Despite progress in improving the safety culture of the San Onofre Nuclear Generating Station, the plant still ranked highest in the nation last year for both substantiated and unsubstantiated safety complaints at nuclear plants, according to figures from federal regulators.

The number of substantiated safety allegations at San Onofre in 2011 was more than six times the national average, a significant drop from its peak in 2010 when it was 15 times the average. But even with the decline, San Onofre was — for the third consecutive year — the national leader in safety allegations substantiated by the U.S. Nuclear Regulatory Commission.

And in the first two months of this year, the plant again generated more safety complaints from workers than any of the country’s other 64 nuclear plants. The San Onofre plant has been shut down since the end of January when a broken tube caused a small radiation leak.

More than 7 million people live within 50 miles of the plant, which is just south of San Clemente.

The leak has led to renewed calls from residents, activists and some local officials to have the plant better monitored or shut down. Earlier this month, the NRC’s top official visited the plant and vowed a full accounting of the tube failure.

Despite the plant’s poor record, its operator, Southern California Edison, continues to issue assurances that safety is their top concern.

“Our No. 1 priority is, and always has been, the health and safety of the public and our employees,” said Edison’s president, Ron Litzinger, in a recent video message about San Onofre.

Nonetheless, in the past four years San Onofre has far exceeded all other American nuclear plants in every category of safety complaint to federal regulators, with nearly 300 allegations of safety problems, 33 complaints of discrimination for reporting safety issues and 63 substantiated safety allegations.

San Onofre also generated 118 more safety complaints in the same period than the second-highest ranked plant, Susquehanna Steam Electric Station in Salem Township, Pa.

Federal regulators determined two years ago that some nuclear safety issues at San Onofre don’t receive the attention they deserve, with many workers fearing retaliation for reporting safety issues to the government.

Edison did not return calls seeking comment on the plant’s recent safety record.

Last year, workers and others lodged 48 safety complaints against San Onofre, with eight substantiated by federal regulators.

The complaints are allegations of ignored government safety regulations or plant safety procedures and are mostly reported by workers who either fear retaliation for reporting the issue to superiors or feel that management simply won’t address the problem, according to the NRC.

Through interviews with plant workers in late 2009, the NRC found that fear of retaliation was unusually high among San Onofre’s employees.

“Approximately 25 percent of those interviewed indicated that they perceived that individuals would be retaliated against if they went to the NRC with a safety concern,” the agency wrote.

In March 2010, federal regulators issued a “chilling effect” letter on San Onofre, in which they described an environment where “nuclear plant safety issues may not always receive the timely, focused attention warranted by their significance.”

The NRC then asked Edison to develop a plan to help workers feel more comfortable reporting safety concerns. By September 2011, the NRC was content that Edison’s response was “effective in addressing the underlying issues” of the chilled safety environment, and regulators announced they would end their heightened monitoring of San Onofre’s safety culture.

But in recent interviews regulators say they are still watching the plant carefully.

“Although the numbers are down substantially, they still have more allegations than the other sites, and that concerns us,” said Victor Dricks, an NRC spokesman.

Nuclear safety expert David Lochbaum agrees that San Onofre’s declining complaints are a positive development. But he adds that “there’s really no excuse” for plant operators to not resolve safety issues as they come up.

“Even one unsubstantiated allegation is too many, because in theory the workers should feel free to raise these issues with their supervisors,” said Lochbaum, director of the nuclear safety project at the Union of Concerned Scientists and a former NRC instructor. “If they don’t have trust that management will do something, why should the public?”

Lochbaum added that it should make economic sense to simply deal with safety issues as soon as possible. “When you find problems at the earliest opportunity, and you stop them the first time, that [is] really the key,” he said.

While San Onofre continues to rank high in specific safety allegations, it did make significant progress in complaints of actual discrimination, where workers report that they were treated unfairly or retaliated against for reporting safety concerns.

From 2010 to 2011, discrimination allegations fell from 14 to three. The average for other U.S. nuclear plants is a little more than one per year.

Federal regulators say that in all of these discrimination cases, the allegations were never substantiated because Edison and the workers settled the issue. Settlements can include promotion, reinstatement to a position, or monetary compensation, according to the NRC.

January’s leak, which Edison and NRC officials say posed no risk to workers or the public, was the result of extremely rapid deterioration to steam generator tubes, an important radiation barrier at the plant.

The degradation was in turn caused by tubes vibrating and rubbing against one another, Edison and the NRC say. They have yet to comment, however, on what they believe to be the ultimate cause of the tube wear.

In the absence of an official explanation, nuclear engineer Arnie Gundersen has concluded that the quick degradation was caused by major design changes — including adding hundreds more tubes and removing a key generator component — avoided a thorough government review by Edison asserting they wouldn’t increase the risk of a safety incident. Gundersen’s reports were commissioned by the environmental group Friends of the Earth.

Edison, meanwhile, insists it “provided open and transparent information” to federal regulators “at all times” when the changes were proposed. The NRC also says it approved all modifications before the generators were installed.

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