The Nuclear Regulatory Commission on Wednesday directed Energy Northwest and Pacific Gas and Electric Company, operators of the Columbia Generating Station in Washington state and the Diablo Canyon nuclear power plant in California, to take the next step in a review of seismic hazards by assessing the risks to plant components posed by tectonic conditions mapped out in recently conducted evaluations.
The NRC ordered the analysis to be completed by June 2017. But the agency said in a statement that despite the risks, the regulatory agency was confident the plants could operate safely, while the studies were ongoing.
In March, PG&E handed in a study of seismic threats to the plant near San Luis Obispo, Calif. That report said the plant would be safe even when hit with the most severe earthquake deemed likely to hit the area in 10,000 years.
PG&E on Wednesday asserted that the plant was safe to operate, pointing out to the press that the NRC deems the plant safe. The analysis ordered is not a new seismic study, as previously reported here. It is an analysis of the plant's equipment based on the study completed in March.
The next step of the review process was expected.
"As expected, the NRC has provided to Diablo Canyon and other Western U.S. plants the initial next steps in the regulatory review process, including when to perform additional seismic risk evaluations. The NRC has also indicated that additional guidance will soon be communicated to PG&E," said Diablo Canyon spokesman Blair Jones.
"Most importantly, the NRC stated they are confident Diablo Canyon remains safe to operate while additional analysis is undertaken. Even after this work is performed, PG&E will continue its ongoing seismic research efforts to ensure the safety of the plant and our surrounding communities," Jones said.
Diablo Canyon, California’s only operating nuclear power plant, has been the subject of repeated seismic studies. Similar to other operating plants, advances in tectonic plate studies have revealed underground fault lines that were unknown when the plant was built. Since Diablo Canyon began operating, three fault lines near the plant have been discovered. One of them is estimated to be 650 yards away from the plant’s reactors.
The Diablo Canyon plant’s license sets its shutdown earthquake limit at 0.4g, which means it is thought to be able to shut down safely in the event of an earthquake 0.4 times the force of gravity. But the plant has been built much sturdier than that, as the license also estimates the plant would be safe at 0.75g or 0.75 times the force of gravity.
"The updated seismic hazard assessment was performed at the NRC's direction and used the latest regulatory guidance, scientific methods and models, site-specific information and independent expertise to re-evaluate the impacts that earthquakes could have on the Diablo Canyon facility. While this invaluable examination shows a change in the overall seismic hazard, the analysis also re-confirms Diablo Canyon continues to be seismically safe," Jones said.
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