Bad Circuit Card Forced Nuke Down

Monday, October 29, 2012 @ 09:10 AM gHale


Dominion Virginia Power will replace a faulty electronic circuit card that caused a reactor to shut down at its North Anna power station.

Unit 2 at the Louisa County plant tripped automatically shortly before 2 a.m. Wednesday.

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The circuit card failed, causing four valves to close, said Rick Zuercher, Dominion Virginia Power spokesman. The valves control the flow of steam in the turbine system. The unit sensed a problem and shut down automatically.

Zuercher said the reactor should be back on line soon.

Gerald McCoy, a Nuclear Regulatory Commission 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 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.

This was at least the fourth automatic shutdown in the last three years for Unit 2, which 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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