Aftershock prompts `unusual event’ declaration at North Anna

Yet another aftershock near Mineral in Louisa County prompted operators at North Anna Power Station to declare an unusual event just before 7 Monday. Like many others, the magnitude 3.2 aftershock of the Aug. 23 earthquake was widely reported by area residents. Dominion power says the aftershock didn’t affect operations or equipment, and that both units remain in operation under full power. A report to the Nuclear Regulatory Commission said newly installed Free Field Seismic Instrumentation equipment—designed to detect damaging ground motion—did not actuate. Ground motion from the Aug. 23 quake shut down North Anna’s two reactors—the first time that has happened in a U.S. plant. North Anna’s Units 1 and 2 remained idle after the magnitude 5.8 quake until last November, when they were restarted.

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