By Eileen O'Grady
HOUSTON (Reuters) - Dominion Resources workers were inspecting the North Anna nuclear power plant in Mineral, Virginia on Wednesday, a day after the largest earthquake to hit the U.S. East Coast in six decades knocked both reactors offline, the company said.
A series of plates that recorded Tuesday's 5.8 magnitude quake were sent to an outside company for analysis, a Dominion spokesman said.
"This is the first time a seismic event has shut down one of our power stations," said Dominion spokesman Jim Norvelle. "We are seeking a quick turnaround."
Dominion reported no "major" damage to the North Anna station which automatically shut when the earthquake disrupted the flow of outside power needed to operate the plant's many safety systems.
Diesel generators started up, as designed, to keep the reactors' radioactive cores cool until off-site power was restored about seven hours after the 2 p.m. EDT earthquake.
In addition to looking for possible quake damage at North Anna, federal nuclear regulators want to see seismic data from the site to determine if the quake was stronger than the plant was designed to withstand.
That will be critical in determining how long the 1,806-megawatt station will remain shut, officials said.
"In light of the quake's strength and proximity to the plant, the NRC will soon decide whether to conduct a follow-up inspection, aimed at determining how the quake compares to what the plant was designed to withstand," the NRC said in a statement.
The agency has not decided whether to send a special team of inspectors to the plant as it often does after emergencies or equipment failure, according to a release.
Norvelle said the North Anna reactors, which entered service in 1978 and 1980, were designed to withstand an earthquake of up to 6.2 in magnitude.
In the meantime, the NRC's resident inspectors are working with Dominion officials to inspect the station.
"There will be an extensive walk-down, including inside the containment (vessel) once both units are in cold-shutdown," said Joey Ledford, a spokesman for the Nuclear Regulatory Commission's regional office in Atlanta.
"They will go over this with a fine-tooth comb, with our resident inspectors beside them, to make sure there is no damage of any kind," Ledford said.
The company said several aftershocks were felt but had no impact on the plant, 80 miles southwest of Washington. North Anna canceled its emergency alert on Wednesday afternoon.
North Anna is unlikely to be affected by the approach of Hurricane Irene as it moves up the East Coast, NRC officials said.
Other nuclear stations, however, including Dominion's Surry plant in Virginia and Progress Energy's Brunswick Station on the North Carolina coast, are preparing for the storm, NRC officials said.
Owners of 12 other nuclear power plants that also felt Tuesday's quake, including Exelon Corp, Public Service Enterprise Group, American Electric Power Co,
Constellation Energy, PPL Corp; Entergy Corp and Progress Energy have canceled emergency event warnings after inspections for quake-related damage.
These plants were: Peach Bottom, Three Mile Island, Susquehanna and Limerick in Pennsylvania; Salem, Hope Creek and Oyster Creek in New Jersey, Calvert Cliffs in Maryland, Surry in Virginia, Shearon Harris in North Carolina and D.C. Cook and Palisades in Michigan.
(Additional reporting by Roberta Rampton in Washington; Editing by David Gregorio, Bernard Orr)