The utility that runs the Southern California nuclear plant where a radiation leak occurred is asking federal regulators for permission to restart one of the steam generators at reduced power.

Southern California Edison Co. said today it will be safe to run San Onofre Nuclear Generating Station's Unit 2 generator at 70 percent power. Experts who have studied problems at the plant have concluded that operating that unit at the lower level will prevent the vibration that led to wear on tubes carrying radioactive fluid, said Pete Dietrich, Edison's senior vice president and chief nuclear officer.

"By reducing to 70 percent will eliminate the conditions that create and enable fluid elastic instability," Dietrich said, referring to the process that created tube damage.

The utility plans to shut down the unit again in five months and evaluate whether its strategy was effective.

The Nuclear Regulatory Commission will evaluate the request. The facility cannot restart without NRC's permission.

"The agency will not permit a restart unless and until we can conclude the reactor can be operated safely," NRC Chairwoman Allison Macfarlane said in a statement. "This could take a number of months. Our inspections and review will be painstaking, thorough and will not be rushed."

The plant in northern San Diego County has been closed since Jan. 31, when a radiation leak occurred in the Unit 3 steam generator. The Unit 2 generator had been shut down earlier that month for routine maintenance and was not put back online because of a NRC investigation. Problems later were found in the Unit 2 generator, as well.

The facility supplied power to about 1.4 million homes.

Both generators came from Mitsubishi Heavy Industries, which used a computer model to approximate water and steam levels when it made the equipment. That analysis was faulty, underestimating velocities of steam and water inside the generators by factors of three to four times.

Those underestimates combined with faulty design of the generators caused the equipment to vibrate, which led to abnormal wear on tubes that carry radioactive fluid. Both units suffered tube-to-tube degradation, with greater damage in Unit 3. Eight steam generator tubes there failed "to maintain structural integrity," the NRC report says.

Unit 3, which was older than Unit 2, did not have some of the structural updates of the newer component. But an NRC report this summer detailed that while there were far more extensive problems with tube wear in Unit 3, Unit 2 has some similar design flaws that put it at risk (Greenwire, July 20).

Friends of the Earth said there are serious concerns about whether Edison should restart San Onofre.

"The damage to these tubes is without precedent in the industry," said Bill Walker, spokesman with Friends of the Earth. "Attempting to restart it would be just a disaster waiting to happen.

"Our view is that shutting down a number of tubes and running at reduced power does not constitute repair," Walker added.

An analysis by Fairewinds Associates, conducted for Friends of the Earth, said Edison has taken more tubes out of service at San Onofre than the total for all other nuclear plants in the country combined.

Major work might be needed to get San Onofre operating at full power, Edison has told investors. Edison said today it is unclear how long it will take to get the Unit 3 steam generator operating again, or whether ultimately it can be repaired or if it will need to be replaced. It is not known whether it will be operating by next summer, when power demand is higher.

Meanwhile, Edison customers are paying as much as $54 million per month for San Onofre's two failed generators, the California Public Utilities Commission's (CPUC) Division of Ratepayer Advocate has said, citing the $650 million total cost of both units.

Edison did not address the cost during today's briefing, saying only that the CPUC would decide what customers will pay.

The CPUC may open an investigation into what happened at San Onofre. That agency, however, appears unlikely to take any action before Nov. 1. The commission has said it makes more sense to look at San Onofre in November because that is when Edison will need to submit a report on the status of the facility. CPUC rules require the agency to open an inquiry on any facility that has not operated in nine months.

Residents oppose restart

A poll funded by Friends of the Earth showed that a majority of residents oppose restarting San Onofre.

When the survey by David Binder Research asked people whether they favored keeping San Onofre closed and replacing the power it supplies with renewable energy, 58 percent said they supported it, compared with 32 percent who opposed.

That response came after the residents were told that "a three-month federal probe blamed a significantly flawed computer analysis of major generator design changes, which ultimately resulted in heavy wear to the alloy tubing. The operator, Southern California Edison, has yet to determine how to correct the problem."

The state's grid operator has said renewable power on its own cannot replace San Onofre because green energy provides intermittent power.

When asked how concerned they were about a nuclear accident at San Onofre, 73 percent of poll respondents said they were concerned. Out of all those asked, 30 percent said they were very concerned, while 22 percent were somewhat concerned and 21 percent were a little concerned.

The survey also asked whether people believed that, "generally speaking," nuclear power reactors currently operating in California are safe or unsafe. A majority, or 55 percent, said the reactors are safe, 30 percent said the reactors are unsafe, and 15 percent said they didn't know.

Asked to identify their political position from a list, 35 percent of those surveyed said they were somewhat to very conservative, while 31 percent answered moderate, and 28 percent said they were somewhat to very liberal.

The poll surveyed 700 registered voters in the Edison service area Sept. 11-17 on both cellphones and land lines. The poll has a margin of error of plus or minus 3.7 percentage points.