Officials Study If Design Flaws Led Edison’s San Onofre to Shut

Federal regulators are focusing on whether design modifications caused excessive wear in steam generator tubes at Edison International’s San Onofre nuclear plant in California.

U.S. Nuclear Regulatory Commission officials are expected to describe the design issues and other preliminary findings at a meeting tonight in San Juan Capistrano, Lara Uselding, an NRC spokeswoman, said in a telephone interview.

The Associated Press reported today that inspectors think corrosion that had forced the nuclear station off line was probably caused by extensive design alterations to two steam generators, including a decision to add 400 tubes to each generator.

The plant’s closing increases the risks of blackouts in Southern California, where San Onofre provided power to about 1.4 million homes, federal regulators said last month. State grid operators are encouraging conservation and have called up two retired natural-gas-fired plants to help replace the output from Edison’s crippled reactors.

San Onofre will be shut through August as Edison develops a plan to restart its reactors, which have been off line since January, Chief Executive Officer Ted Craver said in a statement on June 8.

The NRC, which sent extra inspectors to the plant after a small leak shut its Unit 3 reactor in January, found unusual wear on some steam generator tubes that carry radioactive water at both reactors. San Onofre’s Unit 2 was shut in January for planned maintenance and refueling.

Repair Work

Some tubes were rubbing, causing them to degrade, Craver said on May 30. Edison has plugged and repaired about 3 percent of the tubes in the generators, Craver said.

Edison’s plan to repair and start its reactors will probably be submitted by the end of July, the company has said.

The steam generators, built by Mitsubishi Heavy Industries Ltd., were installed in 2009 and 2010 at a total cost of $671 million.

Edison estimated its share of inspection and repair costs to be in the range of $55 million to $65 million, according to a filing in May. The utility paid $30 million for replacement power through March 31 and those costs are probably to be higher for the summer, Edison said in the filing.

Edison’s Southern California Edison utility and Sempra Energy’s San Diego Gas & Electric Co. will pay $2.5 million a month for power from two AES Corp. generating units to help make up for lost capacity from San Onofre, the state’s grid operator California ISO said on May 11.

Edison owns 78.21 percent of San Onofre, while Sempra owns 20 percent and the city of Riverside owns 1.8 percent, according to Edison’s website.

San Onofre, located about 60 miles (97 kilometers) south of Los Angeles, can produce enough power for 1.76 million average homes, based on Energy Department statistics.

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