March 14th, 2011 – Drywell Failure Probability and Pedestal Melt-Through Given Wet Drywell

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From: Circle, Jeff
Sent: Monday, March 14, 2011 6:26 PM
To: Ward, Leonard InCX’Q
Subject: Containment Failure Values

Len,
Here are some values from the James A. Fitzpatrick IPE PRA (licensee updated):

Drywell failure probability with DW at > 30 psig, high H2 concentration and deflagration burn – 0.61.
Drywell failure probability with DW at > 30 psig, medium H2 concentration and deflagration burn-0.057
Drywell failure probability with high DW pressure, low RPV pressure – 0.016.
Pedestal melt-through given wet drywell and superheated debris 0.84
Some of these are related to the conditions at Fukushima – long term SBO, complete loss of decay heat removal, loss of injection and no containment venting. If they vent containment and not ignite hydrogen, the failure probability drops off significantly, For clarification, I will check this against the analysis in NUREG/CR-4550 on Wednesday morning.

Jeff.

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