LOS ANGELES (AP) -- An Edison International unit that operates California's troubled San Onofre nuclear plant is looking at a possible June restart, while costs related to the long-running shutdown could climb over $100 million, a senior executive said Thursday.
Southern California Edison is drafting a plan under which the twin reactors would run at lower power, at least for several months. Engineers believe that will solve a problem with vibration that has been causing unusual wear in tubing within the plant's massive steam generators.
"By operating at lower power ... the vibration does not occur," executive vice president Stephen Pickett said.
The plant has been offline since late January, and federal regulators would have to approve a restart.
The trouble at San Onofre began to unfold in late January, when the Unit 3 reactor was shut down as a precaution after a break in a steam generator tube carrying radioactive water. Traces of radiation escaped, but officials said there was no danger to workers or neighbors.
Unit 2 had been taken offline earlier that month for routine maintenance. But investigators later found unusual wear on tubing in both units. Hundreds of tubes that were heavily damaged will be taken out of service at the two reactors, well within the margin to allow them to keep operating.
SCE projects that the bill for repairs and tests could run as high as $65 million, and $30 million was spent on replacement power through March 31 — a bill that keeps mounting.
Gradual wear is common in such tubing, but the rate of decay at San Onofre was startling in some cases because the equipment is relatively new. The generators were installed in a multimillion-dollar makeover in 2009 and 2010.
Nuclear Regulatory Commission Chairman Gregory Jaczko visited the plant in April and promised a thorough review of the suspect tubing. He said at the time that there must be a "clear understanding" of the cause of the excessive tube wear before either of the twin reactors is restarted.
Ted Craver, chairman of SCE parent Edison International, told investors in a phone call Wednesday that unusual wear was found in about 1 percent of nearly 39,000 tubes in the steam generators. He said it's possible one, or both, of the reactors could remain offline into the summer, and the company has been working with state officials to secure replacement power for the region.
The tubes are a critical safety barrier — if one or more break, there is the potential that radioactivity could escape into the atmosphere. Also, serious leaks can drain cooling water from a reactor.
About 7.4 million Californians live within 50 miles of San Onofre, which can power 1.4 million homes.
The plant is owned by SCE, Sempra Energy's 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.