San Onofre nuclear plant’s flawed system

March 11, 2013

The Nuclear Regulatory Commission has released a report detailing how a flawed system of steam generators led to the shutdown of the San Onofre nuclear power plant, which has now lasted more than a year.

Mistsubishi Heavy Industries, which replaced the steam generators for Unit 2 and Unit 3 at San Onofre, constructed the report on what went wrong with their replacement generators.

San Onofre has not generated any electricity since January 31, 2012, when officials discovered an 82 gallon per day fluid leakage in the Unit 3 replacement generator. Unit 2 was undergoing a refueling outage at the time of the shutdown. The third reactor, Unit 1, has been decommissioned since 1992.

Upon shutdown, San Onofre officials discovered higher than expected tube wear in the replacement generators of both reactors. The Mitsubishi Heavy Industries report determined that tube wear from contact with other tubes, anti-vibration bars and retainer bars in the Unit 3 replacement steam generator caused the leakage.

The report also says that San Onofre officials considered design changes to the replacement generators before their installation, but rejected the proposed fixes in part because they required additional regulatory approval.

Mitsubishi Heavy Industries received the contract to replace Southern California Edison’s original steam generator in 2003. The Japanese engineering firm installed the Unit 2 replacement generator between September 2009 and April 2010 and the Unit 3 replacement generator between October 2010 and February 2011.

Due to the indefinite shutdown of San Onofre, Diablo Canyon is now the only operating nuclear power plant in California and on the entire Pacific Coast.