Criticality 1969

Nuclear criticality training film, UKAEA, 1969.

[@zx6rtt]

those old timers really knew how to make educational films back then. Clear and concise.

[@LucasGarrow]

zx6rtt lost art

[@FBI-ej8zr]

and weird/creepy

[@josephastier7421]

With information and everything!

[@legneil]

Now they hide it.

[@kbtechandmedia]

Being in elementary school in the 1990s, you know it was gonna be a good day when your teacher pushes in a projector.

[@k225]

So instead of just saying "Do as you're told and follow the rules", they teach workers enough theory to understand why the rules exist and why a seemingly harmless shortcut might be dangerous.

[@adder3597]

Yep. The best way to ensure safety culture is to teach people why shortcuts and failure to follow safety procedure is not allowed.

[@genericamerican7574]

And they still kept messing up

[@leechowning2712]

See Plainly Difficult's nuke accident playlist to see why just having rules in place isn't enough when dealing with this stuff.

[@theymusthatetesla3186]

Calder Hall. I was a Reactor Operator there, for 17 years!

[@theymusthatetesla3186]

Some VERY clever clever people built those things.

[@theymusthatetesla3186]

'Windscale' (as it was known then) was-and is- the Nuclear reprocessing site, across the river Calder from Calder Hall. The incident in 1957, was brought about, by 'Wigner Energy' (brought about by neutron bombardment of the graphite core) of the Atomic Piles, that were Piles 1 and 2. This Wigner Energy, built up in the graphite core of the Reactor, and eventually gave itself up in a burst of heat energy, which gave rise to the fuel rods catching fire in the core. To stop the fire, the huge fans were turned off, and the core was flooded with water. The original Pile Chimney still stands (and is currently being slowly dismantled, as it is contaminated inside) The large areas on top, were filter galleries, built, at great expense after the original building was erected, They were built because Sir John Cockcroft knew that if anything happened to the core, filtration would be needed. He was right! They were known as 'Cockcroft's Follies' but as it happened, they turned a disaster into a crisis. I've stood on top of that chimney, and it's a great view, I can tell you! They're 350 feet high. Someone once named them the 'biggest hot-air machines in the world'. Indeed, they used to blow holes in low clouds! The idea behind them, was to make Plutonium, from 'burning' Uranium. Plutonium, is called a 'transuranic' material. That is, it is man-made. It is heavier than Uranium, and isn't found in Nature. The heaviest being Uranium, on the Periodic Table of Elements. It is a terrible substance. It has a half life (the time taken for an isotope to decay to half its original strength) of over 24,000 years (though it goes through several metamorphoses in the meantime) Both it, and Purified Uranium, are classed as 'fissile' materials. That is, in enough quanitity, and being brought into close proximity with one another, will cause what's called a 'criticality' (which is precisely what happens in the heart of a nuclear reactor, to give heat) Not only heat, but a GREAT deal of Neutron and Gamma radiation. That is why the cores of a reactor, are heavily shielded. Well, that's about it. I bet you never thought you'd get such a comprehensive reply, did you? That'll teach you to ask questions ;)

[@theymusthatetesla3186]

No: really, I was! Why is that so hard to believe? Oh, we're on You Tube, I guess! :) But seriously...I was.

[@theymusthatetesla3186]

....then your country is responsible for the excellent CANDU Reactor!

[@theymusthatetesla3186]

Haven't really followed them closely, but Calder was closed for good in March 2003. (I wanted to press the 'trip' button for the last time) but it went into a hat, and my friend got to do it instead. However, they're just about to gbreak ground on NEW reactors, right next door. They won't be Magnox reactors, though. Calder was very small....each Reactor giving only about 250MW 'Thermal' and that equating to about 60 MW 'Electrical' (Generated in the Turbine Halls)

[@Charlie1821]

I learned more about nuclear fission in this 20 minute video than the last 20 years.

[@JCarey1988]

50 odd years later this is still fascinating stuff!!!

[@FixItStupid]

Cancer For ALL

[@paulbuswell6566]

Probably the most simple and concise explanation of critical mass I've ever seen.

[@mrbeast85]

That was a great information film. I love the 1950's/60's British style and the rather prosaic descriptions of a criticality (something which could, depending on circumstances, fataly irradiate someone in seconds). Still I think it gives a pretty good basic lesson.

[@FBI-ej8zr]

why are science lessons in school not more like this? just over 20 minutes and in school it would take 20 lessons to teach us this.

[@portobellomushroom5764]

School would also teach you associated calculations to figure out the criticality

[@richcast66]

It’s as if educating the mass’ was actually a goal many years ago. This was so informative and packed with solid explanations

[@Drforbin941]

so correct

[@tomkandy]

This isn't for "the masses", it's a training film for nuclear industry workers.

[@rjowen]

Imagine if this same documentary was being made now in the USA. It would span 3 episodes 1 hour each and after every commercial break you'd hear "Previously, on Criticality, we saw how a scientist walked along a corridor using his feet. Now let's see how she manages to walk across a room towards some fissile material. Can it be done?"

[@xiro6]

dont forget all the drama,about 8 "almost died" parts and one "almost doomsday" on each chapter.

[@Dutch3DMaster]

Lol or in the "Seconds from disaster" type of narration: "Now all the combinations of errors that will lead to the disaster come together. With cutting-edge computer technology we are capable of returning to the moment leading up to the disaster. Earlier we saw operator [name] operate the valve for mixing waste material, without realising there was to much of a different substance in the waste container he was operating on, causing a chain reaction." *reverts back to the thing we already saw 2 times while showing crappy computer animation*....

[@rjowen]

@@Dutch3DMaster yes. Maximum lol.

[@Kitsudote]

I'm enticed by the quality of the illustrations for this time.

[@flaplaya]

taken me 39 years of studying nuclear fission (on my own) to gather the understanding of it at a modest level. Must hand it to the Brit's on this one. Excellent presentation and it's probably 50 Years old :)

[@Donkusdelux]

I love these old videos, very informative and well explained :)

[@godfreypoon5148]

Does it always make a cymbal sound when it goes critical?

[@AaronGilliland]

Godfrey Poon I'm afraid that's just how physics works.

[@clearingbaffles]

Yes it does and that was always a problem on submarines as we are trying to be QUIET Thanx from the left coast near the Krapitol of California

[@mikestevens8012]

Perhaps we can tell you ,but you'll have to sign this waver...

[@toyplasticcello]

Yes, it's how the neutrons let you know to duck and cover.

[@magicstix0r]

Actually it's more like a buzzing sound... Like bees... Like angry, radioactive bees...

[@orangejoe204]

17:27 - "Blood-y hell... guess it's off to the Job Centre for me."

[@videosuperhighway7655]

I keep my plutonium ingots spaced out 5 feet away and boron doped neutron shields to prevent criticality in my garage.

[@ramjamholder9405]

VIDEOSUPERHIGHWAY Well, as per 9.20, I limit myself to one Slag my garage at a time. Maybe if I got some suitable shielding, I could up this to 2 slags, but unfortunately it they ever touched I'd be risking criticality

[@PeterWalkerHP16c]

you only need to walk between them to get the blue light baby!

[@realSethMeyers]

Aaaaaand you're on a list

[@WadcaWymiaru]

I would throw plutonium in to the trash can! Plutonium is *Pu* ...sounds like poo... Thorium is better for nuclear energy!

[@mitchellrose2940]

VIDEOSUPERHIGHWAY thank you good citizen.

[@glennmrosek3358]

Excellent. Very jolly music, simple graphics, and a nice, calm cup-of-tea voice. TEPCO probably still use this.

[@777jones]

Glenn Mrosek the jolly music is essential for gentlemen to understand today’s fissile materials, so they can be handled by hand at work

[@johnbennett3714]

I’m glad I found this video BEFORE I started my plutonium go kart

[@FBI-ej8zr]

did you finish it yet?

[@mamaboocee]

This was a great explanation on radioactive fuel. Thanks for teaching me all about how the fuel works.

[@laurelviolet]

Fantastic. Thank you for sharing!

[@esmolol4091]

Wow this documentary is just amazing. I understood everything and that means something. Keep it plain and simple.

[@TBrady]

It's one thing to just watch this and another to watch it knowing this was filmed weeks before Windscale.

[@giftson79]

One of the best nuclear science video i have seen so far. awesome!

[@TRPGpilot]

Very informative. Thank you!

[@derekp2674]

That's a reasonably tidy copy of that film. As regards Windscale, this film was released the year before the criticality accident at Windscale, and that is the only process criticality accident that has occurred in the UK.

[@sbreheny]

D D Doesn't this film say "1969"? Wasn't the Windscale fire in 1957?

[@derekp2674]

As noted on other posts here, the date of the Windscale fire was 1957. The "1969" here is only the date when the film was released.

[@AddisonGuynn]

@Oliver Mayo They're talking about the 1970 Windscale criticality accident, which was as of 2000, the only PROCESS criticality accident in the UK. It involved plutonium solutions during scrap plutonium recovery.

[@derekp2674]

@Googly Pops Did you mean this report? www.orau.org/ptp/Library/accidents/la-13638.pdf

[@hominidaetheodosia]

As a matter of absolute hard-core fact that’s not true. In terms of what the public know to be absolute hard-core fact it’s true. There was that one time that that chap died and they stuffed his dead body into a concrete barrel sealed it inside the failed reactor and dump the whole lot in the north sea but we don’t talk about that. Instead we ban his daughters KZbin channel and leave her to quietly go insane with grief. It’s just like the opium wars if China won’t grow our bloody opium we bloody well will send them free shipments of it, grown somewhere else, until they have enough addicts to consider our offer reasonable! The Jolly old British establishment what they don’t know won’t hurt them what what.. I will never understand why governments behave in such disgraceful ways around things that they think are worth keeping secret. If the citizens of Britain knew the filthy secrets of the government the entire thing would be overthrown in a matter of days and it isn’t any different for any other government. This would be fine if those establishment twits learnt how to behave honestly, but it seems unlikely this will ever become the case, it’s very hard to accept the dichotomy between reality and the horse and pony show the public are told is the truth. The establishment have such a comforting way of making all the boo-boos go away, thank you nanny state for keeping everyone safe.

[@jurajtrent5477]

Ďakujem za video

[@kbtechandmedia]

-turn on projector -push play on the audio cassette Wait for it...BEEP! -advance a frame

[@2.7petabytes]

Excellent video!

[@tallyankeegal]

I feel like I'm ready to work with fissile materials in 1969, but I was only 8 years old back then... ;)

[@Charlie1821]

Thanks, will check them out!

[@MajorKoenig156]

golly, this nuclear marvel is completely safe

[@matthewweitz1949]

I learned so much from this video! Awesome

[@saiwon1137]

Very informative!

[@whangie1]

This is a really interesting film, thanks for uploading it!

[@nelsonclub7722]

Uranium arrives at Springfield - Homer - 'Woohoo I've got this....."

[@dotslashsatan]

This chan is full of treasure!! Shame it took 10 years for me to find!!! Hope ur well

[@Dutch3DMaster]

The whole safety-standard thing might have been a little much, but if I would've been shown this in natural science class I might just have gotten the whole neutron/electron lessons of the material in high school...I didn't get any of it at the time, but this makes it so much more clear than the drawings of several states in my book...

[@2.7petabytes]

Monorail! Monorail!!!! MONORAIL!!!!! 🎵🎶🎶🎶🎶🎵🎵

[@TrueIndie88]

Unplanned criticality almost always means certain death. It shreds anyone close like an atomic shotgun with barrel sized atomic shells. Shreds DNA and protein. The story of the 2 Japanese researchers was extremely horrific.

[@PeterWalkerHP16c]

@TrueIndie88 Daghlian & Slotin didn't do too well either ...

[@derekp2674]

Not all reported criticality accents have been fatal - many have occurred without operators being in close proximity to the fissile material. See: www.orau.org/ptp/Library/accidents/la-13638.pdf

[@pgarrett6665]

Still bumpin this

[@Hermpiokkr]

A really excellent video ! Thanks a lot !

[@estelja]

Guess the folks at Rocky Flats never watched this film...

[@WSADKO]

If only dyaltov considered all that

[@Joemama555]

in the pub you mind the pints and quarts, in the lab you mind the dollars and cents!

[@wyldeman0O7]

I call bullshit, Homer Simpson was not in charge of nuclear safety.

[@alexscott8736]

“Sphere is the worst shape”

[@oddiosanto]

19:13 windscale... good example of careful design?!

[@WadcaWymiaru]

Before the fire...

[@Acoustic_Theory]

@@WadcaWymiaru Before the heatsink design was modified for higher operating temperatures. Once you've removed material, you can't put it back if needed.

[@WadcaWymiaru]

@@Acoustic_Theory Idiots from Windscale should have huge tank of nitrogen or even argon gas for something like that!

[@pilskadden]

The stupidity behind an air cooled reactor is just mind blowing. And all Windscale produced was bomb fuel - not a single watt of power was generated.

[@Acoustic_Theory]

Mr MMJ It has one job to do, which it did, for a while. It probably was never producing very high power. But I would imagine that it put a lot of heat into the atmosphere locally.

[@iguanapete3809]

This was very interesting.

[@nadtz]

Guess this is pre windscale happened or being made public.

[@wallycleaver8267]

Now I know why my homemade reactor didn't work.

[@marcusfleuti2672]

Back in the days when science shows were not all about political propaganda…

[@Ghosthuntert1]

I think my wife is radioactive, If she ever finds out what tools I have spent money on, She'll go critical !! Thats why my tools are in my shed..

[@richardcarew4708]

My father taught reactor theory at Catholic University in Washington DC.. he also worked at Sandia base during the building of weapons tested in New Mexico between 1945 and 55.. he came back in 50 with a brand new BSc in physics from Berkeley and Lawrence labs.. Plutonium is probably the closest thing to a perfect energy source we have... it's not an alpha emitter like uranium, thorium or radium... it's in the island of stability that occurs throughout the periodic table and especially the lanthinides... beta emissions are electrons, but are the product of fission of a neutron becoming a proton to try to balance the equation correctly with 94 protons... and 150 neutrons... it's within the Golden Ratio, which is caused by the growth of all populations.. 150/94 == 1.5957446809... the Golden Ratio is between 1.5 and 1.7 we assign 1.6169 to the ratio, but it varies depending on the numbers, consecutive Fibonacci sequence numbers... or the ratio between two numbers in a population.. ie.. the Universe grows today by an amount equal to the growth yesterday and the day before combined

[@richardcarew4708]

So if you do this with the various isotopes of radioactive material you will see the relationship... between the stability and the ratio between protons and neutrons... my father said one could hold plutonium in the hand safely 🙏.. it's true.. it's not quite as dangerous as old fashioned television tubes.. inside us is very different, because we can't eliminate heavy metals from our system.. and they lodge in bones and soft tissue around joints.. it's the primary cause of cancer among us.. even though our medical industry does not recognize this... when the motivation behind research is driven by how much money it can make... and only government approved research is allowed... guess what? The mountains behind my house are aluminum oxide with AuPt in a very cubic structure... it is face centered cubic hexagonal symmetry... with AuPt with double double covalent bonds in the planes of cleavage.. with U238 around the hexagonal positions and a target which becomes Pu244 over time... and leaves a few mg of U235 behind to decay to thorium some time in the next 4 billion years At no time is there ever more than a cube of any isotope larger than 4 or 5 mm... separated by cubes of AuPt... about 5 orders of magnitude more dense than lead It's not magic.. it's a technology left by the civilization prior to our own... they thought it was OK to go to war.. until someone bigger came along.. fortunately he wants Peace for the rest of the galaxy.. and we are prisoners of a war most people don't even know about

[@blurglide]

I was hoping to see a video of a real life criticality event in open air. Anyone know if there's anything available?

[@derekp2674]

I've never seen one of those, but that's not to say that one doesn't exist. These days, on KZbin and elsewhere, there are plenty of water reactor criticality videos, e.g. kzbin.info/www/bejne/hXrPp5h5Zr9opdk. Filming in air would be more difficult due to potential radiation effects on any electronic cameras and you wouldn't necessarily expect the camera to see a bluie glow, see: kzbin.info/www/bejne/q4rVmYqFlL9_j9k for why the water glows.

[@Petr75661]

try not banging rocks together if they're from U235 :-)

[@phx4closureman]

20:17 *great summary!!*

[@Bushcraft-xz6xd]

Leaders and first in the world of Nuclear energy. 50 years later we can’t build a new Nuclear power station ourselves and submit to French engineering and Chinese financial help to possibly build one.

[@derekp2674]

@Googly Pops Those working on naval reactors at Rolls-Royce might beg to differ.

[@derekp2674]

I'm not sure that it is correct o claim that the UK was ever uniquely first in the world of nuclear energy. I think it fairer to say that it has always been an international affair.

[@derekp2674]

@Googly Pops I take it you've not heard of small modular reactors (SMR's) then?

[@derekp2674]

@Googly Pops I'd expect the level of regulation to be set so as to give give acceptable safety standards for any size of civil nuclear reactor. And, ultimately, most countries will be regulated in accordance with IAEA standards and guides.

[@derekp2674]

@Googly Pops We may have to wait and see. A year or two ago, it seemed like they were the newest and greatest idea for countering the huge capital costs of more conventional large PWR's.

[@hypercomms2001]

00:12 what is the name of this Reactor? What are the elements radiating out from the centre, which I assume is the reactor?

[@rubberswan]

Michael John Little This looks like Berkeley, Gloucestershire. The elements radiating from the reactor are the pipelines carrying high pressure (and very hot) carbon dioxide gas from the core outlet to the external heat exchangers. The return pipes from the heat exchangers back to the core inlet were at ground level.

[@hypercomms2001]

rubberswan Crikey! Thank you. Was this reactor built with a containment structure? What were the regulators thinking when they approved the design???

[@rubberswan]

Michael John Little Amazingly enough, it was only in the later Advanced Gas-Cooled Reactors that the heat exchangers were placed within the primary containment. The older Magnox reactors, such as Berkeley, operated at lower temperatures and pressures, so the risks were relatively low. I’m pretty sure the pipelines were well protected.

[@tomroland2315]

@@rubberswan Enjoyed the video, in fact the later Magnox reactors Oldbury and Wylfa both have their primary heat exchangers ( or boilers) within their concrete pressure vessels.

[@benruniko]

“Unenriched uranium rods can be handled and stored without special precaution” … *thyroid cancer intensifies*

[@josephastier7421]

2:33 Awesome.

[@TheSilmarillian]

I learnt that moderators where there before the internet and social media ,I had to say that lol hello from Australia

[@mikeh.7499]

and hello back at you from San Francisco

[@TheSilmarillian]

@@mikeh.7499 :)

[@chriskratzke4844]

I would really like to see what happens when the same stuff is done at time stamp 10:10 in this video to the element “U” in a “metallic glass” state🤔

[@garethjohnstone8662]

Imagine starting a criticality event, knowing full well what the implications were. Terrifying. Waiting for your body to begin shuting down. Anyway, little joke: Proton walks into a bar and orders a drink. He drinks it and asks how much, the neutron replies "No charge".

[@azonicrider32]

ok, ready to play some fallout 4.

[@AliasUndercover]

If you see a blue flash, time to move your ass.

[@PeterWalkerHP16c]

yeah, straight to the hospital decon unit then to the palliative care unit. :-)

[@wazza33racer]

Wheres smiling Joe Fission??

[@Microbex]

That factory is frightening just to look at. A job there would give me ulcers.

[@robinhoodtheorem]

If you find that story about Rocky Flats interesting, I recommend the following 3 part video. "Practices of the Rocky Flats Nuclear Weapons Plant - Part 1 of 3" watch?v=-tkRFP7cUXA Pt 2, watch?v=Sl8EmQK5kow P3, watch?v=9Kot1THqBII

[@eddiemorrone870]

Nice use of graphic matching.

[@haraldkrieger6562]

❤

[@longdefeat]

Hi grandad

[@sionatube]

1:17 No need to be so jolly about radioactivity

[@mikebon8352]

If population stayed at pre WW1: 1 billion... Then should be no need for more daily exponentially energy use... Or even more dangerous methods to get more energy daily compared to 50, 100 years ago..

[@chrisL50764]

Would have to disagree, heavy pollution from burning coal was much worse 100 years ago. We've developed better cleaner ways to get energy.

[@mikebon8352]

No we aint@@chrisL50764 we just put it all in China... see how many coal burning plants each year have opened up each year since 1990... and closed in the west (US & EU). Mining stuff from deep underground and put in fragile biosphere which is just maybe 5 miles, high 10 miles is minus 50 degrees... Plus people just need 30% of fossile energy, to clean, cook, wash etc... industry which makes rubbish.. see cars are 5 years being paid and rusted... and military see ships and airplanes uses up 70%... So what is the point of humans on this planet... Enjoy the ride... soon it will all tumble down... in evry way u can imagine, financial, biological etc. u name it.

[@danr5105]

"Using natural uranium as fuel?" That is a trick we should have learned from these old timers.

[@willhouse]

Chernobyl used low-enriched Uranium fuel, too.

[@CyberspacedLoner]

Make Nuclear Power Great Again !

[@JabbaTiure]

18:31 - Yeah, just don't- 18:45 - "Diluting a solution means adding a moderator" Screw it. I won't go into nuclear engineering! D; So much to memorize, so little time!

[@xiro6]

also,remember that "moderator" means it will accelerate the reaction. like inflamable means flamable. kzbin.info/www/bejne/h2nQdWWeqN2lnrM nucelar energy is complicated,

[@Tacsmoker]

11:01 evil face?

[@romanbotello15]

I like squirrels.

[@21tryhard97]

this is litrally 1969

[@robinhoodtheorem]

There was a once fire at the Rocky Flats weapons plant. Two security guards fought the fire with fire hoses. There is a stirring recounting of the event in the following video, "Kirsten Iversen, Full Body Burden: Growing Up in the Nuclear Shadow of Rocky Flats". The men were scared shitless because the fire hoses could cause criticalities in two ways, by blowing the ingots into close enough proximity to cause a criticality, and by the water acting as a moderator. watch?v=wWqJQY4GthE

[@hominidaetheodosia]

Come on chap I’m pretty sure we can mate these flanges if we try hard enough, you’re holding it wrong you silly goose!

[@breakingbolts8871]

criticality is when Chuck Norris and Fred Dibnah go out for pints.

[@Chiavaccio]

😀😀👏👏

[@billpugh58]

17:28 Gor blimey and stone the crows guv, me henriched huranium as gone fer a swim……..

[@JanicekTrnecka]

18:12 Kids trying to insert rectangular shaped piece in a triangle shaped hole...

[@sbrinkerhoff8069]

1.21 JIGAWATTS!!!!!!!

[@Ann-sj4pt]

Creepy

[@exet]

uranium has about 1% u235 99% of uranium is u238 until the separate the atoms

[@donaldmccutcheon6455]

We need nuclear power now more than ever. Let's power up America.

[@princeofcupspoc9073]

4:05 Sends every physics student into fits of cringe. The Bohr model is only mentioned in historical reference, groundbreaking as it was. DO NOT think of the atom as a solar system. 5:10 I don't know if I'll be able to make it through this. Neutrons do not BOUNCE OFF of nuclei. I can't even... A better term might be "interact" via the strong/nuclear force. We can't even start this without understanding the 3 1/2 known forces. 5:30 Uranium is NOT UNIQUE in respect to this property. Plutonium does an even better job of it. It's just a question really of which isotopes of which elements can we get a large enough quantity. 7:15 Criticality is NOT required for the source to emit gamma rays. Gamma rays are emitted constantly. At criticality there is much more gamma radiation. I won't even touch the blue glow from ionization. 7:50 Did they actually have a physicist write this, or a high school kid? Uranium IS A METAL. It has nothing to do with the quantity. OK, I'm done. I need a tranquilizer. Hopefully someone else will take up the commentary.

[@derekp2674]

You have to bear in mind that this film was produced as part of nuclear safety training for plant workers (and everyone else) on the UK's main nuclear sites. That inevitably requires some simplifications to be made, particularly around topics such as the microscopic mechanicals nuclear fission reactions, as opposed to their observable macroscopic effects. With regard to your specific points: 4.05 I agree the use of "solar system" is not needed here. 5.10 I think "bounce off" is a reasonable representation for neutron scattering reactions, given the target audience. The authors probably had reactor grade graphite in mind when they wrote that. As a point of omitted detail, graphite does also capture some neutrons, but its capture cross section is very small. 5,30 I think you missed "unique in nature" which was mean to refer to U-235 being the only fissile nuclide that occurs naturally in measurable quantities. 7,15 I think you missed the point that 'intense' radiation is only emitted if criticality is achieved. Under safety subcritical conditions, unirradiated nuclear fuel does not emit enough radiation to require either remote handling or handling within shielded containments. So whilst it will only be handled within Radiation Controlled Areas, the resulting external radiation doses to workers will be very small, relative to the annual routine dose limit for a Classified Radiation Worker. BTW, the blue glow is a real effect and can be observed in KZbin videos of water moderated research reactors. It's not caused by ionisation though... 7.50 The footage here shows the reduction of uranium ore in into highly pure uranium metal, as used to fuel early British reactors. Later reactors used other chemical forms of uranium, including uranium dioxide. As the credits show, the lead technical advisor for this film was John Daniels. I don't think his background was in theoretical nuclear physics or even reactor physics theory, but I think he was Head of Profession for Nuclear Criticality Safety in UKAEA at the time. I believe also, Ed Woodcock, the UK (and world?) originator/inventor of Monte Carlo neutron transport codes, also make a brief appearance in this film. Some of the technical papers that they wrote are still used as cardinal references today.

[@hwirtwirt4500]

The title of this video should be "Criticality For Dummies".