Gregory Jaczko, chairman of the U.S. Nuclear Regulatory Commission, refused to give a timetable as to when the San Onofre nuclear plant could resume operation.

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Located near San Clemente, the San Onofre nuclear plant's twin reactors are "Southern California's largest and most reliable sources of electricity, " according to Southern California Edison's website.

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The San Onofre nuclear power plant is perched right on the San Diego beach and the reactor is cooled by ocean water.

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