NRC agrees to reevaluate seismic risk at Diablo Canyon

“This is a major step forward and a clear acknowledgment that our concerns are valid,” said Diane Curran, legal counsel for Mothers for Peace, about the NRC’s decision. “It’s rare for the [commission] to review a petition of this nature, highlighting the . . . seriousness of the seismic risks involved.”

Critics of Diablo Canyon, which is California’s only remaining nuclear plant, say previous environmental reports about the site significantly underestimate the likelihood of a severe earthquake.

Owner Pacific Gas & Electric has long contested claims of danger due to seismic activity, since Diablo Canyon was built and retrofitted to withstand powerful earthquakes. In March 2023, PG&E received approval from the NRC in the form of a “timely renewal” exemption to continue operating the Diablo Canyon reactors beyond their retirement dates of 2024 and 2025. Later that year, in December, the California Public Utilities Commission voted to extend the life of the plant an additional five years. A 20-year license renewal application for plant’s two reactors is currently under review with the NRC.

From the company: “Updated seismic assessments confirm previous analyses that the plant is designed to withstand ground motions from potential earthquakes in the region and that major components can continue to perform their safety functions during and after a major seismic event,” PG&E spokesperson Suzanne Hosn said in an email.

“Because of decades of industry-leading research and ongoing evaluations of regional geology and global seismic events as part of Diablo Canyon’s Long-Term Seismic Program (LTSP), the seismic region around Diablo Canyon is among the most studied and understood areas in the nation. The LTSP is implemented by professional geosciences experts who work with independent seismic experts on an ongoing basis. Their processes and results have been independently verified by participatory peer review panels—an external panel from the UCLA Garrick Institute for the Risk Sciences, and the Diablo Canyon Independent Safety Committee—and have been formally accepted by the NRC,” Hosn added.

Background: The San Luis Obispo Mothers for Peace—along with the Environmental Working Group and Friends of the Earth—requested an NRC hearing to consider the groups' safety concerns regarding Diablo Canyon. They argue that PG&E has not acquired the proper environmental permits to continue operating the facility.

The groups believe that the location of the power plant—near Avila Beach in San Luis Obispo County—makes it susceptible to an earthquake that could cause a catastrophic nuclear meltdown.

The NRC hosted a Petition Review Board (PRB) on July 17, where Peter Bird, professor emeritus of geosciences at University of California–Los Angeles, shared testimony and new data on the seismic risks posed by thrust faults near the plant. A video explaining Bird’s study of Diablo Canyon can be seen here.

What’s next: The PRB said in an August 28 letter that the following issues would be investigated:

• A 2012 study from PG&E that failed to fully account for the threat posed by thrust faults beneath Diablo Canyon and the nearby Irish Hills.
• PG&E’s 2018 estimate of the risk of core damage from an earthquake is too low, with updated seismic data suggesting the risk is much higher than previously believed.
• A case study of a magnitude 7.5 earthquake that occurred in January in Japan, which scientists maintain is similar to what could occur near Diablo Canyon.
• Faults in the Irish Hills, near the plant, are capable of generating large earthquakes approximately every 715 years.

Quotable: “We are pleased with the NRC’s decision to take a closer look at the risks that an earthquake could pose at Diablo Canyon,” said Hallie Templeton, legal director for Friends of the Earth. “We will watch closely as [the] NRC conducts this renewed analysis and will not shy away from continuing to fight for public engagement around the safety of this aging nuclear power plant.”