San Onofre Steam Generator defects identified and repaired by Mitsubishi prior to installation in 2009

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Newly released documents from the US Nuclear Regulatory Commission show that cracks associated with welding defects were identified in a Japanese steam generator for a nuclear reactor in California in 2009 before its delivery to the plant.  The steam generator installed at the No. 3 reactor at the San Onofre nuclear power plant, was produced and later repaired by Mitsubishi Heavy Industries Ltd, in late January.

According to the NRC documents, cracks and damage were found in the steam generator of the unit 3 reactor during checks by Mitsubishi Heavy in March 2009.  Mitsubishi Heavy and Southern California Edison both declined to comment, saying they are under investigation.  A follow-up probe found heat treatment prior to welding caused the problem and the NRC informed the utility and others concerned.

Despite the fact that known defects were already repaired in 2009, and have continued to experience accelerated wear, Edison is not planning to decommission the steam generators.  The company has stated in press releases that they will be plugging the affected pipes and attempt to restore the units to service, if allowed by the NRC.

SCE is still conducting a battery of tests and performing a root cause evaluation on the Unit 3 tube water leak.   Southern California Edison showed a loss for the full year of $0.11 per share, due primarily to impairment charges at EMG.  Planned inspections of the steam generators in Unit 2 found isolated areas of wear in some of the heat transfer tubes.  The two huge steam generators at Unit 2, each containing 9,700 tubes, were replaced in fall 2009, and a year later in its twin plant, Unit 3, as part of a $670 million overhaul.

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