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.

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! 👏👏👏

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

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.

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.

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.

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.

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

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.

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 "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.

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.

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

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!

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

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.

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

Ah I finally get it, thanks for the explanation

Only video that makes sense and is clear and proper. Ty so much ❤

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!

excellent explanation, very informative.

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

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.

Great explanation. Wonderful job. Thank you.

By far the best video to explain. Thanks a lot!!

Excellent summary. Thank you.

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

3.6 roentgen - not great, not terrible

Awesome explanation! Thank you!

Amazing explanation!

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

Your video is spot on... More concise and indeed a no nonsense one

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.

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🤗

the best explanation of what happened..... i watched the series, many videos but got confused...this video made it very clear

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

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.

finaly , watched so many , finaly i could understand thanks to u

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.

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

Very nicely presented! Very good video!

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

That was an excellent explanation.

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

Very nice explaination!

was about to go and watch the actual movie but thought it would be better if i had an idea at least of what happened, nice vid and thanks.

Excellent documentary.

Excellent explanation 👍

Samantha you are a really good presenter. Love your channel and your clear voice. You earn my sub.

Straight forward explanation of Chernobyl...thanks so much. 👍👍

The best and only video that actually help to understand what had happened in Chernobyl! 🙏

Great explanation!

Excellent video 👍🏼👍🏼👍🏼

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...

Amazingly explained

Best explanation ever 👍🏼

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.

CLEAR & EFFECTIVE explanation

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.

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.

Very well explained. Defective design and improper operation.

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".

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’re godam right madam ! Thank you for clear explanation and a great video

Great vids cheers🙏

Very nicely explained👌👌

Excellent video

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

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.

Very good explanation

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

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.

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.

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

Thank you, using this in a project

5:40 xe 135 was only being created because it hadnt been given the chance to power down properly due to running longer the night before than initially intended. its important to mention these things as youre otherwise implying that other safety systems and routines were not being followed due to x y or z occurring which inadvertedly leads to lies and or deceit occurring over the whole event

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.

nice video and thanks.

Most explainable and understandable video to clear incident of chernobyl...

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.

Best explanation ever!!!!!

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...

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.

Very clear! Thanks for making this video

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 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

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 :)

It’s Criminal and Insane to build a reactor without a Contaminant Building

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

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.

I finally understand what happened, thank you!

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

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

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.

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...

thanks a lot for explain very well.

To give you and idea how fast the nuclear reaction spiraled out of control.All boilers have safety valves dimensioned for their size,these are very large valves that open up by pressure and release the pressure and protect the boiler(reactor) from overpressure and thus rupture.The rmbk reactor has 12 safety valves,although all of these valves should have opened the reactor managed to build up heat and boil water at that rate that the pressure build up until the whole reactor ruptured.Its quite mindblowing, it had to create so much heat that all the water boiled to steam in an instant .Also a boiler/reactor is built in with a safety margin,a boiler will withstand a pressure much higher than its normal operating pressure.I work on a powerplant with a low pressure boiler with a maximum operating pressure of 8 bars,the safety valves will open at 9 and 10 bars respectively and it is pressure tested at 16 bars,but it would probably take at least 50 bars or much more for it to rupture.Applying that to the rmbk reactor which at my knowledge operates at something around 70 bars its most likely built to withstand pressure many many times that.Yet it still managed to build up pressure to rupture with all of its safety valves open.