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The “pinhole”-sized leak in a steam generator tube that caused a partial shutdown at the San Onofre nuclear power plant Tuesday is to be expected when a plant has new generators, according to one expert.

San Onofre recently replaced its old generators.

Whenever generators are new or very old, leaks can occur, and engineers know to be alert for the problem, said David Lochbaum, director of the Nuclear Safety Project for the Union of Concerned Scientists.

Lochbaum said that as long as sensors detected the problem and the operators were prepared, “it’s not the fault of [owner] Southern California Edison. It just happens” with new generators as they are being broken in.

Edison announced the “precautionary shutdown” Tuesday evening because “sensors installed for this purpose detected a possible leak in one of the unit’s steam generator tubes.”

Lara Uselding, a spokeswoman for the United States Nuclear Regulatory Commission, said Wednesday there was no public danger. The leak was “very, very small, minuscule, almost undetectable,” she said.

Edison serves about 14 million people in central, coastal and Southern California.

The company said it had enough reserves to serve all its customers, even with one generator shut down by the leak and another shut down for routine maintenance.

— TRACY WOOD

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