March 21, 2011 – Probability of NPP Ground Motions Exceeding DB high as 6%

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From: Burnell, Scott
Sent: Monday, March 21• ;20.11 3:32 PM
To: Kammerer, Annie; Munson; Clifford
Cc: Bensi, Michelle
Subject: RE: FAQ questions posted – Corrections to Answer #12

So bug the boss!!! Please.


From: Kammerer, Annie
Sent: Monday, March 21,. 2011 3:31 PM
To:. Burnell, Scott; Munson, Clifford
Cc: Bensi, Michelle
Subject: RE: FAQ questions posted – Corrections to Answer #12

OK, with me, but Cliff is the boss….


From: Burnell, Scott — –i .
Sent: Monday, March 21, 2011 3:23 PM
To:- Munson, Clifford; Kammerer, Annie
Subject: RE:: FAQ questions posted – Corrections- to Answer# 12
Importance:, High

This version is acceptable???? We’d like to post the update today.
1) What is the likelihood of the design basis or “SSE” ground motions being exceeded over the life of a nuclear plant?

The ground motions that are used as seismic design bases. at US’nuclear plants are called the Safe Shutdown Earthquake ground motion (SSE). In the mid to late 1990s, the NRC staff reviewed the potential for ground motions: beyond the design basis as part of the Individual Plant Examination of External Events (WEEE).

From this review, the staff determined that seismic designs of operating nuclear plants in the US have adequatew. safety margins for withstanding earthquakes. Currently, the NRC is in the process of conducting GI- 199 to -again assess the resistance of US nuclear plants to earthquakes,

Based on NRC’s preliminary analyses to date, the mean probability of ground motions exceeding the SSE over the life of the plant for the plants in the Central and Eastern United States is less than about 1%. [SEE BELOW REFERENCE BEFORE EDITING]

It is important to remember that structures,. systems and components are required to have “adequate margin,” meaning: that they must continue be able withstand shaking levels that are above the plant’s design basis.


From: Munson, Clifford – 1Q-•,.
Sent: Monday, March 21, 2011 12:15 PM
To: Kammerer, Annie; Harrington, Holly
Cc: McIntyre, David; Brenner, Eliot; Hayden, Elizabeth; Ake, Jon; Burnell, Scott
Subject: FAQ questions posted – Corrections to Answer #12

My corrections to Answer #12

12) What is the likelihood of the design basis or “SSE” ground motions being exceeded over the life of a nuclear plant?

The ground motions that are used as seismic design’bases at US nuclear plants are called the Safe Shutdown.  Earthquake ground motion (SSE). In the mid to late 1990s, the NRC staff reviewed the potential for ground motions beyond the design basis as part of the Individual Plant Examination of External Events (IPEEE).

From this review, the staff determined that seismic designs of operating nuclear plants in the US have adequate safety margins! for withstanding earthquakes. Currently, the NRC is in the process of conducting GJ-199 to again assess the resistance of US nuclear plants to earthquakes.

Based on NRC’s prelminar analyses to date, the mean probability of ground motions exceedlgthe SSE  Overthe Life of the plant forthe planits IN the Central and Eastern United States is less than about 1% with values ranging from a low of 0.1% to a high of 6%

It is important to remember that structures, systems and components are required to have “adequate margin,” meaning that they must continue be able withstand shaking levels that are above the plant’s design basis.


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