One thing that was missed, mentioning the lack of a containment structure. Fukushima had 3 meltdowns, compared to Chernobyl's 1, only releasing 10% of the amount of radiation into the surrounding area and atmosphere. The RBMK had no containment structure, hence its massive level of contamination.
I find it pretty lacking tbh. Maybe it seems simple to understand if you don´t know anything about nuclear reactors, but there is quite a bit more to it than explained in this video, however short and condensed it is.
I was first against nuclear power after this horror 1986 I was 9. Now, with all the studies of the incident showing it was obviously a badly designed event at a not so well designed reactor one can just say understanding the science of this can make people see.
@@martintheiss4038 To bad there's such a stigma against nuclear energy. If it is researched more, it can be made safer. Imagine if ships were banned after the Titanic sank. That killed a lot of people, but ships are safer now because they were still researched.
There was a great presentation on it by an American nuclear engineer. He explained the how the why and also showed how that same type of failure can't happen in western style reactors.
Without exaggeration, this is the best explanation of the incident I have seen. It lacks some deeper technical details, but it manages to perfectly summarize what others cannot in less than 40--60 minutes.
This is the 8th video that I’ve watched about Chernobyl and the first time I have understood what actually happened! I can’t thank you enough for explaining it so well!! Amazing! 👏👏👏
This isn't an entirely accurate explanation, nor was the HBO series. The rods were not "graphite" tipped. Almost half of a rod was made of graphite, with almost another half being made of boron, with space in between. The rods would go in and out exposing either the graphite end, or the boron end. The problem with Chernobyl is that once the Xenon gas ran out, the reaction spun out of control damaging the rod movement system and locking the rods in a position where mostly graphite was exposed.
That is very true. I think they used carbide as moderator in RBMK reactors because of their use of low-grade enriched uranium. Because of this, water by itself was not enough to provide good moderation so they had to use carbide which is a very good moderator even for low enriched uranium.
The reactor is designed too continuously "burn off" the xenon (actually, to transmute it with neutrons into a less poisonous xenon isotope) created when it is running at 80-100% of rated capacity. When running at below 50% rated, the xenon starts building up faster than it is burned. When the reactor gets loaded with xenon, there are two things that can be done. The first is to simply stop the reactor. The xenon will decay away in about three days, and the reactor can then be started up normally. The other is to raise the power to burn the extra xenon. With the xenon present acting like control tods, that can only be done by withdrawing the control rods maximally. When the burn starts, the xenon is being converted and the reactor has to be closely watched, inserting rods to replace the xenon as the power rises, but not so many as to quench the reaction. They were on the slope of another positive feedback, which ran away and ultimately took them to 3,000 times the full rated power of the reactor for a few milliseconds, long enough to wipe out all the rest of the xenon "control" and boil all the coolant water away.
Another thing this video overlooked is that Xenon-135 is rarely created directly from fission, rather it is a decay product of the heavier isotopes typically created when fission occurs. Once it absorbs a neutron, it becomes the extremely stable non-absorbing isotope Xenon-136, and it is always present in an operating core. At a stable power level, it is at an equilibrium value, where it is being converted to Xenon-136 at the same rate it is being produced by fission-product decay. When you drop from nearly 100% power to 7% or so as Chernobyl did, it builds up as the fission-products that will create it are already in the core, but the reactor is no longer creating enough neutron flux to burn it out.
The other issue is a large (power) plant using low enriched U. On the power reduction, a situation could arise in which the control rods become separated from the region where reactions are taking place, in part because of where the xenon is generated. This coupled with the control rod tips being graphite. I might disagree with the positive coefficient because this is inherent in large reactors running on low enrich. Had they a different rod sequence strategy and perhaps a graduated graphite-boron in the rod tips, it would not have produced initial positive reactivity resulting in prompt criticality
@@jimfrazier8104 Well, the largest problem with Xenon is it's a gas. As it expands it cracks and breaks up the solid fuel rods in all reactors that use solid fuel. It is the primary reason why these rods can never be "burned" for more than around 2% of their potential before being discards, which is a pathetically stupid design. In a LiFTR reactor Xenon simply boils out of the molten salt and can be captured since it is commercially valuable, but even if it does escape it's a noble gas.
I've watched lots of videos attempting to explain the Chernobyl disaster. This is the only one that does so in an easy to follow fashion. It explains the physics of fission in a very clear way.
5 ปีที่แล้ว +60
The tips weren't made of graphjite, there were whole graphite rods attached to the control rods, so that when removed, there would be a moderator. When the control rods were lowered, the graphite rod at the bottom displaced water, that was inhibiting the reaction, which in turn accelerated it.
The "graphite tip" she's referring to is a few meters long. It's the moderator rod, attached to the control rod. One goes in, the other is pushed (or pulled) out.
I've been doing research on nuclear science and engineering for months, but never really understood the mechanics of what went down at Chernobyl, but now I know. This was super clear and easy to understand, best video I've seen explaining it by far.
7:27 They didn’t do that. They instead had a graphite rod attached to the control rod in order to make the control rods a better controller of the nuclear reactor's reactions. The graphite rod was also shorter at the top and at the bottom to balance neutron flux levels (neutron movement). So when that rod goes into the bottom half of water, the power went up and jammed the rods in the position.
but why this construction? i see the befit in a normal reaction but again what happen, if u have to scram the reactor? and ok they have driven it beyond all safety protocols.
It’s cheaper for one, since you have the benefit of having the neutron-absorbing, reaction-slowing boron and the neutron-moderating, reaction-accelerating graphite in one assembly. The emergency stop procedure “””should””” have worked in basically most circumstances, but “most” doesn’t include the edge case of ALL of the control rods being put in at once. If only some of the control rods are simultaneously inserted, the ones that are *already in* are generally enough to stop the spike from being catastrophic. In ‘86 though since all the control rods were being put in at the same time, there wasn’t anything to stop the spike.
The graphite tipped rods were an effort to increase the reactor's efficiency because, when the rods were fully pulled from the core, the boron still had the effect of slightly blocking the reaction. The graphite, which is a moderator, would isolate the tips of the boron rods. Reinserting the graphite tipped control rods therefore initially cause a spike in reaction...in this case...BOOM.
@@bambam144 It gave them a way to both accelerate and decelerate the chain reaction's intensity with one assembly. Nuclear power plants are expensive as hell, so in a bid to reduce costs the USSR designed it to have both on one assembly. Now, the reason they did this is because it's graphite and not water moderated, which was done intentionally because graphite is a far better moderator than water and allowed the reactor to run on (much cheaper) naturally occurring or lower enriched Uranium (~0.72% U-235 is natural, as opposed to power-grade enriched which is usually in the area of 5% U-235). Water acts as an absorber here because the graphite is far more effective at thermalizing neutrons (i.e. slowing them down) and is not as good at absorbing them when compared to water. Water can be used as a moderator (see: PWRs, BWRs, SCWRs), but it needs (higher) enriched fuel. As for the SCRAM problem... Yep. Big problem, one that had to be rectified post-Chernobyl. Every other RBMK received major updates to the control rods (as I understand it) to prevent this from happening in the event of another loss-of-coolant event.
Ultimately, they tried to ramp it too quickly. Ramping refers to increasing or decreasing the power output of a power plant. You can ramp a hydro electric dam within minutes. A coal plant can be ramped over an hour or two. Natural gas and oil a bit quicker. Nuclear plants need to be ramped very slowly. Optimally, you use your nuclear plants for base loading and run them as close to full capacity as you can, and when the grid requires higher capacity during peak hours, you use more conventional power plants to make up the difference. The operators at Chernobyl attempted to ramp too quickly, with disastrous results. Once the reactor output dropped and refused to increase they should have re-inserted the control rods and let the xenon burn off and then began the day long process of ramping up again. Instead someone panicked and tried to strong arm the reactor back to it's normal capacity. RBMKs are possibly the most temperamental reactors ever developed. The only other reactor that even comes close in my mind was the reactor in the Alfa Class soviet nuclear submarines. They used lead cooled fast reactors. If you had to SCRAM one of those reactors, the lead would cool and solidify rendering the entire reactor a giant useless pile of nuclear waste. This happened to more than a few of these submarines.
I read a story about an Alfa that sprung a coolant leak leading to not only a loss-of-coolant accident but also a reactor compartment knee-deep in solidified lead. It might have been a decent idea for a reactor but it was also a complete pain in the arse to clean up if something ever went wrong.
The other downside of the Alfa's was that lead (well, lead-bismuth) is Dense-as-fuck™ and the reactor alone composed around 30% of the overall weight of the sub, making them a bitch to surface if anything ever went wrong. But they had a stunning career.
Lead cooling sounds like a good safety system,in reality the reactor can't have 'problems' like a car! it is more like an aeroplane,only one chance - stay in the air. If it gets upset,best lock it up in lead.
I would not be surprised that Dyatlov forced the power back up because he believed that it could be easily and safely done with RBMK reactor, just as it could be with a small submarine reactor. Dyatlov has worked on submarine reactors prior coming to Chernobyl and probably never received proper training for RBMK reactors ("as he already knew how to operate reactors from his previous job").
Of the many videos on this event that I've watched ... after watching this video... I now actually understand what happened and how it happened. Thank you for making it.
god - again this "graphite tip on the control rods" thing - this is so misleading and even the graphic on 7:27 is making you think its a small layer of graphite - only on the tip of the rod
7:45 No, graphite burning did not explode... The most common explanation is hot fuel rods create hydrogen causing an explosion, or water split into hydrogen + oxygen which then exploded. First time hearing carbon fire explosion
Great explanation of the accident. It unfortunately set back the acceptance of nuclear energy by the general public, though it’s still the ‘cleanest’ energy choice we currently have available.
Tips were not made out of graphite. Neither water pumps were shut down (point of test was to just redirect power to the pumps). Actually rods did not have tips at all instead a different rod made out of graphite to accelerate reaction. When they pulled out boron rods they pulled in graphite rods. Flaw was the emergency shut down system. When they clicked the shut down button all the rods started moving down at once creating neutron flux spike at the bottom. That's what caused explosion. This tv series is no less lie then soviet union. In fact you can listen to actual Legasov tapes and find out for yourself.
I read that the team doing the test were not nuclear experts but experts on the (non-nuclear) back-up test areas only. They did not consult with the nuclear experts and weren't aware of the nuclear risks from what they were doing. When the explosion happened, we were visiting Wales at the time and I remember some fallout cloud eventually came over Wales because some of the grass and sheep there could not be consumed afterwards as they were radioactive. It's ironic that the disaster was a consequence of a 'safety test' which wasn't safely carried out.
@@jojojimys I read somewhere that the explosion fallout was worse than the effects of many hydrogen bombs. I think it was 100 times worse but I can't recall exactly. I'm a non-scientist, interested in learning how the accident happened.
Ive watched quite a few videos to better explain this process and many only talk about it. This video visually and verbally explains it simultaneously which is way more effective in the understanding of the concepts! Amazing video, thanks!
This video is a lie. I commented above...in newest comments. You do not know how a reactor works and neither does she. I am coming out with a website called DISSECTING PROPAGANDA..and we will be exposing the lies of COVID and these alleged "accidents" with Chernobyl and Fukushima. but...this young woman....does not know how a Nuclear Reactor Plant Operates. I do. I was in the US navy's nuke program and have operated power plants in subs and at on land facilities. I have been inside a Reactor room where a "core" sits. It does not operate as shown here.
This video maybe old, but I have to point out that the control rods did not have graohite tips. Yes, they were designed with graphite, but the whole lower sections of each rod were made of graphite. Like, half od the whole rod. Once those rods were lowered into the reactor, the graphite sent the reaction skyrocketing, destroying the interior and causing a near instantaneous build-up of pressure that caused the initial explosion and it all fell down from there.
One of the best explanation videos out there. Again they messed up with the "graphite tips". They were not "tips". There were about 4.5 meters worth of graphite. That's not a "tip".
a very good explanation of answering the " what " went wrong with the reactor design question ...but as to answering the " why " it went wrong question, it seems to be that all to common work pressure environment from upper level management , to get it done and disregard safety protocol if needed...........which unfortunately still goes on to this day.............
Why do so many people keep saying the control rods were “tipped” with graphite? They weren’t. They had a graphite rod which was pulled into the core when the control rod was pulled out. That’s what allowed them to have better control of the reactor. It was a hot spot that developed at the bottom of the reactor, due to the low water flow, that caused the problem. As the control rods were inserted, the water in the bottom of the reactor was displaced by the descending graphite part of the control rod. This caused a huge change in neutron flux which had the consequence of breaking some of the fuel rod channels and preventing the control rods from moving further. From then on, it was simply a run-on chain reaction.
1:38 also wrong the chernobyl reactor had all the right safety features on it except for 2, external shielding of a reactor which is commonly left out from nearly all reactors built even today, but the main one in question was the graphite didnt cover the bottom of the rods. so once they were inserted into the core to cool the core down and force it to shut down it caused any water beneath the rods to immediately turn into steam instead of it being able to cool the rods down. this was mostly done to save money but also because at the time it was considered impossible for meltdowns to ever occur in a npp
I saw a documentary on a experimental VLF atmospheric test that was being conducted the same night only 40 KM away from Chernobyl. Engineers knew that this high power VLF had in the past interfered with Chernobyl instrumentation in the past. They had not told each other the either testing that evening. Did the VLF test interfere with the instruments in the control room of Chernobyl?
You missed out the fact that the workers Akimov and Leonid (who were in the reactor control room moderating the power output) actually considered to slowly raise the power in the reactor over the period of 24 hours considering xenon poisoning of the core... They even suggested it to Anatoly Dyatlov. However, Comrade Dyatlov violated the safety regulations and protocols and went forward with the testing, unaware of the design flaw of the control rods(graphite tips). They tried to bring up the power output, it starts to increase drastically. Trigger was pulled when AZ-5 was initiated which lowered all the *graphite tipped* control rods at once into the core. That's when RBMK reactor exploded. Everything else was covered well in this video.
@@galvanizedcorpse Y'know, a lot of people in the west were born AFTER Chernobyl and the HBO series may have been their first close exposure to it (so to speak).
Actual Its not the Best explanation, this video just copys the mini serie from hbo, The control rod tips made from graphite where not exactly the cause of the disaster, The control rods where also the acceleration rods not like shown here, 7 meters where boron and 4 metere graphite and worked togheter not separatly like shown în here, The cause of disaster was that AT the bottom of the reactor because of graphte tips got stuck, water boiled and create uneven fission which ultimatly provoked the events, sorry for my bad gramar, i am a nuclear scientist from a forme comunist country
7:43 The cause of the second explosion could have been ignition of hydrogen which had been produced by the reaction of steam with zirconium fuel cladding. The explosions at Fukushima were from hydrogen.
It was said there were two primary explisions. One when the lid popped off from steam build up enough to blow a 200 ton lid high enough to take the roof off above and then come down to rest sideways and then a much larger bammo when the oxygen rushed in the crucible reactor vessel and the rest is history. The entire real bad part of the event was within roughly 45 seconds. Although far fetched, I'm looking forward to the Russian take on the event that they plan to make. It is quite a coincidence that the iron curtain fell soon after. I can't help but wonder if Dyatlov and or others in the program had other motives.
This is incorrect, they are explaining what happened in the accident of the HBO series, not what happened in reality. The tips of the control rods were not made of graphite... That was an oversimplification they did in the series
CANDU reactors have a very small positive void coefficient, in certain configurations. This is mitigated but your statement about RBMKs being the only ones to have this are not completely correct.
CANDU reactors are built with 2 shut off mechanisms, first the control rods and the 2nd is a chemical that stops the reaction dead as well. Both operate at the same time automatically (or manually if needed). So the chances of it blowing up is impossible.
Why does nobody show the correct control rod layout? They were not tipped with graphite.. The top half was boron and the bottom half was graphite... With a slight empty space inbetween
I'm glad to know that you watched Chernobyl by HBO, but you shouldn't take an explanation from episode 5 as the basic truth. Actually power was at relatively low level and had low rate of increase before AZ-5. It started increasing momentarily AFTER pressing AZ-5. This action wasn't an emergency one.
You gave vague informatiom about those control rod tips, some say they displaced water and not steam, on top of that positive feedback loop, the tip of graphite rods gone into the gaps in the bottom, which remained empty when the control rods were completely removed, as water is denser than the steam, the graphite tips which got inserted into the bottom gap quickly escalated the reaction rate on top of positive void loop, and then turned the bottom water directly into steam, thats the reason it exploded...
The accident that happened at the Fukusima plant was the eventual lack of cooling water to the reactor cores (obviously because of the tsunami and systematic loss of emergency power). Units 1, 2 & 3 reactor cores eventually melted. Is the BWR reactor a negative coefficient reactor. No water, no problem. One thing for sure, if a catastrophic accident does occur, the clean-up is going to cause multiple deaths and decades before the contaminated area is fully safe.
1) The tips weren't graphite. The entire bottom part of the control rod was graphite. The top was the boron part and the bottom was the graphite part. When the rods were lowered, the boron would be at level with the fuel and the graphite below the fuel. When the rods were raised, the graphite would be at level with the fuel and the boron above the fuel. 2) The control rods also had their own water cooling system. This is where the key to the major flaw was. If the water got heated enough, the pressure would prevent the control rods from fully lowering.
i understood everything , but can anybody tell me why reducing the power over a limit is bad ? it is essentially like switching off the reactor right ? why were they concentered to increase the power
You did not explain why the Xe135 was still increasing at the low power level because of the I135 left over from when the RBMK was running at full power and why bringing it up slowly allows time for the I135 to decay and the Xe135 to both decay and burn up from the increasing power. Slow buildup after a power reduction is of course required for safe operation of any reactor.
You missed 1 important detail. When the rods went it, they take 18 seconds to be fully inserted at that time (now it has been reduced to 4 seconds), there was a hot spot already in the core by the time the rods were being reinserted into the core. Which then blew up the core making it so the rods could not be fully inserted and the graphite tips remained in position increasing the reaction.
RBMK reactors are not the only commercial reactors with a positive void coefficient. Candu reactors also have a very small positive void coefficient, but nowhere near as large as RBMK reactors.
Schematics for the control rods are not correct - they were half boron and half graphite, so essentially when the rood is completely out it actually means that graphite water displacer is in. The problem is they had gaps above and beneath them tho move neutron flux to the center of the reactor. When water boiled out beneath the rods and they started to move down, displacing steam instead of water, that caused instant flux displacement to the bottom and reactor acceleration, and increased pressure has ruptured the channels, and rods were jammed in acceleration position. Designers were well aware of positive feedback systems dangers, but that type of reactor was required for growing USSR industry not only because it was cheaper to build, unlike PWRs it could also been built in sight, produced twice more power, used regular water as coolant and unenriched uranium as fuel and could be refueled while running, which allowed it to be used as an isotope factory for chemical and medical industries. Being not able to calculate all extreme conditions, designers introduce various safety systems and strict instructions. The main reactor flaw was actually that operators had an access for shutting down safety systems - which they did, considering unexplained restrictions as unnecessary. The most ironic is that after the Leningrad RBMK incident they in fact figured out the problem and how to fix it, but because of how unlikely the repeat chance was (as no one was supposed to push the reactor beyond the limits), it was decided to improve reactors at their next scheduled shutdowns, which was supposed to occur right after the safety test. So the disaster was an insanely improbable combination of reactor flaw, safety system flaw, global power management fault, local test management fault and very bad timing - if only only one link of that chain if disaster was not there, no one would ever hear of Chernobyl... Reality is far more sad then fiction - it were not lies and conspiracy caused the disaster, it were everyday carelessness and negligence, as no one thinks his actions could be combined into a tragedy...
I was an industrial safety manager for over thirty years. There has never been a safety system designed that operators have not figured out a way to override and did not try to do so, for even the most irrational reasons. There are Homer Simpsons everywhere. Fubars in nuclear energy plants are bigger and more expensive.
@@jackfanning7952 true, but when you're designing a vehicle that becomes extremely uncontrollable over 100mph, you have only two choices - to make a system that will under no circumstances allow it to reach that speed or don't make such vehicle at all. And in a first case you shouldn't make a switch for it and definitely shouldn't place it to the dashboard. Btw, a lot of scientists familiar with RBMK back then had the same point, including Legasov, but now we have what we have...
@@jackfanning7952 It would be the case it's there was such an option. But, as I explained, there basically wasn't - bunch of low cost/high power power plants needed to be built like yesterday. They wanted to help country's wealth growth, but in the end made an opposite. The road to hell is paved with good intentions...
I am no expert, but another cost cutting measure was there wasn’t a containment structure around the reactor. (The proper materials on the beginning of the video) This is steel reinforced concrete (think bomb shelter material) that keeps the nuclear fuel inside and not escape into the atmosphere. Three mile island, Fukushima and literally every nuclear reactor in the world have this.
Water is mainly a neutron moderator. So water enhances nuclear reaction. So it shouldn't be called an absorber as it may only be slowing down the fast-moving neutrons and not absorbing them very effectively as boron would. Boron is used in the control rods to slow down and ultimately stop all reaction if necessary. In modern fail-safe reactor designs, water is both the moderator and coolent. So if the coolent water is lost or excessive heat in the core is causing steam voids in the reactor channels, this will trigger an automatic reaction slow down due to lack of moderation, preventing a run-away reaction that would cause a reactor core explosion or melt down.
Clear & wrong explanation you should say. Control rods don't have any graphite tips at all and the real cause of the explosion was the neutron flux that built up at the bottom because rods couldn't be inserted fully
There is a saying in Turkish, if the things you told cant be understood by no one, it indicates that even you could not understand exactly what you are trying to tell the people. This is the only video where i could understand exactly how the accident mechanism was after watching 10 videos. Thanks a lot...
Graphite in the control rod sped up the reaction exponentially, acting as a moderator itself during a scram, can i say that without trying to sound like a physicist?
The graphite moderator was actually already increasing the reactivity prior to the scram and creating the feedback loop for the positive void coefficient. The problem was that during the scram the graphite tipped moderator had broken off and had jammed in a position that further displaced the water. Water was already vaporizing pretty quickly due to a combination of all the Xenon-135 being burned off, almost all of the Boron rods being taken out (their graphite tips still in place controlling reactivity and producing steam) as well as less neutron absorption taking place from the shut off of some of the pumps due to the test. This scram was just the final nail in the coffin, but by itself wouldn't have led to the kind of event that occurred in Chernobyl. The problem was the overall reactor configuration the engineers created combined with some of the design flaws of the RBMK itself.
what iisnt explained is how the modern reactors negative co efficent works. if the negative feed back loop water starts to run low "HOW" does it drop reactor power when its already become a run away freight train?
trying to figure this out. all ive got is that the the hotter things get for modern reacxtor the less reactions there are. where as the rmbk if it gets hotter. it will not slow but increase reactiona
@@corydemeray7594 Because most modern reactors use water as a moderator. So if all the water boils off you don't get slow neutrons to sustain a reaction. The RBMK used graphite for this, which allowed it to run on less refined fuel.
One of the unspoken causes of the Chernobyl accident was the fact that the Nuclear Engineers do not fully understand the RMBK reactor at low power. The RMBK reactors are usually very unstable at low power. The test which was supposed to start around 1pm was delayed due to the demand for power until 11pm. By 11pm, the experiment started and the reactor power was decreased. So at low power, they were unable to stabilize the reactor due to Xenon poisoning. In trying to stabilize the reactor, they removed all but 6 Control Rods (CR) as far as possible. With more than 200 CRs removed, the power was able to come up to 200MW before starting the experiment. As water evaporated, creating more bubbles (Positive Void Coefficients), the reactor power increased, more neutrons were available that the remaining 6CRs could not compensate the neutrons. The void coefficient of reactivity is used to estimate how much the reactivity of a nuclear reactor changes as voids (usually steam bubbles) form in the reactor moderator or coolant. The available shift supervisor requested the insertion of all CRs but the insertion speed was too slow, in less than a minute, the temperature at the core was above 3000 degrees leading to a transient nuclear reaction that was followed by an explosion, releasing radioactive materials 400 times more toxic than the Hiroshima bomb explosion. If they had understand the operations of an RMBK at low power, what would have happened was for the graphite tipped control rods to be moved in and out consistently in order to stabilize it. In fact, the operators had no manuals or control rods on how to operate the reactor at an unstable condition. Like someone said, whether you watch the video or read the comments, there are useful information in both. Lol
It wasn't the first time an RBMK-100 had suffered a power excursion during a shutdown for refueling. One of the units at the Ignalina plant had also had this happen, but with no catastrophic effects. The Atomic Energy Bureau buried the report, which is why the Chernobyl engineers were so oblivious. Hell, it wasn't even Dyatolov's first nuclear accident, but they were so conditioned to toeing the party line that the concerns of the reactor operator (Leonid Toptunov) and the shift supervisor (Aleksei Akimov) were completely over-ruled.
Water acts as a moderator of neutrons, increasing their probability of interacting with u235 to create fission. Loss of liquid water stops the moderation, and neutron interactions with u235 decrease.
One thing I struggle to understand. If the water pump was switched off, and the remaining water turned into steam, wasn't that steam supposed to be channeled somewhere, thus, controlling the pressure inside the reactor? if there was not water in the reactor what was ramping up the pressure? Mere increase in temperature? I am not really good with physics, probably asking some basic questions :)
1 operator named Toptunov, the guy who pulled all the control rods because Dyatlov asked him died at 25 and only been working there for 6 months, no clear instruction about the safety test protocol whatsoever. Rest in piece to all the victims involved.
Seriously, a very big thanks to u😭🙏🏻. It was one of the BEST and the most informative video i could find to understand what actually happened at Chernobyl. Ur way of explaining is soo simple and clear. U were a savoir to me today💖. Once again, thnqq soo much💓 and i mean it by heart💕💕🙏🏻🙏🏻💜💜💜💜💜💜💜💜💜💜💗💗💗💗💗💗 keep going🤗
One thing that was missed, mentioning the lack of a containment structure. Fukushima had 3 meltdowns, compared to Chernobyl's 1, only releasing 10% of the amount of radiation into the surrounding area and atmosphere. The RBMK had no containment structure, hence its massive level of contamination.
The clearest and simplest explanation about Chernobyl. Thank you.
@Carlo Noccioli agreed
Illinois Energy Professor has an excellent video on Chernobyl too
I find it pretty lacking tbh. Maybe it seems simple to understand if you don´t know anything about nuclear reactors, but there is quite a bit more to it than explained in this video, however short and condensed it is.
i watched so many vids on this reactor....and this is the only one that actually made any sense....thank you 😭
I was first against nuclear power after this horror 1986 I was 9. Now, with all the studies of the incident showing it was obviously a badly designed event at a not so well designed reactor one can just say understanding the science of this can make people see.
@@martintheiss4038 To bad there's such a stigma against nuclear energy. If it is researched more, it can be made safer. Imagine if ships were banned after the Titanic sank. That killed a lot of people, but ships are safer now because they were still researched.
This is basically what Valery Legasov explained in Vienna
There was a great presentation on it by an American nuclear engineer. He explained the how the why and also showed how that same type of failure can't happen in western style reactors.
I have a degree in nuclear physics from hbo university 😎
“Every lie we tell incurs a debt to the truth. Sooner or later that debt is paid”
-Dr. Valery Legasov, **Chernobyl**
@A Malevolent That's why I included Chernobyl at the end for the show.
"What is the cost of lies?"
@A Malevolent another lie has been told
Dr Gonzo but the truth is still there
@@Bludgeoned2DEATH2 lol after he made the comment idiot
Without exaggeration, this is the best explanation of the incident I have seen. It lacks some deeper technical details, but it manages to perfectly summarize what others cannot in less than 40--60 minutes.
Higgsino Physics has a visualization that is by far the best explanation of what went wrong. Enjoy! 😊
This is the 8th video that I’ve watched about Chernobyl and the first time I have understood what actually happened! I can’t thank you enough for explaining it so well!! Amazing! 👏👏👏
really true
This isn't an entirely accurate explanation, nor was the HBO series. The rods were not "graphite" tipped. Almost half of a rod was made of graphite, with almost another half being made of boron, with space in between. The rods would go in and out exposing either the graphite end, or the boron end. The problem with Chernobyl is that once the Xenon gas ran out, the reaction spun out of control damaging the rod movement system and locking the rods in a position where mostly graphite was exposed.
That is very true. I think they used carbide as moderator in RBMK reactors because of their use of low-grade enriched uranium. Because of this, water by itself was not enough to provide good moderation so they had to use carbide which is a very good moderator even for low enriched uranium.
The reactor is designed too continuously "burn off" the xenon (actually, to transmute it with neutrons into a less poisonous xenon isotope) created when it is running at 80-100% of rated capacity. When running at below 50% rated, the xenon starts building up faster than it is burned. When the reactor gets loaded with xenon, there are two things that can be done. The first is to simply stop the reactor. The xenon will decay away in about three days, and the reactor can then be started up normally. The other is to raise the power to burn the extra xenon. With the xenon present acting like control tods, that can only be done by withdrawing the control rods maximally. When the burn starts, the xenon is being converted and the reactor has to be closely watched, inserting rods to replace the xenon as the power rises, but not so many as to quench the reaction. They were on the slope of another positive feedback, which ran away and ultimately took them to 3,000 times the full rated power of the reactor for a few milliseconds, long enough to wipe out all the rest of the xenon "control" and boil all the coolant water away.
Should of left the water on.
I understand it more now thanku
Another thing this video overlooked is that Xenon-135 is rarely created directly from fission, rather it is a decay product of the heavier isotopes typically created when fission occurs. Once it absorbs a neutron, it becomes the extremely stable non-absorbing isotope Xenon-136, and it is always present in an operating core. At a stable power level, it is at an equilibrium value, where it is being converted to Xenon-136 at the same rate it is being produced by fission-product decay. When you drop from nearly 100% power to 7% or so as Chernobyl did, it builds up as the fission-products that will create it are already in the core, but the reactor is no longer creating enough neutron flux to burn it out.
The other issue is a large (power) plant using low enriched U. On the power reduction, a situation could arise in which the control rods become separated from the region where reactions are taking place, in part because of where the xenon is generated. This coupled with the control rod tips being graphite. I might disagree with the positive coefficient because this is inherent in large reactors running on low enrich. Had they a different rod sequence strategy and perhaps a graduated graphite-boron in the rod tips, it would not have produced initial positive reactivity resulting in prompt criticality
@@jimfrazier8104 Well, the largest problem with Xenon is it's a gas. As it expands it cracks and breaks up the solid fuel rods in all reactors that use solid fuel. It is the primary reason why these rods can never be "burned" for more than around 2% of their potential before being discards, which is a pathetically stupid design. In a LiFTR reactor Xenon simply boils out of the molten salt and can be captured since it is commercially valuable, but even if it does escape it's a noble gas.
I've watched lots of videos attempting to explain the Chernobyl disaster. This is the only one that does so in an easy to follow fashion. It explains the physics of fission in a very clear way.
The tips weren't made of graphjite, there were whole graphite rods attached to the control rods, so that when removed, there would be a moderator. When the control rods were lowered, the graphite rod at the bottom displaced water, that was inhibiting the reaction, which in turn accelerated it.
3.5 m rods count as tips, don't the?
@@KarlKarpfen No.
Correct.
@@KarlKarpfenno fuck the tip means "the end of the rod" going into the bottom gap...
A very clear concise explanation of what happened at Chernobyl causing a very sad and avoidable event.
I've watched dozens of vids on the exact steps of this disaster - even the movie. This one is by far and away the best layman's explanation!
This was the best easy-to-understand explanation I've come across about Chernobyl and how reactors work. Thanks!
The "graphite tip" she's referring to is a few meters long. It's the moderator rod, attached to the control rod. One goes in, the other is pushed (or pulled) out.
I've been doing research on nuclear science and engineering for months, but never really understood the mechanics of what went down at Chernobyl, but now I know. This was super clear and easy to understand, best video I've seen explaining it by far.
Really well written and the graphics are terrific...combined to create a great explanation.... Kudos to Sam and the team
7:27 They didn’t do that. They instead had a graphite rod attached to the control rod in order to make the control rods a better controller of the nuclear reactor's reactions. The graphite rod was also shorter at the top and at the bottom to balance neutron flux levels (neutron movement). So when that rod goes into the bottom half of water, the power went up and jammed the rods in the position.
but why this construction? i see the befit in a normal reaction but again what happen, if u have to scram the reactor? and ok they have driven it beyond all safety protocols.
It’s cheaper for one, since you have the benefit of having the neutron-absorbing, reaction-slowing boron and the neutron-moderating, reaction-accelerating graphite in one assembly.
The emergency stop procedure “””should””” have worked in basically most circumstances, but “most” doesn’t include the edge case of ALL of the control rods being put in at once. If only some of the control rods are simultaneously inserted, the ones that are *already in* are generally enough to stop the spike from being catastrophic. In ‘86 though since all the control rods were being put in at the same time, there wasn’t anything to stop the spike.
The graphite tipped rods were an effort to increase the reactor's efficiency because, when the rods were fully pulled from the core, the boron still had the effect of slightly blocking the reaction. The graphite, which is a moderator, would isolate the tips of the boron rods. Reinserting the graphite tipped control rods therefore initially cause a spike in reaction...in this case...BOOM.
@@bambam144 It gave them a way to both accelerate and decelerate the chain reaction's intensity with one assembly. Nuclear power plants are expensive as hell, so in a bid to reduce costs the USSR designed it to have both on one assembly. Now, the reason they did this is because it's graphite and not water moderated, which was done intentionally because graphite is a far better moderator than water and allowed the reactor to run on (much cheaper) naturally occurring or lower enriched Uranium (~0.72% U-235 is natural, as opposed to power-grade enriched which is usually in the area of 5% U-235). Water acts as an absorber here because the graphite is far more effective at thermalizing neutrons (i.e. slowing them down) and is not as good at absorbing them when compared to water. Water can be used as a moderator (see: PWRs, BWRs, SCWRs), but it needs (higher) enriched fuel.
As for the SCRAM problem... Yep. Big problem, one that had to be rectified post-Chernobyl. Every other RBMK received major updates to the control rods (as I understand it) to prevent this from happening in the event of another loss-of-coolant event.
The flash steam didn't allow the rods to move down further...
3.6 roentgen - not great, not terrible
It's not 3.6 Roentgen, it's 15000.
@@sumeetdadwal9313 This man's delusional, get him to the infirmary.
that stuff was pure propaganda, i'm waiting for the series on the gulf of tonkin, the wtc-7, or the lusitania, or the unnecessary nuking of Japan
ankit gupta you’re delusional.
Ankit... he is just quoting the remark the Chernobyl inquiry guy's said!
Thank you. There is still some areas left unanswered but this is much better than the last video I watched...
Ultimately, they tried to ramp it too quickly. Ramping refers to increasing or decreasing the power output of a power plant. You can ramp a hydro electric dam within minutes. A coal plant can be ramped over an hour or two. Natural gas and oil a bit quicker. Nuclear plants need to be ramped very slowly. Optimally, you use your nuclear plants for base loading and run them as close to full capacity as you can, and when the grid requires higher capacity during peak hours, you use more conventional power plants to make up the difference. The operators at Chernobyl attempted to ramp too quickly, with disastrous results. Once the reactor output dropped and refused to increase they should have re-inserted the control rods and let the xenon burn off and then began the day long process of ramping up again. Instead someone panicked and tried to strong arm the reactor back to it's normal capacity.
RBMKs are possibly the most temperamental reactors ever developed. The only other reactor that even comes close in my mind was the reactor in the Alfa Class soviet nuclear submarines. They used lead cooled fast reactors. If you had to SCRAM one of those reactors, the lead would cool and solidify rendering the entire reactor a giant useless pile of nuclear waste. This happened to more than a few of these submarines.
I read a story about an Alfa that sprung a coolant leak leading to not only a loss-of-coolant accident but also a reactor compartment knee-deep in solidified lead. It might have been a decent idea for a reactor but it was also a complete pain in the arse to clean up if something ever went wrong.
The other downside of the Alfa's was that lead (well, lead-bismuth) is Dense-as-fuck™ and the reactor alone composed around 30% of the overall weight of the sub, making them a bitch to surface if anything ever went wrong. But they had a stunning career.
Lead cooling sounds like a good safety system,in reality the reactor can't have 'problems' like a car!
it is more like an aeroplane,only one chance - stay in the air.
If it gets upset,best lock it up in lead.
so basically a lousy design badly operated by Homer Simpsonski , obeying comrade Burnski
I would not be surprised that Dyatlov forced the power back up because he believed that it could be easily and safely done with RBMK reactor, just as it could be with a small submarine reactor. Dyatlov has worked on submarine reactors prior coming to Chernobyl and probably never received proper training for RBMK reactors ("as he already knew how to operate reactors from his previous job").
Of the many videos on this event that I've watched ... after watching this video... I now actually understand what happened and how it happened. Thank you for making it.
Brilliant documentary and so well presented and delivered too, clear, concise and easy to follow with all the drama of the real event. Well done .
Don't bother watching the video, it seems all the nuclear experts are in the comment section
They stayed at the Holiday Inn last night.
Mofs all nuclear scientist became youtuber here, so chrnobyl disaster happened
Every McJob moron is a nuclear engineer.
Lol
@Jeremy Kirkpatrick you said it.
god - again this "graphite tip on the control rods" thing - this is so misleading
and even the graphic on 7:27 is making you think its a small layer of graphite - only on the tip of the rod
I don’t understand this error, either. The “tip” was 4.5m long and an integral part of the rod.
Ah I finally get it, thanks for the explanation
7:45 No, graphite burning did not explode... The most common explanation is hot fuel rods create hydrogen causing an explosion, or water split into hydrogen + oxygen which then exploded. First time hearing carbon fire explosion
Great explanation of the accident. It unfortunately set back the acceptance of nuclear energy by the general public, though it’s still the ‘cleanest’ energy choice we currently have available.
Tips were not made out of graphite. Neither water pumps were shut down (point of test was to just redirect power to the pumps). Actually rods did not have tips at all instead a different rod made out of graphite to accelerate reaction. When they pulled out boron rods they pulled in graphite rods. Flaw was the emergency shut down system. When they clicked the shut down button all the rods started moving down at once creating neutron flux spike at the bottom. That's what caused explosion. This tv series is no less lie then soviet union. In fact you can listen to actual Legasov tapes and find out for yourself.
How many different languages were being spoken that night in the control room ? Why wasn't Brukonov there that night to oversee testing ?
so why did they use the positive void coefficient. Im confused how that cuts costs or is even a remotely good idea???
After searching for dozens of videos, this was the stop for me. Thanks a lot for explaining in such a wonderful way.
I have watched several videos trying to understand, and this is the best explanation I have seen. 👍🏼
I read that the team doing the test were not nuclear experts but experts on the (non-nuclear) back-up test areas only. They did not consult with the nuclear experts and weren't aware of the nuclear risks from what they were doing. When the explosion happened, we were visiting Wales at the time and I remember some fallout cloud eventually came over Wales because some of the grass and sheep there could not be consumed afterwards as they were radioactive. It's ironic that the disaster was a consequence of a 'safety test' which wasn't safely carried out.
The cover-up by the Russians was one of the most disgusting parts, aside from sacrificing people to clean up the mess.
worse than using an atom bomb?
@@jojojimys, Apples and oranges. The Tuskegee Syphilis Experiment is closer to that mark imo.
@@jojojimys IQ of 42 spotted.
@@jojojimys I read somewhere that the explosion fallout was worse than the effects of many hydrogen bombs. I think it was 100 times worse but I can't recall exactly. I'm a non-scientist, interested in learning how the accident happened.
*Soviets.
Ive watched quite a few videos to better explain this process and many only talk about it. This video visually and verbally explains it simultaneously which is way more effective in the understanding of the concepts! Amazing video, thanks!
This video is a lie. I commented above...in newest comments. You do not know how a reactor works and neither does she. I am coming out with a website called DISSECTING PROPAGANDA..and we will be exposing the lies of COVID and these alleged "accidents" with Chernobyl and Fukushima.
but...this young woman....does not know how a Nuclear Reactor Plant Operates. I do. I was in the US navy's nuke program and have operated power plants in subs and at on land facilities. I have been inside a Reactor room where a "core" sits. It does not operate as shown here.
This video maybe old, but I have to point out that the control rods did not have graohite tips. Yes, they were designed with graphite, but the whole lower sections of each rod were made of graphite. Like, half od the whole rod. Once those rods were lowered into the reactor, the graphite sent the reaction skyrocketing, destroying the interior and causing a near instantaneous build-up of pressure that caused the initial explosion and it all fell down from there.
this is the best eplanation of the incident ive seen. thank you so much!
One of the best explanation videos out there. Again they messed up with the "graphite tips". They were not "tips". There were about 4.5 meters worth of graphite. That's not a "tip".
WRONG !
There where no graphite tips !
When the boron rods are pulled out they pull in a graphite rod.
This is the best explanation of Chernobyl on TH-cam
This was the most comprehensive explanation! Thank u!
a very good explanation of answering the " what " went wrong with the reactor design question ...but as to answering the " why " it went wrong question, it seems to be that all to common work pressure environment from upper level management , to get it done and disregard safety protocol if needed...........which unfortunately still goes on to this day.............
Why do so many people keep saying the control rods were “tipped” with graphite? They weren’t. They had a graphite rod which was pulled into the core when the control rod was pulled out. That’s what allowed them to have better control of the reactor. It was a hot spot that developed at the bottom of the reactor, due to the low water flow, that caused the problem. As the control rods were inserted, the water in the bottom of the reactor was displaced by the descending graphite part of the control rod. This caused a huge change in neutron flux which had the consequence of breaking some of the fuel rod channels and preventing the control rods from moving further. From then on, it was simply a run-on chain reaction.
1:38 also wrong the chernobyl reactor had all the right safety features on it except for 2, external shielding of a reactor which is commonly left out from nearly all reactors built even today, but the main one in question was the graphite didnt cover the bottom of the rods. so once they were inserted into the core to cool the core down and force it to shut down it caused any water beneath the rods to immediately turn into steam instead of it being able to cool the rods down. this was mostly done to save money but also because at the time it was considered impossible for meltdowns to ever occur in a npp
I saw a documentary on a experimental VLF atmospheric test that was being conducted the same night only 40 KM away from Chernobyl. Engineers knew that this high power VLF had in the past interfered with Chernobyl instrumentation in the past. They had not told each other the either testing that evening. Did the VLF test interfere with the instruments in the control room of Chernobyl?
When did the operators have any erroneous readouts or their equipment failed to respond during the accident?
You missed out the fact that the workers Akimov and Leonid (who were in the reactor control room moderating the power output) actually considered to slowly raise the power in the reactor over the period of 24 hours considering xenon poisoning of the core... They even suggested it to Anatoly Dyatlov. However, Comrade Dyatlov violated the safety regulations and protocols and went forward with the testing, unaware of the design flaw of the control rods(graphite tips). They tried to bring up the power output, it starts to increase drastically. Trigger was pulled when AZ-5 was initiated which lowered all the *graphite tipped* control rods at once into the core.
That's when RBMK reactor exploded.
Everything else was covered well in this video.
Nuclear energy can be the green solution to power grid issues 2/3 nuclear 1/3 renewable and we’d be good to go
That's why nuclear energy is demonized. There have been quiet a lot of Fossil fuels, gaa, coal disasters bur Chernobyl one is rhe most talked about
7:49 you forgot the haunting words "The chain of desaster is now complete!"
Only video that makes sense and is clear and proper. Ty so much ❤
As far as I can tell this video explains the complicated stuff that went on in the best and simplest way. Not an easy task = Amazing! 😊💚
A nice expansion on Episode 5 of the Chernobyl series, Thanks guys :)
jeez you're braindead
@@galvanizedcorpse Y'know, a lot of people in the west were born AFTER Chernobyl and the HBO series may have been their first close exposure to it (so to speak).
This is the best video explaining the complicated events that struck the disaster
Thanks for explaining it in a nutshell👍
@@crist0000s lol moron
Actual Its not the Best explanation, this video just copys the mini serie from hbo, The control rod tips made from graphite where not exactly the cause of the disaster, The control rods where also the acceleration rods not like shown here, 7 meters where boron and 4 metere graphite and worked togheter not separatly like shown în here, The cause of disaster was that AT the bottom of the reactor because of graphte tips got stuck, water boiled and create uneven fission which ultimatly provoked the events, sorry for my bad gramar, i am a nuclear scientist from a forme comunist country
7:43 The cause of the second explosion could have been ignition of hydrogen which had been produced by the reaction of steam with zirconium fuel cladding. The explosions at Fukushima were from hydrogen.
It was said there were two primary explisions. One when the lid popped off from steam build up enough to blow a 200 ton lid high enough to take the roof off above and then come down to rest sideways and then a much larger bammo when the oxygen rushed in the crucible reactor vessel and the rest is history. The entire real bad part of the event was within roughly 45 seconds. Although far fetched, I'm looking forward to the Russian take on the event that they plan to make. It is quite a coincidence that the iron curtain fell soon after. I can't help but wonder if Dyatlov and or others in the program had other motives.
@@gstyle1911 Oxygen by itself does not cause an explosion. It must combine with something else (e.g., hydrogen) to cause an explosion.
This is incorrect, they are explaining what happened in the accident of the HBO series, not what happened in reality. The tips of the control rods were not made of graphite... That was an oversimplification they did in the series
well, this was made in part with PBS, so really, not much better than the reactor design itself...
CANDU reactors have a very small positive void coefficient, in certain configurations. This is mitigated but your statement about RBMKs being the only ones to have this are not completely correct.
CANDU reactor a the best. I live near one
CANDU reactors are built with 2 shut off mechanisms,
first the control rods and the 2nd is a chemical that stops the reaction dead as well. Both operate at the same time automatically (or manually if needed).
So the chances of it blowing up is impossible.
Why does nobody show the correct control rod layout? They were not tipped with graphite.. The top half was boron and the bottom half was graphite... With a slight empty space inbetween
Why would the control rods have graphite? I'm always amazed by people's ability to repeat things without understanding what they're saying.
@@ddrse why not?
All has to do with the flux available in their lower enriched fuel.
@@hiddenInsight486 why were they tipped with graphite?
@@ddrse they weren't
@@hiddenInsight486 the control rods weren't tipped with graphite?
I'm glad to know that you watched Chernobyl by HBO, but you shouldn't take an explanation from episode 5 as the basic truth. Actually power was at relatively low level and had low rate of increase before AZ-5. It started increasing momentarily AFTER pressing AZ-5. This action wasn't an emergency one.
Your video is spot on... More concise and indeed a no nonsense one
It’s sufficient for a non-technical audience. Some things were left out or glossed over, but you get the general idea.
Excellent explanation
I have been trying to find a video like this that made what occurred more understandable
Thanks
Very well made presentation and clear explanations. Thank you!
You gave vague informatiom about those control rod tips, some say they displaced water and not steam, on top of that positive feedback loop, the tip of graphite rods gone into the gaps in the bottom, which remained empty when the control rods were completely removed, as water is denser than the steam, the graphite tips which got inserted into the bottom gap quickly escalated the reaction rate on top of positive void loop, and then turned the bottom water directly into steam, thats the reason it exploded...
The accident that happened at the Fukusima plant was the eventual lack of cooling water to the reactor cores (obviously because of the tsunami and systematic loss of emergency power). Units 1, 2 & 3 reactor cores eventually melted. Is the BWR reactor a negative coefficient reactor. No water, no problem. One thing for sure, if a catastrophic accident does occur, the clean-up is going to cause multiple deaths and decades before the contaminated area is fully safe.
1) The tips weren't graphite. The entire bottom part of the control rod was graphite. The top was the boron part and the bottom was the graphite part. When the rods were lowered, the boron would be at level with the fuel and the graphite below the fuel. When the rods were raised, the graphite would be at level with the fuel and the boron above the fuel.
2) The control rods also had their own water cooling system. This is where the key to the major flaw was. If the water got heated enough, the pressure would prevent the control rods from fully lowering.
i understood everything , but can anybody tell me why reducing the power over a limit is bad ? it is essentially like switching off the reactor right ? why were they concentered to increase the power
You did not explain why the Xe135 was still increasing at the low power level because of the I135 left over from when the RBMK was running at full power and why bringing it up slowly allows time for the I135 to decay and the Xe135 to both decay and burn up from the increasing power. Slow buildup after a power reduction is of course required for safe operation of any reactor.
Cool video, thanks Doctor Jones!
Best explanation ever 👍🏼
the best explanation of what happened..... i watched the series, many videos but got confused...this video made it very clear
You missed 1 important detail.
When the rods went it, they take 18 seconds to be fully inserted at that time (now it has been reduced to 4 seconds), there was a hot spot already in the core by the time the rods were being reinserted into the core. Which then blew up the core making it so the rods could not be fully inserted and the graphite tips remained in position increasing the reaction.
Graphite was already inside the reactor in inserted state. Then how it effected the final surge
The graphite displaced the water at the bottom of the core and it resulted in an increase in moderation and thus power.
Most explainable and understandable video to clear incident of chernobyl...
RBMK reactors are not the only commercial reactors with a positive void coefficient. Candu reactors also have a very small positive void coefficient, but nowhere near as large as RBMK reactors.
Schematics for the control rods are not correct - they were half boron and half graphite, so essentially when the rood is completely out it actually means that graphite water displacer is in. The problem is they had gaps above and beneath them tho move neutron flux to the center of the reactor. When water boiled out beneath the rods and they started to move down, displacing steam instead of water, that caused instant flux displacement to the bottom and reactor acceleration, and increased pressure has ruptured the channels, and rods were jammed in acceleration position. Designers were well aware of positive feedback systems dangers, but that type of reactor was required for growing USSR industry not only because it was cheaper to build, unlike PWRs it could also been built in sight, produced twice more power, used regular water as coolant and unenriched uranium as fuel and could be refueled while running, which allowed it to be used as an isotope factory for chemical and medical industries. Being not able to calculate all extreme conditions, designers introduce various safety systems and strict instructions. The main reactor flaw was actually that operators had an access for shutting down safety systems - which they did, considering unexplained restrictions as unnecessary. The most ironic is that after the Leningrad RBMK incident they in fact figured out the problem and how to fix it, but because of how unlikely the repeat chance was (as no one was supposed to push the reactor beyond the limits), it was decided to improve reactors at their next scheduled shutdowns, which was supposed to occur right after the safety test. So the disaster was an insanely improbable combination of reactor flaw, safety system flaw, global power management fault, local test management fault and very bad timing - if only only one link of that chain if disaster was not there, no one would ever hear of Chernobyl... Reality is far more sad then fiction - it were not lies and conspiracy caused the disaster, it were everyday carelessness and negligence, as no one thinks his actions could be combined into a tragedy...
I was an industrial safety manager for over thirty years. There has never been a safety system designed that operators have not figured out a way to override and did not try to do so, for even the most irrational reasons. There are Homer Simpsons everywhere. Fubars in nuclear energy plants are bigger and more expensive.
@@jackfanning7952 true, but when you're designing a vehicle that becomes extremely uncontrollable over 100mph, you have only two choices - to make a system that will under no circumstances allow it to reach that speed or don't make such vehicle at all. And in a first case you shouldn't make a switch for it and definitely shouldn't place it to the dashboard. Btw, a lot of scientists familiar with RBMK back then had the same point, including Legasov, but now we have what we have...
@@evilbabai7083 I vote for Plan B. Don't make the vehicle.
@@jackfanning7952 It would be the case it's there was such an option. But, as I explained, there basically wasn't - bunch of low cost/high power power plants needed to be built like yesterday. They wanted to help country's wealth growth, but in the end made an opposite. The road to hell is paved with good intentions...
The best and only video that actually help to understand what had happened in Chernobyl! 🙏
I am no expert, but another cost cutting measure was there wasn’t a containment structure around the reactor. (The proper materials on the beginning of the video) This is steel reinforced concrete (think bomb shelter material) that keeps the nuclear fuel inside and not escape into the atmosphere. Three mile island, Fukushima and literally every nuclear reactor in the world have this.
By far the best video to explain. Thanks a lot!!
excellent explanation, very informative.
Water is mainly a neutron moderator. So water enhances nuclear reaction. So it shouldn't be called an absorber as it may only be slowing down the fast-moving neutrons and not absorbing them very effectively as boron would. Boron is used in the control rods to slow down and ultimately stop all reaction if necessary. In modern fail-safe reactor designs, water is both the moderator and coolent. So if the coolent water is lost or excessive heat in the core is causing steam voids in the reactor channels, this will trigger an automatic reaction slow down due to lack of moderation, preventing a run-away reaction that would cause a reactor core explosion or melt down.
Straight forward explanation of Chernobyl...thanks so much. 👍👍
Very clear! Thanks for making this video
CLEAR & EFFECTIVE explanation
Clear & wrong explanation you should say. Control rods don't have any graphite tips at all and the real cause of the explosion was the neutron flux that built up at the bottom because rods couldn't be inserted fully
@@akiratablet2281 great point
There is a saying in Turkish, if the things you told cant be understood by no one, it indicates that even you could not understand exactly what you are trying to tell the people. This is the only video where i could understand exactly how the accident mechanism was after watching 10 videos. Thanks a lot...
Nucleus not actual size!? Now i know why i haven't been seeing them lying around
I KNOW RITE! We were pretty mind blown when we learned that too...
Yer their not carbon rods..
Graphite in the control rod sped up the reaction exponentially, acting as a moderator itself during a scram, can i say that without trying to sound like a physicist?
The graphite moderator was actually already increasing the reactivity prior to the scram and creating the feedback loop for the positive void coefficient. The problem was that during the scram the graphite tipped moderator had broken off and had jammed in a position that further displaced the water. Water was already vaporizing pretty quickly due to a combination of all the Xenon-135 being burned off, almost all of the Boron rods being taken out (their graphite tips still in place controlling reactivity and producing steam) as well as less neutron absorption taking place from the shut off of some of the pumps due to the test. This scram was just the final nail in the coffin, but by itself wouldn't have led to the kind of event that occurred in Chernobyl. The problem was the overall reactor configuration the engineers created combined with some of the design flaws of the RBMK itself.
Samantha you are a really good presenter. Love your channel and your clear voice. You earn my sub.
what iisnt explained is how the modern reactors negative co efficent works. if the negative feed back loop water starts to run low "HOW" does it drop reactor power when its already become a run away freight train?
trying to figure this out. all ive got is that the the hotter things get for modern reacxtor the less reactions there are. where as the rmbk if it gets hotter. it will not slow but increase reactiona
@@corydemeray7594 Because most modern reactors use water as a moderator. So if all the water boils off you don't get slow neutrons to sustain a reaction. The RBMK used graphite for this, which allowed it to run on less refined fuel.
That's not exactly what happened. There is so much information missing.
One of the unspoken causes of the Chernobyl accident was the fact that the Nuclear Engineers do not fully understand the RMBK reactor at low power. The RMBK reactors are usually very unstable at low power. The test which was supposed to start around 1pm was delayed due to the demand for power until 11pm. By 11pm, the experiment started and the reactor power was decreased. So at low power, they were unable to stabilize the reactor due to Xenon poisoning. In trying to stabilize the reactor, they removed all but 6 Control Rods (CR) as far as possible. With more than 200 CRs removed, the power was able to come up to 200MW before starting the experiment. As water evaporated, creating more bubbles (Positive Void Coefficients), the reactor power increased, more neutrons were available that the remaining 6CRs could not compensate the neutrons. The void coefficient of reactivity is used to estimate how much the reactivity of a nuclear reactor changes as voids (usually steam bubbles) form in the reactor moderator or coolant. The available shift supervisor requested the insertion of all CRs but the insertion speed was too slow, in less than a minute, the temperature at the core was above 3000 degrees leading to a transient nuclear reaction that was followed by an explosion, releasing radioactive materials 400 times more toxic than the Hiroshima bomb explosion.
If they had understand the operations of an RMBK at low power, what would have happened was for the graphite tipped control rods to be moved in and out consistently in order to stabilize it. In fact, the operators had no manuals or control rods on how to operate the reactor at an unstable condition. Like someone said, whether you watch the video or read the comments, there are useful information in both. Lol
It wasn't the first time an RBMK-100 had suffered a power excursion during a shutdown for refueling. One of the units at the Ignalina plant had also had this happen, but with no catastrophic effects. The Atomic Energy Bureau buried the report, which is why the Chernobyl engineers were so oblivious. Hell, it wasn't even Dyatolov's first nuclear accident, but they were so conditioned to toeing the party line that the concerns of the reactor operator (Leonid Toptunov) and the shift supervisor (Aleksei Akimov) were completely over-ruled.
Is light water a net neutron moderator (encouraging fission), or a net neutron absorber (discouraging fission)?
Water acts as a moderator of neutrons, increasing their probability of interacting with u235 to create fission. Loss of liquid water stops the moderation, and neutron interactions with u235 decrease.
Amazing video! I rate this video 15 000/3.6.
hahaha love it.
@@ACSReactions I recommend watching this: HOW THE 4th UNIT OF CHERNOBYL NPP WAS BLOWN UP (channel-KS).
Thank you, using this in a project
Great explanation. Wonderful job. Thank you.
Very nicely presented! Very good video!
One thing I struggle to understand. If the water pump was switched off, and the remaining water turned into steam, wasn't that steam supposed to be channeled somewhere, thus, controlling the pressure inside the reactor? if there was not water in the reactor what was ramping up the pressure? Mere increase in temperature? I am not really good with physics, probably asking some basic questions :)
1 operator named Toptunov, the guy who pulled all the control rods because Dyatlov asked him died at 25 and only been working there for 6 months, no clear instruction about the safety test protocol whatsoever. Rest in piece to all the victims involved.
What benefit did the graphite on the control rod tips give? Obviously it was a bad idea, but I'm trying to figure out why graphite was there at all.
Graphite was needed on the control rods to act as a moderator. Otherwise, the water would have robbed too many neutrons for fission to occur.
Very well explained. Defective design and improper operation.
Seriously, a very big thanks to u😭🙏🏻. It was one of the BEST and the most informative video i could find to understand what actually happened at Chernobyl. Ur way of explaining is soo simple and clear. U were a savoir to me today💖. Once again, thnqq soo much💓 and i mean it by heart💕💕🙏🏻🙏🏻💜💜💜💜💜💜💜💜💜💜💗💗💗💗💗💗 keep going🤗
Excellent explanation 👍
One of the best explanations on TH-cam. Thank you so much!