Leak Shuts Nuke; Worker Falls in Reactor Pool

Friday, February 3, 2012 @ 12:02 PM gHale

After sensors detected a leak in one of the unit’s steam generator tubes, Southern California Edison (SCE), operator of the San Onofre Nuclear Generating Station, shut down of Unit 3.

Meanwhile, over at Unit 2, a worker fell into the reactor pool while the reactor was undergoing scheduled maintenance.

San Onofre Nuclear Generating Station remained off-line for a second day after a small gas leak that possibly spread to the atmosphere.

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Officials first detected the leak at 6 p.m. Tuesday, according to the U.S. Nuclear Regulatory Commission (NRC). Personnel then immediately began shutting down the reactor.

The two-day shutdown is likely costing the power plant $600,000 to $1 million a day, said Murray Jennex, an associate professor with San Diego State University’s Homeland Security Program and also a consultant for San Onofre for several years.

Because the steam generator where the leak occurred was only installed in 2010, Jennex questioned whether there are manufacturing problems with the generator or if it is not being properly maintained.

“As an engineer I’d like to have seen it go a few years without having a tube leak occur,” he said.

Jennex said he suspects a “weird flow condition” might have caused problems with the tube.

“To me that just says perhaps we need to make sure that we’re taking care of the steam generator in the right way,” he said.

Gil Alexander, spokesman for SCE, confirmed more than one tube suffered damage.

“We are detecting some accelerated wear in very small areas on one or two of the tubes,” he said.

Radioactive gas “could have” escaped the San Onofre Nuclear Generating Station on the northern San Diego coast after the Tuesday shutdown, said NRC spokesman Victor Dricks.

Alexander said the amount would have been “extremely small” and possibly not detectable by monitors.

The company and federal regulators said the release would not have posed a safety risk for the public.

“It would have been very, very small, low level, which would not pose a danger to anyone,” Dricks said.

Unit 2 is currently offline for a planned maintenance, refueling and technology upgrade outage. SCE said it has ample reserve power to meet customer needs while Unit 3 is offline.

Meanwhile, a worker fell inside the plant’s Unit 2 reactor pool last week, but officials determined he did not suffer significant radiation exposure.

The worker, employed by a private contractor assigned to replace the reactor’s vessel head, “momentarily lost his balance” and fell into the pool Jan. 27 while leaning over to retrieve a flashlight, Alexander said.

“He was wearing all of the appropriate safety equipment, including a life preserver vest. We immediately began a thorough medical screening to determine if there had been any injury,” Alexander said.

The pool is more than 20 feet deep and holds water that continually circulates through the reactor core.

Workers already had removed the highly radioactive uranium fuel that normally sits at the bottom of the pool, officials said.

Without the fuel present, the most likely source of deadly radiation would be stray fuel particles that could have been floating in the water, Dricks said.

Alexander said Edison decontaminated the worker and conducted tests to determine whether he had swallowed any dangerous particles.

Alexander said initial tests showed no significant radiation exposure.

The worker was a well-known veteran at the plant with no history of security problems, Alexander said. He said Edison will revisit its procedures for working around the reactor pool and may require that workers tie off with ropes to a surrounding structure as a way of preventing another incident.

Edison officials called the NRC to tell them about the fall, Dricks said, but the incident did not appear on a regular list of incident notifications all nuclear operators must make to the NRC.

Dricks said it was not technically a reportable incident under federal rules. The incident would have been reportable if the worker had received a radiation dose greater than 5,000 millirem, he said.

Alexander said the worker was determined to have received 5 millirem of radiation from the fall. The federal government allows nuclear workers to receive no more than 5,000 millirem of radiation in a calendar year.

“The worker was able to return to work the same day,” Alexander said, adding Edison continued to monitor the worker for several days after the fall but found no signs that he had received a harmful dose of radiation.

A person receives about a 4 millirem dose of radiation during a chest X-ray, according to the U.S. Environmental Protection Agency.

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