Washington: The risk that an earthquake would cause a severe accident at a US nuclear plant is greater than previously thought, 24 times as high in one case, according to an Associated Press 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 US that a preliminary Nuclear Regulatory Commission review has said may need upgrades. That is 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 will not be determined until all operators recalculate their own seismic risk based on new assessments by geologists, which the agency plans to request 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 nuclear disaster in Japan in March, marks the first complete update to seismic risk in years for the 104 existing reactors in the United States, despite research showing greater hazards.
The NRC and the industry say reactors are safe as they are, for now. But emails obtained in a more than 11,000-page records request by The Associated Press show that NRC experts were worried privately this year that plants needed stronger safeguards to account for the higher risk assessments.
The nuclear industry says last week's quake proved reactors are robust. When the rumbling knocked out offsite power to the North Anna plant in Mineral, Virginia, the reactors shut down and cooled successfully, and the plant's four locomotive-sized diesel generators turned on. The quake also shifted about two dozen spent fuel containers, but Dominion Virginia Power said Thursday that all were intact.
Still, based on the AP analysis of NRC data, the plant is 38 per cent more likely to suffer core damage from a rare, massive earthquake than it appeared in an analysis 20 years ago.
That increased risk is based on an even bigger earthquake than the one last week. Richard Zuercher, a spokesman for Dominion, the plant operator, says the earlier estimate "remains sound because additional safety margin was built into the design when the station was built."
The safety cushion would shrink, though, if the plant's risk were found to be greater.
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