US nuclear agency head to visit troubled Calif reactors

HOUSTON, April 5 Thu Apr 5, 2012 6:59pm EDT

HOUSTON, April 5 (Reuters) - The chairman of the U.S. Nuclear Regulatory Commission and several California lawmakers are scheduled to tour the troubled San Onofre nuclear station in the state on Friday, the agency said.

NRC Chair Gregory Jaczko will visit Southern California Edison's 2,150-megawatt San Onofre nuclear station near San Diego, where both reactors have been shut since January due to the discovery of premature wear on tubes inside giant steam generators.

The steam generator tubes provide an additional barrier inside the containment building to prevent a release of radioactive steam.

Accelerated wear, which thins the tube walls, in new steam generators is unusual, NRC officials have said. A special NRC inspection team arrived at the site on March 19.

The NRC on March 27 said it would not allow the utility to restart the plant until the agency is sure that the premature degradation of tubes in the plant's steam generators has been addressed.

Environmental and local citizens' groups have called for a thorough investigation of the problems at San Onofre and for more public disclosure from SCE.

The California Independent System Operator is looking at ways to bolster the power grid in southern California should the San Onofre outage continue into the summer, when power demand rises.

Located about halfway between San Diego and Los Angeles, San Onofre's location makes it an integral part of the high-voltage grid in the southern part of the state, not only for generation but to allow power to be imported to the area.

SCE shut San Onofre Unit 2 on Jan. 9 to refuel the unit and replace the reactor vessel head, an outage expected to last about two months. However, an inspection of the tubes inside the steam generators installed in 2010 uncovered early wear.

A few weeks later, on Jan. 31, SCE shut San Onofre Unit 3 after station operators detected a small leak from a generator tube that released a small amount of radioactive gas. Steam generators in Unit 3 were installed in 2011.

The steam reactors were manufactured by Mitsubishi Heavy Industries.

Workers have conducted a number of tests on the tubes and a small number have been plugged and taken out of service.

Last summer, Jaczko visited two nuclear stations dealing with record flooding on the Missouri River.

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