The Dominion (NYSE:D) North Anna 1 nuclear unit in Louisa County, Va., was forced offline unexpectedly on Feb. 26, according to an event report filed with the Nuclear Regulatory Commission (NRC).
The unit was operating at 95% generation when an “automatic reactor trip” occurred, according to the brief report that Dominion filed with NRC.
Unit 1 “automatically shut down Thursday afternoon after a regulating valve controlling the flow of water from the condenser to one of the steam generators closed unexpectedly. The water flow is part of the secondary system that converts water into steam to turn the electric turbine generator,” according to a Dominion summary.
Station personnel are evaluating what happened. The unit is expected to be returned to service soon, Dominion said.
The Unit 1 shutdown was not associated with a minor earthquake that was reported in Goochland County on the morning of Feb. 26. The tremor – which measured 2.5 on the Richter Scale by the U.S. Geological Survey – was not detected at North Anna and was too low to be picked up on the station’s seismic equipment.
“By comparison, the 5.8 magnitude earthquake that occurred on Aug. 23, 2011 about 10 miles from North Anna was 1,000 stronger than yesterday’s tremor in Goochland County,” Dominion said in a summary distributed to employees.
Operated by Dominion’s Virginia Electric Power subsidiary, the two units are pressurized water reactors (PWRs) and each unit has a capacity of roughly 950-MW, according to GenerationHub data.