Seismic Safety at Diablo Canyon

Safety has and always will be PG&E's top priority. That's why Diablo Canyon Power Plant was built to withstand the strongest potential earthquakes in the region.

It's also why PG&E maintains a Long Term Seismic Program (LTSP) for Diablo Canyon, which continually assesses seismic safety at the facility. The LTSP is a unique program in the U.S. commercial nuclear power plant industry. It is comprised of a geosciences team of professionals who partner with independent seismic experts on an ongoing basis to evaluate regional geology and global seismic events to ensure the facility remains safe.

The Nuclear Regulatory Commission (NRC), the chief safety regulator for the nation's commercial nuclear power plants, continuously evaluates Diablo Canyon. This includes assessing Diablo Canyon’s seismic design, and the potential strength of nearby faults. The agency continues to find the expected seismic activity from these faults are at or below the levels that the plant has been designed to withstand.

Extensive scientific research recently performed in the area surrounding Diablo Canyon demonstrates the facility remains seismically safe and able to withstand the largest potential earthquakes in the region.

In September 2014, a report on the research was provided to the NRC. The report was also presented to the California Public Utilities Commission’s (CPUC) Independent Peer Review Panel (IPRP), an advisory task-force that reviewed how the seismic studies would be performed and provided insight and comments to the utility's researchers.

PG&E conducted advanced seismic research to provide a more detailed picture of the region's complex geology. The research has further defined the level of seismic activity that earthquake faults near Diablo Canyon are capable of producing.

PG&E completed the survey portion of the studies in 2012, and installed ocean-bottom seismometers in 2013 to detect and record seismic activity. An evaluation of the survey data was submitted in September 2014.

This research has given PG&E, scientists and regulators an unprecedented view into the Earth to significantly and fundamentally improve the knowledge of the seismic characteristics near Diablo Canyon.

This research confirms previous analyses that the plant is designed to withstand the ground motions from earthquakes in the region, and that major components can continue to perform their safety functions during and after a major seismic event.

The full report contains a summary and 12 detailed, technical reports of key regional seismic features. It also provides updated information on the level of potential ground motions, or shaking that could be produced by earthquakes on local geologic faults.

PG&E will use the research to support its Long Term Seismic Program (LTSP), which continually assesses seismic safety at Diablo Canyon.

The research will also support a new, NRC-mandated seismic hazard re-evaluation required for all U.S. nuclear power plants.

Under this process at Diablo Canyon, existing and new seismic information is being peer-reviewed and publically evaluated by independent experts as part of the NRC required Senior Seismic Hazard Analysis Committee (SSHAC) process. The SSHAC process conclusions will be used to update the models that characterize the seismic hazard near Diablo Canyon. The seismic hazard re-evaluation is due to the NRC in March 2015.

Even after this update is performed, PG&E will continue its study of the seismic characteristics of the region to ensure the safety of Diablo Canyon.

In 2012, PG&E completed 2D/3D low - and high-energy onshore studies and 3D low-energy offshore studies. Ocean-bottom seismometers were installed in 2013 to detect and record seismic activity. An additional 3D high-energy offshore study proposed by the utility did not receive approval by the California Coastal Commission in 2012.

Using state-of-the-art scientific methods, the data derived from PG&E's advanced seismic studies helped further define the level of seismic activity and ground motions that onshore and offshore earthquake faults in the region are capable of producing.

2D/3D Onshore Low - and High-Energy Research: From 2010-2012, vibroseis and accelerated weight drop trucks produced sound waves that penetrated the Earth's crust several kilometers deep. More than 2,000 strategically-placed recording devices captured the reflected sound waves, producing data that experts interpreted to help further define the seismic characteristics of nearby onshore faults.

PG&E Demonstrates Seismic Test Equipment for Public »

3D Low-Energy Offshore Research: In 2012, PG&E completed low-energy seismic research work off portions of California's Central Coast. PG&E began the first phase of this low-energy offshore study in 2010, and completed the second portion in 2011. The third phase, finished in 2012, studied offshore faults near San Luis Bay, Estero Bay and Point Sal.

To perform the work, equipment onboard a research vessel generated low-energy sound waves that were directed toward the ocean bottom. An array of sensors, or hydrophones, towed behind the vessel captured the sound waves as they reflected back to the surface. The data were recorded and used to create a detailed three-dimensional map of offshore seismic faults. Like the onshore work, this data helped further define the seismic characteristics of nearby faults.
DCPP Seismic Offshore

Ocean Bottom Seismometer Project:
In 2013, PG&E deployed four long-term and two temporary seismometers on the sea floor as part of the Ocean Bottom Seismometer Project. The seismometers are passive listening devices that will detect and record seismic activity in the region of Diablo Canyon Power Plant. The devices are located three nautical miles offshore at an approximate depth of 110 meters. An underwater cable connects the sensors to an onshore recording station, which relays data to researchers. The data derived will be used by experts in their continual study of the region’s complex geology, supporting PG&E’s continual commitment to seismic safety.

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