Worn Tubes: CA Nuke Back in Play

Friday, October 5, 2012 @ 05:10 PM gHale

Southern California Edison (SCE) wants to restart one of the two reactors at its San Onofre nuclear plant, shut down since January over unusual wear on steam generator tubes.

The plant’s Unit 2 reactor was offline for routine inspections and maintenance when a steam generator tube in Unit 3 sprung a leak Jan. 31. That leak released a small amount of radioactive steam. That led to the discovery the tubes in the newly replaced steam generators were wearing out more quickly than expected, including some that showed an unusual type of wear caused by tubes rubbing against adjacent tubes.

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The U.S. Nuclear Regulatory Commission (NRC) sent a special inspection team to the plant and ordered SCE to keep the plant down until the company could show that it fully understood the cause of the issues and how to fix them.

In a plan submitted Thursday, Edison proposed to restart Unit 2 and run it at 70% of full power for five months before taking it offline for inspections to make sure the tube wear is not continuing. Unit 3, which had a more serious issue, would remain offline indefinitely.

Edison wrote the unusual wear was a result of “fluid elastic instability” — high-velocity steam flow and low moisture in certain areas that caused the tubes to vibrate excessively and rub against each other. Running the plant at reduced power would reduce the steam velocity to an acceptable level, the company said.

“Safety is our top priority, and after conducting more than 170,000 inspections to understand and prevent the problem, and confirming the corrective actions we have taken to solve the problem with the top experts from around the world, we have concluded that Unit 2 at San Onofre can be operated safely and within industry norms,” said SCE President Ron Litzinger. “When implemented, this plan will get San Onofre Unit 2 back to providing reliable and clean energy to Southern Californians.”

Out of the more than 300 tubes that showed tube-to-tube wear, only two were in Unit 2, and the rest were in Unit 3, officials said.

The NRC would need to sign off on Edison’s plan before Unit 2 could restart, a process than NRC Chairwoman Allison Macfarlane said could take months.

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