The East Coast's magnitude-5.8 earthquake knocked out electric power for two nuclear reactors at the decades-old North Anna Power Station in Louisa, Va., about 14 miles from the temblor's epicenter.

Two pressurized water reactors at Dominion Resources' 1,806-megawatt North Anna plant lost power and automatically shut down this afternoon when the earthquake occurred and are now running on four emergency diesel generators, the Nuclear Regulatory Commission said.

The North Anna plant, about 40 miles northwest of Richmond, Va., sits along an earthquake fault, according to reporting in The Free Lance-Star in Fredericksburg, Va., earlier this year. Dominion told the newspaper that the plant was designed to withstand any quake known to have occurred in the seismic zone. The biggest earthquake ever recorded in Virginia was a magnitude-5.9 event in the southwest part of the state in 1897.

Today's earthquake may have damaged power lines leading into the North Anna plant or the electric switchyard near the reactors, but officials are still investigating what happened, said Roger Hannah, a spokesman for NRC. After the event, Dominion started up five diesel generators, but one malfunctioned due to a coolant leak, he said.

Dominion was not immediately available for comment this afternoon.

There does not appear to be any damage to the plant's safety structure, and the plant should be able to run for about seven days on the diesel generators, Hannah said. During that time, Dominion should be able to obtain more fuel or secure off-site power, he added.

NRC records indicate the North Anna plant is designed to withstand 0.12 Gs in an earthquake. They also indicate it has four hours of battery backup. Unit 1 began commercial operation in June 1978, and Unit 2 followed in December 1980. The plant's license was renewed in 2003.

The North Anna plant declared an "alert" after the event -- the second-highest of four NRC emergency classifications -- and 11 other plants in Pennsylvania, Maryland, Virginia and New Jersey declared an "unusual event," the lowest of the commission's classifications denoting something out of the ordinary.

The North Anna plant is one of 27 reactors in the eastern and central United States chosen to be first in an NRC analysis using cutting-edge technology and the most recent data to assess how well they can withstand earthquakes.

The modeling is expected to give clearer indications of the risks facing each of the plants, providing details on the ground shaking that plant operators can expect at any given site (Greenwire, May 18).

NRC is also stepping up safety reviews in the wake of Japan's nuclear disaster, which occurred after a magnitude-9 earthquake and tsunami struck the Fukushima Daiichi nuclear plant on the country's northeast coast. NRC inspections have since found deficiencies and gaps in compliance at the United States' 104 operating nuclear power plants.

Dominion officials are continuing with plans for a third reactor after the Fukushima earthquake, though the company has not made a final decision whether to build the third unit. A fourth nuclear generator, not in the permitting process, is also on the books for the future, according to NRC.

Reporter Mike Soraghan contributed.