Federal report says San Onofre nuke plant might need to replace steam generators

San Onofre Nuclear Plant

Grant Slater/KPCC

A runner passes by the San Onofre Nuclear Power Plant on April 6, 2012.

Federal regulators released more details Thursday on damage at the San Onofre nuclear power plant. The Nuclear Regulatory Commission (NRC) report comes at the same time as another new analysis commissioned by a nuclear watchdog group.

The Fairewinds Associates report said problems with the steam generators at the San Onofre Nuclear Generating Station are the most severe found in comparable generators anywhere in the U.S. nuclear industry. San Onofre is operated by Southern California Edison.

“Edison and the NRC have admitted that the problems with San Onofre’s steam tubes are an anomaly, but they haven’t been forthcoming about just how historically off-the-charts the damage is in comparison to the rest of the nuclear industry,” said Arnie Gundersen, a nuclear engineer at Fairewinds and co-author of the report.

The plant has been shut down since radiation leaked from a damaged steam tube last January.

The Fairewinds report was commissioned by Friends of the Earth (FOE) which wants San Onofre shut down permanently.

The Fairewinds report said operating the reactors with the remaining unplugged — but worn — tubes could create cascading tube failures, leading to a domino-like catastrophic failure that would release significant radiation to a large area of Southern California.

The detailed data, posted on the Nuclear Regulatory Commission website, has implications for the future of the seaside plant.

The records show the extent of wear from friction and vibration in 3,401 tubes, among a total of nearly 40,000 inside the plant's four steam generators. Evidence of wear was found in 15,000 places in those tubes at varying degrees. In about 280 spots — virtually all in the Unit 3 reactor — more than 50 percent of the tube wall was worn away.

"We have looked at the numbers put out by the NRC and they confirm our analysis," said Damon Moglen, director of climate and energy programs at Friends of the Earth. "The information put out by the NRC is absolutely astonishing. We're talking about 4,000 tubes in these new steam generators showing significant damage and these reactors can't be operated with this level of degradation."

Southern California Edison did not return requests for comment on the Fairewinds Associates report.

"It's really a scary situation, but yet, federal regulators and Southern California Edison still have not explained what the cause of the problem is and we think the plant should remain shut down," said Moglen with FOE.

An earlier report by Fairewinds Associates said a series of design changes made to the steam generators by SCE is one of the causes for the accelerated tube wear.

"We have to get to that root cause of what's wrong with the steam generators and it has to be solved before the plant can be restarted," Moglen said. "The real issue here is how do the millions [of] people in Southern California feel about running this nuclear plant like a science project?"

Gradual wear is common in such tubing, but the rate of erosion at San Onofre startled officials since the equipment is relatively new. The generators were replaced in 2009 and 2010 in a $670 million overhaul.

The company has said previously that 1,300 tubes will be taken out of service, although the number is well within the margin to allow the generators to keep operating. Tubes have to be retired if more than a third of the alloy tube wall wears away.

The generators function something like a car radiator, which controls heat in a vehicle's engine. The generator tubes circulate hot, radioactive water from the reactors, which heat a bath of non-radioactive water surrounding them. That makes steam, which is used to turn turbines to make electricity.

The tubes represent a critical safety barrier — if a tube breaks, there is the potential that radioactivity can escape into the atmosphere. Also, serious leaks can drain protective cooling water from a reactor.

The four generators each have nearly 10,000 alloy tubes.

The trouble began to unfold in January, when the Unit 3 reactor was shut down as a precaution after a tube break released traces of radiation. That began a spiral of events that led to a months-long federal probe.

The NRC blamed a botched computer analysis for creating excessive vibration inside the generators that damaged tubes, with agency officials saying last month it's not known how the generators can be fixed.

The NRC left open the possibility that one or more of the huge machines might have to be replaced.

"We're dealing with very old, dangerous, decrepit reactors," said Moglen with nuclear watchdog, Friends of the Earth. "We could spend billions and billions of dollars on 1980s technology and still have dangerous reactors. We should be spending that money on renewable and clean energy rather than limping along with these dangerous reactors at San Onofre."

Decaying generator tubes helped push San Onofre's Unit 1 reactor into retirement in 1992, even though it was designed to run until 2004. The following year, the Trojan nuclear plant, near Portland, Ore., was shuttered because of microscopic cracks in steam generator tubes, cutting years off its expected lifespan.

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