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US Army experimental nuclear power reactor SL-1 underwent a steam explosion and meltdown on January 3, 1961, killing its three operators. THIS film explains what was done after the accident was discovered.
Film re-enacting HOW the accident may have occurred:
Public domain film from the Prelinger Archives, slightly cropped to remove uneven edges, with the aspect ratio corrected, and mild video noise reduction applied.
The soundtrack was also processed with volume normalization, noise reduction, clipping reduction, and/or equalization (the resulting sound, though not perfect, is far less noisy than the original).
The SL-1, or Stationary Low-Power Reactor Number One, was a United States Army experimental nuclear power reactor which 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. The event is the only known fatal reactor incident in the United States. The incident released about 80 curies (3.0 TBq) of iodine-131, which was not considered significant due to its location in a remote desert of 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 40 miles (64 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). Operating power was 200 kW electrical and 400 kW thermal for space heating.
In the incident 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 Army] contracted with Argonne National Laboratory to design, build, and test a prototype reactor plant to be called the Argonne Low Power Reactor (ALPR)...
Incident and response
On December 21, 1960, the reactor was shut down for maintenance, calibration of the instruments, installation of auxiliary instruments, and installation of 44 flux wires to monitor the neutron flux levels in the reactor core. The wires were made of aluminum, and contained slugs of aluminum--cobalt alloy.
On January 3, 1961, the reactor was being prepared for restart after a shutdown of eleven days over the holidays. Maintenance procedures were in progress, which required the main central control rod to be manually withdrawn a few inches to reconnect it to its drive mechanism; at 9:01 p.m. this rod was suddenly withdrawn too far, causing SL-1 to go prompt critical instantly. In four milliseconds, the heat generated by the resulting enormous power surge caused water surrounding the core to begin to explosively vaporize. The water vapor caused a pressure wave to strike the top of the reactor vessel, causing water and steam to spray from the top of the vessel. This extreme form of water hammer propelled control rods, shield plugs, and the entire reactor vessel upwards. A later investigation concluded that the 26,000-pound (12,000 kg) vessel had jumped 9 feet 1 inch (2.77 m) and the upper control rod drive mechanisms had struck the ceiling of the reactor building prior to settling back into its original location. The spray of water and steam knocked two operators onto the floor, killing one and severely injuring another. One of the shield plugs on top of the reactor vessel impaled the third man through his groin and exited his shoulder, pinning him to the ceiling. The victims were Army Specialists John A. Byrnes (age 27) and Richard Leroy McKinley (age 22), and Navy Seabee Construction Electrician First Class (CE1) Richard C. Legg (age 26). It was later established that Byrnes (the reactor operator) had lifted the rod and caused the excursion, Legg (the shift supervisor) was standing on top of the reactor vessel and was impaled and pinned to the ceiling, and McKinley, the trainee who stood nearby, was later found alive by rescuers. All three men succumbed to injuries from physical trauma, however the radiation from the nuclear excursion would have given the men no chance of survival...
There were no other people at the reactor site. The ending of the nuclear reaction was caused solely by the design of the reactor and the basic physics of heated water and core elements melting, separating the core elements and removing the moderator...
The remains of the SL-1 reactor are now buried near the original site...