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More problems found at Calif. nuclear plant

 The failure of tubes that carry radioactive water at the San Onofre nuclear station prompted a reactor shutdown.
The failure of tubes that carry radioactive water at the San Onofre nuclear station prompted a reactor shutdown. Mike Blake/Reuters/REUTERS

LOS ANGELES - Four more tubes that carry radioactive water at a Southern California nuclear power plant failed pressure tests, prompting new safety concerns, officials disclosed Friday.

The four tubes in a massive steam generator failed Thursday in the Unit 3 reactor at the San Onofre coastal plant in northern San Diego County, according to Southern California Edison. Three other tubes failed earlier tests, the company said Wednesday.

The utility shut down Unit 3 and began testing samples from thousands of tubes on Jan. 31 after a leak was found. Traces of radiation escaped during the leak, but officials said there was no danger to workers or neighbors.

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The Nuclear Regulatory Commission said Thursday it was sending a special team of inspectors to determine why the metal tubes, which were installed in Unit 3 in 2010, have become frail enough to pose a risk of leaks.

“This is a significant issue,’’ said NRC spokeswoman Lara Uselding. “A tube rupture is really the concern.’’

Investigators have been looking into excessive wear on Unit 3 tubes and its twin, Unit 2, which has been off line for maintenance and refueling. In a $670 million overhaul, two huge steam generators, each with 9,700 tubes, were replaced in Unit 2 in 2009 and a year later in Unit 3.

Nineteen percent of all power used by SCE customers comes from nuclear generation.

A spokeswoman for the agency that operates the state’s wholesale power system, the California Independent System Operator, said the San Diego and Los Angeles areas could see rotating power outages this summer if both reactors remain off line. The agency is taking steps to prevent those shortages.

“It’s all about balancing supply and demand,’’ said ISO spokeswoman Stephanie McCorkle. “You have to have a certain amount of plant [power] generation where the heavily populated areas of California are.’’

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Inside a steam generator, hot, pressurized water flowing through bundles of tubes heats nonradioactive water around them. The steam is used to turn turbines to make electricity.

The tubes are one of the primary barriers between the radioactive and non-radioactive sides of the plant, the NRC said.