America’s Worst Nuclear Disaster Was in California. Who Knew? >

Don’t feel bad if you think America’s worst nuclear disaster was Three Mile Island. Everybody does. But a nuclear accident up to a thousand times worse than Three Mile Island occurred 20 years earlier, just over the sandstone formations of the Simi Hills northwest of Los Angeles. On top of a hill there was the most secretive Area IV of the Santa Susana Field Laboratory, a lab that meant to prove nuclear power was not just for bombs and missiles, but that it could be used to provide electric power to America’s cities—as in “atoms for peace.”

Not where you were expecting America’s biggest nuclear accident? The Sodium Reactor Experiment (SRE) was one of 10 nuclear reactors in Area IV of the Santa Susanna Field Laboratory near Los Angeles. (Image courtesy of

On Monday July 13, 1959, an experimental nuclear reactor in Area IV was showing skyrocketing temperatures that would indicate a runaway reaction. Workers plunged control rods into the core to stop the reaction. It didn’t work, so they shut it down manually. They released radioactive gases into the air to relieve pressure and prevent an explosion. Inexplicably, they turned the reactor back on. They had no idea a partial meltdown was occurring.

The radioactive gases they released could have been as much as 13,000 curies of iodine-131 and 2600 curies of cesium-137[1]. By contrast, Three Mile Island released 17 curies of iodine-131 and no cesium.

The reactor was off and on for two weeks…

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