The North Anna nuclear power plant in Louisa, Va., has restored its normal power supply after a 5.8-magnitude earthquake forced it to operate on back-up generators briefly Tuesday, but the plant remains offline as inspections continue.
Jim Norvelle, spokesman for plant operator Dominion Virginia Power, said Wednesday that the plant “will be shut down until it is safe to restart,” though he could not say when exactly that would be. Both reactors at the North Anna plant will be going into a cold shutdown this week, which changes the atmospheric conditions of the coolant system to make it safe for inspectors to walk through the containment structure and check for any quake damage.
The 36-year-old facility, which is located eight miles west of the quake’s epicenter in Mineral, Va., normally generates enough electricity for 450,000 homes. Dominion is meeting power demand in the area through its other stations and through energy purchase from the grid, Norvelle said, adding that the mild weather had lightened energy demand.
Four back-up diesel generators supplied power to the station when it lost power from the grid, and emergency cooling pumps were activated. One of the diesel generators had to be taken offline to repair a coolant leak, according to plant operator Dominion Power, but a fifth generator was brought on in its place.
Grid power was restored later in the day, and the plant downgraded its emergency status from Alert to Unusual Event on Wednesday before canceling it altogether.
The Mineral earthquake and the North Anna shutdown were a disturbing reminder that serious seismic risk for U.S. nuclear plants is not confined to the West Coast. Norvelle said that though there have been a number of smaller seismic events in the region that had been felt at North Anna, “this is the first time we’ve had an earthquake cause the units to trip offline.”
Notably, part of North Anna’s back-up generator plan was among the concerns pointed out by the Nuclear Regulatory Commission just three months ago, when the NRC conducted inspections of all U.S. nuclear plants in the wake of the disaster at Japan’s Fukushima Daiichi plant.
“The inspector determined that during a loss of power scenario there was no procedural guidance to obtain on-site diesel fuel from an underground tank located away from the plant protected area,” the post-Fukushima report said.
In addition, the report noted that one of the plant’s portable generators was not functional when tested, though that was not one of the large, non-portable diesel generators used on Tuesday.
Among other concerns related to seismic risk, inspectors found other small vulnerabilities at the plant, such as seismic floodwalls being located in a non-seismic building and certain safety equipment that was not designed to withstand an earthquake.
Joey Ledford, spokesman for the Nuclear Regulatory Commission, said that the lack of instructions for obtaining generator fuel at North Anna was one of “a number of minor issues” identified at the plant in May. But he called it a “low-priority issue,” saying that the plant had a seven-day supply of diesel fuel for its back-up generators. Likewise, Norvelle said that none of the issues identified by the NRC in May were a factor in Tuesday’s response, and that all safety operations went as expected.
Coincidentally, the Nuclear Regulatory Commission had scheduled for Wednesday the announcement of a new senior resident inspector for the North Anna plant. At least two resident inspectors are assigned to every U.S. nuclear plant, according to the NRC. Despite the timing of that release, the new inspector had been on site at North Anna for several weeks, and the announcement was unrelated to the earthquake, Ledford said.
Twelve other nuclear plants along the East Coast declared Unusual Event status Tuesday, the NRC’s lowest emergency classification. Those plants are operational and being monitored by their own personnel, the NRC said in a press release.