ML20209E015

Apprises of Status of Probabilistic Safety Assessment Review Effort & of Decision to Terminate Review.Review Did Not Identify Any Safety Issues Which Merit Immediate Action

ML20209E015
Person / Time
Site:	Seabrook
Issue date:	02/27/1985
From:	Speis T Office of Nuclear Reactor Regulation
To:	Thompson H Office of Nuclear Reactor Regulation
Shared Package
ML20209C800	List: ML20209C798 ML20209C897 ML20209D266 ML20209D278 ML20209D286 ML20209D327 ML20209D479 ML20209D512 ML20209D547 ML20209D870 ML20209E015 ML20209E274 ML20211C165 ML20211C259 ML20211C363 ML20211C389 ML20211C430 ML20211C484 ML20211C558 ML20211C632 ML20211C641 ML20211C679 ML20211C769 ML20211C792 ML20211C841 ML20211C904 ML20211C920 ML20211C942 ML20211D042 ML20211D068 ML20211D076 ML20211D092 ML20211D109 ML20211D129 ML20211D140 ML20211D169 ML20211D178 ML20211D191 ML20211D198 ML20211D208 ML20211D226
References
FOIA-87-6 NUDOCS 8503110134
Download: ML20209E015 (3)

Text

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• mn a MEMORANDUM FOR: Hugh L. Thompson, Director Division of Licensing FROM: Themis P. Speis; Director Division of Safety Technology

SUBJECT:

SEABROOK PSA REVIEW

REFERENCES:

1. Memo from Speis to Eisenhut " Initial Review of the Seabrook Station Probabilistic Safety Assessment",

January ,30, 1985

2. Draft Review of the Seabrook Station Probabilistic Safety Assessment, Lawrence Livermore National Laboratories, Enclosure to Reference 1, January 30, 1985 The purpose of this memorandum is to apprise you of the status of the Seabrook PSA review effort and our decision to terminate this review. -

A summary and evaluation of the salient features of the draft review report _

from Lawrence Livermore Laborateries was provided to DL on 1/30/85, (Reference 1) along with the LLNL report (Reference 2) constituting the Phase I review of the Seabrook PRA.

Our review of the Seabrook PSA did not identify any safety issues which merit immediate action. The largest contributor, Station Blackout, comprising 4 of the top 22 accident sequences is; an issue currently being generically pursued as Unresolved Safety Issue A-44. Any recommendation for action addressing these sequences would be forthcoming through the resolution of this issue. Overall, the review did not identify a discrepancy or error which is estimated, at this point, to significantly change the quantitative results of the PSA. The areas of disagreement and questions are documented in the review report (Reference 2).

The review has been impeded by circumstances and problems in several areas.

This PSA was submitted to the NRC voluntarily by Public Service of New Hampshire during a period of severe financial problems surrounding the Fc A 8 7-ec6

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Contact:

3 Sarah Davis, RRAB .

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fEB27 y completion of the Seabrook plants and the stability of the applicant utility.

Since the PSA has not been tied to a specific licensing action, the applicant made the decision that they were not able to allot resources for the support of the review of this document. They did provide staff to

, conduct a plant visit in late August, but did not provide any further support in terms of supplying all documentation requested, timely answers to questions from our contractor and the staff, and, having severed their contract with their consultant who performed the PSA, could not provide an avenue for answers or documentation from the authors of the PSA. We

, acknowledge these decisions were not made in a spirit of non-cooperation >

but rather financial circumstances which outweighed their desire to provide support, but nonetheless seriously affected the< ability to provide a thorough and conclusive review.

From another source, the PSA itself, problems arose regarding the -

contractor's ability to perform a review which provided verification of the methods, assumptions, and results of the PSA. More importantly, the review was fragmented due to the structure and documentation of the PSA which resulted in the inability to assess the impact from areas of disagreement on the perception of plant safety, overall risk, and core melt frequency as reported in the PSA. - -

As stated in Reference 1, the Seabrook PSA estimate of overall core melt _

frequency is about 2 x 10 4/ reactor year. However, a very large number of sequences contributing to the overall core melt probability with the single most dominant sequence contributing less than 15% to the total and the top 22 sequences contribute approximately 50% to the total. The Seabrook PSA included consideration and quantification of 58 initiating events. These

! were collapsed to initiating event groups and the contribution to core melt

! frequency by these initiator groups. A rough aggregation of accident sequences with similar characteristics to better identify dominant contributors to core melt frequency was performed. Sequences initiated by Loss of Offsite Power overwhelmingly dominate core melt fr6quency followed by Fire-initiated and Small LOCA sequences with significantly smaller contributions.

Since neither the submittal nor the review of this PSA resulted from a requirement, and since issues meriting immediate attention or regulatory action have not been identified, and impediments still exist that seriously affect the ability to review this PSA, we are terminating the review at this I

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MEMORANDUM PS ;11 L

NH YA;YIE DIV.

March 6, 1985 To V. Nerses Date From R. E. Sweeney Group h SBB-85-133 Subject Seabrook Project PRA: y,g,3,9 Highest Ranking Accident In our meeting with Hugh Thompson Jr., he requested that we inform you of the lin.iting event based on our PRA. Per his request, herein we describe the highest ranking event sequence.

The highest ranking accident sequence with respect to core melt frequency was found to be a " station blackout" sequence initiated by loss of offiste power. This particular station blackout sequence includes failure of both onsite diesel generators to start or to run while the offsite power remains unavailable. To be able to progress to the point of core damage along this sequenge, it is further necess,ary to postulate failure to recover offsite or onsite power before the resultant loss of coolant inventory at the damaged reactor coolant pump seals leads to core uncovery.

The damage to the reactor coolant ppmp seas l is a dependent failure caused by the loss of seal water injection which cannot be maintai'ned without the primary component cooling water system. The PCC system is in turn dependent on AC power. The loss of the PCC system and AC power also results in dependent failure of the containment building sprays. Although the emergency feed-water system is postulated to successfully operate along this particular sequence, and, hence, decay heat removal by the steam generators is assumed to be available, the resultant core damage that is postulated occurs because of loss of coolant inventory.

I hope the above provides sufficient detail to satisfy Mr. Thompson's concern regarding our PPA. Please advise, shculd you have any additional concerns.

Thank you, rb Robert E. Sweeney Bethesda Cffice Manager Seabrook Project I

cc S. Davis (NRR/RRAB)

G. Knighton (NRR/DL) g_ h'[-Cd h K. Kiper D. Maidrand SBB-FILE g

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