Cooling System Leak Shuts Down San Onofre Nuclear Plant Reactor

Reactor Unit 3 at the San Onofre nuclear power plant was shut down Tuesday night after operators discovered what was described as a “barely detectable” leak in the reactor’s cooling system.

Because the leak was dripping water contaminated by the reactor’s radioactive core, Southern California Edison Co. officials declared an “unusual event”--the lowest on a scale of four levels of emergencies that can occur at a nuclear power plant.

That declaration requires utility officials to notify nearby law enforcement and government agencies.

In this case, according to utility and Nuclear Regulatory Commission spokesmen, the leak was small and discovered quickly.

Unit 3, which was being restarted after being inactive for 44 days, was immediately shut down and the alert canceled.

‘Mechanical Failure’

“This was basically a mechanical failure of a thermal weld,” Perry Stewart, the regulatory commission acting senior inspector at San Onofre, said Wednesday. He said there was nothing that utility operators could have done to prevent the leak, which he described as a small drop of water.

Becky Sordelet, an Edison spokeswoman, said the leak was dripping at the rate of “about a teaspoon an hour.” She said the reactor was shut down as soon as the leak was discovered, at about 8 p.m. Tuesday.