SL-1
Stationary Low-Power Reactor Number One, also known as SL-1 or the Argonne Low Power Reactor (ALPR), was a United States Army experimental nuclear reactor in the western United States at the National Reactor Testing Station (NRTS) in Idaho about forty miles (65 km) west of Idaho Falls, now the Idaho National Laboratory. On January 3, 1961, at 9:01 pm MST, an operator fully pulled out the reactor’s central control rod, causing the reactor to go prompt critical. The intense heat generated an extreme water hammer which propelled the reactor vessel to the roof of the reactor building. The operator standing on top of the reactor lid was pinned to the roof of the reactor building with expelled control rod shield plugs, while the reactor expelled water, debris, and fuel. The release of materials hit two other operators, killing them. The reactor vessel then fell down to its original position. Press reported a steam explosion killed all three of its young military operators, pinning one of them to the ceiling with a reactor vessel plug. It remains the only U.S. reactor accident to cause immediate deaths.
November 29, 1961: The reactor vessel being removed from the reactor building, which acted substantially like the containment building used in modern nuclear facilities. The 60-ton Manitowoc Model 3900 crane had a 5.25-inch (13.3 cm) steel shield with a 9-inch (23 cm) thick lead glass window to protect the operator. | |
| Date | 3 January 1961 |
|---|---|
| Location | National Reactor Testing Station, west of Idaho Falls, Idaho, U.S. |
| Coordinates | 43.5182°N 112.8237°W |
| Outcome | INES Level 4 (accident with local consequences) |
| Deaths | 3 |
SL-1 Location in the United States SL-1 Location in Idaho | |
Part of the Army Nuclear Power Program, SL-1 was a prototype for reactors 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 before 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, causing the explosion. The direct cause was the over-withdrawal of the central control rod that absorbed neutrons in the reactor's core. 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.