow Westing.

house the opportunity to verify the staff's conclusions, if, after that time, you do not request that all or portions of the inforraatica in the enc!osures be withheld from public disclosure in accor.

- dance with 10 CFR 2.790, this letter will be placed in the Nuclear Regulatory Commission Public-Document Room.

If you have any questions regarding this matter, you may contact me at (301) 415-1132.-

Sincerely, -

_3 original signed by:-

_ Joseph M. Sobrosky, Project Manager

, Standardization Project Directorate.

I Division of Reactor Program Management f

Office of Nuclear Reactor Regulation-

[_

Docket No.52-003

Enclosure:

As stated cc wlencl: See next page hh h{

DISTRIBUTION:

See next page DOCUMENT NAME: A:PRA LV2.SD

• See previousconcurrence 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 D:SCSB:DSSA l D:PDST:DRPM l l

NAME-JMSebrosky:rgM CBerlinger*

TRQuay TT DATE 12/O/97

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12/17/97 12/IV/97 OFFICIAL RECORD COPY 9902030132 971218 PDR ADOCK 05200003 A

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DISTRIBUTION:- Letter to Mr. Nicholas J.- Lloarulo. dated: December 18. 1997 _

• Docket File ? Enclosure to be held for 30 days

• PUBLIC POST R/F TQuay TKenyon

- WHuffman JSebrosky -

' DScaletti JNWilson ACRS (11)

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s Mr. Nicholas J. Liparulo Docket No. 52 003 Westinghousi 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 P.O. Box 355 Box 355 Pittsbutgh, PA 15230 Pittsburgh, PA 15230 Enc!ooure to be distributed to the following addressees ofter the result of the propr'etary evaluatien is received from Westinghouse:

Mr. Russ Bell Ms. Lynn Connor Senior Project Ms 4.pr, Programs DOC Search Associates Nuclear Energ / Institute Post Office Box 34 1776 i Street, NW Cabin John, MD 20818 Suite 300 Washington, DC 20006-3706 Mr Robert H. Buchholz GE Nuclear Energy Dr. Craig D. Sawyer, Manager 175 Curtner Avenue, MC 781 Advanced Reactor Programs San Jose, CA 95125 GE Nuclea Energy 175 Curtner Avenue, MC-754 Mr. Sterling Franks San Jose, CA 95125 U.S. Department of Energy NE50 Barton Z. Cowan, Esq.

19901 Germantown Road Eckert Seamans Cherin & Mellott Germantown, MD 20874 600 Grant Street 42nd Floor Pittsburgh, PA 15219 AP600 Certification Mr. Charles Thompson, Nuclear Engineer Mr. Frank A. Ross NE 50 U.S. Department of Energy, NE-42 19901 Germantown Road Office of LWR Safety and Technology Germantown, MD 2087A 19901 Germantown Road Germantown, MD 20874 Mr. Ed Rodwell, Manager PWR Design Cerbstion Electric Power Reaarrh Institute 3412 Hillview Avenue Palo Alto, CA 94303 l

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Additional Informution Needed Regarding Level 2 PRA Analysis for Shutdown Conditions 720.458F WEC needs to identify the operating mode assumed for each of the $ plant damage states or accident classes used in the level 2 analysis.

720.45gF In the level 2 analysis provided by letter dated September 17,1997, WL 1 Indicates that the split fractions assigned to the phenomena nodes of the shutdown CETs were based on the scalar values from the at power CETs for the corresponding accident classes. WEC needs to demonstrate that the at power split tractions are appropriate for shutdown conditions, and are not impacted by differences in plant conditions, system alignments, or system / component availability allowed by technical soecifications (TSs) at shutdown.

720.460F in the level 2 analysis provided by letter dated September 17,1997, WEC Indicates that the fault trees used to quantify the system nodes of the shutdown CETs were based on the fault tree linking results of the surge line flooding case.

WEC needs to identify the fault trees used to quantify each system top event (e.g., by providing tables similar to Table 361), and indicate how each fault tree was modified from the at power model to reflect changes in equipment / system availability permitted during modes 5 and 6. The response should justify that for each system related top event in each CET, the assumptions regarding equipment / system availability are consistent with the TSs or availability targets for the respective operating m' te. Assumptions regarding DAS, isolation valves, cavity flooding valves, and Igniters should be specifically addressed.

720.461F in the response to RAI 720.306, the probability of failure to achieve containment closure is.shown to be small and have insignificant impact on the estimated failure probability for containment Isolation. However, the underlying HEP analysis includes several assumptions that are either inconsistent with or not assured by ths AP600 TSs. Specifically:

It is assumed that each open penetration will be manned by 2 persons having a.

specific responsibility for closing the penetration. The means by which this assumption will be met (e.g. TS, administrative controls) should be provided b.

It is assumed that detailed written procedures for closing the openings wil! be developed and used. This should be identified as a COL action item In quantifying the HEP for failure to achieve containment closure, it is c.

assumed that the hatches / penetrations ce open at 28 hours3.240741e-4 days <br />0.00778 hours <br />4.62963e-5 weeks <br />1.0654e-5 months <br /> (when the time to coolant boiling is about 17 minutes). Consequently, actions to achieve containment closure are required (End assumed) to take place under harsh conditions following steam release to containment. TS 3.6.8 does not permit the subject penetrations to be open unless they are capable of being closed prior to steaming into the containment. Since the minimum closure time in Enclosure

2-the scenario (45 minutes, based on 15 minutes for decision making and 30 minutes for implementation) is longer than the time to steam release to the conta,nment, the situation which forms the basis for the HEP assessment would not be permitted. The HEP analysis should be updated to be consisterst with constraints of the T8s. The time between loss of RNS and the receipt of the alarm inside containment, and the time required fe,< the crew res,7onsible for closing the equipment hatch to exit ccatainmeni needs to be accounted for in the revised HEP analysis d.

the alarm which provides the cue in the staff manning the penetrations should be identified, and TSs for the alarm should be provided 720.462F Operation of stage 4 of ADS would significantly impact the time to steam release to the containment, and the likelihood of achieving containment closure. Please explain how operation (or failure) of 4th stage ADS should be accounted for in determining the time to steam release to containment under TS 3.6.8.

720.463F Footnote 3 to Table 54 7 Indicates that a separate fault tree was not constructed for containment isolation during loss of offsite power (LOOP) events since LOOP does not dominate the shutdown CDF. The response to RAI 720.306 Indicates that appreximately 20 percent of the shutdown CDF involves LOOP The revised surge line flooding analyses submitted by letter dated October 8, igg 7 indicates a somewhat lower contribution from LOOP in the base case, but LOOP dominatas tha focussed PRA shutdown CDF. Please discuss the impact that LOOP would have on containment isolation and containment closure capability, and justify why separate containment isolation fault trees or a bounding treatment of containment isolation is not needed for LOOP events, t

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