Wear and tear problem on tubes carrying radioactive water

According to the Nuclear Regulatory Commission, more than a third of the wall had been worn away in two tubes at Unit 2, which will require them to be plugged and taken out of service. At least 20 percent of the tube wall was worn away in 69 other tubes, and in more than 800, the thinning was at least 10 percent.

Inspectors find ‘unusual’ wear on new tubes carrying radioactive water at Calif. nuclear plant Washington Post, By Associated Press, : February 2 LOS ANGELES — Unusual wear has been found on hundreds of tubes that carry radioactive water at Southern California’s San Onofre Unit 2 nuclear plant, raising questions about the integrity of equipment the company installed in a multimillion-dollar makeover in 2009.

The disclosure came two days after a tube leak at the plant’s other unit prompted operators to shut down the reactor as a precaution. The problems at Unit 2 were discovered during inspections of a steam generator, after the plant 45 miles north of San Diego was taken off-line for maintenance and refueling. The two huge steam generators at Unit 2, each containing 9,700 tubes, were replaced in fall 2009, and a year later in its twin plant, Unit 3, as part of a $670 million overhaul.
According to the Nuclear Regulatory Commission, more than a third of the wall had been worn away in two tubes at Unit 2, which will require them to be plugged and taken out of service. At least 20 percent of the tube wall was worn away in 69 other tubes, and in more than 800,
the thinning was at least 10 percent.

“The amount of wear that we are seeing on these tubes is unusual for a
new steam generator,” NRC spokesman Victor Dricks said. “If you have
that kind of thinning anywhere along the length of the tube, you have
a problem because it degrades the integrity of the tube, which can
contribute to leaks.”…
According to company officials, the new steam generators were
manufactured by Japan-based Mitsubishi Heavy Industries. The company
did not respond to an email sent Wednesday. Alexander said Mitsubishi
officials are assisting with the tube analysis at the plant.

Retired NRC engineer and researcher Joram Hopenfeld said the company
will have to determine why the tubing is degrading so quickly “before
they do anything else.”

“I’ve never heard of anything like that over so short a period of
time,” Hopenfeld said.

“The safety implications could be very, very severe,” Hopenfeld added.
“Usually the concern is in older steam generators, when they have
cracks all over the place.”

According to the regulatory commission, the tubes have an important
safety role because they represent one of the primary barriers with
the radioactive side of the plant. If a tube breaks, there is the
potential that radioactivity from the system that pumps water through
the reactor could escape into the atmosphere…..
Radioactive gas that leaked from that tube was vented into a building
that contains auxiliary equipment, according to the NRC. The radiation
was detected by monitors in that building, which is separate from the
sealed structure that houses the reactor.

Because the auxiliary building is not sealed — people come and go
through doors — it’s possible radiation escaped into the
atmosphere…..
http://www.washingtonpost.com/national/inspectors-find-heavy-wear-on-new-tubes-carrying-radioactive-water-at-san-onofre-nuclear-plant/2012/02/02/gIQAir4ykQ_story.html