Diablo Canyon Deemed Safe From New Earthquake Fault

Pacific Gas & Electric, which operates the plant 12 miles southwest of San Luis Obispo, California, notified the NRC in November 2008 about the potential Shoreline Fault, approximately 15 kilometers in length located one kilometer (.6 mile) offshore from the Diablo Canyon power plant.

PG&E provided the commission with data from the company’s collaboration with the U.S. Geological Survey regarding the potential fault.

PG&E's Diablo Canyon nuclear power plant is located on the Pacific Ocean at Avila Beach. (Photo courtesy San Luis Obispo County)

NRC staff independently reviewed the USGS information to determine the fault’s potential implications for Diablo Canyon’s operation. The staff concluded the plant’s existing design already accounts for ground motions that could be generated by the potential fault’s largest possible earthquake.

In an April 8 letter to John Conway, chief nuclear officer at the Diablo Canyon Power Plant, NRC Project Manager Alan Wang of Plant Licensing Branch IV wrote, "Fault will not likely cause ground motions that exceed those for which the DCPP has already been analyzed."

The staff also concluded the potential fault does not alter Diablo Canyon’s tsunami hazard.

"The NRC staff also concludes that the potential Shoreline Fault has a dominant strike-slip faulting mechanism," wrote Wang. "It is highly unusual for strike-slip faulting to cause the type of significant seafloor elevation change necessary to cause a sizable tsunami and so the NRC staff would not expect any significant changes in the tsunami hazard assessment."

"Therefore," wrote Wang, "based on the currently available information, the NRC staff concludes that the design and licensing basis evaluations of the DCPP structures, systems, and components are not expected to be adversely affected and the current licensing basis remains valid and supports continued operability of the DCPP site."

The staff will continue to analyze additional information on the potential fault as it becomes available.

The Diablo Canyon Power Plant has been generating nuclear power since 1985. The plant currently provides electricity to more than 1.6 million homes in northern and central California through two 1,100 megawatt reactors.

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