VA Nuke Starts, then Shuts Down

Thursday, October 25, 2012 @ 04:10 PM gHale

Just one week after powering back up, Dominion Virginia Power is investigating what caused one of the two nuclear reactors at its North Anna power station to automatically shut down.

The shutdown came less than a week after the unit had been restarted following repairs.

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A preliminary report filed with the U.S. Nuclear Regulatory Commission (NRC) said Unit 2 at North Anna, in Louisa County, VA, 45 miles northwest of Richmond, tripped automatically at 1:47 a.m. Wednesday.

“The unit is in a normal post-trip electrical configuration. All systems functioned as required,” the NRC report said.

The commission’s report, filed one hour after the event, said Richmond-based Dominion was focusing on turbine intercept valves or reheat valves that malfunctioned “for reasons unknown at this time.”

North Anna’s Unit 1 did not suffer from the automatic Unit 2 shutdown and continues to operate at full power, the NRC said.

Dominion spokesman Richard Zuercher said the utility had been able to trace the shutdown of Unit 2, which is more than three decades old, to four valves that govern the flow of steam in the turbine system for spinning the unit’s generator.

“They inadvertently all closed, which caused the unit to sense the issue and shut down automatically,” Zuercher said.

Gerald McCoy, an NRC branch chief whose oversight area includes North Anna, said once the valves malfunctioned and the water levels dropped, Unit 2’s automatic shutdown system proceeded flawlessly.

“Everything worked on the plant protection system,” McCoy said.

The Unit 2 shutdown came a matter of days after the reactor had been restarted and brought back up to full power following two weeks of being offline for repairs to failing reactor coolant pump seals.

Dominion manually shut down Unit 2 on Oct. 7 after determining that a seal was degrading on a reactor coolant pump, and officials decided that while the unit was down, crews should go ahead and replace the seal package on another coolant pump as well.

The utility restarted Unit 2 last weekend, and NRC figures showed it was back at full power Monday morning.

McCoy said it was unlikely today’s shutdown related to the seal repair and replacement work.

“This is a totally different part of the plant,” McCoy said. “I’d be real surprised.”

This was at least the fourth automatic shutdown in the last three years for Unit 2, which originally went online in December 1980 and has a license to operate until 2040.

Lightning strikes spawned automatic shutdowns on May 28, 2010, and June 16, 2010, and an earthquake knocked both North Anna reactors offline on Aug. 23, 2011. They remained out of service until last November.

Having one of its four commercial nuclear reactors in Virginia offline can cost Dominion, the state’s largest electric utility, as much as $500,000 to $1 million a day for replacement power.

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