Washington, D.C. – Last month’s 6.0 earthquake in California’s Napa Valley has again raised the issue of whether the U.S. nuclear regulatory system adequately accounts for seismic activity in its safety analysis of the 2,000-MW Diablo Canyon plant. Diablo Canyon is the last operating nuclear station in the state and located well away from the Napa quake.

A “differing professional opinion” by a former Nuclear Regulatory Commission resident inspector at the Pacific Gas & Electric’s two-unit Diablo Canyon nuclear plant has called for the agency to shut the plant while the agency again reviews the ability of the two-unit pressurized water reactor to withstand a major temblor. Seismic issues have dominated the history of the plant near San Luis Obispo on the California coast.

The opinion by Michael Peck, for five years the top NRC official on site at the plant located on a convergence of faults, came in July 2013. That’s more than a year before the most recent Bay Area earthquake. The feisty environmental group Friends of the Earth, which led the successful campaign to shut down the San Onofre Nuclear Generating Station near San Diego, obtained the report and gave it to the Associated Press.

Peck’s 42-page argument for shutting down the plant during a new assessment of earthquake safety does not claim that the plant is unsafe. Rather, he makes a case that a 2011 analysis concluding that it is safe was inadequate. PG&E in 2011 submitted a safety analysis for the plant, based on geologic discoveries in 2008 of new faults in the area of the plant that could result in greater shaking of the plant than originally considered in its design. Peck wrote that the utility’s report “included deterministic evaluations concluding that three local earthquake faults are capable of generating significantly greater vibratory ground motion than was used to establish the facility safe shutdown earthquake (SSE) design basis.”

The NRC staff concluded that the potential from the newly-discovered faults “are at or below those levels for which the plant was previously evaluated” This conclusion, said Peck, was in error. “The staff’s conclusion of a ‘reasonable assurance of safety’ does not provide an acceptable basis for not enforcing existing NRC quality assurance, safety analysis, and license requirements. The staff’s corrective action also failed to address the Los Osos and San Luis Bay faults. The new seismic information concluded that these faults were also capable of producing ground motions in excess of the current plant SSE design basis.”

Earthquake issues have gotten more attention following the March 2011 catastrophe at Fukushima in Japan. The Napa quake in late August raised the visibility of the issue. Sen. Barbara Boxer (D-Calif.), chairman of the Senate Environment and Public Works Committee and a foe of nuclear power, issued a statement saying, “When I have questioned the NRC about seismic issues at Diablo Canyon in the past, the response has been evasive and insufficient. Damaging earthquakes can occur at any time, and the NRC’s failure to act constitutes an abdication of its responsibility to protect public health and safety.” She said her committee will hold hearings on the issues Peck raised.

The NRC has hasn’t responded to Peck’s analysis and refused to comment to the wire service, as did Peck. PG&E insisted that the plant is safe and has been in full compliance with its license since it began operating 30 years ago.

The plant has a long and twisted history, most of it associated with seismic issues. PG&E in the early 1960s originally wanted to build a single nuclear power plant at a site on the Nipomo Dunes inland from San Luis Obispo, known as Diablo Canyon (it would be hard to pick a worse name). The site was located over the famed and feared San Andreas Fault. The Sierra Club, then under the leadership of the late David Brower (who subsequently founded Friends of the Earth after the club sacked him for being too confrontational) pushed back. The utility agreed to the coastal site, but retained the devilish name for the plant.

In 1969, Shell Oil geologists discovered the Hosgri Fault not far offshore from the Diablo Canyon site. During the resulting furor, the generating project got repeatedly delayed. That included an embarrassing episode in the early 1980s, when the regulators discovered that PG&E had flipped the image of the electrical network for the second unit. The NRC was poised to approved an operating license when the engineering foul-up surfaced.That put another couple of years’ delay into the project. It did not become commercial until 1984, some 14 years after the start on construction.