A California utility said Thursday it has notified the Nuclear Regulatory Commission of potential sabotage, possibly by an employee, of a crucial piece of safety equipment attached to one of its nuclear power reactors.

Southern California Edison said the incident did not pose an immediate safety threat because the plant involved, the San Onofre Nuclear Generating Station near San Clemente, is currently offline. But the plant operator found engine coolant had been poured into an oil reservoir on an emergency backup generator, which would have likely caused the generator to malfunction if needed to help cool the reactor during a power failure. The tampering is being taken seriously and security at the plant has been tightened, SCE said.

"The comprehensive investigation has included rigorous tests, a review of station logs and employee interviews to determine the cause of the presence of the residual engine coolant," the company said in a statement late Thursday. "Based on the unexpected discovery of the coolant in the diesel oil system and the ongoing investigation, security at the plant has been enhanced."

An employee at the plant who asked not to be named because he feared reprisals from management said supervisors told employees on Thursday that the FBI would be taking over the investigation and that criminal charges were possible. A company spokeswoman declined to comment on whether the FBI was involved.

The incident was first discovered in late October and was reported to an on-site NRC inspector shortly thereafter. "The plant initiated a review of the incident, which is still ongoing, and subsequently reported the incident as a security-related incident on November 27," said Scott Burnell, a spokesman for the NRC. "Because the NRC’s review is ongoing and the incident is security related, we have no further information to share at this time."

The backup diesel generator, attached to Unit 3, one of the site's two nuclear reactors, would be needed to help keep the reactor cool if off-site power was somehow lost.

According to the Voice of Orange County, which first reported the incident in early November, NRC's on-site inspector said the coolant likely would have made the generator run unpredictably.

The beleaguered San Onofre plant has been the locus of heated controversy since both of its active reactors were taken offline earlier this year. While reactor Unit 1 was decommissioned in 1992, new steam generators were installed at reactor Unit 2 and Unit 3 in 2010. Unit 2 was shut down in January for routine maintenance, but was kept offline after a small radioactive leak was discovered in steam generator tubes in Unit 3 later that month. Further investigation revealed significant degradation in steam-generation tubes in both active reactors, and the entire plant has been idled since.

The NRC, which has been monitoring the San Onofre facility as it scrambles to repair the failed equipment and bring the plant back online, was scheduled to meet with SCE representatives on Friday for updates "on the basis, methodology, and conclusions of [SCE's] efforts to identify the cause(s) of the unexpected steam generator tube wear, the corrective actions taken to address the cause(s), and the basis for continued safe operation of Unit 2," according to an announcement of the public meeting posted to the NRC website.

Unit 3 has been de-fueled and a clear path to reactivation has not been established.

The problems have caused outrage among SCE customers, who contributed some $167 million to help pay for the new equipment, supplied by Mitsubishi Heavy Industries of Japan. As of this month, losses tied to the idled plant have topped $300 million, according to SCE's third quarter earnings report. California state utility regulators launched an investigation into the prolonged outage and losses in October.

Environmental and civil society groups have been lobbying to shutter the plant permanently.

Union members and management at the plant, meanwhile, have been locked in bitter contract negotiations, and the atmosphere further deteriorated after the company announced in August that more than 700 employees would be laid off before the end of the year.

"Most of us are kind of baffled by it," the SCE employee said of the alleged tampering. "While morale is as low as it has ever been and the environment is as chilled as it has ever been, no one I know could imagine doing such a thing. First of all, the chances of getting caught are so high. But more importantly, what are you accomplishing? You're only endangering yourself and your coworkers and the surrounding public. I can't understand the logic behind it.

"On the other hand, I'm also not completely surprised because the environment really is so harsh. People can do crazy things when they are under extreme stress."

David Lochbaum, a nuclear engineer and former employee of the NRC who leads the nuclear safety division of the Union of Concerned Scientists, an environmental group based in Cambridge, Mass., said it was not uncommon for workers facing layoffs at nuclear power plants "to express themselves in destructive ways."

Lochbaum pointed to previous incidents of minor sabotage at the Browns Ferry plant in Alabama, the North Anna facility in Virginia, and other plants where disgruntled workers were known to have cut electrical wires, put coins in the lubricating oil cases for emergency diesel generators, and used super glue to fasten doors shut. "Does this history mean that the fuel oil at San Onofre was intentionally watered down?" Lochbaum said. "No, but they sure set the stage for such a reaction when they laid off hundreds of workers who had access to vital areas of the plant."

A Nov. 2 letter addressed to SCE management from a representative of the local branch of the Utility Workers Union of America, which represents nearly 800 employees at the San Onofre facility, known as SONGS -- and which was shared with The Huffington Post by the environmental group San Celemente Green -- suggested that employees were concerned about plans to restart reactor Unit 2 with a diminished workforce.

"Local 246 cannot support the restart of SONGS Unit 2 if we do not have sufficient confidence that it can be operated and maintained safely by, and without undue risk, to our members," wrote Daniel Dominguez, the business manager of UWUA Local 246.

"Without a dramatic change in direction," Dominguez added, "we are unlikely to be able to say that the SONGS workforce is ready to restart and operate Unit 2."

Over the last four years, San Onofre has logged more safety concerns raised by employees than any other plant in the United States, according to NRC data. The plant's workers have complained openly of retaliation from management and fear of reprisals for reporting problems.



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