More than 1,300 steam generator tubes have been plugged at the 2,150 MW San Onofre Nuclear Generating Station (SONGS) as plant owner Southern California Edison (SCE) continues to investigate the cause of the accelerated wear.

According to Reuters, a total of 510 tubes in Unit 2 and 807 tubes in Unit 3 were plugged. SCE has said that the accelerated tube wear was caused by vibration inside the generators causing the tubes to rub against adjacent tubes and components inside the generators.

Unit 2 has been offline since January 9 for a planned maintenance outage, while Unit 3 has been shut down since January 31 after workers found a leak in one of the steam generator tubes. Unit 2 will remain shut down after workers discovered the same type of wear previously seen in Unit 3.

The generators were supplied by Mitsubishi Heavy Industries and are under warranty for an initial 20 years from acceptance. SCE said on May 3 that costs associated with inspections and repairs could cost upwards of $65 million.

The U.S. Nuclear Regulatory Commission sent a Confirmatory Action Letter, which SCE received on March 27, outlining what actions SCE had to complete before asking the NRC to restart both units. There is no set date on when either unit will return to service.

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