In a decision written by Executive Director for Operations Mark Satorius, the agency concluded there is no immediate or significant safety concern at the Diablo Canyon plant, which sits on a seaside bluff midway between Los Angeles and San Francisco.
Michael Peck, who for five years was Diablo Canyon's lead NRC inspector, said in a confidential report disclosed by The Associated Press last month that no one knows whether the plant's equipment can withstand strong shaking from those faults — the potential for which was realized decades after the facility was built.
Peck, now a senior reactor instructor for the NRC in Tennessee, argued the NRC is not applying safety rules it set out for the plant's operation.
Blair Jones — a spokesman for plant owner Pacific Gas and Electric Co. — said in a statement the NRC decision reaffirms that the plant "has been and continues to be seismically safe."
The disaster preparedness of the world's nuclear plants came into sharp focus in 2011, when a coastal plant in Japan suffered multiple meltdowns because of a magnitude-9 earthquake and tsunami. The NRC has since directed U.S. nuclear plants to re-evaluate seismic risks, with studies due by March 2015.
The agency's ruling was issued on the same day that PG&E released hundreds of pages of scientific research that found a fault 650 yards from the reactors, known as the Shoreline, is twice as long as initially believed, making it capable of producing potentially stronger earthquakes, and intersections between some faults in the region could create larger earthquakes than previously considered. PG&E said in a statement that the plant remains seismically safe and able to withstand the largest potential earthquakes in the area.
Former California Sen. Sam Blakeslee, a geophysicist who has previously raised seismic concerns at Diablo, said "it's premature to declare the plant is safe in light of this new information."
The NRC, which oversees the nation's commercial nuclear power industry, and the company have maintained the nearly three-decade-old reactors are safe and that the facility complies with its operating license, including earthquake safety standards.
Damon Moglen, a spokesman for Friends of the Earth, an advocacy group critical of the nuclear power industry, said in a statement that the plant "should not be allowed to operate for another day without being closed and subjected to a full public safety review."
The NRC's Wednesday announcement ends the commission's consideration of Peck's 2013 analysis, which was filed under rules that allow NRC employees to appeal agency decisions.
According to his report, PG&E research in 2011 determined that any of three nearby faults — the Shoreline, Los Osos and San Luis Bay — is capable of producing significantly more ground motion during an earthquake than was accounted for in the design of important plant equipment.
The analysis, released by the NRC Wednesday, argued that the agency should shut down the plant until it is proven that piping and other systems can meet higher stress levels, or approve exemptions that would allow the reactors to continue to operate.
Satorius noted that an internal review panel disagreed with Peck on key points, concluding that the three faults "do not exceed the level of ground motion already considered in the design and licensing" of the plant.
While disagreeing with his conclusions, the decision said Peck raised "important concerns with our processes which merit further consideration" and that the agency would evaluate how the NRC reviews new seismic hazard information.