Sorry for the long post, but I need to make a correction and clear up a bit of misinformation. As a licensed nuclear reactor operator with 20 years of experience, who has operated 11 different individual reactors of 3 different designs in his career, I can tell you that you are absolutely wrong about having to wait 3 days to restart a reactor. Not only is it not impossible to restart before then, it's not even dangerous or uncontrollable as long as it is done properly. I have personally performed fast-recovery startups on US Navy reactors anywhere from a couple of minutes to a couple of hours after a scram. I have also personally shut down US civilian reactors and restarted them the very next day, due to various maintenance needs. In either case, xenon does have to be taken into account, and there are procedural limitations, of course. But, in fact, some of the xenon heavy startups I've personally done have been the smoothest and easiest startups, because you can essentially ride the xenon curve as it decays away, which makes it so that you don't have to add nearly as much positive reactivity as you ramp up, since xenon burnout provides you with that. The rate at which you ramp down absolutely affects your xenon concentration. In Chernobyl, they let power drop extremely fast, which created an absolutely huge concentration of xenon. Their reactor went completely subcritical. In all of my training and all of our procedures, if we ever end up in a state where the reactor is truly subcritical (-1/3 DPM SUR), we are required to shut it down. If you end up creating that large of a xenon concentration, it would require far too much positive reactivity to be added to offset it, just to maintain power, let alone raise it back up. That's the problem with what happened at Chernobyl. It's not that shutting down a reactor means you can't restart it for 3 days, it means improperly controlling your reactor to let it get that far out of bounds, and then adding too much positive reactivity too quickly will get you into trouble. If done properly, you do not need to wait 3 days. Respectfully, I am not a nuclear engineer. But I have been trained by the US Navy, to operate their reactors, as well as being trained by my current company, and licensed by the NRC to operate their reactors, and I have 2 decades of experience, combined. I studied all of the reactor physics formulas, and used to be able to calculate the various values, most of which I have long since forgotten the specifics of, because you don't calculate those things on a daily basis...or ever...in regards to operating a reactor. I would expect reactor engineers to know more specifics about fuel loading, enrichment, and all of the engineering calculations to evaluate a reactor's performance. But actual operators, who physically control the reactors on a daily basis, have a lot better knowledge on actual operations. A chemical engineer, for instance, would know a lot more about engine management and fuel control for an engine, but the truck driver with a CDL and 20 years experience would surely know a lot more about the nuances of what gear to select when approaching a certain grade with different sized loads behind him. No offense intended. I am not meaning to criticize anyone, here, I am just trying to clear up a bit of a misconception that you seem to have. Because I have absolutely done this myself on numerous occasions, with no ill effect, and in a perfectly smooth and controlled manner. There is no 3 day limit before you can restart a reactor. That's just absolutely not true.
How does this comment not have more likes? It's great to see people with experience commenting in this - great to have you Adam. E.g. I'm a physicist, and while I understand the detailed particle physics, the engineering/practical aspects of this are *way* beyond me. For instance, when you comment "ride the xenon curve" so it's easier to increase reactivity without having to remove further control rods, I've got not idea roughly what fraction would typically have to be removed. I understand approximately that this is to offset other negative reactivity coefficients of temperature (void, thermal expansions etc), and that Chernobyl's positive void coefficient was on reason it ramped up so quickly after the xenon shut-down, but have no "feel" for how this works in practice. So it's great to read this. Having said that, these videos are still Nuclear Physics 101 - a great intro, but fairly basic details, so I think that his statement about "needing to shut down for three days" is close enough of an approximation to be justified.
Oh, and BTW Adam - when you mention " I studied all of the reactor physics formulas, and used to be able to calculate the various values, most of which I have long since forgotten the specifics of, because you don't calculate those things on a daily basis...or ever...in regards to operating a reactor." this was one of the issues at Chernobyl - their computer, SKALA, to calculate these things took 15 minutes to estimate reactivity through various calculations, and even then I suspect it didn't do a good job, since the reactor was so large, the reactivity varied a lot over the core. So all the fancy nuclear engineering theory in the world (at the time) could not have helped them, and they should have just followed the ****ing safety protocols.
@@clancyjames585 In response to your second comment (I saw them out of order in my notifications) I agree with you 100%. I don't know the specifics about the day to day reactivity calculations at Chernobyl, of course. With a reactor design like theirs, with a graphite moderator giving it a positive void coefficient, and thus positive temperature feedback, my understanding is that they quite frequently had rods moving fairly regularly to maintain everything. We very seldom move rods, because it's just not needed at our plants. Our plants are very stable when it comes to reactivity. The Navy reactors I used to operate were small enough in size, and were very VERY responsive, due to a very high enrichment of U-235, so on those, you really didn't need to calculate anything. You just basically moved control rods a small bit, and you pretty much knew the result from a certain amount of rod motion, and it was very even and predictable. Like driving your car, you don't have to calculate how far to push the gas pedal to drive. Plus, the Navy reactors were responsive enough to negative temperature feedback that you usually would not even need to adjust control rods when you changed power. Raise or lower turbine steam flow, and within a few seconds, the reactor would respond and stabilize at the new power level. The commercial reactor I operate now is a different beast entirely. Much lower enrichment, and very large in size (though smaller than Chernobyl, by quite a bit). We do have negative temperature feedback (unlike Chernobyl), but it's a bit slower to respond than the Navy cores. Our reactor design is inherently very stable, and it has all of the negative feedback aspects to make it essentially remain stable with no continuous manipulations or input at all. Normally, we only make a slight adjustment to the boron concentration every few hours, but that's all it takes to remain stable. Moving the plant around is a bit more involved, but our rods operate automatically to maintain temperature, and we simply have to adjust boron concentration to keep rods from moving too far and changing the power distribution. Easily managed, with no complex calculations required. A spreadsheet can calculate the required adjustments almost instantly. A few simple thumbrules are also used for rapid power reductions, so the reactivity spreadsheet really isn't even needed. Probably one of the biggest differences in our fundamental operation is that if we ever drove the reactor subcritical, like they did at Chernobyl, we would immediately trip/scram our reactor. We would never let power fall so quickly in the first place, and even if we did, we would not rapidly add tons of positive reactivity to quickly restore power, and certainly not outside of design limits. It's just not something we would do. We just have a different safety culture, and of course, the industry has learned quite a lot from accidents like the one at Chernobyl.
@@clancyjames585 In response to your first comment Completely true. I certainly don't want to come off as bashing this video, I mainly just wanted to correct that one particular point, but you are right, this is basic level stuff here, and it doesn't need to be needlessly overcomplicated for most people. To get a little more in depth about riding the xenon curve, the biggest thing we aim to control at my plant is temperature. Sure, there is a limit on power that we cannot exceed, but at the end of the day, the main thing we are driving by is the temperature. We have a certain temperature to maintain at any given power level. If temperature is too high, it means the power output of the reactor is higher than the turbine. If temperature is too low, it means the turbine is making more power than the reactor. What basically happens is that to raise power, we have to open our governor valves and admit more steam to the turbine, to push the generator harder, and make more electrical power. As the governor valves open, it draws off more steam, which cools down the reactor. The turbine power is rising above the power of the reactor, so you have to add positive reactivity to bring reactor power up to match the turbine, and bring temperature back to where it is supposed to be. We have two ways of doing that at my plant (PWR reactor), rods and boron. We have a certain amount of boron dissolved in the coolant which is a neutron absorber. Need to add positive reactivity? Either dilute out some boron (add fresh water with no boron in it, and drain out a little bit of water that has boron in it), or move control rods out. If you move rods out, it makes the power distribution move physically higher up in the core. If you dilute boron out, it moves power lower in the core. So we move rods a little bit, and dilute a little bit to keep power balanced in the middle of the core. More steam to the turbine, cools the reactor, dilute or withdraw rods to keep the reactor temperature up, repeat. As power goes up, it also adds negative reactivity due to the fuel temperature going up, though, so we have to add a little bit more positive reactivity (rods/dilutions) to overcome that bit of negative reactivity. It's all fairly balanced and easy to predict and manage. The only wild card is xenon. If you start with a xenon free core (like it would be a few days after shutdown) and startup the reactor and raise power, xenon will build up as you raise power. So, in that case, you have to add positive reactivity to overcome the temperature change from drawing off more steam, add positive reactivity to offset the negative reactivity from rising fuel temperature, and then add some more positive reactivity to offset the negative reactivity due to xenon building up. I hope all that is clear and makes sense. What's different is if, for instance, you were to trip/scram the reactor, and then start up the next day. On a shutdown or significant down power, xenon builds up rapidly, as explained in the video. You end up with a huge concentration of xenon. Now when you go to start up, the opposite happens. You're raising power, and burning xenon out, rapidly. As xenon burns out, it's adding positive reactivity. This is basically what got the Chernobyl guys in trouble, and started off their problems. But, if you're doing things in a controlled manner, the xenon burnout can help you. You're drawing off more steam to raise turbine power, so you still need to add positive reactivity to keep temperature up and to offset the negative reactivity of fuel temperature rise, but now, xenon is burning out, not building up, so xenon is giving you positive reactivity to help you out. It makes it so that you end up moving rods less, and diluting less boron out of the reactor, because xenon is giving you positive reactivity. In the end, it's all going to balance out, though. But starting up with xenon burning out can make the startup and power rise go a lot smoother, because it can sort of raise power on its own. Oh, and as to what fraction of rods would typically be removed, that's not quite how it works with our cores. Our cores are designed to operate with all rods completely removed, once everything is balanced out at 100% power. We are not at all designed like Chernobyl. Specifically, at my plant, we have 6 banks of rods that are removed one bank at a time, with some small overlap between banks. We are designed to go critical when the last bank is about 3/4 of the way from being completely removed. We calculate how much boron we need to go critical at a given rod height, and we set those conditions before we remove any rods. Once we start up and go critical, we still have about 1/4 of the rod height on that last bank, to help control and manage things as we ramp up in power. Over the next week or so after a startup, we slowly adjust boron concentration and slowly withdraw the rods fully. We really only use rods for "shaping flux" and controlling where the reactor makes power, but it will naturally center itself, and we can get the rods fully removed from the core. What I was basically saying is "riding xenon" will make it so that you don't have to pull rods out as quickly, and don't have to dilute as much or as often. We're still going to end up moving rods all the way out, we just go from maybe moving rods every 10 or 20 minutes, to maybe every hour. Since xenon burnout gives us some positive reactivity, we don't have to add as much positive reactivity due to rods/dilutions. I know this was very wordy, but I hope it makes some sense. Feel free to ask any questions if you're curious or want to know more, or if something isn't clear.
There was a hot spot in the bottom of the core, of which the controllers were unaware. That certainly must have contributed to the explosion. And while I am sure that could be done with western reactors, I am not so sure about the RMBK-1000 reactors those engineers were operating. Hopefully, you never had to operate a reactor capable of going runaway like those.......
I'm not even THAT interested in nuclear engineering, but I'll watch a lot of introductory level lectures that I wouldn't otherwise watch when there's this good of a teacher. Of course, you can't really know that what he's saying is true for sure unless you do some much more serious studying, or at least look more deeply into his credentials. But just watching stuff like this casually as a non-student can be very edutaining..
When I was in the Navy I saw the effects of Xenon poisoning first hand. We were near end of core life, had maybe 9 months or so left max (we where scheduled to decommission in about 8 months), and we had been steaming down the coast of California at all ahead full for better part of a day. All ahead full is 100% power. We were passing San Francisco and Captain wanted to slow down and come to periscope depth to tow the radio lines and get the mail as well as to give the crew practice tracking surface ships in a busy shipping lane. Coming off the bell, reduced our power demand on the reactor significantly so the Xenon spiked very high. Being an old core, she produced a LOT of Xenon and handled it not too well. The reactor operator (I was on watch as the throttleman controlling the steam valves on the main steam turbines) had to start shimming the control rods out to keep temperature steady. He kept going until all the control rods were pulled out and still we remained at 1/3 power. Finally, he couldn't maintain temperature in the operating band anymore and we watched as the reactor began to cool off as it struggled to maintain power. So the reactor operator advised to the officer of the watch to come back up on the bell so reactor power would rise and burn off the xenon faster and that he was unable to keep temperature in the operating band anymore. The officer of the watch informed the con (control center) and told the Captain we needed to come up on the bell or Xenon poisoning would shut down the reactor. So the order went out to pull the radio cables back in and 2 minutes later I was ordered to open the throttles back to all ahead full. I did as ordered and we began drawing much more steam again and in so doing, cooled the reactor coolant even more. This colder water caused reactor power to rise, as expected, and this in turn warmed the reactor back up. It also increased the neutron flux and burned off the Xenon transient faster and in short order the reactor operator was able to start shimming control rods back into the core. We had all been trained on this, the theory and physics as part of our nuclear training by the Navy. To see this first hand and to see the reactor behave EXACTLY as expected in a Xenon transient was pretty cool. When it comes to handling them and reducing power responsibly, it is wisest to reduce power slowly and gradually over a period of 24-48 hours so the Xenon transient is controlled the entire way through. Newer reactor cores don't have to worry about this near as much since the ambient neutron flux is so high, even at lower power, that it burns the Xenon decay products off fairly fast.
Very interesting info but let me correct your last statement. The so called by you newer cores do not worry much about the xenon indeed but for a different reason than the one you said. The freshly reloaded core has a lot of excess reactivity while the old one has almost none. The xenon poisoning eats some of the remaining excess reactivity. Since the newer core has plenty of excess reactivity the poisoning effect is significantly reduced. And the neutron flux is less in newer core than the older one. That is because the newer core has more fissile elements and less poisons (decay products) and therefor needs less flux to reach rated power. The older core (near end of campaign) has less fissile elements and more poisons and therefor needs more flux to reach rated power.
@@piotrd.4850 All military designs are meant for multiple decades. But, that is subject to a disclaimer: Mileage may vary depending on use. So the time a core is good for depends on how heavy a load and for how long said load is placed upon it. Those 2-3 decade life expectencies are based on the accumulated logs of decades of reactor operation from hundreds of nuclear powered ships since the USS Nautilus was first launched. The amount of reactivity in a core is dependent upon: 1) Core geometry (physical layout of components) 2) Core physical size 3) Age 4) Amount of rated power consumed to date (The "fuel" tank of a reactor is rated in "EFPH" "Effective Full Power Hours" or how many hours at 100% power is the core engineered for) 5) Uranium purity. Civilian reactors try to get as close to 20% enrichment with U-235 without actually reaching 20%. 20% is the point Uranium is considered highly enriched and minimum for weapons grade, thus restricted. Military reactors are not bound by this restriction... Continued refinement in all of these categories is what allows for such length lifespans for such tiny sized reactors despite being capable of 100+ megawatts of output at full power.
I've read descriptions of the Chernobyl accident that mentioned xenon poisoning and it's effect on the reactor but never really understood what it was. This video provided an excellent explanation of the phenomena.
Nope. Going over the regulation list was the cause. Akimow should use the water for "cooling" the rector...it would end with the moderate damage. Because it was SL-1 in bigger version...
There were a bunch of different things that combined to create the Chernobyl disaster. Xenon poisoning was definitely one of them. Xenon poisoning was the entire reason that the flow of coolant was reduced greatly AND the reason that the safety system that operated the control rods was disabled so more than the allowed number of control rods could be removed in an attempt to overcome the Xenon poisoning. The runaway reaction was caused directly by the lack of control rods in the reactor (creating serious "hot spots" since the minimum 24 rods arranged throughout the reactor that were ALWAYS supposed to stay put were mostly removed) and the lack of coolant being pumped was what caused steam voids to form in the coolant channels in these hot spots. Once those two things happened it was all over. Obviously the positive void coefficient and the flaw in the control rods were instrumental too.
@@danlorett2184 Those "rods" are called buffers. They were created to suppress the "power jumps" during the shut-down. Of course you can flood reactor with water and whole reaction would be killed. Diatłow thought about that but Akimow, pissed enough on rough old man, used AZ-5 thus blowing the nuclear reactor. No one listened young Tuptonow... P.S. I believe it was iodine, no the xenon that caused the problem. I-135 with half-life of HOURS! (6.57 h) Also open to neutrons.
@@danlorett2184 Xenon poisoning is not cause of Chernobyl disaster for the same reason that gravity wasn't a cause of Columbia disaster. Xenon poisoning is just a physical fact. You design your system to deal with it. And if you did not design it to deal with it the cause of the disaster is you, not Xenon poisoning.
This has to be some of the most interesting content on TH-cam. Your explanation, and clarification of complex topics makes this so much easier to understand for people who have not gone to 8+ years of university.
The new Moltex plant going through safety homologation at New Brunswick in Canada has a highly negative power coefficient. It can sit with the load disconnected at full power settings and not overheat. It’s fully self regulated. They have avoided the Xenon problem by venting the fuel tubes. The reactor core uses a uranium chloride fuel in a chloride salt carrier contained in vented fuel rods. The primary coolant is the same chloride salt (without fuel) which transfers heat by convection to a tertiary salt. That is the exact same as used in thermal solar power. Iodine and caesium react to salts so do not vent into the vents. Systems are in place to manage that if it happens.
Yes the Moltex design is very interesting. Though I'm puzzled why they switched from fluoride salts to chloride salts. I thought the negative void coefficient was because the fluorine had some moderating effect so a void in the coolant would reduce moderation. I'll have to read up on their new design.
This is like the 5th video I watch from this professor and I am a law student with nearly no knowledge of chemistry and physics , but nuclear energy has caught my attention so much. I know is more complex than just some videos in TH-cam, yet I feel fascinated.
I graduated with my ME and EE degrees decades ago, and I find these 'lecturettes' really interesting and very well done. Nice to know they appeal to non-technical people too.
I am not sure which to be more impressed by: the detailed knowledge of nuclear fission which you can effortlessly relay or the way in which you can write backwards perfectly... I think I'll chose both.
This was an extraordinary lecture. I knew the details about what happened and I know about Xe poisoning.....but all the interlaced physics of the decay chain I did not know about. This professor is really good; very very good at explaining this stuff.
the guy tells garbage. Chernobyl did not explode because of xenon poisoning, it was human error and unknown technical problems for all reactors of this type (by the way, an American design and not a Russian development). The nuclear industry has learned a lot from Chernobyl and abolished graphite moderators, since once they burn they can no longer be extinguished.
1. Thanks TH-cam Algorithm for waking up this video. 2. One thing he gets wrong is that the engineers at Chernobyl knew about Xenon. They weren't stupid. They knew they were working with a poisoned reactor, but in the rush to finally get this stupid test out of the way, they tried to run the experiment anyway. They thought they could SCRAM the reactor and shutdown if anything went wrong. They figured, what's the worst that could happen, they shutdown and try again later? The reduced coolant flow (part of the test) triggered the rapid burnoff of Xenon, They tried to shutdown, but the control rod design caused them to increase reactor power at first before they started slowing the reaction and then pent up steam pressure from the overpowered reactor bent the rods to the point where they got stuck, and then coolant lines in the reactor exploded, but the reactor was designed to contain one or two exploding coolant channels. They thought it was a super safe design but in reality it was so unstable no one ever expected they would blow three or more at once. This blew the lid open, exposed the superheated graphite to oxygen in the air, and that caused the main explosion. Soviet physicists knew about the control rods. They knew that the rods could cause an unexpected spike in power when first inserting them. They saw this happen in a previous incident, but they purposely withheld this information from the plant engineers. If they had known they wouldn't have messed around like this.
Does anyone appreciate that not only is he a great professor, but he IS writing backwards for us to see it the right way? Just shows how his brain works. Intelligent.
I'm pretty sure the video is mirrored. Pins usually go on the left side of the lapel and his is on the right. Also, his wedding ring is on his right ring finger.
Wonderful lecturer. Plain talk for lay people like me. I read a bit about Chernoble and the technical issues that led to the explosion. Now I understand it better. The wow factor for me is that after a shut down, one must wait many hours before restarting it....if you don't big bang!
Good pickup. Didn't notice that! It seems that Xe-135 is radioactive and emits electrons with a half life of 9hrs - so it would be quickly exhausted anyway
Dear sir, I would like to say: Thank You for this footage, about the Reactor Xenon poisoning. I am not nuclear specialist, only great enthusiast. Your videos are understandable for ordinary people. And even more: You describe all issues so good, that Your lectures are usefull also for visually impaired folks. That is my case, because I am unfortunatelly blind and therefore are such descriptions really important for me to understanding and learning new facts as best way as my handicap allows. So, thank You, sir! All the best from The Czech republic, stay safe and be healthy!
WOW, the best explanation and a great revision for me as a scientist (Ok I'm not a nuclear engineer). Fantastic. I just showed this to my 8 year old and even he understood this. I'll be subbing! Thanks for posting!
Just cause i am missing it in the video: It is not that removing the control rods made it "suddenly" tip over and caused a runaway-effect. Rather - the reactor was now running at a far too low level, extremely poisoned due to the way it was handled before, most safety-systems shut of, the automatic-control disabled, the steamturbines partially shut down and most control rods, even those that should always stay inside the core, were many retracted entirely out of the core. Now this is a big problem as the water started to boil at the rods and this reactor-design actually made the reactor More active when boiling, further increasing the output and the neutron-flux. This is 2:30 hours after the shutdown started - the xenon-release from iodine has slowed down already. When this problem was noticed they started inserting the control-rods again and that had another problem: Those rods had a graphite-tip that would at first increase the power output before the moderating-part reached the core. Now the power-output went up significantly and some of the fuelrods broke in jammed the control rods. So now we have a reactor with nearly no cooling, graphite that does not absorb but moderate the neutrons, the water boiling which also does not absorb the neutrons, little xenon being produced but a high flux burning the existing xenon away and a buildup of temperature and pressure. at this point the reactor was also outputting several times its maximum rated capacity leading to the pressure form the steam rising extremely quickly to the point of rupturing the cooling-system and the first explosion. The cause of the second explosion is not fully understood as well - there are no sensory-readings or useful survivor-accounts of what went on there - so there are a few hypothesis, the most likely nowadays seems to be yet another steam-explosion: after the first explosion the reactor had no more cooling, the molten core heating up further and melting its way down likely came into contact with the rest of the water - you can imagine what happens when several tons of extremely hot molten metals, some of which are also very chemically active, come in contact and cover a large body of water - a really big explosion.
ABaumstumpf The second explosion was most likely a hydrogen detonation. You flash boil a bunch of water, as happens in a steam explosion, you have alot of leftover hydrogen, which likes in explode in of itself. Modern reactors are designed with blow out panels for this reason.
The second explosion might also be small nuclear explosion (a "fizzle"). The IAEA report www-pub.iaea.org/MTCD/Publications/PDF/Pub913e_web.pdf page 3 says that the total loss of water (e.g. after the first explosion has ruptured a lot of the pressure tubes) can lead to an increase reactivity of 4-5 beta. An addition of one beta alone to a normally running chain reaction means the reactor core is prompt critical.
@@willh8950 I assume the blow out panels are (as in other regular thermal power plants) in the secondary circuit of a PWR to relieve pressure if there are problems in the turbine/condensor etc. Venting the containment (if the pressure rises to high) is another thing.
Yes, they do, but as LaserFur says, it tends to just collect at the top of the reactor and is drawn off. In general, a lot of fission products are poisonous (though none as much as Xenon), but in the LFTR they are in the liquid fuel/coolant, which is continuously drawn off, has the FPs removed, and is rebalanced with thorium and uranium, and then injected back into the reactor. Never stop for refueling, FPs always kept at a low level.
In fact, delayed neutrons is what making all of humanity's application of nuclear energy even possible at all. At least, until the reactors like BN-800 will become a mainstream solution.
Very interesting. I have clue about half of the time but the explanations are perfect and help me connect the dots. Another note, is he writing backwards while giving this lecture? If so I’m even more impressed
Almost a complete picture. What he omits is that when you DO manage start a Xenon-poisoned reactor, you rather rapidly burn off that Xenon. This burnoff occurs dozens of times faster that the Xenon built up in the first place, and hundreds of times faster than the Xenon would normally have cleared itself. So once your Xenon-poisoned reactor is running, you have to actively increase the control rods over the next couple of minutes, failure to do so will cause a runaway. And a runaway, releasing more neutrons, burns off the Xenon even faster, speeding the runaway!! Add to that the fact that the Soviet reactor at Chernobyl used water as part of its moderating structure. Lose the water, and the moderation increases, further accelerating the reactor! So the moment your runaway causes your water to turn to steam, its bye-bye. The reactor instantly jumps to a higher state, burns off the remaining Xenon, jumps to a yet higher state, and all of a sudden you have a 30Gigawatt heatsource occurring in your 1 Gigawatt reactor housing, which simply cannot contain it.
it *probably* wasn't 30GW (nobody can tell for sure as all the instrumentation simply pegged), most likely "just" single digits of multiples, but still enough to eventually throw the reactor lid through the roof :D In case of Chernobyl, what added insult to injury was the fact that the control rod mechanism was so painfully slow...had it been capable of a SCRAM by modern reactor standards, the plant would (probably...Dyatlov did a lot of things that night that he should not have ever done) still be in one piece. Damaged reactor, but probably still in one, albeit partially molten piece ;-)
@richard mccann Bear in mind that even if the reactor went prompt critical in 3 miliseconds, even with 30GW of power creation, it would take a couple seconds to heat up the ~ 5 tons of core to the point where it explodes. This inertia is actually a bad thing, as it delays the disruption of the core , allowing more energy to build up before it stops the reactor by disassembly.
But losing your moderator causing the reactor to shut down, not increase in power. The problem was not the water, it was the fact that the graphite provided moderation even without the water. Moderators slow down neutrons and only slow neutrons cause fission in U-235.
"Lose the water, and the moderation increases," this is certainly wrong. Water has two effects: it moderates the speed of neutrons from fast (directly after fission) to slow (thermal), as the cross section for splitting U-235 is much higher. But it also acts as a (mild) neutron poison, by neutron capture from hydrogen to deuterium (H-2). In a BWR or PWR, the sentence is: loose the water, and the moderation decreases, which brings down the reactivity. In RBMKs, the water is not primarily used for moderation, as graphite is used for this purpose. If the water goes away, the moderation is still fine but the neutron absorber qualities of water are lacking and the reactivity goes up. That is the reason for the positive void coefficient of RBMKs.
@@gunnarkaestle sigh. Lose the water, and the percentage of neutrons that are moderated by the graphite (becoming suitable for fission) increased, *because* less are absorbed by the steam as compared to water. Thus the reactor *as a whole* has more moderated neutrons capable of inducing fission. This is what I mean by "the moderation increases". Which is, frankly, exactly what you are saying, but you are being an ass and arguing just for the sake of arguing simply because you do not understand english.
@104th_Maverick It rather depends on what kind of materials (elements, compounds) one uses for control rods. See here for an explanation --> en.wikipedia.org/wiki/Control_rod
@MegaSexfanatic That's basically true, but there's a little more to it. I am a licensed operator at at PWR, and we do use boron as our primary reactivity control. We either borate (inject boric acid, which is water with dissolved boron) or dilute (add fresh water without boron) to control how much boron is in the reactor coolant (which is just ultra pure water with a certain amount of boron in it). We have a system that automatically maintains a certain volume, so whether you pump in boric acid to borate, or pump in fresh water to dilute, the same amount of water that's already in the system drains out to a large collection tank, which gets cleaned up and processed and eventually released to the environment once it's clean. But, we do use control rods, as well. Our control rods are made of silver, indium, and cadmium. The control rods are normally used for starting up the reactor, and for controlling where in the core the power is being produced. But the control rods are also our emergency shutdown method - a reactor trip literally drops all of the control rods into the core to shut it down in an emergency.
There is a limit, of course. The way neutron absorbing materials work is to...well...absorb a neutron. That changes it into a different isotope. Some elements have several stable isotopes, some have very few. Each time an atom absorbs a neutron and becomes a different isotope, it may be better or worse at capturing another neutron, it may be stable and never absorb another neutron, or it might be unstable and decay (radioactive). I can't speak for all the different absorber materials, but generally, control rods are going to be made out of materials that can capture a very high number of neutrons before they lose that ability. Speaking from personal experience, I have about 15 years experience at my current plant, and in that time, out of 96 control rods combined between two reactors, we have only replaced one single control rod. And that was due to a mechanical issue, not a neutron absorber issue. So, simple answer, yes, there is a finite number of neutrons a control rod can absorb, but it's a huge number, and replacing control rods is not at all a common thing. We reuse the same exact control rods over and over and over again.
Theoretically, yes, but I've never heard of it being done. The materials from which the reactor vessel is constructed is more likely to reach its end of useful life first due to neutron embrittlement.
I'd disagree. I believe in 5th part of "Chernobyl" mini-series they've described pretty well in quite clear and understandable way what had happened and all major factors which contributed.
@@МихайлоСєльський Well, at that point it's a matter of personal preference. But the technical explanations laid here are overall more interesting to me, althought the serie was indeed quite good as well.
Maybe the only question not directly addressed was that since xenon is a gas, why does it stay behind rather than ventilating out of the core. Being trapped in the solid fuel rods well enough that the escape rate is low or nil is perhaps the explanation.
I think I need a bit of clarification. If you stop a reactor and have a large build up of xenon, why can't you start back up again? Starting up would mean increasing reactivity right? Since xenon is absorbing any neutron produced can't you just start up and wait for the xenon to decay back to its steady state? Would the issue be like he said where since it's so negatively reactive it's difficult to do this precisely and overshoot, leading to uncontrolled critical reaction?
This was one of those videos which got suggested to me, even though it's not something I was intending to watch, or have any major interest in knowing about. Even though it's basically just an oral presentation, with a whiteboard kind of thing, I stayed glued to it until the end. Impressive :)
They did know about Xenon-poisoning. The reactor could detect it ( by the typical drop of energy production) it even had a shut-down-automatic for this case. Only this automatic was disabled by a manual override.
i read somewhere that they knew about it, and even had a safety protocol , which pointed out to shut down the reactor in such a case, but Djatlov didnt give a fck and wanted to start the test anyways.
And that is why you do not let nuclear plant engineers watch old episodes of Star Trek, where Scotty and Mr Spock breaks the laws of physics, and restarts reactor, and saves Enterprise from Burns up in the atmosphere.
The American media, even the latest popular Web series named Chernobyl looks over Xenon poisoning. All they focus on is the bad design of the RBMK reactor. No media attention on the stupid things done by the operators. It's like removing all the brakes of a car and complaining when the car crashed. The lack of understanding of Xenon poisoning is the PRIMARY reason for Chernobyl compared to the graphite tipped control rods.
@@mpk6664 Exactly! They are good enough with in built safety systems that insert control rods much before the reactor becomes unstable. That prick Dyatlov oversaw disabling ALL automatic safety systems and ignored the computer warnings. The only flaw I see was the absence of an extra containment building
The show actually discussed both, and set them up as legitimate reasons. First, I think the show actually did a bad job calling these graphite tipped. The way a RBMK reactor is designed there is a graphite rod at the bottom of the control rod, if you lift the control rod up, you are lifting the graphite rod up into the reactor to replace the control rod. There is also a void between the two rods which has some displaced water between them. The issue is that when the graphite moderator is fully elevated, displaced water goes into the bottom, like a cap, because the fuel rods are longer than the graphite rods. The issue in this design, is that as soon as you scram the reactor and inserts all of the control rods, the first thing that is going to happen is the water will displace, and the graphite will fill the void. When this happened it created a hotspot of intense heat, for just a few seconds, this was enough to burst and break the control rods, fixing them in place. Since they were fixed in place, the reaction never slowed, vaporizing all of the water and turning it into a steam bomb that blew off the top of the reactor, allowing oxygen in, which should never be present there, and that triggered the explosion and fire. So yes, xenon poisoning contributed the disaster, but the real cause was an emergency shutdown system that was literally a nuclear bomb detonator. Sure, xenon poisoning caused the reactor to go critical, but the emergency shutdown should have instantly shut down the reaction, and instead made a huge explosion of thermal energy. Hope that helps.
I'm not sure if you completed the web series, but the last episode had a huge section dedicated to just explaining the Xenon Poisoning. Azimov even tells Dyatlov, "the reactor is in a xenon pit, we have to shut down, we have to wait 24 hours." He then asks Dyatlov to record his order in the book, who then smacks it out of his hands and orders him to do it or never work in any reactor, anywhere, ever again. There was absolutely someone in that room, that not only knew this rule, but protested the orders they were being given. Dyatlov knew all about this rule as well, this wasn't ignorance. He was defiant, because in his younger years there was an accident that had exposed him to lethal doses of radiation and he was fine, he lived believing he was invincible. Despite this, his son died of Leukemia, due to contamination that he brought home from the earlier incident. He was a stubborn idiot, who literally ordered his crew to turn a reactor into a nuclear bomb, despite every regulation otherwise. Valery says this in his speech at the end "Dyatlov broke every rule we had, every one of them, but he did so with the belief that there was an emergency shutdown system that could prevent what happened." I'll remind you that even after the incident, Dyatlov was so certain that this event could have never happened, that he sent his men into the core, killing them with radiation poisoning.
What is your take on the fully integrated, molten salt, thermal spectrum, graphite moderated reactor? Do you think the plumbing and the separation chemistry will work? Including helium - vacuum sparging of the molten salt? without helium sparging the neutron economy won't work, agree?
I shuddered when he said "by pushing the control rod into the reactor" and drew an up arrow. As a former US Navy reactor operator, I believe control rods should be inserted from top to bottom. If power is lost to the control rod drive mechanisms, the rod should fall into the core, instead of falling out.
I think it depends on the type of reactor. A PWR does exactly as you say, dropping control rods in. A BWR pushes it in from the bottom. There are advantages to bottom-entry control rods such as being able to refuel without removing the rods. Bear in mind I'm just interested in this stuff rather than an expert and have only read this up on Wikipedia.
As the other comment said, 3 days might be excessive. You could restart it immediately. But don't expect any power output until the xenon has absorbed enough reaction. Whatever you do, don't do something stupid like pulling out control rods.
Sorry if I'm mistaken, but is it really true that they "accidentally" turned off the reactor during/before the Chernobyl disaster? (12:56). I was under the impression that the reactor had been running at half-power for a couple of hours, which led to the Xenon poisoning.
It ran at half power for many hours, around 1600MW but the test was supposed to be run between 700 and 900 MW, so they further decreased power. The xenon poisoning was building in amounts from the reactor running at full 3200MW earlier in the day and as you say then at 1600 MW for many hours- when they decreased the power it unexpectedly continued to fall below 700 MW( perhaps from xenon concentrations) all the way to 30MW! So in effect the reactor was completely shut down and likely loaded with xenon.
@@brianmohr4674 This test was supposed to be done between 700 MW and 900 MW of electric power but they ran it at 200 MW. Chief guy ordered to perform the test at 200 MW, reasoning that it will be safe but it turned out that reactor doesn't care about experimenters thought on the matter. As the result, due to interference of one idiot, the humanity is still dependent on fossil fuels like oil and gas.
@@brianmohr4674 By the way, ALL of RBMK based blocks had the same test performed successfully, without any kind of accidents. The only difference was that this test was done properly, according to regulations, without one-sided alteration of instruction done by one person in charge. Chernobyl #4 was quite a surprise because nobody even had a thought that somebody would dare to do such a thing.
David correct me if I’m wrong but , Xenon is a by product of the nuclear fission that occurs and over 50 hours it keeps it’s left in check as long as the nuclear reaction is being powered . Once you shut the reactor down you have to wait 3 days to power it back up because the xenon can no longer keep its self is a control state. What happens in Chernobyl was that the reactor was being powered down and the engineers powered it back up to do their test . But since xenon was not being controlled it was choking the reactor and they began to pull control rods to boost the reactors power , and when they did that the run off of xenon and lack of control rods made a complete switch from being choked to highly powered thus causing the explosion
In a power plant, you want a constant number of reactions (the neutron dance he talks about), which means each fission event on average you want to cause exactly 1 more fission event- less and you would continually lose power over time, more and you would start to exponentially grow power. So you need to constantly absorb just the right number of neutrons to maintain this balance. Control rods do this by being inserted more, or less, increasing or decreasing the amount of neutron absorption respectively. If the reactor is full of Xenon 135 it acts like a control rod- absorbing neutrons. However, when a neutron hits a control rod, it is still a control rod. When a neutron hits Xenon 135, it becomes Xenon 136, which IS NOT a neutron absorber. This means as you 'burn off' the xenon, you are a burning off neutron absorption, and increasing the probability of reaction, which in turn increases the rate of xenon burn off- a positive power feedback loop (i.e. instability).
How big uranium power loss appears when we start reactor before that time? As there was 9h times 6% of decay product, then it should take less 30 minutes of total neutron absorbtion without power production. But I believe that is not fully operating reactor, so just start of reactor is difficult... How much time/energy would it take for starting reactor??
Super interesting , a verry clear explanation you are a good teacher Thank you verry much. Could you get rid of the xenon 135 in those 60 hours just by ventilating the reactor ? Can you explain the process of the thorium reactor as clear as this cycle of the xenon gas.
Ventilating the reactor wouldn't help, because the xenon is not in the water. The xenon is physically in the uranium fuel pellets. We are not talking about bubbles of gas in the reactor, we are talking about random atoms of xenon scattered throughout the fuel pellets. The xenon is physically trapped within the core materials.
The xenon cant just be vented, it has to decay, which requires lots of heat. So normally all the workers in the plant hold their hair dryers against the reactor and that does the trick.
@@p5satanael Even with the safety upgrades after Chernobyl, the RBMK design (still 10 units in operation in Leningrad, Kursk and Smolensk) allows an explosion. A sudden loss of significant water masses (i.e. a large size LOCA), will increase the reactivity by 4-5 betas. A beta stands for the amount of delayed neutrons, which is the reason you can control a chain reactor in a nuclear reactor. One beta is the difference between prompt critical and (delayed) critical. Prompt critical means boom! as in atom boomb (even though badly designed atom bombs may fizzle and tear themselves apart before splitting a significant part of the nucleii). www-pub.iaea.org/MTCD/Publications/PDF/Pub913e_web.pdf page 3
@@iasimov5960 what does the power structure in a control room have to do with an economic system? I think maybe you're using words you don't understand comrade.
Can you do a video about the thorium reactor as supposedly a better reactor than the uranium one? In other words, has the uranium industry prevented the development and use of the Thorium reactor?
Thorium vs Uranium is just a different fuel, which should last much longer. As of today, the problem for nuclear reactors are the not fuel costs, the high CAPEX is the reason that there is no real nuclear renaissance (except the Chinese activities) www.worldnuclearreport.org/IMG/pdf/figure_12_nuke-world-constructionstarts-1951-2019_china.pdf
@@SteveJohnson007 Thank you Steven for your very informative videos. I am degreed in Electrical and Computer engineering, but I have always taken an interest in Nuclear engineer. Great content!
Not always true. In commercial reactors generally they restart the next day - 20-24 hours is enough for a lot of the Xenon to decay and the rest can be overcome by careful startup procedure.
no, thats jibberish. reactors DO NOT NEED three days between shut down and start up. building up that much xenon is a symptom of poor management, nominal levels will decay within the day
What about the gas (water-vapor) bubbles? Because Chernobyl was a BWR reactor, not a PWR, and the fuel cells were become hot, boiling the water... So what bubbles does in a reactor? (way less h2o in a bubble than in water itself)
I used to build ion drives for the UK military. Xenon was our fuel; and a great fuel it was too. My old boss, the late great Dr David Fearn, used to complain that Xenon wasn't as good as mercury, which they used in ion drives in the 60s. Xenon did have the upside that you didn't have to put on chemical weapons suits when you opened the vacuum chamber and took a drive out. Mercury plasma is not particularly good for one's health. They used to have mercury alarms in the 3m vacuum chamber building. Scary.
All of the world's Helium supply comes from Alpha decay underground. Nature is okay with fission, but not this chain-fission ox we've yoked. The element Promethium was discovered as a result of nuclear experiments. I think it's the most aptly named of any Element artificially discovered. Promethius stole fire from the gods. We stole fission from God while treading on his domain. We must treat lightly.
I have heard that fission wells are found in nature where a hollow in the surrounding fissile material fills with water, which acts as a moderator: it goes critical and boils the water out, and so on in cycles.
These video are great. These informative videos are all over TH-cam. There are many videos of nuclear engineers out there talking about nuke safety. You got to wonder if these video where out prior to TMI and Chernobyl would we have had those to events.
This is a good explanation of the physics behind nuclear reactors. I have one questrion, if the reactor is turned off, how has the xenon managed to build uip so much iafter an hour or two if the half life of the iodine is over six hours?
Could you restart it _very soon after_ (for whatever value of "very soon" you choose) the shutdown, before "too much" xenon had accumulated? Or is the xenon growth curve much steeper than presented here?
In principle, maybe? In practice, this would still risk needing to pull the control rods out enough that the reactor would easily run away? So instead of designing in some kind of automatically controlled rapid-restart process, they just flatly say that you must wait?
Absolutely, which is what the opeators did in Chernobyl. Every minute you waste after an accidental power drop helps the Xenon build up. The reason it's called a "pit" is because if you don't immediately restart the reaction, you literally won't be able to start it for a few days. The operators didn't do anything wrong and Xenon poisoning contributed little to nothing to the accident.
So what is the "special attribute" that makes Xe 135 so effective to poison a reactor? The electron orbits? Some attribute of the nucleus? I ask because I wonder if studying it can help uncover secrets of "quantum gravity".
This was a fascinating video. It helped me understand the Xenon poisoning and reckless behavior at Chernobyl. I do have a question. In current day reactors can they measure the Xe-135 concentration in a reactor ? Could they do so at Chernobyl or any reactor of that time period ?
Sorry for the long post, but I need to make a correction and clear up a bit of misinformation.
As a licensed nuclear reactor operator with 20 years of experience, who has operated 11 different individual reactors of 3 different designs in his career, I can tell you that you are absolutely wrong about having to wait 3 days to restart a reactor. Not only is it not impossible to restart before then, it's not even dangerous or uncontrollable as long as it is done properly. I have personally performed fast-recovery startups on US Navy reactors anywhere from a couple of minutes to a couple of hours after a scram. I have also personally shut down US civilian reactors and restarted them the very next day, due to various maintenance needs.
In either case, xenon does have to be taken into account, and there are procedural limitations, of course. But, in fact, some of the xenon heavy startups I've personally done have been the smoothest and easiest startups, because you can essentially ride the xenon curve as it decays away, which makes it so that you don't have to add nearly as much positive reactivity as you ramp up, since xenon burnout provides you with that.
The rate at which you ramp down absolutely affects your xenon concentration. In Chernobyl, they let power drop extremely fast, which created an absolutely huge concentration of xenon. Their reactor went completely subcritical. In all of my training and all of our procedures, if we ever end up in a state where the reactor is truly subcritical (-1/3 DPM SUR), we are required to shut it down. If you end up creating that large of a xenon concentration, it would require far too much positive reactivity to be added to offset it, just to maintain power, let alone raise it back up. That's the problem with what happened at Chernobyl. It's not that shutting down a reactor means you can't restart it for 3 days, it means improperly controlling your reactor to let it get that far out of bounds, and then adding too much positive reactivity too quickly will get you into trouble. If done properly, you do not need to wait 3 days.
Respectfully, I am not a nuclear engineer. But I have been trained by the US Navy, to operate their reactors, as well as being trained by my current company, and licensed by the NRC to operate their reactors, and I have 2 decades of experience, combined. I studied all of the reactor physics formulas, and used to be able to calculate the various values, most of which I have long since forgotten the specifics of, because you don't calculate those things on a daily basis...or ever...in regards to operating a reactor. I would expect reactor engineers to know more specifics about fuel loading, enrichment, and all of the engineering calculations to evaluate a reactor's performance. But actual operators, who physically control the reactors on a daily basis, have a lot better knowledge on actual operations. A chemical engineer, for instance, would know a lot more about engine management and fuel control for an engine, but the truck driver with a CDL and 20 years experience would surely know a lot more about the nuances of what gear to select when approaching a certain grade with different sized loads behind him.
No offense intended. I am not meaning to criticize anyone, here, I am just trying to clear up a bit of a misconception that you seem to have. Because I have absolutely done this myself on numerous occasions, with no ill effect, and in a perfectly smooth and controlled manner. There is no 3 day limit before you can restart a reactor. That's just absolutely not true.
How does this comment not have more likes? It's great to see people with experience commenting in this - great to have you Adam. E.g. I'm a physicist, and while I understand the detailed particle physics, the engineering/practical aspects of this are *way* beyond me. For instance, when you comment "ride the xenon curve" so it's easier to increase reactivity without having to remove further control rods, I've got not idea roughly what fraction would typically have to be removed. I understand approximately that this is to offset other negative reactivity coefficients of temperature (void, thermal expansions etc), and that Chernobyl's positive void coefficient was on reason it ramped up so quickly after the xenon shut-down, but have no "feel" for how this works in practice. So it's great to read this. Having said that, these videos are still Nuclear Physics 101 - a great intro, but fairly basic details, so I think that his statement about "needing to shut down for three days" is close enough of an approximation to be justified.
Oh, and BTW Adam - when you mention " I studied all of the reactor physics formulas, and used to be able to calculate the various values, most of which I have long since forgotten the specifics of, because you don't calculate those things on a daily basis...or ever...in regards to operating a reactor." this was one of the issues at Chernobyl - their computer, SKALA, to calculate these things took 15 minutes to estimate reactivity through various calculations, and even then I suspect it didn't do a good job, since the reactor was so large, the reactivity varied a lot over the core. So all the fancy nuclear engineering theory in the world (at the time) could not have helped them, and they should have just followed the ****ing safety protocols.
@@clancyjames585 In response to your second comment (I saw them out of order in my notifications)
I agree with you 100%. I don't know the specifics about the day to day reactivity calculations at Chernobyl, of course. With a reactor design like theirs, with a graphite moderator giving it a positive void coefficient, and thus positive temperature feedback, my understanding is that they quite frequently had rods moving fairly regularly to maintain everything. We very seldom move rods, because it's just not needed at our plants. Our plants are very stable when it comes to reactivity.
The Navy reactors I used to operate were small enough in size, and were very VERY responsive, due to a very high enrichment of U-235, so on those, you really didn't need to calculate anything. You just basically moved control rods a small bit, and you pretty much knew the result from a certain amount of rod motion, and it was very even and predictable. Like driving your car, you don't have to calculate how far to push the gas pedal to drive. Plus, the Navy reactors were responsive enough to negative temperature feedback that you usually would not even need to adjust control rods when you changed power. Raise or lower turbine steam flow, and within a few seconds, the reactor would respond and stabilize at the new power level.
The commercial reactor I operate now is a different beast entirely. Much lower enrichment, and very large in size (though smaller than Chernobyl, by quite a bit). We do have negative temperature feedback (unlike Chernobyl), but it's a bit slower to respond than the Navy cores. Our reactor design is inherently very stable, and it has all of the negative feedback aspects to make it essentially remain stable with no continuous manipulations or input at all. Normally, we only make a slight adjustment to the boron concentration every few hours, but that's all it takes to remain stable. Moving the plant around is a bit more involved, but our rods operate automatically to maintain temperature, and we simply have to adjust boron concentration to keep rods from moving too far and changing the power distribution. Easily managed, with no complex calculations required. A spreadsheet can calculate the required adjustments almost instantly. A few simple thumbrules are also used for rapid power reductions, so the reactivity spreadsheet really isn't even needed.
Probably one of the biggest differences in our fundamental operation is that if we ever drove the reactor subcritical, like they did at Chernobyl, we would immediately trip/scram our reactor. We would never let power fall so quickly in the first place, and even if we did, we would not rapidly add tons of positive reactivity to quickly restore power, and certainly not outside of design limits. It's just not something we would do. We just have a different safety culture, and of course, the industry has learned quite a lot from accidents like the one at Chernobyl.
@@clancyjames585 In response to your first comment
Completely true. I certainly don't want to come off as bashing this video, I mainly just wanted to correct that one particular point, but you are right, this is basic level stuff here, and it doesn't need to be needlessly overcomplicated for most people.
To get a little more in depth about riding the xenon curve, the biggest thing we aim to control at my plant is temperature. Sure, there is a limit on power that we cannot exceed, but at the end of the day, the main thing we are driving by is the temperature. We have a certain temperature to maintain at any given power level. If temperature is too high, it means the power output of the reactor is higher than the turbine. If temperature is too low, it means the turbine is making more power than the reactor.
What basically happens is that to raise power, we have to open our governor valves and admit more steam to the turbine, to push the generator harder, and make more electrical power. As the governor valves open, it draws off more steam, which cools down the reactor. The turbine power is rising above the power of the reactor, so you have to add positive reactivity to bring reactor power up to match the turbine, and bring temperature back to where it is supposed to be.
We have two ways of doing that at my plant (PWR reactor), rods and boron. We have a certain amount of boron dissolved in the coolant which is a neutron absorber. Need to add positive reactivity? Either dilute out some boron (add fresh water with no boron in it, and drain out a little bit of water that has boron in it), or move control rods out. If you move rods out, it makes the power distribution move physically higher up in the core. If you dilute boron out, it moves power lower in the core. So we move rods a little bit, and dilute a little bit to keep power balanced in the middle of the core.
More steam to the turbine, cools the reactor, dilute or withdraw rods to keep the reactor temperature up, repeat. As power goes up, it also adds negative reactivity due to the fuel temperature going up, though, so we have to add a little bit more positive reactivity (rods/dilutions) to overcome that bit of negative reactivity.
It's all fairly balanced and easy to predict and manage. The only wild card is xenon. If you start with a xenon free core (like it would be a few days after shutdown) and startup the reactor and raise power, xenon will build up as you raise power. So, in that case, you have to add positive reactivity to overcome the temperature change from drawing off more steam, add positive reactivity to offset the negative reactivity from rising fuel temperature, and then add some more positive reactivity to offset the negative reactivity due to xenon building up.
I hope all that is clear and makes sense. What's different is if, for instance, you were to trip/scram the reactor, and then start up the next day. On a shutdown or significant down power, xenon builds up rapidly, as explained in the video. You end up with a huge concentration of xenon. Now when you go to start up, the opposite happens. You're raising power, and burning xenon out, rapidly. As xenon burns out, it's adding positive reactivity. This is basically what got the Chernobyl guys in trouble, and started off their problems. But, if you're doing things in a controlled manner, the xenon burnout can help you. You're drawing off more steam to raise turbine power, so you still need to add positive reactivity to keep temperature up and to offset the negative reactivity of fuel temperature rise, but now, xenon is burning out, not building up, so xenon is giving you positive reactivity to help you out. It makes it so that you end up moving rods less, and diluting less boron out of the reactor, because xenon is giving you positive reactivity.
In the end, it's all going to balance out, though. But starting up with xenon burning out can make the startup and power rise go a lot smoother, because it can sort of raise power on its own.
Oh, and as to what fraction of rods would typically be removed, that's not quite how it works with our cores. Our cores are designed to operate with all rods completely removed, once everything is balanced out at 100% power. We are not at all designed like Chernobyl. Specifically, at my plant, we have 6 banks of rods that are removed one bank at a time, with some small overlap between banks. We are designed to go critical when the last bank is about 3/4 of the way from being completely removed. We calculate how much boron we need to go critical at a given rod height, and we set those conditions before we remove any rods. Once we start up and go critical, we still have about 1/4 of the rod height on that last bank, to help control and manage things as we ramp up in power. Over the next week or so after a startup, we slowly adjust boron concentration and slowly withdraw the rods fully. We really only use rods for "shaping flux" and controlling where the reactor makes power, but it will naturally center itself, and we can get the rods fully removed from the core.
What I was basically saying is "riding xenon" will make it so that you don't have to pull rods out as quickly, and don't have to dilute as much or as often. We're still going to end up moving rods all the way out, we just go from maybe moving rods every 10 or 20 minutes, to maybe every hour. Since xenon burnout gives us some positive reactivity, we don't have to add as much positive reactivity due to rods/dilutions.
I know this was very wordy, but I hope it makes some sense. Feel free to ask any questions if you're curious or want to know more, or if something isn't clear.
There was a hot spot in the bottom of the core, of which the controllers were unaware. That certainly must have contributed to the explosion. And while I am sure that could be done with western reactors, I am not so sure about the RMBK-1000 reactors those engineers were operating. Hopefully, you never had to operate a reactor capable of going runaway like those.......
Don't know how the youtube algorithm brought me here but I find these lectures extremely interesting
I'm not even THAT interested in nuclear engineering, but I'll watch a lot of introductory level lectures that I wouldn't otherwise watch when there's this good of a teacher. Of course, you can't really know that what he's saying is true for sure unless you do some much more serious studying, or at least look more deeply into his credentials. But just watching stuff like this casually as a non-student can be very edutaining..
It's because the TH-cam algo is perfect. You watch one freakin Pointer Sisters video - and here you are ;)
When I was in the Navy I saw the effects of Xenon poisoning first hand. We were near end of core life, had maybe 9 months or so left max (we where scheduled to decommission in about 8 months), and we had been steaming down the coast of California at all ahead full for better part of a day. All ahead full is 100% power.
We were passing San Francisco and Captain wanted to slow down and come to periscope depth to tow the radio lines and get the mail as well as to give the crew practice tracking surface ships in a busy shipping lane. Coming off the bell, reduced our power demand on the reactor significantly so the Xenon spiked very high. Being an old core, she produced a LOT of Xenon and handled it not too well. The reactor operator (I was on watch as the throttleman controlling the steam valves on the main steam turbines) had to start shimming the control rods out to keep temperature steady.
He kept going until all the control rods were pulled out and still we remained at 1/3 power. Finally, he couldn't maintain temperature in the operating band anymore and we watched as the reactor began to cool off as it struggled to maintain power. So the reactor operator advised to the officer of the watch to come back up on the bell so reactor power would rise and burn off the xenon faster and that he was unable to keep temperature in the operating band anymore.
The officer of the watch informed the con (control center) and told the Captain we needed to come up on the bell or Xenon poisoning would shut down the reactor. So the order went out to pull the radio cables back in and 2 minutes later I was ordered to open the throttles back to all ahead full.
I did as ordered and we began drawing much more steam again and in so doing, cooled the reactor coolant even more. This colder water caused reactor power to rise, as expected, and this in turn warmed the reactor back up. It also increased the neutron flux and burned off the Xenon transient faster and in short order the reactor operator was able to start shimming control rods back into the core.
We had all been trained on this, the theory and physics as part of our nuclear training by the Navy. To see this first hand and to see the reactor behave EXACTLY as expected in a Xenon transient was pretty cool.
When it comes to handling them and reducing power responsibly, it is wisest to reduce power slowly and gradually over a period of 24-48 hours so the Xenon transient is controlled the entire way through. Newer reactor cores don't have to worry about this near as much since the ambient neutron flux is so high, even at lower power, that it burns the Xenon decay products off fairly fast.
this story was badass, nuclear engineering fascinates me. Its ashame its applications aren't recognized more often.
Very interesting info but let me correct your last statement. The so called by you newer cores do not worry much about the xenon indeed but for a different reason than the one you said. The freshly reloaded core has a lot of excess reactivity while the old one has almost none. The xenon poisoning eats some of the remaining excess reactivity. Since the newer core has plenty of excess reactivity the poisoning effect is significantly reduced. And the neutron flux is less in newer core than the older one. That is because the newer core has more fissile elements and less poisons (decay products) and therefor needs less flux to reach rated power. The older core (near end of campaign) has less fissile elements and more poisons and therefor needs more flux to reach rated power.
@@dgenov Except....aren't newer designs ....supposed to have to retain single fuel load for 2-3 decades? Shouldn't that impact this excess reactivity.
I thanks for the reactor story. Very interesting.
@@piotrd.4850 All military designs are meant for multiple decades. But, that is subject to a disclaimer: Mileage may vary depending on use. So the time a core is good for depends on how heavy a load and for how long said load is placed upon it.
Those 2-3 decade life expectencies are based on the accumulated logs of decades of reactor operation from hundreds of nuclear powered ships since the USS Nautilus was first launched.
The amount of reactivity in a core is dependent upon:
1) Core geometry (physical layout of components)
2) Core physical size
3) Age
4) Amount of rated power consumed to date (The "fuel" tank of a reactor is rated in "EFPH" "Effective Full Power Hours" or how many hours at 100% power is the core engineered for)
5) Uranium purity. Civilian reactors try to get as close to 20% enrichment with U-235 without actually reaching 20%. 20% is the point Uranium is considered highly enriched and minimum for weapons grade, thus restricted. Military reactors are not bound by this restriction...
Continued refinement in all of these categories is what allows for such length lifespans for such tiny sized reactors despite being capable of 100+ megawatts of output at full power.
well thanks I am now more confident to run my reactor responsibly
Do you work at the Springfield reactor?
@Will K
Why you little...
Homer can do it so we all can.
@@willk6464 Cedar creek :D
Best response 😂😂😂
I've read descriptions of the Chernobyl accident that mentioned xenon poisoning and it's effect on the reactor but never really understood what it was. This video provided an excellent explanation of the phenomena.
Nope. Going over the regulation list was the cause.
Akimow should use the water for "cooling" the rector...it would end with the moderate damage. Because it was SL-1 in bigger version...
There were a bunch of different things that combined to create the Chernobyl disaster. Xenon poisoning was definitely one of them. Xenon poisoning was the entire reason that the flow of coolant was reduced greatly AND the reason that the safety system that operated the control rods was disabled so more than the allowed number of control rods could be removed in an attempt to overcome the Xenon poisoning. The runaway reaction was caused directly by the lack of control rods in the reactor (creating serious "hot spots" since the minimum 24 rods arranged throughout the reactor that were ALWAYS supposed to stay put were mostly removed) and the lack of coolant being pumped was what caused steam voids to form in the coolant channels in these hot spots.
Once those two things happened it was all over. Obviously the positive void coefficient and the flaw in the control rods were instrumental too.
@@danlorett2184
Those "rods" are called buffers. They were created to suppress the "power jumps" during the shut-down.
Of course you can flood reactor with water and whole reaction would be killed.
Diatłow thought about that but Akimow, pissed enough on rough old man, used AZ-5 thus blowing the nuclear reactor.
No one listened young Tuptonow...
P.S. I believe it was iodine, no the xenon that caused the problem. I-135 with half-life of HOURS! (6.57 h) Also open to neutrons.
Sounds so simple ... and logical.
@@danlorett2184 Xenon poisoning is not cause of Chernobyl disaster for the same reason that gravity wasn't a cause of Columbia disaster. Xenon poisoning is just a physical fact. You design your system to deal with it. And if you did not design it to deal with it the cause of the disaster is you, not Xenon poisoning.
This has to be some of the most interesting content on TH-cam. Your explanation, and clarification of complex topics makes this so much easier to understand for people who have not gone to 8+ years of university.
it makes it easier for me(a person who have gone to 8+ years of university) to understand too.
The new Moltex plant going through safety homologation at New Brunswick in Canada has a highly negative power coefficient. It can sit with the load disconnected at full power settings and not overheat. It’s fully self regulated. They have avoided the Xenon problem by venting the fuel tubes.
The reactor core uses a uranium chloride fuel in a chloride salt carrier contained in vented fuel rods.
The primary coolant is the same chloride salt (without fuel) which transfers heat by convection to a tertiary salt. That is the exact same as used in thermal solar power.
Iodine and caesium react to salts so do not vent into the vents. Systems are in place to manage that if it happens.
Yes the Moltex design is very interesting. Though I'm puzzled why they switched from fluoride salts to chloride salts. I thought the negative void coefficient was because the fluorine had some moderating effect so a void in the coolant would reduce moderation. I'll have to read up on their new design.
This is like the 5th video I watch from this professor and I am a law student with nearly no knowledge of chemistry and physics , but nuclear energy has caught my attention so much. I know is more complex than just some videos in TH-cam, yet I feel fascinated.
I graduated with my ME and EE degrees decades ago, and I find these 'lecturettes' really interesting and very well done. Nice to know they appeal to non-technical people too.
"Like a really good paper towel" 😂😂😂 gold, "Honey, can you get the neutron absorbent towels? I split a bowl of U-235"
As Mork (Mork & Mindy) said, “Oh come on folks. Just use a can of NukeAway”.
Your lessons are amazing. I've learned so much in just a day. If only every professor could be as good as you.
This guy is so good at writing backwards it's hard to pay attention sometimes
He is almost certainly writing normally and the video is mirror in post production.
Note that his coat buttons are on the wrong (left) side. He’s writing left handed but is most likely right handed.
@@dp4racinggood eye. there's gotta be someone out there that could pull that off for real tho. Or not. But boy o boy do I hope there is. Cheers.
@@trainthetopchef This would be clever but not a realistic expectation for a professor.
I'd buy a coat with the buttons on the wrong side JUST to mess with guys like @@dp4racing
I am not sure which to be more impressed by: the detailed knowledge of nuclear fission which you can effortlessly relay or the way in which you can write backwards perfectly... I think I'll chose both.
Check my Oct 15 post to learn how he writes "backwards."
Thank you so much Professor. Your explanations are always clear and so well presented.
Best explanation I heard so far about Xe poisoning. Thank you professor. Wished I had this guy as my professor at university... LOL.
This was an extraordinary lecture. I knew the details about what happened and I know about Xe poisoning.....but all the interlaced physics of the decay chain I did not know about. This professor is really good; very very good at explaining this stuff.
What a fantastic presentation! Also, what a fantastic demonstration of the ability to both write, and draw Backwards!!!
You’re assuming he’s left-handed and the video hasn’t been mirrored. But you could be right.
Huh, I wasn't expecting to understand Chernobyl disaster better after this video, but here I am.
the guy tells garbage. Chernobyl did not explode because of xenon poisoning, it was human error and unknown technical problems for all reactors of this type (by the way, an American design and not a Russian development). The nuclear industry has learned a lot from Chernobyl and abolished graphite moderators, since once they burn they can no longer be extinguished.
1. Thanks TH-cam Algorithm for waking up this video.
2. One thing he gets wrong is that the engineers at Chernobyl knew about Xenon. They weren't stupid. They knew they were working with a poisoned reactor, but in the rush to finally get this stupid test out of the way, they tried to run the experiment anyway. They thought they could SCRAM the reactor and shutdown if anything went wrong. They figured, what's the worst that could happen, they shutdown and try again later? The reduced coolant flow (part of the test) triggered the rapid burnoff of Xenon, They tried to shutdown, but the control rod design caused them to increase reactor power at first before they started slowing the reaction and then pent up steam pressure from the overpowered reactor bent the rods to the point where they got stuck, and then coolant lines in the reactor exploded, but the reactor was designed to contain one or two exploding coolant channels. They thought it was a super safe design but in reality it was so unstable no one ever expected they would blow three or more at once. This blew the lid open, exposed the superheated graphite to oxygen in the air, and that caused the main explosion. Soviet physicists knew about the control rods. They knew that the rods could cause an unexpected spike in power when first inserting them. They saw this happen in a previous incident, but they purposely withheld this information from the plant engineers. If they had known they wouldn't have messed around like this.
@@johns8364 Either way it was still human error whether they intended to run a poisoned reactor or not.
I only wish you had more of these online. You are obviously well informed. Thank you for these great videos.
Me and my daughter love your channel. You are assume sir. Thanks for sharing your teachings.
You are very talented at explaining difficult topics in a simple and intuitive way, and I appreciate what you're doing!
Does anyone appreciate that not only is he a great professor, but he IS writing backwards for us to see it the right way? Just shows how his brain works. Intelligent.
I'm pretty sure the video is mirrored. Pins usually go on the left side of the lapel and his is on the right. Also, his wedding ring is on his right ring finger.
pokemoncars as if this channel doesn’t make feel dumb enough....
Wonderful lecturer. Plain talk for lay people like me. I read a bit about Chernoble and the technical issues that led to the explosion. Now I understand it better.
The wow factor for me is that after a shut down, one must wait many hours before restarting it....if you don't big bang!
At 5:56 you say "and Iodine-135, unlike Xenon-135, is radioactive". At 7:55 you say "It turns out that Xenon-135 itself is also radioactive".
Keeping you in suspense.
Good pickup. Didn't notice that! It seems that Xe-135 is radioactive and emits electrons with a half life of 9hrs - so it would be quickly exhausted anyway
Dear sir,
I would like to say: Thank You for this footage, about the Reactor Xenon poisoning. I am not nuclear specialist, only great enthusiast. Your videos are understandable for ordinary people. And even more: You describe all issues so good, that Your lectures are usefull also for visually impaired folks. That is my case, because I am unfortunatelly blind and therefore are such descriptions really important for me to understanding and learning new facts as best way as my handicap allows. So, thank You, sir! All the best from The Czech republic, stay safe and be healthy!
You were in the toilet while running the reactor core
I love these videos but the squeaky marker is just...extra. Thanks for doing such a great job! Very informative.
Stunning science channel here !! How I would have enjoyed to have this teaching passion at college. Hats off.
Excellent presentation. Thank you, I learned something.
A brilliantly clear explanation of the basics of fission & Xenon "poisoning". Thank you. Thank you. Thank you.
Dyatlov does not approve this video.
Why?
@@markthorne2296 - In the case that you are being funny: LOL!!! In the case that you are being serious: WHOOOOOSH....
He's still on the toilette.
Presentation seems sketchy. Send this man to the vent block roof to determine the truth!
He is delusional. Send him to infirmary: Comrade Dyatlov
This was outstandingly well explained and very interesting. Thank you for this video.
WOW, the best explanation and a great revision for me as a scientist (Ok I'm not a nuclear engineer). Fantastic. I just showed this to my 8 year old and even he understood this. I'll be subbing! Thanks for posting!
Sci-Fi author here with a rudimentary understanding of nuclear physics. This video was very helpful!
Just cause i am missing it in the video:
It is not that removing the control rods made it "suddenly" tip over and caused a runaway-effect.
Rather - the reactor was now running at a far too low level, extremely poisoned due to the way it was handled before, most safety-systems shut of, the automatic-control disabled, the steamturbines partially shut down and most control rods, even those that should always stay inside the core, were many retracted entirely out of the core.
Now this is a big problem as the water started to boil at the rods and this reactor-design actually made the reactor More active when boiling, further increasing the output and the neutron-flux. This is 2:30 hours after the shutdown started - the xenon-release from iodine has slowed down already.
When this problem was noticed they started inserting the control-rods again and that had another problem: Those rods had a graphite-tip that would at first increase the power output before the moderating-part reached the core. Now the power-output went up significantly and some of the fuelrods broke in jammed the control rods.
So now we have a reactor with nearly no cooling, graphite that does not absorb but moderate the neutrons, the water boiling which also does not absorb the neutrons, little xenon being produced but a high flux burning the existing xenon away and a buildup of temperature and pressure.
at this point the reactor was also outputting several times its maximum rated capacity leading to the pressure form the steam rising extremely quickly to the point of rupturing the cooling-system and the first explosion.
The cause of the second explosion is not fully understood as well - there are no sensory-readings or useful survivor-accounts of what went on there - so there are a few hypothesis, the most likely nowadays seems to be yet another steam-explosion:
after the first explosion the reactor had no more cooling, the molten core heating up further and melting its way down likely came into contact with the rest of the water - you can imagine what happens when several tons of extremely hot molten metals, some of which are also very chemically active, come in contact and cover a large body of water - a really big explosion.
ABaumstumpf The second explosion was most likely a hydrogen detonation. You flash boil a bunch of water, as happens in a steam explosion, you have alot of leftover hydrogen, which likes in explode in of itself. Modern reactors are designed with blow out panels for this reason.
The second explosion might also be small nuclear explosion (a "fizzle"). The IAEA report www-pub.iaea.org/MTCD/Publications/PDF/Pub913e_web.pdf page 3 says that the total loss of water (e.g. after the first explosion has ruptured a lot of the pressure tubes) can lead to an increase reactivity of 4-5 beta. An addition of one beta alone to a normally running chain reaction means the reactor core is prompt critical.
@@willh8950 I assume the blow out panels are (as in other regular thermal power plants) in the secondary circuit of a PWR to relieve pressure if there are problems in the turbine/condensor etc. Venting the containment (if the pressure rises to high) is another thing.
I am so happy that I found this channel. Thank you.
In Soviet Union, reaction controls you!
I love this comment
Fascinating video. I knew nothing about Xenon poisoning, or how it related to the Chernobyl disaster. Thanks Professor!!!
what about Liquid Fluoride Reactors? Do they have the same "xenon problem" as typical lightwater reactors do?
I would guess not since the xenon would float to the top.
Yes, they do, but as LaserFur says, it tends to just collect at the top of the reactor and is drawn off. In general, a lot of fission products are poisonous (though none as much as Xenon), but in the LFTR they are in the liquid fuel/coolant, which is continuously drawn off, has the FPs removed, and is rebalanced with thorium and uranium, and then injected back into the reactor. Never stop for refueling, FPs always kept at a low level.
@@puncheex2 Sounds like a cheap way to make radioactive Xenon, or Cessium.
@@Zamolxes77 If that is your goal, yes.
@@puncheex2 I wonder how easy it is to maintain the operation of this "kidney" function. What were the servicing cycles at the Oak Ridge MSR?
Delayed neutrons is what’s making a nucleair reactor controllable. Love your video’s!
In fact, delayed neutrons is what making all of humanity's application of nuclear energy even possible at all. At least, until the reactors like BN-800 will become a mainstream solution.
I am a 14 year old nuclear science enthusiast from India , btw loved your explanation, that complex thing entered into my mind within 16 minutes.
Very interesting. I have clue about half of the time but the explanations are perfect and help me connect the dots.
Another note, is he writing backwards while giving this lecture? If so I’m even more impressed
Very good explonation!! Thank you :)
I like your professorial delivery.
Almost a complete picture.
What he omits is that when you DO manage start a Xenon-poisoned reactor, you rather rapidly burn off that Xenon.
This burnoff occurs dozens of times faster that the Xenon built up in the first place, and hundreds of times faster than the Xenon would normally have cleared itself.
So once your Xenon-poisoned reactor is running, you have to actively increase the control rods over the next couple of minutes, failure to do so will cause a runaway.
And a runaway, releasing more neutrons, burns off the Xenon even faster, speeding the runaway!!
Add to that the fact that the Soviet reactor at Chernobyl used water as part of its moderating structure. Lose the water, and the moderation increases, further accelerating the reactor!
So the moment your runaway causes your water to turn to steam, its bye-bye. The reactor instantly jumps to a higher state, burns off the remaining Xenon, jumps to a yet higher state, and all of a sudden you have a 30Gigawatt heatsource occurring in your 1 Gigawatt reactor housing, which simply cannot contain it.
it *probably* wasn't 30GW (nobody can tell for sure as all the instrumentation simply pegged), most likely "just" single digits of multiples, but still enough to eventually throw the reactor lid through the roof :D
In case of Chernobyl, what added insult to injury was the fact that the control rod mechanism was so painfully slow...had it been capable of a SCRAM by modern reactor standards, the plant would (probably...Dyatlov did a lot of things that night that he should not have ever done) still be in one piece. Damaged reactor, but probably still in one, albeit partially molten piece ;-)
@richard mccann Bear in mind that even if the reactor went prompt critical in 3 miliseconds, even with 30GW of power creation, it would take a couple seconds to heat up the ~ 5 tons of core to the point where it explodes. This inertia is actually a bad thing, as it delays the disruption of the core , allowing more energy to build up before it stops the reactor by disassembly.
But losing your moderator causing the reactor to shut down, not increase in power. The problem was not the water, it was the fact that the graphite provided moderation even without the water. Moderators slow down neutrons and only slow neutrons cause fission in U-235.
"Lose the water, and the moderation increases," this is certainly wrong. Water has two effects: it moderates the speed of neutrons from fast (directly after fission) to slow (thermal), as the cross section for splitting U-235 is much higher. But it also acts as a (mild) neutron poison, by neutron capture from hydrogen to deuterium (H-2). In a BWR or PWR, the sentence is: loose the water, and the moderation decreases, which brings down the reactivity. In RBMKs, the water is not primarily used for moderation, as graphite is used for this purpose. If the water goes away, the moderation is still fine but the neutron absorber qualities of water are lacking and the reactivity goes up. That is the reason for the positive void coefficient of RBMKs.
@@gunnarkaestle sigh.
Lose the water, and the percentage of neutrons that are moderated by the graphite (becoming suitable for fission) increased, *because* less are absorbed by the steam as compared to water.
Thus the reactor *as a whole* has more moderated neutrons capable of inducing fission. This is what I mean by "the moderation increases".
Which is, frankly, exactly what you are saying, but you are being an ass and arguing just for the sake of arguing simply because you do not understand english.
All explanations should be this clear. I tip my hat to you sir.
Do control rods ever become so saturated with neutrons they have absorbed that they need to be replaced?
@104th_Maverick It rather depends on what kind of materials (elements, compounds) one uses for control rods. See here for an explanation --> en.wikipedia.org/wiki/Control_rod
@@kurt44mg42 I read this article, and unfortunately it still doesn't answer 104th_Maverick's excellent question.
@MegaSexfanatic That's basically true, but there's a little more to it. I am a licensed operator at at PWR, and we do use boron as our primary reactivity control. We either borate (inject boric acid, which is water with dissolved boron) or dilute (add fresh water without boron) to control how much boron is in the reactor coolant (which is just ultra pure water with a certain amount of boron in it). We have a system that automatically maintains a certain volume, so whether you pump in boric acid to borate, or pump in fresh water to dilute, the same amount of water that's already in the system drains out to a large collection tank, which gets cleaned up and processed and eventually released to the environment once it's clean.
But, we do use control rods, as well. Our control rods are made of silver, indium, and cadmium. The control rods are normally used for starting up the reactor, and for controlling where in the core the power is being produced. But the control rods are also our emergency shutdown method - a reactor trip literally drops all of the control rods into the core to shut it down in an emergency.
There is a limit, of course. The way neutron absorbing materials work is to...well...absorb a neutron. That changes it into a different isotope. Some elements have several stable isotopes, some have very few. Each time an atom absorbs a neutron and becomes a different isotope, it may be better or worse at capturing another neutron, it may be stable and never absorb another neutron, or it might be unstable and decay (radioactive). I can't speak for all the different absorber materials, but generally, control rods are going to be made out of materials that can capture a very high number of neutrons before they lose that ability.
Speaking from personal experience, I have about 15 years experience at my current plant, and in that time, out of 96 control rods combined between two reactors, we have only replaced one single control rod. And that was due to a mechanical issue, not a neutron absorber issue. So, simple answer, yes, there is a finite number of neutrons a control rod can absorb, but it's a huge number, and replacing control rods is not at all a common thing. We reuse the same exact control rods over and over and over again.
Theoretically, yes, but I've never heard of it being done. The materials from which the reactor vessel is constructed is more likely to reach its end of useful life first due to neutron embrittlement.
Well done! Clear, thorough and enlightening.
This is possibly the best video about Chernobyl, and I mean that with all categories considered.
I'd disagree. I believe in 5th part of "Chernobyl" mini-series they've described pretty well in quite clear and understandable way what had happened and all major factors which contributed.
@@МихайлоСєльський Well, at that point it's a matter of personal preference. But the technical explanations laid here are overall more interesting to me, althought the serie was indeed quite good as well.
@Bill Laswell Saw it as well! It was pretty good too that's true.
@@МихайлоСєльський Isn't that the same mini-series that claimed the reactor would explode with a force between 2 and 4 megatons?
best explanation yet of the Xenon problem. Thanks!
Maybe the only question not directly addressed was that since xenon is a gas, why does it stay behind rather than ventilating out of the core. Being trapped in the solid fuel rods well enough that the escape rate is low or nil is perhaps the explanation.
David Ruzic: * Checks the comment section *
>> [marker squeaking sound intensifies]
I think I need a bit of clarification. If you stop a reactor and have a large build up of xenon, why can't you start back up again? Starting up would mean increasing reactivity right? Since xenon is absorbing any neutron produced can't you just start up and wait for the xenon to decay back to its steady state? Would the issue be like he said where since it's so negatively reactive it's difficult to do this precisely and overshoot, leading to uncontrolled critical reaction?
How does he write so effortless in mirror image?: "I know something you do not know; I am NOT left handed!"
I suspect the video was mirror flipped when edited.
This was one of those videos which got suggested to me, even though it's not something I was intending to watch, or have any major interest in knowing about. Even though it's basically just an oral presentation, with a whiteboard kind of thing, I stayed glued to it until the end. Impressive :)
"Like really good paper towel" 7:14
literally made me laugh out loud
Bounty vs the competition.
Because paper can block alpha emissions/neutrons.
Fantastic story of technical details of nuclear reactors in general and specefics of the Chernobyl disaster.
They did know about Xenon-poisoning. The reactor could detect it ( by the typical drop of energy production) it even had a shut-down-automatic for this case. Only this automatic was disabled by a manual override.
i read somewhere that they knew about it, and even had a safety protocol , which pointed out to shut down the reactor in such a case, but Djatlov didnt give a fck and wanted to start the test anyways.
Dr. David, you are a great teacher! Thank you
Remember kids, "If you go to power down state, 3 days must you wait!"
And that is why you do not let nuclear plant engineers watch old episodes of Star Trek, where Scotty and Mr Spock breaks the laws of physics, and restarts reactor, and saves Enterprise from Burns up in the atmosphere.
Dr mosfet, Ah, the antimatter implosion calculation. Seems to have sent them back in time a few days too.
The Pointer Sisters "Neutron Dance" featured in Beverly Hills Cop! Great tune!
Glad I'm not the only one that caught this
The American media, even the latest popular Web series named Chernobyl looks over Xenon poisoning. All they focus on is the bad design of the RBMK reactor.
No media attention on the stupid things done by the operators.
It's like removing all the brakes of a car and complaining when the car crashed.
The lack of understanding of Xenon poisoning is the PRIMARY reason for Chernobyl compared to the graphite tipped control rods.
Funnily enough, the RBMK reactors aren't that bad. Besides the carbon tipped control rods.
@@mpk6664 Exactly! They are good enough with in built safety systems that insert control rods much before the reactor becomes unstable.
That prick Dyatlov oversaw disabling ALL automatic safety systems and ignored the computer warnings.
The only flaw I see was the absence of an extra containment building
There's a reason nobody else uses commercial graphite moderated reactors
The show actually discussed both, and set them up as legitimate reasons. First, I think the show actually did a bad job calling these graphite tipped. The way a RBMK reactor is designed there is a graphite rod at the bottom of the control rod, if you lift the control rod up, you are lifting the graphite rod up into the reactor to replace the control rod. There is also a void between the two rods which has some displaced water between them. The issue is that when the graphite moderator is fully elevated, displaced water goes into the bottom, like a cap, because the fuel rods are longer than the graphite rods. The issue in this design, is that as soon as you scram the reactor and inserts all of the control rods, the first thing that is going to happen is the water will displace, and the graphite will fill the void. When this happened it created a hotspot of intense heat, for just a few seconds, this was enough to burst and break the control rods, fixing them in place. Since they were fixed in place, the reaction never slowed, vaporizing all of the water and turning it into a steam bomb that blew off the top of the reactor, allowing oxygen in, which should never be present there, and that triggered the explosion and fire. So yes, xenon poisoning contributed the disaster, but the real cause was an emergency shutdown system that was literally a nuclear bomb detonator. Sure, xenon poisoning caused the reactor to go critical, but the emergency shutdown should have instantly shut down the reaction, and instead made a huge explosion of thermal energy. Hope that helps.
I'm not sure if you completed the web series, but the last episode had a huge section dedicated to just explaining the Xenon Poisoning. Azimov even tells Dyatlov, "the reactor is in a xenon pit, we have to shut down, we have to wait 24 hours." He then asks Dyatlov to record his order in the book, who then smacks it out of his hands and orders him to do it or never work in any reactor, anywhere, ever again. There was absolutely someone in that room, that not only knew this rule, but protested the orders they were being given. Dyatlov knew all about this rule as well, this wasn't ignorance. He was defiant, because in his younger years there was an accident that had exposed him to lethal doses of radiation and he was fine, he lived believing he was invincible. Despite this, his son died of Leukemia, due to contamination that he brought home from the earlier incident. He was a stubborn idiot, who literally ordered his crew to turn a reactor into a nuclear bomb, despite every regulation otherwise. Valery says this in his speech at the end "Dyatlov broke every rule we had, every one of them, but he did so with the belief that there was an emergency shutdown system that could prevent what happened." I'll remind you that even after the incident, Dyatlov was so certain that this event could have never happened, that he sent his men into the core, killing them with radiation poisoning.
What is your take on the fully integrated, molten salt, thermal spectrum, graphite moderated reactor? Do you think the plumbing and the separation chemistry will work? Including helium - vacuum sparging of the molten salt? without helium sparging the neutron economy won't work, agree?
I shuddered when he said "by pushing the control rod into the reactor" and drew an up arrow. As a former US Navy reactor operator, I believe control rods should be inserted from top to bottom. If power is lost to the control rod drive mechanisms, the rod should fall into the core, instead of falling out.
I think it depends on the type of reactor. A PWR does exactly as you say, dropping control rods in. A BWR pushes it in from the bottom. There are advantages to bottom-entry control rods such as being able to refuel without removing the rods.
Bear in mind I'm just interested in this stuff rather than an expert and have only read this up on Wikipedia.
So you have to understand the Xenon curve…really well. Fascinating, read through some comments very insightful.
Great video!
Remember: three days folks!
But more importantly don’t let your fellow comrade convince you to build a RBMK reactor.
As the other comment said, 3 days might be excessive. You could restart it immediately. But don't expect any power output until the xenon has absorbed enough reaction. Whatever you do, don't do something stupid like pulling out control rods.
Sorry if I'm mistaken, but is it really true that they "accidentally" turned off the reactor during/before the Chernobyl disaster? (12:56). I was under the impression that the reactor had been running at half-power for a couple of hours, which led to the Xenon poisoning.
It ran at half power for many hours, around 1600MW but the test was supposed to be run between 700 and 900 MW, so they further decreased power. The xenon poisoning was building in amounts from the reactor running at full 3200MW earlier in the day and as you say then at 1600 MW for many hours- when they decreased the power it unexpectedly continued to fall below 700 MW( perhaps from xenon concentrations) all the way to 30MW! So in effect the reactor was completely shut down and likely loaded with xenon.
@@brianmohr4674 This test was supposed to be done between 700 MW and 900 MW of electric power but they ran it at 200 MW. Chief guy ordered to perform the test at 200 MW, reasoning that it will be safe but it turned out that reactor doesn't care about experimenters thought on the matter. As the result, due to interference of one idiot, the humanity is still dependent on fossil fuels like oil and gas.
@@brianmohr4674 By the way, ALL of RBMK based blocks had the same test performed successfully, without any kind of accidents. The only difference was that this test was done properly, according to regulations, without one-sided alteration of instruction done by one person in charge. Chernobyl #4 was quite a surprise because nobody even had a thought that somebody would dare to do such a thing.
That was a great lecture!!! But remember kids don't let your mom pick out your clothes. This is important. :-)
Especial in the 80s😁
Excellent video. Maybe I missed it but how and why does Xenon cause instability in the reaction process? Anyone know?
David correct me if I’m wrong but , Xenon is a by product of the nuclear fission that occurs and over 50 hours it keeps it’s left in check as long as the nuclear reaction is being powered . Once you shut the reactor down you have to wait 3 days to power it back up because the xenon can no longer keep its self is a control state. What happens in Chernobyl was that the reactor was being powered down and the engineers powered it back up to do their test . But since xenon was not being controlled it was choking the reactor and they began to pull control rods to boost the reactors power , and when they did that the run off of xenon and lack of control rods made a complete switch from being choked to highly powered thus causing the explosion
In a power plant, you want a constant number of reactions (the neutron dance he talks about), which means each fission event on average you want to cause exactly 1 more fission event- less and you would continually lose power over time, more and you would start to exponentially grow power. So you need to constantly absorb just the right number of neutrons to maintain this balance. Control rods do this by being inserted more, or less, increasing or decreasing the amount of neutron absorption respectively. If the reactor is full of Xenon 135 it acts like a control rod- absorbing neutrons. However, when a neutron hits a control rod, it is still a control rod. When a neutron hits Xenon 135, it becomes Xenon 136, which IS NOT a neutron absorber. This means as you 'burn off' the xenon, you are a burning off neutron absorption, and increasing the probability of reaction, which in turn increases the rate of xenon burn off- a positive power feedback loop (i.e. instability).
I read this as xenos can be a problem and you’d still be right
filthy Xenos are always a problem unless you need target practice. lol
Purge the xenos...and the xenon
A great explanation about something I know only the basics about...I feel smarter...by a bunch. Thanks.
I wish I could also write things into the air when explaining things to people
Is the professor left handed and adept at writing backward or is this a 180 flip during rendering? Nevertheless he's good.
@@fiftystate1388 its a horizontal flip. same trick a lot of 'void talkers' use (like because science with Kyle)
Just get good.
i have always been fascinated by atomic energy, and videos like these are exactly what makes me happy
I just can't get beyond the squeaky pen
He does write well backwards.
Scarakus lol, yeah that's the first thing i noticed. First if this production style I've seen to be smart enough to flip the image.
i feel like they could remove it with a bit of a low-pass filter w/o affecting his speaking
Or the late '70s haircut.
More I try to focus on neutrons more I hear the squeaky pen
How big uranium power loss appears when we start reactor before that time? As there was 9h times 6% of decay product, then it should take less 30 minutes of total neutron absorbtion without power production.
But I believe that is not fully operating reactor, so just start of reactor is difficult...
How much time/energy would it take for starting reactor??
So Xenon is both a noble gas, and a Chernobyl gas
How dare you! 😂
Super interesting , a verry clear explanation you are a good teacher Thank you verry much.
Could you get rid of the xenon 135 in those 60 hours just by ventilating the reactor ?
Can you explain the process of the thorium reactor as clear as this cycle of the xenon gas.
Ventilating the reactor wouldn't help, because the xenon is not in the water. The xenon is physically in the uranium fuel pellets. We are not talking about bubbles of gas in the reactor, we are talking about random atoms of xenon scattered throughout the fuel pellets. The xenon is physically trapped within the core materials.
@@adamhutchins1981 Than you very much for the explanation it is very clear.
The xenon cant just be vented, it has to decay, which requires lots of heat. So normally all the workers in the plant hold their hair dryers against the reactor and that does the trick.
Dude the marker sounds
...
Cameron Wichman makes it great?
Good explication ! Thx from Brussels
This man is delusional get him to the infirmary
please explain.
@@c0461-e1s wow, thanks for answering without sarcasm, cause i was literally about to ask the same thing
@@c0461-e1s you're confused rbmk reactor don't explode
@Bill Laswell You must not get around TH-cam much. And/Or you never leave the realm of videos on nuclear reactions.
@@p5satanael Even with the safety upgrades after Chernobyl, the RBMK design (still 10 units in operation in Leningrad, Kursk and Smolensk) allows an explosion. A sudden loss of significant water masses (i.e. a large size LOCA), will increase the reactivity by 4-5 betas. A beta stands for the amount of delayed neutrons, which is the reason you can control a chain reactor in a nuclear reactor. One beta is the difference between prompt critical and (delayed) critical. Prompt critical means boom! as in atom boomb (even though badly designed atom bombs may fizzle and tear themselves apart before splitting a significant part of the nucleii).
www-pub.iaea.org/MTCD/Publications/PDF/Pub913e_web.pdf page 3
I just have to sub. This man knows how to teach.
Quite strange at the operators of Chernobyl didn't know the basic things how nuclear reaction is running.
Adelram Wolfrik They did but the man in charge allegedly overruled them in order to finish the test 😯
That's Socialism for ya.
@@iasimov5960 what does the power structure in a control room have to do with an economic system?
I think maybe you're using words you don't understand comrade.
At 6:00, he said that I-135, unlike Xe-135, is radioactive. And then, at 8:00, he said that Xe-135 is also radioactive. Which is it?
The Prof's screeching marker: not great, terrible.
It's keeps the attention! I think it's deliberate. He orders noisy markers.
Can you do a video about the thorium reactor as supposedly a better reactor than the uranium one? In other words, has the uranium industry prevented the development and use of the Thorium reactor?
Thorium vs Uranium is just a different fuel, which should last much longer. As of today, the problem for nuclear reactors are the not fuel costs, the high CAPEX is the reason that there is no real nuclear renaissance (except the Chinese activities) www.worldnuclearreport.org/IMG/pdf/figure_12_nuke-world-constructionstarts-1951-2019_china.pdf
Ooooooh! You are supposed to wait 3 days. Well I have been running my reactor at home incorrectly this whole time.
I'm really grateful for this information as well. Absolutely a must share for all my friends with reactors.
@@SteveJohnson007 Thank you Steven for your very informative videos. I am degreed in Electrical and Computer engineering, but I have always taken an interest in Nuclear engineer. Great content!
Not always true. In commercial reactors generally they restart the next day - 20-24 hours is enough for a lot of the Xenon to decay and the rest can be overcome by careful startup procedure.
no, thats jibberish. reactors DO NOT NEED three days between shut down and start up. building up that much xenon is a symptom of poor management, nominal levels will decay within the day
@@SteveJohnson007 too bad the three day thing is completely wrong
What about the gas (water-vapor) bubbles? Because Chernobyl was a BWR reactor, not a PWR, and the fuel cells were become hot, boiling the water...
So what bubbles does in a reactor? (way less h2o in a bubble than in water itself)
I thought this was about an Intel processor.
Xeon, not Xenon. lol
I thought this was about the warrior princess.
I used to build ion drives for the UK military. Xenon was our fuel; and a great fuel it was too. My old boss, the late great Dr David Fearn, used to complain that Xenon wasn't as good as mercury, which they used in ion drives in the 60s. Xenon did have the upside that you didn't have to put on chemical weapons suits when you opened the vacuum chamber and took a drive out. Mercury plasma is not particularly good for one's health. They used to have mercury alarms in the 3m vacuum chamber building. Scary.
My depdantism wishes me to point out that Xe-136 isn't stable, but its half-life is 10^21 years, so I'll let it slide
My "depdantism" wishes me to point out that you spelled pedantism wrong, but it's a youtube comment so I'll let it slide
Half life longer than the life of the Universe? Yeah it's STABLE !!!
Great Stuff! Brilliantly presented. Thank you.
It amazes me that nature seems to be trying NOT to do fission.
Or, at least, not steady, controlled fission. It is always a bit like balancing an inverted pendulum.
The problem with fission naturally is that it is typically all or nothing if you have enough fuel to go critical.
and yet ....
th-cam.com/video/pMjXAAxgR-M/w-d-xo.html
All of the world's Helium supply comes from Alpha decay underground. Nature is okay with fission, but not this chain-fission ox we've yoked. The element Promethium was discovered as a result of nuclear experiments. I think it's the most aptly named of any Element artificially discovered. Promethius stole fire from the gods. We stole fission from God while treading on his domain. We must treat lightly.
I have heard that fission wells are found in nature where a hollow in the surrounding fissile material fills with water, which acts as a moderator: it goes critical and boils the water out, and so on in cycles.
Is he writing in mirror image throughout the talk? Not some green screen trick? AWESOME!!!!
No. He's writing normally and they flip the entire video. It's the same thing Kyle Hill does.
How the hell does he write backwards like
they mirror the video in post
his jacket buttons are on the wrong side
@@AlexiLaiho227 - How observant of you.
These video are great. These informative videos are all over TH-cam. There are many videos of nuclear engineers out there talking about nuke safety. You got to wonder if these video where out prior to TMI and Chernobyl would we have had those to events.
Stop that squeegeeing sound
I can't handle that squeaky sound either.
Do they make a marker that is squeak free?
This is a good explanation of the physics behind nuclear reactors. I have one questrion, if the reactor is turned off, how has the xenon managed to build uip so much iafter an hour or two if the half life of the iodine is over six hours?
Interesting and informative, you do a great job, thank you for the video.
Could you restart it _very soon after_ (for whatever value of "very soon" you choose) the shutdown, before "too much" xenon had accumulated? Or is the xenon growth curve much steeper than presented here?
In principle, maybe? In practice, this would still risk needing to pull the control rods out enough that the reactor would easily run away? So instead of designing in some kind of automatically controlled rapid-restart process, they just flatly say that you must wait?
Absolutely, which is what the opeators did in Chernobyl. Every minute you waste after an accidental power drop helps the Xenon build up. The reason it's called a "pit" is because if you don't immediately restart the reaction, you literally won't be able to start it for a few days. The operators didn't do anything wrong and Xenon poisoning contributed little to nothing to the accident.
So what is the "special attribute" that makes Xe 135 so effective to poison a reactor? The electron orbits? Some attribute of the nucleus? I ask because I wonder if studying it can help uncover secrets of "quantum gravity".
This was very well explained. Other sites just left me more confused.
This was a fascinating video. It helped me understand the Xenon poisoning and reckless behavior at Chernobyl. I do have a question. In current day reactors can they measure the Xe-135 concentration in a reactor ? Could they do so at Chernobyl or any reactor of that time period ?