ML20029D670

Forwards LaSalle County Station IPE Submittal Rept, Per Generic Ltr 88-20

ML20029D670
Person / Time
Site:	LaSalle
Issue date:	04/28/1994
From:	Vonk M COMMONWEALTH EDISON CO.
To:	Russell W NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM), Office of Nuclear Reactor Regulation
Shared Package
ML20029D671	List: ML20029D670 ML20029D673
References
GL-88-20, NUDOCS 9405090227
Download: ML20029D670 (4)

Text

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' Comm*nwnith Edison

- 1400 Opus Place Downers Grove, Ilhnois 60515

. April 28,1994 Mr. William Russell, Director Of11ce of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, D.C. 20555 Attn: Document Control Desk

Subject:

LaSalle County Nuclear Power Station Individual Plant Examination and Individual Plant Examination (External Events) Submittal NRC Dockets 50-373 and 50-374 i

References:

(1) Generic Letter 88-20, Individual Plant Examination for Severe Accident Vulnerabilities, dated November 23, 1988.

(2) D.J. Chrzanowski to U.S. NRC letter dated September 15,1993.

(3) Analysis of the LaSalle Unit 2 Nuclear Power Plant:

Risk Methods Integration and Evaluation Program (RMIEP), NUREG/CR-4832, SAND 92-0537, ten volumes.

(4) Integrated Risk Assessment of the LaSalle Unit 2 Nuclear Power Plant: Ph,nomenology and Risk Uncertainty Evaluation Program (PRUEP),

NUREG/CR-5305, SAND 90-2765, three volumes.

Mr. Russell:

Enclosed are 5 ccpics of the LaSalle County Station Individual Plant Examination (IPE). The foundation of this submittal consists of the analysis l performed under the NRC's Risk Methods Integration and Evaluation Program {

(RMIEP) as published through 1993 and reflecting the LaSalle plant as of 1985. i This combined internal and external events IPE submittal is being provided as requested by the Reference (1) Generic Letter in a time frame identified in  ;

Reference (2).

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94o5090227 940428 PDR ADOCK 05000373 PDR

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Mr. W. Russell (2) April 28,1994 Commonwealth Edison (CECO) determined that no vulnerabilities regarding severe accident issues were indicated by the results of the RMIFsP analysis of LaSalle County Station Unit 2. The RMIEP results are well within the safety goals established by the Nuclear Regulatory Commission (NRC).

CECO believes the LaSalle RMIEP project was a very comprehensive PRA.

To assure that the objectives of Generic Letter 88-20 (Reference 1) were met for both internal and external events, CECO established an analysis team with many years of experience in plant operations and systems engineering as well as PRA experience. As discussed in the submittal, this LaSalle IPE submittal is the result

, of a detailed review of the RMIEP analysis for applicability to the accomplishment of the objectives of Generic Letter 88-20 (Reference 1).

During the performance of the RMIEP study, a " sneak circuit" in the reactor core isolation cooling (RCIC) system control circuitry was identified. This " sneak t circuit" could cause RCIC to be unavailable under certain plant conditions. The

( results of RMIEP, therefore, included the influence of this sneak circuit on the e risk profile of LaSalle. Subsequent to the RMIEP modeling, this problem was corrected. CECO has determined that this modification would reduce the internal events core damage frequency by approximately 21% from the value reported in RMIEP.

As a result of performing these reviews of the RMIEP analysis, CECO has attained a new level of understanding of the plant and its behavior under a variety of postulated accident scenarios. During this review process, numerous insights applicable to LaSalle County Station were obtained from the previous CECO BWR IPEs, IPEs of similar plants and directly from the RMIEP analysis.

These insights will be provided to the station for disposition.

The principal purpose of the LaSalle County Station RMIEP IPE/IPEEE was to develop an understanding of the severe accident behavio of LaSalle and of the severe accidents postulated by the analysis. It accomplished this purpose.

During its review, however, CECO identified several technical concerns with the RMIEP analysis process, including:

The RMIEP human reliability assessment results appear to be non-conservative.

. The " Beta factor" common cause analysis process is too conservative.

Considering main feedwater in medium and large loss of coolant accidents appears to be non-conservative.

Considering that the emc gency core cooling pumps would be made unavailable due to low net positive suction head is too conservative.

The data used in the RMIEP analysis was generic rather than plant specific.

The plant configuration represented in the RMIEP analysis was " frozen" in 1985.

The fire initiating event frequencies used in the RMIEP are very conservative.

Mr. W. Russell (3) April 28,1994

- Taken collectively, these technical concerns are expected to significantly impact the current set of dominant sequences. Therefore, CECO will limit the application of the RMEIP analysis to narrow scope probabilistic evaluations.

CECO is currently finalizing the project plan to perform an independent, comprehensive Level II internal events LaSalle PRA, which will provide an analysis of LaSalle that can be considered to be an update to the applicable portions of the RMIEP analyses. This " updated" LaSalle internal events PRA will be comparable to the other CECO IPEs. Upon its completion, CECO intends to periodically evaluate changes in equipment reliability, plant design and operation as part of a periodic review and update of this latter LaSalle PRA.

The RMIEP analysis only examined Unit 2 at the LaSalle County Station.

The units at LaSalle share the services of a swing diesel generator. Therefore, at least one dual unit initiator exists, Dual Unit Loss of Offsite Power, which would be considered in a complete " station PRA". In updating the PRA on LaSalle, CECO will perform a detailed examination for unit-to-unit system differences and other events that could potentially be simultaneous initiators in both units.

However, based upon the results of unit-to-unit system comparisons on it's other BWRs, similar units generally retain that similarity. Furthermore, similar units would be expected to display similar risk profiles for initiators that do not impact the units differently through shared (swing) components.

Plant modifications have occurred since the RMIEP models were developed in 1985 and the impact of these modifications on the RMIEP plant model has not been quantified. A top level review of these modifications was performed by CECO personnel and no modifications which would have a significant, adverse impact on the LaSalle County Station risk profile were identified. The detailed impact of these modifications on the plant models will be assessed in the future update of the LaSalle PRA analysis.

The LaSalle RMIEP IPE/IPEEE Submittal Report is contained in a single summary document. An Executive Summary and a comparison of the NUREG-1335 requirements to this submittal are attached separately for your convenience.

References (3) and (4) contain the complete results of the RMIEP analysis.

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1 Mr. W. Russell (4) April 28,1994 l

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. J To the best of my knowledge and belief, the statements in the attachment l contained herein are true and correct. These statements are not based on by personal knowledge but upon information furnished by other Commonwealth ,

Edison employees. Such information has been reviewed in accordance with Company practice and I believe it to be reliable.

Please direct any questions that you may have concerning this response to this office.

< OFFICIAL SEAL M ARY JO YACK Respectfully, h) NOT ARY PUBLIC ST ATE of ILUNOls 4 MY COMMISStoN f XP1R[S 11/29/97 w :::::::::::::::::::::::.

q A artin J. Vonk jVh Or % erL #>lf/ Generic Issues Administrator

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Nuclear Regulatory Services Attachments: 1) LaSalle RMIEP IPE Submittal Executive Summary

2) LaSalle RMIEP IPE Submittal Summary

3) Comparison of NUREG-1335 Requirements to the LaSalle County Station RMIEP IPE Report cc: J.B. Martin, Regional Administrator - RIII, w/ Attachment J. Dyer, Project Director III-2 NRR w/o Attachment A. Gody, Jr., LaSalle Project Manager, NRR, w/o Attachment l D. Hills, Senior Resident Inspector, LaSalle, w/o Attachment l l

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