In the current climate of sabre-rattling between North Korea and the USA (with heartfelt hopes that it won’t go further than that), here is a little piece about ‘scram’ as the word to use for the sudden shutting down of a nuclear reactor usually by rapid insertion of control rods. 

According to legend it was an acronym for Safety Control Rod Axe Man, the man in question being Norman Hilberry. In 1942 at the Chicago Pile (CP-1) – the first atomic reactor developed by the Manhattan Project – the first sustained chain reaction was to take place. Hilberry’s job was to kill a possible runaway reaction by using an axe to cut a rope to allow the backup safety control rod to drop into the pile, which was a liquid cadmium solution to poison the reaction. This version is the oft-told legend.

However, Manhattan Project scientist Warren Nyer who was present that day has another explanation for ‘scram’. On that day another Manhattan collaborator, physicist Volney “Bill” Wilson, was assembling a panel that included a big red button. Someone asked him the reason for the red knob and Wilson replied it was to be hit it if there was a problem. Then what do you do, asked the enquirer. “You scram … out of here.” Wilson reportedly replied. 

So, it seems scram switches may not be an acronym but merely American slang.