Earthquake risk to reactors greater than thought

WASHINGTON – 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 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 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.

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.

The overall risk at a typical reactor among the 27 remains very slight. If the NRC’s numbers prove correct, that would mean no more than one core accident from an earthquake in about 30,000 years at the typical reactor among the 27 with increased risk.

But emails obtained in a more than 11,000-page records 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 off-site power to the North Anna plant in Mineral, Va., 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 percent 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.”