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Pipe Problems Keep Nuclear Plant Closed

Thursday, June 14, 2012

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Plagued by inexplicably rapid pipe wear, both nuclear-power units at the San Onofre Nuclear Generating Station will remain closed indefinitely, Southern California Edison has announced.

The problem—described alternately as “corrosion” and “wear” in various reports—afflicts bundles of pipes in the four relatively new steam generators of Unit 2 and Unit 3. (Unit 1 of the San Clemente, CA, facility was closed years ago.)

 San Onofre Nuclear Generating Station

 Images: Southern California Edison

San Onofre Nuclear Generating Station’s Unit 1 has been closed for years. Units 2 and 3 were shut down this year, and a restart date is not known.

Unit 2 was taken out of service for a planned outage on Jan. 3. Unit 3 was shut down Jan. 31 after inspection showed unusual wear in the pipes, which are part of a $671 million steam generator system installed in 2009 and 2010.

Each generator—65 feet high, 22 feet wide, and weighing more than 600 tons— has 9,727 tubes.

SCE said Unit 2 would be offline until at least August; repairs and approval for restart of Unit 3 will take longer, the company said.

The plant supplies 19% of Edison’s power.

Wearing Thin

SCE, the majority owner and operator of the plant, discovered in February that the bundled tubes in both units were wearing thin, due to “vibrating and rubbing” against “certain supports” and one another, according to an SCE Fact Sheet.

Officials reported excessive wear on more than 300 tubes; pressure testing on 129 tubes in Unit 3 revealed that eight had failed. SCE also identified similar accelerated wear in some tubes in Unit 2.

 San Onofre steam generators

San Onofre Steam Generators 

The two Unit 2 steam generators at San Onofre were replaced in 2009. The two Unit 3 generators were replaced in 2010. Officials say the steam pipes are rapidly thinning.

The company says it is plugging all tubes that show excessive wear and plugging additional tubes as a precautionary measure.

SCE is still investigating the cause of the problem. Advocacy group Friends of the Earth recently blamed a design change that added 377 tubes to each generator, accelerating the vibration and degradation.

‘Safety, Not Timelines’

The problems drew a Confirmatory Action Letter in March from the Nuclear Regulatory Commission. The letter outlines actions that the operator must take before seeking permission from the NRC to restart the units.

Edison International Chairman and CEO Ted Craver said in a statement that “safety, not timelines, would determine when” the units are restarted. The company is also evaluating backup power sources to help the region weather the summer.

Meanwhile, SCE says it will approach Mitsubishi Heavy Industries, maker of the steam generators, for the price of repair.

The license for the plant expires in 2022. Edison has not yet decided whether to apply for a 20-year extension.

The NRC has scheduled a public meeting for June 18 to discuss the findings of its Augmented Inspection Team at the San Onofre site.

   

Tagged categories: Corrosion; Nuclear Power Plants; Pipeline

Comment from sasha bacic, (6/15/2012, 8:13 AM)

Would material certificates show eventual error or difference between selected and installed pipe material?


Comment from Tom Schwerdt, (6/20/2012, 12:29 PM)

If you can trust the material certificates. Better to check the alloy with a portable XRF. Too bad for SONGS - I did a couple of projects for them some years ago.


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