Radiation Alerts


September 3,


Cause of shutdown at North Anna nuclear plant sought - Post Earthquake Tour of Nuclear Power Station


Dominion Virginia Power officials are working to discover exactly what caused the North Anna nuclear reactors to trip off line in the Aug. 23 earthquake.

Knowing precisely what prompted the shutdown of the station's two 980-megawatt reactors is critical for validating the safety of the plant's design.

"We felt the shaking (in) the control room," said Unit 1 senior reactor operator Jason Russell, 30, of Henrico County. "I thought we may have ruptured a steam pipe in our turbine building."

Realizing that whatever was happening could affect the plant, Russell said, he immediately told his reactor operators to bring their reactor off line. "By the time the operators reached for the switches, the (automatic system) shutdown was already over."

Damage at the plant: cracks between concrete blocks in an administration building wall, a slight buckling in a corridor floor in that building, and damaged seals on some large electrical transformers.

Plant officials also said they found a horizontal crack in a non-safety-related wall of a room inside the Unit 1 reactor containment building.

The temblor also caused 25 of the 115-ton steel casks storing highly radioactive used nuclear-fuel rods to shift as much as 4½ inches out of position on their concrete storage pad.

Though the power company has not completed its analysis of the event, the earthquake apparently produced combinations of shaking forces larger than the plant was initially designed for, Stoddard said Friday.

North Anna's reactors remained out of service Friday as company officials continued detailed inspections of the station structures and systems. A Nuclear Regulatory Commission's augmented inspection team also is reviewing the effects of the earthquake. Stoddard said the final analysis is expected to be completed by the end of next week.

Utility officials had said earlier that electrical switches in the systems carrying power to the generating station had shaken open, signaling the reactors to trip. "We believe right now that was not the case," Stoddard said.

"There were multiple trip signals coming in," North Anna Site Vice President Larry Lane said. "We're talking about a difference of a second."

Source: www2.timesdispatch.com


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