March 25th, 2011 – Probability of Containment Failure – NUREG/CR 6920 – 1150

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From: Richards. Stuart
To: Sheron. Brian
Cc: Gibson. Kathy; Case. Michael
Subject: NUREG/CR-6920
Date: Friday, March 25, 2011 5:54:21 PM


A quick look at NUREG/CR-6920 indicates the following preliminary information:

– The purpose of 6920 was to look at the impact of assumed degradation of the containment on the probability of containment failure. For instance, 6920 assumed cases
of 25% or 50% corrosion of various locations within the containment as part of the study.

The study looked at both PWRs and BWRs.

– 6920 used information from NUREG-1 150 as a starting point.

– NUREG-1 150 estimates about a 56% probability of early containment failure at Peach

Bottom (Mark I containment) from all scenarios, and about a 36% probability from a direct melt-through of the containment once the core has breached the RPV. These numbers are relatively consistent with the 6920 numbers. 6920 concluded that the corrosion scenarios don’t impact the numbers much because the probability is so dominated by the core melt through scenario.

– NUREG-1 150 lists station blackout as the dominant risk.

Note that the probability of a melt-through of containment assumes a breach of the RPV. I think it also assumes a fairly quick accident progression, so the fact that the Japanese event started two weeks ago may impact the probability of containment failure.

We can provide more info on Monday.


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