Dominion Virginia Power's plant lost off-site electrical power during the earthquake, prompting operators to use backup diesel generators and shut down its two reactors as a precautionary measure. The quake measured 5.8 on the Richter scale.
"The emergency diesel generators started as off-site power from the grid was lost," said Bonita Billingsley Harris, a spokeswoman for the utility.
Emergency backup power is necessary at nuclear plants to keep the reactors and spent fuel pools cool when off-site power is lost. It remained unclear when the company would restart the plant.
No damage was reported at North Anna, Harris said, where the quake was "not very strongly felt." But the plant declared an "alert," which the Nuclear Regulatory Commission defines as a situation where "events are in process or have occurred which involve an actual or potential substantial degradation in the level of safety of the plant."
None of the nation's 103 other nuclear power plants was directly affected by Tuesday's quake, and all continue to operate safely, the NRC reported.
"There are several [nuclear plants] that declared 'unusual events' out of caution when they felt the seismic activity," NRC spokesperson Beth Hayden told National Journal. The "notification of unusual event" is the lowest level of four emergency classifications designated by the NRC. The "alert," as declared at North Anna, is the second-lowest level.
Even so, the incident did not prevent Congress' leading skeptic of nuclear energy from issuing a Twitter post shortly after the quake. "Lessons to all nukes to check emerg[ency] power," said Rep. Edward Markey, D-Mass., in the Tweet.
Tuesday's earthquake comes less than six months after a massive magnitude-9.0 earthquake and subsequent tsunami in Japan led to a loss of power and eventually a triple meltdown at the Fukushima Daicchii nuclear plant. The Japanese government reported this week that radiation contamination from that disaster could leave areas within several miles of the plant uninhabitable for years.
In the United States, the NRC has been reviewing a variety of safety proposals that a commission safety panel developed following the disaster in Japan. On Friday, the NRC ordered its staff to prioritize the changes that should be implemented "without unnecessary delay."