Human error and equipment problems have shut down a San Onofre nuclear reactor four times in 12 months, according to the Nuclear Regulatory Commission. None caused safety or health hazards, but they have triggered extra inspections.
The incidents all occurred in Reactor Two, one of two operating at the plant, which is on the coast south of San Clemente.
On Feb. 27, 2002, "a maintenance worker inadvertently worked on the wrong panel and basically shut the power off coming into the plant," NRC Region IV spokesman Victor Dricks said Friday.
"If that flow of power is interrupted, a lot of safety systems don't have immediate power sources, so they shut down."
On Nov. 2, 2002, the reactor and a turbine automatically shut down after a "low lubrication pressure" alert -- similar to a car's low-oil light -- activated, Dricks said.
Two days later, as power was being restored, the reactor was manually shut down when operators saw an indication of low pressure in the reactor coolant system because a spray valve was stuck open, according to Ray Azua, a commission project engineer.
The valve regulates the flow of cooling water into the reactor, he said.
Most recently, on Feb. 1 of this year, the main generator experienced trouble in an electromagnetic field, causing the turbine and reactor to shut down.
The commission allows three automatic shutdowns in a 365-day period. Because the limit was exceeded, the regulatory agency will conduct additional inspections of equipment, Dricks said.
Commission staff also will discuss the plant and answer questions about safety at a quarterly meeting open to the public Thursday at 7 p.m. at the Country Inn in San Clemente.