The Nuclear Regulatory Commission will soon require all 104 U.S. nuclear power plants reexamine their sites vulnerability to earthquakes.

While the matter is part of a years-long effort by the group to reexamine seismic hazards for plants in the eastern and central U.S., it faced renewed urgency amid the earthquake in Japan earlier this year and the one that shook Virginia last week.

A draft requirement for the plants was released Thursday for public comment, the same day Dominions (D) North Anna nuclear power station in Virginia felt a 3.4-magnitude aftershock.

The plant, which is coated about 40 miles northwest of Richmond, lost power and was temporarily shutdown following last weeks 5.8-magnitude earthquake, the biggest in Virginia in a century. Emergency diesel generators were used to maintain its cooling operations.

The stations foul reaction to the earthquake led to a preliminary investigation by the NRC that determined it might not have been built to sustain such a shaky disruption. The agency has formed a special group to look into the matter more deeply.

While no significant damage to the North Anna station has been identified, the site will remain closed until all risks are assessed and the company can demonstrate that no functional damage occurred to those features needed for its continued safe operation.

A trade group that represents nuclear plant owners, the Nuclear Energy Institute, said it would look over the NRC proposal and respond by Oct. 31, the public comment deadline.

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