The chief nuclear officer of Dominion (NYSE: D) on Oct. 21 told the U.S. Nuclear Regulatory Commission (NRC) that the 1,806 MW North Anna Power Station successfully withstood an earthquake without any significant damage because its robust design included multiple, designed-in safety margins.
David A. Heacock, president and chief nuclear officer of Dominion, said the lack of damage from the Aug. 23 earthquake clearly demonstrated that North Anna's seismic capability is greater than design basis of the station.
"The plant tells the story," Heacock said. "We have gone over North Anna very systematically – every safety system, structure and component – and found no safety-related functional damage. The seismic, thermal and mechanical stress margins designed in to all safety-related piping, equipment and structures made it more than able to withstand this earthquake. These margins, in effect, add up to form multiple layers of strength and safety."
Heacock told the NRC that both North Anna units are ready to restart and resume safe operation once the agency completes its independent review, analysis, and on-site inspections and grants permission. At the NRC's request, the company has agreed to perform additional seismic analysis on certain components after restart to quantify and further demonstrate they can meet specific seismic requirements.
Both units at North Anna shut down automatically at 1:51 p.m. on Aug. 23, 2011 when an earthquake struck Central Virginia. The epicenter was about 11 miles from the station and approximately four miles underground. Both units were at full power when the event occurred. Heacock said North Anna's designers anticipated significantly greater stresses on safety-related systems than occurred during the quake. While the station may have briefly experienced accelerations that exceeded seismic accelerations to which it was originally licensed, Dominion said its multiple layers of strength and safety provided a safety margin that was not exceeded.
Dominion said it has spent approximately $21 million on its inspection, testing and analysis program, including repairs, since the earthquake occurred.
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