SL-1 Nuclear Accident

Nuclear Disasters Disasters 








The SL-1, or Stationary Low-Power Reactor Number One, was a United States Army experimental nuclear power reactor in the United States that underwent a steam explosion and meltdown on January 3, 1961, killing its three operators. The direct cause was the improper withdrawal of the central control rod, responsible for absorbing neutrons in the reactor core.

SL-1 Nuclear Accident
The event is the only reactor accident in the U.S. that resulted in immediate fatalities. The accident released about 80 curies (3.0 TBq) of iodine-131, which was not considered significant due to its location in the remote high desert of eastern Idaho. About 1,100 curies (41 TBq) of fission products were released into the atmosphere.


The facility, located at the National Reactor Testing Station (NRTS) approximately forty miles (65 km) west of Idaho Falls, Idaho, was part of the Army Nuclear Power Program and was known as the Argonne Low Power Reactor (ALPR) during its design and build phase. It was intended to provide electrical power and heat for small, remote military facilities, such as radar sites near the Arctic Circle, and those in the DEW Line. The design power was 3 MW (thermal), but some 4.7 MW tests were performed in the months prior to the accident. Operating power was 200 kW electrical and 400 kW thermal for space heating.

During the accident the core power level reached nearly 20 GW in just four milliseconds, precipitating the steam explosion.

From 1954 to 1955, the U.S. Army evaluated their need for nuclear reactor plants that would be operable in remote regions of the Arctic. The reactors were to replace diesel generators and boilers that provided electricity and space heating for the Army's radar stations. The Army Reactors Branch formed the guidelines for the project and contracted with Argonne National Laboratory (ANL) to design, build, and test a prototype reactor plant to be called the Argonne Low Power Reactor (ALPR). More details