LOS ANGELES - Federal regulators Wednesday pressed the operator of the San Onofre nuclear power plant for more analysis on its damaged steam generators, as the government considers when - or if - one of the seaside reactors can be restarted safely.
San Onofre hasn't produced electricity since January, after a tiny radiation leak led to the discovery of excessive wear on hundreds of generator tubes that carry radioactive water.
In a letter to Southern California Edison, Nuclear Regulatory Commission officials asked for more information on how tubes would interact with each other if a reactor is running at full power.
The inquiry represents a possible stumbling block for the company, which has submitted a plan to run the Unit 2 reactor at reduced power, up to 70 percent, in hopes that will end vibration that has damaged tubing in the huge machines.
According to the NRC letter, the plant - located between Los Angeles and San Diego - is required to ensure that tubes retain "structural integrity" during "the full range of normal operating conditions."
The agency wants to see an analysis "that shows they can operate the plant at full power, 100 percent," NRC spokesman Victor Dricks said.
Edison had no immediate comment on Wednesday.
Dricks declined comment when asked if meeting the full-power threshold could be a condition of restarting Unit 2.
The problems center on steam generators that were installed in San Onofre's reactors during a $670 million overhaul in 2009 and 2010. After the plant was shut down, tests found some tubes were so badly corroded that they could fail and possibly release radiation, a stunning finding inside the nearly new equipment.
The generators, which resemble massive steel fire hydrants, control heat in the reactors and operate something like a car radiator. At San Onofre, each one stands 65 feet high, weighs 1.3 million pounds, and has 9,727 U-shaped tubes inside, each three-quarters of an inch in diameter.
Company executives have left open the possibility that the heavily damaged generators in Unit 3 might be scrapped.
Cracked and corroded generator tubing has vexed the nation's nuclear industry for years.
Decaying generator tubes helped push San Onofre's Unit 1 reactor into retirement in 1992, even though it was designed to run until 2004. The following year, the Trojan nuclear plant, near Portland, Ore., was shuttered because of microscopic cracks in steam generator tubes, cutting years off its expected lifespan.
San Onofre is owned by SCE, San Diego Gas & Electric and the city of Riverside. The Unit 1 reactor operated from 1968 to 1992, when it was shut down and dismantled.