RBMK Reactors - Design Overview | The Nuclear Reactor that was used in Chernobyl
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- čas přidán 13. 07. 2020
- Sources:
- Ignalina RBMK-1500 Source Book: www.lei.lt/ or drive.google.com/file/d/1yiQ2...
- The Chernobyl Reactor: Design Features and Reasons for Accident by Mikhail M. Malko: www.rri.kyoto-u.ac.jp/NSRG/re...
- ESTIMATION OF THE INVENTORY OF C AND OTHER KEY RADIONUCLIDES IN IRRADIATED RBMK-1500 GRAPHITE BASED ON LIMITED MEASUREMENTS AND FULL 3D CORE MODELING by Narkunsas, et al: www.researchgate.net/publicat...
- Effect of Long-Term Thermal Influence on Mechanical Properties of Welded Joints for Carbon Steels used in Power Engineering by Zilvinas Bazaras & Boris Timofeev : www.researchgate.net/publicat...
- Decay Heat Generation in Fission Reactors by M. Ragheb: mragheb.com/NPRE%20457%20CSE%...
- Neutron Moderators: www.nuclear-power.net/neutron...
- Neutron Capture & Neutron Cross section: www.nuclear-power.net/neutron...
www.nuclear-power.net/nuclear...
- Void Reactivity: www.nuclear-power.net/nuclear...
Ending song: Noisestorm - Crab Rave (earrape version) - Věda a technologie
Now I know how a reactor works.
Seriously, you managed to explain this complex subject very understandingly.
Now I don't need you anymore
@@huyphamuc6372 hahaha, that was a great line in the series.
now you can throw this youtuber out of the helicopter
"GET US OVER THAT BUILDING!! OR ILL HAVE U SHOT"
@@TitanPicturesStudio Loved the character development of Boris Scherbina
I'm surprised at the low views, this is a well informed and put together video.
Hang on I'm going door knocking.
Pretty good views for a channel with 409 subs
Probably not a lot of people searching for it. I came across it by mistake.
I found this channel by searching for the accident. I also searched for RBMK reactors. That's how I found the channel.
That may be exactly the reason.
“the core is gone” *crab dance* 😂😂
*_dyatlov trying to get water into his core *_** : *visible confusion**
Uhhhh thats not funny cuz is killed 4000+ peopel 🙄
@@shruthisrikumar5907 r/woosh
@@pajis_xd what
@@shruthisrikumar5907 you didnt get the joke so I wooshed ya
You didn't see graphite because IT'S NOT THERE!
It was thiere people has it as show items No clue why they would tho .. and pictures just Google Graphite chernobyl and you see chunks and stuff but tragity No matter if east or west when so many dies on a ,,accident" the Uranium 235 basicly got fission so it did the same as WW2 bomb that had it and said booom and Graphite is why unlike japan etc they build that shield cus it keeps it going
@@simon990055its a quote from the show
@@simon990055its joke from HBO miniseries chernobyl when anatoly dyatlov said
you DIDN'T!!!
Excellent breakdown. I'd like to see more coverage of how the RBMK refueling system operates, and the specifics of how the control rods are physically actuated (what actually moves them, its not shown in most schematics).
Yes. I was initially planning to cover that part as well. However, I didn't really want the video to be too long so I kinda skipped it. If you want to know more about that, I included a link in the description to the RBMK-1500 source book. It should be found on page 69 at chapter 4.
@@antares2767 Awesome. Should be some great light reading, lol. ! Thank you.
from what I understand, since we've a steam separator sitting on top, control rods are interested bottom up instead of top down like in PWRs, where gravity is the driving force. they use a gas cylinder and actuators pushing them down so that their natural state still remains "inserted."
as for refueling: I simply don't know. but the CANDU rector (which also uses lowly enriched-or not at all, even-fuel) also does hot refueling. there, the entire block sits ninety degrees rotated sidewards so that the rods are horizontal. they're made up by individual discs and when a new one is inserted at one end, the last one at the other end gets pushed out and directly falls into the wet storage. this happens mechanically and actually bears the risk of getting stuck.
Its so specific and the humor is quite spectacular. Very nice video bro!!
RBMK-1000 and RBMK-1500 have equal cores, but -1500 has turbolizers inside fuel channels. Because of fuel assembly cracks, the power of -1500 had been reduced.
Thank you for putting this together! I've been curious about exactly what was inside an RBMK for years, this was the clearest explanation I've yet seen.
This is a FANTASTIC overview! The HBO series left me wondering about core design of the RBMK-1000s. This video and the excellent reference links filled that gap. Thank you - a former US Navy nuclear sub officer. And I continue to wonder about the 2% U235 enrichment number. The point has not been emphasized about alpha-T - the temperature reactivity coefficient. Typically the lower the enrichment, the closer the alpha-T value comes to a positive number, or at least a lower magnitude negative number. One wonders if a higher enrichment could have lessened the ultimate power excursion with a more negative alpha-T.
I think so, I know modern RMBKs use more enriched fuel as part of the changes that made the temperature coefficient negative more of the time.
in theory yes, but perhaps the operaters would have made the same mistake, and continue to push the core. a meltdown was already occuring and that alpha T difference probably wont have helped a ton.
Not boring at all. 🍻 Good explanation.
I read "Midnight In Chernobyl". It gives a great explanation of the construction of the rbmk and how it functions. It also goes into great detail of the politics used to try and hide this disaster from the world. Anybody interested at all about this disaster should read it. If you are a nuke reactor nerd it is a real page turner.
Thank you! I'll have a look at it some day.
Antares - I have not seen the movie series yet but when I look at clips on CZcams I know exactly who and what they are talking about.
The cover-up and clean-up are disastrous.
Superb breakdown of this monster sir. I was born and raised in Belarus in 1979. Felt the wrath of 1986 disaster. Multiple safety and operational guidelines were overlooked in favor of getting this thing online ahead of schedule. Kurchatov scientist refused to take the blame for their poor design and blamed the operators. RBMK 1000 was flawed from the beginning. Chief Nuclear Physicist and main designer of RBMK 1000 Anatoly Alexandrov refused to accept the fact that his reactors were flawed and basically were a ticking time bomb. The result of their arrogance is still being felt by the people in Ukraine, Belarus, Russia and Europe.
Really nice presentation, technical yet concise. I’ll take this over an HBO drama any day. Well done 👍
This is is an interesting post accident documentary. Prepare for horrible voice overs. But it gets deep into what was going on after the explosion. It's funny hearing Gorbachev trying to sell the fact they knew nothing and Sweden actually told them something happened. czcams.com/video/2FOoooFsFdU/video.html
Excellent production mate.
Now I know how a nuclear reactor works. I don’t have to throw you out of the helicopter
The ending was 10/10
Thank you very much for the video, its nice and very informative. The equipment shown at 5:01 is not a steam drum, but the steam generator of a VVER reactor (Soviet-type PWR).
the job you've made is simply incredible, it's very detailed and comprehensible for the non initiated. Thank you, and best reguards for the future
Amazing explanation, it felt effortless to learn from you. Great way of presenting. All hail the core crab!
Such a well made video.
Laughed at the end lmao
Wow it's almost like the Fast acting Scram Rods should have been mandated after the Leningrad incident. And thus avoided the explosion.
I thoroughly enjoyed the ending, cheers for the informative video
Did you read the IGNASS reports? They´re linked even at WIkipedia, is the official accident report, very interesting, if véry heavy reading. There were numerous problems, 99% related to protocol. The official Soviet ´Vienna´ report was INGASS-1 but later it became INGASS-7, which is now the official version... Should look for a link, just remind me. It´s fascinating because the computers they used were too weak to effectively monitor such a physically large reactor (there´s 4000 sensors in those so-called ´technical channels´ at the edge/center of the core) and it had a *way* too low sampling rate. There was officially only 30MW left, but in reality the fission-rate at the bottom of the core was outside human control for hours probably. It takes a couple of microseconds for the amount of neutrons to double, and the energy released by fission builds up two-fold every few microseconds INSIDE the fuel itself in a (evidently) exponential curve. However, the heat transfer takes much longer, and hence the most important thing to measure is the amount of neutrons being generated at any one given moment. Reactors ´pulse´ continuously between super and subcritical, as you can imagine it´s impossible to keep it stable at say 2,184295 billion trillion neutrons :-) In fact, RBMKs had survived multiple power excursions, because they´re strongly build things and each fuel assembly sits in it´s own ´midget core´ so to speak (hence every channel can be isolated immediately in case of trouble) and this was another ´plus´ for the Soviets that came back to haunt them... All these channels are welded to the upper biological shield, and from 7 channels failing simultaneously at a specific pressure, the lid starts rising and has enough energy to pull open the whole channel-assembly. Since a disaster where 7 channels undergo catastrophic failure at any given time was considered unlikely, since this would be *really* a bad day at work, I suspect Soviet engineers just stock to this semi-modular approach, even if beyond a certain point ´doom accumulation scenarios´ may be looming.
The computer is responsible for calculating the amount of ´effectively present control rods´ or ORC if I recall it correctly. The computer had switch out all neutron detectors, detecting only 30MW, suspected to be decay heat. So they always got a ´positive´ reading during the whole buildup to/into the accident. Even worse was the sampling time, which was into the minutes. So regardless of the situation, the situation reported to the operators trough SKALA-computer was outdated by the time it was printed/presented on the panels. Only the direct analog detectors remained,and since there was no direct neutron-counter readout in the control room they were literally operating this thing blindly in the nuclear sense.
You gotta read this!
Enjoyed this too however :-)
www-pub.iaea.org/MTCD/publications/PDF/Pub913e_web.pdf
PS. It remains a way too complex matter to effectively distill to the point everybody will understand... Even the operators didn´t understand, and even I broke my head for the last 20 years if if they HAD known what was going on (the operators) if there was a way out... There was not, as the report explains, since they didn´t learn from the operator-mistake made at TMI-2 in 1976.
keep in mind that many aspects of the reactor were a state secret...the operators knew the procedures that expressly forbade them from just yeeting all the control rods out if the reactor was stuck in an "iodine pit", but they didn't know why, so after some heated discussing, they just did what Dyatlov told them to.
I strongly suspect that if they had known just how bad of an idea this was and what could happen, they would have straight up told Dyatlov to piss off and never come back, taking the test procedure with him.
The SKALA computer was indeed a very low tech system, even by 80’s standards and the mostly mechanical nature of its IO interfaces meant that it was very slow at relaying information back and forth from the control room to the reactor. However the simplistic design of SKALA meant that it was very reliable and seldom had issues. Information on existing RBMK reactors still operating in Russia is very scarce but from what information I have found it would appear that the original SKALA systems are long gone and control rooms have much more modern systems. Chernobyl is like a time capsule and will likely be the only place you can still see the original computer and analogue control rooms.
This is some quality content. Keep up the good work!
Your video is probably the best on this topic, and I've seen a ton
Very informative.
The music at the end is ridiculous I love it.
Very cool, great detailed description. Hope to see future work!
Very good explanation of a very complex structure! Thank you!
THANK YOU
I've been playing with the HBM's Nuclear Tech Mod in Minecraft which just added RBMK Reactors to the game and have been wondering about the actual design of their IRL counterparts and every video I've found has focused on the Chernobyl Incident itself but never going into any actual detail about how the reactor works.
Excellent content and explanations. Keep up the good work
From start to finish this is great content my friend! This is a certain gem of a channel. I hope you soon have many people subscribe just like I just did. 👍🙋♂️😃
Realistically this would have never happened had they either broaught the reactor back up to a higher operating power when the test was delayed to prevent poisoning, or when the reactor fell to critically low power and stalled in a xenon pit, just shut it down and wait for the xenon to decay before restarting. They rushed the unstable reactor because they had no idea about the quirks caused by the positive void reactivity and the operation of the control rods. They also removed nearly all of the control rods, pumps were running a lower pressure , and steam voids were created. There were a lot of things done wrong to cause that accident. Worst yet, as they activated A3-5, there were already ruptured fule rod and control rod chanels, and the rods got jammed.
I give it a 3.6. Not great, not terrible. :)
There is no granite because there is no granite
@Lucas lazarim czcams.com/video/ocBVLMHK6c8/video.html
@Lucas lazarim it's from the HBO miniseries "Chernobyl"
@Lucas lazarim watch HBOs chernobyl
It’s not 3.6… It’s 15,000!
This is a great vid.
you explain very well, I think this is the first time I can say that I understand what really happened and why there was an explosion, thank you
Im so glad you have made this video
This video should have way more views.
I just subscribe to your channel so continue this great work.
Rbmk was comparatively easier to run and to train operators on. The earlier VVER reactors required intricate switching sequences to keep the water under constant pressure and to remove gases from the coolant. The VVER had a negative void coefficient compared to the positive void coefficient in RBMK, which made catastrophic risk much lower. VVER was basically a scaled up pressurized light water reactor and had inherent safety features but the horizontal arrangement of the steam generators and complex pump systems made getting operators trained to run them difficult.
I've never heard that the RBMK was easy. The RBMK was almost impossible for the SIUR to handle before the automatic control systems were implemented. There even rumors that the Sredmash plants were using two SIURs simultaneously, moving control rods manually as if they were piano players.
And then of course at low power and in transient regimes the RBMK was a nightmare, where the basic instruments stopped being reliable, and coolant parameters were hard to keep under control, lots of reactor trips, etc.
The RBMK was easy to operation...
Looking back now, many of the scientists and experts, both within and outside of the Soviet Union, all say that the initial design of the RBMK reactor should've _NEVER_ been approved for use in _ANY_ generating station, let alone built or put into service!
I'm no expert, but I have to say after viewing all this, I would have to agree with the majority... There are far too many flaws in the design... Far too many parameters that must be monitored and adjusted on a never-ending basis throughout the entire process from reaction control to heated water through the turbine hall, condensers, and finally back to the reactor vessel itself! There's just far too much that could've gone wrong, and actually _DID_ go wrong, especially with that generator power wind down/coolant pump testing that led to the disater... Thank you for this very in-deprh presentation!
Now please explain to me how an RBMK reactor core "explodes", comrade.
Excellent upload thanks for you time on this !
Best RBMK video on CZcams......well done👌👌👌
Well done explanation and plenty of diagrams/figures. Congratulations.
Very good vid. Great info great ending. Deserves more views.
Well spoken and informative many of these deliveries about the rbmk tend to waffle
Very very good and broad explanation, especially for "beginners" in reactor technology. Very understandably visuals too with examples and explanations 👏👍
Excellent!! Thank you so much!
The fuel assembly shown at 4:15 is for the CANDU reactor, not RBMK )
the outro had to be the best part
Very good video and narrator!
Very well made an explained. Graphite displacers moved back into the reactor first, during normal operation this wouldn't really matter. But because when they hit A3-5 almost all the control rods moved back in at once, the heat and steam pressure caused a series of those channels to rupture as illustrated. Now you have graphite displacers next to graphite neutron moderators. Reactivity went haywire, running away like a runaway diesel until that heat and pressure couldn't be contained anymore. The results of which we're still grappling with today.
What a fantastic overview! Very thorough
Some reason I find Chernobyl and SL-1 reactor accidents similar. In both cases the operators were performing assigned task or drills that they seemed to not fully understand the associated risk and dangers.
Wonderful, understandable presentation....Thank you!
3:57 Canadians left the video
edit: forgot to add: thank you for adding a picture of diablo canyon-the most idyllic plant in existence.
Very informative explanation
Good to know the reactors have been upgraded to addresses some of the issues.
So Akimov should've turned the БАЗ switch first, and only after insertion of those turn the АЗ-5? I remember reading about a somewhat similar incident at Leningrad NPP in 1975, where the operator did just that, ending up destroying a single channel and damaging a few others, instead of blowing up the whole reactor like at Chernobyl.
No ,they should’ve turn it back up slowly
Love it, very good explanation.
Awesome content fella
Love these videos :) I’m obsessed with reactors
Thank you for this vid.
Best in the WEST, there's no such type of reactor as "western reactor" RBMK is one of the design which is still being used in Russia alongside light water reactors of VVER series, which are considered "western" after chernobil explosion
Yeah, I was having trouble on the correct way to say that as well at first. Thanks, I'll address that in the future if I decide to make more vids.
Now I know how a reactor works I don’t need you
On a serious note it is to my understanding that AZ-5 is the very last resort to emergency shutdown that should have only been used before 4 other actions need be taken
MOAR!!!! Thanks for this!!
Im glad they have imporved the CPS and the other safety features of the RMBK reactors but it should have been done before the disaster
An amazing video preety much spot on the rbmk.
I ve spent countless hours studying the rbmk design and the official accident report.
Generally it is a badly regarded reactor because of the accident.
The issue is that with any design the moment you deviate from the officially stated operational parameters you risk causing harm.
All of the operators knew what had happened...they just did not know it could happen....
And Dyatlov wasn't a mad man as depicted by the hbos miniseries.
Yeah, building reactors with numerous safety issues and then lying to the operators about them being perfectly safe wasn't a great idea. Sure the government wanted to tell the general public that the reactors were perfectly safe, but the people in the control room? It seems like it would have been worth explaining to them which parts of the manual were there to avoid operational hiccups and which parts were there to make sure Eastern Europe wasn't destroyed. I doubt the crew at Chernobyl would have disabled quite that many safety mechanisms if those things had been explained to them.
@@johanolofsson2702 A common misconception is that the Chernobyl crew disabled many safety features in all reality the did not they just disabled the ones officially needed in order to perform the test.
Very informative video, thankyou.
In RBMK-1500 insertion time of control rods was reduced to 12s due to higher MW(t)[4500-4800MW(t)] power of the reactor than RBMK-1000 [3000-3200 MW(t)]
Did every channel with water flowing on it have it's own feed and return pipe? And these must have their own cutoff valves to refuel on the go? What an amazing structure...
I cant help but wonder if turning the feed water pumps back on after rather than hitting the shut down would have prevented this horrible disaster?
Great video - thanks very much.
A very good video!!! Thanks!!!
Nice video my guy
13:00 RIP headphone users.😎
If I understood things correctly the RBMK reactors are not using a heat exchanger to power the turbines instead they use circulated highly radioactive water from the core to power the turbines?
Are there any major benefits compared to a pressurized water reactor except lower production cost?
Yes. The RBMK uses normal water H2O for cooling and operating instead of heavy water for operating that other types of reactors use. And under normal conditions it can not explode...
The main benefit is that the operators can change the reactor fuel while the reactor is in operation.
That’s a good question, I was always under the impression that a heat exchanger was used to drive the turbo-generators also but looking at the diagram of the cooling loop I don’t see one. Kind of makes you wonder how they would service that generator given the high radioactivity of it, plus the turbine buildings weren’t anything substantial unlike the reactor buildings.
So was it the radiation that made the crabs dance like that? If so, it seems like that was one positive outcome of the explosion. Seriously, though... great job explaining the RBMK 1000/1500 reactors.
Everybody gangsta, till Mister Crabs start dancing.
Great video.
I believe I have a correction here. Since water has the capacity to absorb and slow down neutrons, the presence of water shall increase the reactivity as the chances of a neutron colliding increases. at 6:16 you mentioned, reactivity increases as water leaves the system.
Light water can either act as a neutron absorber(absorb neutrons = slows down reaction) or moderator(slows down neutrons = increases reactivity) depending on the design of the reactor. It is typically used as a moderator in reactors with higher levels of U-235 enrichment(3-5%).
That's not the case for RBMK reactors, where the enrichment is only around 2%. Here, water actually acts more as an absorber rather than a moderator, which slows down the reaction. So when a void is formed, the reactivity increases as only graphite(a stronger moderator than light water) and the fuel are left in the system.
This was a great video for the knowledge and to top it off crab rave was used as the outro 10/10
I agree with You, Anatolij Stepanovic... 😔😏
Great video !!! A school boy question: where does the very first neutron come from ? The neutron that initiates the first fission? Thx
well done mister!
That was excellent. Now do more.👍
The RBMK (Russian: реа́ктор большо́й мо́щности кана́льный, РБМК; reaktor bolshoy moshchnosti kanalnyy, "high-power channel-type reactor") is a class of graphite-moderated nuclear power reactor designed and built by the Soviet Union. The name refers to its design where, instead of a large steel pressure vessel surrounding the entire core, the core is surrounded by a cylindrical annular steel tank inside a concrete vault and each fuel assembly is enclosed in an individual 8 cm (inner) diameter pipe (called a "technological channel"). The channels also contain the coolant, and are surrounded by graphite.
The RBMK is an early Generation II reactor and the oldest commercial reactor design still in wide operation. Certain aspects of the original RBMK reactor design, such as the large positive void coefficient, the 'positive scram effect' of the control rods[3] and instability at low power levels, contributed to the 1986 Chernobyl disaster, in which an RBMK experienced an uncontrolled nuclear chain reaction, leading to a steam and hydrogen explosion, large fire, and subsequent core meltdown. Radioactive material was released over a large portion of Europe. The disaster prompted worldwide calls for the reactors to be completely decommissioned; however, there is still considerable reliance on RBMK facilities for power in Russia. Most of the flaws in the design of RBMK-1000 reactors were corrected after the Chernobyl accident and a dozen reactors have since been operating without any serious incidents for over thirty years.[4]
Nine RBMK blocks under construction were cancelled after the Chernobyl disaster, and the last of three remaining RBMK blocks at the Chernobyl Nuclear Power Plant was shut down in 2000. As of February 2024 there are still 7 RBMK reactors and three small EGP-6 graphite moderated light-water reactors operating in Russia.[1][5] All have been retrofitted with a number of safety updates. Only two RBMK blocks were started after 1986: Ignalina-2 and Smolensk-3.
History
The RBMK was the culmination of the Soviet nuclear power program to produce a water-cooled power reactor with dual-use potential based on their graphite-moderated plutonium production military reactors. The first of these, Obninsk AM-1 ("Атом Мирный", Atom Mirny, Russian for "peaceful atom," analogous to the American Atoms for Peace) generated 5 MW of electricity from 30 MW thermal power, and supplied Obninsk from 1954 until 1959. Subsequent prototypes were the AMB-100 reactor and AMB-200 reactor both at Beloyarsk Nuclear Power Station.
By using a minimalist design that used regular (light) water for cooling and graphite for moderation, it was possible to use fuel with a lower enrichment (1.8% enriched uranium instead of considerably more expensive 4% enrichment). This allowed for an extraordinarily large and powerful reactor that could be built rapidly, largely out of parts fabricated on-site instead of by specialized factories. The initial 1000 MWe design also left room for development into yet more powerful reactors. For example, the RBMK reactors at the Ignalina Nuclear Power Plant in Lithuania were rated at 1500 MWe each, a very large size for the time and even for the early 21st century. For comparison, the EPR has a net electric nameplate capacity of 1600 MW (4500 MWthermal) and is among the most powerful reactor types ever built.
The RBMK-1000's design was finalized in 1968. At that time it was the world's largest nuclear reactor design, surpassing western designs and the VVER (an earlier Soviet PWR reactor design) in power output and physical size, being 20 times larger by volume than contemporary western reactors. Similarly to CANDU reactors it could be produced without the specialized industry required by the large and thick-walled reactor pressure vessels such as those used by VVER reactors, thus increasing the number of factories capable of manufacturing RBMK reactor components. No prototypes of the RBMK were built; it was put directly into mass production.
The RBMK was proclaimed by some as the national reactor of the Soviet Union, probably due to nationalism because of its unique design, large size and power output and especially since the VVER was called the American reactor by its detractors in the Soviet Union, since its design is more similar to that of western PWR reactors. A top-secret invention patent for the RBMK design was filed by Anatoly Aleksandrov from the Kurchatov Institute of Atomic Energy, who personally took credit for the design of the reactor, with the Soviet patent office. Because a containment building would have needed to be very large and expensive, doubling the cost of each unit, due to the large size of the RBMK, it was originally omitted from the design. It was argued by its designers that the RBMK's strategy of having each fuel assembly in its own channel with flowing cooling water, was an acceptable alternative for containment.
The RBMK was mainly designed at the Kurchatov Institute of Atomic Energy and NIKIET [ru], headed by Anatoly Aleksandrov and Nikolai Dollezhal respectively, from 1964 to 1966. The RBMK was favored over the VVER by the Soviet Union due to its ease of manufacture, due to a lack of a large and thick-walled reactor pressure vessel and relatively complex associated steam generators, and its large power output, which would allow the Soviet government to easily meet their central economic planning targets.[6]
The flaws in the original RBMK design were recognized by others, including from within the Kurchatov Institute before the first units were built, but the orders for construction of the first RBMK units, which were at Leningrad, had already been issued in 1966 by the Soviet government by the time their concerns reached the Central Committee of the Communist Party of the Soviet Union and the Soviet Council of Ministers. This prompted a sudden overhaul of the RBMK. Plutonium production in an RBMK would have been achieved by operating the reactor under special thermal parameters, but this capability was abandoned early on.[7] This was the design that was finalized in 1968. The redesign did not solve further flaws that were not discovered until years later. Construction of the first RBMK, which was at Leningrad Nuclear Power Plant, began in 1970. Leningrad unit 1 opened in 1973.
At Leningrad it was discovered that the RBMK, due to its high positive void coefficient, became harder to control as the uranium fuel was consumed or burned up, becoming unpredictable by the time it was shut down after three years for maintenance. This made controlling the RBMK a very laborious, mentally and physically demanding task requiring the timely adjustment of dozens of parameters every minute, around the clock, constantly wearing out switches such as those used for the control rods and causing operators to sweat. The enrichment percentage was increased to 2.0%, up from 1.8% to alleviate these issues.
The RBMK was considered by some in the Soviet Union to be already obsolete shortly after the commissioning of Chernobyl unit 1. Aleksandrov and Dollezhal did not investigate further or even deeply understand the problems in the RBMK, and the void coefficient was not analyzed in the manuals for the reactor. Engineers at Chernobyl unit 1 had to create solutions to many of the RBMK's flaws such as a lack of protection against no feedwater supply. Leningrad and Chernobyl units 1 both had partial meltdowns that were treated, alongside other nuclear accidents at power plants, as state secrets and so were unknown even to other workers at those same plants.
By 1980 NIKIET realized, after completing a confidential study, that accidents with the RBMK were likely even during normal operation, but no action was taken to correct the RBMK's flaws. Instead, manuals were revised, which was believed to be enough to ensure safe operation as long as they were followed closely. However, the manuals were vague and Soviet power plant staff already had a habit of bending the rules in order to meet economic targets, despite inadequate or malfunctioning equipment. Crucially, it was not made clear that a number of control rods had to stay in the reactor at all times in order to protect against an accident, as loosely articulated by the Operational Reactivity Margin (ORM) parameter.[8] An ORM chart recorder and display were added to RBMK control rooms after the Chernobyl disaster.
A 45-year lifetime is envisaged for many of the units, after mid-life refurbishment
Nice one. Thank You!
excellent video!!!!
First of all, nice video. I appreciate your work. Regarding the AZ-5 emergency shutdown button: isn't it the one on the left upper corner instead of the middle one you are showing here? In the various photo's I saw, including those from the control room of reactor 3, the infamous az-5 button is not in the middle. Thanks again!
Oh, that picture was taken from reactor 1. It's probably because reactors 3 and 4 were newer than 1 & 2. I guess you can call them '2nd generation' rbmks, and they had relatively minor-moderate number of modifications.
And the picture I showed does in fact has an 'АЗ-5' writing on it so, yeah.
11:03 Look up Chernobyl Unit 2, there's images of Unit 2's Reactor Hall
11:45 ..at the time the reactor is already at the critical state..
Actually "critical state" means a completely different thing in the nuclear reactor world:
"A critical state reactor is a nuclear reactor that is operating at a steady state, where the number of neutrons being produced is equal to the number being absorbed. This means that the reactor is controlling a self-sustaining fission chain reaction, where each fission event releases enough neutrons to maintain a series of reactions.
"
Yeah I noticed I got carried away a bit. What I meant by "Critical" in that case ig it's more like "situation critical". Sloppy word choices on my part ig.
I relly like your video, and how detailed it is, you´ve clearly put a lot of work into this! However, I have a few pet peeves if you´d like - not major concerns, but something that boggles me a bit. For instance, 0.25m X 0.25m is defined as a square. Rectangular shapes does include the squares, but squares are not very often referred to as rectangular, so your reference is quite weird at this point. And I understand that you want to teach me something about a pretty advanced structure, namely a Soviet nuclear reactor. Also, constantly using the SI metre as your basis for all measurements makes me question your qualifications. Any engineer in "the west" would automatically use mm for this purpose in a high tech application as a nuclear reactor clearly is.
About positive void coefficient - one western reactor actually operates under this condition - the CanDU - I suspect you also know this, but I think it could easily have been mentioned. However, they have really extensive measures in place to safeguard their operation as they are well aware of the problem. I think the main problem with the RBMK was that it also had a problem with the safety measures. If the RBMK could have been thoroughly scrutinised with the intent of mending all of its safety concerns, they would be perfectly safe to operate even today. Sure, it is a flawed design - but looking back through history, which design hasn´t been flawed? It´s all about how we address the problems and then deal with them, isn´t it?
One single thing about your video really provokes me, though! When you imply that the "wrecklessness of the operators" was the main issue, as you continue to tell that other circumstances "also contributed" to the accident, my claim is that you´ve got it all a$$backwards. The operators could never have known about this danger, as every single bit about this construction error was kept from them. None of the operators should ever have been blamed, not even Dyatlov, as none of them could have known. They were all teached and told that these reactors could never fail, and they could always rely on the AZ-5 button to shut the reactor down if that insane case would ever occur. It compares somewhat to you driving your car around. One day, you wanted to stop for a child crossing at a ped-x. Everyone blames you for not engaging the brakes, even though you know you did. Except they didn´t work on that day. The manufacturer knew they wouldn´t work because it was the first tuesday after a full moon, but they didn´t tell anyone. However, they find it convenient to just blame it on you and shut the f up.
Nice!
Very informative and easy to understand. Well done.
So does water circulate through the graphite channels or does everything happen inside the closed fuel assemblies that are inside the graphite channels? I guess it makes sens that each assembly gets cooled separately.
Technological channels run through holes in the graphite blocks. Graphite stays dry but is bathed in various gasses for cooling and other purposes. Technological channel contains both the water and the fuel assemblies.
10/10 outro
This video is perfect, i have been doing research on the chernobyl disaster and this video helped me out, and i'm quite surprised to such low views,
Try to post it on r/Chernobyl and the views will go up dramatically
So the steam directly produced in the core goes through the turbines?
No heat exchangers?
Doesn’t that make the turbines and condenser radioactive?
Technically yes. From what I understand, that's how BWR reactors work as well(i.e. fukushima). When you mentioned 'heat exchangers', I think you might be referring to PWRs.
Great video.
But I suggest you to not crop old footage shot in 4:3 ratio to fit a 16:9 frame, leave black bars at the sides if you want, but don't crop the video.
There are other two interesting things not mentioned in video. In rbmk-1000 core, there was an empty space at the bottom. This space was intended to be filled with graphite and control rods. But later it turned out graphite and rods need to be cut shorter, probably to equalize fuel burn. This led to a fact that there was a lot more water at the bottom. Additionally, bottom control rods WERE NOT CONNECTED to the AZ-5 button at the time of disaster (reactors were designed and build in rush because their designers over promised), they were meant to be connected later. This meant that upper rods had to go all the way to the bottom, creating spikes in reactivity, and it took a lot of time, allowing this water at the bottom to boil even more. If the bottom rods were operational, they would stop reactivity at the bottom of the core earlier. When you read about those flaws it's hard to blame mainly dyatlov. Designers such as Dollezhall and Alexandrov that was supervising him, should have gone to jail.
It is more that there were voids at the bottom of the chamber, the graphite tips on the Boron rods were lowered, the graphite on these tips as a moderator created more slow neutrons which vastly increased the U235 fission reactions that caused a huge surge in power in an already out of control fission reaction process. This caused the thermal/steam explosion.
I am looking answer for my question and i think you didnt told about this. How the control rods are moving? There is a hydraulic actuator, or some mechanical gearbox with electrical motors?
If I'm not mistaken I answered this question a while back. I provided a link in the description to the RBMK-1500 sourcebook. Refer to pages 70-72 regarding the control rod drive. You'll find your answers there. Thank you
If the operators initiated BAZ instead of AZ-5 would that have made a difference? Only the boron rods would move keeping the Graphite rods withdrawn
I'm not entirely sure, but I don't really think it would. Maybe it would sort of delay and give more time before the explosion occurs, but in the end, I don't think the Boron rods (without graphite tips) alone could compensate for the entire control rod array that was withdrawn to entirely shut down the reactor during such a critical state at that time, since there was only a handful of them.
Good video! I still do not understand how the fuel assembly works. Inside the 11.4 cm diameter graphite channels, there is a fuel assembly. How, then, is this fuel assembly brought into contact with water? Is the inside of the graphite block assembly actually a high pressure tube made out of zircalloy? But if that's true, then online refulling is impossible, you have to disassemble the pressure tube ? As another point, do you know if emergency reactivity control is also achieved with boric acid injection in the water (nowadays?)
Inside the 0.114m bore openings of the graphite blocks, there is a fuel channel made of zircalloy placed in it. The fuel channel is connected to the tubes from the MCPs, which pump water to channels.
The fuel assemblies are placed inside the fuel channel, in which water flows through. That way, only the fuel assemblies that need to be replaced during refueling, not the entire fuel channel.
And yes, boric acid is quite common use in PWR designs.
@@antares2767 How much space is there between the fuel assembly and the interior wall of the channel? That is, how much space for water to flow?
I think the problem with boric acid is that it takes way too long to charge it into the plant. My limited experience - had to mix the boric acid then place in a charging water tank, then charge at a very low flow rate. Not practical for this near-prompt critical casualty.
*Watches in PWR operator*
Good information that gets glazed over/ignored/misunderstood.
Great video. Nothing more to say. Just a really great video. :thumbsup:
Question, why do meltdowns cause reactors to explode?
We heat up the core so we can create steam, does the same principle hold true once Corium is made? Does the heat become so high that the core can’t hold the pressure and it bursts? How do positive feedback loops with RBMK reactors even work?
Also, I see core schematics have this circular-like grid around it? Not sure what it’s called. Is this special to RBMK reactors or do many types of reactors have them?
In case of RBMK, it was because steam forming in the core actually ramped up the reaction, instead of ramping it down (like on VVER).
In this case it was most lilkely a steam explosion. For Fukushima is was a hydrogen explosion. A meltdowm is mostly referred to the core melting down in a PWR reactor, which Chernobyl was not.