Hello Scott. Retired nuclear engineer here. I was on the DOE's emergency response team, bags packed and ready to fly to Chernobyl but as you know, in the end Detente' had not progressed enough for them to trust and accept us. Anyway, This is probably the best explanation of what happened I've seen or read. First a small thing. In the US, the xenon buildup is referred to as the "Xenon well". You should witness the scramble in a power plant if someone accidentally trips the reactor by, for example, valving in a water level transmitter in the wrong sequence. EVERYBODY is running, trying to get through the restart procedure before the reactor sinks too far into the well. There is one critical part that you left out which is probably the major reason the transient was so large. In each control rod, below the bottom of the boron carbide is about a foot long void, filled with air or whatever they fill the control rod with. When this void passed by a section of fuel, there was no moderation and no neutron absorption which let the fuel go prompt critical. This prompt critical reaction continued until disassembly started. At the very beginning of the prompt critical reaction, the rod channel was distorted enough to freeze the rod in place. This was NOT a small nuclear explosion. This was easily determined by looking at the fission product profile from air samples. A nuclear device profile is much different than a prompt critical excursion. This is because the device begins disassembly so rapidly that the first generation fission products are not in the neutron field long enough to either be burned or transmuted to another isotope. A prompt critical excursion, by contrast, lasts relatively forever. Some first generation fission products are burned and others transmuted to other isotopes. Eyewitness testimonies I've read from operators who survived stated that the first explosion was large enough to rattle the fuel insertion shield plugs and shake some out but that the big one happened maybe a minute or two later. The delay was long enough for operators to run to an observation deck and see the shield plugs rattling. That's consistent with a buildup of H2/O2 and then detonation. This difference in air samples over Europe is the first indication that there had been a reactor accident and not the Sovs having conducted a very small above-ground nuclear device test. My guess, based both on what I know and from what I've seen of small samples of graphite smuggled back from Chernobyl is that this was a hydrogen-oxygen explosion. Of course, like everyone else, mine is only a guess. There are two catalogs on the net. One is the catalog of the isotopes using an NaI detector and the other is the same but using a GeLi detector. On the last page of the GeLi catalog is a spectrum of fission products of an atmospheric explosion taken seconds after an atmospheric test. It's so dense it looks like white noise on a spectrum analyzer. John
@@merrittw83 Ionisation is the process by which an atom or molecule is excited to a new energy level by acquiring or losing electrons. That was the blue light that they saw
@@merrittw83 Dr de Geer wrote in the study: “It is well known that criticality accidents emit a blue flash, or rather glow, which derives from fluorescence of excited oxygen and nitrogen atoms in the air
@@merrittw83 A strong enough pulse of radiation will cause the Cherenkov effect in the vitreous humor inside your eyes. That's the blue flash they mean, and it's a death sentence.
I remember a joke from one of the plant technicians at the New containment unit... "You have nothing to worry about, Soviet radiation is the best radiation!"
But seriously, funny comment 🤪, and as you haven’t had many replies, I’m going to squeeze this in, which would otherwise be lost in the wash: Fukushima was 40 years old Technology with a clear record, and got simultaneously everything that mother nature could chuck at it: earthquake magnitude 7 and a subsequent massive Tsunami which apart from destroying the town, swamped The reactor building, knocking out the diesel powered water pumps. But it still failed. There are three causes of accidents: men women and children. One way or another.
@@Johnny-sj9sj Fukushima had evrything right except some minor details that made everything went kablooey. It had no hydrogen recuperation system that was mandatory, but wasn't implemented, and diesel generators weren't build up the hill, where Tsunami didn't reached. And third, Fukushima reactors too had a design flaw, they would stop the coolant go into the reactor after the emergency without personnel knowing about it. Thus the reactors had a meltdown.
I was 7 years old when the explosion happened. We were a group of kids playing outside, having fun, suddenly our parents came out and started screaming at us to come inside quickly. I got a pill that I had to swallow and I asked why. My mother said "it's for something in the air". I was like wtf is in the air - she said nevermind that. When I saw this series I got shivers down my spine. I remeber reading about it in my teens but never put much thought about it. Really weird feeling. But later on, in 1989, the revolution started and we were hearing bullets hitting the trees around us while playing so a bit of radiation was nothing. What a childhood...
I lived near a nuclear power plant as a kid (still do actually) and one day in elementary school we had an unannounced nuclear preparedness drill. Years later, I got a job at the plant and found out that there had actually been a fuel channel breach that resulted in a loss of coolant accident.
@@Ravi-xf8dw The whole point of the test was to ensure the safety shutdown mechanisms worked correctly. The reason Chernobyl exploded was because of communist quotas requiring that they keep the reactor on and at maximum power for the majority of the day before the test so that industrial sectors could have enough power to meet their end of the month quotas. Had the reactor had time to cool down before running the test it’s possible it wouldn’t of exploded.
@@spacekiller6856 The number of things they didn't do that they were supposed to, and did do that they weren't supposed to, was the issue. They did the safety test without meeting the required initial conditions, but they also disabled other safety features without any procedure telling them to do so. There are serious design issues with RMBK, but to say that it failed is unfair. Modern designs are also unsafe when operated with such disregard
This was a classic Soviet shortcut. Western reactors use fuels enriched to 3 to 5% U235. This is very expensive and time consuming. In fact, getting to 5% U235 is a significant portion of the effort required to reach all the way to the 80 to 90% of weapons grade (kind of the way LEO is most of the way to anywhere in the solar system). RBMK's used around 2% enrichment. While this sounds like small difference, it is not. It meant much cheaper, faster fuel production and an increase in the enrichment industrial capacity available for weapons production. Unfortunately, is also meant a relatively sluggish fuel. So, the RMBKs use fixed channels literally made from a reaction accelerating (neutron moderating) material: graphite. This "juices" the reactor in order to make the low quality fuel work. This is the primary driver underlying the positive void coefficient (unstable) nature of the RBMK. The Soviets also chose this design, so that it would be common with those dedicated entirely to weapons grade plutonium production. Plutonium slowly builds up as a byproduct in fission reactors and is harvested from fuel rods. The RBMK has the unique ability of replacing its fuel rods quickly without shutting down the reactor, making plutonium production more efficient. (And yes, Scott... this is actually me: @torybruno. Great job on the video!)
Not quite. RBMKs had a POSITIVE void coefficient - hence the runaway power excursion once the core began to overheat. More heat = more voids = more moderated neutrons = more fissions = more power = more heat etc, etc, etc. The instability of the core having so few/little control rods inserted, plus the graphite tips on the rods, were additional errors of operation/design/operator training & knowledge. Chernobyl rocketed from less than 15% power to an estimated 10000% power in well under 2 seconds. That equals BANG! I wonder if they ever completed any maximum design accident analysis or modelling? No secondary containment? Madness! Underlying the fundamental design flaw of the +ve void coefficient, etc, may have been many other aspects of the USSR economy and 'limited' industrial/technical capabilities at the time. These combined to feed into the USSR's urgent need for more and more cheap power as quickly as possible. To build up their power generation industry quickly, however, meant too many corners were cut & too much operational secrecy also led to the point that the operators had no idea what dangers they were facing/creating for themselves and others... A sad, potentially avoidable, day for many people.
@@louisdrouard9211 Great comment and yes, you're right. The French built 10 units of the UNGG reactor design. There were some significant design differences, compared with the RBMKs, which made them much safer to operate. One of the other big advantages of the UNGG was its use of a huge concrete containment structure. That would have prevented the huge radiation release of Chernobyl.
@@Jabbatic There were two types of reactors in USSR - RMBK's and VVER's (PWR class). The second one has a concrete containment around. The RMBK designers thought about containment but it was just impossible to build any concrete containment over reactor. Its not only the reactor itself but also auto crane that can hold inside 7m fuel pipes with uranium. So you can change the pipes with uranium and keep the reactor running. Every state in USSR had a choice to build one of the reactor types so Ukraine took RMBK 1000.
@@dmitrigutorin944 Yes, I knew that and you are spot on. Your comment about the size of the containment building was very important and was one of the limiting cost/time/material factors for selecting one design over the other. The VVER design is inherently safer, but the RBMK design gave access to electricity generation from large, 'simple' plants that could be constructed in large numbers within a reasonable timescale, at an acceptable cost. Crucially, the RBMK design minimised the personnel training/operations requirements and also the technical challenges that had to be met by the major industries manufacturing the largest and more critical systems & components. The RBMK could be refuelled whilst still operating due to having no containment building - thereby enabling the USSR to recover plutonium from the spent fuel much sooner than with the VVER design. The VVER design 'family' has seen considerable development over many years and is now an impressive design in its Gen III+ configuration. I look forward to seeing how far the VVER design can go and how it shall measure against other designs in the future. My great hope is to see the first operating fusion power reactor. Still 35 to 40 more years to wait? ;-)
My favorite thing about the series is that it explained why the test was gone ahead with despite all the negative conditions. It was necessary if they were to sign off on the reactor by May Day, and if that happened several higher ups would get promotions and move up to nicer offices.
The reason was that every aspect of soviet industry was micro-managed from Moscow. The on-site operators and engineers didn't want to do the test with the reactor going into a Xenon well but Moscow ordered it anyway. For example, the Chief Engineer of the unit wrote a book. Weeding through the massive ass-covering and buck-passing in just about any soviet document regarding Chernobyl, he described how 2 days after the explosion, he was receiving orders from Moscow to continue pumping emergency cooling water into a reactor that no longer existed.
@@cptnoremac Because the Graphite rods ( an accelerant) were in the middle portion of the fissile material, the visual is like the Price is Right Range Finder. Fuel in that range, adjacent to the graphite, becomes way more active. As they moved down to exit, the bottom of the rods began generating more energy and more heat. So, yes, of course the steam leaves at the top, but it is boiling - and generating voids - lower and lower in the water as the graphite moves down.
@@briancorrigan5350 Before any movement, the middle part, where the graphite is, would be the hottest part, right? So why would moving the rods down and displacing the water make the bottom the hottest part? Up until then, it had water helping to cool it. It should never be able to catch up with the middle as long as both have the same moderator. But everyone portrays it like the very bottom is the part that got too hot first. Seems to me the AZ-5 button couldn't have made things worse.
@@cptnoremac I understand the rods where inserted very fast and the graphite tips broke, getting stuck essentially in the middle of the channel, increasing the moderation and the number of slow neutrons, increasing the reaction. A positive feedback loop.
@@amramjose Nah, the graphite was already in the middle of the reactor before the button was pressed. What everyone says is the area where the water was displaced by the graphite at the bottom got too hot and that started the chain reaction of problems.
Me: [has seen every nuclear documentary he can in the last 15 years, half of which on chernobyl] Scott: Wanna watch yet another explanation on chernobyl? Me: Yes.
Basically, they swerved left, then they swerved right trying to compensate, then they swerved left again trying to compensate for that, then they flew right off the road.
The RMBK reactor design is instable so it will increase power when control rods are taken out. Compared to a car that oversteer, when you loose control it will spin off. More modern designs are stable so if somethings goes wrong you take control rods out of the core. Compared to a car that understeer and you just brake harder.
Yes, but when they finally hit the brakes the wheels locked up and the car completely lost control and hit a tree, after which it blew up and started a massive radioactive forest fire.
I was surprised at how well the series was done. I had learned a lot about Chernobyl since 1986, but the graphite tips on the control rods threw me for a loop. I was a manufacturing engineer for some very special control rods at one point in my career and the tips were not made of graphite or any other moderator. If you have to SCRAM the reactor the first thing the fuel sees should NOT be moderator.
When they made the statement in the series about it being cheaper to make them that way, they didn't mean the rods, they actually meant the reactor itself. By making the rods dual material, they were also dual purpose, and because of that only needed one operating mechanism, not a separate channel and operating mechanism for each. Under normal circumstances, it would never have been a problem, but sadly these weren't normal conditions, and thus the mess that occured.
It's sort of a design cop-out, where the control gradient is made larger by attaching moderators to the control rods. I think to avoid such a scenario, it would make more sense for the graphite ends of the rods to be flush with the bottom of the reactor at full extension, so that there is only a decrease in power when the boron is reinserted. That being said, you're entirely 100% correct! There should simply be a different system for the control rods and moderator rods. Makes the control of the reactor much safer, as removing moderator and inserting absorbers at the same time will arrest the reaction much more safely and quickly!
@@keatoncampbell820 The reason they weren't "flush" was to allow for neutron flux throughout the reactor, avoiding hotspots and uneven reaction rates in different parts of the reactor. Vlogbrothers video explains this well. Possible that gradually introducing the rods to stagger the graphite introduction near the bottom would have averted disaster, but how were they to know.
@@ComeWhatThey I'm not a nuclear physicist, to be sure, no matter how interested in it I am or however much math I'm doing. I am an engineer though and first principles design is fairly important for something like a nuclear reactor. Generally, the function of emergency aborts, E-Stops, and SCRAM functions is to completely and safely arrest reactivity and as immediately as possible make the core inert. That being said, most reactors are designed in such a way that it is physically impossible for E-Stops to increase reactivity in any way. It may and often does sacrifice performance, efficiency, and thermal loading to limit the geometries of the core elements to those which function but do not increase reactivity in any state, configuration, or environment. Elegant design would accomplish this through geometry of the components of the core, though operation logistics is also sufficient to achieve safe E-Stops, but that would mean including the possibility of failure, which is entirely unacceptable for something with so much value and so much risk.
Former nuclear control systems engineer here -- this is an accurate explanation of what went wrong at Chernobyl. Scott, I am legit impressed how you're able to totally switch fields and still be technically competent. You're like a Scottish Neil deGrasse Tyson! The tldr in case the video wasn't clear enough: in certain situations, a scram (emergency drop of the control rods to kill the reaction) actually boosted reactivity (i.e. neutron multiplication rate) instead of killing it. Which turned the RBMK "emergency shutdown" system into an "initiate steam explosion" system. It was just 100% pure engineering failure. Separately, I love those USSR corrective actions after the disaster: "Prevention of the emergency safety systems from being bypassed while the reactor is operating." Just... profound.
There were no engineering (design) mistakes. Not by that time's standards, anyway. The operations put a dangerous engine way beyond its limits. Of course today that design is not considered safe. People turned out to be more dummies than anyone could expect.
@@vladimirdyuzhev Didn't the Soviet Union know that the RBMK reactor's had a design flaw in the form of the control rods? If I remember correctly there was a similar (though much smaller) accident involving the control rods at another nuclear plant well before Chernobyl ever happened. They just didn't tell their plant opperator about it in typical Soviet Fashion.
@@madcourier6217 > They just didn't tell their plant opperator about it in typical Soviet Fashion. AFAIR, no, that information was available. Not to general public, mind you, but to the operations on RBMK plants. Your understanding of "typical Soviet fashion" has very little with the reality. The nuclear industry was one of the best in the documentation and control. Well, a few dedicated people can break even a fail-hardened system, as we can see.
@@vladimirdyuzhev According to Soviet standards, maybe. The lack of a containment building and a two stage emergency coolant backup would have been considered flaws so fundamental that a reactor of this design would not have been allowed to be built outside the USSR. Furthermore fixed graphite moderation and a positive void coefficient were considered inexcusable flaws in reactor designs back in the 70s in the West. Reactor #1 was finished in 1977 with #4 (the one that blew up) finished in 1983. There was a previous accident involving a power surge when scram was initiated in another RBMK reactor (IIRC in 1983?) and a few of the higher ranking nuclear officials and scientists knew about this flaw. However, they did not tell the operators of the reactors about this - instead they gave them a rigid framework of conditions that they were never to deviate from. Unfortunately, the political pressure put on the operators to complete this safety test motivated them to try and cut corners and that was the main cause of the disaster. The real issue with the Soviet nuclear program was the culture of secrecy that permeated basically the entirety of the Soviet bureaucracy. Safe nuclear energy REQUIRES open and accountable culture to be effective which is why the worst nuclear accidents have always involved places that don't have that culture. This is why the West has used nuclear energy longer and with many more reactors than anyone else - but has far fewer serious accidents.
7:30 - he says that the test was never successful at the Chernobyl #4. In fact previous test was successful in powering the pumps but their recording equipment failed and they were unable to provide measurements to confirm so they had to repeat it.
@@youonlyliveonce12ish the pumps worked and it was registered in the computer but additional equipment which was supposed to make detailed record of turbine performance failed. And if they lied - they wouldn't need to repeat the test on April 26.
@@AlexDemidov "And if they lied - they wouldn't need to repeat the test on April 26." You are missing the other option: they lied to meet a deadline but still intended to do the test because they weren't /completely/ stupid.
Thank you this in depth explanation! Another video suggestion: The plugging of the 2011 Deepwater oil spill was basically a space mission on earth. Really fascinating engineering designs were proposed to stop it, but no good UA-cam video exists on the matter because 11 years ago, ScienceTube was still too niche. I'd be so happy to see this subject covered by you.
Having worked in the "power generation" industry for a number of years (albeit diesel), I have a great respect and appreciation for the invisible energy that allows you to see at night, cooks your food and keeps you cool OR warm. When you are responsible for the power and the lights go out, it is truly a sickening feeling...... With regard to nuclear power production - *_To think all that physics and chemistry just to boil water._*
I remember some one stating, and I paraphrase, that using nuclear energy to produce electricity is similar to opening the front door of your house with a canon.
steve ducell an interesting proverb. But environmentally if made safe, nuclear is the best solution. Chernobyl exploded because of a combination of the flaws of the communist System and the reactor design itself and the people operating it Fukushima exploded because of the government deciding to build nuclear reactors near the ocean in a country that experiences tsunamis and earthquakes pretty regularly compared to other countries. We didn’t throw away the idea of the aeroplane because we could fall out of the sky and die. We should not just discard the benefits of nuclear energy.
@Rockhopper1163: Regarding your last sentence - yes, you’d think there’d be a more effective way to harness nuclear energy instead of essentially just using it as fuel for your steam engine. On a side note - imagine building a steam locomotive or steam boat with a nuclear reactor. 🤔
@@董家琪 I echo that sentiment. As a US Navy Nuclear Propulsion enlistee, I had the privilege of having a Reactor Principles instructor who would 'talk shop' after class every several days. The one time I remember clearly was when he talked about other nuclear designs, and talked through Chernobyl from much the same standpoint that Scott just did. This video was "Outstanding."
I'm an old US Naval Nuke (1960s era) Excellent explanation. I was once involved in a hot restart in a War Zone. Very dangerous. It worked out OK. We did have to calculate the Xenon poisoning to know where (how many inches out for the control rods) criticality was likely.
As a submarine officer and nuclear engineer, this was a great description of the accident, in terms that many can understand. All US and most other country's reactors are designed with far greater safety and a negative temperature coefficient. The control rods are completely released and fall rapidly into the reactor core. For a submarine, we immediately shut the throttle reducing energy taken from the core. We also shift power supply from the electric turbine generators to the ship's batteries. We shift to reduced electric load for the batteries to last longer. If needed, we come to periscope depth and use the diesel and the ship snorkel mast. Control room crew immediately bring the ship up to 150 feet. All these actions are immediate after the Engineering Officer of the watch announces "Reactor Scram". We practice the event often in ship drills.
@@BorkomoraThe vast majority of this information is either public already or easily inferred. The batteries, diesels, and snorkel mast are standard equipment on nuclear submarines and not classified. The procedures to provide power to the cooling pumps are logical and easily inferred from first principles: you want to shift power to the pumps to the batteries as rapidly as possible and let those batteries power the pumps for as long as possible, so cutting power is essential to the process, no different than preserving your phone battery when you know you can’t charge it for a while. Snorkeling submarines are easier to detect, so you want to minimize the snorkeling time. The only thing that gives me any pause is depth orders.
@@Borkomoraopsec refers to things like troop locations, make up, and tactics. If they were talking about how the reactor is built I could see a case for screaming OPSEC at someone but they aren't so its fine.
Now most of russian rbmk 1000 are operaring at 1060-1080 MW, since there was inicially planned an increase of power Why RBMK: No need to stop all of the reactor to refuel it Faster refueling meaning less exposure of station personell to radiation Easier regular maintenance Easier increase in power (up to 1600 MW in project and up to 3000 hypothetical) Much fasterand easier construction requiring less complex, expensive and dangerous operations Less manipulations with simply large and heavy constructions, allowing for easier logistics Lesser fuel quality requirement and easier compensation for fuel burn inequality in different parts of the reactor The downs are The water from reactor hot zone goes directly to turbine, not to heat other water, possible danger The fuel rods are thicc, long rods for a large corezone making a 100% thicc secondary confinement prohibitevely expensive and requiring still large buildings and machinery to operate. Legasov in his memoirs in the tape remembered the council about these reactors design where he participated before construction and he regrets not putting enough pressure on making a safe confinement for the reactor, and suffers greatly from the responsibility. The graphite blocks inside the zone is slowly damaged by radiation and heat and deforms, with a possibility to cause a jam. Overall, not great not terrible, 3.6/comrade
Why the heck do we even need politicians? Why? Really! I know, I know, democracy right? But why do we make all these smart scientists led by these morons, who we stay will stand by what the majority wants, then just steal what they possibly can, then playing mindgames for power again? I do not know what the solution is, but we defo should make the next step after democracy, because it does not work well.
@@cjstrashvideoemporium6484 I agree, and I proposed something similar in a comment under a different video. The only issue is that for these changes to be implemented, we would need those high up who are willing to implement these rules, and these rules would make them a sudden decrease in income. Just take Hungary for example: the head of the general attorney has no reporting obligation to anyone, and for roughly 25 years in charge, he never ever launched an investigation against the now leading political party. So even if the votes will land on the opposing party, they have no chance to do a single thing against the former leaders. So yes, your solution is good, and it would work, but we cannot see it happening. It is like a disaster movie, where you can't avoid the disaster, just minimise the casualties. They up there do not want to be transparent, just looking like they are transparent. And here we are :-/
Because while individuals can be very smart, people are idiots. We are ALL herd animals and will irrationally chose the popular opinion over any factual information. Until humans evolve, we won't change. It would be nice to find some safeguards to improve things, but I don't see a massive improvement in my lifetime @@peterbalogh2646
They really outdid themselves cutting all the corners on this reactor from start to “finish”. To the many victims of this, my heart goes out to you, you are not alone or forgotten!
Not so much corner cutting as poor design choices. The void between the control rod and the graphite moderator should never have been there. In a SCRAM, that's is the very thing you don't want passing through your reactor. Also, taking ~18s to fully insert the control rods is a very bad idea.
@@jfbeamThat’s wrong. Those points basically were unavoidable from an engineering point of view. The stress on the control rods would have been to high if they were pushed with a higher force into the reactor due to the water displacement. Many of the reactor flaws were indeed corner cutting: no containment, pressure tubes instead of a pressure vessel and mixing the functions of moderation and emergency-shutdown.
@@GrandProtectorDark well then those who made the car made a mistake, so still a man-made accident I know that this is not what you mean, but I agree with random user above (danger of nuclear is there, it is because of the people operating them, but it is there) I guess what's important is educating the naysayers that it's not some mysterious nuclear danger, but simply the human factor that is responsible for the accidents we don't boycott alcohol because of car accidents, but instead try to prevent drunk driving I don't know how this translates to making nuclear plants safer, but the first step would probably be for people to stop boycotting nuclear power Side note, and I know this is very ignorant of me, but I really only learned that Chernobyl was entirely a man-made accident from this video edit for some clarity
Control what you eat. Don't eat things with high glycemic index. That causes a sugar spike (high energy) which then causes an insulin spike to control the sugar levels, which causes the low energy and subsequent hunger afterwards. You end up weak and fat.
You don't actually need to understand the coefficients, the values relative to each other is enough to give you an indication of how important each one is to the process.
Im glad that you made a follow-up to the show as i've been having a hard time understanding the idea of the "graphite tipped control rods" and how they caused the crux of the incident. Most sources reinforce that this graphite was one of the major causes but didn't elaborate on what it meant to be graphite tipped. In my mind it sounded as if literally just the tip of the rods were covered in graphite for some unknown reason but seeing the control rod assembly as basically a dual use mechanism with boron connected to an ~equal length rod of graphite clears this up immensely.
I think what normally would happen is that, if you inserting control rods, you would gradually insert a few at a time, then others, then others, so that at no point would there be an overall increase in neutron flux throughout the reactor. But of course, in a panic situation, this is not how it happened. Worse yet, once the neutron shit hit the graphite fan, the rods got stuck. At least my impression is that at least some of them got stuck in positions where the graphite tips were accelerating the reaction. Then everything went wrong at once. Think of a stack of Swiss cheese slices, where the holes accidentally got all lined up, letting trouble shoot right through. Sort of like Fukushima, except there the slices were different, but similarly bad luck.
It's like desigining an automobile where stomping on the brake pedal for a panic stop gives you several seconds of maximum acceleration before switching to braking. What could possibly go wrong!?
The issue was that boron rods were 7 meter, while graphite rods connected were only 5 meters length, so when rods started to fall down one meter layer of the water in the bottom of the reactor was replaced by graphite. What Scott doesn't mention is the true reason why nuclear plants exist in the first place. Uranium fission and neutron absorbtion happen in the reactor immidiately (neutrons in RBMK have the speed of 2 km/s) thus if one uranium atom are to fissure another uranium atom the reaction would've been so fast it becomes unstable, therefore reactors usually have only 85% of its reactivity due to neutrons directly from Uranium atoms. The other atoms Uranium fissues to can decay and produce neutrons, these neutrons are used to govern the reaction in the core, because the number of the isotopes that just decay but doesn't support chain reaction grows much slower than the speed of the chain reaction. Thus normally 15% of reactor's reactivity is from fission products. In Chernobyl the reactor was in the iodine pit, which mean that part of those 15% positive reactivity had to compensate xenon negative reactivity. Thus, instead of 15% of reactivity that can be govern the reactor had only (let's assume) 2-5% of the positive reactivity from the fission products. Therefore when rods fell down and replaced 1 meter of water with graphite, for a short period of time 95-98% of reactivity that was due to the chain reaction had the opportunity to change into completely positive chain reaction (105% for example), thus reactor core that was under critical condidtions went over critical and chain reaction became unstoppable, and because chain reaction happens with the speed of 2 km/s an explosion occured.
I concur, Scott is exceptional. I worked on the other side of the coin - we wanted super prompt criticality in picoseconds or nanoseconds - I worked at the Nevada Test Site 1975-1986. I feel much more comfortable with fusion for power gen, but we are still a long way off I fear, Livermore has done a substantial amount of work on it in the past, but not sure where it stands now. One question you may be able to answer - what is the (average) time delta between a reactor SCRAM, and enough absorption to kill the reaction? Or are there so many variables that its not an "average" situation. Thanks for your thoughts on that. and Peace.
Cynthia Klenk excellent! Thanks! I am binge reading these comments. They make a change from the usual rude, bickering and puerile arguments on other subjects and channels. If I wasn’t in my 70s I would want to be a nuclear physicist when I grow up, and I’m not joking Dr Feynman 😎 PS: Love your channel content. I feel another binge coming on!
@@cynthiaklenk6313 oh man, that's awesome. Shutdown can be achieved pretty rapidly after a SCRAM depending on reactor design. Even being slightly subcritical can take some reactors out of the power range in seconds, so a SCRAM can basically turn startup rate instantly (again, depending on design) the big issue is decay heat. Even with all fission basically stopped decay heat can produce several percent of the last running thermal power. If you lost your heatsink temps can build up fast (check out TMI accident)
Hi Scott, that was a really well put together explanation of some pretty complex issues, in just 20 minutes! I was a mechanical engineer at Windscale/Sellafield in the early Eighties. Just like you explained, it was 'known' that (Western) civil power reactors could never go 'prompt' critical (as a result of sound nuclear engineering design). Unfortunately it was not so true for RBMK's when being abused by the operators. I'd happily live near a civil power reactor, but I was a little uneasy while I lived close to the nuclear powered submarine bases on the Clyde in the Nineties. At high burn up levels, near the end of their operational life, I believe these highly enriched reactors become a little 'sensitive' !! Cheers Paul (now in nice safe NZ)
@@jtcruz125 I certainly wouldn't go as far as to say they are 'unsafe', they have a good track record so far, but just not 'as safe' as Western civil power reactors. In the real world nothing is absolutely safe or carries zero risk. Most of us accept the risk of driving a car, having a general anaesthetic, getting a Covid jab (contentious one this!!) despite there being various levels of risk associated with each one. Regards Paul
What about 3 mile Island? While it didn't go prompt critical, they did have a partial core meltdown and radiation release, and then you also have the Japan disaster (which was of western design).
@@m16ty Nothing is 100% safe or immune to human error. But, good design can reduce the risks to an 'acceptable' level. Defining what is an acceptable risk is the most tricky subject, it gets totally mired by politics and ignorance of the subject matter. Good Western reactor design has kept the number of major accidents to a handful, each with fairly low casualty numbers. I can't do this subject justice in a few sentences but hopefully you get my point. Cheers Paul
@@pauln1557 the actual problem is even wider: Most people as is "all but a very few" can hold a competent and grown-up real conversation about risks, probabilities and acceptable failure rates. But politics, policies and investment decisions are voted on by common politicians and people who usually only have a concept of fear levels instead, which demonstrably is an unhelpful stand-in for assessing actual risks in the modern (post savanna roaming) human world.
@@GamingEntertainment12 You don't really have a choice when your entire nation is on a fault line and the best source of industrial quantities of reactor cooling water is the ocean
It's important for people to realize just how rare an earthquake and resulting tsunami of that size is. Having one in 2004 and then another in 2011 makes it seem like they are common, but historically they are a fluke. Hindsight is 20/20 and whatnot.
This shows that even the operators of such potentially dangerous plants are not thoroughly trained in the real world and do not know exactly what the consequences of their actions are. I suspect that only the shift supervisor is a trained nuclear physicist and even he was at a loss at the crucial moment. All the others are semi-skilled operators. That is why this technology is complete crap and must be shut down.
@@Medley3000 Soviet culture is to blame for this incident alongside pressure to complete the test (Or wait another year for a second chance to complete it), lack of safety and arrogance by superiors thinking they built an indestructible machine and lastly a culture in where workers below their superiors had absolute no say in the final decision. Nuclear power is the cleanest and efficient power as long as it’s done correctly so no this type of technology should not be abandoned.
@@swarmer5 Then the following also applies to the Three Mile Island incident: To blame for this incident is American culture, the pressure to complete the work, the lack of security and arrogance of superiors who think they've built an indestructible machine, and finally a culture where workers under their superiors had absolutely no say in the final decision.
Thank you for taking the time to go through this in full detail. Most videos attempt to explain it in 5 minutes and fail to discuss the actual physics of what caused it, leaving gaps in understanding. Very well done and as a young nuke engineer, I'm glad you dispelled the misconceptions of nuclear power at the end!
Yes, this is in the style of real Valerij Aleksejevic, despite I have no evidence for that. I think, He could say something similar in real world... He was used to think deeply about world around Him, was known for his high sense for responsibility to his loved wife, family, people, motherland and the world. His personality was not easy to understand and was slightly complicated. I know It well, therefore He is my soul mate, teacher, inspiration.... I know, It seems to be crazzy, but that is the way I feel... All the best from the Czech republic, stay safe and be healthy!
Absolutely. The only moment they "unstalled" the reactor was when it managed to burn off the xenon poisoning and increased its power tenfold right before the explosion. It wasn't safe to operate and should've followed its routine maintenance.
@@PeterMilanovski Not really. A stalled reactor doesn't mean it's going to explode. However, it does mean that restarting should be done very slowly and carefully, and the Chernobyl operators did the exact opposite.
@@Tuppoo94 that's exactly what I mean, had they got out and never came back, history would have never been made and Chernobyl would be like, who, what, where? Never heard of it! But then I guess that it just would have happened somewhere else! Well, at least not in Australia! But somewhere else, definitely! The amount of reactor failures throughout history is staggering but what comes to me as a shock is that after Fukashima, with the release of details on what and how it went wrong, France conducted an overhaul of their nuclear power plants! I have forgotten what year Fukashima happened but honestly! I would have thought that there's nothing left to understand about nuclear reactor technologies! I watched a video that went through step by step what was happening and what was done at the Fukashima plant, I can't believe that no one asked a single question (I'm referring to the people who worked there) regarding the operation procedure during an emergency situation! I don't know you and irrespective of your position on the use of nuclear energy but as for me! Had I been working there! Mate, I would be full of questions! I would want to know which manual control is where, actually go there and physically see it, that's where I would have seen the type of valves being used and that's where I would have been asking more questions like what would happen if we lost power? Can we still operate this valve? Are all the gauges going to work? It's not like you can sneak a peek into the reactor to find out what's going on in there LoL... But anyway that's just me, I have always been like that with everything! If I'm working at a place, I sleep it, I dream it, I eat it, I am it! I think that it goes to show how little we knew about nuclear reactor technologies during the Chernobyl event and that another explosion happened in the 2000's at Fukashima just scares me! What else and where else is next!
@@PeterMilanovski Nuclear accidents are serious, but nevertheless nuclear power is still by far the safest form of energy relative to the amount of electricity produced. There have been only 3 major accidents. Three Mile Island in 1979, with no fatalities or significant radiation releases, Chernobyl in 1986, which this video is about, and Fukushima in 2011. The massive earthquake and tsunami that caused the accident at Fukushima, killed over 15 000 people, while one cancer death has been attributed to radiation. The operators at Fukushima did pretty much everything according to established procedure. Unfortunately, the massive tsunami that struck the place had flooded the backup generators needed for cooling, so their efforts were in vain. The reactor itself also functioned as designed, and shut down safely when the earthquake happened. So it's not like the engineers were clueless about what to do when there are problems, and even if they had been, the system was designed to fail safe, and it did. In the end, the meltdowns were caused by Mother Nature.
I wish there was no such stigma against nuclear power. I think it's a great opportunity and people should be educated about it instead of being told it's spooky and dangerous.
@Jen farmer I'm not disputing that. But when literally every single news outlet, politician, and scientist is saying the opposite is true, it's a little hard to debate or change anyone's mind. Trying to do so just ends up with you being labeled a climate change denier, trump supporter, nazi, right wing nutjob etc.
Well, here in the grand USA, the regulation and funding required to make them safe will never fly, and there is the issue of where you put the leftovers (NIMBY). Also, no one even wants the reaction near them, so double-NIMBY.
BINARYGOD most modern design use up current nuclear waste/leftover fuel as fuel and can reduce the half-life of it to below 1000 years. I suggest reading up on molten salt reactors or thorium nuclear power :) we could never have to worry about electricity if we embraced nuclear a bit longer or at least until we improve solar, wind and water power enough for it to produce enough electricity for the entire nation without any pollution. Instead we shun nuclear and chose to rely more on coal power while we try to improve the renewable powers sources. It’s ironic that once upon a time some countries didn’t use any coal generated electricity at all because nuclear power destroyed the need for it, and now it’s back and it’s back strong because of the stigma against nuclear power :/
@@v44n7 I learned earlier on about the control rods being tipped with graphite, which by then I knew would aggravate the reaction as they went back into the reactor. But when I learned in this vid that those "tips" were _four-and-a-half-metres long_ (about 14') *and* would take 18 seconds to fully get out of the way so the boron could do its work, I winced.
v44n - Try pausing on that write up near the end of the video. It explains it again in text. However, I understand your confusion, and I've actually had to re-watch the video to try to explain it. I AM NOT A NUCLEAR PHYSICIST - HOPEFULLY SOMEONE COMES ALONG TO EXPLAIN IT BETTER TO BOTH OF US, BUT HERE GOES: So, I think the confusion is between the terms "moderator" and "absorber". A moderator is a material that makes neutrons bounce around more so that they're more likely to hit something, and less likely to just fly out of the reactor. If there isn't a thing that makes the neutrons bounce around then they won't hit anything that will split them, so they don't split, so they don't keep the reaction going, because the reaction only keeps going so long as it has neutrons to split. A absorber is a material that soaks up the neutrons, like a sponge. It takes a neutron and holds on to it so it doesn't go anywhere. If the neutron is held onto and absorbed then it can't hit anything *at all* so it's not gonna split. A moderator is good for making the reaction continue because it slows down more neutrons to increase the chances of splitting. An absorber is bad for the reaction because it reduces the neutrons. Water is both a moderator, (in that it makes neutrons bounce around more) and a absorber (in that it soaks up the neutrons.) So, when it's being used to moderate the reaction the water helps make more neutrons, and when it's being used to absorb it helps remove neutrons. But, water is *always* both a moderator *and* an absorber, even if you'd really like it to be just one or the other. In the case of the Chernobyl reactor they really wanted it to be an absorber and not a moderator, but it's both. This is where my understanding starts to break down, but I believe that in the reactor they needed the water to only be an absorber, and not a moderator at the bottom of the channels under the graphite. Now here comes the issue. If you look at the chart at the beginning of the video that Scott put up at 4:46 you can see that what water is made out of (2 Hydrogen-1's, and one Oxygen, H2O) the components of both of those elements are better at scattering/bouncing/moderating neutrons than the Carbon tips (which is what graphite is) at the bottom of the control rods. So, at the bottom of the channels where the water was being both a moderator and an absorber the water boiled away to a point where it wasn't being a good enough absorber, but it was still acting as a fairly good moderator. So, it was slowing down neutrons enough that the reaction was reacting, but because water is better at moderating than even the carbon tips are the reaction was slightly stronger at the bottom of the channels than at the top, despite the water (even as steam) absorbing some neutrons. Basically, if the water had stayed as the very dense liquid form it would have absorbed more neutrons, but at a lower density it scattered more neutrons. -Let's arbitrarily say that as the density of the water decreased due to becoming steam the absorbtion:moderation ratio went from 5:4 to 3:6, and it keeps increasing in favor of moderation rather than absorption. Meanwhile the graphite above it in the rod is like, 1:8.- [1. See my guesswork at the bottom] So, now the bottom is reacting faster than you would like it to, but it would have been fine because the water still absorbing *some* neutrons. Except that now as the rods are moved down all of a sudden all of the absorbtion that was there is gone, and the reaction at the bottom that's been teetering at slightly-more than the top, all of a sudden has *even more* neutrons that can hit other neutrons, and then those neutrons all hit a bunch of other neutrons at once, which start hitting even more neutrons inside the uranium rods regardless of both the moderators and the absorbers elsewhere in the reactor because there's enough neutrons to have a high-chance of hitting other uranium atoms all on their own and then all of a sudden you've got your mini nuclear reaction and everyone dies. The end. --------------------------------------------------- That's the best I can do. I realized trying to explain this that Scott did his absolute best trying to explain it, and that I do understand it a bit more, but there's some important bits in there that I sort of have to guess at. But, if I have to guess: ------------------------------------------------ 1. I think that *actually* somehow with the water density being low (because it's steam) the reaction at the bottom worked it's way up to being semi-self sustaining. Because I don't think just trading it off for more moderation would explain it, because if the carbon rods were worse moderators than the water then It wouldn't make sense to me that when they took the place of the steam the reactor would get worse. I think that there were enough neutrons coming off of the uranium at the bottom of the uranium rods where the steam was that they were splitting on the uranium like they would in a nuclear bomb, but not enough to make it go critical - the water was still a necessary moderator to slow enough neutrons down that the reaction would continue. But then, when the carbon moderator - which was a better moderator - moved down to the bottom of the channels all of those extra neutrons that were there, but not quite slow enough to split again, all of a sudden were made slow enough to hit something to split again. So, all of those neutrons split, and with each split energy was released in addition to another neutron, so then it all went kaplooey.
@@v44n7 still fuzzy in my head because so many different opinions on the graphite ends, I hear that they were overheated to the point they expanded just enough when the "kill switch" activated and all the graphite rods and block moderators rubbing the hot graphite was like a match creating spark and hydrogen bubbles split from the temperature exploded at once, the second explosion in theory was the mass going critical but it could have just been the overpressure, the criticality theory sounds terrifying though.
18 Seconds for full control rod insertion is just mind blowing! I work at a research reactor and twice a year we have to verify that all the control rods will fully insert in less than a second.
Guys. Of course it is a professional joke in russian/soviet nuclear power engineering society :) Scott had a correct/real version. But do you know what VVER reactor is? :)
brilliant explanation of the physics with the exception perhaps of the fast fission component. I worked at LNPP after the event upgrading the SKALA B system for flux calcs and we gathered lots of evidence that first explosion was steam shock as you say but second was hydrogen / oxygen recombination from superheated steam reaction with graphite. There were fuel ejections also but from primarily mechanical ejection. Also important was the control room 'human' factor of leadership, deference to Moscow etc.
and he did great job on that as well, it sounded like a physics professor after a several strong beers but nevertheless perfectly understandable! good job
Nuclear reactors are a bit like airplanes. They're by far the safest mode of travel, but once something happens it does so spectacularly, leading people to be scared of it.
The difference being, that with an airplane crash at most the airplane and whatever it crashes into is destroyed. With a nuclear reactor potentially an entire continent can be wiped out.
@@Jundl77 If the year is 1986 and your nuclear reactor is placed in the Union of Soviet Socialist lack-of-safety-procedures-Republic, then yeah. For everywhere else, not so much. That doesn't mean accidents can't happen due to outside interference, it just did in Japan after all. But all in all it's extremely safe compared to how much damage coal and gas is doing. Of course, even better would be to use sun, wind and hydro power, but there's an economic aspect to it all as well. Hydro can be fairly good for those countries where that is available, but Solar and wind is problematic in terms of actually earning money on it. Tho there are continuous breakthroughs in solar panel technology, so that one is getting better by the day.
@@Excludos Why does everyone forget Three Mile Island? It partially melted down in the not union of soviet socialist safety protocols USA 7 years prior and everyone forgets it happened. Fusion is the only viable alternative to Fission, and alot safer, but it's hard and may take another couple decades to work commercially.
The DGs at the PWR plant I worked operations performed an Operational Surveillance Test every 30 days. The DG had to reach speed and rated power (16MW) in seven seconds. At the time we used a highspeed 10 channel paper recorder that monitored certain values at startup. This produced about 30 ft of paper for a ten-second record.
Question at Radio Erevan: -Is it true that following Chernobyl nuclear accident,people's teeth began to fall? -Yes but only to those who didn't keep their mouth shut!
Do You know, comrade Nikolaj Maximovic graduatet from nuclear enginering via corespondence lectures? He was highly educated in the Machine enginering, but as the nuclear specialist was Greenhorn... 😔😲
This is probably the largest misconception out there which is skewing people’s perspective on the subject. Everyone I’ve spoken to believes that nuclear power is unsafe because it might blow up, and often cite Chernobyl. And when I try to explain that it failed because it was poorly designed, cut corners, and was improperly maintained, and that modern reactors are much safer to the extent that one almost never fails to human error or design flaws, they just look at me like I’m dumb and say something dismissive. Then they go on to say that solar panels or wind turbines are the safest and most sustainable source of energy to replace coal
I remember visiting a nuclear reactor while it was going through its 3 yearly reload cycles (so had access to the inner core) (my parents worked in the business) - Visited Fessenheim (a 920MW PWR design) and was assured that at all times they always had a Diesel turbine running continuously (and a weekly check for the backup) If the backup failed an orderly shutdown was instantly ordered by the plant "pilot". That was 30+ years ago. Another story I have about this nuclear plant is that during design and construction they had thousands of microphones installed along the pipes. Then they had a big room full of drawers containing headsets and some guy would come regularly and listen to all those pipes... If he heard anything unusual happened, he would order a shutdown.. then 1) they had to find the bolt or nut involved.. 2) figure out where it came from (probably not too hard each and every of these parts have serial numbers) and 3) figure why it came off in the first place - last occurrence they had the time involved a full 6 month inquiry and reactor shutdown !
@@ImperativeGames That and the fact that Germany is run differently. In post-war Germany, which is a Democracy, there are no quotas to fulfill any any cost (like in the USSR back when), and in that xenon pit the reactor would have been shut down and kept that way for a safe amount of time.
@@Widestone001 As I've lived in 90s in Russia, I still remember the late-USSR principle of "minimized responsibility". "Quotas to fulfill at any cost" ended in late 50s after the death of Stalin. 95% of various directors during 80s didn't care about anything except their career (and many didn't care much about it), not "building Communism" or "fear before horrible KGB" - it's all propaganda (Soviet and Western respectively). Drop that "Democracy" crap and see real people for what they are.
@@ImperativeGames @Christian Breitenstein Fessenheim, while it sounds very German is actually french lol. Aslo there has been some controversy because testing has shown that the Building isnt fully earthquake proof. (And the Region is known to have more geological activity than other regions) I think they are working on shuting it down atm, not quite sure.
That is THE BEST explanation of physics of that reactor in those conditions....even russian-language sources have no such a easy and yet informative explanation. Many thanks , Scott!!!
If you haven't yet, I wish you could explain a thorium reactor and why we don't have them and why we are stuck with light-water reactors. Love your channel!
@@HECKAKYH-ADEKBATEH Yeah, but the 'Chernobyl' mini-series was fucking excellent in getting the story across to a Western audience fed mostly on vague news reports at the time.
@@exidy-yt Yes but I hated how they portrait those with radiation poisoning as being infectious. It brings the integrity of the show into question imo.
@@pretzelstick320 I think you have misjudged something. Humans are superstitious and some will not sit on a chair where a cancer sufferer once sit, let alone someone with AIDS or advanced radiation poisoning! No where on the show was it ever said radiation poisoning was contagious in the disease way, but people often react that way anyway. Especially in a fairly backwards society like Soviet Ukraine where even most of the plant workers at Chernobyl knew almost nothing about radiation poisoning. (Also it IS a fact that a human suffering radiation sickness is radioactive themselves now and can be a source of contamination to other people, but you have to get within hugging distance for it to be a real danger.)
I've just started watching the HBO series and so far it's pretty decent! I'm eternally grateful that they didn't make the Brits put on fake Russian accents! Thanks for making an accessible explanation of the Chernobyl Disaster, I love how you just stuck to the facts and left politics out of it.
I've been in the industry for nearly five decades, and despite a few flaws, the HBO series is THE ONLY thing I have EVER seen on TV or in a movie about a nuclear plant that was even close to being accurate.
I'm russian and it was painful to look at those grotesque characters and fairy tales about the KGB and vodka. it's a good show, but just a show unfortunately with a bunch of errors and stereotypes.
Hey scott. could you make a video series about nuclear reactors? The series about nukes was awesome. I would really like to see a series about peaceful nuclear technology.
I second this request. How do the various types of commercial reactors work? Why did nuclear power become so unpopular years before Chernoyl? What are the advantages of the more recent designs? Is there a realistic chance of seeing thorium fueled commercial reactors in the near future?
They became unpopular because oil and coal power, the ones truly threatened by nuclear power, financed environmentalist groups to fearmonger about radiation.
@@WalkaCrookedLine In two words, Cost Effectiveness. Nuclear power isn't cheap, really isn't cheap. All Nuclear reactors need to be built to incredibly high safety standards, this means a lot of upfront costs, and I mean a LOT. Between 1975 and 1985, the American Utility industry spent $125 Billion on nuclear, thats billion with a B in 1970s money, nowadays adjusting for inflation? The mind boggles. And unlike Gas, Oil, Solar and Wind, there has been no drop in operating or construction costs. So it costs a lot to make, and then costs you even more money in maintenance. Also when it stops, because it turns out a nuclear reactor will not work forever, you then have to dispose of them. Which means even more money you're not getting back. I really hope that there is a way to break the nuclear cycle or build them a little cheaper, because the planet can't afford it not working.
In US, one major reason the nuclear power plants are closing is: natural gas is really cheap. And, natural gas is a fossil fuel. One way to approach this issue would be to price the externalities of using fossil fuels into the price of natural gas. Emission pricing/carbon tax, or any equivalent scheme.
The problem was also that the fuel was quite burned up during the test, as the reactor was meant to be shut down for maintenance, so they did not have any fresh fuel in it (the RBMK can be refuelled while running). So there was a small reactivity left, which was also a big factor influencing the reactor control. At the Leningrad power plant, which has the same RBMK reactors, they ran a similar test without the reactor exploding on November 30 ,1975. They kept only 6 to 8 control rods in the core, meaning the "minimum admissible reactivity margin" was very low. The conditions were practically identical to Chernobyl. With two main differences. 1. The fuel was not burned up - it was practically fresh, as the test was being run on a reactor after it was shut down for maintenance, not before shutting down for maintenance (only 3.6 GWd/t vs. 14 GWd/t in Chernobyl) and 2. They did not press the AZ-5 scram when running the test. Still the reactor was in a very unstable configuration when they made the test. The "end effect" of the control rods would not show its full potential, as not all of them were inserted at once into the core at once (AZ-5), as in Chernobyl. So the reaction did not have enough time to run away. They observed that when pushing the control rods in, the energy output rised for a short period of time (some seconds) instead of declining, but it did not result in the reactore becoming promplty critical on fast neutrons (which is what happened in Chernobyl by some soruces). Since 1975, the temporary "end effect" of the control and emergency rods was known, but this was not seen as a safety issue back then. This was a huge mistake. More info can be found in the book by N.A.Dolležal and I.J.Jemeľjanov, called "Kanaľnyj jadernyj energetičeskyj reaktor" (1980).
He said in the video that when the control rods were pushed in it pushed water out and that caused the explosion? He explained that part very poorly. Why would it cause a short rise and then stabilization after?
@@benb9151 It wasn't that they pushed the water out that caused the explosion, it was that they replaced the water (which was only moderately-enhancing the reaction) with Graphite (which dramatically enhanced the reaction).... in the part of the reactor where the reaction was already too-enhanced (the core). Think of it like trying to get a fire truck to a road fire, but to get the fire truck there, you have to push a fuel-tanker-truck into the flames first, and then you can basically visualize the problem with pushing all the graphite into the core at once while trying to insert the control rods.
Because the rods had graphite ends, which mean that when fully retracted, they actually boosted the neutron moderation. The problem is that the graphite part was shorter than the core. When inserting, it first displaced the water from the channels, which lead to an incerase in neutron moderation in the lower part of the core. Normally this is not a problem, because the safety systems and opearting instructions are designed properly. It is just by switching off all safety systems and disobeying any instructions that you can get the reactor into a very unstable state of operation, where a small change in its configuration can have dramatic consequences.
You are all wrong! The only reason this happened was there was not enough hard bass playing in the reactor chamber 🙄 and if they would have just covered the core in several layers of the finest adidas none of the radiation would have escaped 😞
Scott is an international treasure. As usual, very complex stuff explained clearly, concisely and with just the right amount of detail to be insteresting to almost any audience. Reminds of Feynman.
19:17 THIS IS STILL UNSOLVED THE 2ND EXPLOSION: It cant be a hydrogen explosion, as the recovered fuel rods had NO ZrO on them, so it wasn't a hydrogen explosion from dissociation of H2O.. So was it a fissle? No there was no evidence of that either. So why did it explode 2 seconds later?
When I attended US Naval Nuclear Power School in 1980, we covered the hazards of graphite moderated reactors and I distinctly remember being taught that such designs were susceptible to "runaway excursions" which is we we operated PWRs. Ergo, there were experts who believed in such a vulnerability.
One of the principal reasons the west avoided graphite moderated reactors was the near disaster the Brits had at Windscale in (IIRC) the late 50s, a disaster avoided only because of British professionalism. Everyone knew the dangers from graphite were very real, but reactors of that type were cheap and the USSR was having money problems.
In the book Midnight in Chernobyl, the Soviets openly mocked the West's use of water based reactors. To them, graphite, even in huge reactors, was the superior design.
@@302Diane Graphite moderated reactors "avoided" in the west obviously doesn't include virtually all the power producing reactors built in the UK. There were 11 Magnox stations containing 2+ reactors each and 7 AGR stations with 2+ reactors each. Many of these are now shut down but some still operate.
@@chriswilliams1096 True, Magnox and AGR are graphite moderated. However they are gas cooled, so they do not have the risk of a runaway reaction due to coolant boiling. It would be better to specify that "graphite moderated water cooled" reactors have significant additional risk of a runaway reaction. (Although even then there were several such reactors in the west used for plutonium production.)
@@nathancampbell06 I mean looking at construction costs versus power output, the RBMK was an excellent design. Its just the costs were that low because too many concessions had been made when it came to safety.
Fun(?) history fact: That 10 hour delay was in fact caused by the peculiarities of Soviet Economics. You may remember the show briefly mentioned that they were requested to hold due to factories having to run overtime at the end of the month, the accident did take place on the 26th of April. Well this overtime was a side effect of the quota system used by the USSR's planned economy, i.e each factory has a set number of goods it has to produce before the month is out, if they don't they can be punished in by having the KGB set on them, or even worse, wages being cut. Though the usual response was typically short sighted, the quota for the next month would be raised. So this let to a situation whereby factory output was at its highest in the first and last weeks of the month, as workers rushed to meet quota and get paid on time. This is why Soviet goods had so many...erm 'quality' issues, there was a good chance it had just been chucked out the door at the last minute. Plus workers infrequently staged passive protests by just working slowly and dragging everything out. So when that delay happened it was because the factories had to make up the slack period of the last two weeks and quota would be coming due that Wednesday. So there you have it, another little piece of the puzzle.
> can be punished in by having the KGB set on them, or even worse LOL, ROFL! Things you folks believe in are... anyway. The directors of plants that fail to meet the plan goals were losing the "13th salary" - i.e. the bonus. If they do it regularly, they'd be fired from the director's chair. That's all. No KGB. No "worse" (there is something worse than KGB in your delusional world view? Tell me what it is.). Your massmedia-induced fantasies aside, yes, the end of month typically had a higher output - and hence higher power demands.
@@AverageJoe8686 LOL! Dude. The worst thing about socialism was that you couldn't fokking FIRE a drunkurd from a plant. Because you see - the Constitution guaranteed the Right for Work. And the drunkurd was waltzed right into the Party representation and was restored the next day, and the manager got to hear a lection how it is his responsibility to support _every_ worker. That was really a morale killer for all honest workers. And a lazy worker could tell the director to go and eff himself, and the director couldn't do anything as long as there was no physical violence. Gulag, my ass. :-/ I wish....
@@DiThi Probably true. I'm describing the specific version of USSR socialism and the alleged "sending of workers to Gulag" - which is hilariously false.
So basically : Water - reduce reaction Xenon-135 - reduce reaction Boron - reduce reaction Graphite - Increase reaction Steam - increase reaction there has to be a balance of above elements. First the balance was in favour of reducing elements resulting in significant reduction of power then the operators tried to increase power but it increased too much. They tried to stop the reactor with AZ5 button which was supposed to insert boron rods but these boron rods had graphite tips resulting in explosion.
No, not graphite tips. 4.5 meter long displacers of graphite that functioned to accelerate the reaction and they are never withdrawn from the reactor. When fully withdrawn the graphite is centered in the 7 m tall reactor.
Thanks, that explained the mechanics behind the disaster as best as I have seen, I only have one year of Uni Physics under my beltfrom 30 years ago , but alot of the concepts came back easily from your clear explanations.
I love how men say things are impossible. Titanic people: "This ship can't sink - Why? It's DESIGNED not to. Iceberg: "Hold my beer." Chernobyl ppl: This reactor cannot explode! It's all in the DESIGN. Proceed to ignore all the failsafes and control mechanisms of the DESIGN : Oh shit it exploded. As long as people made it - shit is gonna break and go wrong.
Well, we are all living in denial everyday to some extent or we can't function. You need to take context into consideration and how TV shows need to dramatize to make the narrative flows.
I was an infantry soldier in the US Army from 75 to 79 and went to college on the US GI Bill. I had a hard time with Math and English at first as most students do. When I got to the end of my second year I had to take Physics. When the Instructor asked the question, "If you shot a projectile out of a cannon at this velocity and the cannon was at this angle; how far would the projectile go?" Without thinking I blurted out aloud, "That is the 4.2 Mortar Table calculations." No one in the room even understood what I was saying. However, it was the first time in 2 plus years of math that everything came together. At that point, the instruction asked me to come up and give a short class on the Four Duce Mortar and how we in the Army calculate and shoot mortars accurately. I totally loved Physics. I look back and wish I had changed my degree from Biology to Physics. Physics to me even today 40 years later opened the entire world to me. So thank you for your channel. I spent from 75 to 2003 in the Army as an enlisted Infantry Sergeant to an Airborne Infantry field grade officer and loved my job. However, looking back I would have really enjoyed life in Physics. Our instructor in physics was so great to help open the entire world and how it works. You are doing the same for another generation. Allen Shisler, President Access International Solutions and can be found on LinkedIn and Facebook.
Thanks so much for this clear and understandable explanation! I also really hope that shows like Chernobyl (and to some extent also Dark) don't serve as a deterrent against nuclear power. If anything, the deep dive into why it all went wrong should prove exactly why nuclear power is actually incredibly safe as long as you're not being stupid around it. It should show how much had to go wrong for this to happen, and how unlikely such an event is. Besides, it's been over 35 years, do people really expect that we've learned nothing about nuclear power in 35 years? I'd like to remind them that smartphones didn't exist until the 2000's and that the internet didn't even exist for regular people when Chernobyl exploded. And now we can charge our phones wirelessly, we've got electric cars, we've got machines in our pockets that are hundreds of thousands times more powerful than the rocket used to land people on the moon... so using Chernobyl as an argument against nuclear power just makes no sense in any possible regard. It's much more useful to argue financial reasons, whether they can be built quickly enough, how long it takes to earn back the construction cost, etc. etc.
I think it's navjan13's explanation that summarizes this complex video for me: Water - reduce reaction Xenon-135 - reduce reaction Boron - reduce reaction Graphite - Increase reaction Steam - increase reaction But this video has made me more terrified of nuclear power than I was before because this was, in essence, a coolant flow failure that was actually enhanced by the scram emergency shutdown. You talk about charging our phones wirelessly. How did the Samsung Galaxy Note 7 arrive in the hands of customers with such an unstable battery? How did the Boeing 747 MAX make it into the hands of pilots with a safety-critical MCAS system that took its readings from only one sensor? There will be stupid people.
Different things advance at different rates. The reactors that the West uses are much safer than the Soviet RBMK reactors, but you can hardly claim that they have advanced in the same way as consumer electronic devices when their development has been largely frozen (in the developed world, at least) for several decades. My actual problem with nuclear powerplants is that they become too big to fail projects for both the utility companies, local politicians, and the regulatory bodies. One needs to only needs to look at the Davis-Besse Nuclear powerplant (pretty much a clownshow of near misses) to see that nobody wants to kill the golden goose... In fact, nobody wanted to stop the golden goose from laying eggs long enough to do preventative maintenance to stop a football sized hole from corroding 6 inches into the golden goose's reactor head (3/8" from a 2002 version of 3 mile Island. Yay!) or shut down the powerplant because the people operating it were untrustworthy. Then two decades later, the golden goose wasn't looking so profitable so its owners decided to bribe the State legislature of Ohio to give the Golden Goose a $150 million/year subsidy.
Hey Scott - long time fan. Thank you for this - I've read multiple explanations of the disaster going into Xenon poisoning, the "graphite tipped" control rods, and the positive void coefficient, and yours is perhaps the easiest to grasp out of what I've encountered thus far. Especially the explanation of WHY the control rods had graphite present (I've always scratched my head at that, wondering why you would put a neutron moderator that could conceivably accelerate the reaction at the tip of the control rod - didn't occur to me that it's more accurate to say that they were at the bottom of the rod and already in the reactor, just not the full length of the control rod channel).
*makes reactor at home* Global notice feed: "Man made nuclear reator at home, but lost control of it, exploding his house and injuring the entire neighborhood, leaving it uninhabitable for the next millennium"
the "elephant foot" mass at the bottom of the structure was so radioactive back in 1986 that a fatal dose of radiation was reached in about 3 minutes. as of 2020 (34 years later), a fatal dose takes about 3 hours.
I’ve always wondered why we experience time at the rate we do: Time is ofc relative, but we experience a second as a second (shocking I know), but imagine how our lives/evolution and world would be if we experienced time at a faster or slower rate. Like in what we would call slow motion, would it be relatively tedious? Or would we be on here now imagining if we experienced time faster (our “speed”) and how confusing and crazy it would seem. Ofc we’d evolve and adapt to it (as we have now) but a mayfly only lives a day, does it see us in slow motion? If a tree could perceive would we seem to be in time lapse?
@@Duros360 I don't quote concrete science, but I would say that we are as fast as we need to be. A mosquito react faster than us because all the neuron inside them was built for a single purpose of dodging and sucking blood. For a much bigger animals like whales and elephant, they're slower because law of physics dictate that moving that amount of mass will meet that amount of resistance, even if the electrical pulse in their brain moves at the same speed as the mosquito. So the only way to 'speed it' is to have different impulses happening at the same time, and I think this is where the concept 'human time' came to be. We were at a form that we're slow enough to adjust with the day-night cycle of the universe, and fast enough that we can react to environmental danger big and small. And i think that in this form, we realize there are still excess spaces that we can put more neurons into our brains, without going over the optimized physical limit of our mass to function in nature. And with those extra brain cells, we can analyze the environment in a way that would further increase our survivability. And in that evolution of intelligence, we learn to 'perceive' time. Because time IS relative, not just physical, but also mentally. We feel time flies when we're having fun, and time stagnate when we have to wait for someone. Our perception of time is slower when we're awake, because we have to take in and process our sensory input and mental reasoning all at the same time; while we can ignore all that in a dream and let the neurons flow freely, randomly, which make our perception of time faster. Meanwhile, our internal system that dictate the speed of our heart, our cardiac rhythm, our food energy process, we can't perceive it. So maybe, it's only true intelligent that can perceive time. For every other living things, time is simply not perceivable. Like only our phones and computers can see the wifi signal, our brain reasoning is the sensor that help us see time. Since there are no other race with human level of intelligence, we can't be sure if time perception can be differently. But personally I believe that once they can perceive time, they would become similar to us. A creature that can perceive time fast or slow to adapt to the situation. Like a country person moving to live in a city.
@@Duros360 It was quite an essay, but it's because your question was what I once think really hard about. In a natural world, we dont have these natural radiation that kills us immediately when a thing goes wrong. We don't have bullet that can end us in a flash. So we simply hasn't evolved our time perception to handle these kinds of manmade danger. Yet, I do think our perception of time is accelerating. Kids these days have ADHD from interacting early with the internet. It results from the fact that this speed doesn't correspond to real life, they're used to handle too much information in a short time that when they don't have anything to process, they become absent-minded and hyperactive. It's not a bad thing, but in the future, our society lifestyle will definitely change to account for this. Time perception is as important, if not also the same thing, as our reason to be alive.
In fact, in the first minutes Dyatvlov couldn't believe what had happened, but then he heroically took part in the aftermath of the catostroph. I think to blacken a person that much is simply unfair. Just wanted to share my thoughts.
@@vgeniirshf8913 One of my problems with the show is the disservice they do to all key people involved in Chernobyl. They come across as wilfully ignorant or just cartoonishly evil
@@vgeniirshf8913 Yeah, I was telling myself the whole time that he couldn't have been such an incompetent arogant ass as portrayed in the series, but then, most people probably wouldn't find the show as amusing, if all characters traits had not been exaggerated, so that it was easier to build sympathy or antipathy towards them.
Great presentation, thou to little stress on the fact that reactor design (it's large diameter) and fission cycles were optimized for producing weapon grade plutonium 238. Other Pu isotopes are useless (for nuclear weapon). There's no way to enrich plutonium, so you must get the "right" isotope from the reaction itself. RMBK was a plutonium machine pretending to be civilian power reactor.
He's Scottish, and it's notable that Russian parts in Hollywood movies are often taken by Scottish actors, google Robbie Coltrane, David McCallum, and many Scottish luvvie stalwarts if you don't believe, we do accents with aplomb.
~17:00-18:00 is not quite correct. When they attempted to emergency reinsert the rods, there was so much steam forming that it introduce an unplanned pressure on the graffite rods. More pressure than the rods could handle, this actually broke some of the rods. The pieces of the graffite rods got stuck in the channels, preventing farther insertion of some of the control rods. The graffite which was stuck continued to enhance the reaction. The reaction was producing more steam, until the pressure became so high, the whole thing blew up. Bringing the reactor to an unsafe state and then carelessly proceeding to running a dangerous test has become one of the worst human errors in human history.
When in reality only 28 people died from acute radiation syndrome in Chernobyl which is believe it or not a fairly low number considering how much fear mongering this event had. Purely statistically speaking there are more deaths occurring in wind farm maintenance than nuclear reactors, including Chernobyl and Fukushima. So yeah, people are being hysterical and should stop spreading misinformation.
@bobwatters As much as I support the USSR and its ideology, I disagree with the man above because he has completely disregarded the causes of cancer regarding the radiation from the accident which was up to 30,000
I feel if I don't reply you will think that I have no explanation but if I explain you might argue against the points with no evidence. So before I explain, I'll like to ask, will you allow me to explain without argument?
I was US Navy nuclear trained on an aircraft carrier. We use pressurized water reactors that have a negative temperature coefficient of reactivity which basically means that if a runaway fission reaction starts then as the water heats up it will actually slow the reaction down. Inherent safety built in there (on top on numerous other ways) and is why the US Navy hasn't had a nuclear accident in over 50 years since we learned how to be safe despite operating hundreds of reactors in that time. This reactor had a positive temperature coefficient of reactivity which is a huge safety risk but leave it to the Ruskies to take that risk. Pretty crazy to be honest.
Hello Scott. Retired nuclear engineer here. I was on the DOE's emergency response team, bags packed and ready to fly to Chernobyl but as you know, in the end Detente' had not progressed enough for them to trust and accept us. Anyway, This is probably the best explanation of what happened I've seen or read. First a small thing. In the US, the xenon buildup is referred to as the "Xenon well". You should witness the scramble in a power plant if someone accidentally trips the reactor by, for example, valving in a water level transmitter in the wrong sequence. EVERYBODY is running, trying to get through the restart procedure before the reactor sinks too far into the well.
There is one critical part that you left out which is probably the major reason the transient was so large. In each control rod, below the bottom of the boron carbide is about a foot long void, filled with air or whatever they fill the control rod with. When this void passed by a section of fuel, there was no moderation and no neutron absorption which let the fuel go prompt critical. This prompt critical reaction continued until disassembly started. At the very beginning of the prompt critical reaction, the rod channel was distorted enough to freeze the rod in place.
This was NOT a small nuclear explosion. This was easily determined by looking at the fission product profile from air samples. A nuclear device profile is much different than a prompt critical excursion. This is because the device begins disassembly so rapidly that the first generation fission products are not in the neutron field long enough to either be burned or transmuted to another isotope. A prompt critical excursion, by contrast, lasts relatively forever. Some first generation fission products are burned and others transmuted to other isotopes.
Eyewitness testimonies I've read from operators who survived stated that the first explosion was large enough to rattle the fuel insertion shield plugs and shake some out but that the big one happened maybe a minute or two later. The delay was long enough for operators to run to an observation deck and see the shield plugs rattling. That's consistent with a buildup of H2/O2 and then detonation.
This difference in air samples over Europe is the first indication that there had been a reactor accident and not the Sovs having conducted a very small above-ground nuclear device test.
My guess, based both on what I know and from what I've seen of small samples of graphite smuggled back from Chernobyl is that this was a hydrogen-oxygen explosion. Of course, like everyone else, mine is only a guess.
There are two catalogs on the net. One is the catalog of the isotopes using an NaI detector and the other is the same but using a GeLi detector. On the last page of the GeLi catalog is a spectrum of fission products of an atmospheric explosion taken seconds after an atmospheric test. It's so dense it looks like white noise on a spectrum analyzer.
John
Thank you for this, I love comments that tell me more about the story, it’s all a learning experience for me.
What do you make of the people that reported a bright blue flash? Was this a visual confirmation of the prompt criticality?
@@merrittw83 Ionisation is the process by which an atom or molecule is excited to a new energy level by acquiring or losing electrons. That was the blue light that they saw
@@merrittw83 Dr de Geer wrote in the study: “It is well known that criticality accidents emit a blue flash, or rather glow, which derives from fluorescence of excited oxygen and nitrogen atoms in the air
@@merrittw83 A strong enough pulse of radiation will cause the Cherenkov effect in the vitreous humor inside your eyes. That's the blue flash they mean, and it's a death sentence.
I’d say the reactor worked better than expected. It completed the 5 year heat generation plan in under 10 minutes!
Say what you like about the Soviets, but they sure know how to fill a quota.
Got some real Stakhanovites up in here
My kind of jokes : the one only educated people can enjoy. Thank you guys.
I remember a joke from one of the plant technicians at the New containment unit... "You have nothing to worry about, Soviet radiation is the best radiation!"
When it's either fulfilling your assignment it the gulag, things get efficient
I think you are mistaken comrade. RBMK reactors don’t explode.
Could you imagine spreading disinformation at a time like this?
He's in shock
But seriously, funny comment 🤪, and as you haven’t had many replies, I’m going to squeeze this in, which would otherwise be lost in the wash: Fukushima was 40 years old Technology with a clear record, and got simultaneously everything that mother nature could chuck at it: earthquake magnitude 7 and a subsequent massive Tsunami which apart from destroying the town, swamped The reactor building, knocking out the diesel powered water pumps. But it still failed. There are three causes of accidents: men women and children. One way or another.
@@Johnny-sj9sj Fukushima had evrything right except some minor details that made everything went kablooey. It had no hydrogen recuperation system that was mandatory, but wasn't implemented, and diesel generators weren't build up the hill, where Tsunami didn't reached. And third, Fukushima reactors too had a design flaw, they would stop the coolant go into the reactor after the emergency without personnel knowing about it. Thus the reactors had a meltdown.
Mighty Soviet engineering never fails
I was 7 years old when the explosion happened. We were a group of kids playing outside, having fun, suddenly our parents came out and started screaming at us to come inside quickly. I got a pill that I had to swallow and I asked why. My mother said "it's for something in the air".
I was like wtf is in the air - she said nevermind that. When I saw this series I got shivers down my spine. I remeber reading about it in my teens but never put much thought about it. Really weird feeling. But later on, in 1989, the revolution started and we were hearing bullets hitting the trees around us while playing so a bit of radiation was nothing. What a childhood...
Was it Iodine you were been given?
I lived near a nuclear power plant as a kid (still do actually) and one day in elementary school we had an unannounced nuclear preparedness drill. Years later, I got a job at the plant and found out that there had actually been a fuel channel breach that resulted in a loss of coolant accident.
@@arraikcruor6407 must have been, yh - iodine was given to protect the thyroid (I'm pretty sure)
You were born in/lived in USSR at the time? We are close to the same age but I don’t really remember this event. I didn’t watch much news then.
@@char1ie965 He is most probably from Romania. Only there was violent revolution in 1989 and it is just a few hundreds of kilometers from Chernobyl.
All this fuss over 3.6 Roentgen from the feed water?
I've been told it's the equivalent of a chest X-ray
Why, that's barely as much as a chest X-ray, silly you -_-
Free check-ups for everyone!
[Insert Username Here] you’re delusional, get to the infirmary
@@insertusernamehere9023 You are saying dangerous things. Very dangerous things.
Best comment so far.
It is so tragically ironic that the reactor had been running under high load flawlessly, but failed when they tried to prove it's safety.
Take away in that is that when we run things as they are intended to be run, usually nothing bad happens.
@Peter S they needed the test in case the power went out and something regarding turbine I guess
@@Ravi-xf8dw The whole point of the test was to ensure the safety shutdown mechanisms worked correctly. The reason Chernobyl exploded was because of communist quotas requiring that they keep the reactor on and at maximum power for the majority of the day before the test so that industrial sectors could have enough power to meet their end of the month quotas. Had the reactor had time to cool down before running the test it’s possible it wouldn’t of exploded.
@@spacekiller6856 yes
@@spacekiller6856 The number of things they didn't do that they were supposed to, and did do that they weren't supposed to, was the issue. They did the safety test without meeting the required initial conditions, but they also disabled other safety features without any procedure telling them to do so. There are serious design issues with RMBK, but to say that it failed is unfair. Modern designs are also unsafe when operated with such disregard
This was a classic Soviet shortcut. Western reactors use fuels enriched to 3 to 5% U235. This is very expensive and time consuming. In fact, getting to 5% U235 is a significant portion of the effort required to reach all the way to the 80 to 90% of weapons grade (kind of the way LEO is most of the way to anywhere in the solar system). RBMK's used around 2% enrichment. While this sounds like small difference, it is not. It meant much cheaper, faster fuel production and an increase in the enrichment industrial capacity available for weapons production.
Unfortunately, is also meant a relatively sluggish fuel. So, the RMBKs use fixed channels literally made from a reaction accelerating (neutron moderating) material: graphite. This "juices" the reactor in order to make the low quality fuel work. This is the primary driver underlying the positive void coefficient (unstable) nature of the RBMK.
The Soviets also chose this design, so that it would be common with those dedicated entirely to weapons grade plutonium production. Plutonium slowly builds up as a byproduct in fission reactors and is harvested from fuel rods. The RBMK has the unique ability of replacing its fuel rods quickly without shutting down the reactor, making plutonium production more efficient.
(And yes, Scott... this is actually me: @torybruno. Great job on the video!)
Not quite. RBMKs had a POSITIVE void coefficient - hence the runaway power excursion once the core began to overheat. More heat = more voids = more moderated neutrons = more fissions = more power = more heat etc, etc, etc. The instability of the core having so few/little control rods inserted, plus the graphite tips on the rods, were additional errors of operation/design/operator training & knowledge. Chernobyl rocketed from less than 15% power to an estimated 10000% power in well under 2 seconds. That equals BANG! I wonder if they ever completed any maximum design accident analysis or modelling? No secondary containment? Madness!
Underlying the fundamental design flaw of the +ve void coefficient, etc, may have been many other aspects of the USSR economy and 'limited' industrial/technical capabilities at the time. These combined to feed into the USSR's urgent need for more and more cheap power as quickly as possible. To build up their power generation industry quickly, however, meant too many corners were cut & too much operational secrecy also led to the point that the operators had no idea what dangers they were facing/creating for themselves and others... A sad, potentially avoidable, day for many people.
@@louisdrouard9211 Great comment and yes, you're right. The French built 10 units of the UNGG reactor design. There were some significant design differences, compared with the RBMKs, which made them much safer to operate. One of the other big advantages of the UNGG was its use of a huge concrete containment structure. That would have prevented the huge radiation release of Chernobyl.
@@Jabbatic There were two types of reactors in USSR - RMBK's and VVER's (PWR class). The second one has a concrete containment around.
The RMBK designers thought about containment but it was just impossible to build any concrete containment over reactor. Its not only the reactor itself but also auto crane that can hold inside 7m fuel pipes with uranium. So you can change the pipes with uranium and keep the reactor running.
Every state in USSR had a choice to build one of the reactor types so Ukraine took RMBK 1000.
@@dmitrigutorin944 Yes, I knew that and you are spot on. Your comment about the size of the containment building was very important and was one of the limiting cost/time/material factors for selecting one design over the other. The VVER design is inherently safer, but the RBMK design gave access to electricity generation from large, 'simple' plants that could be constructed in large numbers within a reasonable timescale, at an acceptable cost. Crucially, the RBMK design minimised the personnel training/operations requirements and also the technical challenges that had to be met by the major industries manufacturing the largest and more critical systems & components. The RBMK could be refuelled whilst still operating due to having no containment building - thereby enabling the USSR to recover plutonium from the spent fuel much sooner than with the VVER design.
The VVER design 'family' has seen considerable development over many years and is now an impressive design in its Gen III+ configuration. I look forward to seeing how far the VVER design can go and how it shall measure against other designs in the future. My great hope is to see the first operating fusion power reactor. Still 35 to 40 more years to wait? ;-)
Thank you sir! Very well stated!
My favorite thing about the series is that it explained why the test was gone ahead with despite all the negative conditions. It was necessary if they were to sign off on the reactor by May Day, and if that happened several higher ups would get promotions and move up to nicer offices.
The reason was that every aspect of soviet industry was micro-managed from Moscow. The on-site operators and engineers didn't want to do the test with the reactor going into a Xenon well but Moscow ordered it anyway.
For example, the Chief Engineer of the unit wrote a book. Weeding through the massive ass-covering and buck-passing in just about any soviet document regarding Chernobyl, he described how 2 days after the explosion, he was receiving orders from Moscow to continue pumping emergency cooling water into a reactor that no longer existed.
I'm a former nuclear operator, and your explanation (while somewhat simplified), is one of the better ones I've seen on UA-cam. Well done, sir.
Maybe you can explain to me why the bottom was the hotter part, when the top is where the water would have turned into steam first.
@@cptnoremac Because the Graphite rods ( an accelerant) were in the middle portion of the fissile material, the visual is like the Price is Right Range Finder. Fuel in that range, adjacent to the graphite, becomes way more active. As they moved down to exit, the bottom of the rods began generating more energy and more heat. So, yes, of course the steam leaves at the top, but it is boiling - and generating voids - lower and lower in the water as the graphite moves down.
@@briancorrigan5350 Before any movement, the middle part, where the graphite is, would be the hottest part, right? So why would moving the rods down and displacing the water make the bottom the hottest part? Up until then, it had water helping to cool it. It should never be able to catch up with the middle as long as both have the same moderator. But everyone portrays it like the very bottom is the part that got too hot first. Seems to me the AZ-5 button couldn't have made things worse.
@@cptnoremac I understand the rods where inserted very fast and the graphite tips broke, getting stuck essentially in the middle of the channel, increasing the moderation and the number of slow neutrons, increasing the reaction. A positive feedback loop.
@@amramjose Nah, the graphite was already in the middle of the reactor before the button was pressed. What everyone says is the area where the water was displaced by the graphite at the bottom got too hot and that started the chain reaction of problems.
Me: [has seen every nuclear documentary he can in the last 15 years, half of which on chernobyl]
Scott: Wanna watch yet another explanation on chernobyl?
Me: Yes.
and this explanation is BETTER than 90% of them!
Same.
Yep.
Scott: Most of the documentaries on the subject are terrible and the show does a far better job at explaining what had happened.
You: Oh...
What’s your favorite one? (Not counting this one of course)
Basically, they swerved left, then they swerved right trying to compensate, then they swerved left again trying to compensate for that, then they flew right off the road.
Effectively it was a bit of a tank slapper
Crowd control in effect 😂
The RMBK reactor design is instable so it will increase power when control rods are taken out. Compared to a car that oversteer, when you loose control it will spin off. More modern designs are stable so if somethings goes wrong you take control rods out of the core. Compared to a car that understeer and you just brake harder.
Yes, but when they finally hit the brakes the wheels locked up and the car completely lost control and hit a tree, after which it blew up and started a massive radioactive forest fire.
I want to like your comment, but it has 420 likes.
You get it right?
I was surprised at how well the series was done. I had learned a lot about Chernobyl since 1986, but the graphite tips on the control rods threw me for a loop. I was a manufacturing engineer for some very special control rods at one point in my career and the tips were not made of graphite or any other moderator. If you have to SCRAM the reactor the first thing the fuel sees should NOT be moderator.
When they made the statement in the series about it being cheaper to make them that way, they didn't mean the rods, they actually meant the reactor itself. By making the rods dual material, they were also dual purpose, and because of that only needed one operating mechanism, not a separate channel and operating mechanism for each.
Under normal circumstances, it would never have been a problem, but sadly these weren't normal conditions, and thus the mess that occured.
@@kleetus92 Thanks for that. I haven't had any experience with graphite moderated reactos, but that makes sense.
It's sort of a design cop-out, where the control gradient is made larger by attaching moderators to the control rods. I think to avoid such a scenario, it would make more sense for the graphite ends of the rods to be flush with the bottom of the reactor at full extension, so that there is only a decrease in power when the boron is reinserted.
That being said, you're entirely 100% correct! There should simply be a different system for the control rods and moderator rods. Makes the control of the reactor much safer, as removing moderator and inserting absorbers at the same time will arrest the reaction much more safely and quickly!
@@keatoncampbell820 The reason they weren't "flush" was to allow for neutron flux throughout the reactor, avoiding hotspots and uneven reaction rates in different parts of the reactor. Vlogbrothers video explains this well. Possible that gradually introducing the rods to stagger the graphite introduction near the bottom would have averted disaster, but how were they to know.
@@ComeWhatThey I'm not a nuclear physicist, to be sure, no matter how interested in it I am or however much math I'm doing.
I am an engineer though and first principles design is fairly important for something like a nuclear reactor. Generally, the function of emergency aborts, E-Stops, and SCRAM functions is to completely and safely arrest reactivity and as immediately as possible make the core inert. That being said, most reactors are designed in such a way that it is physically impossible for E-Stops to increase reactivity in any way. It may and often does sacrifice performance, efficiency, and thermal loading to limit the geometries of the core elements to those which function but do not increase reactivity in any state, configuration, or environment.
Elegant design would accomplish this through geometry of the components of the core, though operation logistics is also sufficient to achieve safe E-Stops, but that would mean including the possibility of failure, which is entirely unacceptable for something with so much value and so much risk.
Former nuclear control systems engineer here -- this is an accurate explanation of what went wrong at Chernobyl. Scott, I am legit impressed how you're able to totally switch fields and still be technically competent. You're like a Scottish Neil deGrasse Tyson!
The tldr in case the video wasn't clear enough: in certain situations, a scram (emergency drop of the control rods to kill the reaction) actually boosted reactivity (i.e. neutron multiplication rate) instead of killing it. Which turned the RBMK "emergency shutdown" system into an "initiate steam explosion" system. It was just 100% pure engineering failure.
Separately, I love those USSR corrective actions after the disaster: "Prevention of the emergency safety systems from being bypassed while the reactor is operating." Just... profound.
This is the best explanation of the Chernobyl engineering mistakes on UA-cam. Some of the explanations on UA-cam are so dumbed down they’re offensive.
There were no engineering (design) mistakes. Not by that time's standards, anyway.
The operations put a dangerous engine way beyond its limits.
Of course today that design is not considered safe. People turned out to be more dummies than anyone could expect.
@@vladimirdyuzhev Didn't the Soviet Union know that the RBMK reactor's had a design flaw in the form of the control rods? If I remember correctly there was a similar (though much smaller) accident involving the control rods at another nuclear plant well before Chernobyl ever happened. They just didn't tell their plant opperator about it in typical Soviet Fashion.
@@madcourier6217 They knew. It was not considered a design flaw. Not a big design flaw, anyway.
@@madcourier6217 > They just didn't tell their plant opperator about it in typical Soviet Fashion.
AFAIR, no, that information was available. Not to general public, mind you, but to the operations on RBMK plants.
Your understanding of "typical Soviet fashion" has very little with the reality. The nuclear industry was one of the best in the documentation and control. Well, a few dedicated people can break even a fail-hardened system, as we can see.
@@vladimirdyuzhev According to Soviet standards, maybe. The lack of a containment building and a two stage emergency coolant backup would have been considered flaws so fundamental that a reactor of this design would not have been allowed to be built outside the USSR. Furthermore fixed graphite moderation and a positive void coefficient were considered inexcusable flaws in reactor designs back in the 70s in the West. Reactor #1 was finished in 1977 with #4 (the one that blew up) finished in 1983.
There was a previous accident involving a power surge when scram was initiated in another RBMK reactor (IIRC in 1983?) and a few of the higher ranking nuclear officials and scientists knew about this flaw. However, they did not tell the operators of the reactors about this - instead they gave them a rigid framework of conditions that they were never to deviate from. Unfortunately, the political pressure put on the operators to complete this safety test motivated them to try and cut corners and that was the main cause of the disaster. The real issue with the Soviet nuclear program was the culture of secrecy that permeated basically the entirety of the Soviet bureaucracy. Safe nuclear energy REQUIRES open and accountable culture to be effective which is why the worst nuclear accidents have always involved places that don't have that culture. This is why the West has used nuclear energy longer and with many more reactors than anyone else - but has far fewer serious accidents.
7:30 - he says that the test was never successful at the Chernobyl #4. In fact previous test was successful in powering the pumps but their recording equipment failed and they were unable to provide measurements to confirm so they had to repeat it.
that would be the definition of an unsuccessful test.
Is there any chance they lied about the last test? The reason it failed afterall was because they did not have prove that it passed the test
@@youonlyliveonce12ish the pumps worked and it was registered in the computer but additional equipment which was supposed to make detailed record of turbine performance failed. And if they lied - they wouldn't need to repeat the test on April 26.
he is delusional. send him to the infirmary
@@AlexDemidov "And if they lied - they wouldn't need to repeat the test on April 26." You are missing the other option: they lied to meet a deadline but still intended to do the test because they weren't /completely/ stupid.
Thank you this in depth explanation!
Another video suggestion:
The plugging of the 2011 Deepwater oil spill was basically a space mission on earth. Really fascinating engineering designs were proposed to stop it, but no good UA-cam video exists on the matter because 11 years ago, ScienceTube was still too niche. I'd be so happy to see this subject covered by you.
I'd love to but I really don't know much of anything about off-shore drilling. I have seen at least one vid on utoob about the sealing effort.
Having worked in the "power generation" industry for a number of years (albeit diesel), I have a great respect and appreciation for the invisible energy that allows you to see at night, cooks your food and keeps you cool OR warm.
When you are responsible for the power and the lights go out, it is truly a sickening feeling......
With regard to nuclear power production - *_To think all that physics and chemistry just to boil water._*
I remember some one stating, and I paraphrase, that using nuclear energy to produce electricity is similar to opening the front door of your house with a canon.
@@steveducell2158 But it is nice if made safe. Uranium has *MUCH* more energy than coal.
steve ducell an interesting proverb. But environmentally if made safe, nuclear is the best solution.
Chernobyl exploded because of a combination of the flaws of the communist System and the reactor design itself and the people operating it
Fukushima exploded because of the government deciding to build nuclear reactors near the ocean in a country that experiences tsunamis and earthquakes pretty regularly compared to other countries.
We didn’t throw away the idea of the aeroplane because we could fall out of the sky and die. We should not just discard the benefits of nuclear energy.
Guess what bsh our country don't have neuclear power plant and we still have electricity 😎
That goes off evry hour 😭😭😭
@Rockhopper1163: Regarding your last sentence - yes, you’d think there’d be a more effective way to harness nuclear energy instead of essentially just using it as fuel for your steam engine.
On a side note - imagine building a steam locomotive or steam boat with a nuclear reactor. 🤔
Excellent presentation. As an engineer I’m always fascinated with how convoluted events are presented understandably! Good job!
Fellow engineer here. This guy did such a great job explaining everything I didn't even realize this was a 21 minute video!
@@董家琪
I echo that sentiment. As a US Navy Nuclear Propulsion enlistee, I had the privilege of having a Reactor Principles instructor who would 'talk shop' after class every several days. The one time I remember clearly was when he talked about other nuclear designs, and talked through Chernobyl from much the same standpoint that Scott just did. This video was "Outstanding."
Doc. Richard Feynman was a master at that :-)
@@董家琪 I realised the duration only now 😀
I'm an old US Naval Nuke (1960s era) Excellent explanation. I was once involved in a hot restart in a War Zone. Very dangerous. It worked out OK. We did have to calculate the Xenon poisoning to know where (how many inches out for the control rods) criticality was likely.
Glad the US Navy has a better record with their reactors than the 14 cores dumped in the Kara sea.
As a submarine officer and nuclear engineer, this was a great description of the accident, in terms that many can understand. All US and most other country's reactors are designed with far greater safety and a negative temperature coefficient. The control rods are completely released and fall rapidly into the reactor core. For a submarine, we immediately shut the throttle reducing energy taken from the core. We also shift power supply from the electric turbine generators to the ship's batteries. We shift to reduced electric load for the batteries to last longer. If needed, we come to periscope depth and use the diesel and the ship snorkel mast. Control room crew immediately bring the ship up to 150 feet. All these actions are immediate after the Engineering Officer of the watch announces "Reactor Scram". We practice the event often in ship drills.
does the word OPSEC mean anything to anyone? 🤔
@@BorkomoraYou don't know what you're talking about.
@@Oberon4278 considering i was also on a submarine, i think i do.
@@BorkomoraThe vast majority of this information is either public already or easily inferred. The batteries, diesels, and snorkel mast are standard equipment on nuclear submarines and not classified. The procedures to provide power to the cooling pumps are logical and easily inferred from first principles: you want to shift power to the pumps to the batteries as rapidly as possible and let those batteries power the pumps for as long as possible, so cutting power is essential to the process, no different than preserving your phone battery when you know you can’t charge it for a while. Snorkeling submarines are easier to detect, so you want to minimize the snorkeling time. The only thing that gives me any pause is depth orders.
@@Borkomoraopsec refers to things like troop locations, make up, and tactics. If they were talking about how the reactor is built I could see a case for screaming OPSEC at someone but they aren't so its fine.
Now most of russian rbmk 1000 are operaring at 1060-1080 MW, since there was inicially planned an increase of power
Why RBMK:
No need to stop all of the reactor to refuel it
Faster refueling meaning less exposure of station personell to radiation
Easier regular maintenance
Easier increase in power (up to 1600 MW in project and up to 3000 hypothetical)
Much fasterand easier construction requiring less complex, expensive and dangerous operations
Less manipulations with simply large and heavy constructions, allowing for easier logistics
Lesser fuel quality requirement and easier compensation for fuel burn inequality in different parts of the reactor
The downs are
The water from reactor hot zone goes directly to turbine, not to heat other water, possible danger
The fuel rods are thicc, long rods for a large corezone making a 100% thicc secondary confinement prohibitevely expensive and requiring still large buildings and machinery to operate. Legasov in his memoirs in the tape remembered the council about these reactors design where he participated before construction and he regrets not putting enough pressure on making a safe confinement for the reactor, and suffers greatly from the responsibility.
The graphite blocks inside the zone is slowly damaged by radiation and heat and deforms, with a possibility to cause a jam.
Overall, not great not terrible, 3.6/comrade
@Fernando Reis 3.6/товарищ
"When did u became an expert in thermo nuclear science?"
Last night
I turn up the volume around family so they think I'm smarter than I really am
It was actually “thermonuclear astrophysics” 😛
Marksman230591 of course it was
My take away lesson is that water and 300giga watts of power don't mix
Typically when you have a PHD in physics you could be considered at least a mild expert in Nuclear Physics
Imagine explaining all of this to some politician who ask you why the hell you couldn't run the test today.
Kirkov! Gyet ze puppets. We go to Moscow.
Prolly would have taken em about 20 minutes.
Why the heck do we even need politicians? Why? Really! I know, I know, democracy right? But why do we make all these smart scientists led by these morons, who we stay will stand by what the majority wants, then just steal what they possibly can, then playing mindgames for power again? I do not know what the solution is, but we defo should make the next step after democracy, because it does not work well.
@@cjstrashvideoemporium6484 I agree, and I proposed something similar in a comment under a different video. The only issue is that for these changes to be implemented, we would need those high up who are willing to implement these rules, and these rules would make them a sudden decrease in income. Just take Hungary for example: the head of the general attorney has no reporting obligation to anyone, and for roughly 25 years in charge, he never ever launched an investigation against the now leading political party. So even if the votes will land on the opposing party, they have no chance to do a single thing against the former leaders. So yes, your solution is good, and it would work, but we cannot see it happening. It is like a disaster movie, where you can't avoid the disaster, just minimise the casualties. They up there do not want to be transparent, just looking like they are transparent. And here we are :-/
Because while individuals can be very smart, people are idiots. We are ALL herd animals and will irrationally chose the popular opinion over any factual information. Until humans evolve, we won't change. It would be nice to find some safeguards to improve things, but I don't see a massive improvement in my lifetime @@peterbalogh2646
They really outdid themselves cutting all the corners on this reactor from start to “finish”.
To the many victims of this, my heart goes out to you, you are not alone or forgotten!
Not so much corner cutting as poor design choices. The void between the control rod and the graphite moderator should never have been there. In a SCRAM, that's is the very thing you don't want passing through your reactor. Also, taking ~18s to fully insert the control rods is a very bad idea.
@@jfbeamThat’s wrong. Those points basically were unavoidable from an engineering point of view. The stress on the control rods would have been to high if they were pushed with a higher force into the reactor due to the water displacement.
Many of the reactor flaws were indeed corner cutting: no containment, pressure tubes instead of a pressure vessel and mixing the functions of moderation and emergency-shutdown.
*List of people who are to blame for the Chernobyl disaster:*
1. No
2. One
3. They
4. All
5. Did
6. The
7. Best
8. They
9. Could
10. Dyatlov
11: graphite tips
12: Xenon
1. Russian system keeping control rod issue secret
2. Dyatlov
13. The CIA (according to Putin)
@@chrisholdread174 14. The KGB (the organization which promoted Putin as president)
This is the first (of many) explanations of the Chernobyl desaster after which I really feel like I now understand what actually happened. Thank you.
@romaneeconti02 just leave their thank you alone without adding anything more or taking anything away >:[ you poop head
@@CallMeAshen stop trying to censor wisdom, sheeple.
@romaneeconti02 Define the difference between a "real nuclear accident" and a "man-made accident."
@sgg Matters little as long as reactors are run by people.
@@GrandProtectorDark well then those who made the car made a mistake, so still a man-made accident
I know that this is not what you mean, but I agree with random user above (danger of nuclear is there, it is because of the people operating them, but it is there)
I guess what's important is educating the naysayers that it's not some mysterious nuclear danger, but simply the human factor that is responsible for the accidents
we don't boycott alcohol because of car accidents, but instead try to prevent drunk driving
I don't know how this translates to making nuclear plants safer, but the first step would probably be for people to stop boycotting nuclear power
Side note, and I know this is very ignorant of me, but I really only learned that Chernobyl was entirely a man-made accident from this video
edit for some clarity
I get that feeling "getting stuck in the xenon pit" around 3pm every day
I've been stuck in the xenon pit all my life.
Have you tried removing all your control rods at once?
Stop jamming in and out, the graphite bars. You should control your energy consumption and usage better.
Xenon pit is an excellent name for a grungy nightclub.
Control what you eat. Don't eat things with high glycemic index. That causes a sugar spike (high energy) which then causes an insulin spike to control the sugar levels, which causes the low energy and subsequent hunger afterwards. You end up weak and fat.
Scott: *Explains Coefficients.*
Me: "I like your funny words, magic man."
You don't actually need to understand the coefficients, the values relative to each other is enough to give you an indication of how important each one is to the process.
@@beardedchimp You: *Explains why I don't need to understand.*
Me: "I like your funny words too magic man."
@@jkfilms6738 Me: *Asks why you like funny words.*
You: "I like your funny words, magic man."
@@Darenz-cg9zg man, funny magic.
man
@@Darenz-cg9zg I like your funny, man words
Im glad that you made a follow-up to the show as i've been having a hard time understanding the idea of the "graphite tipped control rods" and how they caused the crux of the incident. Most sources reinforce that this graphite was one of the major causes but didn't elaborate on what it meant to be graphite tipped. In my mind it sounded as if literally just the tip of the rods were covered in graphite for some unknown reason but seeing the control rod assembly as basically a dual use mechanism with boron connected to an ~equal length rod of graphite clears this up immensely.
Yes, I had the same problem. I tried to look for videos like this one explaining the design in details but I couldn't find a good video on UA-cam.
I think what normally would happen is that, if you inserting control rods, you would gradually insert a few at a time, then others, then others, so that at no point would there be an overall increase in neutron flux throughout the reactor. But of course, in a panic situation, this is not how it happened.
Worse yet, once the neutron shit hit the graphite fan, the rods got stuck. At least my impression is that at least some of them got stuck in positions where the graphite tips were accelerating the reaction. Then everything went wrong at once.
Think of a stack of Swiss cheese slices, where the holes accidentally got all lined up, letting trouble shoot right through. Sort of like Fukushima, except there the slices were different, but similarly bad luck.
It's like desigining an automobile where stomping on the brake pedal for a panic stop gives you several seconds of maximum acceleration before switching to braking. What could possibly go wrong!?
@@Dabbleatory it's more like in old cars where the brakes can lock, if the engine is cold and you slam the brakes then you lose the ability to steer.
The issue was that boron rods were 7 meter, while graphite rods connected were only 5 meters length, so when rods started to fall down one meter layer of the water in the bottom of the reactor was replaced by graphite.
What Scott doesn't mention is the true reason why nuclear plants exist in the first place. Uranium fission and neutron absorbtion happen in the reactor immidiately (neutrons in RBMK have the speed of 2 km/s) thus if one uranium atom are to fissure another uranium atom the reaction would've been so fast it becomes unstable, therefore reactors usually have only 85% of its reactivity due to neutrons directly from Uranium atoms. The other atoms Uranium fissues to can decay and produce neutrons, these neutrons are used to govern the reaction in the core, because the number of the isotopes that just decay but doesn't support chain reaction grows much slower than the speed of the chain reaction. Thus normally 15% of reactor's reactivity is from fission products.
In Chernobyl the reactor was in the iodine pit, which mean that part of those 15% positive reactivity had to compensate xenon negative reactivity.
Thus, instead of 15% of reactivity that can be govern the reactor had only (let's assume) 2-5% of the positive reactivity from the fission products.
Therefore when rods fell down and replaced 1 meter of water with graphite, for a short period of time 95-98% of reactivity that was due to the chain reaction had the opportunity to change into completely positive chain reaction (105% for example), thus reactor core that was under critical condidtions went over critical and chain reaction became unstoppable, and because chain reaction happens with the speed of 2 km/s an explosion occured.
So basically the engineers told the reactor, Just calm down!" and then it overreacted and blew up.
Most underrated comment on here
I didn't say female. I'll let you apply your own misogyny as if guys never blow up. Ha.
@@romulus1969 He only said that reactor was a female and you ovvereacted and blowed up misogyny at him... "Just calm down!"
Perhaps you should review the definition of misogyny. Ha.
Im offended
Boom
as someone who has spent years as a reactor operator. this is an excellent explanation.
Gotta Love Scott.
I concur, Scott is exceptional. I worked on the other side of the coin - we wanted super prompt criticality in picoseconds or nanoseconds - I worked at the Nevada Test Site 1975-1986.
I feel much more comfortable with fusion for power gen, but we are still a long way off I fear, Livermore has done a substantial amount of work on it in the past, but not sure where it stands now. One question you may be able to answer - what is the (average) time delta between a reactor SCRAM, and enough absorption to kill the reaction? Or are there so many variables that its not an "average" situation. Thanks for your thoughts on that. and Peace.
Cynthia Klenk excellent! Thanks! I am binge reading these comments. They make a change from the usual rude, bickering and puerile arguments on other subjects and channels. If I wasn’t in my 70s I would want to be a nuclear physicist when I grow up, and I’m not joking Dr Feynman 😎 PS: Love your channel content. I feel another binge coming on!
@@cynthiaklenk6313 oh man, that's awesome. Shutdown can be achieved pretty rapidly after a SCRAM depending on reactor design. Even being slightly subcritical can take some reactors out of the power range in seconds, so a SCRAM can basically turn startup rate instantly (again, depending on design) the big issue is decay heat. Even with all fission basically stopped decay heat can produce several percent of the last running thermal power. If you lost your heatsink temps can build up fast (check out TMI accident)
Hi Scott, that was a really well put together explanation of some pretty complex issues, in just 20 minutes!
I was a mechanical engineer at Windscale/Sellafield in the early Eighties. Just like you explained, it was 'known' that (Western) civil power reactors could never go 'prompt' critical (as a result of sound nuclear engineering design). Unfortunately it was not so true for RBMK's when being abused by the operators.
I'd happily live near a civil power reactor, but I was a little uneasy while I lived close to the nuclear powered submarine bases on the Clyde in the Nineties. At high burn up levels, near the end of their operational life, I believe these highly enriched reactors become a little 'sensitive' !!
Cheers Paul (now in nice safe NZ)
Are you saying that Trident is unsafe?
@@jtcruz125 I certainly wouldn't go as far as to say they are 'unsafe', they have a good track record so far, but just not 'as safe' as Western civil power reactors.
In the real world nothing is absolutely safe or carries zero risk.
Most of us accept the risk of driving a car, having a general anaesthetic, getting a Covid jab (contentious one this!!) despite there being various levels of risk associated with each one. Regards Paul
What about 3 mile Island? While it didn't go prompt critical, they did have a partial core meltdown and radiation release, and then you also have the Japan disaster (which was of western design).
@@m16ty Nothing is 100% safe or immune to human error. But, good design can reduce the risks to an 'acceptable' level. Defining what is an acceptable risk is the most tricky subject, it gets totally mired by politics and ignorance of the subject matter.
Good Western reactor design has kept the number of major accidents to a handful, each with fairly low casualty numbers. I can't do this subject justice in a few sentences but hopefully you get my point.
Cheers Paul
@@pauln1557 the actual problem is even wider: Most people as is "all but a very few" can hold a competent and grown-up real conversation about risks, probabilities and acceptable failure rates. But politics, policies and investment decisions are voted on by common politicians and people who usually only have a concept of fear levels instead, which demonstrably is an unhelpful stand-in for assessing actual risks in the modern (post savanna roaming) human world.
As a nuclear physisist myself I say - Kudos to Scott! Excellent video!
physicist?
@@jonathanhill8691 Not a linguist, apparently, but that's okay.
Yeah, I am gonna go ahead and assume that if you can't spell physicist... You probably aren't one
J Blob I think he is Russian or just Slavic so just give em a break
@@richardhouston736 that or German/Austrian by the surname, no matter what, clearly not a native english speaker. Thanks for standing up for us!
This is the best video I've seen explaining the Chernobyl disaster.
No it isn't. You're delusional. Get to the infirmary!
100 % agree, this video is simply great! :-) Thank You for this job, sir! All the best from the Czech republic. Stay healthy and be safe!
@@sms4668 Keep up. Would you rather seeing it on the Discovery channel with all the dramatics?
Can you do a similar breakdown on the physics of Fukushima?
Children would know to not put pumps lower than the highest property you could put them on. Silly design flaw.
@@superchuck3259 or just don't put a nuclear reactor on a coast in an earthquake region
@@GamingEntertainment12 You don't really have a choice when your entire nation is on a fault line and the best source of industrial quantities of reactor cooling water is the ocean
It's important for people to realize just how rare an earthquake and resulting tsunami of that size is. Having one in 2004 and then another in 2011 makes it seem like they are common, but historically they are a fluke. Hindsight is 20/20 and whatnot.
@Yáhuar Huácac So.... shitty design?
As a former reactor operator, you did a great job explaining.
Me too
This shows that even the operators of such potentially dangerous plants are not thoroughly trained in the real world and do not know exactly what the consequences of their actions are. I suspect that only the shift supervisor is a trained nuclear physicist and even he was at a loss at the crucial moment. All the others are semi-skilled operators.
That is why this technology is complete crap and must be shut down.
@@Medley3000 Soviet culture is to blame for this incident alongside pressure to complete the test (Or wait another year for a second chance to complete it), lack of safety and arrogance by superiors thinking they built an indestructible machine and lastly a culture in where workers below their superiors had absolute no say in the final decision. Nuclear power is the cleanest and efficient power as long as it’s done correctly so no this type of technology should not be abandoned.
@@swarmer5 Then the following also applies to the Three Mile Island incident:
To blame for this incident is American culture, the pressure to complete the work, the lack of security and arrogance of superiors who think they've built an indestructible machine, and finally a culture where workers under their superiors had absolutely no say in the final decision.
@@Medley3000 Don’t know anything about that incident so I can’t say anything.
WHEN YOU FULLFILL THE 5 YEAR ENERGY DEMAND OF THE COUNTRY IN 0.4 MILISECONDS!
Heh, not great not terrible
GREAT SUCCESS COMRADE!
Mother Russia salutes you!
stonks
Heros of Soviet Labour, everyone of them.
Could you eplxain it with red and blue plastic signs?
Thank you
I wouldn't mind a bit of neon too.
I loved those plastic signs
@@MadameMishka The plastic signs likes you as a friend
Either goes up... or it goes down....
@@HarryNixonTube All the operators do is maintain balance... as they all should.
Thank you for taking the time to go through this in full detail. Most videos attempt to explain it in 5 minutes and fail to discuss the actual physics of what caused it, leaving gaps in understanding. Very well done and as a young nuke engineer, I'm glad you dispelled the misconceptions of nuclear power at the end!
You didn't see graphite because it wasn't there!!
you didn't
YOU DID-ENT
BECAUSE IT'S NOT THERE
OG fake news
Are you saying the reactor didn't use graphite, or are you saying the reactor didn't explode?
@@realkarfixer8208 no comrade I'm saying RBMK reactors can't explode.
wow very creative i totally dont see this on EVERYTHING related to chernobyl....
“Every lie we tell incurs a debt to the truth...and sooner or later that debt is paid”
Yes, this is in the style of real Valerij Aleksejevic, despite I have no evidence for that. I think, He could say something similar in real world... He was used to think deeply about world around Him, was known for his high sense for responsibility to his loved wife, family, people, motherland and the world. His personality was not easy to understand and was slightly complicated. I know It well, therefore He is my soul mate, teacher, inspiration.... I know, It seems to be crazzy, but that is the way I feel... All the best from the Czech republic, stay safe and be healthy!
1. Errors
2. Mistakes
3. Accidents
4. Catastrophe
5. Comrade Dyatlov
Voltaire of Paris is delusional. Get him out of here
Name is spelled wrong, he is Comrade Blyatlov.
Not greet
Not terrible.
You can’t blame this on Dyatlov
So when they stalled the reactor, they should've called off the test.
Absolutely. The only moment they "unstalled" the reactor was when it managed to burn off the xenon poisoning and increased its power tenfold right before the explosion. It wasn't safe to operate and should've followed its routine maintenance.
When they stalled the reactor, they should have gotten the fuxck out of Dodge! Fast!
@@PeterMilanovski Not really. A stalled reactor doesn't mean it's going to explode. However, it does mean that restarting should be done very slowly and carefully, and the Chernobyl operators did the exact opposite.
@@Tuppoo94 that's exactly what I mean, had they got out and never came back, history would have never been made and Chernobyl would be like, who, what, where? Never heard of it!
But then I guess that it just would have happened somewhere else!
Well, at least not in Australia! But somewhere else, definitely!
The amount of reactor failures throughout history is staggering but what comes to me as a shock is that after Fukashima, with the release of details on what and how it went wrong, France conducted an overhaul of their nuclear power plants! I have forgotten what year Fukashima happened but honestly! I would have thought that there's nothing left to understand about nuclear reactor technologies! I watched a video that went through step by step what was happening and what was done at the Fukashima plant, I can't believe that no one asked a single question (I'm referring to the people who worked there) regarding the operation procedure during an emergency situation!
I don't know you and irrespective of your position on the use of nuclear energy but as for me! Had I been working there! Mate, I would be full of questions! I would want to know which manual control is where, actually go there and physically see it, that's where I would have seen the type of valves being used and that's where I would have been asking more questions like what would happen if we lost power? Can we still operate this valve? Are all the gauges going to work? It's not like you can sneak a peek into the reactor to find out what's going on in there LoL... But anyway that's just me, I have always been like that with everything! If I'm working at a place, I sleep it, I dream it, I eat it, I am it!
I think that it goes to show how little we knew about nuclear reactor technologies during the Chernobyl event and that another explosion happened in the 2000's at Fukashima just scares me! What else and where else is next!
@@PeterMilanovski Nuclear accidents are serious, but nevertheless nuclear power is still by far the safest form of energy relative to the amount of electricity produced. There have been only 3 major accidents. Three Mile Island in 1979, with no fatalities or significant radiation releases, Chernobyl in 1986, which this video is about, and Fukushima in 2011. The massive earthquake and tsunami that caused the accident at Fukushima, killed over 15 000 people, while one cancer death has been attributed to radiation.
The operators at Fukushima did pretty much everything according to established procedure. Unfortunately, the massive tsunami that struck the place had flooded the backup generators needed for cooling, so their efforts were in vain. The reactor itself also functioned as designed, and shut down safely when the earthquake happened. So it's not like the engineers were clueless about what to do when there are problems, and even if they had been, the system was designed to fail safe, and it did. In the end, the meltdowns were caused by Mother Nature.
It happened during a SAFETY TEST.
"In Soviet Union, safety tests YOU!"
In Russia, safety tests US!
We do this together comrade
@@johnsmith1474 Changes made by a bureaucrat to maintain his good standing in the party.
A test that was 2 years overdue...
@Jonas Ukrainians are basically baby russians
@@AndyGraumann1 tell it to ukrainian... he will punch you in the face for that
I wish there was no such stigma against nuclear power. I think it's a great opportunity and people should be educated about it instead of being told it's spooky and dangerous.
@Jen farmer Except one produces much more energy much more cleanly than the other.
@Jen farmer I'm not disputing that. But when literally every single news outlet, politician, and scientist is saying the opposite is true, it's a little hard to debate or change anyone's mind. Trying to do so just ends up with you being labeled a climate change denier, trump supporter, nazi, right wing nutjob etc.
Well, here in the grand USA, the regulation and funding required to make them safe will never fly, and there is the issue of where you put the leftovers (NIMBY). Also, no one even wants the reaction near them, so double-NIMBY.
BINARYGOD most modern design use up current nuclear waste/leftover fuel as fuel and can reduce the half-life of it to below 1000 years. I suggest reading up on molten salt reactors or thorium nuclear power :) we could never have to worry about electricity if we embraced nuclear a bit longer or at least until we improve solar, wind and water power enough for it to produce enough electricity for the entire nation without any pollution. Instead we shun nuclear and chose to rely more on coal power while we try to improve the renewable powers sources. It’s ironic that once upon a time some countries didn’t use any coal generated electricity at all because nuclear power destroyed the need for it, and now it’s back and it’s back strong because of the stigma against nuclear power :/
@Jen farmer You do understand algae bloom is entirely caused by humans right?
Thanks for covering the xenon poisoning. That's been the hardest thing for me to explain to people since this show hit the airwaves.
for me was the graphite rods tips, man I could not understand It
@@v44n7 I learned earlier on about the control rods being tipped with graphite, which by then I knew would aggravate the reaction as they went back into the reactor.
But when I learned in this vid that those "tips" were _four-and-a-half-metres long_ (about 14') *and* would take 18 seconds to fully get out of the way so the boron could do its work, I winced.
v44n - Try pausing on that write up near the end of the video. It explains it again in text. However, I understand your confusion, and I've actually had to re-watch the video to try to explain it.
I AM NOT A NUCLEAR PHYSICIST - HOPEFULLY SOMEONE COMES ALONG TO EXPLAIN IT BETTER TO BOTH OF US, BUT HERE GOES:
So, I think the confusion is between the terms "moderator" and "absorber".
A moderator is a material that makes neutrons bounce around more so that they're more likely to hit something, and less likely to just fly out of the reactor. If there isn't a thing that makes the neutrons bounce around then they won't hit anything that will split them, so they don't split, so they don't keep the reaction going, because the reaction only keeps going so long as it has neutrons to split.
A absorber is a material that soaks up the neutrons, like a sponge. It takes a neutron and holds on to it so it doesn't go anywhere. If the neutron is held onto and absorbed then it can't hit anything *at all* so it's not gonna split.
A moderator is good for making the reaction continue because it slows down more neutrons to increase the chances of splitting. An absorber is bad for the reaction because it reduces the neutrons.
Water is both a moderator, (in that it makes neutrons bounce around more) and a absorber (in that it soaks up the neutrons.) So, when it's being used to moderate the reaction the water helps make more neutrons, and when it's being used to absorb it helps remove neutrons. But, water is *always* both a moderator *and* an absorber, even if you'd really like it to be just one or the other. In the case of the Chernobyl reactor they really wanted it to be an absorber and not a moderator, but it's both.
This is where my understanding starts to break down, but I believe that in the reactor they needed the water to only be an absorber, and not a moderator at the bottom of the channels under the graphite.
Now here comes the issue. If you look at the chart at the beginning of the video that Scott put up at 4:46 you can see that what water is made out of (2 Hydrogen-1's, and one Oxygen, H2O) the components of both of those elements are better at scattering/bouncing/moderating neutrons than the Carbon tips (which is what graphite is) at the bottom of the control rods.
So, at the bottom of the channels where the water was being both a moderator and an absorber the water boiled away to a point where it wasn't being a good enough absorber, but it was still acting as a fairly good moderator. So, it was slowing down neutrons enough that the reaction was reacting, but because water is better at moderating than even the carbon tips are the reaction was slightly stronger at the bottom of the channels than at the top, despite the water (even as steam) absorbing some neutrons. Basically, if the water had stayed as the very dense liquid form it would have absorbed more neutrons, but at a lower density it scattered more neutrons.
-Let's arbitrarily say that as the density of the water decreased due to becoming steam the absorbtion:moderation ratio went from 5:4 to 3:6, and it keeps increasing in favor of moderation rather than absorption. Meanwhile the graphite above it in the rod is like, 1:8.- [1. See my guesswork at the bottom]
So, now the bottom is reacting faster than you would like it to, but it would have been fine because the water still absorbing *some* neutrons. Except that now as the rods are moved down all of a sudden all of the absorbtion that was there is gone, and the reaction at the bottom that's been teetering at slightly-more than the top, all of a sudden has *even more* neutrons that can hit other neutrons, and then those neutrons all hit a bunch of other neutrons at once, which start hitting even more neutrons inside the uranium rods regardless of both the moderators and the absorbers elsewhere in the reactor because there's enough neutrons to have a high-chance of hitting other uranium atoms all on their own and then all of a sudden you've got your mini nuclear reaction and everyone dies. The end.
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That's the best I can do. I realized trying to explain this that Scott did his absolute best trying to explain it, and that I do understand it a bit more, but there's some important bits in there that I sort of have to guess at. But, if I have to guess:
------------------------------------------------
1.
I think that *actually* somehow with the water density being low (because it's steam) the reaction at the bottom worked it's way up to being semi-self sustaining. Because I don't think just trading it off for more moderation would explain it, because if the carbon rods were worse moderators than the water then It wouldn't make sense to me that when they took the place of the steam the reactor would get worse.
I think that there were enough neutrons coming off of the uranium at the bottom of the uranium rods where the steam was that they were splitting on the uranium like they would in a nuclear bomb, but not enough to make it go critical - the water was still a necessary moderator to slow enough neutrons down that the reaction would continue. But then, when the carbon moderator - which was a better moderator - moved down to the bottom of the channels all of those extra neutrons that were there, but not quite slow enough to split again, all of a sudden were made slow enough to hit something to split again. So, all of those neutrons split, and with each split energy was released in addition to another neutron, so then it all went kaplooey.
@@RailRide I too thought it was 'just the tip' not almost the whole fucking thing.
@@v44n7 still fuzzy in my head because so many different opinions on the graphite ends, I hear that they were overheated to the point they expanded just enough when the "kill switch" activated and all the graphite rods and block moderators rubbing the hot graphite was like a match creating spark and hydrogen bubbles split from the temperature exploded at once, the second explosion in theory was the mass going critical but it could have just been the overpressure, the criticality theory sounds terrifying though.
This is perhaps the most detailed explanation of this accident that I have encountered so far.
18 Seconds for full control rod insertion is just mind blowing! I work at a research reactor and twice a year we have to verify that all the control rods will fully insert in less than a second.
I would not be surprised if the Chernobyl accident is one of the reasons they designed your reactor to be able to do this.
I now understand what my dog goes through when I'm talking to him.
me too.......
LOL underrated comment
Hahaha
..why?
Is this explanation too hard?
Woof woof woof, woof woof, woof.
RBMK is actually Reaktor Bolshoy Mettallicheskiy Krugliy (Reactor, Big, Metal and Round)
Reaktor Bolšoj Moščnosti Kanalnyj
Hilarious. ;D
that's a very stupid name for a reactor, though RBMK as an acronym on the other hand sounds so sick and badass...
Guys. Of course it is a professional joke in russian/soviet nuclear power engineering society :)
Scott had a correct/real version.
But do you know what VVER reactor is? :)
@@gluck3d Yes, there are several of them in my country. Vodo-vodnoy energeticheskiy reaktor. Or something like that, anyway
brilliant explanation of the physics with the exception perhaps of the fast fission component. I worked at LNPP after the event upgrading the SKALA B system for flux calcs and we gathered lots of evidence that first explosion was steam shock as you say but second was hydrogen / oxygen recombination from superheated steam reaction with graphite. There were fuel ejections also but from primarily mechanical ejection. Also important was the control room 'human' factor of leadership, deference to Moscow etc.
I just have the video paused to appreciate your efforts to pronounce "РБМК". Well done, Scott!
A great Scott Scott and manly! ;)
good ukrainian Щ spelling. not russian :)
and he did great job on that as well, it sounded like a physics professor after a several strong beers but nevertheless perfectly understandable! good job
@Marionette Loves Gaming reaktor bolshoy mos'hnosti kanal'niy. Smth like that. Scott did extremely well!
Reactor Bolshoy Moshnosti, kanalya!
Nuclear reactors are a bit like airplanes. They're by far the safest mode of travel, but once something happens it does so spectacularly, leading people to be scared of it.
The difference being, that with an airplane crash at most the airplane and whatever it crashes into is destroyed. With a nuclear reactor potentially an entire continent can be wiped out.
@@Jundl77 If the year is 1986 and your nuclear reactor is placed in the Union of Soviet Socialist lack-of-safety-procedures-Republic, then yeah. For everywhere else, not so much. That doesn't mean accidents can't happen due to outside interference, it just did in Japan after all. But all in all it's extremely safe compared to how much damage coal and gas is doing.
Of course, even better would be to use sun, wind and hydro power, but there's an economic aspect to it all as well. Hydro can be fairly good for those countries where that is available, but Solar and wind is problematic in terms of actually earning money on it. Tho there are continuous breakthroughs in solar panel technology, so that one is getting better by the day.
@@Excludos Why does everyone forget Three Mile Island? It partially melted down in the not union of soviet socialist safety protocols USA 7 years prior and everyone forgets it happened.
Fusion is the only viable alternative to Fission, and alot safer, but it's hard and may take another couple decades to work commercially.
@@Chrinik You mean the year 1979 in United States of privatised-companies-who-doesn't-give-a-shit-about-safety America? Yeah not much better, really.
@Stephen Ritger Tiny amount of radiation? Not great. Not terrible...
Dyatlov: let’s begin the test
Reactor 4: I’m about to end this man’s whole career
And subsequently... his life.
Imagine that, dyatlov was such an asshole that the reactor got mad at him
I'm sorry Dave, I can't do that...
Officers in Kiev: we can't afford maintaining the reactor below 1.600 MW for much longer. Rise the power up!
RBMK reactor: Ok. Take my 300.000 MW.
Dyatlov: Let's begin the test.
Reactor 4: Hold my beer.....
It would have been Great if the reactor just ended dyatlovs career, but it killed and posioned millions
The DGs at the PWR plant I worked operations performed an Operational Surveillance Test every 30 days. The DG had to reach speed and rated power (16MW) in seven seconds. At the time we used a highspeed 10 channel paper recorder that monitored certain values at startup. This produced about 30 ft of paper for a ten-second record.
Thank you for being such a great role model for us all, thx Scott ❤️
ThatOneGuy Suddenly I feel like maybe I should’ve paid attention in school
@@troyp9485 hahahahaaa! What's his day job? Obviously he is some sort of scientist. I first tuned on to him for Kerbal.
Steve Miller I’d guess a professor
WTF??? Role model? LOL!
Question at Radio Erevan: -Is it true that following Chernobyl nuclear accident,people's teeth began to fall? -Yes but only to those who didn't keep their mouth shut!
dalsenov ah good old Radio Erevan jokes
Haha, haven't read/heard Radio Erevan jokes for quite some time 🤣
Nikolai Fomin: "Please, tell me how an RBMK reactor explodes. Reactor 4: "OK no problem"
Reactor 4 hold my beer
Watch carefully, I shall do this only once!
Why? Because it's cheaper!
Do You know, comrade Nikolaj Maximovic graduatet from nuclear enginering via corespondence lectures? He was highly educated in the Machine enginering, but as the nuclear specialist was Greenhorn... 😔😲
You are over reacting comrade. The leak is only 0.2 millisieverts, no more than a chest X-ray. Which reminds me comrade. Have you had your check up?
This is probably the largest misconception out there which is skewing people’s perspective on the subject. Everyone I’ve spoken to believes that nuclear power is unsafe because it might blow up, and often cite Chernobyl. And when I try to explain that it failed because it was poorly designed, cut corners, and was improperly maintained, and that modern reactors are much safer to the extent that one almost never fails to human error or design flaws, they just look at me like I’m dumb and say something dismissive. Then they go on to say that solar panels or wind turbines are the safest and most sustainable source of energy to replace coal
I remember visiting a nuclear reactor while it was going through its 3 yearly reload cycles (so had access to the inner core) (my parents worked in the business) - Visited Fessenheim (a 920MW PWR design) and was assured that at all times they always had a Diesel turbine running continuously (and a weekly check for the backup) If the backup failed an orderly shutdown was instantly ordered by the plant "pilot". That was 30+ years ago.
Another story I have about this nuclear plant is that during design and construction they had thousands of microphones installed along the pipes. Then they had a big room full of drawers containing headsets and some guy would come regularly and listen to all those pipes... If he heard anything unusual happened, he would order a shutdown.. then 1) they had to find the bolt or nut involved.. 2) figure out where it came from (probably not too hard each and every of these parts have serial numbers) and 3) figure why it came off in the first place - last occurrence they had the time involved a full 6 month inquiry and reactor shutdown !
Well, 30 years ago was 1990... It's after Chernobyl. People learn from mistakes.
@@ImperativeGames That and the fact that Germany is run differently. In post-war Germany, which is a Democracy, there are no quotas to fulfill any any cost (like in the USSR back when), and in that xenon pit the reactor would have been shut down and kept that way for a safe amount of time.
@@Widestone001 As I've lived in 90s in Russia, I still remember the late-USSR principle of "minimized responsibility". "Quotas to fulfill at any cost" ended in late 50s after the death of Stalin.
95% of various directors during 80s didn't care about anything except their career (and many didn't care much about it), not "building Communism" or "fear before horrible KGB" - it's all propaganda (Soviet and Western respectively).
Drop that "Democracy" crap and see real people for what they are.
@@ImperativeGames
@Christian Breitenstein
Fessenheim, while it sounds very German is actually french lol. Aslo there has been some controversy because testing has shown that the Building isnt fully earthquake proof. (And the Region is known to have more geological activity than other regions) I think they are working on shuting it down atm, not quite sure.
It's the difference between a rich country and a poor country.
That is THE BEST explanation of physics of that reactor in those conditions....even russian-language sources have no such a easy and yet informative explanation. Many thanks , Scott!!!
If you haven't yet, I wish you could explain a thorium reactor and why we don't have them and why we are stuck with light-water reactors.
Love your channel!
Incredible explanation. I only have highschool education and I was able to follow almost everything. Thank you so much, Scott!
You just made me binge a whole 5 hour HBO series. Was totally worth it
HBO is trash.
@@HECKAKYH-ADEKBATEH Yeah, but the 'Chernobyl' mini-series was fucking excellent in getting the story across to a Western audience fed mostly on vague news reports at the time.
@@exidy-yt Yes but I hated how they portrait those with radiation poisoning as being infectious. It brings the integrity of the show into question imo.
@@pretzelstick320 I think you have misjudged something. Humans are superstitious and some will not sit on a chair where a cancer sufferer once sit, let alone someone with AIDS or advanced radiation poisoning! No where on the show was it ever said radiation poisoning was contagious in the disease way, but people often react that way anyway. Especially in a fairly backwards society like Soviet Ukraine where even most of the plant workers at Chernobyl knew almost nothing about radiation poisoning. (Also it IS a fact that a human suffering radiation sickness is radioactive themselves now and can be a source of contamination to other people, but you have to get within hugging distance for it to be a real danger.)
Exidy YT even doctors wouldn’t know?
I've just started watching the HBO series and so far it's pretty decent! I'm eternally grateful that they didn't make the Brits put on fake Russian accents! Thanks for making an accessible explanation of the Chernobyl Disaster, I love how you just stuck to the facts and left politics out of it.
I've been in the industry for nearly five decades, and despite a few flaws, the HBO series is THE ONLY thing I have EVER seen on TV or in a movie about a nuclear plant that was even close to being accurate.
I agree with You.... No politic, only explanation of the disaster. That is the way, I like...
I'm russian and it was painful to look at those grotesque characters and fairy tales about the KGB and vodka. it's a good show, but just a show unfortunately with a bunch of errors and stereotypes.
Hey scott. could you make a video series about nuclear reactors? The series about nukes was awesome. I would really like to see a series about peaceful nuclear technology.
I second this request. How do the various types of commercial reactors work? Why did nuclear power become so unpopular years before Chernoyl? What are the advantages of the more recent designs? Is there a realistic chance of seeing thorium fueled commercial reactors in the near future?
They became unpopular because oil and coal power, the ones truly threatened by nuclear power, financed environmentalist groups to fearmonger about radiation.
@@WillaevYeah, let's skip the conspiracy theories, though.
@@WalkaCrookedLine
In two words, Cost Effectiveness. Nuclear power isn't cheap, really isn't cheap. All Nuclear reactors need to be built to incredibly high safety standards, this means a lot of upfront costs, and I mean a LOT. Between 1975 and 1985, the American Utility industry spent $125 Billion on nuclear, thats billion with a B in 1970s money, nowadays adjusting for inflation? The mind boggles. And unlike Gas, Oil, Solar and Wind, there has been no drop in operating or construction costs.
So it costs a lot to make, and then costs you even more money in maintenance. Also when it stops, because it turns out a nuclear reactor will not work forever, you then have to dispose of them. Which means even more money you're not getting back. I really hope that there is a way to break the nuclear cycle or build them a little cheaper, because the planet can't afford it not working.
In US, one major reason the nuclear power plants are closing is: natural gas is really cheap. And, natural gas is a fossil fuel. One way to approach this issue would be to price the externalities of using fossil fuels into the price of natural gas. Emission pricing/carbon tax, or any equivalent scheme.
I've watched several videos explaining the disaster, and this is the best and easiest to follow. Thanks...and I feel much safer now!
I would like to say: Thank You Scott for this video!
I wish I had a physics teacher like you back then in 1986. Great explaination!
I wish Dyatlov had a teacher like Scott!
In 1986 I was in my first year of college and uninterested in physics. I was too busy chasing girls.
My physics teacher was the gym teacher "on loan"
Original poster: just FYI, I like your handle. It was the name of one of our beloved pets.
My mother described her politics teacher during that time as, going all in on the "we're alle gonna die" train.
The problem was also that the fuel was quite burned up during the test, as the reactor was meant to be shut down for maintenance, so they did not have any fresh fuel in it (the RBMK can be refuelled while running). So there was a small reactivity left, which was also a big factor influencing the reactor control. At the Leningrad power plant, which has the same RBMK reactors, they ran a similar test without the reactor exploding on November 30 ,1975. They kept only 6 to 8 control rods in the core, meaning the "minimum admissible reactivity margin" was very low. The conditions were practically identical to Chernobyl. With two main differences. 1. The fuel was not burned up - it was practically fresh, as the test was being run on a reactor after it was shut down for maintenance, not before shutting down for maintenance (only 3.6 GWd/t vs. 14 GWd/t in Chernobyl) and 2. They did not press the AZ-5 scram when running the test. Still the reactor was in a very unstable configuration when they made the test. The "end effect" of the control rods would not show its full potential, as not all of them were inserted at once into the core at once (AZ-5), as in Chernobyl. So the reaction did not have enough time to run away. They observed that when pushing the control rods in, the energy output rised for a short period of time (some seconds) instead of declining, but it did not result in the reactore becoming promplty critical on fast neutrons (which is what happened in Chernobyl by some soruces). Since 1975, the temporary "end effect" of the control and emergency rods was known, but this was not seen as a safety issue back then. This was a huge mistake. More info can be found in the book by N.A.Dolležal and I.J.Jemeľjanov, called "Kanaľnyj jadernyj energetičeskyj reaktor" (1980).
He said in the video that when the control rods were pushed in it pushed water out and that caused the explosion? He explained that part very poorly. Why would it cause a short rise and then stabilization after?
@@benb9151 It wasn't that they pushed the water out that caused the explosion, it was that they replaced the water (which was only moderately-enhancing the reaction) with Graphite (which dramatically enhanced the reaction).... in the part of the reactor where the reaction was already too-enhanced (the core).
Think of it like trying to get a fire truck to a road fire, but to get the fire truck there, you have to push a fuel-tanker-truck into the flames first, and then you can basically visualize the problem with pushing all the graphite into the core at once while trying to insert the control rods.
Because the rods had graphite ends, which mean that when fully retracted, they actually boosted the neutron moderation. The problem is that the graphite part was shorter than the core. When inserting, it first displaced the water from the channels, which lead to an incerase in neutron moderation in the lower part of the core. Normally this is not a problem, because the safety systems and opearting instructions are designed properly. It is just by switching off all safety systems and disobeying any instructions that you can get the reactor into a very unstable state of operation, where a small change in its configuration can have dramatic consequences.
You are all wrong! The only reason this happened was there was not enough hard bass playing in the reactor chamber 🙄 and if they would have just covered the core in several layers of the finest adidas none of the radiation would have escaped 😞
Okay can you actually explain how burnt fuel would lead to this, in my mind it would have less fissionable material.
Scott is an international treasure. As usual, very complex stuff explained clearly, concisely and with just the right amount of detail to be insteresting to almost any audience. Reminds of Feynman.
Richard Feynman is probably the only person who I would watch give a university lecture on quantum electrodynamics for entertainment.
19:17 THIS IS STILL UNSOLVED THE 2ND EXPLOSION: It cant be a hydrogen explosion, as the recovered fuel rods had NO ZrO on them, so it wasn't a hydrogen explosion from dissociation of H2O.. So was it a fissle? No there was no evidence of that either. So why did it explode 2 seconds later?
When I attended US Naval Nuclear Power School in 1980, we covered the hazards of graphite moderated reactors and I distinctly remember being taught that such designs were susceptible to "runaway excursions" which is we we operated PWRs. Ergo, there were experts who believed in such a vulnerability.
One of the principal reasons the west avoided graphite moderated reactors was the near disaster the Brits had at Windscale in (IIRC) the late 50s, a disaster avoided only because of British professionalism. Everyone knew the dangers from graphite were very real, but reactors of that type were cheap and the USSR was having money problems.
In the book Midnight in Chernobyl, the Soviets openly mocked the West's use of water based reactors. To them, graphite, even in huge reactors, was the superior design.
@@302Diane Graphite moderated reactors "avoided" in the west obviously doesn't include virtually all the power producing reactors built in the UK. There were 11 Magnox stations containing 2+ reactors each and 7 AGR stations with 2+ reactors each. Many of these are now shut down but some still operate.
@@chriswilliams1096 True, Magnox and AGR are graphite moderated. However they are gas cooled, so they do not have the risk of a runaway reaction due to coolant boiling. It would be better to specify that "graphite moderated water cooled" reactors have significant additional risk of a runaway reaction. (Although even then there were several such reactors in the west used for plutonium production.)
@@nathancampbell06 I mean looking at construction costs versus power output, the RBMK was an excellent design.
Its just the costs were that low because too many concessions had been made when it came to safety.
Fun(?) history fact: That 10 hour delay was in fact caused by the peculiarities of Soviet Economics. You may remember the show briefly mentioned that they were requested to hold due to factories having to run overtime at the end of the month, the accident did take place on the 26th of April. Well this overtime was a side effect of the quota system used by the USSR's planned economy, i.e each factory has a set number of goods it has to produce before the month is out, if they don't they can be punished in by having the KGB set on them, or even worse, wages being cut. Though the usual response was typically short sighted, the quota for the next month would be raised.
So this let to a situation whereby factory output was at its highest in the first and last weeks of the month, as workers rushed to meet quota and get paid on time. This is why Soviet goods had so many...erm 'quality' issues, there was a good chance it had just been chucked out the door at the last minute. Plus workers infrequently staged passive protests by just working slowly and dragging everything out. So when that delay happened it was because the factories had to make up the slack period of the last two weeks and quota would be coming due that Wednesday.
So there you have it, another little piece of the puzzle.
> can be punished in by having the KGB set on them, or even worse
LOL, ROFL!
Things you folks believe in are... anyway. The directors of plants that fail to meet the plan goals were losing the "13th salary" - i.e. the bonus. If they do it regularly, they'd be fired from the director's chair. That's all. No KGB. No "worse" (there is something worse than KGB in your delusional world view? Tell me what it is.).
Your massmedia-induced fantasies aside, yes, the end of month typically had a higher output - and hence higher power demands.
@@AverageJoe8686 LOL!
Dude. The worst thing about socialism was that you couldn't fokking FIRE a drunkurd from a plant. Because you see - the Constitution guaranteed the Right for Work. And the drunkurd was waltzed right into the Party representation and was restored the next day, and the manager got to hear a lection how it is his responsibility to support _every_ worker. That was really a morale killer for all honest workers.
And a lazy worker could tell the director to go and eff himself, and the director couldn't do anything as long as there was no physical violence.
Gulag, my ass. :-/ I wish....
@@vladimirdyuzhev That's not an issue with socialism. That's an issue with Stalin vision and methods. Karl Marx would have *hated* the USSR.
@@DiThi Probably true. I'm describing the specific version of USSR socialism and the alleged "sending of workers to Gulag" - which is hilariously false.
@@AverageJoe8686 People who escaped to West often ... say _inflate_ ... their suffering to get better chances of getting asylum.
So basically :
Water - reduce reaction
Xenon-135 - reduce reaction
Boron - reduce reaction
Graphite - Increase reaction
Steam - increase reaction
there has to be a balance of above elements. First the balance was in favour of reducing elements resulting in significant reduction of power then the operators tried to increase power but it increased too much. They tried to stop the reactor with AZ5 button which was supposed to insert boron rods but these boron rods had graphite tips resulting in explosion.
I too watched Chernobyl
No, not graphite tips. 4.5 meter long displacers of graphite that functioned to accelerate the reaction and they are never withdrawn from the reactor. When fully withdrawn the graphite is centered in the 7 m tall reactor.
Thanks, that explained the mechanics behind the disaster as best as I have seen, I only have one year of Uni Physics under my beltfrom 30 years ago , but alot of the concepts came back easily from your clear explanations.
An absolutely excellent video, thanks. It's great to hear someone talk about nuclear power without obvious bias.
why, until now you've listed only to explanations from wind turbines?
I love how men say things are impossible.
Titanic people: "This ship can't sink - Why? It's DESIGNED not to.
Iceberg: "Hold my beer."
Chernobyl ppl: This reactor cannot explode! It's all in the DESIGN.
Proceed to ignore all the failsafes and control mechanisms of the DESIGN
: Oh shit it exploded.
As long as people made it - shit is gonna break and go wrong.
You ain't never lied.
"What is the cost of lies?"
@@jaywalk1n The explosion of an RMBK reactor
@@jaywalk1n lies or lives? Fine line as to what those in people were referring to.
Well, we are all living in denial everyday to some extent or we can't function. You need to take context into consideration and how TV shows need to dramatize to make the narrative flows.
I was an infantry soldier in the US Army from 75 to 79 and went to college on the US GI Bill. I had a hard time with Math and English at first as most students do. When I got to the end of my second year I had to take Physics. When the Instructor asked the question, "If you shot a projectile out of a cannon at this velocity and the cannon was at this angle; how far would the projectile go?" Without thinking I blurted out aloud, "That is the 4.2 Mortar Table calculations." No one in the room even understood what I was saying. However, it was the first time in 2 plus years of math that everything came together. At that point, the instruction asked me to come up and give a short class on the Four Duce Mortar and how we in the Army calculate and shoot mortars accurately. I totally loved Physics. I look back and wish I had changed my degree from Biology to Physics. Physics to me even today 40 years later opened the entire world to me.
So thank you for your channel. I spent from 75 to 2003 in the Army as an enlisted Infantry Sergeant to an Airborne Infantry field grade officer and loved my job. However, looking back I would have really enjoyed life in Physics.
Our instructor in physics was so great to help open the entire world and how it works. You are doing the same for another generation.
Allen Shisler, President Access International Solutions and can be found on LinkedIn and Facebook.
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Thanks so much for this clear and understandable explanation!
I also really hope that shows like Chernobyl (and to some extent also Dark) don't serve as a deterrent against nuclear power. If anything, the deep dive into why it all went wrong should prove exactly why nuclear power is actually incredibly safe as long as you're not being stupid around it. It should show how much had to go wrong for this to happen, and how unlikely such an event is.
Besides, it's been over 35 years, do people really expect that we've learned nothing about nuclear power in 35 years? I'd like to remind them that smartphones didn't exist until the 2000's and that the internet didn't even exist for regular people when Chernobyl exploded. And now we can charge our phones wirelessly, we've got electric cars, we've got machines in our pockets that are hundreds of thousands times more powerful than the rocket used to land people on the moon... so using Chernobyl as an argument against nuclear power just makes no sense in any possible regard.
It's much more useful to argue financial reasons, whether they can be built quickly enough, how long it takes to earn back the construction cost, etc. etc.
I think it's navjan13's explanation that summarizes this complex video for me:
Water - reduce reaction
Xenon-135 - reduce reaction
Boron - reduce reaction
Graphite - Increase reaction
Steam - increase reaction
But this video has made me more terrified of nuclear power than I was before because this was, in essence, a coolant flow failure that was actually enhanced by the scram emergency shutdown.
You talk about charging our phones wirelessly. How did the Samsung Galaxy Note 7 arrive in the hands of customers with such an unstable battery?
How did the Boeing 747 MAX make it into the hands of pilots with a safety-critical MCAS system that took its readings from only one sensor?
There will be stupid people.
Different things advance at different rates. The reactors that the West uses are much safer than the Soviet RBMK reactors, but you can hardly claim that they have advanced in the same way as consumer electronic devices when their development has been largely frozen (in the developed world, at least) for several decades.
My actual problem with nuclear powerplants is that they become too big to fail projects for both the utility companies, local politicians, and the regulatory bodies. One needs to only needs to look at the Davis-Besse Nuclear powerplant (pretty much a clownshow of near misses) to see that nobody wants to kill the golden goose... In fact, nobody wanted to stop the golden goose from laying eggs long enough to do preventative maintenance to stop a football sized hole from corroding 6 inches into the golden goose's reactor head (3/8" from a 2002 version of 3 mile Island. Yay!) or shut down the powerplant because the people operating it were untrustworthy. Then two decades later, the golden goose wasn't looking so profitable so its owners decided to bribe the State legislature of Ohio to give the Golden Goose a $150 million/year subsidy.
As much as I love 'space stuff' I think your nuclear series is the best thing on youtube. Always l.ove watching these. Great video!
Hey Scott - long time fan. Thank you for this - I've read multiple explanations of the disaster going into Xenon poisoning, the "graphite tipped" control rods, and the positive void coefficient, and yours is perhaps the easiest to grasp out of what I've encountered thus far. Especially the explanation of WHY the control rods had graphite present (I've always scratched my head at that, wondering why you would put a neutron moderator that could conceivably accelerate the reaction at the tip of the control rod - didn't occur to me that it's more accurate to say that they were at the bottom of the rod and already in the reactor, just not the full length of the control rod channel).
Same, it was actually just like a light switch
It didn't explode, you're in shock.
Get him to the infirmary, he is delusional.
3.6 Roentgen, not great but not fucking horrifying
@Ghostrangerz So if you're overdue for your annual checkup...
skreef geore it’s not the equivalent of a single Chest x Ray, actually it’s closer to 400 chest X-rays
Fact: Beagles Are Best You’ve been around the feed water all night
Excellent, clear explanation of what happened at Chernobyl. Thank you.
Thank you for taking a moment to talk with us about this tragedy. Very informative.
Everybody in the comment section quoting Dyatlov‘ words in all these nuclear disaster videos is killing me lol
Your comment is equivalent to one chest X-ray
I fucking love you 😂😂
What disaster? I was in the toilet
Your delusional! Get to the infirmary!!
idontcare9797 one chest x-ray, not great not terrible
300Gigawatt?! Thats almost 258 time travels!
Great Scott!
Thomas Richter
“Jiga Watts!” :)
Whoa, that's heavy.
@@LisaBowers Weight has nothing to do with it.
@@thomasesr Lol! 😄
This is for sure the most detailed spoiler I have ever had.
Good, now I know how a nuclear reactor works.
*makes reactor at home*
Global notice feed: "Man made nuclear reator at home, but lost control of it, exploding his house and injuring the entire neighborhood, leaving it uninhabitable for the next millennium"
No joke, one kid created nuclear reactor in his barn x)
EDIT. I found the wiki page wiki/David_Hahn
I love how Boris was eager to learn
@@marcing115 No he didn't. The media sensationalized that story as usual. It wasn't a nuclear reactor. The wiki article you mention even says this.
@@ryrin6091 my bad
But still... radioactive materials
the "elephant foot" mass at the bottom of the structure was so radioactive back in 1986 that a fatal dose of radiation was reached in about 3 minutes. as of 2020 (34 years later), a fatal dose takes about 3 hours.
You are right, as I know....
That’s actually a lot better than I would have assumed.
The great thing about quantum physics is that even seconds are a lifetime too slow.
Probably the most terrifying part , life can change in the blink of an eye anywhere though doesn't take a nuclear weapon
@@travislindsey7256 One second, you're alive and well. The next, you could be instantly dead or permanently changed....
I’ve always wondered why we experience time at the rate we do:
Time is ofc relative, but we experience a second as a second (shocking I know), but imagine how our lives/evolution and world would be if we experienced time at a faster or slower rate.
Like in what we would call slow motion, would it be relatively tedious?
Or would we be on here now imagining if we experienced time faster (our “speed”) and how confusing and crazy it would seem.
Ofc we’d evolve and adapt to it (as we have now) but a mayfly only lives a day, does it see us in slow motion? If a tree could perceive would we seem to be in time lapse?
@@Duros360 I don't quote concrete science, but I would say that we are as fast as we need to be.
A mosquito react faster than us because all the neuron inside them was built for a single purpose of dodging and sucking blood. For a much bigger animals like whales and elephant, they're slower because law of physics dictate that moving that amount of mass will meet that amount of resistance, even if the electrical pulse in their brain moves at the same speed as the mosquito.
So the only way to 'speed it' is to have different impulses happening at the same time, and I think this is where the concept 'human time' came to be.
We were at a form that we're slow enough to adjust with the day-night cycle of the universe, and fast enough that we can react to environmental danger big and small. And i think that in this form, we realize there are still excess spaces that we can put more neurons into our brains, without going over the optimized physical limit of our mass to function in nature. And with those extra brain cells, we can analyze the environment in a way that would further increase our survivability.
And in that evolution of intelligence, we learn to 'perceive' time.
Because time IS relative, not just physical, but also mentally. We feel time flies when we're having fun, and time stagnate when we have to wait for someone. Our perception of time is slower when we're awake, because we have to take in and process our sensory input and mental reasoning all at the same time; while we can ignore all that in a dream and let the neurons flow freely, randomly, which make our perception of time faster.
Meanwhile, our internal system that dictate the speed of our heart, our cardiac rhythm, our food energy process, we can't perceive it. So maybe, it's only true intelligent that can perceive time. For every other living things, time is simply not perceivable.
Like only our phones and computers can see the wifi signal, our brain reasoning is the sensor that help us see time. Since there are no other race with human level of intelligence, we can't be sure if time perception can be differently. But personally I believe that once they can perceive time, they would become similar to us.
A creature that can perceive time fast or slow to adapt to the situation.
Like a country person moving to live in a city.
@@Duros360 It was quite an essay, but it's because your question was what I once think really hard about.
In a natural world, we dont have these natural radiation that kills us immediately when a thing goes wrong. We don't have bullet that can end us in a flash. So we simply hasn't evolved our time perception to handle these kinds of manmade danger.
Yet, I do think our perception of time is accelerating. Kids these days have ADHD from interacting early with the internet. It results from the fact that this speed doesn't correspond to real life, they're used to handle too much information in a short time that when they don't have anything to process, they become absent-minded and hyperactive. It's not a bad thing, but in the future, our society lifestyle will definitely change to account for this.
Time perception is as important, if not also the same thing, as our reason to be alive.
I’ve heard a lot of Chernobyl meltdown explanations but, yours is by far the clearest and most informative I’ve heard!
*"If it can't happen then it didn't happen"* -Comrade Dyatlov 1986
In fact, in the first minutes Dyatvlov couldn't believe what had happened, but then he heroically took part in the aftermath of the catostroph. I think to blacken a person that much is simply unfair.
Just wanted to share my thoughts.
@@vgeniirshf8913 Interesting, thanks for sharing.
@@vgeniirshf8913 One of my problems with the show is the disservice they do to all key people involved in Chernobyl. They come across as wilfully ignorant or just cartoonishly evil
Dimitri Khalezov 2005
B/c aluminum won't cut steel under such conditions.
@@vgeniirshf8913 Yeah, I was telling myself the whole time that he couldn't have been such an incompetent arogant ass as portrayed in the series, but then, most people probably wouldn't find the show as amusing, if all characters traits had not been exaggerated, so that it was easier to build sympathy or antipathy towards them.
Great presentation, thou to little stress on the fact that reactor design (it's large diameter) and fission cycles were optimized for producing weapon grade plutonium 238. Other Pu isotopes are useless (for nuclear weapon). There's no way to enrich plutonium, so you must get the "right" isotope from the reaction itself. RMBK was a plutonium machine pretending to be civilian power reactor.
Lots of the early reactors were used to produce plutonium, some were only used for this including windscale in the UK.
Pu 238 is for RTGs Pu 239 is for weapons.
@@JNelson_ you beat me to the punch
Which is why RBMK could be found only in the USSR and lot of operating principles were kept secret from the personnel.
I'm native russian speaker. DAT PRONUNCIATION! Almost nailed it! High five!
Да, дядька жжот
He's Scottish, and it's notable that Russian parts in Hollywood movies are often taken by Scottish actors, google Robbie Coltrane, David McCallum, and many Scottish luvvie stalwarts if you don't believe, we do accents with aplomb.
~17:00-18:00 is not quite correct.
When they attempted to emergency reinsert the rods, there was so much steam forming that it introduce an unplanned pressure on the graffite rods. More pressure than the rods could handle, this actually broke some of the rods. The pieces of the graffite rods got stuck in the channels, preventing farther insertion of some of the control rods. The graffite which was stuck continued to enhance the reaction. The reaction was producing more steam, until the pressure became so high, the whole thing blew up.
Bringing the reactor to an unsafe state and then carelessly proceeding to running a dangerous test has become one of the worst human errors in human history.
This was absolutely fascinating. Thank you for explaining this without it seeming “dumbed down”.
Scott must have really enjoyed this topic. He's glowing.
no, I think thats from the 3.6 roentgen...
Not great, but not terrible
I'm green with envy. 😉
Don't worry, it's just the Cherenkov effect.
He's radiating science.
Mans face is melting off from radiation
Russians: You're being hysterical, go sit down!
That's just a cold to the Russians
It's just from the feed water, he'll be fine.
When in reality only 28 people died from acute radiation syndrome in Chernobyl which is believe it or not a fairly low number considering how much fear mongering this event had. Purely statistically speaking there are more deaths occurring in wind farm maintenance than nuclear reactors, including Chernobyl and Fukushima. So yeah, people are being hysterical and should stop spreading misinformation.
@bobwatters As much as I support the USSR and its ideology, I disagree with the man above because he has completely disregarded the causes of cancer regarding the radiation from the accident which was up to 30,000
I feel if I don't reply you will think that I have no explanation but if I explain you might argue against the points with no evidence. So before I explain, I'll like to ask, will you allow me to explain without argument?
I was US Navy nuclear trained on an aircraft carrier. We use pressurized water reactors that have a negative temperature coefficient of reactivity which basically means that if a runaway fission reaction starts then as the water heats up it will actually slow the reaction down. Inherent safety built in there (on top on numerous other ways) and is why the US Navy hasn't had a nuclear accident in over 50 years since we learned how to be safe despite operating hundreds of reactors in that time. This reactor had a positive temperature coefficient of reactivity which is a huge safety risk but leave it to the Ruskies to take that risk. Pretty crazy to be honest.
Great explanation, I was just looking for a explanation of what happen to Chernobyl. Thanks Scott!
Nothing happened, it was only a measly 3.6 roentgens. Not great, but not that bad either.