North Anna closure might be a first

The earthquake-induced shutdown at the North Anna nuclear-power-generating station in Louisa County last week appears to be the first such occurrence among U.S. commercial power plants, the Nuclear Regulatory Commission said.

Federal and Dominion Virginia Power officials are concerned that the shaking from the Aug. 23 central Virginia earthquake may have been greater than the plant was designed for.

The utility said it is still planning for a proposed third nuclear unit at North Anna, which would be designed to resist more than four times the force that the first two reactors were built to handle.

An NRC augmented inspection team arrived at the North Anna nuclear-power station Tuesday to review the effects of last week's earthquake, the operators' response and the plant staff's activities to check equipment.

"Until we get more information about what the plant experienced, it's difficult to say what steps the NRC may require Dominion to take going forward," said NRC spokesman Roger Hannah in Atlanta.

The utility said Tuesday that it had completed about a fourth of the detailed inspections of the two plants and about a third of the related civil-engineering inspections of the power station's facilities.

"We didn't find anything significant," company spokesman Jim Norvelle said.

Damage, which he described as minor, includes a hairline crack in the cinderblock wall of a fuel storage building in the power station, and insulation falling off piping in the turbine building and off the refueling water storage tank, though no damage occurred to the tank, Norvelle said.

Neither Dominion Virginia Power nor NRC officials would speculate on how long the two 980-megawatt nuclear units would be out of service.

The utility said it plans to move up its planned refueling of North Anna 2, originally scheduled for late September. In the U.S. nuclear-power industry, refuelings average a month, the company said.

"We're not going to operate the plant in an unsafe mode," said David A. Christian, Dominion Resources Inc.'s executive vice president and CEO of its power generation business.

"I don't think this earthquake introduced any new considerations to cause us to think the North Anna plant can't continue to operate safely and offer low-cost electricity to our customers," Christian said.

Dominion Virginia Power is a subsidiary of Richmond-based Dominion Resources.

The two North Anna units were built to withstand an earthquake-induced shaking at the site of 0.12 times the force of gravity — or the approximate equivalent of a magnitude-6.2 event.

The Aug. 23 earthquake, centered about 11 miles from the plant, had a magnitude of 5.8, according to the U.S. Geological Survey.

Acceleration is a measure of how hard the earth shakes, and a g-force of 1 corresponds to the vertical acceleration force due to gravity. Roller coaster riders experience a g-force of 2 or more, and fighter pilots can handle accelerations of 8 g or more without passing out.

The largest earthquake forces measured are about 1 g to 2 g, according to the California Geological Survey. Most earthquakes have much lower forces, the California agency said, but those forces can still damage many structures.

The proposed North Anna 3 power reactor would be built to take a g-force acceleration of 0.535. The company could not say Tuesday what the approximate equivalent magnitude would be of the design-basis earthquake used for North Anna 3.

The current North Anna units were designed in the late 1960s and built in the 1970s.

"Since the original units were built, different predictive modeling tools for evaluating seismic activity have become available and Unit 3 was evaluated based on this new technology," Norvelle said.

The designs of the existing units remain sound because additional safety margin was built into them, Norvelle said.

North Anna is in what earthquake scientists describe as the central Virginia seismic zone.

Recent information suggests that the potential seismic hazard at some nuclear-power plants in the central and eastern U.S. may be greater than earlier estimates, the NRC said. However, the agency said in a May report, "all operating nuclear plants remain safe with no need for immediate action."

The NRC requires that nuclear-power plants be designed to take into account the most severe natural phenomena historically reported in a nuclear plant's area.

"North Anna had an earthquake at or near what it was designed for," said Dave Lochbaum, director of the Union of Concerned Scientists' nuclear-safety project in Chattanooga, Tenn., "and it shut down like it was designed for."

However, "They were lucky in that the earthquake wasn't worse than that," Lochbaum said. "The NRC should take steps to lessen that risk, rather than waiting for luck to run."

Plants can be retrofitted with systems to increase their ability to withstand the earthquake damage, officials said.