San Onofre: The Nuclear Plant That Steam Generators Killed

The twin concrete domes you can see from the freeway belong to the San Onofre Nuclear Generating Station, a plant that produced electricity for Southern California for decades before a botched equipment upgrade ended it in a controversy that still lingers.

Unit One came online in nineteen sixty-eight. Units Two and Three followed in the early nineteen eighties, and for thirty years the plant supplied roughly twenty percent of the electricity used by Southern California Edison's customers. The site between Camp Pendleton and the beach required no dramatic imagination to find slightly surreal: nuclear reactors perched between a Marine Corps base and the Pacific Ocean, visible to tens of thousands of drivers every day on one of the busiest stretches of freeway in the United States.

The plant's end came from an internal decision rather than a public one. Beginning in two thousand nine, Southern California Edison replaced the steam generators in both reactors with new units manufactured by Mitsubishi Heavy Industries in Japan, finishing the second reactor in twenty eleven. The replacement generators cost six hundred seventy million dollars and were supposed to last twenty years. They lasted less than one.

In January twenty twelve, sensors detected a leak in a heat-transfer tube in Unit Three. Inspectors found premature wear on more than three thousand tubes in the new generators, caused by vibration that Mitsubishi's computer modeling had failed to predict. Both reactors were shut down for inspection and never restarted. On June seventh, twenty thirteen, Southern California Edison announced it was permanently retiring both units.

The decommissioning is one of the most complex nuclear cleanups ever undertaken in the United States, expected to take decades and cost billions. More than three million pounds of spent nuclear fuel remain on site in dry-cask storage, within sight of the ocean, awaiting a permanent federal repository that does not yet exist.