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Senior nuclear expert urges regulators to shut down California’s last plant via The Guardian

In confidential report, lead inspector said NRC must determine whether Diablo Canyon’s twin reactors are ‘seismically safe’

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.”

[...]

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. In many ways, the history of the plant, located halfway between Los Angeles and San Francisco on the Pacific coast and within 50 miles of 500,000 people, has been a costly fight against nature, involving questions and repairs connected to its design and structural strength.

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.

The conflict between Peck and his superiors stems from the 2008 discovery of the Shoreline fault, which snakes offshore about 650 yards from the reactors. A larger crack, the Hosgri fault, had been discovered in the 1970s about 3 miles away, after the plant’s construction permits had been issued and work was underway. Surveys have mapped a network of other faults north and south of the reactors.

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Peck disagreed with his supervisors’ decision to let the plant continue to operate without assessing the findings. Unable to resolve his concerns, Peck in 2012 filed a formal objection, calling for PG&E to be cited for violating the safety standards, according to his filing. Within weeks, the NRC said the plant was being operated safely. In 2013 he filed another objection, triggering the current review.

The NRC says the Hosgri fault line presents the greatest earthquake risk and that Diablo Canyon’s reactors can withstand the largest projected quake on it. In his analysis, Peck wrote that after officials learned of the Hosgri fault’s potential shaking power, the NRC never changed the requirements for the structural strength of many systems and components in the plant.

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