Scram - Etymology

Etymology

Scram is usually cited as being an acronym for safety control rod axe man; however, the term is probably a backronym. The actual axe man at the first chain-reaction was Norman Hilberry. In a letter to Dr. Raymond Murray (January 21, 1981), Hilberry wrote:

When I showed up on the balcony on that December 2, 1942 afternoon, I was ushered to the balcony rail, handed a well sharpened fireman's ax and told, "if the safety rods fail to operate, cut that manila rope." The safety rods, needless to say, worked, the rope was not cut... I don't believe I have ever felt quite as foolish as I did then. ...I did not get the SCRAM story until many years after the fact. Then one day one of my fellows who had been on Zinn's construction crew called me Mr. Scram. I asked him, "How come?" And then the story.

The US Nuclear Regulatory Commission gives contradictory information. Their glossary supports this etymology of SCRAM, stating:

Also known as a “reactor trip,” “scram” is actually an acronym for “safety control rod axe man,” the worker assigned to insert the emergency rod on the first reactor (the Chicago Pile) in the United States.

However, a May 17, 2011, entry on their official blog from NRC historian Tom Welleck argues that this account is effectively an urban legend and arose many years after the event.

Articles from Oak Ridge National Laboratory (ORNL) indicate that the term stands for "safety cut rope axe man", referring in that case to the early neutronic safety mechanism of using a person equipped with an axe to cut the rope suspending the control rods over the Chicago Pile nuclear reactor, at which point the rods would fall by gravity into the reactor core, shutting the reactor down. Specifically, Wallace Koehler, a technician working for the Manhattan Project at Chicago Pile 1, under Stagg Field at the University of Chicago, and later a research physicist at ORNL, reportedly said that Enrico Fermi coined the term as this acronym. Although Koehler did not serve as a rope-cutting control rod axe-man, he was responsible for dumping a bucket of aqueous cadmium solution into the reactor if reactor period entered into the sub-optimal range.

Leona Marshall Libby, who was present that day at the Chicago Pile, recalled that the term was coined by Volney Wilson:

he safety rods were coated with cadmium foil, and this metal absorbed so many neutrons that the chain reaction was stopped. Volney Wilson called these "scram" rods. He said that the pile had "scrammed," the rods had "scrammed" into the pile.