Federal regulators Wednesday directed nuclear power plants in California and Washington state to conduct additional, in-depth research into earthquake risks by June 2017, part of a broad review of seismic threats following Japan's Fukushima Dai-ichi disaster.
Among commercial U.S. nuclear plants, the Diablo Canyon reactors near San Luis Obispo and the Columbia generating station in Richland, Washington, face "the highest ... hazard" when potential strong shaking is evaluated against the plants' designs, the Nuclear Regulatory Commission found.
Bill Dean of the NRC's Office of Nuclear Reactor Regulation said in a statement that evidence so far leaves the agency confident that the plants are safe to continue operating while operators do more analysis.
"Plants must also do shorter-term work to see if they should enhance key safety equipment while the more substantial analysis is being done," Dean added.
Diablo Canyon, which sits within a web of earthquake faults on the California coast, one 650 yards away from the reactors, has faced questions for decades about its ability to withstand a strong earthquake. Last year, a former chief NRC inspector at the plant urged regulators to shut down the reactors until they can determine whether they can withstand shaking from nearby faults, a recommendation rejected by the NRC.
Last year, two Seattle-based groups, Heart of America Northwest and Washington Physicians for Social Responsibility, called for shutting down the Columbia plant, citing a report by a nuclear power critic on risk posed by a stockpile of spent nuclear fuel and a potential earthquake. Operator Energy Northwest said the report was marred by errors.
Anti-nuclear activists said the NRC directive confirms concerns that Diablo Canyon's design might not account for the threat of nearby faults discovered after the twin-reactor plant was constructed decades ago.
"The order is yet more evidence that earthquakes surrounding Diablo Canyon are capable of more ground motion than the reactors were built to withstand," Friends of the Earth said in a statement.
Blair Jones, a spokesman for Diablo Canyon owner Pacific Gas and Electric Co., said in an email that extensive research has found the plant is safe.
"Most importantly, the NRC stated they are confident Diablo Canyon remains safe to operate while additional analysis is undertaken," he wrote.
Research released by PG&E in March found that shaking from a powerful earthquake could exceed Diablo Canyon's design, but the reactors are safe because components were built with more than enough strength to withstand the potential stress. Also, company officials said there is no equipment in the plant that would be at risk from the type of shaking found to slightly exceed the design.