Another nuclear 'incident'

Utility investigating vibrations that caused shutdown of nuclear reactor

Idled unit was being restarted when vibrations occurred

Times Despatch,

11 May, 2013

Dominion Virginia Power had a crew of about 20 working Friday to determine what caused the shutdown of its North Anna power facility’s Unit 2 nuclear reactor earlier in the day.

The unit was idled April 7 for a scheduled refueling.

The utility was in the process of restarting it, and the unit was at 60 percent power shortly after 6 a.m. Friday, when operators detected greater-than-normal vibrations in part of the mechanism used to start the reactor. They manually shut it down.

The excessive vibrations were detected in the exciter, which is used during start-up to initiate the flow of electricity from the generator to the grid. The exciter spins with the turbines and electric generator on one long shaft.

“By midafternoon our crews were able to get into the enclosure around the exciter to begin more detailed troubleshooting,” said Dominion Virginia Power 

spokesman Jim Norvelle. “This is a high-voltage area with exposed parts spinning at 1,800 rpm at the end of the turbine generator shaft. The team had to wait until the shaft stopped spinning.”

He said they were working to determine if the issue is a mechanical or an electrical problem.

Norvelle said the crew working on the unit is a mix of Dominion Virginia Power employees, contractors and technicians from Siemens, the equipment supplier. 

He said the crew members were on site for the refueling outage that ended Thursday when the unit had returned to service.

Norvelle said the U.S. Nuclear Regulatory Commission was notified of Friday’s shutdown.

Dominion Virginia Power does not give estimates of when nuclear power units will return to service, Norvelle said. Because of the mild weather, “there’s very little demand out there right now,” he said.

The North Anna nuclear power plant is along Lake Anna in Louisa County, about 45 miles northwest of Richmond. The plant’s Unit 1 is operating at full power, as are the utility’s other two nuclear reactors in Virginia, at the Surry nuclear station along the James River in Surry County.

Dominion said refueling outages, which are typically scheduled every 18 months, are planned this fall at North Anna Unit 1 and Surry Unit 1.

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