Keeping Tabs on Diablo Canyon’s Evolving Seismic Situation

Lara Uselding
Public Affairs Officer
Region IV

diabloThe NRC has added two items to the growing list of documents on seismic issues related to the Diablo Canyon Power Plant, near San Luis Obispo, Calif. Our Region IV office in Arlington, Texas, sent the plant operator, PG&E, an inspection report and our headquarters Office of Nuclear Reactor Regulation in Rockville, Md. sent PG&E a letter about the plant’s seismic hazard reevaluation due in March 2015.

The Region IV inspection report discusses the agency’s independent assessment of the operability determination completed by PG&E associated with its September report on the Shoreline and other faults near the plant. PG&E provided the report to the state under California Assembly Bill 1632. That bill required the report so the California Energy Commission could assess if California’s largest baseload power plants are vulnerable to a seismic event as those plants age.

The NRC did not request this analysis, but PG&E committed to keep us updated on any new information that would indicate the Shoreline fault is more energetic or capable than was presented in the January 2011 Shoreline Fault Report. PG&E further committed to provide the NRC with an interim analysis of any new Shoreline-related information before the post-Fukushima evaluations are due in March 2015.

Our regional review of PG&E’s operability determination indicates there is considerable design margin for the plant’s systems, structure, and components. The staff did not identify any concerns with PG&E’s determination that the plant is operable. The analysis adds to the evidence that the plant’s systems, structures, and components would function properly after an earthquake and not pose undue risk to public health and safety.

Our letter from headquarters confirms PG&E will incorporate the September report’s findings into its ongoing, post-Fukushima, full seismic re-analysis due in March 2015. The NRC believes this more rigorous analysis will provide the most accurate assessment of faults affecting the site.

The bottom line is that the effect of earthquakes has been extensively evaluated during the construction, licensing, and operation of the plant. Diablo Canyon’s systems, structures, and components are designed to withstand the area’s earthquakes and perform their safety functions.

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.