Pacific Gas & Electric (PG&E) Corp.’s Diablo Canyon nuclear station in California could withstand an earthquake generated by an offshore fault identified in 2008, the Nuclear Regulatory Commission (NRC) said.
The NRC’s report focuses on the latest identified earthquake source, called the “Shoreline fault,” just offshore from the plant in San Luis Obispo County, about 183 miles northwest of Los Angeles.
PG&E welcomed the NRC finding “which confirms that Diablo Canyon is seismically safe and is designed to withstand the maximum ground motions that seismic faults in the region are believed capable of producing.”
PG&E notified the NRC about the Shoreline fault in 2008. At 2,240 megawatts, Diablo Canyon is the larger of the state’s two nuclear power plants, supplying about 10 percent of the state’s power needs.
“Both PG&E and the NRC are continuing to look at the seismic characteristics of the Shoreline fault,” said NRC spokesman Victor Dricks. “This research information letter represents the staff’s latest analysis and basically concludes that the plant, as designed, would withstand any earthquake the Shoreline fault would generate.”
An NRC team visited the site in 2011, the agency said. Analysis from the visit and available information indicates that ground motion from earthquakes the Shoreline fault could potentially generate would fall within Diablo Canyon’s existing design limits, the agency said.
The plant’s design limits come from ground motion associated with an earthquake from the larger Hosgri fault near the plant, the NRC said.
Separately, PG&E is performing a $64 million seismic research effort mandated by the state legislature using three-dimensional seismic tests to better understand the hazards posed by potential earthquakes near the plant.
In August, the California State Lands Commission voted to allow the utility to move forward with the advanced tests using powerful sonar devices despite concerns about the impact on marine life.
At the request of the utility, its NRC application to extend the two Diablo Canyon reactors’ operating licenses beyond 2024 and 2025 will not finalize until the advanced seismic research called for by the state is completed.
Diablo Canyon must perform additional earthquake evaluations, as well as a “walkdown” to identify any near-term actions for enhancing earthquake resistance as part of the agency’s ongoing response to the 2011 Fukushima Dai-ichi nuclear accident in Japan which ended up triggered by an earthquake and tsunami.