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San Onofre: Report blames generator design changes for shutdown

March 27, 2012 | 11:39 am

San Onofre in 2011
This post has been updtated.

Advocacy group Friends of the Earth released a report Tuesday claiming design changes in newly installed steam generators at the San Onofre nuclear plant led to issues that have shut down the plant for the last two months.

The report prepared by Arnie Gundersen, a former nuclear industry executive and chief engineer of the energy consulting company Fairewinds Associates, who is critical of the nuclear power industry, also suggested that San Onofre's operator, Southern California Edison, sidestepped federal review of the new generators.

The four steam generators at San Onofre were replaced in the last two years in a $671-million project to be paid for by ratepayers. The new equipment was intended to last until the plant's license expires in 2022, but in recent months officials have discovered unexpected wear on hundreds of steam generator tubes that carry radioactive water in both of the plant's working reactors.

One tube in Unit 3 sprung a small leak, releasing a small amount of radioactive steam, and eight more failed pressure tests. Tubes in the other reactor, Unit 2, also showed unusual wear, and 192 were plugged as a precautionary measure.

Edison and U.S. Nuclear Regulatory Commission officials are trying to determine what is causing the tubes to wear out but have not said what they think the root of the problem is.

Gundersen's report contends that because of design changes -- including a different alloy used to make the tubes, a change in the flow rate, addition of more tubes and changes in the support structure that holds the tubes in place -- the U.S. Nuclear Regulatory Commission should have reviewed the new steam generators' design before they were installed.

But because Edison represented the replacement as a "like-for-like" swap, federal regulators did not put the project through a full review and approval process, the report states.

[Updated at 12:53 p.m.: "At all times during the steam generator replacement process and the ongoing outages in Unit 2 and 3, Southern California Edison (SCE) has provided open and transparent information to the Nuclear Regulatory Commission," Edison officials said in a statement.

"SCE's top priority is the health and safety of the public and our workers," the statement continued. "As is standard practice in the nuclear industry, SCE has been conducting tests and inspections as part of an in-depth analysis. SCE has been committed from the beginning to not returning Unit 2 or Unit 3 to service until we are satisfied it is safe to do so."]

Lara Uselding, a spokeswoman with the NRC, said she was aware of the Friends of the Earth report but had not read it.

"The NRC has been conducting a thorough and comprehensive inspection of the steam generator problems at San Onofre," she said in a written statement. "The plant is currently shut down and will remain so until the cause of the unusual steam generator wear is fully understood and appropriate corrective actions have been taken."

The steam generators at San Onofre were manufactured by Mitsubishi Heavy Industries. Uselding said that one other nuclear plant in the U.S., Fort Calhoun Nuclear Generating Station in Nebraska, has steam generators made by Mitsubishi. But she said the design at San Onofre was unique. Fort Calhoun has not experienced the same issues.

Officials have said that both reactors at San Onofre will remain out of service until the cause of the problem is determined. Damon Moglen, director of the climate and energy project at Friends of the Earth, said he is concerned that Edison may try to restart the Unit 2 reactor before the problem is thoroughly investigated.

"I think Edison needs to make very clear that they are treating both reactors the same way and they need to make a definitive statement that neither reactor is going to come back up until we've got a root cause and they've addressed everything," he said.


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-- Abby Sewell

Photo: San Onofre nuclear power plant in 2011. Credit: Allen J. Schaben / Los Angeles Times.