01 Overview
On the evening of January 3, 1961, the Stationary Low-Power Reactor Number One (SL-1) at the National Reactor Testing Station experienced a steam explosion following a sudden criticality event. Three military personnel were killed - the first fatalities from a nuclear reactor accident in U.S. history.
02 Cause
The accident resulted from the manual withdrawal of the central control rod by approximately 50 cm - far beyond the allowed 5 cm maximum. This caused an instantaneous supercritical nuclear excursion. The enormous energy release instantly vaporised coolant water, creating a steam explosion.
03 Impact
All three personnel present were killed. One worker was found impaled on the ceiling by a control rod. The reactor building was heavily contaminated. Emergency responders received the highest radiation exposures seen in the U.S. at the time. No radioactive contamination spread off-site significantly.
04 Response
Recovery crews worked in shifts of seconds to minutes due to intense radiation. Specialised remote equipment was developed to handle and examine the bodies. All three victims were buried in lead-lined coffins due to their radioactivity.
05 Legacy
SL-1 led to fundamental changes in nuclear reactor design, making it physically impossible for a single control rod to cause criticality. It established the principle that safety systems must require multiple simultaneous actions. The reactor vessel was buried on-site as radioactive waste.