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Demon Core (wikipedia.org)
153 points by agarttha on June 17, 2019 | hide | past | favorite | 55 comments

I like this comment from Metafilter (https://www.metafilter.com/159810/Blue-flash#6535495):

> This is a good occasion to ask yourself: am I including "now wedge a screwdriver in there" as part of some important work that I do? Shouldn't I use my screwdrivers only for driving screws, one might ask, and not for, say, keeping this plutonium assembly from going critical?

There are lots of reasonable uses for flathead screwdrivers other than driving screws, though! Random examples:

* Many clips (dryer faceplate, window sash, ...) are designed to be pried open with a screwdriver.

* When repairing a popped drywall nail, a screwdriver is a good tool for removing the joint compound under the nail.

* When you buy a lock it usually comes with a rounded faceplate. To swap the faceplate, they'll tell you to use a screwdriver to pry it off.

A flathead screwdriver is a good tool for general light prying, not just for putting in slotted screws. This heuristic has a lot of false positives.

Prying with a flathead screwdriver is totally standard. Examples from manufacturer instructions:

* "Use a small flathead screwdriver to pry wire connectors off." http://www.crystalcoolers.com/CMIL/ServiceManual/EverestElit...

* "Use a flathead screwdriver to GENTLY push the wire harness from the board." https://www.carlisleft.com/library/SI06031si.pdf

* "Carefully remove the airbag plastic logo. This plastic piece is set deep into the door so be sure to pry it with some force by inserting a small flathead screw driver just under the plastic piece and pushing it out." https://bimmian.com/content/pdfs/CMC46.pdf

* "Use your flathead screwdriver to release the two clips on each side." https://lib.americanmuscle.com/files/contentgenerator/deatsc...

A prybar is for when you need a lot more force.

This is just SnapOn's attempt to get you to buy a 50$ 12" prybar. Also to stop you from sending your screwdrivers back on the truck every week.

But who cares, they're replaced for free and delivered :)

Or buy four or five Pittsburgh ones from Harbor Freight.

Those have a lifetime warranty now too.

I would love to have SnapOn stuff, if I were made of money or found it second-hand, but it's just stupid expensive new, especially for stuff that tends to get abused.

Some of the Harbor Freight stuff is great. For wrenches and ratchets that get pushed to the limit though I'll exclusively use one of the more pricey brands just out of fear of slamming my knuckles after a tool snaps. Its one of my biggest fears working on anything even after having it happen with minimal damage enough times. For everything else I'll use whatever is closest.

You're thinking bigger rather than smaller. I learned my lesson about prying with screwdrivers after gouging a couple of PCBs I was trying to repair when my sharp metal "pry tool" slipped, so now I exclusively use nylon pry tools around my electronics. They are cheap and disposable in a good way. Get a 50 pack for $10 on Amazon :)

Fortunately I don't work with any electronics. I never had the patience for dealing with PCBs or even breadboards.

Flathead screwdrivers are indeed very useful.

But I think you'll find that the iFixit Guide to Nuclear Warhead Testing recommends more specialised tooling.

Why hello fellow Craftsman loyalist! Did you also notice that my sibling's meme is an ad for a competing brand that doesn't have an unlimited return policy?

a screwdriver is an exemplar of an inclined plane, so seems to make sense. I mean I guess you could have asked the metallurgists to make you a perfectly angled inclined plane on the mill (since everything else associated with the core was milled to thou precision) but that would just be wasting money.

I've seen this page posted twice and both times it escaped me that this core had not one but TWO fatal accidents. Why didn't they build a rig??

i was fascinated with the criticality accident that claimed Slotin's life when i first learned about it. in particular, there was a schematic made up after the accident estimating everyone's distance to the apparatus and how much radiation they may have been exposed to: https://en.wikipedia.org/wiki/Louis_Slotin#/media/File:Sloti...

there was a second sketch made from that drawing which i also found fascinating. it doesn't add any additional information or analytical ability, but is just a sort of interesting and slightly dark translation of a rote schematic diagram into an artistic rendering of the event: https://en.wikipedia.org/wiki/Louis_Slotin#/media/File:Sloti...

I searched around for awhile trying to find the purpose and/or author of that second sketch but to no avail. however i did use it as the cover for an EP i released. please enjoy!


There's a guy who is making a cartoon about the demon core.


Tickling the dragons tail seems very appropriate. I'd be sweating bullets manaually adjusting a nuke core with a screw driver.

Not to advocate risky behavior, but this doesn't surprise me at all. Experience increases the perception of safety at a rate faster than actual safety. Every place I've worked where you could put yourself, expensive equipment or customer satisfaction in danger to make something easier for yourself people would do it. Deploying straight to prod, doing surgery on live databases, soldering on equipment plugged into mains, servicing a UPS without disconnecting 48V worth of lead acid batteries (that was one HELL of an arc weld).

The corners people will cut never cease to amaze me.

I used the phrase "tickling the dragon's tail" recently when I ran some maintenance code in production without testing it first (because there really wasn't a way to test it outside of production, long series of failures to get to this point, I know). I used to call it cowboy coding.

FWIW, this was the first time I'd done something like that in about 5 years and I felt horrible during and afterwards even though nothing went wrong. I felt like I should have given up a sobriety coin or something. Feels bad. Like falling off the wagon.

I think it’s a good thing that you feel a bit unsettled. It shows you have the professionalism to know it was a bad plan, but you also had the knowledge to know sometimes a bad plan is the only plan you have. Don’t dwell on it though, that would be unhealthy since you already know the lesson of the experience.

Good old normalization of deviance: https://www.ncbi.nlm.nih.gov/m/pubmed/25742063/

This is why power paper cutters have two widely separated on buttons.

> Experience increases the perception of safety at a rate faster than actual safety.

I learned to drive nine months ago, and I've been watching myself do this every time I get on the highway in the past few months. Even knowing that I'm doing it, it's hard to avoid.

I learned to drive 40 years ago. Watching yourself drive and noticing situations where you're taking unneeded risks is what separates good drivers from mediocre ones. Never assume you can't do better.

Or remove half of the bolts from top to bottom of a crane (instead of one level at a time) to speed up its deconstruction by a couple of hours?

https://en.wikipedia.org/wiki/Seattle_crane_collapse https://www.seattletimes.com/seattle-news/what-caused-seattl...

> soldering on equipment plugged into mains


I've cut a LOT of corners, but that one is just insane...

"But this is the ground wire so it's okay".

Hint: Lots of people have daisy chained outlets backward, and lots of AC circuits still work with the wiring reversed.

Pretty sure we found one where they had reversed them twice, so black was hot at the end of the circuit but not in the middle.

I have no idea why I never considered this possibility. That's terrifying.

I inspected all my outlets after finding out what 60VAC feels like going up one arm and down the other (touched two server cases, one on a grounded outlet, the other floating). I found several suprises: a knob and tube circuit had been "upgraded" to 3-prong faceplates without wiring the ground to _anything_, and some outlets were backwards. You never know if it's the work of a DIY electrician unless you get it checked out.

Someone hooked the washer and dryer into the mains at my Grandma’s house. It was interesting seeing my Dad go from confused to realization to angry without having caused the transition. Getting that fixed was an exercise in careful. As Dad is fond of saying “I’m amazed you thought of it and appalled you actually did it.”

I ran into that, in an old house.

Some decades ago, the house had two meters. One was just for the hot water heater. But when they removed that one, they just connected the water heater to the main meter. Directly. Not through the breaker panel.

Damn. Almost killed me.

Would have probably killed someone in our group except my Dad and one of my uncles had a bad feeling about it. Apparently working for Ma Bell will give one a sense of those things.

> Someone hooked the washer and dryer into the mains at my Grandma’s house.

Do you mean they wired it in parallel with the main breaker panel, so you couldn't disconnect it to work on it?

Yep. We flipped off all the breakers and the damn washer & dryer were still hot. My memory was a bit off and the the water heater and maybe stove were also hot. We had to replace all of that. I was 10 at the time so I was working on other stuff while Dad and the uncles took care of it. Putting in a new structural support beam was also enlightening.

Funnily enough that's a normal practice in the UK/Ireland. In all the places I've lived, washer and dryer are plugged straight into a regular outlet (sometimes with an extension cord if it can't be reached).

Makes me wonder, why not make a 110v washing machine and save the trouble of having both 110v and 220v at home?

Most (all?) washing machines are 120V. Electric dryers rarely are, because they need a lot more power. I had a small washer/dryer combo unit years ago that used 120V, and it took about four hours to dry a load that was about half the size of a normal dryer’s capacity.

Running both voltages into a house isn’t much of a burden. Residential electricity in the US is two-phase. A 120V circuit pulls from one phase, with the various circuits in your house divided between them to even out the load. A 240V circuit just connects to both phases.

Well yes, but we usually segment areas into their own circuits and in a well-built residence the laundry appliances get a fused circuit to themselves (or, at the very least, share one with the kitchen sockets). So your amperage/fuse-trip-point is isolated to that one group of sockets.

Plus as you semi-observe, everything on a socket here is 220V

I get the sense some of these posts are talking about devices connected directly to the building's supply wiring (not to a receptacle downstream of the circuit breaker panel).

In the US all residential washing machines are 110V, as are gas dryers, but electric dryers take 220V.

The US uses split phase 240VAC for residential. 240VAC is really two 120VAC 'hots' 180 degrees out of phase. So 240V between phases, but 120V to ground/neutral.

Industrial 240 usually is single or 3phase.

110 (120 really) volt washing machines are very common, at least in the US. Dryers, on the other hand, are 240 here.

The most common examples are probably driving and smoking.

The scene is fictionalized in the movie Fat Man and Little Boy with John Cusack performing the role of Slotin under a different name.


Came here to say this. At the time I saw this in the early 90s, it really disturbed me-an awful way to go for such a mundane act.

I'm wondering, even if everything had gone right and the dome had not been dropped to cause the core to go critical -- surely being in close contact with even a non-critical nuclear weapon core is not safe??

What's the amount of radiation that thing gave off simply from decay, in a non-critical state?

The Uranium and plutonium isotopes used in weapons generally aren't themselves super dangerous in terms of radioactivity. The most dangerous radioactive elements produced in a nuclear explosion or disaster such as Chernobyl are the short half life fission products, such as isotopes of iodine, strontium, caesium, etc.

> What's the amount of radiation that thing gave off simply from decay, in a non-critical state?

Not much. U-235 has a 700M year half-life. Pu-239's is 24,000 years.

You're more at risk from ingesting/inhaling bits of it.

>You're more at risk from ingesting/inhaling bits of it.

This is the vaaaast majority of the risk profile for radioactive anything.

The half life doesn't really tell you the whole story, Pu-239 mostly decays into alpha particles which is what makes it "safe", it's still not good for you, and very bad if ingested, but externally alpha radiation doesn't really penetrate deep enough into the body to be a big problem.

To put it another way - from an "immediate risk" point of view, the largest danger from critical-capable amount of fissile material is the prompt radiation emitted during a criticality: the pulse of neutrons, gamma and x-rays thrown off during that period the unit is sustaining a chain reaction.

For relatively brief power excursions like this one (which Slotin himself stopped by removing the reflector), the prompt burst was well over a lethal level but the radiation dose-rate from fission product decay even a tiny time later would not be immediately hazardous.

For those looking to learn more, Los Alamos has a great writeup of every publicly-known incident (in the US, USSR, and elsewhere) that details just how many times similar incidents happened: https://www.orau.org/ptp/Library/accidents/la-13638.pdf

Alex Wellerstein, author of the NYer article, has a bit more info on his blog (http://blog.nuclearsecrecy.com/2016/05/23/the-blue-flash/), including an answer to the question of what happened to the core. (It was melted down into the overall plutonium stockpile, apparently.)

Didn’t know this! Really interesting

Before I clicked, I was convinced the article was going to be about some GLaDOS core that I’ve forgotten.

How ironic, that a bomb core would kill. Truly,

The authority on the subject: https://youtu.be/lJXwRdbbQ50

Why "authority"?

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