An environmental group filed a petition Tuesday seeking to shut down California's last remaining nuclear power plant until regulators have taken a more extensive look at its ability to withstand an earthquake.
The filing by Friends of the Earth came a day after the group released a confidential document submitted to the U.S. Nuclear Regulatory Commission in July 2013 by a former inspector at the plant, in which he argued that the plant should be shut down until operator Pacific Gas & Electric proves it is earthquake-safe.
Diablo Canyon was retrofitted in the 1970s after the Hosgri fault -- capable of delivering a 7.5-magnitude quake -- was discovered. In 2008, geologists discovered a new 6.5-magnitude-capable fault just offshore from the plant.
Federal regulators concluded that the plant's current design can withstand an earthquake from the offshore fault, and said Monday that they stand by that finding. A spokeswoman for the Nuclear Regulatory Commission said the agency is still reviewing the former inspector's concerns and has not issued a final response.
But Friends of the Earth argued that the plant should be required to seek a license amendment -- a potentially lengthy process that can include trial-like hearings -- because of the new earthquake risk information. The plant should be ordered to shut down until a decision has been made on the license, the group argued.
The petition noted that PG&E had requested a license amendment after the Shoreline fault was discovered in 2008, but commission staff were poised to deny it because the earthquake safety analysis didn't meet the required standards. The company withdrew its request and agreed to do more review of earthquake risks around the plant.
"Rather than holding a public hearing process as required by the [Atomic Energy Act] -- where the public could challenge the NRC staff’s and PG&E’s unsubstantiated assertions that the plant is safe -- the staff has used a closed-door process between itself and the licensee to work a de facto license amendment," the Friends of the Earth petition said.
The group made similar arguments when the San Onofre nuclear plant closed due to faulty equipment in 2012. The plant's operator, Southern California Edison, proposed to restart a portion of the plant at partial power, but Friends of the Earth argued that to do so would require a license amendment.
The closure was initially expected to be temporary, but Southern California Edison announced in June 2013 that it would be closed for good. Diablo Canyon is the state's only remaining nuclear plant.
[Updated at 5:37 p.m.: Blair Jones, a spokesman for PG&E, said the Friends of the Earth petition is "mischaracterizing the facts" and that the plant is in compliance with its license and with safety requirements.
"As an electricity generating facility regulated by the NRC, the plant is continuously evaluated to ensure the facility is safe," he siad in an emailed statement. "This includes the ongoing evaluation of the seismic design of the plant. If the NRC or PG&E felt for any reason that the facility was unsafe all operations would cease."
A spokewoman with the NRC said only that the agency will "review [the petition] according to its procedures and respond accordingly."]
Follow Abby Sewell on Twitter: @sewella.