Fortunately, thanks to existence of a Wikipedia article, we don't have to take ESR's word for the etymology of the word. The article is neutral in asserting that Fermi coined the acronym, but does suggest that the usage derived from the existing usage of scram, meaning to GTFO with all due expediency. Other possible expansions are posited to be backronyms:
So here's a question that I'm sure a good answer exists to: given that an untested safety mechanism is guaranteed not to work when you need it most, how are SCRAM systems tested?
There are various ways you can test it. But it obviously depends on what the mechanism is. If you’re cutting physical wires used to raise or lower something then hopefully it is obvious the mechanism will work (but maybe it goes wrong if the cut end of the wire is caught somewhere.)
In a computer system, you ought to be able to test systems to make sure they behave correctly under the consequences of a switch press. You could also test them—there may be times when it is ok to press the switch, or where you have redundancy such that two switches must be pressed but you only press one to test.
But I think another alternative is to not have the mechanism used extremely rarely. I think it can be good to accept cases where things go wrong a bit from time to time so that people have practice dealing with them as the alternative is to only have things go wrong under some enormous catastrophe when no one will have any idea what to do.
For nuclear power your third paragraph isn’t anywhere in the same universe.
SCRAM drills are held regularly, but under no circumstances is any intentional level of risk in critical safety systems accepted on the plants I worked on.
I was present in a data center during a scheduled complete shut-down so that some significant power and equipment moves could be done. At the designated time, the manager ceremoniously pressed the Big Red Button by the door and.... nothing happened.
So an electrician was sent to throw some switches elsewhere in the building.
I never got a clear explanation of what went wrong, only that it had been "fixed" and would work if needed in the future.
Typically they are tested at very low/no power levels when the reactor is first started after any kind of significant overhaul. We are talking staying subcritical, retracting your control elements a tiny bit in banks, and dropping them until every section is tested.
Additionally, the system and crew are tested on a regular basis with live drills. Sometimes surprise live drills. Its one of the most commonly-tested systems on the ship. Not to the point of actually causing a reactivity excursion, but the physical act of rapid rod insertion using the scram control switches (or breakers) happens all the time.
Please note my precise use of language; as stupid as it sounds if you were involved in the program (your language is precise enough that I’d lay a bet you were in some fashion) you signed documents indicating your inability to utilize certain words.
It’s stupid and I’m calling attention to it by this, and Wikipedia uses those words, but we sign NDAs and it’s the Government. No one ever claimed it all makes sense.
I’m in no way judging the other commenter. I think that particular restriction is stupid since the information is in the public domain. However it IS still a binding legal restriction. My comment was as much about the stupidity as about any possible breach.
'cause you came across as an asshole. It doesn't bother me that much. Nuclear safety relies on ~~assholes~~ attention to detail to work, to be honest.
> but no comments
Its not exactly a jumping off point for discussion, is it? I've been out for 15 years and still regularly fail to recognize when I'm being a dick. Look back at what you wrote and think about for a minute.
I don’t know why the downvotes but I’m scratching my head trying to figure out what words in the OP would be forbidden. But I guess you wouldn’t be able to answer that question.
Suffice to say the reason you can’t identify it is why it’s stupid. Everyone knows them and yet the Navy requires we not reference them because that gives away design and operational characteristics of our plants.
I think that's probably why they went with cutting the rope with an axe instead of some mechanical mechanism like moving the pawl from the ratchet that lifts the rods.
Incident report: shortly before the meltdown, we believe the safety supervisor was knocked unconscious by an improperly secured axe head that became detached from the handle swung by the junior safety officer. We recommend increased testing of axe head attachment mechanisms in future nuclear safety devices.
In a previous career I was a Nuclear Reactor Operator for the US Navy.
The acronym/story we were told regarding SCRAM was “Super Critical Reactor Axe Man”; as in the guy who would cut the rope to drop the control devices into the fission pile if they detected its reactivity going TOO super critical.
Interestingly this usage doesn’t seem well known outside of those circles. It is/was, however, directly printed in rather old publications I used (60s perhaps?).
According to Rhodes A-Bomb book, for the original Pile in Chicago there was a rope, and there was a guy with an axe.
There was a backup to the backup: people with a solution of something (borate?) to pour into the pile to soak up surplus neutrons. This was a really bad thing to do, for the future use of the pile: the carbon would be soaked, useless, the reactivity of the pile would be next to impossible to get back without completely re-constructing it so the Scram by lowering rods, was the preference, and was done by a counter for accellerated scaling aside from the guy with the axe after a while.
ESR's outline is more-or-less correct. Electric current is required to maintain a magnetic field. When the field collapses some mechanical device takes over using stored energy (springs and/or gravity) Here's a practical example to give some more context to the idea:
> The acronym/story we were told regarding SCRAM was “Super Critical Reactor Axe Man”
Another ex-Navy nuke here. When I went through nuclear power school (the West Coast one at Mare Island) in the 1970s, the version we heard was "Safety Control Rod Axe Man."
It's mildly annoying that the web site is encoded in Latin-1 but displayed in UTF-8. The xml content says 'encoding="ISO-8859-1"', but the server says 'Content-Type: text/html; charset=utf-8'. It causes some characters to show up as � (REPLACEMENT CHARACTER).
(I tried telling ESR about this several years ago, but the email bounced.)
38 comments
[ 2.2 ms ] story [ 86.9 ms ] threadhttps://en.m.wikipedia.org/wiki/Scram
> “Scram” was in origin a backronym for “Safety Cut Rope Axe Man” coined by Enrico Fermi himself.
Basically it was how they shut-down nuclear reactors by cutting a rope that would drop the controls rods into the reactor.
Side-note: I know this because I played an Atari 800 game called SCRAM growing up. It was pretty good!
Also reminds me of SNAFU - Situation Normal All Fucked Up.
https://public-blog.nrc-gateway.gov/2016/02/18/refresh-putti...
https://en.wikipedia.org/wiki/Scram#Etymology
In a computer system, you ought to be able to test systems to make sure they behave correctly under the consequences of a switch press. You could also test them—there may be times when it is ok to press the switch, or where you have redundancy such that two switches must be pressed but you only press one to test.
But I think another alternative is to not have the mechanism used extremely rarely. I think it can be good to accept cases where things go wrong a bit from time to time so that people have practice dealing with them as the alternative is to only have things go wrong under some enormous catastrophe when no one will have any idea what to do.
SCRAM drills are held regularly, but under no circumstances is any intentional level of risk in critical safety systems accepted on the plants I worked on.
So an electrician was sent to throw some switches elsewhere in the building.
I never got a clear explanation of what went wrong, only that it had been "fixed" and would work if needed in the future.
It’s stupid and I’m calling attention to it by this, and Wikipedia uses those words, but we sign NDAs and it’s the Government. No one ever claimed it all makes sense.
I’m in no way judging the other commenter. I think that particular restriction is stupid since the information is in the public domain. However it IS still a binding legal restriction. My comment was as much about the stupidity as about any possible breach.
'cause you came across as an asshole. It doesn't bother me that much. Nuclear safety relies on ~~assholes~~ attention to detail to work, to be honest.
> but no comments
Its not exactly a jumping off point for discussion, is it? I've been out for 15 years and still regularly fail to recognize when I'm being a dick. Look back at what you wrote and think about for a minute.
I appreciate the call out. We can always learn and grow!
Then it's as mechanically as simple as possible
The acronym/story we were told regarding SCRAM was “Super Critical Reactor Axe Man”; as in the guy who would cut the rope to drop the control devices into the fission pile if they detected its reactivity going TOO super critical.
Interestingly this usage doesn’t seem well known outside of those circles. It is/was, however, directly printed in rather old publications I used (60s perhaps?).
Was there really a rope, and you really cut it with an axe?
What did this do to the life expectancy of the ax operator?
Does any of this have anything to do with your HN username? If there's a story, would you tell?
There was a backup to the backup: people with a solution of something (borate?) to pour into the pile to soak up surplus neutrons. This was a really bad thing to do, for the future use of the pile: the carbon would be soaked, useless, the reactivity of the pile would be next to impossible to get back without completely re-constructing it so the Scram by lowering rods, was the preference, and was done by a counter for accellerated scaling aside from the guy with the axe after a while.
For my username: I actually started using this name before I was involved in nuclear power, and that’s the first time that’s been asked!
https://patents.google.com/patent/US3721462A/en https://patents.google.com/patent/US8811561B2/en
Another ex-Navy nuke here. When I went through nuclear power school (the West Coast one at Mare Island) in the 1970s, the version we heard was "Safety Control Rod Axe Man."
(I tried telling ESR about this several years ago, but the email bounced.)