A tiny amount of radiation may have escaped from the San Onofre nuclear power plant after a water leak prompted operators to shut down a reactor as a precaution. The leak was detected Tuesday afternoon in reactor Unit 3.
Also concerning was that “many” tubes that carry pressurized radioactive water were damaged, according to a spokesman for the Nuclear Regulatory Commission.
The tubes are part of equipment that is virtually new, having been installed in 2010.
“The damage that they have found to many other tubes is unusual, and they are attempting to identify the reason,” NRC spokesman Victor Dricks said.
News of the possible leak was slow to emerge. Shortly after the incident, Southern California Edison (SCE) issued a statement saying, “There has been no release to the atmosphere.”
On Wednesday morning, however, Dricks said a small amount of radioactive gas “could have” escaped from a building that houses auxiliary equipment.
The Unit 3 reactor returned to full power in February 2011 after its two aging steam generators were replaced. The plant’s other reactor, Unit 2, had similar work. The retrofit cost more than $670 million.
Daniel Hirsch, who lectures on nuclear policy at the University of California, Santa Cruz, said he was concerned that the problem occurred with recently installed equipment.
“Edison has historically not been candid about the problems at San Onofre. That lack of transparency causes tremendous distrust and increases risk,” Hirsch said.
“It makes one wonder about the quality assurance for the replacement equipment,” he added. “This is not due to old equipment breaking but new equipment that wasn’t up to snuff in the first place.”
The latest leak occurred in one of thousands of tubes carrying radioactive water from the plant’s reactor. The leak was initially estimated at a rate of 85 gallons a day — an amount about half of what would require the plant to shut down.
Dricks said radioactive gas that leaked from that tube in the plant’s steam generator was vented into the auxiliary building. The radiation was detected by monitors in that building, which is separate from the sealed structure that houses the reactor. Because the auxiliary building is not sealed — people come and go through doors — it’s possible radiation escaped into the atmosphere.
Each steam generator can contain as many as 16,000 tubes, each about 0.75 inch in diameter. The hot, pressurized water flowing through the tubes heats non-radioactive water outside the tubes. The resulting steam is used to turn turbines to make electricity.
According to the NRC, the tubes have an important safety role because they represent one of the primary barriers between the radioactive and non-radioactive sides of the plant. If a tube breaks, there is the potential that radioactivity from the system that pumps water through the reactor could escape into the atmosphere.
Gil Alexander, spokesman for SCE, said he could not confirm any additional damage to other tubes, pending an inspection of the equipment.