ML20137Y693

Discusses Efforts Concerning Plant Core Melt Frequency estimate.PRA-type Study Indicates Plant Core Melt Frequency Presently Approx 1.2x10-3/yr.Recommendation Re Restart Will Be Made Prior to 851211

ML20137Y693
Person / Time
Site:	Byron
Issue date:	12/05/1985
From:	Thompson H Office of Nuclear Reactor Regulation
To:	Harold Denton Office of Nuclear Reactor Regulation
Shared Package
ML20137Y697	List: ML20137Y693 ML20138G421 ML20138G429
References
NUDOCS 8512110119
Download: ML20137Y693 (1)

Text

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! *"**s m 5 1995 l NOTE TO: Harold R. Denton, Director, NRR-i e

FROM: Hugh L. Thompson, Jr, Director l Division of PWR Licensing-A, NRR .

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SUBJECT:

CORE MELT FREQUENCY ESTIMATE FOR BYRON 1

, ~ In his note to you dated December 2,1985, Themis Speis stated that recent review of a Byron PRA-type study indicates the Byron I core melt frequency is presently about 1.2x10-3/yr. The staff and Brookhaven National Laboratory (BNL) met with the Commonwealth Edison (CECO) and Westinghouse on December 3 1985, and there were several conference calls on the following day, to discuss this matter. As a result, the following efforts are currently underway:

1. BNL reanalysis - It was learned that the modeling of the cooling tower fans was not in accordance with operating reality. . This modification, plus several others, are being made and BNL is re-running the model to compute a new core melt frequency. The

results should be available by Friday, December 6.

I

2. Induced seal LOCA - Westinghouse and BNL assumed that the

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probability for an induced reactor coolant pump seal LOCA, given loss of seal cooling, is 0.5. Westinghouse now claims that recent

, testing done in France should justify a lower probability.

3. Interim owration - The Unit 2 essential service water (ESW) pumps will not ,>e fully operable for several months. CECO is investigating various modes of operating in the interim until the

,- Unit 2 pumps are fully operable. These include leaving both Unit 1 pumps running continuously, not allowing maintenance of either pump, or making a Unit 2 pump available, though not fully operational, to l pump water if the emergency need arises. BNL is assessing the  !

effect of these various options on the core melt frequency.

__f .v.y.,-, l All these issues will be discussed at a meeting with CECO and Westinghouse I

n scheduled for Friday, December 60 Byron - -

- Fi Wednesday, December 11,' unless we issue an(order to not restart.is The plant schedule to restart i

currently meets all our rules and regulations. I will make a reconnendation regarding. restart prior to December 11, 1985.

.r.

Hu L. Thompson J., irector -

Di ion of PWR Li ens ng-A, NRR ,

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