The owner of the Diablo Canyon nuclear power complex asked federal regulators to delay issuing extended operating permits until comprehensive studies are completed on earthquake faults in the area, officials said Monday.
The move by Pacific Gas and Electric Co. came after a public outcry over possible safety risks at the California plant, which were heightened by the huge earthquake and tsunami that plunged Japan into a nuclear crisis.
Diablo Canyon, perched on an 85-foot bluff above the Pacific Ocean, sits within three miles of two earthquake faults. Lawmakers have been pushing the company to perform more thorough testing to assess earthquake risks before new licenses are granted.
More than 400,000 people live within 50 miles of the site, located midway between Los Angeles and San Francisco.
At a legislative hearing last month, company officials said the plant was safe and gave no hint that PG&E would agree to complete three-dimensional seismic studies before a renewal of the licenses.
But in a statement Monday, PG&E Senior Vice President John Conway referred to the Japanese crisis and said, "we recognize that many in the public have called for this research to be completed before the NRC renews the plants' licenses. We are being responsive to this concern."
The company wants the NRC to extend the life of the complex for 20 years after its permits expire in 2024 and 2025.
In a letter to the NRC dated Sunday, PG&E said it would be prudent to complete the studies prior to granting new licenses. The company said it wanted the NRC to hold off issuing new licenses, even if approved by the agency, until the three-dimensional studies are finished.
State Sen. Sam Blakeslee, a Republican whose district includes the site, commended the decision and said in a statement that "it's our duty to learn and apply the lessons of Japan." Senate Majority Leader Ellen M. Corbett, D-San Leandro, said "it is unfortunate that it took a major catastrophe in Japan and a (legislative) hearing to prompt quicker action."
NRC spokeswoman Lara Uselding said the agency will consider the company's request to see what, if any, impact it would have on the agency's review schedule.
In its letter, the company said it wanted to complete the research no later than December 2015, which would be long before the current licenses expire.
Diablo Canyon, where reactors began operating in the mid-1980s, has a long history of seismic issues.
The discovery of the offshore Hosgri Fault in 1971, after the plant was mostly completed, forced a major, costly redesign. Then, about two years ago, a geologic fault was discovered about a half-mile from the seaside reactor, raising new concerns about safety.
At issue at Diablo Canyon is not what is known, but what is not. Preliminary research at the site found its twin reactors could withstand a potential earthquake generated by the recently identified Shoreline Fault, just off the coast.
But California regulators say more study is needed on the new fault system. The fear is the two faults could begin shaking in tandem, creating a larger quake than either fault would be capable of producing on its own.
PG&E says the plant is built to withstand a magnitude-7.5 earthquake, the maximum considered possible for the site.