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— A senior federal nuclear expert is urging regulators to shut down California’s last operating nuclear plant until they can determine whether the facility’s twin reactors can withstand powerful shaking from any one of several nearby earthquake faults.

Michael Peck, who for five years was Diablo Canyon’s lead on-site inspector, says in a 42-page, confidential report that the Nuclear Regulatory Commission is not applying the safety rules it set out for the plant’s operation.

The document, which was obtained and verified by The Associated Press, does not say the plant itself is unsafe. Instead, according to Peck’s analysis, no one knows whether the facility’s key equipment can withstand strong shaking from those faults — the potential for which was realized decades after the facility was built. Continuing to run the reactors, Peck writes, “challenges the presumption of nuclear safety.”

Peck’s July 2013 filing is part of an agency review in which employees can appeal a supervisor’s or agency ruling — a process that normally takes 60 to 120 days, but can be extended. The NRC, however, has not yet ruled. Spokeswoman Lara Uselding said in emails that the agency would have no comment on the document.

The NRC, which oversees the nation’s commercial nuclear power industry, and Diablo Canyon owner Pacific Gas and Electric Co., say the nearly three-decade-old reactors, which produce enough electricity for more than 3 million people annually, are safe and that the facility complies with its operating license, including earthquake safety standards.

PG&E spokesman Blair Jones said the NRC has exhaustively analyzed earthquake threats for Diablo Canyon and demonstrated that it “is seismically safe.” Jones said in an email that the core issue involving earthquake ground motions was resolved in the late 1970s with seismic retrofitting of the plant.

The disaster preparedness of the world’s nuclear plants came into sharp focus in 2011, when the coastal Fukushima Dai-ichi plant in Japan suffered multiple meltdowns after an earthquake and tsunami destroyed its power and cooling systems. The magnitude-9 earthquake was far larger than had been believed possible. The NRC has since directed U.S. nuclear plants to reevaluate seismic risks, and those studies are due by March 2015.

The important of such an analysis came into sharp focus on Sunday when a magnitude 6.0-earthquake struck in Northern California’s wine country, injuring scores of residents, knocking out power to thousands and toppling wine bottles at vineyards.

Environmentalists have long depicted Diablo Canyon — the state’s last nuclear plant after the 2013 closure of the San Onfore reactors in Southern California — as a nuclear catastrophe in waiting.

What’s striking about Peck’s analysis is that it comes from within the NRC itself, and gives a rare look at a dispute within the agency. At issue are whether the plant’s mechanical guts could survive a big jolt, and what yardsticks should be used to measure the ability of the equipment to withstand the potentially strong vibrations that could result.

Peck, who holds a doctorate in nuclear engineering and is now a senior instructor at the NRC’s Technical Training Center in Tennessee, declined to comment on the filing.

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