26. Chernobyl — How It Happened

The following content is provided under a Creative Commons license. Your support will help mit opencourseware continue to offer high-quality educational resources for free. To make a donation or view additional materials from hundreds of mit courses, visit mit opencourseware at ocw.mit.edu. So, like I told you, Friday marked the end of the most difficult part of the course and Monday marked the end of the most difficult group, so because the rest of her classes are going at full speed, this one will relax a little, so today. I would say sit back, relax and enjoy a nuclear catastrophe because we are going to explain what

happened

at Chernobyl now that you have the physics and intuitive experience to understand the actual sequence of events to begin with.

I want to show you something real. Footage of the Chernobyl reactor as it burned, so this is the part most people know about this: Footage taken from a helicopter of people inspecting or dropping materials into the reactor, it was probably a bad idea, wait where is it? smoke. Let's analyze what the smoke was, so that red stuff there is actually glowing graphite among other materials from the graphite fire that resulted from the burning of the rbmk reactor after the Chernobyl accident caused by flaws in the physical design of the rbmk reactor and the absolute operator. stupidity and negligence of any kind of safety system or safety culture, we are lucky to live here in the US, where our worst accident at Three Mile Island was actually not that big of an accident, there was a partial meltdown, there wasn't as much of a release of radionuclides into the atmosphere because we do things like build containment in our reactors if you think about what a typical reactor looks like if you consider that the mit reactor is a scaled down version of a normal reactor well let's say a commercial energy reactor , you have the core here, you have a lot of shielding around it and you have a dome that is quite thick that comprises the containment that would be the core, this would be some shielding, so this is what you find in us. and for most of the other reactors for the rbmk reactors there was no containment because it was thought that nothing could happen and boy were they wrong, so I want to explain to you a chronology of what really

happened

in the Chernobyl reactor that you can read in the nea or the nuclear energy agency website, the same place where Janus is located and we are going to reference many of the cross sections of Janus to explain why these types of events happened, so the goal of what What happened at Chernobyl was that they wanted to see if they could use the rotating turbine after shutting down the reactor to power the emergency systems in the reactor.

This would be after something called an external power loss if the external power or grid were to be disconnected from the reactor, the reactor automatically shuts down, but the turbine, as I showed you a couple of weeks ago, is a huge rotating mass of metal and machinery that stops for a long period of, say, hours and while it spins, the generator coils keep spinning and keep producing. electricity or they could be, so they wanted to find out if we can use the rotating turbine to power the emergency equipment if we lose external power, so they had to simulate this event, so what they actually decided to do is lower the reactor to a stalemate. moderate power level or very low power and see what comes out of the turbine itself or the generator.

Instead, there were now a lot of flaws in the design of the rbmk and I'd like to mention it here so we can talk about what it means. It looks and what's wrong with it, so the rbmk doesn't look like any of the US light water reactors you've seen before. Many of the components are the same. There is still a light water reactor cooling circuit where the water flowing around the fuel rods enters. a steam separator better known as a large heat exchanger and the steam drives a turbine which produces power and then this coolant pump keeps it running and then the water circulates.

What makes it different is that each of these fuel rods was inside its own pressure tube. so the coolant was pressurized and this thing here was the graphite composite moderator, unlike the light water reactors in the US, the coolant was not the only moderator in the reactor, there was also graphite, which meant that if the water disappeared, it would normally close. A light water reactor for lack of restraint was still there to slow down the neutrons towards the high fission cross section area and I would like to take out Janus and show you what I mean by the uranium cross section, so let's go again to uranium-235 and raise its fission cross section.

Z fission can also make it a little thicker, so again the goal of the moderator is to take neutrons of high energies, like 1 to 10 mev, where the fission cross section is relatively low, and slow them down. in this region where fission is, let's say, a thousand times more likely and in a light water reactor in the US, if the coolant disappears, so does the moderation and there is nothing left to slow down those neutrons to make the fission is more likely in the rbmk which is not In the case that the graphite is still there, the graphite is cooled with a mixture of helium and nitrogen because the neutron interactions in the graphite are slowing down.

We've always talked about what happens from the point of view of the neutron, but what about from the point of view of the? In other materials, any energy lost by the neutrons is gained by the moderator material, so the graphite gets very hot and has to flow a mixture of gases that do not contain oxygen, such as helium and nitrogen, which is quite inert to maintain the cold graphite and then between the graphite moderators where there were approximately 200 control rods, of which 30 had to be down in the reactor at any given time to control the power and that was a design rule that was broken during the actual experiment and then above here.

On top of this biological shield you could walk on it, so the top of those pressure tubes, despite being pieces of concrete weighing about 350 kilos, you could walk on them, it's also pretty cool, a little scary , so what happened in chronological order was Around midnight the decision was made to undergo this test and start spinning the turbine, but the grid operator came back and said no, you can't just reduce the power from the reactor to nothing, you have to keep it at a fairly high power for a while, about 500 megawatts of electricity or half the nominal power of the reactor and what that had the effect of doing is continuing to create fission products, including xenon 135 We haven't mentioned this one yet, you'll talk about it quite a bit in 2205 in neutron physics.

The black shirt really shows chalk, well what xenon 135 does is it just sits there, it's a noble gas, it has a half life of a few days, so it decays slowly, you know, the fission products go away , but it also absorbs a lot and a lot of neutrons, let's see if I can find which one is xenon, here we go, so here I have plotted the total cross section for xenon 135 and the absorption cross section and observed how, for low energies, practically the entire cross section. The xenon section is made up of absorption. Did you see in your task something that reached about 10 million barns?

No. Xenon-135 is one of the best neutron absorbers available and is constantly produced by reactors, so xenon builds up while they are running. 135 that they need to take into account in their sigma absorption cross section because, as you saw in the assignment, if you want to write what the sigma absorption cross section of the reactor is, it is the sum of each isotope in the reactor multiplied by its number density. its absorption cross section and that would include everything related to water and let's say the uranium and xenon that you are accumulating when the reactor starts, the number density of xenon is zero because you have nothing to have produced it. when it starts operating it will reach the equilibrium level of xenon where it will accumulate up to a certain level which will counteract the reactivity of the reactor and in its effective k expression where its sources over absorption plus leakage, this has the effect of increasing the sigma absorption. and reducing k is effective, the trick is that it doesn't last very long, they both decay with a half life of about five days and when you try to increase the power of the reactor you will also start to burn it out, so if you are operating at a fairly high power level low, they will both be breaking down and burning xenon without really knowing what is going on and that is exactly what happened here, so an hour later let me check the timeline again a little over an hour later, so that the reactor power stabilized at something like 30 megawatts and they said, What's going on?

Why is the reactor power so low? We need to increase the power of the reactor. So what do they do? A couple of things: one was removing all but six or seven of the running control rods. out of design specifications because 30 were needed to keep the reactor at a stable power while the xenon that had been building up was still there preventing the reactor from going critical, that was the main reason the reactor didn't . I even have a lot of power, but it was also burning at the same time, so in the meantime, let's say if we were to show a graph of two things, the xenon inventory time and as a continuous line and let's say the bar value control rod as a dotted line, The xenon inventory at full power would have been at some level and then start to decay and burn, while at the same time the control rod value, as you remove the control rods from the reactor, every time you remove one, you lose some control bar value. continue to taper off to the point where bad things were going to happen, let me make sure I don't lose my place, so anyway, when they started taking out the control rods, a couple of interesting quirks occurred in terms of feedback, so Let's see Going back to this design, like any reactor, this reactor had what is called a negative fuel temperature coefficient, what that means is that when the fuel is heated two things happen: one, the cross section for any absorption or fission would increase, but the number density would also increase.

As the atoms were physically spaced in the fuel, their number density would decrease, reducing the macroscopic cross section for fission and that is possibly a good thing, the problem is below twenty percent power, the reactor had what called a positive vacuum coefficient, which meant that if you boil the coolant, you increase the power of the reactor because the other thing that I think I mentioned once and that you calculated in the assignment is that the absorption cross section of hydrogen is not zero, it's small but pretty significant let's take a look at it because I can always see this on Janus we go back to hydrogen hydrogen one and look at the absorption cross section and of course it started with a linear scale let's go logarithmic ah okay a low energies, you know, 10 to the power of minus 8 to 10 to minus seven is around a barn, not very high but not at all insignificant, which meant that part of the normal functionality of the rbmk depended on the absorption of water to help absorb some of those neutrons without those neutrons, sorry.

Without that water, there was less absorption, but there was still a lot of moderation in this graphite moderator, so they could still get slow, but then there would be more and that would cause the power to increase and then that caused more of the water, the coolant to boil, which would cause less absorption which would cause the power to increase yes Charlie they didn't remove the water from the reactor however when the power started to increase some of the water started to boil so you can still have let's say that the steam flows and still removes some of the heat, however you don't have that denser water to act as an absorbent and that is what really destroyed this reactor.

Also, they decided to disable the eccs or the emergency core cooling system that you have. They weren't supposed to, they shut down several of these systems to see if the others could be powered from the spinning turbine, and then when they noticed the reactor was becoming less and less stable, they pulled out almost all the rods. some of these pressure tubes started crashing and jumping, these 350 kilogram pressure tube caps were just rattling around, I mean, imagine something that weighs, you know, 900 pounds or so, rattling around and there's a few hundred of them, so there was someone in the control room who said the caps are making noise what the hell he didn't make it down the spiral staircase because about 10 seconds later everything went wrong and that's why I want to open this real timeline so you can see it is divided from minutes to seconds due to the speed at whichThis started to go wrong, it was quite surprising, so, for example, the control rods were raised at 1:19 in the morning, two minutes later, when the power begins to become unstable, the channel covers of fuel, which again are like 350 kilogram blocks, begin to jump in their sockets. and a lot of that was we went back to the rbmk reactor when the coolant started boiling here.

That boiling force actually creates enormous pressure instabilities that would cause the pressure tubes to jump up and down, eventually rupturing almost every single one of them with enough force to fire these 350 kilo capsules and what did that do, what? They said, I like the language they used jumping in their sockets, so 50 seconds later the pressure in the steam drums fails, which means there has been some kind of containment leak, so the whole time the coolant was boiling, absorption was going down, power was going up, repeat, repeat, repeat and the power jumped to about a hundred times the rated power in about four seconds, so it was normally a thousand megawatt electric reactor, which is about 3200 thermal megawatts. producing almost half a terawatt of thermal energy over a very short period of time until it exploded now it's interesting that many people called

chernobyl

a nuclear explosion which is actually a misnomer a nuclear explosion would be a nuclear weapon something set off by a huge chain reaction heated mainly by fission or fusion which is not really what happened in Chernobyl or Fukushima, nor the worry at Three Mile Island, not to say it was not something horrible, but it was not a real nuclear explosion.

At first what happened was a pressure explosion, so there was a huge release of steam as the energy built up to 100 times the normal operating power, the force of the steam was so great that it actually blew the lid off. of the reactor. I think I have a photo of that somewhere here too, it should be further down. Yes, to give you a small idea of ​​the scale, the reactor casing, which weighed around a thousand tons, was launched into the air and landed on top of the reactor, sending most of the reactor components up to a kilometer high in the air four seconds later, followed by a hydrogen bomb. explosion, let me go back to that timeline, so yeah, at 123 and 40 seconds in the morning, oh yeah, so I have to mention why this happened.

Emergency insertion of all control rods. The last part that this diagram doesn't mention is these control rods and I'll draw this here, we have a tip with about six inches of graphite, so if these were two channels of graphite, let's say they're carbon and this is your control rod, The objective was to take this control bar to the interior of the reactor. The part they didn't mention was that they had about six inches of graphite in the tip, which only works as an additional moderator. Graphite is one of the lowest absorbing materials on the periodic table, I think only after oxygen, and if we pull up the cross sections of graphite, we have plotted here the total cross section, the elastic dispersion cross section and down here, in At the barn level of 0.001, the absorption cross section is about a thousand times smaller than that of water, so you are pushing more material into the reactor which slows down the neutrons even further, bringing them into the high fission region without absorbing anything and they jammed about halfway down, about two and a half feet down, leaving the extra graphite right in the center of the core, where it could do the most damage and it didn't take long, yeah, um. so I understand that also one of the designs was that the control rods didn't like to go down immediately, but they came down slowly, yeah, so it took about seven to ten seconds, okay, if they had a system where they They'll drop them, right?

I possibly shut down the system correctly, I'm not sure, I don't know if lowering the control rods on something that was experiencing steam explosions would have helped me at this point, it was all over whether you know it or not. the more extra abs what is it the extra moderator that was thrown in was the ultimate kick in the pants this thing needed to go absolutely crazy and if we go back to the timeline on the second level control bars inserted at 123 and 40 seconds of explosion four seconds later, at 120 times its maximum power, it is heading towards terrifying water, so one second later, the thousand ton cap is launched from the first explosion very shortly after the second explosion and that happened because to this reaction, well, anything that corrodes with water will. make virtually anything with oxide plus hydrogen, the same chemical explosion that was the downfall of Fukushima and was the concern on the three mile island that a hydrogen bubble was forming due to corrosion reactions with whatever was in it the nucleus.

This happens with zirconium quite strongly. but it also happens with other materials, if you oxidize something with water, you leave hydrogen behind and hydrogen in a very wide range of concentrations in the air is explosive, we are not actually allowed to use hydrogen at about four percent in any of labs here because that hits the flammability or explosive limit, so we were doing some for my Ph.D. We were doing these experiments corroding materials in liquid lead and we wanted to pour pure hydrogen in to see what happens when there's no oxygen. They told us no.

I had to drill a hole in the side of the wall for the hydrogen to vent to the outside and do some calculations to show if the entire hydrogen bottle was emptied in the lab at once, what I could do if the bottle cap would break. It doesn't reach a four percent concentration, so hydrogen explosions are pretty powerful things, have you ever seen people making water from scratch, mixing hydrogen and oxygen in a bottle and lighting a match? We have a video circulating here because for rtc for the reactor technology course. I do this in front of a group of CEOs and watch them jump out of their chairs to teach basic chemical reactions, but it's loud enough about enough hydrogen and oxygen to just fill this cup or fill a half-liter water bottle, it makes an explosion. . that makes your ears ring, not quite bleeding, but close enough, so that's what happened here, except on a much more massive scale, so there was a burst of steam followed seconds later by an explosion of hydrogen released from the corrosion reaction of everything with the water that was. was already there and that's when this happened, so there's smoke right there from a graphite fire, it's not normal smoke, spoke too soon abroad, this actually provides a perfect conduit for the transition from second to third part of this course, many of you have been waiting for.

Find out what the dose units are and what the biological and chemical effects of radiation are. Well, this is where you get them from neutron physics. You can understand why Chernobyl went wrong. Honestly, you've been doing this for three or four weeks, but With your knowledge of reactor cross-section feedback and criticality, you can begin to understand why Chernobyl had flaws in this design and what we're going to teach you in the rest of the course is what happens next, what happens when the animals absorb the radionuclides. of the human body and what were the main consequences, let's say in the colloquial sense and in the real sense of the Chernobyl reactor, let's look a little at what they did next, although foreign foreign, I think that sums up the state of things pretty well now .

They built a sarcophagus around this reactor, a gigantic tomb that, according to some reports, is not structurally sound and is in danger of partial collapse, so yes, there are more difficult efforts ahead, but now let's talk about what happened next. I'm going to jump to the At the end of this, the actual way the accident was noticed was the spread of the radioactive cloud to Sweden not so close by, so it was noticed that people entering a reactor in Sweden had contaminants that they thought that came from their own reactor. The first assumption, when it was determined that nothing was happening in the reactor in Sweden, people began to analyze the wind patterns and figure out what had happened and then it became clear that the USSR had tried to cover up the Chernobyl accident, but it was not can hide the consequences. and eventually it spread quite a bit covering most of Europe, Russia and surprisingly Spain was unlucky with the wind patterns that day or those few days so what happened is that a few days after the actual accident a graphite fire because graphite when exposed to air well, you can do the chemistry, add graphite more oxygen, you start producing carbon dioxide, so graphite burns when it's hot and as you can see in the video, where is that nice still image of molded graphite?

Yeah, that graphite was pretty hot, so a lot of that. The smoke included burning graphite and many of the materials from the reactor itself. Now, when you build up fission products in a reactor and volatilize them in this way, the ones that tend to come out first would be things like the noble gases, hence the entire inventory of xenon. from the reactor was released, it's estimated around one hundred percent and I can actually come up with those numbers when we talk about how much of what radionuclide was released. That's also a typo. If anyone wants to call, there is no isotope 33 of xenon that is supposed to. be 133. um, that would be interesting if someone wants to call and say that the nea has a bug, so 100 of the inventory release should be pretty obvious because it is a noble gas and it just floats away from the real dangers, although they come of iodine 131 about 50 percent of a three exo-becquerel activity so we're talking like mega curies or it could be giga I can't do those calculations in my head a lot of radiation and the problem with that is that iodine behaves like any other halogens form salts it's pretty volatile if any of you played with iodine before no one does oh okay what happens when you play with it?

I mean, yeah, and it just reacts with similar acids and stuff, okay, turns out I have extensive practice playing with iodine in my house because I did all the things you're not supposed to do as a kid, like build your own step from chemistry, stuff that you somehow know leaks out of your local high school somehow, iodine is pretty good, yeah. Sometimes it happens, um, if you put iodine on your hand, it actually sublimates, the heat from your hand is enough to go directly from solid to vapor, so the iodine was also quite volatile, some of it may have been in form of other compounds, part of it.

It may have been elemental, probably not likely, but there was certainly some iodine vapor and about half of that was released. The problem is that it then condenses and falls on anything green with surface area, so the biggest danger to people living nearby was eating leaves. vegetables because the loads that come out of the leaves lose their surface, iodine is deposited on them and is intensely radioactive for about a month or it is deposited on the grass that cows eat, which led to the problem of radioactive milk and that is why that milk in the Soviet Union was banned for a long time because it was one of the main sources of iodine contamination.

The other one that now also worries us in Fukushima is cesium, which has a chemistry similar to that of sodium and potassium. Again, it's quite a salty compound, quite a salty element. but it has a half-life of 30 years and if we look for it in the nuclide table we will see what it really releases. Oh well, it's back online. Anyone else noticed this broke a couple of days ago. Well luckily Brookhaven National Laboratory has a good version too, but let's take cesium, yes there is a lot of it out there. Cesium-137 beta decays to barium but it also emits gamma rays and most decays end up emitting one of those gamma rays, say a 660 kev gamma ray, so it's both. a beta emitter and a gamma emitter, now which of those types of radiation do you think is more harmful to biological organisms, beta or gamma?

You say gamma, why do you say that? Doesn't it stop? Beta does, but yes, cesium is better. known as yes, that's right, did I tell you this question? The question of the four cookies. Yes, you eat the gamma cookie because most of the gammas emitted by the cookie simply leave you and radiate to your friend, who will be the subject of piece number. eight, you see, that's why you guys are counting your whole bodies, talking about who's gotten your full body counts in uhs amazing, so it's almost everyone. They'll need that data for problem set eight, so schedule it soon, preferably before Thanksgiving, so I'll be able to take a look if anyonefound something interesting in their specters.

I'm glad to hear that, but you see a potassium spike that you can probably integrate and fix some problems, yeah, because it'll be fine anyway, yeah. the betas, that's the real killer, the gammas are going to come out, the cesium enters your body and it will most likely come out the other side because the mass attenuation coefficient of six, what is water to the gammas of 660 kev, let's find that table three, let's say you are? made primarily of water, water, liquid, which is practically human, 660 kv is right here, which leads to about 0.1 square centimeters per gram and with a density of 1 gram, which is a fairly low gamma attenuation, so What this graph actually shows is why most of the gammas of cesium that would be produced from ingestion, just say it, but it's the betas that are terribly short range.

Anybody remember the formula for range in general because it's going to come up again in our discussion of dosage and the integral biological effects of yes, of the stopping power of the negative and that stopping power is this simple formula, let's see what came out as log minus beta squared that simple little formula that I don't expect you to memorize, so don't worry about it, but if you integrate this, you find that the electron range of even one mev of electrons in water is not very high, so most of them stop near or near the cells that absorb them, causing quite a bit of DNA damage, which is eventually what causes the mutagenic effects in cancer cells. death, which we are going to talk about for the entire third part of the course, there is also concern about which organs actually absorb these radionuclides and iodine in particular is preferentially absorbed by the thyroid, so when we start to look at the amount of radioactive substances Remember that they said it was okay around April 26 or May 2, approximately, the release stopped, not according to our data, that was when the graphite fire resumed, in addition, the Chernobyl core, which It had undergone an almost complete meltdown, it was sitting in a pool on top of this concrete platform, so let's call this substance a liquid.

The actual word we use in the language is called corium. It's our ironic word for every element mixed into a hot radioactive soup. First of all, it started. to redistribute itself by reacting with the water that was present, turning it into steam and the steam caused further dispersion of radionuclides and eventually buried its way through and into the ground releasing more, you know, it's, uh, it's the worst nuclear thing ever. has happened in the history of nuclear things, quite a disaster and fortunately it subsided after this, but now let's see what happens next and This is a good introduction to the third part of the course.

Iodine is preferentially absorbed by the thyroid gland somewhere around here. Has anyone ever heard of the idea of ​​taking iodine tablets in the event of a nuclear disaster? Does anyone have any idea why? If you saturate your thyroid with iodine, if you ingest radioactive iodine, it is less likely to be permanently absorbed by the thyroid, so this provided some statistics on the likelihood of getting thyroid cancer from ingesting radioactive iodine. Fortunately, the statistics were quite poor, meaning that not many people were exposed, it was around 1300 or so, not millions, yes, 1300 people in total, but what I want to jump to is the dose versus risk curve and this will disprove our entire discussion of the long-term biological effects of radioactivity.

The most surprising thing you see as part of this curve. That's right, that's the first thing I saw. There are six different models for how dose and increased cancer risk occur, and they all fall within almost all of the error bars of these measurements. I repeat it. Thank goodness the error bars are so high because that means the sample size was very low, so when people say we don't really know how much radioactivity causes how much cancer, they're right because fortunately we don't have enough data on the Exposed people know this very, very well, so some people say we should be cautious.

I agree with them. Some people say there is no consensus yet. I agree with them too, but you can start estimating these kinds of things by knowing how much radiation. the energy was absorbed and in what organ, so I think the only technical thing I want to go over today is the different dosage units because as you start reading things in the reading, which I recommend you do if you haven't already . We're going to find many different units of radiation dose ranging from things like the renkin, which responds to a series of ionizations. You usually won't see this in some kind of biological language because it's the number of ionizations detected by some type. of the gas ionization detector, so the dosimeters that you all put in, did you bring these brass pendometers to the reactor?

Did anyone look through them to see what the dosage unit was? It will be in Renkins because that is directly correlatable. In addition to the number of ionizations that dosimeter has experienced, you will also see four dose units, two of which are only factors of 100 from each other. There is what is called rad and gray and what is called edge and sievert. see these approximated as grays, you will see them as r and they are usually written as rem, so a rad is simple, let's see that 100 rads is the same as a gray and 100 rem is the same as a sievert and gamma for that matter. of gamma radiation these units are actually the same and I particularly like this set of units because this is the if type of radiation units because it comes directly from measurable and calculable quantities like gray for example the actual unit of gray is joules absorbed per kilogram of absorbent It is a fairly simple unit to understand.

If you know how many radioactive particles or gamma particles or whatever you have absorbed, you can multiply that number by their energy, divide it by the mass of the organ absorbing them, and you will get your dose in gray sievert. some quality factor for the radiation multiplied by some quality factor for the specific type of tissue what this says is that some types of radiation are more effective at causing damage than others and some organs are more susceptible to radiation damage than others. Does anyone know anything? Of the organs that are most susceptible to radiation damage, soft tissue is like that because there are a lot of those stomach linings, yeah, yeah, uh, lungs, yeah, what else, thyroid, yeah, there's definitely one for the thyroid, bone marrow, others, your brain, actually, not so much, eyes.

And where else do you find rapidly dividing skin cells on your body? Yes, the dermis. I don't know about the liver, I guess so, it's a pretty active organ, but when people are worried about birth defects of the reproductive organs, the link here is for some. The reason is not told in the reading and I have never found out why the more often a cell divides, the more susceptible it is to having cancer risk because each cell division is a copy of its DNA and each time radiation enters and damages or changes that DNA by causing what is called a thymine bridge where two thymine bases join together or by damaging the structure in some other way, that gene then replicates and the faster they replicate, the more likely the cancer will become apparent , i guess.

This raises a question: when does a rapidly dividing cell become cancer? Is it division number one or is it when you notice it? I guess I'll leave that question to the biologists, but if you notice in the reading you'll see a bunch of different tissue equivalence factors and you'll see them tabulated and you'll say there they are, memorize them. I want you to try to think about the pattern between them, the tissues that basically don't matter, like the non-marrow part of bone dead skin. cells, muscles, things that are basically not on the list, they don't divide very quickly, but anywhere you find stem cells, the lining of your gut, your lungs, which take a lot of environmental damage, need to be replenished, the gonads, What was the other one we found?

Said eyes, these are places that are sensitive tissues or are rapidly dividing, so the sievert is in a sort of equivalent higher risk unit, so if you were to absorb a gamma ray gray versus an alpha gray, be about 20 times more likely to get cancer from alphas than gammas because of the amount of localized damage they cause to cells and we will do all of this in detail very soon and then for the tissue equivalence factor if you absorb a gray throughout your body, which means one joule per kilogram of average body mass versus one degree directly to the lining of your intestine, say, drinking tea with polonium as happened to a poor man, was it current or xkgb?, one of the Russians, no, it's the KGB guys who poisoned them, right?

Yes, remember in 2010 there was a Russian? It was like what was his name, let's see poisoning, did he really die from poisoning by Alexander Lidovenko? I'm not going to comment on politics, but the radiation effect clearly worked, unfortunately, so polonium is an alpha emitter and that caused a massive dose of alpha throughout his gastrointestinal tract and that caused a lot of damage to those cells in a short time. . In the case of cancer, it actually killed a lot of those stem cells and the way radiation poisoning would work is that if you kill the stem cells, the villi in the intestine that are responsible for absorbing nutrients die, you can't absorb the nutrients. nutrients and you basically starve.

It doesn't matter what you eat, it's messed up, yes, it's a bad way to go, it's called gastrointestinal syndrome and we'll talk about the progressive effects of acute radiation exposure, where you have immediate effects, mainly related to the death of someone. organ that is responsible for cell division to keep you alive or in extreme cases your neurological system and nerve function simply stops at the highest dose levels and that corresponds to doses of around four to six grays, four to six joules per kilogram of villi or body mass. it will kill you pretty quickly with very little chance of survival like what happened here and this was the problem with all the people living around and near Chernobyl and Ukraine and Belarus and everywhere where the contamination was quite extensive, it is estimated that about 4,000 people have died or contracted cancer because of this.

I can't believe how low that number is, but that's still 4,000 people that should never happen to and the effects were felt far away in cities like Amel and I can't read that one because there aren't enough pixels. Because of the way that, let's say, the rainwater was formed or, let's say, the steam cloud from the reactor was carried away, the rainwater caused it to fall in certain places that to this day may have an area of ​​contamination really big and this brings me a little He got into what we should care about Fukushima much less than we did about Chernobyl and the reason why Fukushima suffered a hydrogen explosion and released and continues to release cesium-137 into the ocean.

Luckily for us, the ocean is large and, with the exception of fish caught near Fukushima, although concentrations can be measured at hundreds to thousands of times normal concentrations, they can still be hundreds or thousands of times lower than consumption. sure, which is why I don't understand a lot of the problems you see in the news today. I'll call them lies, but I'll call them half-truths. People will show the plume of cesium-137 radiation escaping from Fukushima and that's true. There is radiation escaping. The question is whether it is high enough to cause a noticeable increase in cancer risk.

That's the question reporters should be asking themselves when they're only telling half the story that appeals to viewers and not telling half the story to complete the story and tell them whether they should be afraid or not, because unfortunately fear brings. viewers, this is the problem and I'm happy to go on camera saying this is the problem with today's media, with a half-truth and with a half-story you can incite real panic about non-physical issues that they may not actually exist and so it is important that the media tells the whole story yes it is true that the Fukushima lease releases cesium-137, how much?

However, it is the question that people and the media should be asking themselves and in the rest of this course we are going to answer the question. How much is too much? So I'll stop here since it's two of five and ask you if you have any questions about the whole second part of the course or what happened in Chernobyl. Yes, yes, could you explain the equality factor term? and how do you find that yes, the quality of the fat, well, there are two quality factors, there is the radiation quality factor, which will tell you how much, let's say, how much more cellular damage will be deposited in a certain amount of a certain type of radiation of the same energy.

The cell and tissue equivalence factor tells you what the additional risk is that sometype of defect leads to cell death or cancer or some other defect because of that radiation absorption, so to me the tissue equivalence factor approximates, but not completely, the rate of cell division. and the radiation quality factor will be quite proportional to the braking power. You'll see a term called linear energy transfer or let this be the unit of stopping power used in the biology community, it's stopping power and luckily Turner's reading actually says it's somewhere buried in a paragraph, come on to stop power, so if you start plotting these two together, you might find some surprising similarities.

I saw two other questions up here, yes, it will ask you why Chernobyl is still considered out of bounds most of the half lives of these things are in the range of days to answer that with numbers, most of the half lives were in the range of days to hours, but still cesium-137 with a half-life of 30 years was released in a third of exobecquerel is one of the main sources of contamination that still exist. Also, if we scroll down a little bit, there was quite a bit of inventory of plutonium with a half-life of 24,000 years, so we'll have Jake Heckler on Friday.

He comes in and tells of his travel diary to Chernobyl because one of our elders was in Chernobyl and his boots were so contaminated with plutonium that he will never be able to use them again. They have to stay wrapped in plastic, so some of these things last tens of thousands of years. years and although not many petabeckerals of plutonium were released, they are alpha emitters and are extremely dangerous when ingested, so vegetables and things that absorb radionuclides from the soil like moss and fungi are totally off limits in a wide range. of this area you will find a video online if you watch a mayor of a nearby town saying: "Oh they are perfectly safe to eat, look I eat them right here and I'm just saying read the comments to see what people have to say about". too smart, yeah, so what's the process like now?

What are they doing? The sarcophagus around the reactor has to be shored up to make sure nothing else comes out because most of the reactor is still there and let's say it's raining. The water comes in and starts dragging more things onto the ground or whatever. We don't want that to happen. Soil replacement and disposal as nuclear waste still continues. Removing fungus, moss lichen or anything with any type of radiation exposure. You have to keep going, but the area it covers is enormous. I don't know if we're ever going to get rid of it all. The question is how much do we have to get rid of to reduce our risk of cancer in the future? area at an acceptable rate, there will probably be parts of this that will be inaccessible for thousands or tens of thousands of years, unless, hopefully, we get smarter about how to contain and remove this sort of thing.

However, right now the methods are quite simple: get rid of the dirt fence in the area, some people have been returning and they receive compensation and free medical visits because the background levels there are high, but not that high, so people have started moving away. Going back to some of these areas, but there are many that are still off limits. Any other question. Yes, it is much worse than the atomic bombs dropped on Hiroshima and Nagasaki, because right now they are like fully functioning cities. Yes, the number of deaths from the atomic explosion. The bombs far exceeded the number of deaths that will ever occur in Chernobyl, such as why radiation from those bombs is not a big problem.

There wasn't that much material. There wasn't that much nuclear material in an atomic bomb. What did you get for the radius of the plutonium critical sphere? Yes, it doesn't take much. It takes between 10 and 20 kilos to make a weapon. Now we are talking about tons or thousands of tons of material released, so an atomic bomb. The weapon does not kill by radiation, it kills by pressure wave, the heat wave, the consequences are not a big concern and in fact we will analyze the data from the survivors of Hiroshima and Nagasaki to see who received what dose, what increase in the risk of cancer.

They understand and this is the idea that every little bit of radiation is a bad thing, it's actually true, the answer is you can't say yes or no, no one can say yes or no because we don't have good enough data, the mistake. The bars support either conclusion, so I'm not going to go on the record and say a little radiation is okay, the data hasn't come out yet, I hope there are never any other questions, okay, I'll see you on Thursday .