NRC: San Onofre tanks lacked proper quake analysis

A recent inspection by federal regulators showed that fuel tanks buried at the San Onofre nuclear plant had not been properly analyzed for potential failure during an earthquake, although a follow-up analysis showed the tanks were safe.

The lack of proper seismic calculations was one of six "green" findings outlined by the Nuclear Regulatory Commission in an Oct. 14 letter to San Onofre's chief nuclear officer, Pete Dietrich.
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"Green" means the findings were considered of "very low safety significance."

The findings emerged from a routine but intensive inspection of the plant that went beyond its typical quarterly inspections, and was completed Sept. 13.

"What we are doing here is actually going out and walking through the site, comparing structures and systems, as they are, with their design base, and seeing that there's proper documentation for everything they're looking for," said NRC spokesman Victor Dricks.

Officials at Southern California Edison, operator of the nuclear plant, said the problem was mostly one of paperwork: the proper engineering analysis had been done, but had not been conveyed to the NRC.

It involved calculations of stress placed on the underground tanks, which hold fuel for backup generators in case of an electrical emergency.

The NRC's finding focused on concrete structures built above the tanks. The tanks were buried as a safeguard against earthquakes.

The agency's inspectors said the Edison analysis they saw did not accurately reflect the condition of the tanks. Such an improper analysis could, hypothetically, have left the door open to failure of the tanks during a quake.

But Edison says in this case, the structure actually improved earthquake safety for the buried tanks.

"Southern California Edison agrees with the NRC finding that we failed to modify documentation related to certain components," said Edison spokesman Gil Alexander. "And any failure of this type, regardless of whether it is classified as having a low safety significance, is unacceptable to the company."

Steps were already underway to improve documentation at San Onofre before the inspection finding, he said.

Both sides agreed after the follow-up analysis that the tanks and the structures met proper engineering standards for earthquakes.

Recommended safety measures at San Onofre in light of the nuclear accident at the Fukushima Daiichi plant in Japan are scheduled to be discussed at a San Clemente City Council meeting Tuesday night.

The plant itself was under increased scrutiny by the NRC in recent years because of a variety of personnel issues, including a "chilling effect" said to keep some employees from reporting safety concerns.

Last month, the NRC said San Onofre had corrected the problems, and that the chilling effect was gone.

The recent findings are not an indication that San Onofre's deeper problems have returned, Dricks said.

It also is not unusual to find a few violations at nuclear plants subjected to the higher-level inspection, he said.

"It's unusual when we do a thorough and comprehensive and intrusive inspection that we don't have some findings," Dricks said.

The other five findings appeared to be minor electrical or sensor problems, or necessary changes to drawings of plant systems that had not been made.