During a lengthy discussion with Pacific Gas and Electric Co. on Tuesday, the federal Nuclear Regulatory Commission reaffirmed its determination that Diablo Canyon nuclear power plant could withstand a powerful earthquake on faults surrounding the plant.
Officials with PG&E and the NRC held a highly technical four-hour discussion about the seismic threat facing Diablo Canyon in the aftermath of the Fukushima Dai-Ichi nuclear power plant disaster in 2011.
The intent of the discussion was to update the NRC on PG&E’s efforts to study the extensive system of earthquake faults around the plant and ensure that the plant’s vital safety equipment can continue to function if a powerful quake occurs.
“The real question that needs to be answered is what the plant can withstand,” said Diane Jackson, a geosciences and geotechnical engineer with the NRC.
No regulatory or policy decisions were made at the meeting, which took place at NRC headquarters in Rockville, Maryland, said Nicholas DiFrancesco, with the Office of Nuclear Reactor Regulation.
Following the Fukushima accident in Japan, the NRC required that all nuclear power plants in the nation conduct additional safety inspections. In March, PG&E submitted an interim evaluation of the seismic safety at Diablo Canyon that determined it could withstand a worst-case scenario quake on multiple faults.
This conclusion was disputed as being overly optimistic by several notable local seismologists including former state Sen. Sam Blakeslee and county Supervisor Bruce Gibson. However, at Tuesday’s hearing, the NRC reaffirmed that it is not aware of any significant safety issues at the plant and allowed PG&E to continue its seismic evaluations.
No local anti-nuclear activists attended the meeting, which was easier to watch online, said Jane Swanson with the San Luis Obispo Mothers for Peace. Swanson did not have a comment on the hearing.
The NRC has given PG&E several deadlines to meet in order to complete its seismic safety evaluations. By January 2016, PG&E must demonstrate that key pieces of safety equipment, particularly those that ensure the reactors’ radioactive core will remain cooled if a powerful earthquake strikes the plant.
Lastly, the utility has until the end of 2020 to complete its seismic risk evaluations. The NRC will then determine if any additional safety actions are required.
Norm Abrahamson, a PG&E seismologist, said Diablo Canyon is surrounded by four significant earthquake faults. The Hosgri Fault, which is about three miles offshore from the plant, is the main one.
“The Los Osos, Shoreline and San Luis Bay faults are also defining faults,” he said. “Those dominate the contribution of the seismic hazard at the plant.”
The NRC’s Jackson said that at Tuesday’s meeting PG&E gave the agency the information it was seeking. She said the NRC would expedite its response to PG&E’s seismic program.