By DINA CAPPIELLO and JEFF DONN
Associated Press
WASHINGTON (AP) -- The risk that an earthquake would cause a severe accident at a U.S. nuclear plant is greater than previously thought, 24 times as high in one case, according to an AP analysis of preliminary government data. The nation's nuclear regulator believes a quarter of America's reactors may need modifications to make them safer.
The threat came into sharp focus last week, when shaking from the largest earthquake to hit Virginia in 117 years appeared to exceed what the North Anna nuclear power plant northwest of Richmond was built to sustain.
The two North Anna reactors are among 27 in the eastern and central U.S. that a preliminary Nuclear Regulatory Commission review has said may need upgrades. That's because those plants are more likely to get hit with an earthquake larger than the one their design was based on. Just how many nuclear power plants are more vulnerable won't be determined until all operators recalculate their own seismic risk based on new assessments by geologists, something the agency plans to request later this year. The NRC on Thursday issued a draft of that request for public comment.
The review, launched well before the East Coast quake and the Japan nuclear disaster in March, marks the first complete update to seismic risk in years for the nation's 104 existing reactors, despite research showing greater hazards.
The NRC and the industry say reactors are safe as they are, for now. The average risk to U.S. reactors of core damage from a quake remains low, at one accident every 500 years, according to the AP analysis of NRC data
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http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2011/09/01/MNLM1KV7P8.DTL
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