Two recent academic studies of California earthquake risks undermine assurances by Pacific Gas & Electric Co. (PG&E) and the U.S. Nuclear Regulatory Commission (NRC) that the twin Diablo Canyon nuclear reactors are earthquake-safe. This issue is of paramount concern for San Luis Obispo Mothers for Peace (SLOMFP) and should be for all those living and working in proximity to Diablo Canyon.
The studies by Harvard and Stanford Universities apply new and sophisticated methods to model earthquake risks in the coastal areas near Los Angeles (Harvard) and San Francisco (Stanford). In both investigations, researchers found a larger and more complex system of faults than was previously known, creating the potential for much larger-than-anticipated earthquakes.
In the Los Angeles area, the Harvard study reported the potential for a 7.8 magnitude earthquake. In the San Francisco area, the Stanford study estimated that earthquake faults could generate a 6.9 magnitude earthquake. Earthquakes of these magnitudes could cause destruction equal to that of the Loma Prieta earthquake in 1994, which killed dozens of people and caused billions in property damage.
The discovery by these two recent studies that earthquake faults were more extensive and connected than had been thought in the past is troubling with respect to Diablo Canyon. PG&E previously agreed to retire the reactors in 2024 (Unit 1) and 2025 (Unit 2) with the approval of the State Government and overwhelming public support — but has now been approved by the State legislature and the Governor to operate until 2030. PG&E is now in the process of applying to the NRC for a renewed license.
Similar to the California coastal regions studied by Harvard and Stanford, the area underlying and surrounding the Diablo Canyon nuclear reactors is veined with multiple earthquake faults. These faults include the long-known Hosgri Fault, the recently-discovered Shoreline Fault, and other faults. Still, other faults that could impact Diablo Canyon may exist but have yet to be identified.
Of particular concern, the Harvard and Stanford studies demonstrate that the existing body of knowledge regarding earthquake risks to the Diablo Canyon reactors is based on outdated research. As stated in the Stanford study, “densely populated” regions are at a greater risk than previously understood because the faults “running underneath . . . are particularly difficult to study using traditional geologic methods.”
The cost of PG&E’s and NRC’s complacency in the face of these challenges is high. In a recent survey of existing knowledge about seismic risks at Diablo Canyon, Dr. Edwin S. Lyman, Director of Nuclear Power Safety with the Union of Concerned Scientists, stated that: “Serious questions persist about whether Diablo Canyon’s design basis and ‘current licensing basis’ meet a high enough seismic standard to adequately protect the public.” Dr. Lyman estimates that “the potential costs of an earthquake-induced accident could, by our estimate, cause more than 10,000 cancer deaths and over $100 billion in damages.”
Geophysicist and former California State Senator Sam Blakeslee said, “In virtually every instance where in-depth examinations occur, we discover that California’s offshore faults are larger, more interconnected, and more dangerous than ever previously understood. As a geophysicist, I’m troubled by the NRC’s apparent willingness to grant a 20-year license extension for an aging nuclear power plant without fully understanding the grave risk that these offshore fault systems pose to the state and its residents.” (The legislation calls for a 5-year extension, but the NRC grants no less than a 20-year license.)
While the California Legislature called for an “updated seismic assessment” by PG&E, it did not specify any requirements for the update.
In light of the revelations by the Harvard and Stanford studies, Mothers for Peace spokesperson Linda Seeley said, “If Diablo Canyon is to continue operating past 2025, the faults surrounding Diablo deserve to be studied with the most advanced methods available and subjected to rigorous peer review.” She added, “There is a monumental difference between an earthquake in the northern and southern portions of the state and an earthquake at Diablo Canyon; the reactor site hosts 3.7 million pounds of nuclear waste and each dry cask houses more radiation than the Hiroshima bomb. An earthquake at this site has lethal potential.“
SLOMFP, which has long played a watchdog role over PG&E’s operation of Diablo Canyon as well as NRC’s oversight, will be monitoring PG&E’s performance of the required seismic update.