A former federal inspector has urged regulators to shut down California's last remaining nuclear power plant until it can be determined whether the facility can stand up to an earthquake off the Central Coast.
Diablo Canyon is California's sole remaining nuclear plant.
Michael Peck, former senior resident inspector at Diablo Canyon, made his case to the U.S. Nuclear Regulatory Commission in a confidential July 2013 document, a copy of which was released Monday by the environmental group Friends of the Earth.
The document was first reported by the Associated Press.
Peck argued that it is unsafe to continue running Diable Canyon without evaluating whether it can withstand quakes from nearby faults that are now believed to be capable of producing more ground shaking than was known when the plant was built and licensed.
Allowing it to continue operating "challenges the presumption of nuclear safety," Peck wrote.
A new fault -- known as the Shoreline fault -- was discovered just offshore from the plant in 2008. Federal regulators concluded that the plant's current design would be able to stand up to any earthquakes the fault might produce.
Peck argued that the plant's license needs to be amended in light of the new earthquake information. He also took issue with the methodology used to analyze earthquake risks at the plant in the past.
Damon Moglen, senior strategic advisor with the environmental group, said Peck is "the canary in the coal mine, warning us of a possible catastrophe at Diablo Canyon before it's too late."
Nuclear Regulatory Commission spokeswoman Lara Uselding said the agency stands by its conclusion that the plant would safely withstand an earthquake.
She said the agency "encourages and welcomes differing opinions" from its staff and is still reviewing Peck's concerns, but has not issued a final response.
Blair Jones, a spokesman for plant operator Pacific Gas & Electric, said the plant "was built to withstand the largest potential earthquakes in our region." The plant was retrofitted in the 1970s after the nearby Hosgri fault was discovered, he said.
That retrofit set the plant up to withstand the amount of ground shaking that could be produced by three other nearby faults, Jones said.
Dave Lochbaum, director of the nuclear safety project at the Union of Concerned Scientists, said his group agrees that the methodology used to analyze earthquake risks at the plant was flawed, although he stopped short of calling for it to be shut down.
He pointed out that the plant will be making safety fixes in any case, as a result of the Fukushima Daiichi nuclear disaster in Japan.
"We hold out some hope that the Fukushima fixes will lead to the fixes needed at Diablo Canyon," he said.
California's other nuclear plant, San Onofre, on the coast near San Clemente, was shut down for good last year as a result of faulty equipment that led to a small release of radioactive steam and a heated regulatory battle over the plant's license. Friends of the Earth pushed to keep that plant shuttered.