Both State Nukes Shut Down

Units at both of the state's nuclear facilities, representing more than 2,000 MW of capacity, were shut down this week because of unusual incidents. Diablo Canyon unit 2 was shut down twice. The first time was due to a problem that appeared to be overheating of the reactor core. The second shutdown was because of an explosion and fire. San Onofre Nuclear Generating Station unit 3 was flipped off just as it was ramping up power after a refueling outage due to an oil leak. Diablo Canyon unit 2 was shut down as temperatures inside the reactor reached 300 degrees December 11. That reading, however, may have been erroneous. The heat sensor at the plant warned of a rapidly overheating reactor, which if correct and untreated could have led to a nuclear meltdown. The nuclear plant's owner, Pacific Gas & Electric, suspected the problem was because of a sensor failure, not rising temperatures in the unit, according to spokesperson Sharon Gavin. PG&E reported to federal authorities that the plant's heat sensor may have misread the situation. The action alarmed nuclear power observers. PG&E's report posted at the Nuclear Regulatory Commission showed that the reactor was "critical" and "subcritical" at the same time. A "critical" phase is one that can lead to a meltdown. The two phases cannot simultaneously occur. It is not clear whether the utility or the NRC staff was responsible for the erroneous posting. "It would be like someone in the morgue recording the receipt of another dead body as 'Pulse - 80.' One should realize a dead body and a pulse above 0 are incompatible," noted Dave Lochbaum, director of the nuclear safety project Union of Concerned Scientists. As the unit was restarting December 12, an explosion and fire caused it to shut down again. The fire occurred at the intake valve where over a billion gallons of seawater a day is consumed to cool the unit. The fire caused an automatic electronic trip to shut off the reactor. Control rods had to be inserted into the reactor to cool it down. "It's like tripping a circuit breaker, only at 12,000 volts," explained Gavin. She added that the fire was put out in three minutes. PG&E does yet not know when it will restart the unit. In a statement issued late December 13, PG&E noted that its investigation determined that a surge capacitor for one of unit 2's circulating water pump motors failed, causing an electrical fault and a small fire and shutting down the pump. When this happened, the electrical bus protection systems for unit 2 sensed the resultant drop in voltage and automatically shut down the unit. "The circulating water pumps are non-safety related components that pump ocean water to condense steam that has passed through the plant's turbines," the utility stated. "There are two circulating water pumps for each unit at Diablo Canyon." Also on December 12, Southern California Edison's SONGS unit 3 shut down. According to spokesperson Ray Golden, about one-third of a gallon of lubricant oil leaked through a gasket on the mechanical part of the coolant pump. Because the reactor was being powered up at the time after a maintenance and refueling shutdown, the utility backed the unit down to fix the part. "There was no threat to the reactor," Golden said. He added that if the unit had been operating at full speed, the oil leak could have been ameliorated by adding more oil. But because it was in start-up mode, the company decided to turn off the unit instead. A California Independent System Operator spokesperson said the loss of the two reactors was not hampering operations because it is a low-load time of year. Both nuclear plants were back on line by the end of the week. - J.A. Savage

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Both State Nukes Shut Down

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