The Latest Chapter in Diablo Canyon’s Seismic Saga

Lara Uselding
Public Affairs Officer, Region IV
 
Scott Burnell
Public Affairs Officer, HQ
 

Today, the NRC is looking over a 1,400-page report produced by the owners of the Diablo Canyon nuclear power plant for California state officials who had asked for new seismic information about the plant.

Specifically, Pacific Gas & Electric produced the report to meet part of a 2006 California law, California Assembly Bill 1632. PG&E shared the report with the NRC as they’re required to do as part of the plant’s existing long-term seismic research program.

diabloEarlier research examined the Shoreline fault, just offshore of Diablo Canyon. Both PG&E and the NRC had previously concluded, in 2009 and 2012, the fault could only generate a quake weaker than one from the Hosgri fault, which Diablo Canyon is designed to safely withstand.

For the new report, PG&E performed state-of-the-art surveys of faults near the plant, including the Shoreline fault. The new report’s more detailed information and updated analysis indicates the Shoreline fault is both longer than previously thought and able to produce a slightly stronger earthquake.

As part of its NRC requirements, PG&E must assess the report’s impact on plant operations. NRC Resident Inspectors and Region IV staff experts have already looked at PG&E’s assessment and so far the information provides confidence the plant can keep the public safe after a seismic event.

While PG&E’s new seismic information adds detail about the faults in the plant’s immediate vicinity, the company’s evaluation claims an earthquake generated by movement on the Shoreline fault would not be as energetic as previous studies say a Hosgri-generated earthquake would be.

Just as with the earlier Shoreline fault reports, the NRC will thoroughly review the new information through our existing oversight methods. The agency will take whatever action is appropriate if our review questions PG&E’s conclusions.

PG&E will also use this new information as it re-evaluates its overall seismic hazard as part of the NRC’s response to the 2011 Fukushima nuclear accident. PG&E’s re-evaluation is due to the NRC in March 2015. The NRC remains committed to integrating new information into our understanding of safety at all reactors.