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Putting the Axe to the ‘Scram’ Myth

The NRC glossary defines a “scram” as “the sudden shutting down of a nuclear reactor usually by rapid insertion of control rods.” But where did the word come from? One deeply engrained legend about the origin of the word dates to the first sustained chain reaction on December 2, 1942, at the Chicago Pile (CP-1), the first atomic reactor developed for the Manhattan Project. According to the legend, Enrico Fermi created the acronym, Safety Control Rod Axe Man, for Norman Hilberry. It was Hilberry’s assignment that day 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.

The axe-man story now has a life of its own. A search on Google for “scram” and “axe” yields 124,000 hits. Even the NRC’s glossary attributes scram’s etymology to the axe man story. Eleven years ago, Oak Ridge National Laboratories reported a fanciful variation of this story where Fermi, presumably unimpressed with the physical prowess of his fellow physicists, recruited a lumberjack from the Pacific Northwest to do the job. That version has now spread on the internet, and the acronym itself has mutated into Super-Critical Reactor Axe Man and Start Cutting Right Away, Man.

Hilberry, as it turns out, only learned the story second-hand years later, which lends doubt to the axe-man version, and Hilberry’s own recollection of the event didn’t accord with the memories of several other participants. Leona Marshall Libby, the only female physicist present that day, wrote in her memoir that it was Volney “Bill” Wilson who called the safety rods “scram rods.” She didn’t explain why, but her crediting the term’s invention to Wilson was supported by others involved in CP-1, including Warren Nyer.

I contacted Nyer recently, and he was eager to tell the “scram” story, one that squares well with Wilson’s reported version of events. Nyer’s job that day was to be Hilberry’s backup. If all safety systems failed, he and the other members of the “suicide squad” were to dump a liquid cadmium solution on CP-1 to poison the reaction. The axe-man story is, he recalls, “a bunch of baloney.” But he did offer another explanation for the word. His recollection was that Wilson was assembling a panel that included a big red button. According to Nyer, someone asked Wilson the reason for the red knob. Wilson replied you’d hit it if there was a problem. “Well, then what do you do?” he was asked. Wilson reportedly replied “You scram … out of here.” The word appears to have stuck.

And so it seems likely that scram switches all over the world owe their names not to the nuclear industry’s later penchant for acronyms, but to the slang of twentieth-century America.

Tom Wellock
NRC Historian

28 responses to “Putting the Axe to the ‘Scram’ Myth

  1. Brian Flynn January 4, 2016 at 10:10 pm

    how about secure reactor amid malfunction? –Brian Flynn

  2. Dan May 21, 2015 at 10:40 am

    The word scram or skram is a term from the 1800’s that means “to paralyze or benumb with cold.” (in English English, not American English). The UofC reactor was built by an international team, some of whom either were english or spent time in England. It was typically using by fishermen and coastal workers to describe their hands becoming made clumsy or useless in cold weather. That’s always seemed to me to be the most likely source of the term.

    • Gary Harper January 10, 2017 at 5:32 pm

      Definitely don’t want to benumb a reactor with cold in an emergency or you will have a bigger emergency on your hands.

  3. drbillcorcoran April 3, 2015 at 8:46 am

    I recall reading a (Christian) church sign in Oak Bluffs, MA:

    “Faith is believing for sure what isn’t so.”

  4. paul condon July 14, 2014 at 3:54 pm

    I think the word scram was already in the vocabulary of American slang at that time. Calling some piece of equipment a scram circuit could have meant that its purpose was to allow the experimenters to scram out of there faster, i.e. not having to take the time to shut down the experiment properly before leaving. I had always wondered about the emergency control rod system design. Surely these
    physicists knew about pulleys and ropes from undergrad physics lab. Surely at least a few of them had learned about knots in rope from Boy Scouts. Yet those details seem not to have survived. Cutting a rope under tension is only done by when no one else is close because of the whiplash. But maybe…

  5. Moderator June 12, 2014 at 11:39 am

    Further indication that “scram” was associated with Wilson’s shutdown circuitry and not Hilberry’s axe wielding assignment comes from Enrico Fermi. Information related to the Chicago Pile was declassified in late in 1950, and Fermi authored a 1951 report on the pile (see http://www.osti.gov/scitech/servlets/purl/4414200). On pages 37 and 48, he described and drew the circuitry of the “SCRAM line” designed by Wilson’s team. There is no mention in this article of Hilberry’s role as the axe man.
    Tom Wellock
    NRC Historian

    • Daniel J. Robbins June 17, 2014 at 11:47 pm

      Thank you to the Moderator and to the NRC Historian. I appreciate to strength of supporting comments, but the more contemporary documentation from Dr. Fermi is most compelling. Not only is th author as near to the root as we can get, but it also is much earlier, by two decades, than other sources.

      Thank you for sharing the information.

    • Thomas J. Hill June 25, 2014 at 12:00 pm

      Thank you for the link to that reference to Enrico Fermi’s report. It is not surprising to me that any proposed use of an axe would be intentionally omitted from the content of that report, because it lacks of any new or innovative technology. While the term “scram” may have been associated with Wilson’s shutdown circuitry, it does not necessarily dismiss the presence of Dr. Hilberry nor his axe assignment from the history books.
      Back in the 1960’s, the AEC published a series of booklets, collectively known as “Understanding the Atom Series”. One of those booklets, entitled “The First Reactor”, was published in 1968. It discusses much of the history surrounding the people and the project associated with the Chicago Pile. It is my understandig that this booklet is long out of print, but copies are still available in a few public libraries, and reprints available for sale through online book suppliers. On page 17 of that booklet it reads as follows:
      [ “On the floor of the squash court, just beneath the balcony, stood George Weil, whose duty it was to handle the final control rod. In the pile were three sets of control rods. One set was automatic and could be controlled from the balcony. Another was an emergency safety rod. Attached to one end of this rod was a rope running through the pile and weighted heavily on the opposite end. The rod was withdrawn from the pile and tied by another rope to the balcony. Hilberry was ready to cut this rope with an axe should something unexpected happen, or in case the automatic safety rods failed. The third rod, operated by Weil, was the one which actually held the reaction in check until withdrawn the proper distance.
      Since this demonstration was new and different from anything ever done before, complete reliance was not placed on mechanically operated control rods. Therefore, a ‘liquid-control squad’, composed of Harold Lichtenberger, W. Nyer, and A.C. Graves, stood on a platform above the pile. They were prepared to flood the pile with cadmium-salt solution in case of mechanical failure of the control rods.”]
      A drawing on page 33 of this booklet shows the chandelier of control rods suspended by a rope and tied off at the balcony rail. Although I had not read this booklet in 40 years, I was enthralled to reread it earlier today.
      Tom Hill

      • Thomas J. Hill June 25, 2014 at 5:43 pm

        I noticed a typo in my previous comment. The extracted text from “The First Reactor” was on page 18, not 17. I should also mention that the original story of the first reactor was written in the fall of 1946 by Corbin Allardice and Edward Trapnell, who had conducted interviews with several of those involved in the project, including Enrico Fermi. There is a copy of their booklet at the University of Michigan Library, which can be viewed online at: http://babel.hathitrust.org/cgi/pt?id=mdp.39015034399884

      • Moderator June 26, 2014 at 8:27 am

        Thank you for mentioning the AEC publication “The First Reactor.” It still is one of the better descriptions of the CP-1’s construction and approach to criticality. I’d just like to emphasize that I agree with you, there is no doubt that Hilberry was a significant contributor to the Manhattan Project and did have the assignment that day to use an axe on a backup emergency safety rod. My only intent in writing this article was to clear up some of the confusion about the etymology of the word “scram” as it is used in the nuclear industry.

        Thanks for your interest.

        Tom Wellock

  6. Daniel J. Robbins June 2, 2014 at 12:07 pm


    I agree with you. This “debunking” shares a problem with some other so called debunking efforts. The original story that is being debunked comes from a source closer than any of the debunkers, and no reason for suspecting the original tale is given until years after the primary source is gone and unable to respond.

    I was BSNE, UA class of ’84. I only got to meet Dr. Hilberry a couple of times. Still, I don’t see any reason not to take his word and I’m sticking with the original story.

    • Moderator June 3, 2014 at 10:52 am

      Hello Daniel,

      Yes, there is no way to be absolutely certain the version supplied here is correct—every version of this story, including Hilberry’s, is based on memory. But Volney Wilson and Warren Nyer were likely closer to the origins of this story than was Hilberry. In 1982, upon hearing of Hilberry’s version of the scram story, Nyer contacted Wilson and Hugh Barton. Both men were members of the instrumentation team that designed the scram circuitry for the CP-1. Barton and Wilson, according the Nyer, agreed with his recollection that Wilson invented the term. In 1988, Hilberry’s recollection of the scram story came out in a Nuclear News article (See Nuclear News, August 1988, pg. 105). Nyer wrote a rejoinder to the journal disputing its accuracy (see December 1988, pg. 17 and 18.) that noted his earlier contacts with Wilson and Barton.

      It is, of course, possible that Barton, Nyer, and Wilson are all recalling the same incorrect story. It is even possible, if very unlikely, that Nyer is not telling the truth. There exists, however, at least one independent piece of evidence in favor of their version. In 1979, nearly a decade before the Nuclear News dispute, Leona Marshall Libby wrote a memoir, The Uranium People. In describing the events of December 2, 1942 and the first scram of a critical reactor, Libby wrote: “Electric motors drove in the safety rods. . . . Volney Wilson called these ‘scram’ rods. He said that the pile had ‘scrammed,’ the rods had scrammed into the pile. This word has entered the vocabulary of power-plant operation, and also of nuclear submarines, so that any shutdown of the reactors is called a scram.” (p. 122) If Libby, Nyer, Barton and Wilson are correct that it was Wilson who came up with “scram,” it is unlikely that Wilson’s 1982 account to Nyer was wrong. It is also unlikely that he created the name to apply to Hilberry’s axe-cutting assignment rather than the manually operated scram circuitry that he designed.

      By contrast, Hilberry did not hear from others that he was called “Mr. Scram” until sometime later, long enough for a “scram” acronym and myth to emerge. It is possible the collective memories of Wilson, Nyer, Barton, and Libby are wrong, but I favor their version as being more accurate.

      Tom Wellock

  7. Anonymous January 4, 2014 at 9:26 am

    So if Nyer was the backup man, instead of ATWS, we should call it NYER.

  8. Daniel J. Robbins January 3, 2014 at 9:28 pm

    Let me see if I understand the debunking correctly.

    It is undisputed that Dr. Hiberry was present and part of the project. It is undisputed that “SCRAM” was used in reference to an emergency shut down of Chicago Pile No. 1. Wilson and Nyer each state that they were assisting Dr. Hiberry by backing him up as a “suicide team” to dump a solution of cadmium on the pile in the event of an emergency. What was Dr. Hiberry doing that they were “backing up” if he was not wielding an axe to cut the rope holding the cruciform cadmium emergency rope.

    It may have been a back fit of the term to Dr. Hiberry’s personal role. Maybe it was a conglomeration of the two: “What do we do if Dr. Fermi tells Dr. Hilberry to cut the rope?” and Mr. Wilson (or someone else) says “Scram!” Then the acronym comes later. Or, Dr. Hilberry and Dr. Fermi in discussing a title for Dr. Hilberry’s role, taking place as part of an acronym crazy government bureaucracy (The Manhattan Engineering District) came up with the acronym first.

    I do not know which is the real truth. I don’t think we can ever prove it one way or the other. I am biased having earned my degree in nuclear engineering when Dr. Hilberry was our beloved old hand, the professor emeritus who had been part of the Manhattan Project. I am also well acquainted with the government’s love of acronyms (25 years active duty Air Force and continuing duty as a civilian and volunteer). That being said, I think that Hilberry’s description of the etymology of “SCRAM” is at least as credible as Wilson and Nyer’s, and it has priority.

    It is quite right to provide possible alternatives and to credit Misters Wilson and Nyer. I do think it is a slur against Dr. Hilberry to suggest that his story should be disregarded after he is gone and unable to defend himself.

    • Thomas J. Hill May 29, 2014 at 10:54 am

      Dr. Hilberry was one of my nuclear engineering professors at Univ. of Arizona back in the 1970’s. I recall him telling a class of nuke students about his role as the ax man to cut the rope which supported the chandelier of control rods at CP-1. I am compelled to believe him.

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