SAN JUAN CAPISTRANO, Calif. (AP) -- Federal regulators disclosed Monday that the proposed restart of the long-shuttered San Onofre nuclear power plant in California could lead to an exhaustive review that might last months or even years.
The Nuclear Regulatory Commission is considering if the complex proposal submitted by operator Southern California Edison last week to repair and start the damaged Unit 2 reactor will require an amendment to San Onofre's operating license, Regional Administrator Elmo Collins told reporters.
Such reviews can involve a thicket of public hearings, appeals and commission actions on safety and design issues that can take as long as two years to complete.
In a March letter, federal regulators outlined a series of benchmarks Edison must reach to restart the plant, including determining the cause of vibration and friction that damaged scores of steam generator tubes, how it would be fixed and then monitored during operation.
Those requirements, however, did not involve amending the plant's operating license.
Collins said Edison contends an amendment is not needed, and NRC officials have indicated previously that a staff-level review of the restart plan could be completed within months.
It's "an open question" if a license amendment is needed, Collins said during a news conference. "It's a possibility. I'm not saying yes or no."
Edison spokeswoman Jennifer Manfre said in a statement Monday that the company "will not restart Unit 2 until the NRC states it is safe to do so."
"We have submitted our ... restart plans. SCE won't speculate on what the NRC would determine to be necessary in that evaluation," she said.
The problems at San Onofre center on four steam generators that were installed during a $670 million overhaul in 2009 and 2010.
Anti-nuclear activists have argued for months that restarting the plant, located between San Diego and Los Angeles, would invite catastrophe. About 7.4 million Californians live within 50 miles of San Onofre's twin domes.
In government filings, Friends of the Earth has asserted a license amendment, rather than an NRC staff review, is needed to protect safety and transparency. Critics have also charged that Edison should have sought a license amendment when it replaced the generators, which they claim would have uncovered problems with vibration the led to unexpected tube wear.
"We got into the current situation because Edison bypassed the license amendment process when it replaced the steam generators," said Daniel Hirsch, a lecturer on nuclear policy at the University of California, Santa Cruz, who is a critic of the nuclear power industry. Restarting the plant "without a full adjudicatory hearing that a license amendment would permit would just repeat that mistake."
The trouble began Jan. 31, when the Unit 3 reactor was shut down as a precaution after a break in a tube carrying radioactive water. Traces of radiation escaped at the time, but officials said there was no danger to workers or neighbors.
Unit 2 had been taken offline earlier that month for maintenance, but investigators later found unexpected — in some cases extensive — wear on hundreds of tubes inside steam generators in both units.
Tests found some tubes were so badly corroded that they could fail and possibly release radiation, a stunning finding inside the nearly new equipment.
Edison's proposal calls for operating Unit 2 at up to 70 percent power for five months then shutting it down for inspections. Company officials expressed confidence in the proposal, which followed more than 170,000 tube inspections over more than eight months.
The future of the heavily damaged Unit 3 reactor is not clear.
Collins promised a thorough review, whether or not the agency requires Edison to seek an amendment to its operating license.
"We don't experiment with safety," he said.
In June, a team of federal investigators announced that a botched computer analysis resulted in design flaws that are largely to blame for unprecedented wear in the tubes.
The agency is still considering penalties against the company for issues related to the generator problems that have left the plant dark for more than eight months, Collins said.
The generators, which resemble massive steel fire hydrants, control heat in the reactors and operate something like a car radiator. At San Onofre, each one stands 65 feet high, weighs 1.3 million pounds, with 9,727 U-shaped tubes inside, each three-quarters of an inch in diameter. They were manufactured by Japan-based Mitsubishi Heavy Industries.
Cracked and corroded generator tubing has vexed the nation's nuclear industry for years.
Decaying generator tubes helped push San Onofre's Unit 1 reactor into retirement in 1992, even though it was designed to run until 2004. The following year, the Trojan nuclear plant, near Portland, Ore., was shuttered because of microscopic cracks in steam generator tubes, cutting years off its expected lifespan.
San Onofre is owned by SCE, San Diego Gas & Electric and the city of Riverside. The Unit 1 reactor operated from 1968 to 1992, when it was shut down and dismantled.
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