May 8th, 2012, 8:22 pm
Posted by Pat Brennan, science, environment editor

The San Onofre nuclear plant. Register photo by Ana Venegas.

Operators of the troubled San Onofre nuclear plant now say more than 1,300 steam generator tubes have been plugged in the plant’s two idled reactor units.

And despite statements Thursday from an executive with the operator, Southern California Edison, suggesting a possible restart of the reactors next month, the utility company said Tuesday that no date has been set.

The earlier statement was an estimate, Edison said, and any startup plans must have prior approval from the Nuclear Regulatory Commission.

Both of San Onofre’s reactors have been shut down since January, one unit for routine maintenance and the other after a leaky steam generator tube allowed a minor release of radioactive gas, prompting operators to shut it down as well.

Edison said there was never any danger to employees or the public.

Inspections, meanwhile, revealed hundreds of worn steam-generator tubes, including some that showed an unusual type of wear that indicated the tubes had been rubbing together.

The two steam generators in San Onofre’s Unit 3 reactor have only been operating since February of last year, the two steam generators in Unit 2 since February 2010.

A fact-sheet posted on Edison’s web site Monday said 510 steam-generator tubes have been plugged in Unit 2, 807 in Unit 3. Some were plugged due to wear, others as a precautionary measure, a spokesman said.

That is still within a margin that allows the steam generators to operate safely; plugging of worn tubes is a common practice with such steam generators, and each pair has nearly 20,000 such tubes.

Edison officials have said the more common type of tube wear is one engineers expect, when the tubes rub against support structures.

The more unusual type of wear, however, in which tubes rub together, has been seen in hundreds of tubes in Unit 3 and two in Unit 2, and is considered premature.

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