San Onofre: What Went Wrong?

Tuesday, December 31, 2013 @ 03:12 PM gHale

It may now be retired, but that does not mean safety regulators gave up on trying to get to the bottom of why and how the San Onofre Nuclear Generating Station ended up disabled.

That means an operator of the nuclear power plant is facing a citation from the Nuclear Regulatory Commission (NRC) for failing to properly check the design of faulty replacement steam generators that disabled the plant.

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The violation notice from the NRC carries no explicit penalties but complicates efforts by Southern California Edison to recover an array of plant costs and remaining assets on behalf of its shareholders. The California Public Utilities Commission is considering an initial $94 million refund to customers of Edison and minority plant owner San Diego Gas & Electric, with more extensive plant costs still under review for additional and possibly larger refunds.

Edison has 30 days to appeal the nuclear commission’s determination.

“We will evaluate the final determination letter from the NRC and respond within 30 days with appropriate corrective actions,” said Edison spokeswoman Maureen Brown.

San Onofre stopped producing power in January 2012 when workers found a small radiation leak and traced it back to rapid wear among steam generator tubes carrying radioactive water. Company officials retired the plant’s twin reactors in June.

The NRC found, contrary to regulations, “design control measures were not established to provide for verifying and checking the adequacy of certain designs.”

Edison has laid the blame for the plant’s problems on generator manufacturer Mitsubishi Heavy Industries of Japan and botched computer calculations that underestimated steam velocities within the generators, installed in 2010 and 2011.

Rosemead, CA-based Edison is seeking damages from Mitsubishi through binding arbitration. Mitsubishi is defending the limits of its $137.5 million warranty for its four replacement generators. Attempted repairs, consultants and replacement power have raised disputed costs to well over $1 billion.

Nuclear commission spokesman Victor Dricks said the violation notice itself, first outlined in a September draft, carries no penalties or sanctions.

The plant shutdown was of “low to moderate safety significance” in the federal nuclear agency’s final assessment, following 16 months of on-site inspections and detailed analysis at regional commission offices in Texas and headquarters in Maryland.

U.S. representatives for Mitsubishi were not immediately available for comment. Mitsubishi ended up faulted by the commission in September in a “notice of nonconformance” related to flawed computer codes used in the design of the replacement generators.

Mitsubishi said a generator design team that included Edison experts believed vibration issues ended up fixed after they installed additional tube supports. Mitsubishi said there was no way to anticipate the unprecedented type of tube vibrations that occurred in the exceptionally large generators commissioned by Edison.

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