Southern California Edison asked federal regulators Thursday for permission to restart one reactor at the shuttered San Onofre nuclear plant, but the plant will not return to full power in the near future.
The proposal comes eight months after the plant was powered down over safety concerns when a small amount of radioactive steam was released from one of the plant's generator tubes.
The leak led to the discovery of wear on thousands of tubes that carry water that transfers heat from the reactor core to generate electricity. The steam generators were newly replaced and had been operating for less than one year in one of the reactors, Unit 3, and less than two years in Unit 2.
The U.S. Nuclear Regulatory Commission ordered Edison to keep the plant shut down until it could pinpoint the cause and determine how to address it.
Repairing San Onofre has become an expensive proposition for the utility, and perhaps the ratepayers. Fixing the problem could run into the hundreds of millions of dollars, but keeping the plant offline already has forced Edison and co-owner San Diego Gas & Electric to spend more than $142 million to replace the lost power.
Ratepayers have expressed concern that they might be asked to help pick up the tab on any repair work, even as they continue to pay for operating a plant that produces no energy.
Edison's request to bring San Onofre partially back online comes a month before the California Public Utilities Commission will be required to launch an investigation into San Onofre's extended outage, an inquiry that could take ratepayers off the hook for continuing to pay for the plant's costs.
The commission will also decide whether customers would have to pick up Edison's cost of buying replacement power.
Edison would not comment on the costs associated with the outage. "If the plant can be operated safely, we feel that it's prudent to operate the plant," Edison Senior Vice President and Chief Nuclear Officer Pete Dietrich said.
In its plan, Edison proposed restarting Unit 2 and running it at 70% of full power for five months before taking it offline again for further inspections. The company also committed to installing more sensitive detection equipment to catch vibrations and any future radiation leaks more quickly.
"Safety is our top priority, and after conducting more than 170,000 inspections to understand and prevent the problem ... we have concluded that Unit 2 at San Onofre can be operated safely and within industry norms," Southern California Edison President Ron Litzinger said in a statement.
Unit 3 showed more deterioration and much more of an unusual type of wear caused by tubes rubbing against adjacent tubes. Dietrich said it would be "next summer at the earliest" before the company is ready to submit a plan for solving the problems in that unit.
Edison officials said the unusual wear was a result of "fluid elastic instability" — high-velocity steam flow and low moisture in certain areas that caused the tubes to vibrate excessively — and that running the reactor at lower power would address the problem. They said slight differences in the support structures in Unit 3 made the issue less severe there.
Critics decried the proposal to restart Unit 2 as a dangerous gamble, saying that the design of the steam generators in both units is the same, and it's not clear that running the unit at reduced power will solve the problem.
"I just don't believe it's appropriate to treat Southern California as a science experiment," said Arnie Gundersen, a consultant to environmental group Friends of the Earth, which has adamantly opposed plans to restart the plant.
Sen. Barbara Boxer (D-Calif.) fired off a letter to the Nuclear Regulatory Commission, asking for a commitment that the agency will complete its own investigation into the plant's troubles before signing off on Edison's plan.
Others were skeptical but less apprehensive. David Lochbaum, director of the nuclear safety program at the Union of Concerned Scientists, said that he was not convinced that Edison and its team of outside experts had found the right power level to eliminate the vibration problems, but that installing better monitoring equipment would protect the public if they were wrong.
Nuclear Regulatory Commission officials said the agency will go through several months of inspections and analysis before making a decision on Edison's plan.
Other questions remain open, including the outlook for Southern California's energy grid if the plant fails to return to full power. Under the plan to run Unit 2 at reduced capacity, the plant would be generating about 800 megawatts of energy, instead of the 2,200 megawatts it previously provided.
The region got through the summer without San Onofre using a contingency plan that included conservation measures and temporarily restarting retired generating units at another plant. California Independent System Operator spokeswoman Stephanie McCorkle called the potential restart of Unit 2 "helpful," but noted that it's not certain the regulatory commission will sign off on it, and that the unit could be shut down for testing next summer.
Edison officials have said they will seek to recover the costs of the outage from insurance and from steam generator manufacturer Mitsubishi Heavy Industries. A regulatory commission report blamed errors in computer modeling by Mitsubishi for the problems in the new steam generators.
In a statement Thursday, Mitsubishi pushed back against the suggestion that using a different modeling code would have prevented the problems, saying that the type of tube wear found at San Onofre was unprecedented in the industry.