San Onofre Nuclear Plant Reports More Test Failures

By CASSANDRA SWEET

Testing of critical safety equipment at a Southern California nuclear-power plant turned up additional problems after the plant operator said more pipes that carry radioactive water ruptured under pressure.

Edison International's EIX -0.84% Southern California Edison utility said Friday it was taking the rupture of the four steam tubes at the San Onofre plant seriously. The utility said it would continue testing more than 100 similar tubes as long it takes to determine the safest course. Three other steam tubes ruptured during testing earlier in the week, prompting the Nuclear Regulatory Commission to send a team.

"We're treating it very seriously and we're continuing to test," said Jennifer Manfre, a SoCal Edison spokeswoman. "That is what we're here to do right now."

Two federal inspectors from the NRC were already at the San Clemente, Calif., plant to investigate the situation and oversee the testing. Two to three other members of the team were en route to the facility, an NRC spokeswoman said.

There "was enough of a concern to send a team," said Lara Uselding, the NRC spokeswoman. "That's why [Edison] is conducting the test to get a full understanding of the condition and why our team will be looking at the steam generator to get a full evaluation."

Edison shut down one of two reactors at the San Onofre plant Jan. 31 after one steam tube sprang a leak and released a small amount of radioactive steam. The NRC said the amount of radiation released from the reactor, called Unit 3, posed no harm to workers or the public.

The plant's other nuclear unit, Unit 2, had been shut down for routine maintenance and refueling. Edison, which owns the plant with Sempra Energy's SRE -0.76% San Diego Gas & Electric utility, plans to keep both units offline until it is satisfied that the steam-tube problem is solved and it is safe to operate the plant, said Ms. Manfre.

At each unit, nearly 19,500 tubes carry hot, radioactive water and steam from pools of water that hold nuclear-fuel rods to the generators, which use the steam to produce electricity. The tubes are critical for keeping the plant's nuclear-fuel rods cool.

The steam tubes are contained in a chamber filled with cool water and must be strong enough to withstand pressure from the hot water inside and the cool water outside to ensure that radiation doesn't escape.

During the test, the tubes ruptured after being placed at three times the normal pressure level, Edison said. Those tubes are among 129 the company is testing because they showed premature wear. Because the testing itself wears down the tubes, the tubes will be removed from service, Ms. Manfre said.

The tubes are components of four steam generators that Edison and Sempra bought from Mitsubishi Heavy Industries Ltd. 7011.TO +2.03% and installed in 2009 and 2010 at a cost of $800 million.

Mitsubishi representatives and independent nuclear experts from around the world were on site helping with the testing and analysis, Edison said.