What Technically Happened at Chernobyl

A public lecture on the history, physics, and lessons to be learned from the Chernobyl disaster given by a real-life nuclear engineer, me (Ethan Chaleff).

[@Corristo89]

Props to whoever put that 3D model of the RBMK reactor's piping together, only to be relegated to complete obscurity on the internet. That must be like filming the most brilliant movie in human history, only to end up in a dark shelf on DVD at an abandoned video rental store.

[@Silhalnor]

Ah yes, Nosferatu!

[@firewalker1372]

“When the truth offends, we lie and lie until we can no longer remember it is even there, but it is, still there. Every lie we tell incurs a debt to the truth. Sooner or later that debt is paid”. Brilliant lecture on how this happened.

[@MegaMastiffman]

Very well said

[@coronalight77]

Not well said but totally plagiarized. You're quoting a line from the show and pretending like you're deep. People like you are exactly the problem. Sad.

[@jackvandenbergh3938]

I think he was all over the place. If you're familiar with the matter, you'll follow just fine. But to a layman it's gibberish, jumping from one thing to another, it makes you lose your train of thought. And the show might and certainly will have mistakes in it (probably for effect), but I believe Stellan Skarsgård made a better, more comprehensible, intelligible presentation.

[@SubvertTheState]

​@@jackvandenbergh3938yeah this is not a great video if you dont know how fission reactors work. There are good videos for that though, after knowing about the magic of nuclear fission this lecture is awesome.

[@BosssyBear]

"The future is known. It's the past that keeps changing."

[@clarkrivers20]

As a nuclear safety engineer, this is hands down one of the best presentations I’ve seen. Enough technical while simplifying it down. Well done!

[@majorwedgie8166]

I agree. I feel like I slept at motel 6 after this lecture! No really, the information was spot on!

[@kayakMike1000]

​@@majorwedgie8166 I thought that was a Holiday Inn commercial.

[@EthanChaleff]

Hey thanks! that made my day! I did do a lot of work to prepare for this 😅

[@kojocisco]

And the first comment goes from "nuclear safety engineer" LOL

[@ryanskelly7687]

@@kwnyupstate easy to insult people who are dead, about a topic you dont understand huh?

[@visnjamusa9395]

8:50 There is NOT one turbine on each side of the reactor and there is NOT just one turbine. There are exactly TWO turbines mounted on one side of the reactor, specifically SOUTHERN side at Chernobyl. Steam from left side of the reactor usually drives one turbine, steam from the right side usually drives the other turbine. Steam lines of the far side are routed around the reactor to the turbine room. I said "usually", because there are valves that can route steam from all drums to run just one turbine - ANY turbine of two available. At the night of accident, as the reactor power dropped, the operators did exactly that: they shut down one turbine and left the other to run alone up until the accident.

[@tetchuma]

My stepmother was 6yo, and lived in Pripyat in 1986. Her father, Anatoly (not Dyatlov) has worked at the Chernobyl plant since 1982. Today, he’s part of the maintenance crew. They were evacuated to Kozyn, just south of Kiev. She still has health problems. She had a hysterectomy at 15 because of tumors. Because of this, she had to take hormone replacements at a young age. (That probably why she still looks 19) Her mother had to have a double mastectomy and hysterectomy by 1988. She told stories of Soviet officials waiving Geiger counters over food shipments in the open markets, to make sure they were safe to eat; All the while saying the radiation wasn’t as bad as “the West” was saying. She told me in 2007, that the Soviet Union is still alive. Only in the last 3 months, she was able to migrate her sister and niece to Toronto, due to the Russian invasion.

[@alexanderk7776]

i am from Austria. I was a kid at young age when that happened. Me and nearly all of my hood have health problems. Many died of cancer. It is nit over yet.

[@jeremy605]

@@alexanderk7776 people from austria got cancer from chernobyl?

[@SioxerNikita]

They were right though. The radiation wasn't as bad as the west said, since the western media was on a 24 hour radiation panic cycle, scaring everyone

[@SMGJohn]

Which is ironic considering cancer rates in the West have quadrupled since 1900. Blaming everything on Chernobyl is easy when you are ignorant. But a lot of our food today and even water being treated are full of cancer inducing materials. Mass produced cooking oil has shown to increase your risk of bowel cancer by 70% in fact the countries that consume the most cooking oil also have record bowel cancer. So while Chernobyl was bad, Pravda wrote countless articles on this during the 80s about the health effects. It seems your family member also had the brain size of a 19 year old of she thinks the USSR is still around. Russia and every post-Soviet Republic today is nothing but capitalist Oligarchy ruled by criminals.

[@SioxerNikita]

@@SMGJohn Cancer Rates increased by 4x? No. Finding cancer has increased by a lot. You read like a conspiracy theory

[@johnedwards3621]

I went through Navy Nuclear Power School as a reactor operator 52 years ago. Decades later, I worked with a young PhD Mechanical Engineer (from Ireland) who lent me a copy of the official Soviet account of the Chernobyl disaster. To understand what happened, it helps to bear in mind that there are two types of reality: political and physical. Joseph Stalin represented the former; reactor physics represented the latter. Although Stalin died long before Chernobyl, his influence was still felt by the minds of many. That influence (fear of being shot) accounts for the several-day denial, and why Moscow didn't know what was happening until neighboring countries complained. That's why it's response was so slow. The fatal flaw was that there were two career paths to the top job in the nuclear power plant administration. One path was through the nuclear-physics side, The other path was through the electrical power generating side. [Think Power source vs. Power load] Chernobyl was caused by a person who rose from the electrical power side. Another flaw was ego -- the pursuit of bragging rights. Reactor plants seem simple when everything is running well -- as when tending a fire. But a nuclear fire is caused by energetic neutrons rather than energetic electrons. It occurs much more rapidly as neutrons instantaneously erupt from a variety of fission chains. The key to controlling a plant is to fully understand the influence of those fission chains while staying within narrow limits because the secondary neutrons from intermediate fission reactions introduce enough delay to make a reactor plant controllable. But, the rate of change of neutrons, during adjustments, also affects reactivity which requires things to be done slowly. In other words, you can't simply react without understanding some very abstract processes. There is a narrow range between controllable and uncontrollable conditions. One way plant supervisors can test the safety of a plant is by disabling some safeguards to make sure the control sequences are "fail-safe". Chernobyl was caused by someone from the electrical side who didn't understand reactor physics yet pursued an ultimate bragging right by disabling all backup systems. He believed this would lead to a reactor shutdown. His bragging rights would come when he performed a reactor startup by using the inertia of the huge electrical generators to do a reactor restart. It failed. Reactivity rate changes, due to cooling as well as Xenon poisoning & decay, put the system outside of its controllable range. The reactor, responding to its internal processes produced far more power than the system could handle. The excess power quickly destroyed Chernobyl and shut down the once vibrant city. A mindless "Religion" of bureaucracy is never an alternative to the constant need for observation & respect of behavior -- whether neutrons -- or people. Chernobyl is an important lesson that helped end the cold war. In this increasingly complex world, unrecognized ignorance can cause major problems that can threaten humanity and the Earth, itself.

[@scotsguy422]

Thank you for taking the time to explain this, I think a lot of our younger generation must understand the complex political and economic issues affecting the former Soviet Union at the time and how easily they could effect other nations. You mention "there is a narrow range between controllable and uncontrollable conditions" just like an aircraft pilot knows how to keep a plane trim and level, too steep a climb or rate of descent would result in disaster. All these safety critical sustems should be above the rach of political interference etc... Sadly the people of Chernobyle and wider environs have suffered terribly for over thirty years, inflicted solely by their own government whose first priority should have been the protection of its citizens!

[@TheOnlyAndreySotnikov]

Yep. Dyatlov (the supervisor you are talking about) often bragged before the explosion that the reactor is not more complicated than a Russian kettle (samovar). He wasn't aware of the iodine pit and ordered manual removal of control rods in an attempt to increase the power so they would conduct a stupid experiment.

[@TheOnlyAndreySotnikov]

@@johnkern7075 I partially agree. I am not aware of human stupidity of the personnel at the Fukushima reactor, I thought they acted professionally. First, the nature disaster was unprecedented. Then, there were examples of stupidity during that tragedy, but they were outside the Fukushima engineers: (i) they were sent 4000 liters of drinking water, while they asked for 4000 tons of fresh water; (ii) when they still had time, the top bosses prohibited to pump in the seawater to cool down the reactor. Moreover, I think their idea to collect batteries from surrounding cars and use them to start the pumps was brilliant.

[@TheOnlyAndreySotnikov]

@@johnkern7075 What island :)? Oh, btw, another piece regarding Fukushima. You would think that for Japanese society, following orders is natural. However, eventually, engineers at Fukushima said eff off to the top bosses in Tokyo and started pumping the seawater. It's good they disobeyed the stupid and dangerous orders. Unfortunately, it was too late.

[@dittikke]

@@TheOnlyAndreySotnikov I think anyone that's worked in any kind of engineering context in the former Eastern Bloc has known a Dyatlov. They'll take any challenge or criticism aimed at them as questioning their absolute authority and as a personal attack, and they will fight back with all they've got so it's pointless to even try. Toxic masculinity is bandied around and has become a bit of a cliche but it really applies here. Achimov and Toptunov didn't have the hint of a chance.

[@almondjoy112]

Ethan: 1+1 = 2 Audience: laugh excitedly

[@akio2589]

I'm glad you went into detail about Xe poisoning. A *lot* of "explanations" leave out the Xe, and it's really important for how the nosedive in power came to be to begin with, and why they had to pull out so many control rods to get the reactor back to what they managed.

[@jeffriesj75]

Exactly! Lowering power -> increases Xenon and ultimately keeps declining power (positive feedback loop). They should've never removed almost all (only 6 of 211 remained) control rods, that moment alone sealed the world's fate to this ongoing catastrophe. Especially the control rods in the center of the core. Those boron carbide rods were the most important for neutron flux control which is highest in the middle! Even just withdrawing them partially could've been less catastrophic and avoided the meltdown or the graphite on the other end of the boron rods had been the same length as the boron, the water would've never displaced.

[@supersst838]

@@jeffriesj75 ongoing my ass, it was well over 30 years ago

[@jeffriesj75]

@@supersst838do you not realize all the childhood thyroid cancer & leukemia cases they had following Chernobyl?! These people are in their adult lives now dealing with lifelong health conditions, also the area within 50 miles is still quarantined off and you must obtain Russian permission to only enter the town surrounding the plant for 1 hour due to exposure safe limits.

[@rockytopvfl8350]

The climate has always changed and always will change...

[@akio2589]

@@rockytopvfl8350 ...Ok?

[@jamesspash5561]

I work in hydro electric production. What is happening now, happened over the years, and it's happened before, is there is no one from, design, engineering or operations to for us old guys at all the mentioned levels, to train. I work with folks from all ends who do not have a clue what they are doing. Direct out of school engineers, don't get me wrong, smart folks, but no experience. We are going to do this... We in opps people say NO, that will not work and will cause problems!!. Were told "there are smarter people than you working on this" Shut up. Then when It fails and or doesn't work, we the opps folks get blamed for the failure or hear crickets chirping from the engineering group, while we fix it. My motto is, " I didn't engineer it, my job is to make it work."

[@WhiteSkyMage]

I think you made literally the best technical presentation of what happened at Chernobyl that i managed to find on the net. Good job!

[@EthanChaleff]

Hey thanks! I spent a long time working on this :)

[@monkeyboy4746]

Yes, this is by far the best that I have seen, it is not dumbed down for public consumption.

[@maus92]

Look harder.

[@tuorofgondolin8235]

Some 30 years ago, when I went to the Navy's Nuclear Power School, I recall being taught about going "Prompt Critical". The delayed neutrons are essential for keeping the reactor controllable by slowing down the rate at which new generations of neutrons are being formed. Machines can only move so fast, and maintaining the speed of which neutrons are generated at a "reasonable" rate (which is still extremely fast in an absolute sense of time) allows the control devices to do their work and even makes it possible (to some degree) for humans to react and make adjustments. A "prompt" neutron is when neutrons are generated faster than, IIRC, 10^-13th seconds. If *all* neutrons are formed at this rate (called "prompt critical"), then power in the reactor will increase at a greater than exponential rate -- too fast for most mechanical machines to react to or stop. In the sort of reactor I was taught with (pressured water reactors), there was a negative reactivity coefficient, which meant that heating the water will actually act to moderate power increases and steer changes towards a new equilibrium. The RBMKs had the opposite: a positive reactivity coefficient, which did the opposite. Meaning that in the absence of outside interference, RBMK reactors would continually move towards increased super-criticality, while PWR reactors move towards a return to criticality (stable power levels). I went through Nuclear Power School back in 1989, so Chernobyl was still pretty recent and the Soviet Union was still around. We had some knowledge about what happened, and our instructors talked about it with us. They also talked about Three Mile Island and the SL-1 disaster. Nuclear power can be dangerous, but it is still worth pursuing and perfecting. And while nothing in the Universe is perfectly safe, nuclear power is still pretty safe, and we should continue to rely on it while furthering our knowledge and experience so that we can keep moving our technology forward into the future.

[@ivanskunov9166]

It was very strange to hear from such a specialist that there were no enrichment plants in the USSR. In fact, the cascade centrifuge allowed the USSR to enrich uranium much more efficiently than the method used in the United States.

[@kwestionariusz1]

Yea without enrichment facility u cannot even made uranium fuel rods

[@taiyoqun]

If you listen to what he says, he doesn't say they didn't have the capability, he said they didn't have the same capacity the US had. You can debate that, but it's in no way as outrageous as claiming they had none at all, which again, he didn't. Either English isn't your first language or you're American. Assuming the first, allow me to explain that capacity in this context means how much they can produce, so what he meant was that they could afford to produce less enriched uranium than the US nuclear industry. In case you're American, there's nothing I can do; I can correct a misunderstanding, but I can't cure stupid.

[@Serafimxxxx]

I've watched dozens of Chernobyl explanation videos. This is, by far, the best I've seen. Even as a layperson, I feel like I really understand exactly what went wrong and why. Still, it boggles the mind to think that so many disparate designers and teams tickled the dragons tail like this... that nobody recognized the lack if understanding or danger.

[@jsmithmultimediatech]

A clue maybe to that not understanding the danger, rather some likely did, but when the person in that meeting room who essentially said its about protecting the product as such from labour, than the person who did that labour and made/built whatever that product as if they die they'll just replace them with another. I think I remember reading that that person I don't think even existed, but its for as you said above the layperson so they can understand the mindset of the USSR.

[@benphartine]

2:54 Gets Started 6:00 The good and bad aspects of the Chornobyl reactor. 9:46 The fundamental challenges of reactor design. 12:47 The basics

[@Matthias-ps6vg]

Bro gave up

[@bobmutchseo]

@@Matthias-ps6vg perhas I should do it.

[@BoBaH_BoBaHoB]

05:18 Most significant feature of RBMK

[@ScottBoydathome]

The ONLY reason they used it.

[@xlegiofalco]

Best presentation on Chernobyl I’ve seen. Best combination of technical and nuclear physics and pictorial description for the lay person. Great job!

[@VintageTechFan]

Finally someone who makes the control rod change understandable! The popular opinion is that they were totally retracted out of the core and then they inserted graphite first, which sounds totally crazy. And it is, that's why the didn't do it that way. It's just that the very bottom of the core already was on the verge of power excursion which was triggered by the redistribution of power because of the graphite absorbers. By making them flush with the bottom of the stack, that couldn't happen anymore.

[@VintageTechFan]

@Simon Archbold Eh, both go round and round and round. ;)

[@trinalgalaxy5943]

One of the parts of an RBMK that just astounds me is that due to its size, could be broken down into individual "cores" within the core, each at their own power levels, and the most vulnerable point for the reactor at the bottom had no sensors to provide indication to operators what the hell was going on there... you can kinda understand the middle, but not the outside edges when you know this is a thing (and they did know that issue).

[@Bollibompa]

@Simon Archbold Pronunciations differ in the world, it is the meaning that matters.

[@ddopson]

The mis-understanding stems from describing the control rods as having "graphite tips", which is rather mis-leading because there's actually 1.25m of water between the graphite and the boron. It's not a "tip", it's a "replacer".

[@htspencer9084]

Yeah, having part of your scram process actually increasing the reactivity of a part of the chamber is just... Mind-boggling.

[@monkeyboy4746]

I didn't see it mentioned specifically in the comments, but I have read that the reason for the graphite tipped control rods was because they originally were not able to achieve criticality when the reactor was first started up. They added the graphite to increase neutron moderation and thus were able to get the reactor to go critical. When the control rods were lowered into the core, at first they actually increased the power output because of the increased moderation. Since the reactor core was so large, power was increasing in the part of the core where the graphite tips were traveling.

[@Thunderdog440]

That is well said my friend. I have worked at both NPP in central Wisconsin One is a single reactor(now shutdown) and the other is a dual reactor. In fact, My very first day was 9-11-01. I found it odd that this disaster was NEVER mentioned in class or in the plant as long as I can remember. BUT 3 mile island was. I have actually learned MORE from Chernobyl disaster than I have ever learned from literally working at the plants in WI.

[@taraswertelecki9586]

That was forced on the designers due to the very low enrichment fuel. The graphite displacers were needed to juice the sluggish nuclear fuel into criticality. Had they been long enough to extend all the way to the bottom of the core, there would not have been a "tip effect" that creates a brief power surge when the control rods were lowered into the core to replace the graphite with boron carbide to reduce power or shut it down. This simple modification might have made a difference at Chernobyl, but the tip effect was the final straw needed for the reactor to blow itself and the surrounding building apart.

[@cmillerg6306]

Yes...thank you. Not really a "tip", but a length...

[@klausfleishacker4756]

​@@taraswertelecki9586 I don't understand what you mean by "had they been long enough to extend all the way into the bottom of the core". Now there were graphite tips to the boron rods. What would the rods look like in your explanation?

[@retrocompaq5212]

im a car mechanic and it, not even close to be a nuclear physician but i really wanted to understand what happened like 2 years ago, i watched tons of videos and i barely get everything you mentionned in the video, i wish i would have seen this before, 50min is only what i needed lol thanks alot great work!!!

[@fanBladeOne]

Literally THE most comprehensive and complete explanation I have found so far on KZbin. Thank you!

[@AJsWorld]

Presenter: Serious topics Audience: LOL!

[@ibelieveingaming3562]

gallows humor. its all they've got

[@catc1566]

Um do you want. This was not a big joke ya know

[@Kacccirek]

@@ibelieveingaming3562 jel blnljlb0lklhbjk

[@VenerableBede2510]

He’s the low confidence, trying to be cool, “hey guys” style of presenter. Instead of being serious.

[@JC-lu4se]

@@VenerableBede2510 Maybe he’s just got a sense of humour?

[@michaellicitra7632]

Good job Ethan. I have been in nuclear power engineering since 1976. Your description is good and of sufficient granularity that understanding of the issues is possible.

[@EthanChaleff]

Hey thanks!

[@stevowilliams8279]

what were your initial thoughts when hearing about Chernobyl in 1986?

[@michaellicitra7632]

@@stevowilliams8279 Why no containment building?

[@micahbell122yearsago6]

@@michaellicitra7632 our reactors are so safe we dont need a containment structure

[@ryanmccarthy8625]

@@michaellicitra7632 It's obvious that a number of factors contributed to the Chernobyl disaster but in my opinion, the primary catalyst was the hubris and ignorance of the Soviet government at that time. They knew how dangerous nuclear power could be if mishandled. In essence, it was no different than a child striking a book of matches or playing with a loaded gun.

[@cyclingnerddelux698]

Thank you for not forgetting the human element this story. As a historian, I'm often saddened by the cavalier manner these tragedies are discussed.

[@SMGJohn]

Because the West is more interested in portraying it as a fault of Communism rather than fault of design and corruption.

[@SMGJohn]

@@CBtronica So like your mom?

[@berelinde]

"When I first flipped open a textbook and saw the Chernobyl accident..." I will never forget where I was when I heard about it for the first time. I was 18, in my first year of college, and in a lot of ways, it shaped my generation. It led to a lifelong fascination with nuclear energy, as well as the causes, effects, and prevention of nuclear accidents. But phrased like it was in the first two minutes of the presentation, it just makes me feel old...

[@BillehBobJoe]

@Simon Archbold "Turbin" is an acceptable pronunciation of the word. Not everyone is from Texas..

[@CoffeeAndPaul]

National Geographic Magazine informed me of the event. It was a front page spread published either after the sarcophagus was designed or after it was built. Either way National Geo did an excellent job describing everything and getting the major points through. I read that article when I was, like, 10 years old? and I developed a respect for physics and the regimen ofsafe operation of potentially deadly machinery after that. I'm not afraid of nuclear reactors, I think it's great tech and I look forward to Gen 5 designs taking their due places in America's energy mix.

[@jameson32]

I'm in my late 30s and feel the same when people mention 9/11 in the same way.

[@russwaddel08]

Hi Ethan. My dad was in nuclear engineering for over 25 years at Hanford, Washington. By saying, "this could never have been prevented" is a misnomer. It COULD have been prevented. If Dyatlov had pushed the test out for 48 hours (to allow for cooling and phased start up), it is likely they could have run the test without fail. But, he forged ahead. Dyatlov was intimately familiar with the reactor and it's design. Ergo, his word was law. He should have pushed out the test. But, he didn't. Formin would have listened, especially when the call came in about needing power during the evening when the other power source had a problem. Some people say Dyatlov didn't know the "fatal flaw." He oversaw construction of the plant, and he knew that RBMK reactors were notoriously unstable. I believe he knew, but went ahead with his test because of pride.

[@BasicPlanet]

Dear Sir, I think it is historicly unclear at least if the engieneers and als Dyatlov knew about the grpahit tip surge in power. Most of this special design features and also flaws that came with them were handled as state secret and not teached. I still believe Dyatlov had a reasonable chance to be informed about the problem. I am also quite sure that all the other personal on staff that night did not know. Because if they knew how dangerous this would have been, they would have never run the test. This is exactly what western power plants decided to do: All the plants are designed to handle this test but no one was ever brave enough to actually test it, for good reason. If the saefty net works this is fine, if it doesnt this might result in at least a damaged core. But needless to say: They actually removed multiple saefty system to be able to do this. So there is at least a two stage problem if not three stages if you consider this super critical state to be not covered by passive design elements like non moveable neutron absorbing materials. Lets say this: If you build a powerfull machine and pressure people into wrong decisions, this might happen to any machine in the world. From car to space station.

[@ExaltedDuck]

One interesting theory I saw recently was that the zirconium could have melted and in a molten state had a similar reactivity with the water like a group 1 or 2 metal would. In that case, it's not necessarily just combustion of abstracted hydrogen that's exploding, but possibly the replusion between freed electrons at the surface of the metal that creates an even more powerful blast.

[@SAPANNow]

Any research on molten zirconium's reactivity to water?

[@ronjon7942]

Thank you for this. I'm attempting to educate myself to a laymen's understanding of nuclear power, and I wanted to learn about some of the incidents and accidents that have occurred. I tend to avoid issues, such as Chernobyl, immediately after they happen because the sensationalist media coverage can influence people to form opinions that are based on fear and uncertainty. The emotional and often irrational conclusions drawn, which unfortunately can produce policies and perceptions that are too reactionary and inaccurate, can be very harmful to the industry by stifling continued research, reducing or eliminating funding for development, preventing the construction of new nuclear power plants and even resulting in the closure of existing ones. This highly charged, confrontational and fear based decision making has created an atmosphere where progress was halted, but now it seems enough time has passed that a new generation is able to try again. People are approaching nuclear power rationally, and education, understanding, and awareness is replacing the misguided fear of the previous generations that equated nuclear power generation with proliferation, war and nuclear waste. Even if nuclear power wasn't absolutely necessary to help curb our climate crisis, it still would be a good idea to implement for reasons of energy security, having cheaper and cleaner power made more universally accessible, and reducing conflict in the usual areas because of oil dependence. It was very helpful to listen to a technical, objective and rational explanation of Chernobyl and it will be interesting to cross reference this video with the several others I intend to watch. Thank you again.

[@johnspence8141]

Im sort of amazed how much conflict there is AMONGST NUCLEAR ENGINEERS about what exactly happened.

[@princeofcupspoc9073]

I don't think many would argue against this description. Sure there are details he skipped, but unless you are actually designing a reactor, you probably do not need to hunker down and do the math.

[@melkiorwiseman5234]

Short Version: The reactor was poorly designed such that inserting the control rods in order to slow down the reaction would actually increase the reaction rate for a short time. Due to poor training, the reactor operators inserted the control rods when the reactor was in an unstable state, causing the reaction to go out of control and everything overheated to the extent that the water used for cooling began to break apart into hydrogen and oxygen. Hydrogen is highly combustible and it exploded inside the reactor.

[@getmeagator]

That positive void coefficient of reactivity tho.

[@melkiorwiseman5234]

@@getmeagator In simple words, that means that the reaction rate would increase out of control without the coolant circulating. It's possible to build reactors so that the opposite is true, but I guess it's harder to make weapons-grade plutonium with that type of reactor.

[@JC-lu4se]

Positive void coeff. Massive core. Not enough sensors to measure heat/ flux activity Core so big it resulted in localised power anomalies Graphite "tips" on control rods No containment building Over moderation Operators not informed of flaws in design Too much time for control rods to be inserted in an emergency Zero safety culture Massive secrecy by designers

[@MostlyPennyCat]

It's wasn't poorly designed, lack of safety culture was the problem. They built loads of RBMKs, some are still running I believe. They knew about the flaw, they covered it up because why worry about something that isn't going to happen.

[@epiccollision]

@@MostlyPennyCat the design had no fail safes, every safety system failed due to lack of power, at a power plant...they managed to “stall” a nuclear reactor, that should never be a possibility of reactor design!

[@freestyler3061]

12:29 actually accident with ruptured fuel rod also happened at chernobyl block 1 in 1982 and it was very well covered, one person was blamed and given job at another npp abroad because of that.

[@seho8722]

Not BS???!!!

[@montiro8999]

A similar accident happened in Leningrad a few years before as well

[@swokatsamsiyu3590]

@@montiro8999 And it is only thanks to the coolheaded operators of that time noticing that something was off kilter, together with the fact that they hadn't backed their reactor into a corner like they did with Chernobyl Unit 4, that we are now talking about "Chernobyl Unit 4" and not about "Leningrad Unit 1", because that could have very easily been the case. The same goes for Ignalina. This very dangerous design flaw was well known at least 8-10 years before the accident and not acted upon purely for political reasons, and the poor workers at the Chernobyl plant and the people in Pripyat, as well as the surrounding areas paid a devastating price for it.

[@RawbLV]

There was no explicit power level set in the program. It was written that the power level should meet the self-power needs which is 200 MWt and above. Of course anyone will agree that RBMKs are more stable past that, where 700 MWt is the next best power level. Since they were in some kind of rush they decided to stay at 200 but that is not a violation.

[@shawnstrode3825]

Even at the simplest design we "require" a FMEA (Failure Modes Effects Analysis). I put that in quotes because management will deviate processes.

[@aduboi1534]

I am a nuclear physicist and this was a pretty good presentation for an Engineer. I think your only weakness here is not emphasizing enough the moderation effects of the graphite and the role it placed in the "loop" of heat, moderation, more slow neutrons, more reaction, more heat.. due to the positive temperature coefficient of graphite. Also graphite is highly flammable, and the graphite burn is what provided the energy to lift the particulate uranium and plutonium into the environment.

[@joeymurdazalotmore6355]

Yea I'm less edumacated and less of a big shot. I thought he was masterful making all that make sense to me to the micro granular level. It's like critiquing 2 spelling errors in 48 trillion words n petty af. Men don't do that. He did a brilliant job. Didn't think in fact I'd be able to stand em long n was entralled. Just a counter perspective from a random viewer. That physicist has a tone thing he must be above the engineers pay grade he's the physicist n ur a rank up but he looked smart. N u went clout chasing teenager with a gun didn't you sir? Slap didn't you? Just a simulation I'd be on go on trigger . First time I think I may have just fckd with a super villian who's a fetus for breakfast everyday kinda guy. 50 /50 that or just a pompous ass. Well if Duboi is so edumacated and upvoted he's fckn smart right? Imagine how easy he could have said without adding that dckhead shine ya know. If sure u can appreciate no face no case no wittness no trace. Ssssh

[@austinbarnard-anderson379]

Remember, we need scientists but the public doesn’t generally see their efforts. Engineers take those efforts and make things that we see and feel in everyday life.

[@princeofcupspoc9073]

@@austinbarnard-anderson379 Yeah, but sometimes those people are left with an inaccurate impression of the underlying physics. How many people can explain the "cat in a box" or "age slower going fast" concepts correctly. Most think that the cat is a wave and you don't age in a spaceship. Both COMPLETELY wrong. As he stated at the beginning, most people have a very inaccurate impression of nuclear power, due to over-dramatizations and over-simplifications.

[@chrisp6083]

I would also say this presentation is nowhere near polished. He stumbles over it a lot and says things that are contradictory multiple times due to this stumbling. You can still follow it and all the salient information is present but like I said, not nearly as polished as it could be. The MIT lecture series has a lecture that is smoother and clearer and I think better overall. That said, I cannot say my lecture would be better.

[@TishSerg]

> Also graphite is highly flammable, and the graphite burn is what provided the energy to lift the particulate uranium and plutonium into the environment. Are you really a nuclear physicist? Is your statement true? I have different info from other professionals: the graphite isn't flammable. It can be glowing (red hot) but doesn't burn.

[@ridethecloud]

What an amazing presentation, I understood everything even though I'm a software engineer with a small background studying nuclear in high school. Really shows your detailed and comprehensive knowledge on the topic, being able to explain it so clearly. Wish you all the best in future endeavours. Take care!

[@BarneySaysHi]

I've watched several nuclear mishap documentaries but the explanation you're giving here is by far the best explanation ever.

[@bobmutchseo]

I just wanted to get some feed back to see if I have this correct. The power increase by the movement of the control rod attached graphite displacers from the center of the channels toward the bottom of the channels was not from the graphite, I believe graphite is only 2x better moderator than light water, the increase in power was caused by the graphite displacers displacing water in the bottom of the channel. This water had been acting as a neutron absorber. I believe light water is around 195x better neutron absorber than graphite. So the increase of reactivity in the bottom of the channels was not caused by the graphite displacers but by the loss of the neutron absorbing water in the bottom of the channels that those graphite displacers displaced.

[@MinSredMash]

It is a sad comment that this might be the one of the only KZbin lectures I have seen where the author appears to have *gasp* actually read INSAG-7! Not everything is right, though. Corrections follow: 25:00: Actually the test program specified that only enough power for the 'self-sufficiency' of the reactor was necessary for the test. The turbine had enough inertia to provide sufficient coolant even at 200 MW. The 700-1000 MW limit was set by an electrician, since the reactor was viewed as not even participating in the test. 29:57: Just like the drop in power, there is no clear indication on whether the reactor was fully shut down or just stalled a very low neutron power. 30:35: The test succeeded(!) at 200(!) MW! After the accident the core parameters were analyzed, and it was found that there was only a steady 10-20% reduction in coolant flow, more than sufficient to handle decay heat and bridge the gap. When the reactor exploded, the diesel generators were already almost at full electrical load. 31:00: The test was approved and signed by nuclear engineers Dyatlov, Kryat and Lyutov, who also had input on the procedures. The test was essentially identical to the tests that had been run previously at Chernobyl in years past, and had been submitted to at least regulatory body. But no one in the scientific community really cared about the rundown principle at this point. 33:45: The reactor could have been shut down safely after the beginning of the test too, by dropping control rods in groups (according to the private letter sent to plant directors, this mitigated the tip effect), re-enabling the other 4 MCPs or by inserting an auxiliary set of absorber rods from underneath the reactor. Assuming a time machine where you could warn the operators, of course. 34:18: Read your INSAG-7. It will tell you straight-up that there was no increase in reactor power during run-down. I'm no physicist, but I highly doubt that the small reactivity insertion at this point could have had the slightest impact on xenon concentrations (over just 10 seconds!), which would still be increasing overall. This factor seems to a sort of fan fiction for Western engineers, and to my knowledge is not demonstrated in any actual documents or calculations. 35:00: INSAG-7 will also confirm that it is unknown why AZ-5 was pressed. Given the calm atmosphere in the room at the time, it appears just as likely that it was pressed once the shift supervisor realized that the reactor should have been tripped automatically at the start of the test. 38:30: It's really anyone's guess whether the entire core flashed to steam before or after containment was ruptured. The reactivity insertion of the tip effect and void coefficient was more than enough to cause a prompt criticality. At this point a small nuclear explosion (sending short-lived isotopes to high altitudes) is also a respected theory. The explosion can also be explained by steam pressure alone, without much in the way of hydrogen deflagration. As for the HBO miniseries, other than portraying many of the characters as psychopaths, it also depicts the Soviet propaganda version of the disaster, where the power excursion predates the pressing of AZ-5. This is akin to a show about 9/11 where the WTC catches on fire *before* the airliners crashes into it.

[@EthanChaleff]

Thanks for the detailed feedback. There is such a huge body of research and literature, and only so much has been translated. I appreciate the attention to detail and will incorporate into any future updates.

[@MinSredMash]

@@EthanChaleff Cheers, I thoroughly enjoyed the lecture! The Chernobyl story is certainly full of pitfalls, especially without access to Russian sources. But even then, reading Russian only expands the amount of misinformation and conspiracy theories you have access to!

[@crimony3054]

"Annexes I and II indicate that important problems now recognized in the Chernobyl plant design had in fact been recognized before the accident. INSAG notes the observations made at the Ignalina plant in 1983, when the possibility of positive reactivity insertion on shutdown became evident, and the event at the Leningrad nuclear power plant in 1975 which, in retrospect, indicated that events excited by local reactivity feedback could cause damage to the reactor. These two events pointed to the existence of design problems. Although the events had the semblance of potential precursors to an accident, apparently no thorough analysis was performed. It is a matter of great concern that this important information was not adequately reviewed and, where it was disseminated to designers, operators and regulators, its significance was not fully understood and it was essentially ignored."

[@nazareth978]

@@EthanChaleff besides the INSAG-7, I can highly recommend further readings: www.neimagazine.com/features/featurehow-it-was-an-operator-s-perspective/ www.neimagazine.com/features/featurewhy-insag-has-still-got-it-wrong ...and a webpage which is very hard to understand in English, but contains a lot of detailed information: www.accidont.ru/ENG/main.html Oh, and +1 to MrChyort's list: you keep dividing the world to "western type" and "RBMK" . But if you look to the list of the reactors of the socialist block, it is (and was already in the '80s) full with PWRs. It does not depend on the geographical location of the reactor, but on the type if it can be refuelled continuously, can be shut down with SCRAM, or has a proper cooling for the case of power failure, etc.

[@careernerd2135]

8 corrections... not great, not terrible.

[@MostlyPennyCat]

I read a paper where the analysed the Fission products from unit 4. According to the results, the second explosion was not all hydrogen but was a super critical event, like a fizzled nuke. It's supporting hairs but there you go.

[@gregorymalchuk272]

I've thought about this too. I mean, what is a nuclear bomb but a supercritical event where the fuel vaporizes? That's basically what happened here. It doesn't really matter if the supercritical mass is assembled by an implosion, a gun, or explosive ejection of control rods/neutron absorbing water. It's probably the only nuclear accident that has happend like this. Actually, now that I think about it, the Borax reactor experiments in the USA where a spring mechanism ejected control rods from the core of a small water boiler test reactor in a fraction of a second may have been another example of possible vaporizing of the fuel.

[@ctdieselnut]

Thank you for posting this. Great presentation, perfect mix of technical and simplified explanations.

[@cmillerg6306]

"Why am I here tonight?", so many self referrals ("I", "me", "myself"...), and the audience reactions reminded me of a comedy about a dysfunctional future.

[@JonB55198]

Best visuals I've seen explaining the nuclear physics! Thanks for putting this together!

[@bobdawonderweasel2]

Thank you Ethan for a well presented explanation of some very complicated physics and reactor mechanics. As a non nuclear professional I feel like I have a much better understanding of the physics involved and how this tragedy occured.

[@didikohen455]

Loved this, I've been looking for that kind of information for a few months, I knew about that it was during an experiment (without much details) and the steam and hydrogen explosions, but not about the "dual purpose" rods, and the low capacity that reached.

[@Popdad]

Loved your clarity of thoughts, presentation of physics and possible reasons about the unfaitfull event.

[@goc355]

1966 is not T-17, but T-20, as explosion was in 1986.

[@RonInbar]

Yes, it really bothers me that he says that he studied Chernobyl for a long time and then only a few sentences later he makes such a basic mistake.

[@matchhunter6941]

Big mistake!

[@MrRichievee]

Well if thought Khruschev was in power......????

[@Ronniezim]

Is he referencing the online date for the reactor and not the accident date?

[@CarlosAM1]

Amazing presentation, loved every second of it

[@ExecutiveAutomotiveSociety]

Great description! It needs to be this specific too. I would love to hear someone describe it like a drag race. It's so perfect to think of a car with water flowing too it, but the brakes on full while the gas pedal just keeps getting applied harder and hard until they start the test which makes the brakes shut down and literally nothing will stop the car as it drives down the track, covering the 1/4 mile distance in less than a second. It's insane to think about it.

[@billnu]

This guy is a great speaker. Clicked just to see the format and what kind of quality the vid was. Now I’m stuck for the next 50 minutes.

[@animyosfox8617]

Thank you for this presentation! I researched of the Chernobyl catastrophe too, and I must say I learned some things.

[@anticat900]

This is a good explanation, but as with many I've seen, doesn't show the control rods (even after simplification) as they really were.

[@joshabadie1431]

So much more detail than I've ever heard! Thank you!

[@curtrapp5291]

I read somewhere the graphite was added to the control rods to prevent uncoupling of the top and bottom of the reactor. The voids in the top would result in more power being produced (positive void coefficient) than in the bottom due to fewer voids. The graphite provided more moderator in the lower half which would increase power. The operators weren't told of this additional graphite so when they scrammed to reactor they didn't know it would add more moderation to an already supercritial reactor. The design was considered a state secret and kept from the operators.

[@natcalverley4344]

I would really like to here a well done objective documentary on why we don’t use molten salt reactors.

[@princeofcupspoc9073]

Because the engineering is not there yet. A lot of study still needs to be done before actually building a commercial unit.

[@eyeballz76]

Well done!!! I love this kind of videos.

[@szt1980]

It was the same power plant, but another reactor in 1982. And there was another incident on the same reactor type at the Leningrad power plant in 1975. Both resulted in radioactive steam release

[@sskuk1095]

Being exposed to radiation without giving consent is something I hear for the first time!

[@andrewhaywood531]

Keep advocating Ethan, Nuclear is the most realistic path to clean, reliable energy but does require incredible vigilance.

[@animula6908]

It requires the willingness to accept frequent Chernobyls

[@andrewhaywood531]

@@animula6908 We don't build RBMK reactors anymore with positive void coefficients. Also we don't have people wildly disregarding safety or building reactors with no containment vessels as in Chernobyl's case. Specifically I'm referring to the potential of Thorium reactors which cannot melt down by design. Nuclear has advanced significantly but please know what you are talking about beyond "nuclear bad".

[@animula6908]

@@andrewhaywood531 you can’t even possibly know that someone somewhere isn’t wildly disregarding safety. The next disaster may be something no one saw coming but seems plain in hindsight. It’s one of those things where the extreme unlikelihood of it happening has to be weighed against the guarantee of extreme, widespread, and unmanageable consequences if it ever does. The odds of everything going perfect forever are zero, and anyone who tells you there can never be another major disaster is simply lying.

[@CoastalSphinx]

@@andrewhaywood531 Thorium molten salt reactors will be ready for prime time in what, 40 years at best? Climate change won't wait that long. And I think the upper RPV head at Davis-Besse might want to have a word with you regarding people wildly disregarding safety.

[@YetAnotherGoogleUser]

This video did not advocate what you are implying, I was expecting it to make a comparison of RMBK with other nuclear reactor designs, or to make a point of why a similar accident won't happen in the West, but this was only about how the accident happened, and not even why, as he said himself, since this presentation is mostly about the physics of it. As for the realistic path to clean reliable energy, I think engineers and designers should design with a smaller scale, more efficiency and mobility and less maintenance in mind, because if safety requires educating people, which it does, and incredible vigilance, as you said, well, I would say that's the limiting factor to worldwide implementation of nuclear power as a realistic path to clean reliable energy.

[@taraswertelecki3786]

I have to wonder if there was a supercritical chain reaction within the fuel, given the immense release of energy required to not only blow the reactor apart, but to also throw a 2,000 ton structure hundreds of yards into the air before it crashed down into the burning nuclear reactor as well as blow off the whole top of the reactor building. All I know is the mushroom cloud that was ejected was emitting so much gamma and neutron radiation that everyone outside on the site were irradiated to death, including two men fishing in the cooling pond. Within hours, they had a nuclear tan, which only happens when people receive far more than the lethal radiation dose.

[@JM-nt5fm]

Supercritical where all the neutrons generate new fission events is theoretical but not possible in reality. No one has ever achieved 100% efficiency.

[@kasel1979krettnach]

void effect was probably less important than the graphite insertion into the lower core-half, given the amount of water pumped into the core before the explosion and the low power level at that point in time. Diatlov got it quite in right in the VHS tape interview.

[@thattubesound2214]

This is very well done! I love Mr. Chaleff's balance of lay and technical perspective. I worked as a system engineer at a newer Boiling Water Reactor in the late 1990s (Clinton Power Station). We talked about Chernobyl and the RBMK design, but this was the first discussion of the physics involved that I've seen outside of the industry that makes sense. I agree completely with his conclusions related to why Chernobyl happened and why, as an engineering community, we must still maintain a rigorous focus. Nice work, sir! And a very important contribution!

[@utubeznoone5598]

Dam you made this slideshow? It's so good and you explained so much.

[@stuartgillies8912]

Wow that was very interesting & brilliantly explained in terms that are not too scientific & easy to understand!

[@canberradogfarts]

As a NPO in the USN during the time of "Chernobyl" and for a good long time after, I can see a lot of gaps in the "data" he has studied and drawn his conclusions from. I will say this, the Pu loading in the fuel fraction that "flashed" was significantly above the change out threshold. High enough, in fact, to make prompt supercriticality not only possible, but highly probably. There were several radionuclide contamination surveys in the early days afterwards that confirmed this. In short, this was a puny plutonium bomb style "fizz out." And the fact that it not only happened once, but possibly still exists in tehe ten remaining rbmk s is horrifying to those thousands of us who were on duty at a console, so many years ago.

[@derekp2674]

I think this video says the peak reactivity was +5$, so definitely prompt critical.

[@taraswertelecki3786]

The fact the explosions that blew the reactor and surrounding building apart were estimated to equal 200 tons of TNT would agree with your assessment. That is also the sort of yield one would get during a failed nuclear test or "fizzle."

[@micpic119]

Worst part of this disaster: 1. People think it was a nuclear explosion. 2: The graphite fire spread byproducts for hundreds of miles. Can't happen with water moderated reactors.

[@_CossaCShocK_]

Well, the problem was not in fact that control rods had graphite ends, but that boron part was to short (to be more exactly, whole rod was too short and do not gained the botoom of reactor tank, so that there was a boiling watter, and so then the botom of active zone was overheated, that bloked stream of cool pumped water in time, when reactor was under experiment, when pumps' power supply was turned off (slowed)) and system of throwing control rods down in active zone was too slow. So even positive reactivity was not a critical factor as it is: the problem was in fact, that it was not measured permanently (was not updated in real time mode), and the mesurement procedure lasted from 15 to 30 minutes, while processes in the reactor changes faster. If ivestigate the whole catastrophy timeline you can find out, that there was a chain of power plant operating personnel mistakes caused by informational ignorance of "specialists" that acted too frivolously, thinking they are real high order specialists and that they know reactor very well, but in fact they had bunch of critical and hidden information about reactor design. That's why all thier actions were dangerous, but they acted confidently and in fact explosion was caused by simple turning on AZ-5 switch. And why stopping switcher did become detonator? Cause of hardly repeated combination of correlative construction fatal flaws and reactor working mode, seted by users' actions. And after water steam explosion that caused reactor cap blowing up, this cap taked out not only conrol rods, but also parts of ripped fuel rods, that's why part of fuel started burning inside reactor core remains, and part of fuels was thrown all over the plant and even surrounded territories (small parts of reactor core were found in Pripyat, in a distance of killometers from block-4).

[@_CossaCShocK_]

UPD: turning on AZ-5 is an ordinary operation of sitching of reactor work no matter if you trying to stop nuclear reaction by some problem or you just need to stop reactor. They stoped reactor just because this action was part of experiment and after it procedure of block modernisation had had to start, some parts of which could prevent hapenned catastrophy.

[@jasonkoval9813]

Informative presentation. Especially key points to me are the different influences on reactivity, the delayed neutrons for fission product decay, and the dynamics of interrelated variables like Temperature, water vs. steam, graphite vs water, Xenon poisoning, etc. It is like all major disasters in complex systems: a multiplicity of errors beget more problems that become insurmountable after some point of no return. And the political vs. scientific realities are so relevant even today in the US. Repeat a lie enough times and people will not recognize the truth. It is happening now.

[@josepheller8395]

This was by far the best explanation for how this happened. For people who don't work or understand how nuclear power plants work this is easy to understand.

[@kcreese5586]

Thank you! This was helpful. I do not have a physics background and this was pretty easy for me to follow.

[@PK-or2yr]

8:52 Turbine hall is only on one side. But there are two turbine units (turbogenerators) for one reactor. 13:00 sometimes ten?

[@PK-or2yr]

@Simon Archbold thanks for correction, now it actually makes sense. The nerves and ears are in pretty bad shape lately.

[@Enonymouse_]

For what it's worth I recently reviewed an MIT lecture on a similar subject, your lecture was MUCH better and more comprehensive.

[@jfmezei]

3 simple questions: -Would steam act as moderator while water is poison? -If steam is transparent and does not slow down neutrons, how would these voids in water (or whole channel filled with steam) end up fostering increased fission? -When there is mention of the rods having been pulled up, does this refer to the combo of boron at top and graphite at bottom both being out of the zone where fuel rods interact, or only he boron portion being outside of that zone and graphite still very much in there?

[@drtidrow]

27:40 Really should have mentioned the particular isotope of xenon that was the problem, namely Xe-135. Xe-135 is a massively strong neutron absorber, but Xe-136 (what Xe-135 turns into after absorbing a neutron) rarely absorbs neutrons.

[@michaelashcraft8569]

There were so many hero's at Chernobyl who knew they would die doing their jobs, and, ought to be remembered.

[@Penguin_of_Death]

*heroes

[@antigen4]

Yes though many more survived than expected ... most of them

[@melissa-wilson]

It's so rare you listen to something on KZbin and don't feel more dumb for watching it. I feel so freaking smart after watching this video AND thankful the lesson is more about our future and less about nuclear equals bad.

[@fintonmainz7845]

If you think watching a 50 minute video can give you an understanding of the issues involved I pity you.

[@thomasbummer4361]

@@fintonmainz7845 u are the type of person no one needs, thus may be the reason u feel the need to post such stupid comments

[@garakward6118]

@@fintonmainz7845 No Mel is not going to be a nuclear engineer with what they learned by watching this video, but as a citizen of the world they're learned and grown. That's important. Entertainment media should inspire and enlighten and I'm glad they enjoyed and feel inspired and educated.

[@ackertube83]

@0:14 "i became a nuclear engineer because i´m passionate about climate change. Nuclear power is one of the most powerfull tool we have to fight climate change". @7:48 "if you think that animation was cool, i´ve had a lot of flights recently (smile)". This symptomatic of how well educated and brilliant some people are and on the same time completely blind spotted. Thank you for the presentation. It is indeed very nicely explained. Nethertheless i used to work for nuclear industry, i don´t believe in it beeing a game changer on climate and i don´t believe in it beeing safe on the long run. Add a little stress on the system, difficulty of availability on spare parts, high energy demand combined with lack of gas supply as we have in europe, cost-down on maintenance... and soon you´ll see safety authorities giving exceptional exemption to run the plant despite major problems... 30 years from now, an other brilliant Phd may present a lecture about all we did wrong with the waste disposal and how we could have prevented it.

[@rcsontag]

Mr. Chaleff's refusal to address reality - the NUCLEAR EXPLOSION is astonishing, even after admitting the reactor was "Prompt Critical". Prompt critical is a supercritical condition that is exactly the chain reaction in an atomic bomb. Thankfully it was very localized and self-limiting.

[@fsoiberg]

“Nuclear power is a hell of a way to boil water.”- Albert Einstein (Safe = Figures don't lie, but lairs can figure.) - So basically, Nuclear power is so complicated that when engineers design a shutdown procedure (Scram) the opposite result is produced (Boom). Brilliant!

[@melkiorwiseman5234]

It was partly due to poor reactor design and partly due to operator error caused by them not properly understanding the design.

[@JC-lu4se]

@@melkiorwiseman5234 They didn't understand the design as it was kept secret from them by the secretive ministry that designed it.

[@danny80268]

What do you think is the near future of reactors? MSR, Modular? Also, what do you, being in the industry, foresee in fusion reactors? Lastly, I'm a ME student and understood most everything you explained, I think I think it was very well done.

[@EthanChaleff]

Probably modular is the near term future if anything gets built. Too much risk for larger projects. At least in the west; in Russia and China we'll probably see steady growth in 1 GWe+ reactors being built with todays tech for a while. I'm not a fusion believer but the chance it works someday is high enough I think the amount of funding its getting is reasonable.

[@heyman5525]

At 38:15 if you don't understand the pressure cooker example, it has to do with the physics of evaporation. Water boils at 212 degrees Fahrenheit but it won't boil at that temperature if it's pressurized. Once the lid is removed then all that hot water becomes depressurized and is able to evaporate. It sounds simple but it can be deceiving when you have hot water that isn't producing steam. It appears safe while it's under pressure. It appears like it's still a liquid when it should otherwise be a vapor.

[@ErwinPommel]

That's exactly what he described in the video.

[@heyyo162]

First I thought he made a mistake at 7:00. where he says that steam gets generated "next to the fuel". But then I read at wikipedia that "the coolant boils in the core. The mixture of steam and water is led by the upper steam lines". So a mixture of water and steam?

[@czr7j9]

i seen an interview with a chief scientist in the 90's about cold fusion which has been replicated 8 times. The us patient office changed the the levels of the data and rejected the patient. it didn't prove cold fusion but energy levels were produced at levels of nuclear power. He tried every avenue but got nowhere because of the threat it posed on nuclear hot fusion physicists(in his words) and was stigmatized as it did not follow the current laws of physics. 2 Years after his interview he was found bashed to death in his house.

[@pavlovezdenetsky7824]

Could you please provide some credentials of that scientist?

[@robinwells8879]

You give me a piece of complex equipment and a operation manual to flagrantly ignore and I will give you an incident no matter how much DFMEA you perform. This was a management systems failure with no apparent MOC procedure in place. The other units were a success.

[@jeffriesj75]

Love the video!!! Lowering power -> increases Xenon and ultimately keeps declining power (positive feedback loop). They should've never removed almost all (only 6 of 211 remained) control rods, that moment alone sealed the world's fate to this ongoing catastrophe. Especially the control rods in the center of the core. Those boron carbide rods were the most important for neutron flux control which is highest in the middle! Even just withdrawing them partially could've been less catastrophic and avoided the meltdown or the graphite on the other end of the boron rods had been the same length as the boron, the water would've never displaced.

[@jeffriesj75]

the simple way I think of control rods in a nuclear reactor are (Boron) = Brakes, (Graphite) = Gas, with any reaction to be maintained smoothly even through testing phases, the production has to be smooth sailing, you can't floor it or slam on the brakes, Chernobyl did both unfortunately, they floored the gas by withdrawing all control rods exposing graphite to speed up fission, then panicked when the power was climbing rapidly and slammed the brakes, (scram button), and attempted to place said rods back into the core. The reaction only needed seconds to become unstable to the point of no return. Their brakes locked up.

[@stevemenegaz9824]

Superb presentation. PLain talking the facts and the right amount of analysis combined with no drama. Cold 20/20 lookbacks are what we need and this presentation deliviered.

[@Norm_MacLeod]

Nuclear power plants will not be truly safe until a safe and secure way is found to isolate the waste from the environment. As far as I am aware there is no safe way to dispose of the waste.

[@wendyarenz3429]

I am BEYOND fascinated with Chernobyl!!!!

[@ckw961]

Some of us still remember being given the iodine pills and told to stay indoors. A different level of fascination with the topic/ event.

[@wendyarenz3429]

@@ckw961 I’m so sorry for everyone that went through this...so many live lost and so many heroes that should never be forgotten. I hope you and your family are okay today; I didn’t mean to come off as insensitive. I was 17 living in America...a selfish teenager.

[@ckw961]

@@wendyarenz3429 I understand and thank you for your words. While we did not live in that area, we were not far enough either (in order not to be affected). The radiation clouds spread fast and far, and I still remember when we were told to stay inside and were given iodine pills. As kids, we did not understand what was going on. But what’s sad is that many of the adults didn’t either. Because they weren’t told the truth. We will likely never know how many died due to the Chernobyl disaster.

[@jaeweld19]

I've been fascinated with it ever since I was a kid and found a national geographic magazine that had a whole section devoted to Chernobyl. It's definitely on my bucket list of places to visit.

[@commanderrockwell1123]

Thank you for informing everyone that you’re interested in Chernobyl while watching a video about Chernobyl. You’ve made a tremendous contribution and it’s totally not as if everyone else here is too.

[@TheNavalAviator]

The preceding accident happened at Chernobyl unit 1, not 4. It was a partial meltdown. The last reactor at Chernobyl (No.3) was shut down in 2000.

[@FredFuchs77]

Awesome talk. Thanks for uploading.

[@user-tk5zk5bj1b]

Back when this happened my Uncle Robert Livingston, then a director of programming and planning at Oak Ridge National Labs explained it at length. Someone high in the food chain wanted to know how long the reactor could generate power after being shut down. An apparatchik who knew all about generating power and nothing about nuclear reactors was sent to oversee a test. He devised a test that involved running the reactor hard and for longer than usual resulting in excess quantities of a xenon isotope that absorbs neutrons to build up and slow the reaction, this was countered by withdrawing the control rods. At some point the rods were fully withdrawn relying on the graphite moderator and cooling water to moderate the reaction. Graphite has a positive reactivity coefficient so it needs cooling water and control rods to moderate the reaction. At some point the cooling water was supersaturated with heat and a steam bubble formed somewhere in the reactor. Without control rods or water to moderate the reaction this part of the reactor experienced an excursion which generated huge amounts of heat causing more of the water to flash into steam which eventually overwhelmed the physical strength of the structure. I'm remembering this from nearly forty years ago and my sixty-five year old brain might have confused some of the details but I recall it being a lucid explanation

[@Crusty_Camper]

We still have patches of countryside in the UK that have quite high levels of radioactive elements from Chernobyl. Until 10 years ago livestock raised there had to be moved to clean areas for a couple of years before they could be sold into the human food chain. I have Romanian friends who were on holiday at the Black Sea at the time of the accident. It rained and everyone had burns where the rain hit them. Who knows the long term effects of these kinds of exposure.

[@ferchrissakes]

The Windscale fire wasn’t too kind to UK farmland and livestock either

[@Crusty_Camper]

@@ferchrissakes I live 20 miles from that reactor. The sands on the seashore are still more radioactive than the usual background. In fact, it was the radioactivity meters at the exit gates of Sellafield that gave us the first detection of Chernobyl radiation reaching the UK.

[@visnjamusa9395]

No, you don't. At least not from Chernobyl. Elements that came from Chernobyl decayed looooong time ago. The only still radioactive areas are in proximity of Chernobyl NPP. That's basic knowledge about nuclear physics (and that's why Hiroshima and Nagasaki are safe today and very much habitable).

[@Crusty_Camper]

@@visnjamusa9395 It's always best to check your facts before launching into a subject that you have so little knowledge about. I hardly know where to start with the reply. You say the elements released by Chernobyl decayed long ago. Not true. The worst for contaminating food in the UK turned out to be Caesium 137 which has a half life of 30.05 years. That doesn't mean it's gone in 30 years, it means there is still half of it left after 30 years, a quarter after another 30 years and so on. Huge areas of Europe are highly contaminated with this and other isotopes that have far longer half-lives and will be for centuries to come. Of course, it's worse the closer to Chernobyl you get and Belarus is so badly affected we have hundreds of children from there every year coming to less contaminated areas for a few weeks. Look up Chernobyl Children International or any of the other charities involved in this. Chernobyl released an estimated 400 times as much radiation as the bombs dropped on Japan. Unfortunately for the UK it rained heavily as the cloud came over us and three main areas were heavily contaminated. These are Wales, The English Lake District and Scotland. The government immediately raised the acceptable level of radiation in our food by 20 times ad placed restriction on sale or movement of sheep on contaminated farms that lasted decades. To this day, the worst area is around Loch Ness in Scotland. At first it was hoped the Caesium would be washed from the soil but it was taken up by vegetation and has cycled between the soil and plants ever since. This is a problem that will still be a major issue in Central and Eastern Europe for at least another century.

[@visnjamusa9395]

@@Crusty_Camper I have checked one fact that kills all you've written in your answer, better called it essay: people enter the Chernobyl reactor 4 core for years now. There is no place on the planet more contaminated, yet still people go there, some of them went there several times, spend time there and have no serious consequences. While there are tons of radiaoctive isotopes still inside the tomb, amounts of isotopes still remaining on UK soil is negligible. You'd get MORE radiation from e.g. smoke detectors, old glowing-in-the-dark clocks and lightning protectors than from fallout of the Chernobyl.

[@knutritter461]

27:24 Chemistry here: That guy speaking is clearly a physicist making jokes on chemistry! 😂 That's the reason the audience laughs. In fact even chemists could be called 'electron-physicists'.... so we are all physicists. It's like fans of different teams mocking at each other. Physicists do not care about chemistry e.g. for astrophysicists everything heavier than helium is a 'metal'. 😡😂😉 So for an astrophysicist xenon would be a metal, too when in fact it is a noble gas. It was a pun on another branch of natural sciences. It was a pun on chemistry. 😉 The audience laughs because that xenon does not really disappear.... and they laugh because they know chemists will go crazy when they hear this 'blasphemy'. Xenon absorbs a neutron, it remains xenon and it remains in the rod! 😡😂😉 So for a nuclear physicist it disappears when in reality it does not. He writes 'Not-Xenon' when in fact it remains xenon. 😉 The initially formed isotope of xenon can be called a neutron-scavenger thus 'killing' the nuclear reaction. That special kind of xenon behaves like the cookie monster. COOKIES! COOKIES! == NEUTRONS! NEUTRONS! When the neutron monster has eaten one neutron it stops eating more, gets really stuffed and falls 'asleep'. But like its cookie-eating counterpart it remains a neutron monster that just does not want to eat any more neutrons. It's satisfied. But there is not just one hungry neutron monster.... I make an estimated guess there are about one million billion billion 1.000.000.000.000.000.000.000.000 (10EXP24 should be about the scale) hungry neutron monsters and each and every one wants to 'eat' exactly one neutron. In contrast to western reactors in the RBMK-reactors there is just a fraction of neutrons moving around. By absorbing a neutron another xenon isotope is formed that has no 'poisonous' effect on the nuclear reaction. So only the 'poisoning' effect of a special xenon isotope disappears. 😉 The 'new' xenon is the one that was used for the lights in high priced cars. This kind of xenon remains and is harmless for the reaction and for humans.

[@thundercactus]

Could have boiled this whole comment down to one sentence: "Xe135 is a neutron poison, but once it absorbs a neutron it becomes very stable Xe136 which has a neutron absorption rate only slightly higher than zircaloy"

[@cocosloan3748]

Absolutely no place for jokes in this story - if not because of the victims then because the things he wants to teach the audience are hard to understand while concentrating - and even harder while laughing and missing every second word from the noise of the laughter !

[@GuiTheBest889]

@@thundercactus hes just trying to make it a bit more understandble for the "normal"guy

[@djek1976]

I was just eating some cookies. No joke... Thanks for trying to make it clear. Comments below also.

[@hddun]

I note he stayed away from the more terrible nuclear disaster--Fukushima Nuclear 2011. Why because the nuclear power industry has done a good job covering up that mess--especially destructive is the fact that Chernobyl pushed out tons of toxic waste onto land, Fukushima pushed huge amounts into the Pacific Ocean. It would be far easier to contain nuclear accident on land than in the ocean. So IF LIFE FOLLOWS ART, in another 15-20 years a Godzilla type mutant sea critter will ATTACK TOKYO....

[@douro20]

In the early 1990s there was a huge excess of Zircaloy in Russia so a jeweler decided to buy most of it and turn it into shot glasses. They became so popular that they today they are still in production.

[@nyckhusan2634]

Actually, destruction of reactor No.4 began even before performing of "Rundown of turbine " electrical test. About 2-3 minutes before start of test feed water was introduced into reactor and main circulation pumps were put in a full run decreasing inlet water temperature down to 160 C. At pressure of water of 70 bar , boiling temperature was about 270 C. Normally, fuel rods supposed to be cooling down only by boiling water with a rate of about 530 cal/g C. Because of introducing of not-boiling water into bottom of reactor, cooling effect on Zirconium case of fuel rods with a temperature of 2100 C was considerably reduced. While water was heating up to boiling point it was taking only (270-160)x1=110 cal/g C ( to increase temperature of 1g water for 1 C you need to spend 1 cal of heat ). So, deficit was about 420 cal/g C, causing overheating of Zirconium casing and its cracking. It was accompanied by hydrogen build up.

[@Burgher1605]

Very intriguing.

[@GuiTheBest889]

Awesome presentation ,great joob

[@tof70110]

Explanations very well presented and explained in such a way as to popularize the principle and the reactions that have not resulted!!!

[@mehdibenhassine9601]

Although Zircaloy is very good as a neutron containing medium, it is not good at preventing corrosion and hydriding effects (mostly alpha ZrHx hydrides) which can lead to failures in the long run (mostly cracking), that's why recent designs try to avoid it

[@nevmann]

This was really good Ethan. I live in Norway and I want Norway to jump aboard on the nuclear train, sadly it still seems Norwegians are scared to have a Chernobyl incident. Any idea how long it would take for a country to go from non-nuclear to nuclear? I'm thinking about the nuclear competency required to build and operate a plant.

[@taraswertelecki9886]

It would be a 20 year plus effort to design and build a nuclear power plant.

[@DerUngarischeKitsune]

modern nuclear power plants are safe and clear, theres no reason to be scared of it

[@Anders357]

@@DerUngarischeKitsune There is every reason to be afraid of nuclear power plants, because there is very many examples of leaks, accidents and mishaps, so if you want to build something that is even remotely safe, you should start up with fear. Many places has a history of leaks and accidents, even research reactors in my country were discovered to be heavily contaminated and some of the research was falsified. You cannot make this up. Fear will teach you not to build something close to the ocean, in case of earthquakes. Fear will teach you not to build something that can explode if you lose power. Fear will lead you to start with waste management, and constructing safe spots to handle and store spent fuel, fresh fuel and waste byproducts for 100 000 years. And it will teach you not to store spent fuel on the roof of the reactor (!) Fear will also make you avoid testing a RMBK reactor like a total noob. If you start with having no fear, why not build reactors in densely populated areas, where the power is needed ? Well, because if anything unforeseen happens, a lot of bad things can happen. It is fear that drives you to build something solid. If its not fear, its luck. Try googling Hisashi Ouchi or Mayak or Lake Karachay and you will see, you have every reason to be afraid and scared. And i am actually pro nuclear. But always scared of all the stupid designs people come up with. Fukushima was started up early 1970s and of american design. What people did not understand, was the incredible stupid idea to put it where a tsunami could hit it, and put the emergency power generators in the basement, where they could be flooded. They all thought it was safe and nice, but it was in fact, inherently a combination of many very poor designs put together.

[@DerUngarischeKitsune]

@@Anders357 well we learn from mistakes, both Chnpp and Fukushima disaster was a key factor to avoid stupid mistakes, and since then, no disaster happened. Hopefully though, the current situation with ukraine wont affect the nearby power plants

[@Anders357]

@@DerUngarischeKitsune Thx for input, i hope they learn. Both these disasters, seem to not stop happening, which is part of the problem with decaying isotopes and long half lifes, you then have an ongoing crisis over 20-300 years and the area is an exclusion zone. You evacuate 200 000 people from a large area, and the cleanup and collateral damages cost hundreds of billions of dollars (2016 Fukushima estimate 188 billion $). Fukushima is STILL leaking and they are pumping used radioactive cooling water into the ocean TODAY, thats 12 years doing very little "cleanup". A smaller country could simply go bankrupt, if anything like this would happen in say any small African, middle east, asian or Latin or east european (!) country. Its not a kind of power plant you would want to be spread all over the globe, because many countries are not ready for this, they are poor, undeveloped or have conflict areas. But they still need power.

[@chrisj2848]

Nice work, the misinformation and gross oversimplification of this accident and the physics involved is so frustrating. Glad to see a professional tackle it. INSAG-7 is a fascinating read, but I appreciate your explanation and opinions as a professional in the field! Awesome! Cheers!

[@zashbot]

Yeah I didn’t actually know that RBMK makes plutonium really well, the show glosses over that point which makes the Soviets decision to use it seem stupid and evil. Edit: they knew it could turn into a bomb if only 5 fuel channels ruptured? WTF!

[@JC-lu4se]

@@zashbot The RBMK was modelled on a breeder reactor which made plutonium.

[@derekp2674]

@@JC-lu4se As briefly mentioned in the video, the RBMK core design is not far removed from the USA's Hanford Pu production reactors.

[@henryj.8528]

When the Manhattan Project built the first graphite plutonium production reactors at Hanford, Washington, they had only limited experience operating much smaller reactors and for much shorter times. When the first Hanford reactor went critical, the power level started to decrease.after only a few hours of operation. Eventually, all the control rods were removed but the power level continued to drop. Then, a few hours later, the power level started to rise again. Eugene Wigner figured out (from the time constant) that Xenon was poisoning the reactor. Fortunately, the contractor (DuPont) didn't have any experience operating a reactor either and had insisted that the reactor be designed with spare fuel channels just in case. By adding additional fuel rods, Xenon poisoning was eventually overcome. The Chicago Pile and the graphite reactor at Oak Ridge didn't operate at high enough power or for long enough time for the Xenon poisoning problem to be noticed.

[@5tuartGuy]

thank you for this presentation, I feel I could follow it fairly easily & understand what happened.

[@MegaBadgeman]

I found the pause and rewind buttons invaluable.