Restarting a nuclear power plant where a radiation leak occurred without repairing a troubled generator puts Southern California at risk for a disaster, opponents of the move said today.

Friends of the Earth and a group of nuclear power watchdogs argued that the San Onofre Nuclear Generating Station in San Diego County is not safe in its current condition. They objected to utility Southern California Edison Co.'s plan to run one of the steam generators at 70 percent power.

"We're turning Southern California into a science experiment here," said Arnie Gundersen, nuclear engineer with Fairewinds Associates, a consultancy group that produced a series of reports on San Onofre.

Edison said today that it has submitted to the Nuclear Regulatory Commission a plan to run San Onofre's Unit 2 generator at 70 percent power. Experts who have studied problems at the plant have concluded that operating that unit at that reduced level will prevent the vibration that led to unusually high amounts of wear on tubes carrying radioactive fluid, said Pete Dietrich, Edison's senior vice president and chief nuclear officer.

The utility plans to shut down the unit again in five months and evaluate whether its strategy was effective. NRC will weigh the request, because the facility cannot restart without NRC's permission. NRC Chairwoman Allison Macfarlane said in a statement that the review "could take a number of months. Our inspections and review will be painstaking, thorough and will not be rushed."

Sen. Barbara Boxer (D-Calif.), chairwoman of the Environment and Public Works Committee, today sent a letter to Macfarlane asking for "reassurance" that NRC will investigate the causes of unusual tube wear at the plant.

"I want to make sure that NRC fully understands the causes of the unusual tube deterioration, is confident that the plant can be safely restarted given the current condition of the tubes, and has determined the facility can be safely operated in the future," she wrote.

Boxer asked for a response in writing by Oct. 12.

San Onofre has been closed since Jan. 31, when a small amount of radiation escaped from a tube 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 an NRC investigation. Problems were found later in the Unit 2 generator, as well.

The facility supplied power to about 1.4 million homes. Running one of the generators at 70 percent power will reduce the output to 800 megawatts, which can power about 800,000 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.

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 although 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).

Unintended consequences?

Dietrich and others at Edison this morning said Unit 2 was less susceptible to damage because its support bars were much more effective in preventing excess vibration.

He also said that limiting the generator's power would work to prevent problems. "By reducing to 70 percent will eliminate the conditions that create and enable fluid elastic instability," he said, referring to the process that caused the vibration and excess wear.

But Gundersen said Edison's plan was risky.

"The fluid elastic instability will move" within the generator, Gundersen said. "It's not at all clear it will disappear."

That could cause the pipes to collide with each other, he said, and added that there would be other unintended consequences including "vortex induced vibration" and "turbulence induced vibration."

That could lead to tube cracking, he said.

"The generators are at risk of not a tiny crack like before," Gundersen said. "They remain likely to have a tube failure" with releases of "an enormous amount of radiation" that would necessitate an emergency cool-down.

"They are not out of the woods reducing to 70 percent," Gundersen said.

He said Edison needs to either replace the generators or cut the tops off the reactors and replace the anti-vibration bars on the equipment.

Friends of the Earth spokesman Bill Walker said the 70 percent power plan was similar to someone having a car with bad brakes and simply driving more slowly.

Dietrich rejected that comparison.

"This is not an experiment," Dietrich said. Over eight months, he said, there have been 170,000 tube inspections, and a team of experts has looked at Edison's plan. Their conclusion, he said, is that it's "safe to restart Unit 2 at reduced power."

"We take this responsibility very seriously," Dietrich said. "On Unit 2 we do not see anywhere near the extensive tube-to-tube wear that we see on Unit 3."

Friends of the Earth also argued that San Onofre isn't needed to supply power. Southern California made it through the summer without the plant, advocates said, and conservation and load management will allow the region to get through next summer as well.

San Onofre's closure forced California's grid manager to create a backup plan, which included asking for the restart of two retired AES Corp. natural gas units in Huntington Beach, Calif. (Greenwire, Aug. 2). Those will not be available next summer, Edison said this morning.