Reactors Trip at San Onofre Nuclear Plant Amid Southwest Blackouts

A grid disturbance that led to widespread blackouts across Southern California, southwest Arizona and Baja Mexico caused both reactors at the San Onofre nuclear plant to shut down automatically Thursday.

San Onofre nuclear plant. Source: NRCAccording to a Nuclear Regulatory Commission incident report, units 2 and 3 remained connected to off-site power after reactor safety systems tripped at 3:38 p.m., PST. Safety systems functioned as designed, according to the report, with no primary-to-secondary leakage and no use of emergency relief valves. Diesel generators remained on standby but were not needed.

The president of San Diego Gas and Electric was quoted Friday as saying the units will be back online in the next day or two. Utilities around the Southwest are recovering after a 500 KV transmission line near Yuma failed for unknown reasons during repairs. Low voltage spread across the distribution network Thursday, outpacing grid operators' ability to isolate it. And once San Onofre went offline, the resulting power shortage caused blackouts for millions of customers.

Combined, San Onofre's operating reactors near San Clemente, Calif., produce 2,150 megawatts electric, according to the NRC. Both are Combustion Engineering pressurized water reactors licensed in 1982.

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