(Corrects Aug. 25 story to show plant capacity in gigawatt-hours, not gigawatts an hour, in third paragraph)
By Barani Krishnan
Aug 25 (Reuters) - A federal nuclear inspector urged U.S. regulators to shut down a California nuclear power plant until tests showed its reactors could withstand shocks from nearby earthquake faults, according to the Associated Press and an environmental group.
Michael Peck's call to close the Diablo Canyon Power Plant in San Luis Obispo County was in a report he made to the Nuclear Regulatory Commission in 2013, the AP reported on Monday, a day after a strong earthquake shook California's Napa Valley region.
Peck was the lead on-site inspector for five years at Diablo Canyon, which has two reactors designed to produce about 18,000 gigawatt-hours (GWh) of electricity annually, or 7 percent of California's electricity use. It is owned by Pacific Gas & Electric Co (PG&E).
Peck's report concludes that the nearby Shoreline, Los Osos, and San Luis Bay fault systems are capable of producing ground motions that exceed the plant's safe shutdown precautions, according to the AP, which said it had verified the authenticity of the report.
According to Peck's analysis, no one knows whether the facility's key equipment can withstand strong shaking from those faults - the potential for which was realized decades after the facility was built, the AP said, citing the report.
Continuing to run the reactors, Peck writes, "challenges the presumption of nuclear safety," the AP reported.
Friends of the Earth, an environmental group that wants Diablo Canyon closed, posted what it said was Peck's report on its website on Monday. It did not say how it had obtained it.
"The NRC knows that Diablo Canyon's two reactors are the most vulnerable to earthquakes in the United States, but the agency has failed to heed Dr. Peck's repeated warnings," Friends of the Earth said.
PG&E spokesman Blair Jones said the Diablo Canyon plant, which has been operating since 1985, was built to withstand the largest potential earthquakes in the region.
"The NRC has exhaustively analyzed this issue, concluding that PG&E's ongoing analysis of nearby faults and our engineering assessments of the facility demonstrate that Diablo Canyon is seismically safe," he said.
Peck could not immediately be reached for comment.
NRC spokeswoman Lara Uselding said the agency is confident that the plant is capable of withstanding a powerful quake. Peck's analysis is currently working its way through a review process inside the NRC, she said.
Concerns about Diablo Canyon's safety came into focus after an earthquake and tsunami severely damaged the Fukushima nuclear power plant in Japan in 2011. Diablo Canyon is also located on the California coast where it uses ocean water for cooling.
Sunday's earthquake in Northern California injured more than 100 people, damaged historic buildings, set some homes on fire and caused power and water outages Napa Valley, a picturesque region north of San Francisco that is known worldwide for its wines. (Reporting by Barani Krishnan, additional reporting by Rory Carroll in San Francisco; editing by Paul Simao, Andre Grenon and Lisa Shumaker)