Mitsubishi affirms serious steam generator problem at San Onofre nuclear reactors

Mitsubishi affirms serious steam generator problem at San Onofre nuclear reactors

San Francisco, Calif. — The Japanese firm responsible for fabricating the failing steam generators at Southern California Edison’s San Onofre nuclear reactors announced today that it is undertaking analyses of the causes of the serious, unresolved safety problems.

In papers filed with the Nuclear Regulatory Commission, the firm, Mitsubishi Heavy Industries, revealed that its reviews will extend at least through the end of August — ensuring that the troubled reactors will not be able to operate through the summer.

The severity of the problems at San Onofre first came to light when one of the reactor’s steam generators leaked radiation at the end of January. The subsequent discovery of unusual levels of wear in steel tubing in the steam generators of both units has caused both reactors to remain shut down since.

“The people of southern California need answers to what exactly is happening at San Onofre. It doesn’t exactly instil confidence in Edison or the NRC that we have to learn about the process from the Japanese fabricator of the damaged steam generators,” said Damon Moglen of Friends of the Earth. “At the same time, Edison and the NRC must explain why Mitsubishi is planning on doing separate root cause analyses of the two reactors, and on a staggered schedule, when it is clear that the technical problems are shared at the steam generators of both reactors.”

“It’s clear that any plans Edison has for restarting either of the reactors this summer must be abandoned. It’s essential that Edison immediately disclose what plans it has for initiating efficiency and conservation measures for the coming peak energy demand months of summer. Consumers can have safe and reliable energy without relying on these ageing and dangerous nuclear reactors,” said Moglen.

Mitsubishi’s filing with the NRC reveals for the first time that the firm is responsible for conducting an analysis for San Onofre reactor unit 2, which is to be completed by May 31, 2012, and another analysis for reactor unit 3, which is due by August 31, 2012.The company provided no justification for conducting separate analyses despite the fact that the steam generators at both reactors are experiencing the same rapid and unexplained wear which has already lead to the release of radiation during the failure of a steam generator tube at unit 3 in January.

Last week, a study by nuclear engineer Arnie Gundersen and Fairewinds Associates, commissioned by nuclear watchdog Friends of the Earth, provided the first detailed picture of the extent of design changes made by Southern California Edison at its San Onofre nuclear reactors. These changes likely led to the equipment degradation and failure that has forced the reactors offline, pending a thorough and comprehensive investigation.

Edison confirmed last week that the same type of severe wear in the steam generator tubes in San Onofre unit 3 had been found in unit 2.

The FOE commissioned reports on San Onofre are available at: /wp-content/uploads/2017/legacy/Fairewinds_FOE_Cascading_Steam_Generator_Failures_San_Onofre_2012_4_12.pdf

The NRC event report can be obtained at:


Kelly Trout, 202-222-0722, [email protected]


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