Diablo Canyon Nuclear Plant Design Can Withstand Powerful Earthquakes

Shaking from a powerful earthquake could exceed the design of the Diablo Canyon nuclear power plant, its owners have found, but the reactors are safe because components were built with more than enough strength to withstand the potential stress and no equipment would be at risk, a report concludes.

Pacific Gas and Electric Co. said in documents released Thursday that the design breach revealed in new company research does not affect safety. Diablo Canyon is unique among U.S. nuclear plants, sitting amid a web of earthquake faults in a seismically active state, one just 650 yards from the reactors.

Jearl Strickland, PG&E's director of technical services, said in an interview that the plant's equipment has a robust safety margin above the design, meaning it can withstand greater vibrations. Additionally, there is no equipment in the plant that would be at risk from the type of shaking found to slightly exceed the design, he said.

The conclusion is at the heart of a report that re-evaluates seismic and flooding risks at the coastal plant, located midway between Los Angeles and San Francisco. The research was required by federal regulators after Japan's Fukushima Dai-ichi plant suffered multiple meltdowns after an earthquake and tsunami destroyed its power and cooling systems.

The company told the federal Nuclear Regulatory Commission there is a "reasonable assurance" the plant's key equipment can continue to operate safely, even after being subjected to powerful shaking.

"These updated findings are the culmination of years of study and analysis and further confirm the safety of the plant's design," Ed Halpin, PG&E's senior vice president and chief nuclear officer, said in a statement.

Daniel Hirsch, a lecturer on nuclear policy at the University of California, Santa Cruz, and a critic of the nuclear power industry, called the findings "deeply troubling.”

"As Fukushima demonstrated, earthquakes larger than a reactor was built to withstand can have devastating consequences. PG&E's nonchalant response, that everything is OK anyway, suggests that they just don't get it," Hirsch said.

Because of its proximity to faults, the safety of the twin-reactor plant has been fiercely debated for decades, even before it began operating in the mid-1980s. Release of PG&E's study came just days after the U.S. Geological Survey warned that it's virtually certain that California will be hit by a strong earthquake in the next 30 years.

The Associated Press disclosed in August that a federal expert wanted the NRC to shut down Diablo Canyon until it determines whether the reactors can withstand shaking from nearby faults. The commission rejected that recommendation.