ML030840378

E-mail from s Long to D Marksberry, Frequency of Exceeding 2500 Psig at DB

ML030840378
Person / Time
Site:	Davis Besse
Issue date:	08/12/2002
From:	Long S Office of Nuclear Reactor Regulation
To:	Marksberry D Office of Nuclear Regulatory Research
References
FOIA/PA-2003-0018
Download: ML030840378 (1)

Text

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- excee in >2SOOpsig of exceeding a DB psig at age From: Steven Long U'A P To: Don Marksberry Date: 8/12102 5:04PM

Subject:

Re: Frequency of exceeding >2500psig at DB Don, Well, that's ceratainly less than 1E-5/year!

But, I'm not so sure it's a good estimate for LOFW ATWS Especially for a B&W plant, the ICS may make the conditional probability of LOFW given an ATWS a bigger contributor than the frequency of LOFW combined with the random probability of an ATWS. At least, it's a second path you haven't estimated Steve

>>> Don Marksberry 08/12/02 03:53PM >>>

Steve, The updated frequency of total loss of main feedwater with failure of RPS (i.e., ATWS) is as follows:

Frequency of total loss of main feedwater at Davis Besse (8.OE-2/critical year)(0.79 critical year/calendar year) = 6.3E-2/calendar year From NUREG/CR-5750, Tables G-10 and H-3 Probability of RPS failure = 1.6E-6/demand From NUREG/CR-5500, Vol 11, Reliability Study: Babcock & Wilcox Reactor Procection System, 1984-1998, Table 3-4.

The frequency of total loss of main feedwater with failure of RPS (6.3E-2/calendar year)(1.6E-6) = 1 E-7/calendar year