More than 1,300 tubes that carry radioactive water inside the San Onofre nuclear plant in Southern California are so damaged that they will be taken out of service, the utility that runs the plant said Tuesday.
The figures released by Southern California Edison are the latest disclosure in a probe of equipment problems that have kept the coastal plant sidelined for more than three months.
At issue has been the integrity of tubing that snakes through the plant's four steam generators, which were installed in a multimillion-dollar makeover in 2009 and 2010.
A company statement said that as of Monday, 510 tubes had been plugged, or retired from use, in the Unit 2 reactor, and 807 tubes in its sister, Unit 3. Each of the generators has nearly 10,000 tubes, and the number retired is well within the limit allowed to continue operation.
The statement comes just days after an Edison executive said the company hopes to restart at least one of the twin reactors next month. The company is drafting a plan under which the reactors would run at reduced power, at least for several months, because engineers believe that will solve a problem with vibration that the company believes has been causing unusual wear in the alloy tubing.
Government regulators say there is no timetable for a restart, which would require federal approval.
A joint statement issued Tuesday by Edison and the agency that operates the state's wholesale power system, the California Independent System Operator, said the possible June dates are for planning and subject to change.
"There is no timeline on nuclear safety," Edison President Ron Litzinger said.
Activists viewed the new figures as another alarming sign following a tube break in January, which prompted Edison to shut down the Unit 3 reactor as a precaution. Traces of radiation escaped at the time, but officials said there was no danger to workers or neighbors.
Unit 2 was taken offline in January for routine maintenance, but investigators later confirmed accelerated wear on tubing in both units.
"It seems that these new steam generators are falling apart and Edison doesn't know why. It would be foolhardy to restart, even at reduced power, under the current circumstances," said Daniel Hirsch, a nuclear watchdog who lectures on nuclear policy at the University of California, Santa Cruz.
Ted Craver, chairman of SCE parent Edison International, told investors in a phone call last week that unusual wear was found in about 1 percent of nearly 39,000 tubes in the steam generators.
Costs related to the long-running shutdown could climb over $100 million, company officials say, and state officials have warned about possible rotating blackouts in Southern California while the reactors are offline.
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