Scram as the original and mostly likely accurate basis for the use of scram in the technical context. A persistent alternative explanation posits that scram is an acronym for 'safety control rod axe man', which was supposedly coined by Enrico Fermi when the world's first nuclear reactor was built under the spectator seating at the University of Chicago's Stagg Field. It could also stand for "Safety Control Rods Activation Mechanism" or "Control Rods Actuator Mechanism". Both of these are probably backronyms from the original, non-technical usage. In any reactor, a SCRAM is achieved by inserting large amounts of negative reactivity mass
Enrico Fermi Nuclear Generating Station was achieved on August 23, 1963. On October 5, 1966 Fermi 1 suffered a partial fuel meltdown. Two of the 92 fuel assemblies were partially damaged. According to the United States Nuclear Regulatory Commission, there was no abnormal radioactivity released to the environment. Fermi 1 was a liquid metal (sodium) cooled fast breeder reactor design. It was capable of producing 200 megawatts thermal (MWt) power or 69 MW electrical power with 26% enriched metallic uranium fuel. The enriched uranium section of the reactor (core) was a 30 inch in diameter cylinder by 30 inches high and contained 92 fuel assemblies.