What Exactly Happened at Chernobyl? 

i watched so many vids on this reactor....and this is the only one that actually made any sense....thank you 😭

The clearest and simplest explanation about Chernobyl. Thank you.

“Every lie we tell incurs a debt to the truth. Sooner or later that debt is paid” -Dr. Valery Legasov, **Chernobyl**

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.

Don't bother watching the video, it seems all the nuclear experts are in the comment section

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.

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.

3.6 roentgen - not great, not terrible

Ah I finally get it, thanks for the explanation

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.

A very clear concise explanation of what happened at Chernobyl causing a very sad and avoidable event.

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.

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.

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.

The cover-up by the Russians was one of the most disgusting parts, aside from sacrificing people to clean up the mess.

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

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.

That's not exactly what happened. There is so much information missing.

This was the best easy-to-understand explanation I've come across about Chernobyl and how reactors work. Thanks!

In America, people sacrifice their lives for their country. In Soviet Russia, their country sacrifices them.

Sounds like you didn't do any research and just: 1) copy pasted a childrens explanation of nuclear physics 2) Just took what happened on the chernobyl miniseries as fact. terrible.

This video finally confirms that the Russian mentality was essentially just a bunch of high school kids trying change the brakes on their car by putting peanut butter on the pads to keep them from squeaking.

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.

She’s delusional. Get her out of here.

Really well written and the graphics are terrific...combined to create a great explanation.... Kudos to Sam and the team

It's kind of unforgivable to have a video so amateurishly presented in the wake of HBO's Chernobyl, yeas we saw the series, tell us something that we don't know. As pointed out by some, the whole graphite tipped control rod thing is a bit of a misconception, they were graphite rods that were pulled into the reactor to displace water which is a neutron absorber. They still exist on RBMKs but now extend the whole length of the core so that there can't be sudden power spikes due to voids in the coolant and perhaps more importantly, you can't introduce a moderator into that void. RMBK's are not the only reactors with a positive void coefficient, CANDU reactors also have them.

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.

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'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!

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

''... like all modern reactors??'''

A nice expansion on Episode 5 of the Chernobyl series, Thanks guys :)

Moving on 30 years,the Japanese couldn't handle Fukushima disaster, radiation is still leaking into ocean.

Reactions: this is chemistry at the end. But it was all physics.

Darling, if you would like to explained what happend in Chernobyl, meybe you shouldn't have done it in the same way it was done in chernobyl HBO series, because that simplifyed version was seen already by majority of us who would like to know more. Watch Scott Manley youtube video if you are curious to find out IN detail what really happend, why and how. Trust me, even people in Soviet union were not crazy enough to design reactor the way you are trying to portrait. RTFM ;)

Very good explanation. Chernobyl, Three Mike Island and Fukushima are the main reasons why nuclear power is going away in the US. If people only knew how much technology and safety there is involved in the operation of nuclear power plants, they would change their minds. For the money, nuclear supplies the most reliable clean energy. If you’re thinking wind and solar, remember that the wind doesn’t always blow and the sun doesn’t shine at night. Nuclear is the best we have until something better is invented.

Actually, nuclear power is regarded as safe by those who regard it as safe. The rest of us regard it as inherently and uniquely capable of creating disasters. While the Soviets may have been more careless in design and operation, even the Japanese, the most careful people on earth, are not capable of designing and operating a nuclear power plant safely. The logical conclusion is that doing so is, in general, beyond the capacity of human society. And let's not forget there is no safe place to store all that nuclear waste that is never going away. Apparently, the only solution to long-term power needs that can be both safe and non-polluting is geo-thermal. Other than that, a nice pro-nuclear propaganda piece that implies that there is nothing to worry about these days.

Excellent description of a complicated scenario! Wow, ( if history truly repeats itself I'm so getting a dinosaur.)....

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.

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.

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.

excellent explanation, very informative.

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...

WRONG ! There where no graphite tips ! When the boron rods are pulled out they pull in a graphite rod.

This is the best video explaining the complicated events that struck the disaster Thanks for explaining it in a nutshell👍

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

Who is this beautiful woman narrating?

She’s super cute😍

Another good standard RU-vid affair of the mechanics of the Chernobyl disaster at the reaction chamber itself But I think the YT and general media community is largely missing the cause of the event goes far beyond design and operation 1. The design was built by one set of set of Soviet nuclear engineers but then handed over to a Soviet administrator to finish commissioning 2. In order to get a pat on the head and to avoid recriminations the administrator conspired with the area inspector and site engineer to have the reactor signed off as ready and operational on time despite it failing the turbine run-down tests 3. Some years later, they're trying to still satisfy the safety requirement of passing the rundown test and they get desperate 4. The monolithic nature of Soviet organisation means that asking questions and raising objections comes with all manner of penalties All this shows that whilst the design is weak and operations protocols were bypassed, the *reason* for these failings coming to fruition was because of the human factors behind it

whats her name?

Best explanation ever 👍🏼

Nucleus not actual size!? Now i know why i haven't been seeing them lying around

I can’t wait for the video on how Vlad’s sleepover was the week before the accident. Lol. Awesome graphic

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?

Nuclear energy can be the green solution to power grid issues 2/3 nuclear 1/3 renewable and we’d be good to go

They say that everyone of us have part of that reactor in us.

After searching for dozens of videos, this was the stop for me. Thanks a lot for explaining in such a wonderful way.

In short... An explosion.

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.

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".

The main concept is just 8th - 9th grade physics..but the way she presented it all...man that was much better than the other vids...or I can say that this was the bst vid.. 😘

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.............

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.

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.

2:19 she hot

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.

Very clear! Thanks for making this video

I’m down bad for this women explaining physics to me

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.

(A Z-5) is the button that, put all of the Control Rods into the Reactor, the reason why Chernobyl had its nuclear meltdown was because the tips of the control rods were made of graphite, graphite speeds up the reaction, why was they made of graphite, because it was cheaper, like why Chernobyl didn't have a protective shelter over it. back to A Z-5, so with the graphite rods all locked in to place (because of the amount that they slung the power back), speeding up the reaction, no body at Chernobyl knew that (A Z-5) could act like a detonator.

Damn.. Narrator's beauty is very distracting the lessons 🤩

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! 😊💚

Excellent explanation I have been trying to find a video like this that made what occurred more understandable Thanks

This description is inconsistent with other more credible sources.

there are still about 10 rbmk reactors in use in Russia, video is inaccurate

If you were my physics teacher I would have become a scientist ☺️☺️

I urge all people to watch the DHRUV RATHEE video on Chernobyl... Its in HINDI but he gives ENGLISH subtitles.... That video will clear all lingering doubts, if any.

Amazing video! I rate this video 15 000/3.6.

One of the main problem with this video is oversimplification. If you paid attention and didn't understand if Xe135 is a byproduct of fission, how come Xe135 continued to build up after the reactor power was dialed down to a minimum, and also, how if Xe135 is such a good neutron absorber, how come the reactor works at all, then you are right it wasn't explained. So, if the reactor operates BAU, the neutron flux "burns up" Xe135, there are enough of neutrons to be absorbed by Xe, which then transforms to another Xe isotope no longer absorbing neutrons. So under normal conditions there is an equilibrium. But Xenon 135 isn't immediately produced by fission, first there's tellurium - Te135 which decays after a couple of seconds to Iodine 135, but this one only decays to Xe135 after 6.6 hours. So there's a couple of hours of delay. When the operators lowered the reactor's power, the power grid halted the process, because they needed more power, so the reactor operated on low power for a couple of hours. In the meantime, the previously produced Iodine decayed slowly into Xe135 in quantities that belonged to the FULL POWER o the reactor, so after 6.5 hours you had much more Xenon, the ow power neutron flux was able to burn, and that's why they simply weren't able to raise power again. From that point, the description if still simplified but mostly correct, apart from the graphite "tips" - which is a very unfortunate word many people use. Thoss aren't just tips, they are long (1.5m) parts at the end of the absorber rods and have a function (not the most fortunate design though).

7:49 you forgot the haunting words "The chain of desaster is now complete!"

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

Dear channel authors. I don't want to upset you, but all your reasoning, assumptions and arguments about the main causes of the Chernobyl accident, which you voice and justify in your films, are the most usual falsification. But the fact that you promote that falsified version on your channel is not your fault. Because such false interpretation of the chronology of those events was developed by Soviet specialists to conceal from the world the real truth about the true causes of the Chernobyl accident. If the real causes of the catastrophe had been revealed then, the Soviet Union, and later Russia, would have been obliged to pay huge reparations and compensations to the affected countries and their citizens because of the damage caused to them. Not only that, that false version was later consolidated (paid for) also in INSAG-7, so that later it was possible to refer to some official documents. In the struggle for world domination the Soviet military used the most real psychotronic and climatic weapon against the USA and its population for more than 10 years - ZGRLS (radar) "Duga". During those years (1972-1986) the territory of the USA and all its inhabitants were exposed to high-frequency short-wave radiation, which was generated by the mentioned unit. And this is not conspiracy. And then the United States itself built a similar weapon, the HAARP, in 1997. Russia also currently has a modern version of the ‘Duga’ in service, called the Container radar. Why am I writing all this. If you are a true patriot of your country, and do not have a goal to just make money on RU-vid, you should add to all your videos about the Chernobyl accident the reference to the film, which reveals the true causes of this disaster. Then many viewers will be able to learn and realize the irreparable damage inflicted to the health of millions of people around the world by the Soviet military, which used this weapon (Duga) against its opponents. By the way, in January-February 1986, the Duga underwent state acceptance with appropriate tests. If you remember, the shuttle Challenger crashed on 28 January 1986. It was no different from an intercontinental ballistic missile and could have served as a real combat target for the Duga... And the film that reveals the true causes of the Chernobyl accident is called: HOW THE 4th BLOCK OF CHERNOBYL NPP WAS BLOWN UP. Thank you for your attention.

She cute

"Chernobyl power complex unit 4" Lol😂. Its the chernobyl atomic generating station's block 4

I know this is a sensitive topic but I kinda laughed automatically when I heard they were doing the safety test on that night.

I should have put this in my presentation on Chernobyl.

A lot of people questioned the design of the reactor and why it was designed with a positive coefficient. During the Cold war the Soviets always look to have an edge over the West. Even at the expense of safety. This included building very advanced nuclear reactor designs like the reactors in alpha class submarines with their LED bistis reactor metal cooled. This reactor made them extremely fast today they are still the fastest ever built. Which proved difficult to maintain which resulted in most of the alpha class submarines sitting at the dock waiting for maintenance. We also cannot forget the most recent example of their nuclear powered cruise missile explosion and people that died. Chernobyl was no exception Chernobyl could be operated in two ways one as a simple reactor which produced electric. The other way was it could produce weapons-grade fuel. Unfortunately compromises had to be made incorporating graphite into this design.

I finally understand what happened, thank you!

Watching this after completing HBO's Chernobyl series. What a mindblowing explanation. Fuck Dyatlov

Surge happened after AZ-5 was pushed power was very low the tip effect caused the surge. But great explanation nonetheless

Nuclear power is like having a king cobra for a pet - nice behind the glass, but deadly if the glass breaks.

The RBMK reactor uses natural un-enriched uranium fuel NOT fuel enriched in U-235 as claimed in this video. That was one of the few advantages of this design. The video is also incorrect in calling the cooling water in the core a good neutron absorber. It is not. The Oxygen atom in water has a cross section for neutron absorption close to zero and the two hydrogen atoms have a very low cross section for absorption and serve to scatter and slow down neutrons (i.e. act as a moderator) vice absorbing them and removing them from the fission chain. Water also serves to remove the heat of fission from the nuclear fuel to some sort of steam generator to produce steam to turn the turbo-generator.

The atom DOES NOT BREAK APART WHEN THE NEUTRON HITS IT!!!! Your inability to understand this most basic part of the fission is very troublesome. The neutron is absorbed, it's not the kinetic impact that breaks it apart. It is absorbed and the atom's nucleus becomes unstable with the addition of this new neutron.

Let's stop starting from the beginning in every post! NOT ACTUAL SIZE SAYS IT ALL . The problem was a valve got stuck through lack of use.

Actually they were not past the critical point when pressing AZ-5. It was AZ-5 that in fact mainly caused the explosion. Xenon poisoning was not that much of a factor as commonly believed, also pulling out the control rods shouldn't result in such a catastrophe. The problem was in the AZ-5 and control rods themselves. I encourage everyone to look at the INSAG-7 report of International Atomic Energy Agency. HBO show and ,,Midnight in the Chernobyl" book actually spreaded a lot of misinformation, because they are both based on quite fictional book of Medvedev, frustrated science fiction writer.

The U-235 fuel used at Chernobyl was NOT enriched... this is incorrectly stated in the video and is an important aspect of the functionality and the very design of the RBMK-1000 reactor. Since it’s cheaper to not have to enrich naturally occurring U-235, the frugal substitution was to simply increase the presence of naturally occurring U-235 within the core (without having to enrich it of course) to increase the probability of the chain reaction occurring at levels near that of enriched fuel. This is why the RBMK-1000 consisted of 1,661 fuel rods, meanwhile a typical PWR reactor with an enriched fuel source consists of anywhere between only 200-300 fuel channels.

Void coefficient was positive but nobody knows it before the accident. TEST was completed that time and it was the third test. There was two tests before, 1982-1983 or something like that. You forgot about another 4 pumps...

Everyone making the seem damn video on Chernobyl as if the show didn’t already tell us this shit

The truth about Chernobyl: HOW THE 4th UNIT OF CHERNOBYL NPP WAS BLOWN UP (channel-KS).