Can we stop quoting that fucking show? The show that perpetuated lies about the operators, lies about Soviet officials, and even lies about radioactivity despite the supposed central message?
@@kisaragi-hiu Well the fact of the matter is that is the propaganda the communists were pushing is that the RBMK was so good it couldn't explode. That saying wasn't created for, or by, the show.
@EvilTIMMEH Okay so the hole forming in the bottom of the reactor isn't a problem like it forming in the top when the steam blew the lid off? The steam blows the top off, the melt down literally melts the floor of the reactor. Either way you've now got a giant hole in the reactor and a hydrogen explosion. Almost like what happened at Fukushima.
@@Xershade Also worse as the bubbler pools where under the reactor. So congrats the top doesnt blow off but depending on meltdown pace it may cause to quote Homyuk "A significant thermal explosion".
Imagine you are fighting a fire, the fire is getting out of control and you hit a button to turn on the sprinkler system to stop the fire. Except the first thing out of the Sprinklers is gasoline, then water. That is exactly how those graphite tipped control rods reacted.
Kinda, the graphite itself did not boost the reaction much, it was there to displace the water. The problem is in that circumstance, the water split into hydrogen and oxygen, oxygen being able to light and hydrogen being explosive. Normally that would be fine but there was too much pressure in the core due to the operators pushing the machine to far. The whole thing was designed for normal problems and not worst case scenarios.
The 1.5m long graphite "tips" really should have reached all the way down. For maximum effectiveness and no positive scram effect. Bit late now though 😞
@@TylerParis-qk7ywThere's evidence of the reactor going prompt critical in two locations immediately before the big explosion. The displacers are a good idea, but as is the case with most of communism - the implementation was somewhat lacking. In this particular case, the problem was that they did not reach all the way down the channel with the rods fully withdrawn. This means that there's water under them which takes away reactivity. When the reactor is already in an unstable state and reactivity is too high in areas where there's water in the channels, it is inevitable for graphite to pass through those areas first, before the boron rods make their way there. Unfortunately that leads to a spike in reactivity, in an area which is already exceeding safe limits. Had the implementation been such that the displacers permitted no water at all in the channels, this dangerous level of reactivity would have been reached sooner, perhaps preventing the withdrawal of so many control rods and prompting action from the operators sooner in order to shut it all down. Or it would have happened too quickly and blown up anyway, we'll never know. What definitely wouldn't have happened in that case though, is the positive scram effect which is widely regarded as the trigger of the big explosion. Whichever way we look at it, it's a shit reactor. They never should have built it. And if they hadn't, the whole planet might have been nuclear powered by the '90s.
It will blowup eventually. The AZ5 button was a fatal flawed design. Any scenario that triggered them to emergency scram the reactor will cause it to detonate.
They weren't goofing off. They were running a safety test that was supposed to be done prior to the reactor being certified but the Soviets rushed the reactor into service before it was ready. This safety test unknowingly triggered a critical design flaw in the reactor.
In my opinion, the reactor was lost when the control rods were raised too high to break the xenon poisoning in the core. The use of AZ-5 only made the situation worse. Failure was already inevitable. Interesting and good video.
Exactly. The reactor was in a state that was unrecoverable by any means they had at hand a minute or so before the power surge and explosion. Or maybe, and only really maybe IF they knew the real situation of the reactor with its design flaws, taking into consideration the critical reactivity margin they had as well as the violation of operational procedures they made in order to do the test, they could prevent an explosion by "flooding" the core with "cold" feed-water before the start of the test (thus invalidating it and shutting down the reactor for a longer time) and only after the reactivity dropped below critical inserted the control rods and eventually the scram rods, would they save the reactor from exploding. But this is pure hypothetical situation and they had absolutely no reasons to do what I just described. They wanted to do the test and did everything they could to run it. The test should not have been made. Once the power dropped practically to zero a few minutes before the test, it was clear that it made no sense anymore, especially since they managed to rise power only to about 200 MWt. Which itself is quite impressive considering the Xenon poisoning and burn-up of the fuel rods. The reactor running at 200 MWt was in a very unpredictable state. Maybe my speculation would have not worked anyway and the reactor would experience a power surge. Maybe it would not blow up, but it would certainly cause massive damage to the core, maybe even so as making the reactor inoperable after that. Like what happened at Bohunice A-1 in 1979. The incident was caused by different reasons, but the result might have been similar - melted fuel assemblies, contaminated primary and secondary loop (the RBMK has no secondary loop) and a "bricked" core that only can be written off and eventually dismantled (after decades). Chernobyl would have remained an INES-4 or maybe INES-5 incident, if judged by the IAEA scale introcued in 1991. The question is, if a far worse accident would have not happened on another RBMK design, since it would have been covered up by the soviets and no lessons would have been learned.
Well even if we consider not pressing AZ5, then as well as mentioned would not have made much of a difference. The reactor was much lost when toptunov withdrew almost all rods from the rector. The root of the problem is AZ5 and the reactivity of low grade uranium. Toptunov shld have rather scrapped the test and rather shut down.
Wasn't all of the reserve water already hot? IIRC that's why so much of it started boiling in the first place, they had activated all the extra tanks when trying to reduce power output for the test. And because there was so much water in the loop it was getting pushed back to the reactor after barely falling below boiling.
So to summarize - essentially, to "save" Chernobyl at that point, they would have had to undertake a dedicated series of very rapid, very unintuitive actions - they would have to disable the automatic scram system altogether, they would have to inject cold water to bring reactivity down, and start inserting control rods "slowly" (compared to the scram at least) one bank at a time. In other words, do exactly the set of actions that would destroy literally any other reactor in the world other than an RBMK. That's exactly the kind of thing that they COULD have been TRAINED to do, but nobody in their right mind would ever do unless they were trained. If lessons had been learned from the Leningrad accident, and crews had been trained on an emergency procedure to manage positive scram reactivity, it might have been possible to minimize the damage at Chernobyl, but yeah... that would have required the Soviet Union to admit a flaw in its design and that was never going to happen.
@spazmonkey2131 I imagine it would depend upon the kind of reactor. There are a lot more designs than just the RBMK after all. Of course, the only reason AZ-5 didn't work here was because of the design flaws of the RBMK reactor. Flaws I think (desperately hope) other reactors don't suffer from.
Thank you for another well-done video. There may be one (little known) reason why the guys in Canada did their own report quite quickly after the accident; their own CANDU reactors. The CANDU, like the RBMK, is a pressure tube reactor. It even shares a special characteristic with the RBMK, the positive void coefficient. After the accident, they may have wanted to find out if they would run the risk of a possible similar accident in certain scenarios. However, the CANDU is very well-built, with full containment, a lot of redundancy and two separate safety systems that can independently, _and_ without power or operator intervention, shut the reactor down within 2 seconds flat.
@@markusw7833 Oh, but it does. Look it up. It is the main reason CANDUs have a hard time being licensed in the USA because the US does not allow any reactor design with a positive void coefficient to operate in the States.
@@markusw7833 You're correct. I misread. But the US still is heavily biased against allowing the CANDU because of the positive void coefficient. *Needs new reading glasses.
Candu and IPHWRs are actually well built heavy water reactors. BWRs are also good as they use water as a moderator and an absorber. But it's not as correct to say that the RBMK was not as good. The power output is well enough and it's still being used at kursk and smolensk.
Hindsight is 20/20, but without having such knowledge, the operators might have been in big trouble if they didn't press the AZ-5 button. It's like Titanic would have been saved if they had crashed the ship head first into the iceberg, but it would have looked like incompetent operation, and the crew probably would never sail a ship ever again. Society is funny like that. Instead of doing the safe thing and crash the ship head first into the iceberg, we do all we can to not cause any damage to the ship gambling that it will pay off even if the odds are stacked against you.
I get your point, if you cause something bad in order to maybe prevent something worse, you have the problem to prove that something worse would have happened. Concerning titanic there was a risk to damage too many compartments anyway by unterwater ice right in front of it and/or by causing the iceberg to rotate and cause unforeseeable patterns of damage. Maybe it would have saved the ship, maybe it would have sunk way faster with up to 100% casualties. However an interesting tradeoff.
@@franknachname730 That was hardly the trade-off they thought about: Firstly judging distances at night is very hard, so they had the right to assume that they would pass it (which they nearly did). Secondly the side extension of the submerged part of a berg at night cannot be estimated, even less so when its waterline cannot be seen, as no waves were breaking at its base in that very calm night. Thirdly a head - on collision would cause massive damage (they were at 21 knots), like the chimneys coming down, machinery being torn out of its sockets etc. In reality they hit the berg so gently, that they did not bounce off, nor was their forward momentum impaired. As a result 6 main compartments were sliced open. If it was 1 compartment less the ship might have been saved, or at least kept afloat for many more hours in that very calm night. So any other impact - a harder one and even a head-on one would be preferable to that smooth and long slicing, which given the information they had, was extremely unlikely. Hence in my opinion they made the right decision.
@@nehorlavazapalka you dont know about how ships are built. The front would crumple & maybe the 1st water tight compartment floods, but it gets to New York. This happens to lots of ships.
@@andy99ish I don't think they considered that either and i don't blame them for it because as you say, they couldn't have known. But theoretically I find the question interesting. I'm not completely sure about the damage behind the bow you mentioned since the ship would slow down a bit until impact and the forward compartments would have acted as a crumple zone to spread the impact over several seconds. Did other ships that hit icebergs head on with similar speed suffer that damage? (assume similar mass relations) On the other hand the iceberg more likely might have turned
I've heard it said that in order for a modern nuclear reactor to blow up like Chernobyl's did, someone would have to be in the control room *actively trying* to make it explode. It sounds to me like, in the case of Chernobyl, to have kept the reactor from exploding, someone would have had to have been in the control room actively trying to make it *not* explode.
To quote the english translation of the 1993 report, "The Commission considers that the negative properties of this type of reactor are likely to predetermine the inevitability of emergency situations"
Thank you again for doing our homework for us! This is a great channel. It amazes me how many people are so fascinated with the Chernobyl accident. It amazes me more that we have a few people who are covering it today. 3 channels that cover different aspects of the accident. All are fantastic in their own way. You are the one who covers all of the technical aspects of what happened that night. Personally, I am very thankful for you and your work. I stand amazed at your understanding of the accident and how you help some of us to understand that night a little better. The "what if's" are even more important here. Knowing that the explosion would have most likely happened anyway no matter what. Thank you for your work! You are appreciated.
they had a better one, the pressurized water reactor family VVER. Now RBMK was much easier to build and cheaper, so they went with THAT design. Still, it is amazing, that they kept the remaining twenty RBMK reactors running - without them blowing up into pieces. Wikipedia says they decreased the positive void coefficient by modifying the fuel rods by means of 'increasing the enrichment requirements of the uranium fuel in the fuel rods' (very enigmatic phrase). Also the control rods are said to have been modified, go figure. In the end they always blame some poor operator like Toptunov, who was not aware of the design deficiencies, because they were state secrets. On the other side of the pond it is some Homer Simpson guy, who gets blamed...
@@XtreeM_FaiL No, the reactor didn't work fine, that was literally the point of hiding the inner workings of the graphite displacers on the control rods from everyone. Other plants had channel ruptures when shutting down before this happened. The only difference was those reactors weren't in a state where they were about to fail catastrophically.
This is actually a really interesting topic to explore. I've often wondered whether the die was cast long before the SCRAM function was initiated, or if there could have been a way to gradually reduce reactivity and slow down to a safe stop.
If they hadn’t pressed AZ-5 then likely the worst that would’ve happened would’ve been a reactor meltdown, not an explosion. The main reason the reactor exploded was the immense pressure created by the steam, so if they had kept the valves closed then the reactor likely wouldn’t have exploded.. at least not in a nuclear explosion because the Chernobyl reactor had a positive coefficient.
No, it would only take more time to explode. The xenon was already in the reactor and the reactor could not be switched off as lowering the control rods was the same as pressing AZ5, therefore it would only take more time but have the same effect, the error was rising the control rods before. But a engineer or someone with more knowledge can explain this better probably.
@@midelro97Xenon doesn’t raise reactivity, it lowers it. The control rods could have been inserted a few at a time, because they are graphite tipped, which raises reactivity, but made of boron higher up, which lowers reactivity. The few control rods being inserted would have raised reactivity initially, due to the graphite, but would work against the reactivity as soon as they were fully inserted. This could continue going on, inserting a few at a time, until as many could be inserted as possible. The point the speaker in the video was making that the reactor was already going to sustain some damage, as the reactivity was on the rise and would have risen to the point of causing damage to the fuel and some control rod channels. However, the cause of the explosion was hitting AZ-5, or inserting all the control rods at once. All those graphite tips entering the reactor at once skyrockets the reactivity, ruptures the fuel and control rod channels and locks the control rods in place, preventing them from being fully inserted so that the boron portion of the control rods could work to reduce the reactivity and temperature. The other point the speaker made is that there were systems present that would have SCRAMed the reactor even if AZ-5 had not been pressed, and so the effect and result would have been the same. I’m not sure if it would have even been possible for the operators to have overridden these systems, but if they had been able to insert the control rods a few at a time, the reactor would have escaped with damage and ruined fuel, not the catastrophic explosion that occurred.
@@midelro97 Xenon lowers reactivity, it does not raise it. If the operators were able to lower control rods into the reactor a few at a time, the graphite tips would have raised reactivity briefly, but the boron higher up in the control rods would have been able to enter the reactor and work to lower the reactivity as a whole. Over time, the boron control rods entering the reactor would have prevented the total meltdown that occurred. For sure, damage was inevitable, but nothing like what happened that day.
My understanding is if the control rods were designed to "slam home" when AZ-5 was pressed (vs. operating at "servo speed"), an explosion _might_ have been averted. As far as the explosion being caused by the graphite tips (which is what you're asking), I think they passed the point of no return a while back.
maaaaybe but idk my understanding is the 'drop' or 'slam home' (which they did implement after this) gets the insertion time down to 11 or 12 seconds vs 18-20, but that still seems too long when the graphite is starting to molt and shafts are getting distorted or splitting open... I don't understand why they didn't start the water flowing again before that
@@prismpyre7653 They literally had all main circulation pumps going and the reactor had a very high total flow rate, which is supposed to have contributed to the incident.
@@prismpyre7653 After the 1986 accident, they have given the remaining RBMKs an additional, fast-acting SCRAM system called BAZ (Быстродействующая = Fast-acting, Аварийная = Emergency, Защита = Protection) that can insert 24 special control rods fully into the core in under 2.4 seconds or 7 seconds, depending on the signal sent. These control rods are gas-driven, their channels are cooled by a waterfilm, and they're Boron only. No graphite displacers allowed. They will pull reactivity down by at least -2 β-effective. When an RBMK is scrammed today, this system will go first. After that, the rest of the normal system follows.
When you're talking about a prompt critical excursion, as happened at Chernobyl Unit 4, one second, ten seconds, eighteen seconds doesn't really matter, the reactivity spiked so hard and so fast that even if you "slammed home" the rods, the fuel channels would have still ruptured and jammed a bunch of control rods with graphite moderator still stuck in the lower half of the core. I had a bunch of other stuff below here, but a nuclear fission event happens in 1 "shake" (it is a real term in nuclear physics, it's about 10 nanoseconds, or 10^-18 seconds. An entire chain reaction that blows apart a nuclear bomb is completed in 50 shakes, or 500 billionths of one second. As soon as the reactor reached one dollar of reactivity, or the point where there's enough free neutrons to self-sustain the reaction, that was it, it's over, *boom*. For another fun little tidbit, the amount of uranium-235 fissioned in the Little Boy bomb that blew up over Hiroshima amounted to about 7/10ths of a gram of U-235. The energy from that tiny amount of fissile material was enough to level the city, and the entire reaction happened 500,000 times in the amount of time it took you to realize there's a period at the end of this sentence. Chernobyl was not a nuclear explosion, or anything like it, but the chain reaction and the steam explosion of the reactor happened on the same timescale.
After learning everything i could about this disaster over 10 years. I think there was only one possible way to save the reactor. They would've had to resist the urge to press AZ-5 and instead slowly start reintroducing control rods a dozen or so at a time. Because at that point in the evening the reactor was at its limit. You can't make huge changes to a system under that much strain, it will fail. You have to slowly and carefully walk it back from the edge of disaster first.
They did everything right, the problem was AZ-5 had a "surprise". In any normal system "oh shit" button should stop everything, instead of "stop everything except for accelerate everything in some situation".
Or they could not have broken numerous rules and as a result not ended up in the situation in the first place. Without knowing the issue with AZ-5 there was no reason for them to try anything else.
The problem with this is that the button was sold exactly for this kind of "oh shit" situation - I guess no one would permit nuclear reactor operation without "yes we have a button which will save everyone"
Problem is that the procedures stated to press that button in that exact situation and it was supposed to be a fail safe. None of them knew of the fatal flaw
I read Dyatlov book about what has happenned over there, but the most important thing is AZ-5 portrayal. AZ-5 was not "Oh shit button", but normal turn off switch that was not plumbed and that you use to shut down reactor at normal condition too. In the series they show that there was dense atmosphere, but Dyatlov as a proof kept mails from the people that worked with him that day. Those mails opposed what was being shown in the HBO series. The amosphere was calm and in control. The only reason why the reactor blew was that the government has HIDDEN THE REASON why the crew had to keep more control rods in the reactor despite of what operation manuals stated after the reactors were turned hot. Also, there is a reason why Dyatlov was released after being just 3 years in the prison. He knew, that they knew that he knew and that's why, despide deaths of thousands or hundreds of thousands of people he was free not long after. The party would not want to create a precendence within nuclear engineering society in which operators are being to blame for what was beyond their control, because not much people would like risk it all. Also he described Legasov as government dog that in fact had no competence to judge him (he had bad general knowledge that was not focused in nuclear engineering- he was a chemist) and also Legasov followed the general narrative presented by the party members. Dyatlov was sentenced even before the trial started. Designers of the reactors did not bare the consequences. The best example of that happened in viena where Legasov presented UPDATED manuals, which were released AFTER the accident occured! They kept old manuals hidden.
I have my doubts about all the negative portrayal of Dyatlov in the common narrative. I do believe he was scape goated and railroaded. All of this could have been avoided had the US been open about their own accident with a graphite control rods back a decade or two before this happened too. The US hid it until the 90s and there is still very little written about it despite it being acknowledged. One book that claims to cover every major nuclear accident doesn't even mention it. The clean up is still incomplete and the impact still relatively unknown to the public.
By the time they pressed AZ5 it was already too late. They might have saved it shortly before that by inserting the shorter control rods from the bottom, where the reaction was running out of hand. They didn't have the graphite displacers and could conceivably have slowed things down enough for the main control rods to be lowered a few at time. Of course, shortly before that they could have just not pulled them all out in the first place.
When the button was pushed, the reactor was already highly unstable and experiencing a runaway power excursion. It takes several seconds to insert the control rods (20 seconds to be fully inserted), and it may have been headed to an uncontrollable explosion without regard to pushing the AZ-5 button.
A significant majority of those control rods were already withdrawn before the power drop; it was quite normal for RBMKs to operate in that position :)
@@thatchernobylguy2915 I am sure someone if not everyone in the room that night would've been well aware of the Xenon poisoning that pretty much doomed the test and the reactor from the start.
@@sonicnarcotic. Actually, the person to first start raising the power, Yuri Tregub, was well aware of the xenon pit and did not believe that it mattered. It didn't anyway, because the test could be conducted at any level of power so long as the turbine ran at full speed - 700MW was just an arbitrary number in case other experiments had to be done.
Thank you very much for the great video. I would also like to thank the many commenters for being sophisticated and very scientific. Both the video and the comment section were very entertaining and informative. Thanks.
This reactor would not stabilise. It was badly kicked out of stability by the crew under Diatlov. First they pumped the cold water. Than reactor almost shut down, with power being close to 0, which prompted Diatlov to call for raise of all control rods. Then only a couple of the rods remained inserted, meaning there was almost nothing to catch the neutrons and keep the reaction at value. So, the reactor fell to almost 0, then was raised with almost no brakes. Although I am a noob in nuclear science, I doubt that it would stabilise itself. But when AZ-5 was pressed, all the rods entered their channels at the same time, creating something similar to a spark in a plug. A sudden increase in reactivity, before shutting it down. In conclusion to this yapping, I agree, not pressing AZ-5 would have saved Chernobyl, IF the crew would connect the diesels and started entering the rods in small batches. However, with Diatlov's hot-mind, not the best training of the crew and not safe building (the rest of the reactors were built by Soviet standards with heat-proof materials, but the 4th one wasn't), I doubt that they would pull it off.
I had exposure to the radiation from Chernobyl when the US wanted to make a show of force in Germany. We were out marching in the rain consisting of the fallout from Chernobyl on May 1st 1986. The result is that I have a nodule on my thyroid as well as lesions on my head, neck and shoulders. The biopsy revealed that it is consistent with exposure to radiation. This happened in Regan’s peacetime Army. I’m being treated for it now. There are probably more people suffering from this same exposure. I was literally singing, “I’m a Radioactive” at the time. ☢️
Can you do a video that shows which things they did that was part of the test procedures and what was improvised? I'm still a little confused on what actually happened. I blame HBO and Medvedev's book. Once I heard you say that was inaccurate I ordered Chernobyl: A Documentary Story on your recommendedation. Thanks as always for the great video, this answered the question I had about if it really was the AZ-5 button that was the final nail in the coffin.
All this is a replication of the Soviet lie about the causes of the accident. If you want to know the truth, watch: HOW THE 4th UNIT OF CHERNOBYL NPP WAS BLOWN UP. (KS channel)
Hello Sir. Again an example for how good your videos are and how well you’ve made your investigation into the incident. Please go on doing such great work. Greetings from Germany 🇩🇪
They would have had a loss of coolant event instead. They didn't have any procedure outside of SCRAMing the reactor, so they didn't have time to think it over. The excursion at Stalingrad gave them a hint at what would happen if things got out of control. So it should have been broadcast to the other RBMK operators NOT to let it get into a low power state.
Utterly outstanding - I never knew anything of us, which all makes perfect sense - seems obvious now that the Soviet version of events would be lies. The various temperature coefficients and voids in the cooling water say it all. I get it it might have scrammed anyway and I see now how AZ5 might have saved it - you’ve taught me much tonight, am so grateful to you. Look fwd to more of your vids!!! Thanks again!! Bravo!! Adrian in Bermuda 😊😊😊😊😊
AZ5 was a detonator, not a shutdown Tips of boron rods were made of graphite that induced enough reactivity for an explosion. If they didn't press the button, the active zone would rupture due to tremendous heat and pressure that would result in a meltdown, not an explosion. There would still be consequences like a white hot radioactive magma made of reactor fuel, graphite and concrete that they need to solve to prevent it from seeping into the groundwaters but the grand scale of the disaster would have been tens of times lower
What if when someone who realised xenonpoisoning, had forced some person/s out of the room for about 24 hours in order to get that thing BACK under control?
What I want to know is, when the reactor crashed before the test, if, rather than withdrawing the control rods entirely, the technicians had removed them partially to put the graphite tips in place, could they have brought the reactor up to power in a stable enough way to perform the test?
The graphite tips are in place when the control rods are withdrawn. The "tips" are a chunk of graphite that is about 2/3 the size of the control rod and they're there to displace the water in the channel so the entire control rod channel doesn't fill with water. The reactor was dead, you don't start a reactor in a Xenon pit for very good reasons, as everyone there found out the hard way. The only way to bring it back up was to shut it down completely and reset it, which takes at least a full day.
Xenon, I tried simulation, it was perfect timing for test. Few minutes, maybe seconds before, there was not enough xenon to stall reactor. Few momments later and it would be stalled, no way to power surge to occure.
The automatic control rods did insert, and they consequently brought reactivity back down, without the manual rods. Power only started skyrocketing after AZ-5 was pressed. :)
But it's like reliance, As told in films. The truth was hidden from them, They were in the dark. For any operator of any kind the "Emergency Stop" is the last thing. It's the last ditch effort in a hope that the misery stops. It's like if the train hadn't pulled the emergency brake it wouldn't have derailed. But how can you predict that when a situation is going out of control rapidly the only thing that is meant to stop it will turn out disastrous. They were believed that "this" button will stop it. But that's the thing, the last button should've been made for the safest output.
Im more curious if the test "result" was the worst possible result, or if a significantly greater nuclear event would have occurred if this was done under an overload.
According to calculations by some scientists, the reactor output increased to 100 times its nominal output during the disaster. At the time of the explosion, the entire Soviet Union could have been supplied with electricity using reactor 4 alone. That was already extremely violent. But I can't tell you what would have happened at full load. Perhaps at full load the AZ-5 button would have prevented a catastrophe. During partial load there was a high proportion of xenon gas in the reactor. Without xenon gas in the reactor, nothing might have been unstable.
This is always what I've wondered- did they have a button, like an AZ-3, that would insert *some* of the rods all over the reactor? I would think the thing to do if you are aware of possible xenon poisoning and also that once you cut the water obvi reactivity will spike... I would think the thing to do is as soon as you release the turbine for the run-down test, you IMMEDIATELY switch water back on and start lowering SOME control rods, 25% at a time maybe.. (but I realize that they hadn't been made aware of the issue with the water-displacing tips causing a spike at the bottom of the reactor on insertion). I always wondered if they could have saved it if they didn't panic-- sometimes, accepting that you are going to be in *A* accident instead of trying to avoid it, lets you avert the worst-case scenario.
@@markusw7833 I prevented myself from crashing into the ditch on a freeway earlier this year by doing exactly what he is suggesting here. If I had panicked and tapped the break, the vehicle would have spun out of control on the icy road surface. I simply dropped the throttle and let the physics do the work for me. No accident involved by being smart and remaining calm.
@@erickolb8581 that's good stuff, glad it worked out for you! Staying calm & focused helps solve a lot of problems, for sure. However, I think your success handling that situation also required you to have the right knowledge, skill & instinct, all built from internalizing good lessons & having a decent amount of experience driving on slippery surfaces while paying good attention. Nobody at Chernobyl had the knowledge or instinct required to invent a new procedure on the spot. They thought AZ5 would put it into a good state. It's like if someone was scuba diving & their main air supply gave out so they switched to a backup supply, but that backup was contaminated w/ CO gas, killing them. A mad dash to the surface might've turned out better, but why try that if they didn't know the backup air was bad? Sometimes staying calm isn't enough.
High pressures force gases to become liquids again. If you, for example, took the lid off of the reactor while it was running, all that pressure would be released and the liquid would become gas :)
Ever heard cooking instructions that say you need to boil things longer at high altitude to cook them? It's because there is less air pressure at high altitude, and water boils at a lower temperature at a lower air pressure. The opposite happens at high pressure, so you can keep water from boiling by keeping it under high pressure.
Great video! I remember reading a translation of the Legasov tapes, where it was stated that the whole „test“ was allegedly just a cheap way to save money, as faster diesel generators were readily available. But the responsibles did not want to invest any additional money, do you know if that is really true? And do you by any chance know if better containment could have prevented the worst case scenario of an open reactor? From the tapes I only know that europeans insisted on additional safety precautions but unfortunately there was no detailed information on these precautions. Thanks a lot and good job!
I had always wondered, a little different scenario - if the rods were brought back in one at time vs all at once if it would have made any difference. I've also seen quite a few comments that the lower rods did not have the same positive void coefficient issues due to the lack of the graphite tips? So if they had been brought back in or been triggered by the AZ-5 (which I believe I saw was a later change) it could have also helped or prevented the incident?
At around 1:06 you mentioned that water enters the reactor at a temperature of around 265 degrees Celsius. I don't understand how this can be. I learned at school that water boils to steam at 100 degrees Celsius. Is there a mistake with the units; or am I missing something? Thanks very much for the interesting video.
Water has different boiling points depening on atmospheric pressure. The higher the pressure, the higher the boiling point and vice versa. 100C is the boiling point at 0 sea level.
Only possible save, and it would of been nearly impossible, would of been to flood the reactor with enough coolant tthat it was impossible to boil off. Then when reactivity reduced reinsert the control rods to get the reactor back under control. Again the key problem is with where the reactor was at that moment they would of likely had to turn the pumps on full blast, and I dont mean to whatever their operating level was but to the highest they would go without instantly breaking and flood the coolant channels. Also it was a split second decission and only one answer for that kind of quick thinking with how the reactor was designed, A-35.
I was totally unaware that the water entered already at over 2x the boiling point at ambient. I had always assumed the water entered much cooler and was rapidly heated instead of entering already extremely hot and heated just another 15c
I'd love to see a video where you explain what could still be done to save the reactor at each point in time where they made a mistake EDIT: NEVERMIND I found it in your playlist (What if You Were in Charge at Chernobyl?). ILY you're officially my favorite youtuber
Wasn’t the official operating procedure, that in the event of a low power situation, is that the reactor should be shut down, and then later restarted, with a very gentle and steady rise in power, until the reactor was stable?
Yes, that's the official operating procedure for literally all nuclear reactors in low power situations. You need to hard shutdown and let it reset for at least a day before even attempting to restart it.
So basically the reactor would have automatically done the same thing as pushing the AZ-5 button. But if you could avoid this automatic process, and not press the button, then you likely still have a disaster but not nearly on the same scale because it probably wouldn't have blown up. The only thing I can think of is that you would need to immediately start inserting some control rods in order to try to lower the reactivity in order to not trigger the automatic process, but it's very likely this would still fail.
Yes it does,it just melted like reactor 1 or three miles incident and probably not gonna be useful for future. RBMK already dangerous design and main purpose is generating power and veapon grade plutonium from vver wasted uranium .In theory ,its win win situation but non homogenous fuel of rbmk cause control problems like using gasoline alcohol maybe tinner mix for your car,and lack of safety and soviet style management lead to this unfortunate accident.In soviet doctrine,meltdown must be avoidable in any expense due to high construction cost of a rbmk ,they were thinking to change/clean damaged units ,refurbish it and use again.In. meltdowns this is impossible.I am not even mentioning soviet factor of safety ratios ❤Great content by the way, you rock❤
For the record, an alcohol-gasoline mix for your car is what all gasoline has been mixed with gasoline since the 1920s and mixtures today can be as high as 85% in either direction.
RBMK doesn't have 'non-homogeneous fuel'. Where did you get that idea? It runs on perfectly ordinary uranium oxide. EVERY reactor creates plutonium as a byproduct.
@@MinSredMash ideally it should.today rbmk s run on high quality Uranium.However this doesn't make them adventurous like in 80s.Currently not very financially efficient than expensive vver s .
two things i had read form IAEA report...it is unknown what the avg power density was with all rods out and some channels may have already been promt crit prior to AZ5, also, oscillations in reactor coolant flow were observed via the computer and these may/may not have caused the same thing...in other words, it'll be impossible to ever know, but there is evidence showing that it may have been unavoidable by the time the decision to SCRAM was made..
@ I do not claim to be an expert in anything. I have operated a few different American reactors, and I realize that exactly what happened will never be known.
The only solution would have been to increase the water flow and decrease the rod one-by-one. In the end, what caused the issue was the tips of the rod that were graphite, thus moderating the reaction.
the reactor was flooded with water. I am 100% with diatlovs opinion that the reactor was doomed due to the reactivity insertion via the graphite ends and not via the voiding. the voidiing can only have contributed when it was too late anyhow. he called it " two reactor effect "
Was it really flooded? I was under the impression there was rather less water in the reactor at disaster time. Which had led me to think that infinitely drowning the reactor, with as cool water as possible, could have saved it. Then insert rods one at a time. Did the damn thing have enough power, theoretically, to boil off any amount of cold water and melt itself down, with rods out?
@@k85 No it didn't have enough water pumping through it. Voids can't form when it's under the right water levels and pressure because the reactor is designed to boil water, and pumping enough in at the right pressure pumps the steam into the turbines. The problem is they shut off pumps to cut the pressure and steam to the turbines to simulate a power loss.
AZ-5 Button or not, once the order to restart the reactor without the proper procedures because of either inpatience or incompetence; it meant the reactor was doomed from the beginning. The problem was everyone at the top was either impatient, wanted to save cost, and didn't listen to obvious safety procedures. Had the test been cancelled after the reactor had accidentally shut down, and / or the test been done properly from the beginning without any deviation to it; the disaster would have never happened.
Quick question. They said they disconnected many safety features of the reactor. I always thought the auto scram and the manual were pretty much timed about the same so it was indifferent, as you said, but the question for me remained. Could they turn the auto scram off? Was it part of the safety features that were removed when performing the test? If so, is it possible that simply being a less experienced crew WAS actually the problem. They reacted in a knee jerk way, or would an experienced crew have reacted the same. That's really the two pivot points for me. Once I knew the reactor was spoiled on the run down I would've said, "fire me, but I'm not doing this." A new guy definitely wouldn't have even thought that was an option though. He's following orders. It's such an interesting discussion even if irrelevant for the case. Still, down the road we've seen cases like this in air crashes where the older, more experienced, senior pilot is not corrected, as he should, by the co-pilot who basically allows the jet to crash. It's such a great lesson.
well they didn't know pressing scram button would increase reactivity. It was a working day as normal by all accounts of those who were there. Safety concerns for SCRAM were never explained to personel. AZ-5 was also a normal shut down button. Imagine if you pressed a power off button on your PC and it exploded...
@pedrohenriquemachadocaldas1881 The power level they were on was permitted. The power figure in the testing program was misrepresented by Soviet experts, intentionally. Had they done the test at midnight at >700 MW and more importantly at an ORM >20 they would have been fine, but they had another task left to do that presented a conflicting situation.
So in summary, if the crew hadnt pressed AZ5 could the situation have been saved? No, because the reactivity was already on such an upwards climb that the automatic scram system wouldve been triggered, causing the same issue. Like everyone has been commenting, the issue was the dangerous condition the reactor was in, creating very rapid and uncontrollable reactivity changes.
Even if they overrode the automatic scram, you'd get a meltdown and a big hole in the bottom of the reactor gets you an equally sized boom as a big hole in the top of it. The mess would have been much harder if not impossible to clean up afterwards as well since in reality, they had time before the meltdown started to counter it. In the world AZ-5 wasn't pressed, the melt down is melting its way down into the earth and water systems before anyone knows what's really wrong.
Maybe if they started to lower the rods one by one they could avoid an explosion. But the core would reach out of range tempretaures and it would be damaged anyway
The sad thing is this really isn't even a possibility. The AZ-3 button was *supposed* to be the safeguard - you press the button and it shuts down the reactor. To their knowledge, they did do what they needed to shut it down safely. I mean, why would the emergency shutdown make it worse?
AZ-5 just made the reaction exponentially faster and worse unfortunately. Even without it you’d still have disaster just at a later time. Removing the control rods too far where they couldn’t counteract the Xenon pit was the biggest mistake. It was just too far gone. Unfortunately so many died because the information was withheld.
Its my understanding that once the output (and heat) reached a certain point, nothing was going to save it. AZ-5 wasnt the issue. The graphite mediated rods were the issue. AZ-5 might have made the situation worse. But, there was no recovering Reactor #4 by the time AZ-5 was pressed.
Were you trying to say that prompt criticality would cause the reactor to detonate like a nuclear bomb? I mean, prompt criticality IS what occurred. Whether you intended to suggest this or not, it's a bit irresponsible. There's no way it could've set off the kind of chain reaction necessary to detonate like a nuclear warhead.
The two scenarios are moot really. The reactor should never ever have been in the state it was. That it was driven purposely and with determination into this state was the primary failure mode. The rest is just consequences and symptoms of the failure. Any piece of plant is delivered with operating instructions by legal decree in fact. They’re a formal contractual requirement. Equipment is mixed scrap without them. Deliberately disregarding those operating instructions voids warranty and is usually taken as gross misconduct and would rightly lead to criminal charges against the senior management in the event of accident or injury.
The idea that it was all the operators fault was the early Soviet narrative intended to shift the blame away from the poor reactor design, lack of internal communication about the known deficiencies of the reactor design, and deficient operating guidelines. The staff did not do anything that was unreasonable to them, at the time, with the information they had. This is very well highlighted in the 1993 report from the investigative committee (official english translation by IAEA can be found as annex to INSAG-7): "The personnel violated the Operating Procedures and the Commission notes these violations in this report. Some of these violations did not affect the initiation and development of the accident, others created favourable conditions for the manifestation of the negative design characteristics of the RBMK-1000 reactor. The violations were largely the result of the poor quality of the operating documentation and its contradictory nature caused by the poor quality of the RBMK-1000 reactor design. The personnel were unaware of some of the dangerous features of the reactor and, therefore, did not realize the consequences of the violations."
@@MatthijsvanDuin I understand the sentiment and salute the intention to blame the inanimate but you cannot simply say that breaking procedures was not the problem. The procedures are as much an integral part of the plant as any pump or pipe. We don’t set about the hardware with an angle grinder and not expect consequences.
@@robinwells8879 It's not about blaming the "inanimate", it's about blaming the actual root causes and more importantly, blaming that what can be fixed to prevent future accidents. The main "violation" that caused the accident was the low ORM, which was a parameter that was not regarded by procedures as safety critical and could not be monitored in real-time from the control room. Moreover it was habitually ignored in normal operation (including the previous day) because the calculation was known to be inaccurate in some operating conditions, and ignoring ORM was necessary to keep the reactor running. The designers knew that low ORM turned the AZ-5 button into a "reactor accident now please" button, it had already caused a previous reactor accident, but this was not communicated to the operators.
@@MatthijsvanDuin again I suggest that the design was actually a good piece of value engineering that supplied the bulk of the energy needs of Ukraine for years. The management systems and its endemic failures were the problem. Western reactors by comparison are ludicrously expensive to build and operate and decommission and yet they fail too (Fucashima) containment vessels are costly and still leak in an accident and the high enrichment fuels used have a significant manufacturing energy footprint in their own right. If you believe that the manner in which the reactor was run on the occasion of the disaster was not contributory then you are missing the root cause and need to ask another why question. We gloss over the fact that the other units performed without issue for years. A management system that allows individuals to bully staff into deviation from operational procedures is the root cause.
@@robinwells8879 The RBMK design flaws are well documented, they previously caused the accident at Leningrad Unit 1 (and it was "understood that the accident was a result of the reactor's design characteristics, rather than personnel errors"). The 1993 report bluntly says "The Commission considers that the negative properties of this type of reactor are likely to predetermine the inevitability of emergency situations". Subsequent to Chernobyl the problems were partially mitigated in other RBMK reactors. In particular, under absolutely no circumstances is it acceptable for any nuclear reactor that the emergency shutdown button causes an initial _increase_ in reactivity, ever.
Hmmm... in terms of injury, probably Kurguz, who lost most of his skin in the explosion (worse than Degtyarenko) and still had to crawl through corridors flooded with radioactive steam, or Shashenok, whose injuries were absolutely horriffic. In terms of radiation dose, likely one of the firefighters or the electricians. In terms of overall worst fate, I'd say Ivan Orlov. It's hard to describe in just a comment how truly tragic his death was.
Interestingly the Canadian CANDU reactor is not too dissimilar to an RBMK which makes the Canadians arguably themost knowledgeable in the west on RBMK operation. Of course the reactors are different but they both feature a separated moderator from the coolant system resulting in the positive void coefficient (CANDU uses heavy water RBMK uses graphite) and a couple others things as well. But they are also in many ways different lol!
Yes, for starters they're designed with horizontal fuel channels that can only maintain criticality when the channels are in mechanically sound and pretty much any deformation in a channel will render that channel useless for generating more neutrons. Then if they channels deform enough because of integrity loss and gravity, it will physically touch the moderator channels, which are low temperature because of the heavy water which is also it's coolant, so heat will be transferred into the moderator channels. The control rods are also designed so they are not in the channels generating steam, so there's no way for a steam explosion/void inside the fuel channels to cause problems there. Finally if we need to we have this lovely high pressured gadolinium nitrate neutron absorber that can be pumped into the channels that would honestly make a Xenon pit jealous with how fast it poisons and kills the reactor. So yeah, you'd have to literally be breaking the laws of physics to Chernobyl a CANDU reactor. It literally will not run if it's failing. Plus there are so many ways to kill it you'd have to be trying to make it explode to get around them all, and even then you're essentially guaranteed to fail miserably.
4:25 ... no, prompt criticality is not the same as an atomic bomb, a reactor still needs moderation of neutrons, which slows down the power escalalion... a bomb is prompt-fast critical ....
@@thatchernobylguy2915 chernobyl blew up by prompt thermal(!) neutrons, but a bomb runs on promp fast(!) neutrons .... chernobyl never would have reached criticality with fast neutrons allone ....
@@NuclearSavety Fast neutrons have been modeled in the explosion since 1998, and is largely used as evidence in support of a nuclear-jet style of explosion.
@@thatchernobylguy2915 the capture cross section of fast neutrons is way too high in u238 and way to small for u235 for sustaining a chain reaction in 5% enriched uranium. ... for that reason, in nuclear reactors using 5% enrichment you only get criticality when you moderate the neutrons, making them from "fast" to "thermal". When you enrich fuel further like in atomic bombs, you remove more and more U238, making fast unmoderated neutron capture by U235 more and more likely. But with reactor-type fuel, a fast criticality is physically impossible. There is the concept of fast reactors, these would explode like an atomic weapons in case of reaching prompt criticality, but with thermal nuclear reactors like the RBMK thats not possible. You can get a power excursion to 500GW, destroying the reactor, yes, but thats still not a weapon-type explosion. Latter occurs on a time scale 1000 time shorter than a reactor excursion. For that reason your comparison of Chernobyl to an atomic weapon unfotunately stinks.
If the designer RBMK reactor and soviet authorities not lies or hiding about positive void specials on their cheap reactor,akimov will not suggest or press the scram button and waiting diesel generator to flow water to reactor and stabilize the core,the worse case is only meltdown...
Yeah pressing or not pressing AZ-5 at the point where it was pressed only changed how fast the reactor exploded. They had painted themselves into a corner at that stage and nothing was going to stop that explosion at that point.
What happens to the reactor isn't the concerning part. It's the cleaning up of the mess becomes infinitely harder if it melted down instead. They had time to figure out stuff and work to prevent the meltdown from causing damage in reality. If we start at meltdown, there's no heat exchanger under it, it's probably in the ground water and other systems under the earth before we even get a grasp on it, oh and there's also probably still going to be an explosion causing problems for everyone above ground still anyways. Them blowing up the reactor before the meltdown started basically gave everyone time to work out each problem one at a time before the giant pile of radioactive waste started causing too many irreversible problems underground.
4:34 Not sure if it's because of a different language, but the translated version on the right shows "Californie" where the one of the left shows "California"./
The Netflix show shows Dyatlov exclaiming when he realizes Toptunov pressed AZ-5. I've often wondered if that implied Dyatlov knew AZ-5 would spike the reactivity due to the rod tips.
No they didn't know. The designers knew, but it hadn't been communicated to operators. They pressed AZ-5 at the normal conclusion of the test (the data logs show reactor parameters were still fine at that time) and then all hell broke loose.
What I want to know is if there is a way to reproduce two more elephant's feet and see if shooting it really accelerated decomposition or not. I really want to know if that is why it happened. I like to think it did but I'm doubtful we will ever conduct that test to confirm.
You're delirious, RBMK reactors can't explode. Someone take this man to the infirmary
Well, I have to say, that comment's not great but it's not horrifying...
You didn’t see any graphite, because it’s not there
Can we stop quoting that fucking show? The show that perpetuated lies about the operators, lies about Soviet officials, and even lies about radioactivity despite the supposed central message?
@@kisaragi-hiu Well the fact of the matter is that is the propaganda the communists were pushing is that the RBMK was so good it couldn't explode. That saying wasn't created for, or by, the show.
@@bry12019I think I did
Don't press AZ-5: explosion happens later
Press AZ-5: explosion happens sooner
@EvilTIMMEH You're forgetting about the hydrogen gas, it would've blown the building apart like with Fukushima.
@EvilTIMMEH Okay so the hole forming in the bottom of the reactor isn't a problem like it forming in the top when the steam blew the lid off? The steam blows the top off, the melt down literally melts the floor of the reactor. Either way you've now got a giant hole in the reactor and a hydrogen explosion. Almost like what happened at Fukushima.
@@Xershade Also worse as the bubbler pools where under the reactor. So congrats the top doesnt blow off but depending on meltdown pace it may cause to quote Homyuk "A significant thermal explosion".
Looks like RMBKs were really pieces of sheet. "Yes let's build a main reactor core with a positive thermal coefficient"
@@abloogywoogywooThey did blow up the reactor, there just wasn't a building to contain the hydrogen gas.
Imagine you are fighting a fire, the fire is getting out of control and you hit a button to turn on the sprinkler system to stop the fire. Except the first thing out of the Sprinklers is gasoline, then water. That is exactly how those graphite tipped control rods reacted.
Na... gasolinera Just make thenfire bigger, you are throwing water into a oíl fire
Yes, exactly@@hernanweber3896
Kinda, the graphite itself did not boost the reaction much, it was there to displace the water. The problem is in that circumstance, the water split into hydrogen and oxygen, oxygen being able to light and hydrogen being explosive. Normally that would be fine but there was too much pressure in the core due to the operators pushing the machine to far. The whole thing was designed for normal problems and not worst case scenarios.
The 1.5m long graphite "tips" really should have reached all the way down. For maximum effectiveness and no positive scram effect. Bit late now though 😞
@@TylerParis-qk7ywThere's evidence of the reactor going prompt critical in two locations immediately before the big explosion. The displacers are a good idea, but as is the case with most of communism - the implementation was somewhat lacking.
In this particular case, the problem was that they did not reach all the way down the channel with the rods fully withdrawn. This means that there's water under them which takes away reactivity.
When the reactor is already in an unstable state and reactivity is too high in areas where there's water in the channels, it is inevitable for graphite to pass through those areas first, before the boron rods make their way there.
Unfortunately that leads to a spike in reactivity, in an area which is already exceeding safe limits.
Had the implementation been such that the displacers permitted no water at all in the channels, this dangerous level of reactivity would have been reached sooner, perhaps preventing the withdrawal of so many control rods and prompting action from the operators sooner in order to shut it all down. Or it would have happened too quickly and blown up anyway, we'll never know. What definitely wouldn't have happened in that case though, is the positive scram effect which is widely regarded as the trigger of the big explosion.
Whichever way we look at it, it's a shit reactor. They never should have built it. And if they hadn't, the whole planet might have been nuclear powered by the '90s.
So what you're saying is that the only way unit 4 wouldn't have blown up is if they weren't goofing off with their nuclear reactor at 2am
Why did this make me laugh so much?
@@thing_under_the_stairs Considering they weren't goofing off, I don't know.
It will blowup eventually. The AZ5 button was a fatal flawed design.
Any scenario that triggered them to emergency scram the reactor will cause it to detonate.
They weren't goofing off. They were running a safety test that was supposed to be done prior to the reactor being certified but the Soviets rushed the reactor into service before it was ready. This safety test unknowingly triggered a critical design flaw in the reactor.
@@RainbowManificationit had already failed the tests 4 or 5 times they may as well have been goofing off they were just hoping it would work this time
In my opinion, the reactor was lost when the control rods were raised too high to break the xenon poisoning in the core. The use of AZ-5 only made the situation worse. Failure was already inevitable. Interesting and good video.
?
Exactly. The reactor was in a state that was unrecoverable by any means they had at hand a minute or so before the power surge and explosion. Or maybe, and only really maybe IF they knew the real situation of the reactor with its design flaws, taking into consideration the critical reactivity margin they had as well as the violation of operational procedures they made in order to do the test, they could prevent an explosion by "flooding" the core with "cold" feed-water before the start of the test (thus invalidating it and shutting down the reactor for a longer time) and only after the reactivity dropped below critical inserted the control rods and eventually the scram rods, would they save the reactor from exploding. But this is pure hypothetical situation and they had absolutely no reasons to do what I just described. They wanted to do the test and did everything they could to run it. The test should not have been made. Once the power dropped practically to zero a few minutes before the test, it was clear that it made no sense anymore, especially since they managed to rise power only to about 200 MWt. Which itself is quite impressive considering the Xenon poisoning and burn-up of the fuel rods. The reactor running at 200 MWt was in a very unpredictable state. Maybe my speculation would have not worked anyway and the reactor would experience a power surge. Maybe it would not blow up, but it would certainly cause massive damage to the core, maybe even so as making the reactor inoperable after that. Like what happened at Bohunice A-1 in 1979. The incident was caused by different reasons, but the result might have been similar - melted fuel assemblies, contaminated primary and secondary loop (the RBMK has no secondary loop) and a "bricked" core that only can be written off and eventually dismantled (after decades). Chernobyl would have remained an INES-4 or maybe INES-5 incident, if judged by the IAEA scale introcued in 1991. The question is, if a far worse accident would have not happened on another RBMK design, since it would have been covered up by the soviets and no lessons would have been learned.
@@erikziak1249 In other words you don't know what you're writing about.
Great job completely ignoring the entire video
Well even if we consider not pressing AZ5, then as well as mentioned would not have made much of a difference. The reactor was much lost when toptunov withdrew almost all rods from the rector. The root of the problem is AZ5 and the reactivity of low grade uranium. Toptunov shld have rather scrapped the test and rather shut down.
It doesn't need saving, IT'S FINE. Just get that water flowing, for the love of god, how many more years will I have to wait? The reactor NEEDS WATER
Needs some LaCroix, more like it.
water + CULTURE = LaCroix!!!!!
Oh yea
Wasn't all of the reserve water already hot? IIRC that's why so much of it started boiling in the first place, they had activated all the extra tanks when trying to reduce power output for the test. And because there was so much water in the loop it was getting pushed back to the reactor after barely falling below boiling.
IT BLEW UP
I thought that the reactor needs graphite.
So to summarize - essentially, to "save" Chernobyl at that point, they would have had to undertake a dedicated series of very rapid, very unintuitive actions - they would have to disable the automatic scram system altogether, they would have to inject cold water to bring reactivity down, and start inserting control rods "slowly" (compared to the scram at least) one bank at a time.
In other words, do exactly the set of actions that would destroy literally any other reactor in the world other than an RBMK.
That's exactly the kind of thing that they COULD have been TRAINED to do, but nobody in their right mind would ever do unless they were trained. If lessons had been learned from the Leningrad accident, and crews had been trained on an emergency procedure to manage positive scram reactivity, it might have been possible to minimize the damage at Chernobyl, but yeah... that would have required the Soviet Union to admit a flaw in its design and that was never going to happen.
Alas.
I think the fact they stopped building RBMKs is probably illustrative enough to say they did admit it
Stupid question, what would happen if you tried this with any non rbmk reactors
@spazmonkey2131 I imagine it would depend upon the kind of reactor. There are a lot more designs than just the RBMK after all. Of course, the only reason AZ-5 didn't work here was because of the design flaws of the RBMK reactor. Flaws I think (desperately hope) other reactors don't suffer from.
@@yegorgribenuke6853this fact is procommunistic so we should just ignore it.
Thank you for another well-done video. There may be one (little known) reason why the guys in Canada did their own report quite quickly after the accident; their own CANDU reactors. The CANDU, like the RBMK, is a pressure tube reactor. It even shares a special characteristic with the RBMK, the positive void coefficient. After the accident, they may have wanted to find out if they would run the risk of a possible similar accident in certain scenarios. However, the CANDU is very well-built, with full containment, a lot of redundancy and two separate safety systems that can independently, _and_ without power or operator intervention, shut the reactor down within 2 seconds flat.
I'm guessing it didn't have a positive power coefficient.
@@markusw7833
Oh, but it does. Look it up. It is the main reason CANDUs have a hard time being licensed in the USA because the US does not allow any reactor design with a positive void coefficient to operate in the States.
@@swokatsamsiyu3590 Not void, power.
@@markusw7833
You're correct. I misread. But the US still is heavily biased against allowing the CANDU because of the positive void coefficient.
*Needs new reading glasses.
Candu and IPHWRs are actually well built heavy water reactors. BWRs are also good as they use water as a moderator and an absorber. But it's not as correct to say that the RBMK was not as good. The power output is well enough and it's still being used at kursk and smolensk.
Hindsight is 20/20, but without having such knowledge, the operators might have been in big trouble if they didn't press the AZ-5 button. It's like Titanic would have been saved if they had crashed the ship head first into the iceberg, but it would have looked like incompetent operation, and the crew probably would never sail a ship ever again. Society is funny like that. Instead of doing the safe thing and crash the ship head first into the iceberg, we do all we can to not cause any damage to the ship gambling that it will pay off even if the odds are stacked against you.
you don't know the under-water shape of the berg
I get your point, if you cause something bad in order to maybe prevent something worse, you have the problem to prove that something worse would have happened.
Concerning titanic there was a risk to damage too many compartments anyway by unterwater ice right in front of it and/or by causing the iceberg to rotate and cause unforeseeable patterns of damage.
Maybe it would have saved the ship, maybe it would have sunk way faster with up to 100% casualties.
However an interesting tradeoff.
@@franknachname730 That was hardly the trade-off they thought about: Firstly judging distances at night is very hard, so they had the right to assume that they would pass it (which they nearly did). Secondly the side extension of the submerged part of a berg at night cannot be estimated, even less so when its waterline cannot be seen, as no waves were breaking at its base in that very calm night. Thirdly a head - on collision would cause massive damage (they were at 21 knots), like the chimneys coming down, machinery being torn out of its sockets etc.
In reality they hit the berg so gently, that they did not bounce off, nor was their forward momentum impaired. As a result 6 main compartments were sliced open. If it was 1 compartment less the ship might have been saved, or at least kept afloat for many more hours in that very calm night.
So any other impact - a harder one and even a head-on one would be preferable to that smooth and long slicing, which given the information they had, was extremely unlikely. Hence in my opinion they made the right decision.
@@nehorlavazapalka you dont know about how ships are built. The front would crumple & maybe the 1st water tight compartment floods, but it gets to New York. This happens to lots of ships.
@@andy99ish I don't think they considered that either and i don't blame them for it because as you say, they couldn't have known. But theoretically I find the question interesting.
I'm not completely sure about the damage behind the bow you mentioned since the ship would slow down a bit until impact and the forward compartments would have acted as a crumple zone to spread the impact over several seconds.
Did other ships that hit icebergs head on with similar speed suffer that damage? (assume similar mass relations)
On the other hand the iceberg more likely might have turned
I've heard it said that in order for a modern nuclear reactor to blow up like Chernobyl's did, someone would have to be in the control room *actively trying* to make it explode. It sounds to me like, in the case of Chernobyl, to have kept the reactor from exploding, someone would have had to have been in the control room actively trying to make it *not* explode.
To quote the english translation of the 1993 report, "The Commission considers that the negative properties of this type of reactor are likely to predetermine the inevitability of emergency situations"
Thank you again for doing our homework for us! This is a great channel. It amazes me how many people are so fascinated with the Chernobyl accident. It amazes me more that we have a few people who are covering it today. 3 channels that cover different aspects of the accident. All are fantastic in their own way. You are the one who covers all of the technical aspects of what happened that night. Personally, I am very thankful for you and your work. I stand amazed at your understanding of the accident and how you help some of us to understand that night a little better. The "what if's" are even more important here. Knowing that the explosion would have most likely happened anyway no matter what. Thank you for your work! You are appreciated.
The best way to prevent the Chernobyl disaster would be to go all the way back to the late 60s and design a better/safer reactor
they had a better one, the pressurized water reactor family VVER. Now RBMK was much easier to build and cheaper, so they went with THAT design. Still, it is amazing, that they kept the remaining twenty RBMK reactors running - without them blowing up into pieces. Wikipedia says they decreased the positive void coefficient by modifying the fuel rods by means of 'increasing the enrichment requirements of the uranium fuel in the fuel rods' (very enigmatic phrase). Also the control rods are said to have been modified, go figure. In the end they always blame some poor operator like Toptunov, who was not aware of the design deficiencies, because they were state secrets. On the other side of the pond it is some Homer Simpson guy, who gets blamed...
The reactor worked fine before they start using it wrong. It broke because they break it.
@@XtreeM_FaiL No, the reactor didn't work fine, that was literally the point of hiding the inner workings of the graphite displacers on the control rods from everyone. Other plants had channel ruptures when shutting down before this happened. The only difference was those reactors weren't in a state where they were about to fail catastrophically.
The best way would be to go all the way back to the late 10's and abolish communism
@@XtreeM_FaiLevery block had some fuckups, cover ups, few damaged technological channels every now and than.
This is actually a really interesting topic to explore. I've often wondered whether the die was cast long before the SCRAM function was initiated, or if there could have been a way to gradually reduce reactivity and slow down to a safe stop.
"Leonid Topyunov, who was all of 25 years old, and his mustache of just 18 years old."
Is that's what's on his lip, you say? Hm. Incidentally, want to buy a motorcycle?
I'm sorry guys 😢
@@Anatoly_DyatlovI hate u
@@Anatoly_DyatlovI don’t believe u
@@Anatoly_Dyatlovno
If they hadn’t pressed AZ-5 then likely the worst that would’ve happened would’ve been a reactor meltdown, not an explosion.
The main reason the reactor exploded was the immense pressure created by the steam, so if they had kept the valves closed then the reactor likely wouldn’t have exploded.. at least not in a nuclear explosion because the Chernobyl reactor had a positive coefficient.
No, it would only take more time to explode. The xenon was already in the reactor and the reactor could not be switched off as lowering the control rods was the same as pressing AZ5, therefore it would only take more time but have the same effect, the error was rising the control rods before. But a engineer or someone with more knowledge can explain this better probably.
@@midelro97Xenon doesn’t raise reactivity, it lowers it. The control rods could have been inserted a few at a time, because they are graphite tipped, which raises reactivity, but made of boron higher up, which lowers reactivity. The few control rods being inserted would have raised reactivity initially, due to the graphite, but would work against the reactivity as soon as they were fully inserted. This could continue going on, inserting a few at a time, until as many could be inserted as possible. The point the speaker in the video was making that the reactor was already going to sustain some damage, as the reactivity was on the rise and would have risen to the point of causing damage to the fuel and some control rod channels. However, the cause of the explosion was hitting AZ-5, or inserting all the control rods at once. All those graphite tips entering the reactor at once skyrockets the reactivity, ruptures the fuel and control rod channels and locks the control rods in place, preventing them from being fully inserted so that the boron portion of the control rods could work to reduce the reactivity and temperature. The other point the speaker made is that there were systems present that would have SCRAMed the reactor even if AZ-5 had not been pressed, and so the effect and result would have been the same. I’m not sure if it would have even been possible for the operators to have overridden these systems, but if they had been able to insert the control rods a few at a time, the reactor would have escaped with damage and ruined fuel, not the catastrophic explosion that occurred.
@@midelro97 Xenon lowers reactivity, it does not raise it. If the operators were able to lower control rods into the reactor a few at a time, the graphite tips would have raised reactivity briefly, but the boron higher up in the control rods would have been able to enter the reactor and work to lower the reactivity as a whole. Over time, the boron control rods entering the reactor would have prevented the total meltdown that occurred. For sure, damage was inevitable, but nothing like what happened that day.
@@midelro97inserting a few rods at a time wouldn't have the same effect as all at once
I recommend watching this: HOW THE 4th UNIT OF CHERNOBYL NPP WAS BLOWN UP (channel-KS).
My understanding is if the control rods were designed to "slam home" when AZ-5 was pressed (vs. operating at "servo speed"), an explosion _might_ have been averted. As far as the explosion being caused by the graphite tips (which is what you're asking), I think they passed the point of no return a while back.
maaaaybe but idk my understanding is the 'drop' or 'slam home' (which they did implement after this) gets the insertion time down to 11 or 12 seconds vs 18-20, but that still seems too long when the graphite is starting to molt and shafts are getting distorted or splitting open... I don't understand why they didn't start the water flowing again before that
@@prismpyre7653 They literally had all main circulation pumps going and the reactor had a very high total flow rate, which is supposed to have contributed to the incident.
@@prismpyre7653
After the 1986 accident, they have given the remaining RBMKs an additional, fast-acting SCRAM system called BAZ (Быстродействующая = Fast-acting, Аварийная = Emergency, Защита = Protection) that can insert 24 special control rods fully into the core in under 2.4 seconds or 7 seconds, depending on the signal sent. These control rods are gas-driven, their channels are cooled by a waterfilm, and they're Boron only. No graphite displacers allowed. They will pull reactivity down by at least -2 β-effective. When an RBMK is scrammed today, this system will go first. After that, the rest of the normal system follows.
@@markusw7833they had 4 of 8 pumps going not all 8 hero.
When you're talking about a prompt critical excursion, as happened at Chernobyl Unit 4, one second, ten seconds, eighteen seconds doesn't really matter, the reactivity spiked so hard and so fast that even if you "slammed home" the rods, the fuel channels would have still ruptured and jammed a bunch of control rods with graphite moderator still stuck in the lower half of the core.
I had a bunch of other stuff below here, but a nuclear fission event happens in 1 "shake" (it is a real term in nuclear physics, it's about 10 nanoseconds, or 10^-18 seconds. An entire chain reaction that blows apart a nuclear bomb is completed in 50 shakes, or 500 billionths of one second. As soon as the reactor reached one dollar of reactivity, or the point where there's enough free neutrons to self-sustain the reaction, that was it, it's over, *boom*.
For another fun little tidbit, the amount of uranium-235 fissioned in the Little Boy bomb that blew up over Hiroshima amounted to about 7/10ths of a gram of U-235. The energy from that tiny amount of fissile material was enough to level the city, and the entire reaction happened 500,000 times in the amount of time it took you to realize there's a period at the end of this sentence. Chernobyl was not a nuclear explosion, or anything like it, but the chain reaction and the steam explosion of the reactor happened on the same timescale.
Can you do a video about them not having chefs run the nuclear reactors
Underrated comment
Irony: a good chef would have run the reactor according to the SOP recipe, and nothing bad would have happened. You'd have never heard of an RBMK.
Lolol
That’s hilarious 😂
This channel is a gem I have been looking for for years!
After learning everything i could about this disaster over 10 years. I think there was only one possible way to save the reactor. They would've had to resist the urge to press AZ-5 and instead slowly start reintroducing control rods a dozen or so at a time. Because at that point in the evening the reactor was at its limit. You can't make huge changes to a system under that much strain, it will fail. You have to slowly and carefully walk it back from the edge of disaster first.
They did everything right, the problem was AZ-5 had a "surprise". In any normal system "oh shit" button should stop everything, instead of "stop everything except for accelerate everything in some situation".
Or they could not have broken numerous rules and as a result not ended up in the situation in the first place.
Without knowing the issue with AZ-5 there was no reason for them to try anything else.
The problem with this is that the button was sold exactly for this kind of "oh shit" situation - I guess no one would permit nuclear reactor operation without "yes we have a button which will save everyone"
@@SukSukulent Is that the button that Homer Simpson found using the eenie meenie miney mo search method?
Problem is that the procedures stated to press that button in that exact situation and it was supposed to be a fail safe. None of them knew of the fatal flaw
I read Dyatlov book about what has happenned over there, but the most important thing is AZ-5 portrayal. AZ-5 was not "Oh shit button", but normal turn off switch that was not plumbed and that you use to shut down reactor at normal condition too. In the series they show that there was dense atmosphere, but Dyatlov as a proof kept mails from the people that worked with him that day. Those mails opposed what was being shown in the HBO series. The amosphere was calm and in control. The only reason why the reactor blew was that the government has HIDDEN THE REASON why the crew had to keep more control rods in the reactor despite of what operation manuals stated after the reactors were turned hot. Also, there is a reason why Dyatlov was released after being just 3 years in the prison. He knew, that they knew that he knew and that's why, despide deaths of thousands or hundreds of thousands of people he was free not long after. The party would not want to create a precendence within nuclear engineering society in which operators are being to blame for what was beyond their control, because not much people would like risk it all.
Also he described Legasov as government dog that in fact had no competence to judge him (he had bad general knowledge that was not focused in nuclear engineering- he was a chemist) and also Legasov followed the general narrative presented by the party members.
Dyatlov was sentenced even before the trial started. Designers of the reactors did not bare the consequences. The best example of that happened in viena where Legasov presented UPDATED manuals, which were released AFTER the accident occured! They kept old manuals hidden.
I have my doubts about all the negative portrayal of Dyatlov in the common narrative. I do believe he was scape goated and railroaded. All of this could have been avoided had the US been open about their own accident with a graphite control rods back a decade or two before this happened too. The US hid it until the 90s and there is still very little written about it despite it being acknowledged. One book that claims to cover every major nuclear accident doesn't even mention it. The clean up is still incomplete and the impact still relatively unknown to the public.
By the time they pressed AZ5 it was already too late. They might have saved it shortly before that by inserting the shorter control rods from the bottom, where the reaction was running out of hand. They didn't have the graphite displacers and could conceivably have slowed things down enough for the main control rods to be lowered a few at time. Of course, shortly before that they could have just not pulled them all out in the first place.
I think the problem was getting chefs to run a nuclear reactor
And once more, another great video. Thank you Sir !
Chernobyl was a parable of failures. Perhaps it could, perhaps it wouldn't.
When the button was pushed, the reactor was already highly unstable and experiencing a runaway power excursion. It takes several seconds to insert the control rods (20 seconds to be fully inserted), and it may have been headed to an uncontrollable explosion without regard to pushing the AZ-5 button.
Answer: *OH HELL NO*
Akimov & Toptunov completely withdrew 205 control rods, they were obviously ordered to do everything possible to get the power back up.
A significant majority of those control rods were already withdrawn before the power drop; it was quite normal for RBMKs to operate in that position :)
@@thatchernobylguy2915 I am sure someone if not everyone in the room that night would've been well aware of the Xenon poisoning that pretty much doomed the test and the reactor from the start.
@@sonicnarcotic. Actually, the person to first start raising the power, Yuri Tregub, was well aware of the xenon pit and did not believe that it mattered. It didn't anyway, because the test could be conducted at any level of power so long as the turbine ran at full speed - 700MW was just an arbitrary number in case other experiments had to be done.
I recommend watching this: HOW THE 4th UNIT OF CHERNOBYL NPP WAS BLOWN UP (channel-KS).
ua-cam.com/video/yIA_FMz9n1k/v-deo.html
Thank you very much for the great video. I would also like to thank the many commenters for being sophisticated and very scientific. Both the video and the comment section were very entertaining and informative. Thanks.
This reactor would not stabilise. It was badly kicked out of stability by the crew under Diatlov.
First they pumped the cold water. Than reactor almost shut down, with power being close to 0, which prompted Diatlov to call for raise of all control rods.
Then only a couple of the rods remained inserted, meaning there was almost nothing to catch the neutrons and keep the reaction at value.
So, the reactor fell to almost 0, then was raised with almost no brakes. Although I am a noob in nuclear science, I doubt that it would stabilise itself.
But when AZ-5 was pressed, all the rods entered their channels at the same time, creating something similar to a spark in a plug. A sudden increase in reactivity, before shutting it down.
In conclusion to this yapping, I agree, not pressing AZ-5 would have saved Chernobyl, IF the crew would connect the diesels and started entering the rods in small batches.
However, with Diatlov's hot-mind, not the best training of the crew and not safe building (the rest of the reactors were built by Soviet standards with heat-proof materials, but the 4th one wasn't), I doubt that they would pull it off.
I had exposure to the radiation from Chernobyl when the US wanted to make a show of force in Germany. We were out marching in the rain consisting of the fallout from Chernobyl on May 1st 1986. The result is that I have a nodule on my thyroid as well as lesions on my head, neck and shoulders. The biopsy revealed that it is consistent with exposure to radiation. This happened in Regan’s peacetime Army. I’m being treated for it now. There are probably more people suffering from this same exposure. I was literally singing, “I’m a Radioactive” at the time. ☢️
Can you do a video that shows which things they did that was part of the test procedures and what was improvised? I'm still a little confused on what actually happened. I blame HBO and Medvedev's book. Once I heard you say that was inaccurate I ordered Chernobyl: A Documentary Story on your recommendedation. Thanks as always for the great video, this answered the question I had about if it really was the AZ-5 button that was the final nail in the coffin.
I'm also reading INSAG-7. I've fallen down the rabbit hole haha
All this is a replication of the Soviet lie about the causes of the accident. If you want to know the truth, watch: HOW THE 4th UNIT OF CHERNOBYL NPP WAS BLOWN UP. (KS channel)
The void stuff was good explanation 🎉! Ty
8:56 Vyacheslav Akinfiyev was replaced with Nickolay Fomin not Anatoly Dyatlov
Hello Sir. Again an example for how good your videos are and how well you’ve made your investigation into the incident. Please go on doing such great work. Greetings from Germany 🇩🇪
They would have had a loss of coolant event instead. They didn't have any procedure outside of SCRAMing the reactor, so they didn't have time to think it over. The excursion at Stalingrad gave them a hint at what would happen if things got out of control. So it should have been broadcast to the other RBMK operators NOT to let it get into a low power state.
Utterly outstanding - I never knew anything of us, which all makes perfect sense - seems obvious now that the Soviet version of events would be lies. The various temperature coefficients and voids in the cooling water say it all. I get it it might have scrammed anyway and I see now how AZ5 might have saved it - you’ve taught me much tonight, am so grateful to you. Look fwd to more of your vids!!! Thanks again!! Bravo!!
Adrian in Bermuda 😊😊😊😊😊
AZ5 was a detonator, not a shutdown
Tips of boron rods were made of graphite that induced enough reactivity for an explosion.
If they didn't press the button, the active zone would rupture due to tremendous heat and pressure that would result in a meltdown, not an explosion.
There would still be consequences like a white hot radioactive magma made of reactor fuel, graphite and concrete that they need to solve to prevent it from seeping into the groundwaters but the grand scale of the disaster would have been tens of times lower
It wasn’t a detanoator it was just that the AZ-5 was a 1$ shutdown botton
What if when someone who realised xenonpoisoning, had forced some person/s out of the room for about 24 hours in order to get that thing BACK under control?
Excellent video as always.
What I want to know is, when the reactor crashed before the test, if, rather than withdrawing the control rods entirely, the technicians had removed them partially to put the graphite tips in place, could they have brought the reactor up to power in a stable enough way to perform the test?
The graphite tips are in place when the control rods are withdrawn. The "tips" are a chunk of graphite that is about 2/3 the size of the control rod and they're there to displace the water in the channel so the entire control rod channel doesn't fill with water. The reactor was dead, you don't start a reactor in a Xenon pit for very good reasons, as everyone there found out the hard way. The only way to bring it back up was to shut it down completely and reset it, which takes at least a full day.
Xenon, I tried simulation, it was perfect timing for test. Few minutes, maybe seconds before, there was not enough xenon to stall reactor. Few momments later and it would be stalled, no way to power surge to occure.
Could they have maintained control of the reactor if they started fully inserting some of the control rods as soon as power started rising?
The automatic control rods did insert, and they consequently brought reactivity back down, without the manual rods. Power only started skyrocketing after AZ-5 was pressed. :)
I have said this several times on similar social medial posts. But there are always "internet experts" who say that I am wrong. Thanks for posting!
What is the name of the Sim at the start of the video?
MS flight, steam edition. Just watch out for the Mach 3 ballons
But it's like reliance,
As told in films. The truth was hidden from them, They were in the dark.
For any operator of any kind the "Emergency Stop" is the last thing. It's the last ditch effort in a hope that the misery stops.
It's like if the train hadn't pulled the emergency brake it wouldn't have derailed. But how can you predict that when a situation is going out of control rapidly the only thing that is meant to stop it will turn out disastrous. They were believed that "this" button will stop it.
But that's the thing, the last button should've been made for the safest output.
AZ5 was actually the way they usually shut it down.
Im more curious if the test "result" was the worst possible result, or if a significantly greater nuclear event would have occurred if this was done under an overload.
According to calculations by some scientists, the reactor output increased to 100 times its nominal output during the disaster. At the time of the explosion, the entire Soviet Union could have been supplied with electricity using reactor 4 alone.
That was already extremely violent.
But I can't tell you what would have happened at full load. Perhaps at full load the AZ-5 button would have prevented a catastrophe.
During partial load there was a high proportion of xenon gas in the reactor. Without xenon gas in the reactor, nothing might have been unstable.
They were truly in a lose/lose scenario, they just got the worst possible outcome, honestly would be my luck
This is always what I've wondered- did they have a button, like an AZ-3, that would insert *some* of the rods all over the reactor? I would think the thing to do if you are aware of possible xenon poisoning and also that once you cut the water obvi reactivity will spike... I would think the thing to do is as soon as you release the turbine for the run-down test, you IMMEDIATELY switch water back on and start lowering SOME control rods, 25% at a time maybe.. (but I realize that they hadn't been made aware of the issue with the water-displacing tips causing a spike at the bottom of the reactor on insertion). I always wondered if they could have saved it if they didn't panic-- sometimes, accepting that you are going to be in *A* accident instead of trying to avoid it, lets you avert the worst-case scenario.
"I always wondered if they could have saved it if they didn't panic"
What in the world?
@@markusw7833 I prevented myself from crashing into the ditch on a freeway earlier this year by doing exactly what he is suggesting here. If I had panicked and tapped the break, the vehicle would have spun out of control on the icy road surface. I simply dropped the throttle and let the physics do the work for me. No accident involved by being smart and remaining calm.
@@erickolb8581 that's good stuff, glad it worked out for you! Staying calm & focused helps solve a lot of problems, for sure. However, I think your success handling that situation also required you to have the right knowledge, skill & instinct, all built from internalizing good lessons & having a decent amount of experience driving on slippery surfaces while paying good attention. Nobody at Chernobyl had the knowledge or instinct required to invent a new procedure on the spot. They thought AZ5 would put it into a good state. It's like if someone was scuba diving & their main air supply gave out so they switched to a backup supply, but that backup was contaminated w/ CO gas, killing them. A mad dash to the surface might've turned out better, but why try that if they didn't know the backup air was bad? Sometimes staying calm isn't enough.
Stupid question, but how do they keep water liquid at 165-265 Celsius?
High pressures force gases to become liquids again. If you, for example, took the lid off of the reactor while it was running, all that pressure would be released and the liquid would become gas :)
Pressure.
Ever heard cooking instructions that say you need to boil things longer at high altitude to cook them? It's because there is less air pressure at high altitude, and water boils at a lower temperature at a lower air pressure. The opposite happens at high pressure, so you can keep water from boiling by keeping it under high pressure.
Also water can be boiled at 50 C if the athmospheric pressure is 1/2 of the original.
What simulation did you use there? It looks good.
I have no opinion on this as I'm not remotely qualified to offer one that's in any way educated.
Great video! I remember reading a translation of the Legasov tapes, where it was stated that the whole „test“ was allegedly just a cheap way to save money, as faster diesel generators were readily available. But the responsibles did not want to invest any additional money, do you know if that is really true? And do you by any chance know if better containment could have prevented the worst case scenario of an open reactor? From the tapes I only know that europeans insisted on additional safety precautions but unfortunately there was no detailed information on these precautions.
Thanks a lot and good job!
I loved my tapes
Another banger of a video. Thank you!
Thank you!
I had always wondered, a little different scenario - if the rods were brought back in one at time vs all at once if it would have made any difference.
I've also seen quite a few comments that the lower rods did not have the same positive void coefficient issues due to the lack of the graphite tips? So if they had been brought back in or been triggered by the AZ-5 (which I believe I saw was a later change) it could have also helped or prevented the incident?
The 3D visualisations are quite painful to watch because of how choppy they are.
At around 1:06 you mentioned that water enters the reactor at a temperature of around 265 degrees Celsius. I don't understand how this can be. I learned at school that water boils to steam at 100 degrees Celsius. Is there a mistake with the units; or am I missing something? Thanks very much for the interesting video.
Pressure.
Water has different boiling points depening on atmospheric pressure. The higher the pressure, the higher the boiling point and vice versa. 100C is the boiling point at 0 sea level.
@@madarab I see. Thankyou very much for taking the time to answer.
Great video, Thank you
Only possible save, and it would of been nearly impossible, would of been to flood the reactor with enough coolant tthat it was impossible to boil off. Then when reactivity reduced reinsert the control rods to get the reactor back under control.
Again the key problem is with where the reactor was at that moment they would of likely had to turn the pumps on full blast, and I dont mean to whatever their operating level was but to the highest they would go without instantly breaking and flood the coolant channels.
Also it was a split second decission and only one answer for that kind of quick thinking with how the reactor was designed, A-35.
I was totally unaware that the water entered already at over 2x the boiling point at ambient. I had always assumed the water entered much cooler and was rapidly heated instead of entering already extremely hot and heated just another 15c
what they really should've done is press the quick load button, so they can try again, or maybe they forgot to quick save first, idk I wasn't there
I'd love to see a video where you explain what could still be done to save the reactor at each point in time where they made a mistake
EDIT: NEVERMIND I found it in your playlist (What if You Were in Charge at Chernobyl?). ILY you're officially my favorite youtuber
Another great video. Can we get a half lives story on Akimov
Wasn’t the official operating procedure, that in the event of a low power situation, is that the reactor should be shut down, and then later restarted, with a very gentle and steady rise in power, until the reactor was stable?
Yes, that's the official operating procedure for literally all nuclear reactors in low power situations. You need to hard shutdown and let it reset for at least a day before even attempting to restart it.
Everyone is an arm chair expert until there's a real nuclear meltdown in progress, and then there's no one around to be found.
So basically the reactor would have automatically done the same thing as pushing the AZ-5 button. But if you could avoid this automatic process, and not press the button, then you likely still have a disaster but not nearly on the same scale because it probably wouldn't have blown up. The only thing I can think of is that you would need to immediately start inserting some control rods in order to try to lower the reactivity in order to not trigger the automatic process, but it's very likely this would still fail.
Yes it does,it just melted like reactor 1 or three miles incident and probably not gonna be useful for future. RBMK already dangerous design and main purpose is generating power and veapon grade plutonium from vver wasted uranium .In theory ,its win win situation but non homogenous fuel of rbmk cause control problems like using gasoline alcohol maybe tinner mix for your car,and lack of safety and soviet style management lead to this unfortunate accident.In soviet doctrine,meltdown must be avoidable in any expense due to high construction cost of a rbmk ,they were thinking to change/clean damaged units ,refurbish it and use again.In. meltdowns this is impossible.I am not even mentioning soviet factor of safety ratios ❤Great content by the way, you rock❤
For the record, an alcohol-gasoline mix for your car is what all gasoline has been mixed with gasoline since the 1920s and mixtures today can be as high as 85% in either direction.
@@AiOinc1 but you got the point :)
RBMK doesn't have 'non-homogeneous fuel'. Where did you get that idea? It runs on perfectly ordinary uranium oxide. EVERY reactor creates plutonium as a byproduct.
@@MinSredMash ideally it should.today rbmk s run on high quality Uranium.However this doesn't make them adventurous like in 80s.Currently not very financially efficient than expensive vver s .
@@EJDERMALO-qk7khModern RBMKs run on the same uranium, just enriched 0.4% more.
two things i had read form IAEA report...it is unknown what the avg power density was with all rods out and some channels may have already been promt crit prior to AZ5, also, oscillations in reactor coolant flow were observed via the computer and these may/may not have caused the same thing...in other words, it'll be impossible to ever know, but there is evidence showing that it may have been unavoidable by the time the decision to SCRAM was made..
Which one? Because there were several IAEA reports.
@ I believe the 1997 one, I have it…somewhere in my notes. It’s a rather interesting read.
@@chickenlover657 sorry...92..THE CHERNOBYL ACCIDENT: UPDATING OF INSAG-1
INSAG-7
A report by the International Nuclear Safety Advisory Group
@@JoeHynes284 Yeah, INSAG-7 is more realistic.
@ I do not claim to be an expert in anything. I have operated a few different American reactors, and I realize that exactly what happened will never be known.
The only solution would have been to increase the water flow and decrease the rod one-by-one. In the end, what caused the issue was the tips of the rod that were graphite, thus moderating the reaction.
Crazy to see that guy using an angle grinder by hand on something going into a reactor.
the reactor was flooded with water. I am 100% with diatlovs opinion that the reactor was doomed due to the reactivity insertion via the graphite ends and not via the voiding. the voidiing can only have contributed when it was too late anyhow. he called it " two reactor effect "
Was it really flooded? I was under the impression there was rather less water in the reactor at disaster time. Which had led me to think that infinitely drowning the reactor, with as cool water as possible, could have saved it. Then insert rods one at a time.
Did the damn thing have enough power, theoretically, to boil off any amount of cold water and melt itself down, with rods out?
@@k85 No it didn't have enough water pumping through it. Voids can't form when it's under the right water levels and pressure because the reactor is designed to boil water, and pumping enough in at the right pressure pumps the steam into the turbines. The problem is they shut off pumps to cut the pressure and steam to the turbines to simulate a power loss.
How does water go missing requiring it to be topped up? Like... it's being cycled directly through the core in a closed loop?
probably through steam, but in a manner that seemed to imply accident or emergency i have no idea how they did that
AZ-5 Button or not, once the order to restart the reactor without the proper procedures because of either inpatience or incompetence; it meant the reactor was doomed from the beginning. The problem was everyone at the top was either impatient, wanted to save cost, and didn't listen to obvious safety procedures. Had the test been cancelled after the reactor had accidentally shut down, and / or the test been done properly from the beginning without any deviation to it; the disaster would have never happened.
Quick question. They said they disconnected many safety features of the reactor. I always thought the auto scram and the manual were pretty much timed about the same so it was indifferent, as you said, but the question for me remained. Could they turn the auto scram off? Was it part of the safety features that were removed when performing the test? If so, is it possible that simply being a less experienced crew WAS actually the problem. They reacted in a knee jerk way, or would an experienced crew have reacted the same. That's really the two pivot points for me. Once I knew the reactor was spoiled on the run down I would've said, "fire me, but I'm not doing this." A new guy definitely wouldn't have even thought that was an option though. He's following orders. It's such an interesting discussion even if irrelevant for the case. Still, down the road we've seen cases like this in air crashes where the older, more experienced, senior pilot is not corrected, as he should, by the co-pilot who basically allows the jet to crash. It's such a great lesson.
well they didn't know pressing scram button would increase reactivity. It was a working day as normal by all accounts of those who were there. Safety concerns for SCRAM were never explained to personel. AZ-5 was also a normal shut down button. Imagine if you pressed a power off button on your PC and it exploded...
awesome vid!!
What if the test was conducted within the reccomended levels
Assuming the power didn't fall, then it would have been a successful experiment with no explosion.
The recommended levels of what?
@pedrohenriquemachadocaldas1881 The power level they were on was permitted. The power figure in the testing program was misrepresented by Soviet experts, intentionally. Had they done the test at midnight at >700 MW and more importantly at an ORM >20 they would have been fine, but they had another task left to do that presented a conflicting situation.
So in summary, if the crew hadnt pressed AZ5 could the situation have been saved? No, because the reactivity was already on such an upwards climb that the automatic scram system wouldve been triggered, causing the same issue.
Like everyone has been commenting, the issue was the dangerous condition the reactor was in, creating very rapid and uncontrollable reactivity changes.
Even if they overrode the automatic scram, you'd get a meltdown and a big hole in the bottom of the reactor gets you an equally sized boom as a big hole in the top of it. The mess would have been much harder if not impossible to clean up afterwards as well since in reality, they had time before the meltdown started to counter it. In the world AZ-5 wasn't pressed, the melt down is melting its way down into the earth and water systems before anyone knows what's really wrong.
Tell me how a RMBK reactor core explodes not a meltdown an explosion Id love to know?
Xenon pit .... the reason the rods were so far out of the core. A very dangerous place to operate a fission nuke plant.
Maybe if they started to lower the rods one by one they could avoid an explosion. But the core would reach out of range tempretaures and it would be damaged anyway
Good video
Keep on
Of course no one can blame me for this. How can I be responsible? I was sleeping
Not great, not terrible
When the going gets tough, the clever take a nap
Mea culpa. I spilled borscht on the control panel
The sad thing is this really isn't even a possibility. The AZ-3 button was *supposed* to be the safeguard - you press the button and it shuts down the reactor. To their knowledge, they did do what they needed to shut it down safely. I mean, why would the emergency shutdown make it worse?
a very interesting & educational perspective.
But what has happened has happened.
AZ-5 just made the reaction exponentially faster and worse unfortunately.
Even without it you’d still have disaster just at a later time.
Removing the control rods too far where they couldn’t counteract the Xenon pit was the biggest mistake. It was just too far gone.
Unfortunately so many died because the information was withheld.
Its my understanding that once the output (and heat) reached a certain point, nothing was going to save it. AZ-5 wasnt the issue. The graphite mediated rods were the issue. AZ-5 might have made the situation worse. But, there was no recovering Reactor #4 by the time AZ-5 was pressed.
Were you trying to say that prompt criticality would cause the reactor to detonate like a nuclear bomb? I mean, prompt criticality IS what occurred. Whether you intended to suggest this or not, it's a bit irresponsible. There's no way it could've set off the kind of chain reaction necessary to detonate like a nuclear warhead.
He said that prompt criticality is the same technology as a fission bomb. Weirdly worded but not exactly... False?
The two scenarios are moot really. The reactor should never ever have been in the state it was. That it was driven purposely and with determination into this state was the primary failure mode. The rest is just consequences and symptoms of the failure.
Any piece of plant is delivered with operating instructions by legal decree in fact. They’re a formal contractual requirement. Equipment is mixed scrap without them. Deliberately disregarding those operating instructions voids warranty and is usually taken as gross misconduct and would rightly lead to criminal charges against the senior management in the event of accident or injury.
The idea that it was all the operators fault was the early Soviet narrative intended to shift the blame away from the poor reactor design, lack of internal communication about the known deficiencies of the reactor design, and deficient operating guidelines. The staff did not do anything that was unreasonable to them, at the time, with the information they had. This is very well highlighted in the 1993 report from the investigative committee (official english translation by IAEA can be found as annex to INSAG-7): "The personnel violated the Operating Procedures and the Commission notes these violations in this report. Some of these violations did not affect the initiation and development of the accident, others created favourable conditions for the manifestation of the negative design characteristics of the RBMK-1000 reactor. The violations were largely the result of the poor quality of the operating documentation and its contradictory nature caused by the poor quality of the RBMK-1000 reactor design. The personnel were unaware of some of the dangerous features of the reactor and, therefore, did not realize the consequences of the violations."
@@MatthijsvanDuin I understand the sentiment and salute the intention to blame the inanimate but you cannot simply say that breaking procedures was not the problem. The procedures are as much an integral part of the plant as any pump or pipe. We don’t set about the hardware with an angle grinder and not expect consequences.
@@robinwells8879 It's not about blaming the "inanimate", it's about blaming the actual root causes and more importantly, blaming that what can be fixed to prevent future accidents.
The main "violation" that caused the accident was the low ORM, which was a parameter that was not regarded by procedures as safety critical and could not be monitored in real-time from the control room. Moreover it was habitually ignored in normal operation (including the previous day) because the calculation was known to be inaccurate in some operating conditions, and ignoring ORM was necessary to keep the reactor running.
The designers knew that low ORM turned the AZ-5 button into a "reactor accident now please" button, it had already caused a previous reactor accident, but this was not communicated to the operators.
@@MatthijsvanDuin again I suggest that the design was actually a good piece of value engineering that supplied the bulk of the energy needs of Ukraine for years. The management systems and its endemic failures were the problem.
Western reactors by comparison are ludicrously expensive to build and operate and decommission and yet they fail too (Fucashima) containment vessels are costly and still leak in an accident and the high enrichment fuels used have a significant manufacturing energy footprint in their own right.
If you believe that the manner in which the reactor was run on the occasion of the disaster was not contributory then you are missing the root cause and need to ask another why question.
We gloss over the fact that the other units performed without issue for years.
A management system that allows individuals to bully staff into deviation from operational procedures is the root cause.
@@robinwells8879 The RBMK design flaws are well documented, they previously caused the accident at Leningrad Unit 1 (and it was "understood that the accident was a result of the reactor's design characteristics, rather than personnel errors"). The 1993 report bluntly says "The Commission considers that the negative properties of this type of reactor
are likely to predetermine the inevitability of emergency situations". Subsequent to Chernobyl the problems were partially mitigated in other RBMK reactors.
In particular, under absolutely no circumstances is it acceptable for any nuclear reactor that the emergency shutdown button causes an initial _increase_ in reactivity, ever.
Great video!
I need to ask something, who do you think had the worst fate from the night of 26th april??
Like injury or radiation dose
Hmmm... in terms of injury, probably Kurguz, who lost most of his skin in the explosion (worse than Degtyarenko) and still had to crawl through corridors flooded with radioactive steam, or Shashenok, whose injuries were absolutely horriffic.
In terms of radiation dose, likely one of the firefighters or the electricians.
In terms of overall worst fate, I'd say Ivan Orlov. It's hard to describe in just a comment how truly tragic his death was.
@@thatchernobylguy2915 thanks for your opinion, its very interesting
i dont understand what are saying but its fascinating. Subbed
Interestingly the Canadian CANDU reactor is not too dissimilar to an RBMK which makes the Canadians arguably themost knowledgeable in the west on RBMK operation. Of course the reactors are different but they both feature a separated moderator from the coolant system resulting in the positive void coefficient (CANDU uses heavy water RBMK uses graphite) and a couple others things as well. But they are also in many ways different lol!
Yes, for starters they're designed with horizontal fuel channels that can only maintain criticality when the channels are in mechanically sound and pretty much any deformation in a channel will render that channel useless for generating more neutrons. Then if they channels deform enough because of integrity loss and gravity, it will physically touch the moderator channels, which are low temperature because of the heavy water which is also it's coolant, so heat will be transferred into the moderator channels. The control rods are also designed so they are not in the channels generating steam, so there's no way for a steam explosion/void inside the fuel channels to cause problems there. Finally if we need to we have this lovely high pressured gadolinium nitrate neutron absorber that can be pumped into the channels that would honestly make a Xenon pit jealous with how fast it poisons and kills the reactor.
So yeah, you'd have to literally be breaking the laws of physics to Chernobyl a CANDU reactor. It literally will not run if it's failing. Plus there are so many ways to kill it you'd have to be trying to make it explode to get around them all, and even then you're essentially guaranteed to fail miserably.
4:25 ... no, prompt criticality is not the same as an atomic bomb, a reactor still needs moderation of neutrons, which slows down the power escalalion... a bomb is prompt-fast critical ....
Prompt criticality in a reactor is fission sustained by prompt neutrons alone. It's the exact same thing. That happened at Chernobyl. :)
@@thatchernobylguy2915 chernobyl blew up by prompt thermal(!) neutrons, but a bomb runs on promp fast(!) neutrons .... chernobyl never would have reached criticality with fast neutrons allone ....
@@NuclearSavety Fast neutrons have been modeled in the explosion since 1998, and is largely used as evidence in support of a nuclear-jet style of explosion.
@@thatchernobylguy2915 the capture cross section of fast neutrons is way too high in u238 and way to small for u235 for sustaining a chain reaction in 5% enriched uranium. ... for that reason, in nuclear reactors using 5% enrichment you only get criticality when you moderate the neutrons, making them from "fast" to "thermal". When you enrich fuel further like in atomic bombs, you remove more and more U238, making fast unmoderated neutron capture by U235 more and more likely. But with reactor-type fuel, a fast criticality is physically impossible.
There is the concept of fast reactors, these would explode like an atomic weapons in case of reaching prompt criticality, but with thermal nuclear reactors like the RBMK thats not possible. You can get a power excursion to 500GW, destroying the reactor, yes, but thats still not a weapon-type explosion. Latter occurs on a time scale 1000 time shorter than a reactor excursion.
For that reason your comparison of Chernobyl to an atomic weapon unfotunately stinks.
@@thatchernobylguy2915 fast criticality is impossible in reactor-grade low-enriched fuel. Thats the reason you need high enrichment for weapons....
If the designer RBMK reactor and soviet authorities not lies or hiding about positive void specials on their cheap reactor,akimov will not suggest or press the scram button and waiting diesel generator to flow water to reactor and stabilize the core,the worse case is only meltdown...
You didnt see graphite
If the button was pressed, why the action is not registered in the UN report.
Yeah pressing or not pressing AZ-5 at the point where it was pressed only changed how fast the reactor exploded. They had painted themselves into a corner at that stage and nothing was going to stop that explosion at that point.
What happens to the reactor isn't the concerning part. It's the cleaning up of the mess becomes infinitely harder if it melted down instead. They had time to figure out stuff and work to prevent the meltdown from causing damage in reality. If we start at meltdown, there's no heat exchanger under it, it's probably in the ground water and other systems under the earth before we even get a grasp on it, oh and there's also probably still going to be an explosion causing problems for everyone above ground still anyways.
Them blowing up the reactor before the meltdown started basically gave everyone time to work out each problem one at a time before the giant pile of radioactive waste started causing too many irreversible problems underground.
why did their operators wear those white hats?
4:34 Not sure if it's because of a different language, but the translated version on the right shows "Californie" where the one of the left shows "California"./
The Netflix show shows Dyatlov exclaiming when he realizes Toptunov pressed AZ-5. I've often wondered if that implied Dyatlov knew AZ-5 would spike the reactivity due to the rod tips.
No they didn't know. The designers knew, but it hadn't been communicated to operators. They pressed AZ-5 at the normal conclusion of the test (the data logs show reactor parameters were still fine at that time) and then all hell broke loose.
What I want to know is if there is a way to reproduce two more elephant's feet and see if shooting it really accelerated decomposition or not. I really want to know if that is why it happened. I like to think it did but I'm doubtful we will ever conduct that test to confirm.
Im certain you could build a 4 billion dollar test pit for all that.