Despite being built to sustain more than the maximum expected shaking, last week’s earthquake may have exceeded the design parameters of the two nuclear reactors knocked offline.
That conclusion by Dominion Virginia Power and an independent government analysis prompted the Nuclear Regulatory Commission to send inspectors to the nuclear plant in Virginia.
The Dominion-operated North Anna Power Station 12 miles from the epicenter of the 5.8-magnitude quake in Louisa County temporarily lost power, but there was no significant damage to safety systems, according to the NRC. A low-level emergency was declared temporarily Tuesday after the incident.
The additional inspection should not be interpreted to mean the plant is less safe, the commission said Monday.
Nuclear power plants are built with margins of safety beyond the maximum expected shaking, and the damage detected so far at North Anna has been minimal.
Rep. Ed Markey, D-Mass., sent a letter last week to the NRC pressing the agency to determine whether the ground motion exceeded North Anna's design and to use the most up-to-date geological information to assess risks to nuclear power plants.
“There needs to be a seismic shift in the way in which these plants are protected from earthquakes or other natural disasters,” Markey said in a statement.
The agency is the midst of a review to determine whether some nuclear plants will need to take additional precautions to protect against earthquakes.
A task force convened after a March earthquake and tsunami in Japan caused the worst nuclear disaster since Chernobyl also recommended that the agency do a better job of assessing earthquake risks.
The NRC had already sent a seismic expert and a structural expert out to the facility, in addition to its inspector onsite.
The agency said Monday it would send additional technical experts from its headquarters in Rockville, Md., and its regional office in Atlanta.