Malfunction prompts 'unusual event' declaration at Sequoyah Nuclear Plant

photo The Sequoyah Nuclear Plant in Soddy-Daisy has the fourth-highest earthquake risk of the nation's 104 commercial nuclear plants, according to data from the U.S. Geological Survey analyzed by msnbc.com.
photo Ray Golden, manager of nuclear communications for the Tennessee Valley Authority

TVA and Nuclear Regulatory Commission officials likened the Sequoyah switchyard explosion Sunday morning to a giant fuse blowing.

The result was a loss of incoming power on one of eight massive power lines. The nuclear plant, which makes its own power, did not lose electricity and continued to operate safely, said TVA spokesman Ray Golden.

"There was a malfunction on what they call a power circuit breaker," Golden said. "It's like a circuit breaker in your home. It's a protective device, only it's protecting much higher voltages -- 161,000 volts."

Golden said TVA, because of regulations, had to declare "an unusual event" to the NRC shortly after 8:30 a.m. Sunday. The utility was able to cancel that declaration just before 10:20 a.m.

There were no injuries as a result of the malfunction. Both units continued to operate at full power.

NRC spokesman Joey Ledford said the mishap was "just an example of a mechanical problem."

"Such reports are not uncommon. We'll take a look at what they find is the root cause," Ledford said.

Golden said the damage will keep the affected electrical line out of use until a new power circuit breaker is installed, probably by week's end.

Unlike the outside power loss last year at Brown's Ferry when tornadoes decimated hundreds of TVA power-transmission towers, the Sequoyah incident did not cause the plant to go into automatic shutdown and require diesel generator power for reactor cooling.

In the Sequoyah event, alternate transmission lines remained in working order, so nuclear safety-related equipment was not required or affected, Golden said.

He said about 10 gallons of mineral oil was discharged from a power circuit breaker during the event. The oil, used to cool the internal electrical equipment in the circuit breaker, was contained in the plant's switchyard and is being cleaned up.

Contact staff writer Pam Sohn at 423-757-6346 or psohn@timesfreepress.com.

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