A 650-ton steam generator is moved to the San Onofre Nuclear Generating… (Don Bartletti, Los Angeles…)
In a flurry of letters late last year, Southern California Edison and the manufacturer that designed the steam generators at the now-dark San Onofre nuclear power plant appeared to be at odds over a long-term plan to repair the troubled facility.
In the exchange, Mitsubishi Heavy Industries proposed a repair plan that it said could have the plant back online at full power in about a year and also suggested a far more aggressive and expensive repair job that would take more than five years to complete.
By the end of 2012, however, the companies were unable to come to an agreement on a long-range plan.
At the same time, Edison warned Mitsubishi that the ongoing problems at the nuclear plant had "seriously harmed" the utility and its stakeholders and that it expected the manufacturer to "accept full responsibility" for the problem.
The plant had been offline at that point for nearly a year because of unusual wear on tubes that carry radioactive water in the plant's newly replaced steam generators, which were designed and manufactured by Mitsubishi. The problem came to light in January 2012 after a small amount of radioactive steam leaked from one of the tubes.
Edison asked the U.S. Nuclear Regulatory Commission in October for permission to restart one of the plant's two units and run it at 70% power for a few months to see whether the reduced power would alleviate the conditions that led to the wear.
But the company was pushing Mitsubishi to develop a plan that would allow both units at the plant to return to service at full power for the 40-year intended life span of the steam generators.
The letters between the companies were recently released as part of an examination by the California Public Utilities Commission of the costs of the plant's outage.
Edison Vice President Pete Dietrich told Mitsubishi in a Nov. 28 letter, after several months of discussions, that the lack of a long-term repair plan 10 months into the plant's outage "is not and should not be acceptable to either of our companies."
Mitsubishi responded that the type of tube wear seen at San Onofre had never been seen before in an operating steam generator, making the analysis time-consuming.
The company said it had done mock-up tests of repairs to the support structures and concluded that adding thicker support bars to prevent the tubes from vibrating would be a "practical and viable" option and would take about a year to accomplish.
Other options Mitsubishi presented included redesigning and replacing the entire bundles of more than 9,000 tubes in each of the plant's steam generators and replacing the steam generators completely. Either action, Mitsubishi said, would take more than five years.
The documents did not give cost estimates, but replacing the steam generators the last time cost $768.5 million. The steam generators were installed in 2010 and 2011.
"I am disappointed that it appears that MHI does not have a repair plan despite the passage of many months," Dietrich responded in a Dec. 19 letter.
Mitsubishi's warranty on the steam generators is capped at $138 million, but Edison contends that the cap should not apply to this case.
In a Dec. 20 letter, Mitsubishi noted that Edison had rejected the proposal to install thicker anti-vibration bars. Tom Palmisano, Edison's vice president of engineering, said during a hearing Wednesday that the company had questioned whether the plan would be effective.
Edison and Mitsubishi officials said discussions continue, but the companies still have not agreed on a long-term plan.
"All options are still on the table, and we're developing details for all of them," said Frank Gillespie, a senior vice president at Mitsubishi.
In the meantime, Edison officials have signaled that they may decide by the end of the year to retire the plant permanently if they don't get the go-ahead to restart at partial power.