More Questions Than Answers As North Anna Restart To Take Days

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Tuesday’s earthquake apparently shook small protective devices at the North Anna Power Station enough to shut down the plant’s two nuclear reactors, officials said.

Dominion Virginia Power would not say exactly when it expects the reactors — representing nearly 13 percent of the state’s electric generating capacity — will start producing power again, but it will likely take days, the company said.

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Sequence of Events

1 – Relays are relatively small switches used to protect the electrical transformers from damaging overloads.  However, the relays’ opening interrupted electrical circuits carrying power from off the site to run the two reactors’ cooling systems. Loss of the power in turn tripped the reactors offline.

2 – Power to the reactors was off for about 10 seconds before backup diesel generators picked up the required electrical loads to run the reactors’ critical cooling systems, said Dan Stoddard, senior vice president of nuclear operations for Dominion.

3- Stoddard added that operators in the power station‘s control room were reaching for switches to manually shut down the reactors when the reactors automatically shut down.

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Earlier Wednesday, the company ended its alert condition, the second to least serious of the four Nuclear Regulatory Commission classifications, after starting a reactor cooling pump for each of the two North Anna nuclear units.

The 980-megawatt reactors were cooled by natural circulation and four diesel-powered emergency pumps while the reactor coolant pumps were not running.

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Questions

Why did it take more than 24 hours to restart the coolant pumps?

Why did they only start one pump for each reactor?

Tuesday’s earthquake apparently shook small protective devices at the North Anna Power Station enough to shut down the plant’s two nuclear reactors, officials said.

Is it possible that the “two small protective devices” were two reactor coolant pumps?

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