ML20107K815

Forwards LaSalle County Station PRA Summary Document, Showing Plant Risk Profile Dominated by Listed Initiating Events

ML20107K815
Person / Time
Site:	LaSalle
Issue date:	04/18/1996
From:	Querio R COMMONWEALTH EDISON CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20107K819	List: ML20107K815 ML20107K828
References
GL-88-20, NUDOCS 9604290047
Download: ML20107K815 (2)

Text

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Commonwealth Edimn company laSalle Generating Station 2001 North list Road e' Marseilles, 11.61311-9757 Tel Hli-357 6 61 April 18,1996 United States Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555 l

Subject:

Transmittal of Summary Documentation - LaSalle County Station - Probabilistic Risk Assessment (PRA)

Update NRC Dockets 50-373 and 50-374

References:

1. LaSalle County Station Individual Plant

! Examination (IPE) Submittal Report, M.J. Vonk l to W. Russell,. dated April 28,1994.

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2. M.D. Lynch to D.L. Farrar, dated March 14,1996, providing Staff Evaluation Report of LaSalle County Station IPE Reference 1 provided the LaSalle County Station Indiviaual Plant )

Examination (IPE). In Reference 2, the NRC stated that it had completed its '

, review of the LaSalle IPE submittal for internal events and intemal flooding

! and concluded that Comed has " met the intent of GL 88-20." J Reference 1 also stated that Comed was starting an update to the internal events LaSalle PRA. This update has now been completed. Five (5) copies of the results oriented Summary Document for the Level l PRA update are  ;

enclosed for your information.

]

The Internal Events Core Damage Frequency (CDF) for LaSalle is 1.0E-05 per year (or once in 100,000 years). The enclosed document shows a LaSalle County Station risk profile dominated by a few Initiating Events, including:

1 Loss of Instrument Air, I

Dual and Single Unit Loss of Off-Site Power, and Transients with and without the condenser available.

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96'04570047 960410 PDR ADOCK 05000373 00 P PDR g

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l The IPE models have been significantly revised and updated to reflect the  !

LaSalle station design, operating procedures, and equipment reliability and availability as of May 1994.

In Reference 2, the staff noted that they had identified several weaknesses in the method for common cause and human reliability analysis used in other Comed IPE submittals. They recommended that Comed consider the technical concems pertaining to these two issues in the LaSalle IPE update, as appropriate. Comed has addressed these concerns:  !

The Human Reliability Analysis was completely redone for the PRA update using the EPRI cause based decision tree methodology (EPRI TR-100259) for the cognitive errors and a THERP based method for the execution errors. This reanalysis was performed under the tutelage and direction of an outside, industry recognized "HRA Expert" - Dr. Gareth W. Parry of NUS. The revised HRA is consistent with the reanalyzes performed for the Modified IPEs of other Comed plants.

The common cause treatment in the PRA update was based on the original RMIEP analysis - not the methodology employed in the other i Comed base IPEs. Changes to the RMIEP common cause treatment included the addition of some common cause basic events and the revision of some common cause failure (CCF) factors to more current values as documented in NUREG/CR-4780.

With the completion of this PRA update, LaSalle County Station can now ,

fully develop and implement key PRA applications as discussed in Section  !

Vill of the enclosed document.

If there are any further questions or comments conceming this letter, please refer them to me at (815) 357-6761, extension 3600.

Respectfully, ,

I y . Z& E^

R. E. Querio Site Vice President LaSalle County Station Enclosure cc: H. J. Miller, NRC Region 111 Administrator P. G. Brochman, NRC Senior Resident inspector - LaSalle D. M. Skay, Project Manager - NRR - LaSalle F. Niziotek, Office of Nuclear Facility Safety - IDNS Central File

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