Chernobyl's Unanswered Questions: Did Control Rod Modifications Lead to the Chernobyl Disaster?
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- čas přidán 3. 07. 2024
- The official reports into the Chernobyl Disaster cover a large amount of information surrounding the fateful events that led to the world's worst nuclear disaster. However, these papers still miss key details pointed out by others that dramatically alter the story even scientists have come to expect. These are Chernobyl's Unanswered Questions.
Today, we will be examining how the so-called series of violations presented at Vienna were almost unexceptional events in the operation of an RBMK reactor, and if a simple act of modifying the control rods to improve the safety of the reactors, an event almost entirely forgotten in the history of the RBMK reactors, may have been one of the key factors that led to the world's worst nuclear disaster.
This script was written by Bobby, who has also crafted an incredible history paper exploring how misinformation and disinformation continues to impact the story of Chernobyl. You can read it here: docs.google.com/document/d/1m...
Timestamps:
00:00 - Introduction
00:44 - The positive power coefficient
02:11 - The positive void coefficient
03:13 - The power level and the ORM
05:55 - The sub-cooling of the reactor.
06:45 - The conundrum
07:06 - The 1980 Dollezhal Book
08:22 - The 2003 Kurchatov History Book
09:59 - Shortening the control rods
10:56 - The significance of 25-30cm
11:23 - The possibility
11:56 - Why has this not been further examined?
13:16 - Contradictions in history
13:54 - Alexander Rumyantsev
15:31 - Rumyantsev's biggest allegation
16:16 - Conclusion
16:36 - Credits
Courtesy of Bobby:
A few clarifications: 1:50 - accidont.ru/memo/Karpan_02.html - The Note under the table indicates the power levels. (50-65% meaning over 1600 MW) You find the Operating Reactivity Margin in the table. In general you should be looking at the paragraph below "282" rather than above. 2:35 - www.proatom.ru/modules.php?name=News&file=article&sid=8916 - The focus here was intended to be on a comment at the very bottom of the webpage. The author of the comment cites a lack of additional absorbers corresponding to the just shown association between ~30 additional absorbers and the high positive void coefficient of ~5 in first gen RBMK reactors. He also provides a description of other conditions similar to Chernobyl. Also, control rods were lowered into the Chernobyl core before AZ-5. 8:00 - www-pub.iaea.org/MTCD/publications/PDF/Pub913e_web.pdf - On page 5 (and again on page 128) you can see the known dimensions of the graphite displacers and water columns. You can refer to the two NIKIET and Kurchatov Institute books online: elib.biblioatom.ru/text/dollezhal_kanalnyy-yadernyy-reaktor_1980/go,38/ elib.biblioatom.ru/text/istoriya-atomnoy-energetiki_v3_2003/go,165/ Here are the links to Rumyantsev's articles as well: www.proatom.ru/modules.php?name=News&file=article&sid=6700 proatom.ru/modules.php?name=News&file=article&sid=2842 16:30 - missing sentence - "This topic has so far received almost no attention in sources on Chernobyl."
You may have also noticed that Dyatlov's Soviet stack of Swiss Cheese violations at the start of the video had an * on each slice. The first 53 pages of the paper linked to in the description explain why - a video could be done on these deliberate Soviet lies if there is interest. One of the slices is addressed later in the paper as interestingly Soviet experts did not feature it as a violation - the decision to raise power after it had dropped to ~30 MW. The plan is to also do a few more of these unanswered questions videos as there are multiple paramount questions that reframe the understanding of the causes of the disaster. They pertain to the contemporary understanding of the coefficients of reactivity, why reactor power went below 700 MW, and what the ORM was at the time of the activation of AZ-5. As you can tell the focus here is on substantiation - the documents and sources. If you doubt the substantiation the paper should satiate you with roughly 410 footnotes/endnotes pointing to sources you can immediately access (seems the conversion to a google document turned endnotes into footnotes and messed with some of the spacing). The sources are far fewer but their quality is high - much of the paper deals directly with the hallmark reports and Politburo notes.
For 1:50 - "In order to solve this problem, the designers decided to transfer all RBMKs to fuel with 2% U-235 enrichment and equip the reactors with the LAR system (local automatic regulator). But the real implementation of the LAR system into operation took place only in 1983-84.
The initial loading of second-generation NPP reactors with RBMK-1000 (3 and 4 units of the Leningrad NPP, KNPP, Chernobyl, units 1 and 2 of the SNAPP) was already formed entirely from fuel assemblies with an enrichment of 2% U-235. However, with this fuel, as the burnup increased to values of 1100-1200 MWd/FA and with a scheduled operational reactivity margin of 26-30 PP rods, the value of the vapor reactivity coefficient α φ gradually increased and became close to +5 ßeff.
α N measurements, the fast power coefficient of reactivity, which characterizes the change in the reactivity of the reactor in response to power changes, showed that with an increase in the steam effect α φ up to + 5ßeff , α N also changed its sign and increased from minus 4x10 -4 ßeff/MW (th.) to + 0.6x10 -4 ßeff / MW (th.).
Note . The given values of α φ and α N were obtained during experiments at the reactor power from 50% to 65% Nnom [48]."
Designers: "Ok, here´s a box of candy. Don´t open it, or it will kill you."
Operators: "All right, but is it safe to handle?"
Designers: "Yep, perfectly safe. The safest in the world."
Operators: "Fuuuuuk, why did it explode?!!!"
Designers: "Oh, too bad, turns out its a bomb, not a box of candy. I guess we will have to put you in jail."
For the benefit of the viewers I'd like to attempt to describe the "positive void coefficient of reactivity." Liquid water absorbs more neutrons than steam. One of the main dangers was, if boiling increased too rapidly, the percentage of water in the core would decrease (being replaced by steam "voids"), causing the effective neutron flux to increase, resulting in a higher fission rate, and a runaway condition. This could (and did) happen quite rapidly. There is a solution, which was implemented after the accident in the other RBMK reactors: Increase the enrichment of the fuel from 2% to 2.4% and add more neutron absorbers, this makes the contribution of the steam voids less dominant.
Thanks!
so as the water column gets longer and water boils off as an effect of turning off the main circulation pump and having non-prechilled water entering the core, more sections of the core lost the neutron absorption ability right? So why does the core only explode when the rods started to move down? Wouldn't it explode right away when the water started to boil off?
@@Krasnoye158 Counter-intuitively using all main circulation pumps is supposed to have contributed to the lack of subcooling of water entering the core as the subcooling came from steam that was condensed after going through the turbines. Anyway, it's a matter of magnitude. According to INSAG-7, more specifically Annex I, "both calculations showed that the released void reactivity was negligible" during the test (p. 65). Or as the international section on page 23 puts it, "Some positive reactivity is likely to have been generated from the growth in voids as the coolant flow rate fell [reduction of 10-15% from a higher quantity than normal]. Addition of further positive reactivity by insertion of the control and safety rods that had been fully withdrawn during the test was probably a decisive contributory factor."
@@Krasnoye158 Yes. According to IAEA reporting, and the gist of other reports, the core was on the cusp of boiling already, feed water (makeup water) helps to reduce the temperature of the incoming coolant to the core (as you mention), when the turbine has been isolated (valved off), it is not making any more condensate. There would still be condensate in the reservoir, but not an unlimited amount. Without feedwater, the recirculating coolant temperature is not reduced by the feedwater, so the steam in the steam drums must be condensed and replaced by the isolation condenser. When the control rods moved down, the rod tips displaced the water in the lower core section. Since the rod tips were not boron absorbers (they could not be otherwise they would create an unwanted neutron gradient in the center of the core after they were withdrawn), the rod tips created an effective void, this raised the neutron multiplication factor to greater than 1.0. This chart is shown in the video, please see 11:13. There are 2 different types of charts in use. What matters is the effective neutron flux is increasing. This was a "prompt criticality" with only seconds to spare. "Delayed" neutron scenarios can offer the operators as long as several minutes to adjust the flux balance, to avoid a supercritical state. I hope this may be helpful, if not, please accept my apologies. About the circulating pumps, I think only one pump per side was powered by the turbine spinning down, the other 3 per side were on the grid during the spin-down test, if memory serves. They wanted to record the time (in seconds) of the pump performance, which never met the goal in any of the tests, meaning, if the grid is cut off, there could be trouble because the diesel generators take time to be online (too much time in this case). The prompt criticality in the core resulted in sudden boiling, in my opinion. Please excuse my ignorance, I design power plant safety systems, I am not a certified operator.
@@markusw7833 Yes, and fuel burnup appears to be a key issue. With fresh fuel, more absorber rods are deployed which moderate overall neutron flux. As the fuel ages, more and more absorber rods are removed. The metric employed by SKALA was to calculate the minimum safe number of rods. As fuel ages, less rods are in use and they get closer to the minimum safe number. Withdrawing all the rods with aged fuel is the most dangerous thing. It's really too bad because the RBMK had an excellent online fuel handling system above the core, which was capable of re-locating fuel assemblies one by one, to even out the hot spots by moving rods around. Modern designs are much safer, but few if any offer the ability to re-distribute the fuel assemblies during operation.
I think these videos are great, however I see from the comments, that most viewers seem quite knowledgeable regarding reactors and their operations.
Maybe you could make some videos that are more geared towards those of us that are just interested in these extraordinary events but don’t have technical expertise in the field.
This is the best channel I have found about Chernobyl as it does (seem) to provide facts, not opinions.
I remember when Chernobyl happened and it certainly changed the direction of energy production in the world, which is unfortunate. If nuclear could have prospered, as many think it would have were it not for this event, we would have clean unlimited energy instead of the mess we have today. Keep up the good work. Thanks for posting.
None of us are experts. The thing about Chernobyl is that this is the root of misunderstanding it - it started with a bunch of lies to portray the operators as responsible and people who have failed to engage with the details have propagated this falsehood. In other words, you can't really learn about Chernobyl without understanding it. This doesn't equate to technical expertise but does require effort and patience. Ultimately the level of detail we're dealing with is simpler than you think, for our purposes anyway. That written, it wouldn't surprise me if ThatChernobylGuy decides to do a more general video that would provide a basic frame for understanding things.
"I remember when Chernobyl happened and it certainly changed the direction of energy production in the world, which is unfortunate."
By the way, this is something I'm curious about myself. I "know" it did this, but I don't know any of the specifics, the breadth and extent of the Chernobyl effect on the nuclear power industry globally.
@@markusw7833 It just seemed to fuel the fires of fear as I recall. No, I have no stats, just observation.
@@markusw7833 yes if he could do that it would be helpful. If you have not watched the interview with Dyatlov after his release from prison, you might consider it. Gave me a new perspective on the USSR’s approach to the industry for certain.
The author is doing a great job, if you would like to learn more, start with the INSAG-7 report by the International Atomic Energy Agency available online for free. You will soon be well-versed in these arcane terms, scenarios, and events. It also compares theories and analysis from a number of different sources.
You are amazing! Keep it up please :) I think I speak for all Chernobyl history enthusiasts that we all greatly appreciate your hard work and diligent research.
If I could suggest a future video idea perhaps a rundown of the best and worst Chernobyl books/sources and the pro’s and cons of each, where they are correct and where they stray off accuracy etc. Thanks again :)
There are a number of good sources and you will find they all tell the same story from a different perspective. Despite the glaring flaws, the RBMK was a pretty good design for its day. Its downfall was the lack of critical information passed down to the everyday workers, which has become a consensus of disgust and shame. It was the culture of secrecy that sealed its doom, not the inability to correct the flaws. Working with several Russians I have developed a love for the Russian people. They are good people just like you and me, and they deserve better, then and now.
@@kevinamundsen7646 This isn't true. Not only was the reactor of disastrous design, Soviet experts failed to understand it and apparently suppressed dissent. What was passed down to operators, who were relatively educated, were instructions, information, and facilities that paved the way for actions that were subsequently falsely portrayed as violations. Chernobyl was a thorough embarrassment for the Soviet Union which was accordingly misrepresented by the Soviet Union and the very people who bore responsibility. You have no idea what the sources convey and your sensibilities have nothing to do with the actual topic.
I discovered your channel yesterday and this has honestly become one of my favourite channels, great work!
Same here. Alas, with 4k subscribers, it's not getting the distribution it deserves. I have been looking at Chernobyl videos here for months, and it was not until today that his channel appeared on my feed.
I love the analogy of “attacking the cheese on his decadent cheeseburger of violations.” I’ll have to steal that for one of my work presentations.
I'm just happy to hear someone say "all intents and purposes" right.
So while my longer comment is caught in limbo let me avoid the links and address at least a couple of things.
"Today, we will be examining how the so-called series of violations presented at Vienna were almost unexceptional events in the operation of an RBMK reactor..."
There is a difference between the false violations and the physical factors of the disaster. The alleged violations were used to blame operators for the disaster and were intended to falsely portray their actions as a series of forbidden choices stacking up to eventually blowing up the reactor despite the protective measures that existed - the Soviet Swiss Cheese model of disaster. That is actually a separate topic that you can see beaten to death in the first 50 pages of the paper. The physical factors of the disaster were the actual conditions for it, namely the positive power coefficient, the low Operating Reactivity Margin, and water being close to its boiling point when entering the reactor. I am not sure about treating the power level as independent from the positive power coefficient. This stupid platform not eating up my comments would certainly help in clarifying things. It was these things that appear to have been fairly common.
While I'll refrain from raising other points and bringing in sources at 2:35 this should have been displayed:
"Re: Incident at the Leningrad Nuclear Power Plant in 1975 (Total: 0)
by Guest on 03/06/2020
On the topic of discussion, I offer a quote from the book "Leningrad Nuclear Power Plant: Time, Events, People" under the general editorship of V.I
. Lebedev. Moscow, Energoatomizdat Publ., 1998, pp. 130-131. Here is what 25 years after the accident, the employees of NIKIET direct participants in the investigation (designer Petrov A.A., physicist Borshchev V.P. and thermal physicist Vasilevsky V.P.) write: "By the end of the 2nd year of operation of the reactor, when 32 DPs remained in it (the rest of the initially loaded approximately 240 were replaced by fuel assemblies), the first major accident occurred - the burning of the channel in cell 13-33. This happened during the output of the reactor to power after it was shut down. The accident occurred as a result of a strong imbalance in the distribution of energy release, due, among other things, to the unevenness of xenon poisoning, when the reactor was in the so-called "iodine pit". Its essence lies in the fact that after the reactor is shut down, the Xe-135 isotope, which strongly absorbs neutrons, accumulates in it for several hours, as a result of the decay of J-135 formed during fission. The accumulation of xenon in different places of the reactor depends on the energy distribution before the shutdown and can lead, for example, to a significant shift in energy release to the peripheral regions of the core, where during normal operation the power is small and, therefore, after the shutdown of the xenon reactor, less will accumulate, and the fuel has a lower burn-up and, therefore, a higher ability to multiply neutrons. About two days after the stop, almost all xenon decays and ceases to introduce additional distortions into the shape of the neutron field.
Despite the fact that the reactor control system during the ill-fated output to power showed a skew in the radial distribution of energy release and did not allow the power to rise, there was a high desire to start the reactor and efforts were made to block this system by twisting the current correctors of the side ionization chambersSubsequent computational analysis showed that there was a strong unevenness of energy distribution in height. The small number of CPS rods remaining in the core after the reactor was brought to a critical state (about 10) exacerbated the situation, contributing to increased instability and limiting the ability to regulate the distribution of energy release. The commission of the Ministry of Medium Machinery did not find heroes based on the results of the investigation of the accident. All control room operators were punished in one way or another for specific violations of specific paragraphs of the instructions. The SIUR was punished most severely by suspension from work for 2 months. I hope the above quote will help both visitors and editors to understand why SIUR was punished. And dig deeper to get to the truthAbakumov Vitaliy"
The 32 additional absorbers correspond to the high value of the positive void coefficient in first gen RBMK reactors (in fact, directly to a measurement of it) and this incident was known for an ORM even lower than the underestimate of the ORM at Chernobyl. At Chernobyl control rods were also descending before the button was pressed, in addition to something else. You can notice other similarities between the two incidents.
Very, very informative. Thank you!
succesfull operating shutdowns and succesfull emergency shutdowns are interesting but how many times ( and how fast...) were RBMK's pulled out of a xenon pit succesfully would be even more interesting.
According to Tregub in the book "Chernobyl" by Yurii Shcherbak, this happened at least semi regularly if the operators missed their mark on the automatic regulators. As for how fast, we can't say for certain but given that Tregub was also one of the people assisting in raising the power, probably about the same speed as was done on the night of the explosion.
From some of the materials I read they say there's a window of 15-30 minutes to get the power back up. After that, the window closes and you ought to let the reactor sleep it off for 24 hrs before attempting a restart. Due to their huge core, graphite moderator, and very low enriched fuel, RBMKs are very susceptible to Xenon poisoning. CANDUs have a similar sensitivity to it, they are heavy water moderated, but run on natural Uranium. For them the window is 35 to 40 minutes, then the reactor is "poisoned out", and you're shut down until the Xenon decays away enough for a safe restart. Unlike an RBMK, the CANDU is a very stable reactor. An RBMK can be very capricious and moody, especially towards the end of a fuel cycle. You really do not want to start messing about with one when it is in this state due to its inherent instabilities. That is inviting disaster, to put it very mildly.
The Leningrad reactor was pulled out twice, and the Soviets didn't actually list raising power as a violation. There even appears to have been broader operational experience with successfully intervening during power raises (the paper includes a description of this), which may be why there was some uneasiness during the power rise but once power was stabilized the atmosphere relaxed. The real danger at Chernobyl Unit Four was not the power rise, it was not the test, but the very act of shutting the reactor down after a certain point.
Absolutely right. The huge size of the RBMK core led to the occurrence of local hot spots, which were difficult for the staff to stabilize, even at normal power levels. It was like operating four reactors at once. At low power levels, the instability became essentially impossible to control. It was a travesty to blame the operators, who had their hands full even during the best of times. It was the occupational pressure for power production by the network operator, always a factor, which pushed the operators away from the choice of shutdown and allowing for Xenon decay, perhaps for 24 hours, before trying to restart without dangerous spatial power gradients. It's sad that one of the design's best features, online refueling, was not used to redistribute the fuel bundles and introduce new bundles to prevent the very dangerous operation with a low number of absorber rods after a large amount of fuel burnup.
@@kevinamundsen7646
Not only was it like operating (at least) four reactors at once, each of these reactors had a little will of their own as well. As elaborate and reliable as SKALA was, it was woefully underpowered. The calculations took forever, which is a luxury you do not have when driving a big, grumpy reactor like the RBMK. Especially at low power the operators were pretty much flying by the seat of their pants. The sensors couldn't "look" that far down into the core to convey to the operators what was going on in there. So, they had to intuit what was going on, and hope that they picked the right course of action. Yes, it is every bit as ridiculous and absurd as it sounds. And it is not the reactor's fault either, it didn't have a say in how it was designed and built. That guilt lies fully on the conscience of the designers.
The on-power refuelling feature actually was used in this way. The reason these absorbers are initially placed in the core is to keep the excess reactivity in check when the core is fully loaded with fresh fuel. A PWR does a similar thing after a refuelling outage (a PWR cannot refuel when online), but then with Boron dissolved in the primary cooling water. As the fuel burns out, the Boron is gradually diluted out of the primary system to maintain the required reactivity. But you cannot put Boron in the cooling water of a BWR because it would gum up the innards of your reactor, since you boil the cooling water directly inside its core. So, for the RBMK they devised the removeable absorbers. As the fuel burns up, these absorbers are gradually removed from their respective channels and replaced with a fresh fuel bundle. And fuel bundles do get shuffled about the core to achieve the highest possible burnup. When a particular fuel bundle is completely spent, then it is taken out and replaced with a fresh one. A mature RBMK core will contain completely spent, partially spent, and fresh bundles. It is called the Steady-State, or Stationary Refuelling Mode. It is for this mode that the number of control and protection rods is calculated. Each RCPS rod introduces some kind of negative reactivity, which depends on its location in the core and the shape of the neutron field. A control in the centre of the core is "worth" way more, than one in the periphery.
The problem with the positive void coefficient arises not from the removal of the absorbers per se, but from the fact that the RBMK is graphite moderated. A PWR is water cooled and water moderated. This means that when something happens, and it loses its cooling water, the chain reaction will stop by itself because there is no more moderation going on. But when an RBMK loses its cooling water, the chain reaction can continue since the moderator is still there. And what's worse, because the RBMK is so big, it has so much graphite moderator that it operates in the over-moderated regime. In this regime the water stops being a moderator, and only acts as a neutron poison. The moment that water goes away for whatever reason, whether it be through boiling up in the core or flowing out of a broken pipe somewhere, the chain reaction will immediately speed up because there is less neutron absorption going on. If you have a RCPS that can respond blisteringly fast, this need not be a problem. However, the RCPS they gave the RBMK was excruciatingly slow (talking about adding insult to injury). At that point you might as well put jelly in your pockets because you're about to be toast. By the time the control rods can act, your reactor has already put itself into orbit. Which is what Unit 4 quite literally did that night.
My apologies for the long-winded reply.
Great Reporting! Thanks for all your work
I had you channel subscribed, but not really watch a lot of videos. I’m glad you posted another video
Hmm. I already wondered why I hadn't read/heard this before. And the fact they just wrote up INSAG-7 while assuming this "improvement" to be the base state of the reactor explains a lot. Thanks a lot mate! You're by far the wisest source on this disaster I ran into online. Keep up the good work, and redoing some of the older videos would also be a big win for us!
Do you speak Russian btw?
It's fascinating that this so-called assumption comes from within the Soviet Union, the group of people who were critical of let's call it the establishment comprised of the upper echelons of NIKIET, the Kurchatov Institute, and the Ministry of Medium Machine Building. How did this slip by them?
@5:41 daammmmnnnnn, that many emergency shutdowns....thats insane!
An internal fact that is virtually unknown or unremarked upon. As is mentioned in INSAG-7, it wasn't even necessary for a shutdown to be in response to an emergency to cause an emergency, which, in conjunction with other circumstances, begs the question why it took so long for a disaster to occur. It doesn't seem to be a coincidence that the positive scram effect "was discovered experimentally in November/December 1983 during the physical startup of Ignalina Unit 1 and that of Chernobyl Unit 4, i.e. almost two-and-a-half years before the Chernobyl accident [23]." Incidentally, roughly two and a half years is how long it takes for the fuel to reach a "continuous on-load refuelling regime" with maximal void and power coefficients of reactivity. According to Dyatlov it was at the specific point of reaching the end of this transitional period of operation that the RBMK reactors were most dangerous. At the "conundrum" part That Chernobyl Guy was supposed to show the list of reactors here - en.wikipedia.org/wiki/RBMK . You can see how many RBMK reactors had reached this point and continued to operate with high coefficients of reactivity (topic of next video in the series) without exploding.
Excellent
Now THAT was interesting!
I thought i undestood it but shortening the grafite caused the issue that's insane
There's even more to the "insanity" factor that future videos will touch on. Chernobyl was a debacle that most people misunderstand.
Another very well done video. And this one in particular helped me connect some dots. Except for the Russian books, I have all the reports you mention in this here video, and quite a few more that weren't mentioned. I had read about this alteration etc., but somehow the puzzle pieces refused to fall into place. Only when you laid them out in the video did the picture become clear. Thanks to you I'm getting close (as close as we can anyway) to almost having my Chernobyl puzzle complete. The poor reactor really never could catch a break. They made absolutely sure that they saddled it with every unfavourable characteristic in the Physics book, and then be stingy with the concrete that was supposed to protect it. "Unscrupulous" doesn't even begin to cover this whole USSR mess.
What's missing in your puzzle?
@@markusw7833
That's the thing. I only know I've found a piece when I watch videos like this. The major pieces are there. Have a lot of books, reports, reactor schematics etc, but sometimes you just fail to connect the dots because there is so much information out there. And not all of it good, or trustworthy. For example, I had read about these different lengths in graphite displacer, but couldn't find out the how or why. Now it turns out that they did this on the fly, without consent from designers etc, just to save some money. And that they never bothered to even look at how this would influence the reactor's characteristics and/or safety.
The only thing I would really like to have is an RBMK-1000 manual. I do have the Ignalina Source Book, but that's an RBMK-1500. Yes, I know it is essentially the same reactor model as Chernobyl Unit 4, but they have done something to how the water moves around the fuel assemblies to be able to extract more heat from them.
If you responded youtube ate it. They've got some sort of mass amateur system of "moderation" in place that doesn't even alert you a response has not and will not be displayed.
@@markusw7833
Apparently, YT did eat my comment. Thanks for letting me know. How strange, there was nothing out of the ordinary in it🤔 All I did is list some things I would like to have. Like an RBMK-1000 manual. And pieces of the puzzle I have found etc. Let's see if you can see this reply before I type any more.
-edit- It gets even weirder because I can still see my other reply🤷
@@swokatsamsiyu3590 That is pretty weird. When it ate mine I could refresh and while the reply counts would include the comments they wouldn't be displayed. It's a very amateurish way of doing moderation (AI might exterminate us in the future for what we have been calling AI) but it shows you that ultimately this is a trash platform as far as discussion goes. It has its uses.
This is quite interesting information. Yet, the SUZ (CPS) are only a small fraction of the total rods in the reactor, making it difficult to believe that a change like this could so drastically increase the positive scram effect. Or maybe the design somehow got used with the manual control rods (PP) as well? I was under the impression that their absorber-section was spanning the entire core, 6+4 sections only resulting in 6m of absorber? (I might be wrong about this)
The SUZ (CY3) system refers to all the control rods collectively, including the PP rods. This term is a bit confusing, given a small subset of the rods are referred to as the Accident Protection rods. The PP (manual rods) had the water column and tip effect issue, since the automatic rods had their displacers removed in the early 80s (the bottom-insert USP rods had displacers but there was apparently no tip effect issue at the top of the reactor).
www-pub.iaea.org/MTCD/publications/PDF/Pub913e_web.pdf p. 103
The Reactor Control and Protection System rods were the full set of 211. This seems to correspond to what the Kurchatov text refers to as "control and protection system rods". The specific abbreviations are rather strange and I don't fully understand them. For instance, the NIKIET text quoted does not refer to SUZ rods at all but to "PP, AZ, and USP" rods (at least as far as the translation goes). Also, the changed dimensions of 4.5-meter graphite sections with ~1.25-meter water columns are the commonly known dimensions so this change wouldn't have affected just a small sub-set of rods.
I do not see the boron sections ever spanning the entire core. There may have been some such ideas considered pre-implementation, as per page 43 of INSAG-7. Of course Chernobyl wouldn't have occurred if both sections spanned the entire core, although a positive power coefficient would have been present in total contradiction to their most recent design rules. They could have eliminated that as well through additional absorbers, fuel of higher enrichment, and by altering the graphite stack relative to the fuel (which they appear to have done for third generation RBMK reactors) but their priority was of a different nature (i.e. economic, possibly pertaining to a plutonium production dual-mode as well). Furthermore, they lacked analytical tools, namely computing power it seems (apparently at most they could copy Americans on semiconductors rather than keep up). What makes Rumyantsev a highly notable figure is that exactly this appeared to be his area of expertise.
@@MinSredMash Wouldn't the rods from the bottom have been considered different or did they fall under the RCPS set?
@@markusw7833 Also part of RCPS
@@markusw7833
Before the accident, Unit 4's bottom-up (UPS) rods were NOT connected to the RCPS. When AZ-5 was used, only the top-down rods would fall. The bottom-up rods would stay stationary at their then current position. After the incident in Leningrad (and I think Unit 1 at Chernobyl, but I'm fully sure), it was proposed to include the UPS rods in the AZ-5 signal. However, because it was expensive to do it at all the RBMKs at once, it was decided to do it gradually at the existing reactors when each reactor would go offline for maintenance anyway. Unit 4 was supposed to get this all-important upgrade at the upcoming shutdown for maintenance and repairs. As we all know it never made it to the shutdown date.
In Karpan's book "Revenge of the Peaceful Atom", there are graphs from a full-scale RBMK simulator where they run the Unit 4 parameters as they existed just before the accident. When AZ-5 is pressed, and the UPS rods are not included, the reactor explodes. However, when they ran the simulation with the exact same parameters, but now with the UPS rods connected to AZ-5, the reactor quietly shuts down without any acceleration of power.
The whole thing is just so infuriating to me. All these losses of life, all this mess, all the lives of people being upturned. This reactor didn't have to explode. It was another case of the Soviets wanting to save a rouble, just like with the concrete mentioned in this video. It truly is beyond criminal.
im wondering if az-5 was pressed instantly after test started if the reactor would of still exploded or not?
www-pub.iaea.org/MTCD/publications/PDF/Pub913e_web.pdf p. 11
"This trip [at the beginning of the test] was blocked in accordance with operational procedures and test procedures, and the SCSSINP Commission (Annex I, Section 1-4.7.4) does not support the apportionment of any blame to operating personnel. In the light of new information regarding positive scram, the statement made under the significance column of Table I in INSAG-1 that "This trip would have saved the reactor" seems not to be valid."
p. 68
"As can be seen from the foregoing, the event which initiated the accident was the pressing of the EPS-5 button when the RBMK-1000 reactor was operating at low power with a greater than permissible number of manual control rods withdrawn from the reactor."
Most of the studies that model the accident use the control rod and reactor parameters from 1:22:30, which is 30 seconds before the test began. So while we can never know for sure what would have happened, plenty of studies suggest that the reactor would have been destroyed by an earlier scram. That said, the test did contribute to the processes that made the reactor vulnerable to a power surge.
At the time when the neutron flux fell to zero (possibly because of too much coolant recirculation due to all 8 Main Circulating Pumps running and steam voids collapsing?), that was probably their last chance to drop all the rods by pressing the button and let it cool down for a day or so.
@@kevinamundsen7646
Yep. If they had left the reactor alone, and drop in the rods when the (neutron) power fell to pretty much zero, we wouldn't be talking about this accident right now. All the reactor wanted to do was to shut down on its own due to Xenon poisoning. If they had let the reactor sleep it off for 24 hrs, and then attempt a restart, all would have been fine.
Yes. It would have still exploded. Prompt criticality cannot be controlled!
Decadent cheeseburger of violations....🤣🤣
mmmmmmmmmmmmmm decadent cheeseburger of violations. now im starving
Can you link all sources and books in your other videos? I’m a bit annoyed by this
I plan on a video going over the sources I use. If you want a list of the sources used in this particular video, they are at the end.
On scripts I'm doing I can often give you links as well as page numbers for direct access as I rely on the reports and other online sources. For some of the Eastern European books like Karpan's and Shcherbak's I may also be citing the accidont site rather than the books directly. Politburo notes are also available online. Dyatlov is fully online. Check the pinned comment for the key sources referenced in this video. When it comes to books without online alternatives I've been using four, and I'll rank them by usefulness:
1. Chernobyl: Past, Present and Future by Nikolai Steinberg and Georgiy Kopchinsky
2. Producing Power The Pre-Chernobyl History of the Soviet Nuclear Industry by Sonja D. Schmid
3. Midnight in Chernobyl by Adam Higginbotham
4. History of a Tragedy by Serhii Plokhy
The last two are most recent and popular but they are notable for their deficiencies in not really understanding the incident which tends to come down to not having a good grasp of the reports despite citing them, primarily INSAG-7. Accordingly they get duped by Legasov. Schmid also has laughable misunderstandings but she focuses on a particular topic that renders her book valuable.
Ultimately if you really care about sourcing there's no substitute for reading the paper linked to in this video. I tend to use direct quotes as well.
The operators tried to increase power after it fell bellow a certain level. They should have waited several days for the xenon to decay completely before attempting to increase power. The graphite moderator was always present so that removal of practically all control rods enabled the reactor to go prompt critical once the xenon had decayed enough. It seems that even without +ve void reactivity the reactor would have still gone prompt critical.