LOS ANGELES (AP) -- 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, located between Los Angeles and San Diego, 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.
Southern California Edison asked the Nuclear Regulatory Commission in early October for permission to rekindle one of the twin reactors, Unit 2, and then run it at reduced power. Company officials believe that operating at up to 70 percent power will end vibration and friction that prematurely eroded generator tubing.
In a letter to Edison, NRC officials raised a potentially thorny question for the company.
Under technical operating rules, the plant is required to ensure that generator tubes retain "structural integrity" during "the full range of normal operating conditions," including if the plant is running at full power. NRC said it wanted the company to demonstrate that Unit 2 could meet that threshold, or explain how generator tubes would interact with each other if the plant is operating at maximum capacity.
Any change in those technical rules could trigger a longer, more complex review by the NRC. Agency spokesman Victor Dricks declined comment when asked if meeting the full-power threshold could be a condition of restarting the Unit 2 reactor.
Edison spokeswoman Jennifer Manfre said in a statement that the utility would provide additional information to the federal agency, as requested. A thorough review of the restart plan "is important to both the public and Southern California Edison," she added.
The problems at San Onofre center on steam generators that were installed during a $670 million overhaul in 2009 and 2010. After the plant was shut down, tests found some generator tubes were so badly corroded that they could fail and possibly release radiation, a stunning finding inside the nearly new equipment.
Friends of the Earth, a group critical of the nuclear power industry, is among several environmental groups pushing the NRC to require Edison to seek an amendment to its operating license to restart the plant, a process that could take up to two years. Spokeswoman Kendra Ulrich said in a statement the group is "encouraged that the NRC is asking hard questions" about the restart and its implications, including on the operating license.
The ability of San Onofre to run safely at lower power — and whether that limit would require an amendment to its operating license — came up earlier this month at a hearing of the Atomic Safety and Licensing Board, an arm of the NRC.
Administrative Judge Gary Arnold asked an Edison attorney, Steve Frantz, if he was confident that the plant could operate at 99 percent power with its ailing generators.
"I do not say that," Franz responded. He argued that running at 70 percent power would fall within San Onofre's license and operating rules.
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 with 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, Oregon, 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.