The SL-1 (Stationary Low-Power Reactor Number One) was a prototype nuclear reactor located near Idaho Falls, Idaho, designed for research and testing. On the night of the incident, a power excursion caused a sudden spike in reactor power, which led to a steam explosion. The explosion resulted in a significant release of radioactive materials, leaving three operators dead at the scene. Investigation revealed that mishandling of control rods and inadequate safety protocols were contributing factors to the event's severity. Notably, the SL-1 reactor had been operating under experimental conditions designed to evaluate low-power reactor systems, and the location was primarily utilized by the United States Army for research purposes.

In the aftermath, the U.S. Atomic Energy Commission undertook extensive investigations into the incident, which highlighted deficiencies in operational standards, training, and emergency protocols in nuclear facilities. The wreckage of the reactor was entombed to contain the radioactive contamination. This incident underscored the inherent risks associated with nuclear power and prompted significant reforms in reactor design and operational safety across the industry.

The SL-1 incident not only caused immediate fatalities but also became a pivotal moment in the discussions surrounding nuclear energy and its safety measures. Regulatory changes were instituted to increase safety inspections, improve training for reactor operators, and enhance emergency response strategies.