Dec 13 - The Tribune (San Luis Obispo, Calif.)

A loud explosion and an electrical fire in an ocean water circulation pump at Diablo Canyon nuclear power plant Tuesday afternoon caused an emergency shutdown of one of the plant's two reactors.

No one was injured in the incident, no radiation was released and the public was not required to react to an emergency. Pacific Gas and Electric Co. officials have launched an investigation.

An electrical fault was listed as the cause of the fire. PG&E officials are expected to announce this morning when the reactor will be restarted, plant spokeswoman Sharon Gavin said.

The accident came two days after the same reactor was shut down because a faulty sensor incorrectly indicated that a water circulation pump in a different part of the plant was operating improperly.

"It's been a bad couple of days," Gavin said.

Until the investigation is complete, the utility will not have any explanation for the back-to-back incidents, Gavin said. The plant's other reactor remains in operation.

The incident started at 1:40 p.m., when plant employees heard a loud explosion from one of the plant's four 12,000-volt cooling-water circulation pumps. The pump began emitting black smoke. No one was near the pump when it exploded.

"There's a lot of noise when you have a fault in something that big," Gavin said.

The plant's fire brigade extinguished the fire in three minutes. CDF/County firefighters also responded.

Each of the plant's reactors has two ocean water pumps that circulate cooling water to condense steam that has passed through the electrical generators. Collectively, they circulate nearly 2 billion gallons of seawater through the plant each day.

With one pump inoperable, the reactor could have been reduced to half power. But plant managers decided to shut it down entirely as a safety precaution, Gavin said.

The loss of the reactor is not expected to cause an electrical shortage in the state, Gavin said. Electrical demand is less in the winter because people are not running air conditioners.

"We will have to replace that power, but it is not as critical as it would have been at other times of the year," Gavin said.

At full power, Diablo produces 2,200 megawatts. Over the course of a year, the plant generates 10 percent of the state's power supply.

The accident required that PG&E report an "unusual event" to the federal Nuclear Regulatory Commission. An unusual event is the lowest level of four mandatory reporting thresholds because it does not require the public to take any emergency action.

Donna Jacobs, the plant's director of nuclear services, said this week's emergency shutdowns are not liable to affect the plant's safety rating with the NRC. The agency uses a color-coding system to rank how safely nuclear plants operate in various areas.

Diablo Canyon is usually given a green code in all areas, the highest designation, indicating safe operation. Jacobs said she does not expect the shutdowns will result in the loss of a green ranking.

Reach David Sneed at

781-7930.

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