Diablo Canyon can withstand quake on newly found fault, NRC says

The Nuclear Regulatory Commission has issued a report concluding that Diablo Canyon nuclear power plant could withstand an earthquake from the Shoreline Fault.

The report comes nearly four years after the fault was discovered running just offshore of the plant and confirms analysis released by plant owner PG&E in January 2011. The report concludes that ground motion that would be produced by a quake along the Shoreline Fault would be within the existing design limits based on a quake from the larger Hosgri Fault, which is farther offshore.

“The Shoreline Fault has a low slip rate that is estimated to be an order of magnitude less than the Hosgri Fault, which implies that its overall contribution to the hazard is relatively limited,” the report concluded.

PG&E will continue with its $64 million evaluation of the earthquake faults surrounding the nuclear plant, including controversial high-energy offshore seismic surveys scheduled to begin next month.

The utility will also conduct NRC-required inspections called a “walkdown” to identify any additional earthquake enhancements that are required as a result of lessons learned from the Fukushima Dai-ichi nuclear accident in Japan, which involved a powerful earthquake and tsunami.

Jane Swanson, spokeswoman for the anti-nuclear group San Luis Obispo Mothers for Peace, said she agrees that the Shoreline Fault is probably not the greatest threat to the plant. Other faults in the area, including the Los 

Osos Fault and the San Luis Bay Fault, are capable of delivering more powerful jolts than the Shoreline Fault, she said.

“The Shoreline Fault is only one factor in determining the seismic safety of the Diablo Canyon plant,” she said. “The more fundamental question is whether or not the plant can be shut down safely given the greatest possible ground motion from any fault.”

The Shoreline Fault was discovered by a cooperative research program with PG&E and the U.S. Geological Survey and was reported to the NRC on Nov. 14, 2008. The fault brushes the Diablo Canyon coastline from Point Buchon to Point San Luis.

The Hosgri Fault, the area’s dominant seismo-logical feature, runs about three miles offshore. Diablo Canyon is designed to withstand a magnitude-7.5 quake from the Hosgri Fault.

After the Shoreline Fault was discovered, the NRC sent an inspection team to Diablo Canyon in October 2011. The NRC report was developed with the assistance of a team of consultants from the Center for Nuclear Waste Regulatory Analyses of the Southwestern Research Institute.