One of the causes of the massive problems at Fukushima Daichi after the magnitude 9 earthquake earlier this year was loss of offsite power, which resulted in loss of cooling function and to partial meltdown of reactor fuel rods.
Yesterday afternoon, a magnitude 5.9 earthquake occurred in Virginia (which we felt in Ottawa) with its epicentre just 20 miles away from Dominion Virginia Power's North Anna nuclear power plant. As a result of the earthquake, the power plant lost offsite power from the grid. As happened at Fukushima Daiichi, emergency diesel backup generators fired up, but unlike Fukushima Daiichi, the plant wasn't hit by a subsequent tsunami. Still the plant's operators shut down (inserted control rods to stop the spontaneous nuclear reaction) the plant's two reactors as a precautionary measure. No damage was reported at North Anna, but it is not clear when the company would restart the plant. The plant declared an emergency, officially an "alert", the second level of emergency classification, according to Nuclear Regulatory Commission (NRC) guidelines.
According to the NRC several nuclear plants declared 'unusual events', the lowest level of emergency classification, when they sensed the seismic activity, but none of the US's other nuclear power plants were seriously affected by the earthquake.