Officials at the idled San Onofre nuclear power plant are investigating why coolant was found in an important piece of safety equipment during recent maintenance and are trying to determine whether it was an accident or sabotage, according to federal regulators and the plant’s operator.
Plant officials told regulators on Oct. 30 that they discovered coolant mixed with oil that helps run an emergency diesel generator in Unit 3, federal and utility officials confirmed Thursday.
“They don’t know right now how the coolant got in there,” said John Reynoso, a Nuclear Regulatory Commission inspector at San Onofre.
Southern California Edison, the plant's operator, is conducting a “comprehensive internal investigation” into the incident, which presented no risk to the public, according to Edison's statement.
“While the investigation has not resulted in any evidence of tampering, that scenario has not been ruled out,” Edison stated.
Diesel generators are considered a critical safety component at nuclear power plants. In the event of a power outage, the giant machines power the plant and keep nuclear fuel from overheating.
The failure of emergency generators at Fukushima was cited as one of several factors in that plant’s meltdown last year.
At San Onofre, however, Unit 3 has been shut down since a small radiation leak in January prompted a federal review of the plant’s steam generators. Hundreds of steam generator tubes in Units 2 and 3 were later found to have rapidly deteriorated because of a faulty design.
San Onofre’s diesel generator was taken offline on Oct. 21 for two weeks of maintenance when about two cups of coolant was found in the oil for its governor, Reynoso said.
If the coolant had been left in place and the generators activated, Edison believes the governor, which controls the generator’s speed and prevents it from running too fast, would have failed, Reynoso said.
Edison “is committed to the safety of the public and its employees and takes this matter very seriously,” according to its statement.