Dominion’s North Anna nuclear plant in Virginia shut down on Tuesday following a loss of offsite power as 10 other nuclear stations in Pennsylvania, New Jersey, North Carolina, and Michigan reported “unusual events” to the Nuclear Regulatory Commission (NRC) after a 5.8-magnitude temblor rattled the East Coast.
The quake’s epicenter was about 5 miles from the North Anna Power Station in Mineral, Va., according to the U.S. Geological Survey (USGS), prompting an automatic shutdown of its twin reactors minutes after the quake occurred at 1:51 p.m. EST.
The Surry Power Station, another Dominion facility in southeast Virginia, also felt the quake though “not as strongly,” Dominion said. Both units at that plant continue to operate safely. The earthquake also caused the company’s newest power station, the 580-MW gas-fired Bear Garden plant in Buckingham County, to shut down automatically.
PJM Interconnection, which coordinates the electric grid for 13 states and Washington, D.C., reported that the power grid was stable throughout the incident, but 2,700 MW of capacity were lost in Virginia. Total generation lost was 3,200 MW, including 500 MW at plants in Pennsylvania and Ohio, PJM spokesperson Ray Dotter told POWERnews on Wednesday. “Grid reliability was not affected.”
Offsite power was restored to North Anna later on Tuesday. As designed, four diesel generators supplied power to the power plant while offsite power was unavailable, but one of the four generators was later taken offline to repair a generator coolant leak. Dominion reported that a fifth generator at the station was activated to replace it until offsite power was restored. The faulty diesel generator has now been repaired.
Dominion, which declared an alert (the next to the lowest of the four NRC emergency classifications) said the reactors were shut down safely and no major damage has been reported to systems required to maintain the station in a safe condition. Inspections to the Lake Anna Dam have also shown it sustained no damage. Several aftershocks felt in the region that occurred later on Tuesday did not affect the station, the company said, though it continues to inspect the facility to ensure no resulting damage.
NRC staff, which also felt the temblor at the federal body’s headquarters in Maryland, continue to monitor unusual events declared at Peach Bottom and Three Mile Island 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. All these plants continue to operate while plant personnel examine their sites.
“Nuclear power plants are built to withstand environmental hazards, including earthquakes. Even those plants that are located outside of areas with extensive seismic activity are designed for safety in the event of such a natural disaster,” the NRC said in statement on Tuesday as anti-nuclear groups said the quake served as a warning on nuclear dangers. “The NRC requires that safety-significant structures, systems, and components be designed to take into account the most severe natural phenomena historically reported for the site and surrounding area.”
The Central Virginia quake hit the East Coast as the region braces for the impact of Hurricane Irene, a Category 3 storm with maximum sustained winds of 115 mph that is expected to hit Florida within the next few days and track eastward from South Carolina to New England.
The quake was the first large historical shock from that seismic zone since 1875 (even before the invention of effective seismographs), when a comparable, possibly smaller-intensity quake rocked the region, the USGS said. The region saw a 4.5-magnitude quake in December 2003, which also produced minor damage.
“Earthquakes in the central and eastern U.S., although less frequent than in the western U.S., are typically felt over a much broader region,” the agency said. “East of the Rockies, an earthquake can be felt over an area as much as ten times larger than a similar magnitude earthquake on the west coast. A magnitude 4.0 eastern U.S. earthquake typically can be felt at many places as far as 100 km (60 mi) from where it occurred, and it infrequently causes damage near its source. A magnitude 5.5 eastern U.S. earthquake usually can be felt as far as 500 km (300 mi) from where it occurred, and sometimes causes damage as far away as 40 km (25 mi).”
Sources: POWERnews, Dominion, NRC, USGS