WEBVTT - Three Nuclear Disasters 0:00:04.120 --> 0:00:07.160 Get in touch with technology with tech Stuff from how 0:00:07.200 --> 0:00:13.960 stuff works dot com. Hey there, and welcome to tech Stuff. 0:00:14.000 --> 0:00:16.640 I'm your host, Jonathan Strickland. I'm an executive producer with 0:00:16.680 --> 0:00:20.720 How Stuff Works, and I love all things tech. Well, 0:00:22.000 --> 0:00:24.240 I say a love all things tech. But today I'm 0:00:24.280 --> 0:00:28.920 going to talk about three different disasters involving nuclear power facilities, 0:00:28.960 --> 0:00:34.160 and I don't really love that. It's a very serious subject. Also, 0:00:34.840 --> 0:00:37.720 I am coming down with a cold or a sinus 0:00:37.720 --> 0:00:40.360 infection or something, and I mentioned this in the last episode. 0:00:40.760 --> 0:00:42.920 It is even more true as I sit here now 0:00:43.640 --> 0:00:47.040 one hour after I recorded that last episode, and I 0:00:47.040 --> 0:00:49.599 can feel my body falling apart. So I apologize if 0:00:49.640 --> 0:00:55.600 I sound particularly uh wonky, but I don't want to 0:00:55.640 --> 0:00:59.680 suggest that I'm covering these topics in order to scare 0:00:59.720 --> 0:01:03.520 people will away from the possibilities of using nuclear power 0:01:03.600 --> 0:01:08.279 to generate electricity. I think if you implement nuclear power 0:01:08.480 --> 0:01:13.080 correctly and responsibly, which includes securing a long term storage 0:01:13.080 --> 0:01:16.880 facility for spent nuclear fuel, it can be a viable 0:01:16.920 --> 0:01:20.959 method to generate electricity. But it would be dishonest to 0:01:21.080 --> 0:01:25.760 suggest there are not significant risks involved. And the three 0:01:25.800 --> 0:01:29.920 stories I'm going to cover today illustrate that fact. So 0:01:29.959 --> 0:01:33.560 we're going to start with the Three Mile Island accident. 0:01:33.560 --> 0:01:37.320 We're gonna go in chronological order of when they happened. 0:01:37.440 --> 0:01:40.640 So Three Mile Island is the earliest. It is also 0:01:40.800 --> 0:01:45.640 the worst nuclear power accident to happen in the United States. 0:01:46.640 --> 0:01:48.920 But there's an interesting side to that, and we'll get 0:01:48.920 --> 0:01:52.400 to that. So Three Mile Island is a nuclear power facility. 0:01:52.440 --> 0:01:57.240 It's located near Middleton, Pennsylvania, and at the time of 0:01:57.280 --> 0:02:01.680 the accident it had to water reactors. I mean, it 0:02:01.760 --> 0:02:05.640 was using light water as the coolant. T m I 0:02:05.680 --> 0:02:08.400 one t m I stands for three Mile Island, not 0:02:08.480 --> 0:02:11.880 too much information, and t m I two now t 0:02:12.080 --> 0:02:15.440 m I one had been in operation since nineteen seventy four. 0:02:15.960 --> 0:02:19.360 T m I two came online a couple of years later, 0:02:19.720 --> 0:02:23.680 and then on March ninety nine, that t m I 0:02:23.720 --> 0:02:28.280 two nuclear reactor experienced a partial meltdown. Now, a meltdown 0:02:28.360 --> 0:02:32.600 happens when the heat inside a reactor core builds beyond 0:02:32.680 --> 0:02:36.600 the melting point of the nuclear fuel that's arranged in 0:02:36.760 --> 0:02:41.360 rods inside the nuclear core. Reactors use a combination of 0:02:41.400 --> 0:02:45.880 things like coolant and moderators and control rods to maintain 0:02:45.919 --> 0:02:50.160 the rate of nuclear reactions. And by controlling the rate 0:02:50.160 --> 0:02:53.679 of nuclear reactions, you then by extension, control the reactor 0:02:53.760 --> 0:02:56.760 core temperature. The more reactions there are, the higher the 0:02:56.800 --> 0:03:01.200 temperature goes. The slower the reactions are, the lower you 0:03:01.240 --> 0:03:04.320 can make the temperature. And if you actually insert control 0:03:04.400 --> 0:03:09.280 rods all the way through your bundles, the bundles being 0:03:09.360 --> 0:03:12.720 that where the fuel rods are, then you will absorb 0:03:12.840 --> 0:03:18.640 enough neutrons to stop the reaction overall. Keep in mind 0:03:18.960 --> 0:03:23.320 these are sustained nuclear reactions where a heavy atom splits apart, 0:03:23.600 --> 0:03:26.079 and one of the things that shoots off are high 0:03:26.120 --> 0:03:30.680 speed neutrons, and if another heavy atom of that same type, 0:03:30.960 --> 0:03:35.520 like uranium two thirty five, for example, absorbs that incoming neutron, 0:03:35.800 --> 0:03:39.360 it too will split. And so once you start the reaction, 0:03:39.400 --> 0:03:42.480 it can sustain itself if you have enough uranium two 0:03:42.760 --> 0:03:47.320 five in the mixture the critical mass. So if this happens, 0:03:47.480 --> 0:03:51.000 if these reactions keep on happening and they increase in 0:03:52.000 --> 0:03:55.600 rate to the point where the temperature has grown beyond 0:03:55.680 --> 0:03:58.120 the melting point of the fuel, the fuel starts to 0:03:58.160 --> 0:04:02.680 melt down. This is a big problem. At four am 0:04:02.800 --> 0:04:08.360 on March something went wrong at Three Mile Island. Now 0:04:08.360 --> 0:04:10.680 to understand what happened, it helps to get a general 0:04:10.760 --> 0:04:14.800 understanding of that reactor's design. So you've got the nuclear 0:04:15.000 --> 0:04:20.800 side of the system and the non nuclear side. The 0:04:20.920 --> 0:04:25.840 nuclear side consists of the nuclear reactor which has the fuel, 0:04:25.920 --> 0:04:29.720 which was uranium, and it has the control rods, has 0:04:29.760 --> 0:04:33.320 the coolant in it. The coolant is water, but the 0:04:33.320 --> 0:04:37.440 coolant is water under pressure, so it's a pressurized system. 0:04:37.480 --> 0:04:41.880 The water can circulate through the core, through the rest 0:04:41.920 --> 0:04:44.760 of the system to a heat exchanger more on that 0:04:44.800 --> 0:04:48.240 in a second. And then after it goes through the 0:04:48.240 --> 0:04:51.080 heat exchanger, some of the heat has been pulled away 0:04:51.080 --> 0:04:54.160 from the coolant, it continues to circulate, goes back into 0:04:54.160 --> 0:04:57.159 the core, heats up again, and it's kept under pressure 0:04:57.200 --> 0:05:00.640 so that way the coolant doesn't boil off, because if 0:05:00.640 --> 0:05:02.560 you don't have you know, if you don't keep it 0:05:02.600 --> 0:05:05.920 under pressure, then some of that water would boil off 0:05:05.920 --> 0:05:09.160 into steam, and that would make your whole system less 0:05:09.200 --> 0:05:12.359 efficient and also would create problems when you're trying to 0:05:12.520 --> 0:05:16.640 pump the water through that side, that's the nuclear side. 0:05:17.680 --> 0:05:22.440 Then uh you have the non nuclear section that's a 0:05:22.520 --> 0:05:28.800 secondary water system. Secondary loop of water. The water flows 0:05:28.960 --> 0:05:33.320 into a steam generator essentially a boiler, and that is 0:05:33.360 --> 0:05:36.240 on the other side that heat exchange that's on the 0:05:36.320 --> 0:05:40.000 nuclear side. So the coolant from the nuclear side, which 0:05:40.040 --> 0:05:44.599 is superheated water that's under pressure, transfers heat through the 0:05:44.640 --> 0:05:49.400 heat exchanger. The heat exchanger transfers heat to the steam generator, 0:05:49.440 --> 0:05:53.440 which boils water off from this second closed loop, So 0:05:53.480 --> 0:05:57.720 the two loops are not connected. And then that steam 0:05:57.880 --> 0:06:02.159 goes on to drive a a steam turbine which generates 0:06:02.160 --> 0:06:06.919 electricity and then goes through some cooling process to condense 0:06:07.000 --> 0:06:09.760 back into water and go back through the system again. 0:06:10.320 --> 0:06:12.760 So the important thing to remember is that these are 0:06:12.800 --> 0:06:16.840 two closed systems that do not overlap. So the the 0:06:17.800 --> 0:06:19.960 the water that's being used to turn into steam and 0:06:19.960 --> 0:06:23.680 turn the steam turbines, never has any contact with the 0:06:23.760 --> 0:06:27.120 nuclear fuel. It is just heated by this heat exchange, 0:06:27.960 --> 0:06:31.640 and the other water, the coolant water, that's the one 0:06:31.640 --> 0:06:34.880 that's circulating through the nuclear reactor core. Well, that Monday 0:06:34.880 --> 0:06:39.159 in March, there was a malfunction in that secondary non 0:06:39.400 --> 0:06:46.560 nuclear water system, and that prevented the water from circulating properly. Now, 0:06:46.600 --> 0:06:50.080 the reactions in the reactor core continued, but there was 0:06:50.120 --> 0:06:53.840 no way for the coolant to pass heat to that 0:06:53.960 --> 0:06:57.440 secondary system, right. It could not pass heat through the 0:06:57.480 --> 0:06:59.599 heat exchanger to the secondary system. There was nothing to 0:06:59.640 --> 0:07:03.600 carry that heat away. And without anything to carry the 0:07:03.640 --> 0:07:06.919 heat away, it meant the temperature of the reactor's coolant 0:07:07.040 --> 0:07:10.559 began to rise. So the reactor cores temperature began to rise. 0:07:11.440 --> 0:07:16.840 The actual plant automatically shut down the reactor because it 0:07:16.920 --> 0:07:20.520 detected that this was happening. It saw that the temperature 0:07:20.560 --> 0:07:23.480 was rising, so as a safety measure, it shut down. 0:07:23.560 --> 0:07:27.760 That's a good thing. Then a pressure relief valve on 0:07:27.800 --> 0:07:30.880 the pressure riser on the nuclear side, so where the 0:07:30.920 --> 0:07:34.640 coolant gets pressurized so that it doesn't boil off. There's 0:07:34.640 --> 0:07:37.880 a safety valve there that opens up in the case 0:07:38.120 --> 0:07:41.360 of UH, temperatures rising too high in order to let 0:07:41.360 --> 0:07:46.080 out a little pressure, and it's supposed to open for 0:07:46.120 --> 0:07:48.960 about ten seconds and then close, so that way it 0:07:49.000 --> 0:07:53.040 releases some pressure. It closes, everything is fine, UH, and 0:07:53.400 --> 0:07:56.440 the steam it releases, because you know, you're talking about 0:07:56.680 --> 0:08:00.760 water that's been in contact with the nuclear reactor core, 0:08:01.280 --> 0:08:04.000 all of that is still contained within the facility. It's 0:08:04.040 --> 0:08:07.320 not like it's being vented out into the wilderness and 0:08:07.320 --> 0:08:10.880 suddenly you've got Bambi with eight heads or something. That 0:08:10.960 --> 0:08:14.240 doesn't happen. But what it's supposed to do is have 0:08:14.280 --> 0:08:16.800 that valve shut after about ten seconds, and the valve 0:08:16.880 --> 0:08:22.400 didn't shut, it stayed open, But the instrumentation in the 0:08:22.440 --> 0:08:26.480 control room indicated that the valve had shut, so the 0:08:26.560 --> 0:08:30.520 workers at three Mile Island were working under incorrect information. 0:08:30.640 --> 0:08:33.880 They saw that everything on the nuclear side appeared to 0:08:33.880 --> 0:08:38.120 be fine once this venting process was over, and then 0:08:38.160 --> 0:08:40.840 the valve had shut and everything should be good to go, 0:08:41.960 --> 0:08:45.120 But that valve was open, so the reactor coolant continued 0:08:45.280 --> 0:08:48.880 to escape the reactor. It continued to boil off into steam, 0:08:49.640 --> 0:08:54.320 and that began to drain the reactor coolant uh and 0:08:55.600 --> 0:08:59.160 that meant that the reactor core was losing coolant and 0:08:59.240 --> 0:09:02.160 residual to a heat was starting to build up, and 0:09:02.200 --> 0:09:04.560 the core would be damaged by this because once the 0:09:04.600 --> 0:09:09.440 coolant drains enough, then the reactor is able to the 0:09:09.640 --> 0:09:12.440 uranium inside the reactor is able to have these reactions 0:09:13.080 --> 0:09:17.160 with more regularity, and the temperature will grow very very 0:09:17.200 --> 0:09:20.679 quickly because of that. To make matters worse, the employees 0:09:20.720 --> 0:09:24.080 assumed that the coolant in the core was remaining at 0:09:24.080 --> 0:09:26.040 the right levels. They did not have an easy way 0:09:26.080 --> 0:09:29.440 to monitor how much water was actually in the reactor core. 0:09:30.840 --> 0:09:33.920 Now the plant it had a better idea of what 0:09:33.960 --> 0:09:37.720 was going on. The automated systems had detected this problem, 0:09:37.960 --> 0:09:42.360 and so the automated systems spring into action and began 0:09:42.400 --> 0:09:46.160 to inject water at high pressure into the reactor in 0:09:46.280 --> 0:09:48.960 order to replace the coolant that was being lost with 0:09:49.120 --> 0:09:52.040 the open valve. Now, at this point, the employees still 0:09:52.080 --> 0:09:56.320 thought the valve was closed. Cooling water entered the pressure 0:09:56.400 --> 0:10:01.000 riser in the nuclear reactor coolant system, so the employees 0:10:01.040 --> 0:10:03.480 couldn't see how much water was going into the reactor core. 0:10:03.559 --> 0:10:06.439 They didn't have the instrumentation to detect that. But they 0:10:06.480 --> 0:10:09.960 did see they had instrumentation to detect how much water 0:10:10.000 --> 0:10:13.960 was in the pressurizer, because if the pressurizer had too 0:10:14.040 --> 0:10:17.720 much water in it and attempted to add more pressure 0:10:17.760 --> 0:10:21.440 to the system, it could cause a rupture, which would 0:10:21.440 --> 0:10:25.679 be a really bad thing. Right, So the employees are 0:10:25.720 --> 0:10:27.600 looking at this figure and they're seeing it go up 0:10:27.600 --> 0:10:29.760 and up and up, and they start to think, oh, no, 0:10:30.280 --> 0:10:33.640 something's gone wrong. For some reason, the automated systems are 0:10:33.640 --> 0:10:37.600 pouring more water into the reactor and the pressurizer is 0:10:37.600 --> 0:10:40.920 getting over overloaded with water, so we need to shut 0:10:41.000 --> 0:10:44.160 down that water. They did not realize that that valve 0:10:44.240 --> 0:10:47.280 was still open and that coolant was still boiling off, 0:10:48.480 --> 0:10:53.480 so they were working under incorrect information. Now that allowed 0:10:53.640 --> 0:10:57.840 steam to form inside the reactor system in general, So 0:10:58.000 --> 0:11:00.240 the mixture of water and steam in the system, which 0:11:00.280 --> 0:11:03.120 was supposed to be just high pressure, high temperature water, 0:11:04.320 --> 0:11:07.800 was giving the coolant pumps problems when they were trying 0:11:07.800 --> 0:11:10.760 to pump the liquid through the system. That steam was 0:11:10.840 --> 0:11:13.480 causing issues. It was making the pumps start to vibrate, 0:11:13.880 --> 0:11:16.240 and that could have caused massive damage to the plant. 0:11:16.320 --> 0:11:19.800 So the employees shut down the pumps. The reactor court 0:11:19.960 --> 0:11:23.200 no longer had sufficient coolant. The level was too low 0:11:24.080 --> 0:11:27.240 and it was no longer circulating, so the fuel rods 0:11:27.280 --> 0:11:31.199 got hotter and hotter without sufficient coolant and partially melted. 0:11:31.800 --> 0:11:36.800 That introduced radioactive material into the water itself. Before the 0:11:36.880 --> 0:11:39.240 radioactive material was more or less contained and the water 0:11:39.559 --> 0:11:41.760 would go past it, but not you know, it's not 0:11:41.800 --> 0:11:44.880 like the water was soaking up radioactive isotopes or something, 0:11:45.200 --> 0:11:48.360 But now you had fuel melting off and falling into 0:11:48.360 --> 0:11:52.520 the water itself. Now the water actually is carrying radioactive material. 0:11:53.120 --> 0:11:55.079 At six two in the morning, keep in mind this 0:11:55.160 --> 0:11:58.800 started at four am. Employees were able to finally close 0:11:58.880 --> 0:12:02.280 a blocked valve that was between the pressurizer and that 0:12:02.440 --> 0:12:05.160 open relief valve, so they were able to take care 0:12:05.200 --> 0:12:08.400 of that. They found that problem and so that managed 0:12:08.440 --> 0:12:13.000 to stop the loss of coolant, But the coolant system 0:12:13.120 --> 0:12:16.199 inside the reactor was now partly filled with steam and 0:12:16.360 --> 0:12:19.960 steam from water that had contact with radioactive material, so 0:12:20.000 --> 0:12:23.840 this was very concerning. Eventually, the operators were able to 0:12:23.920 --> 0:12:27.240 condense that steam into water and they were able to 0:12:27.280 --> 0:12:29.920 inject more water into the system and restore the core 0:12:30.000 --> 0:12:34.360 to proper temperatures. They also captured several of the radioactive 0:12:34.360 --> 0:12:37.040 gases that were coming from the reactor. They would vent 0:12:37.760 --> 0:12:41.400 these gases from the reactor, but they vented it into 0:12:42.080 --> 0:12:45.960 trapping systems. It was all meant to go from the 0:12:46.000 --> 0:12:49.760 reactor into compressors that would then send this radioactive gas 0:12:50.440 --> 0:12:55.160 into uh a tank called the makeup tank. Then from 0:12:55.200 --> 0:12:58.040 the makeup tank it would be compressed to move into 0:12:58.200 --> 0:13:02.160 gas decay tanks. These are special containers designed to hold 0:13:02.240 --> 0:13:05.720 radioactive gases. If all of that had worked, yes, there 0:13:05.800 --> 0:13:08.080 still would have been a disaster in the sense that 0:13:08.200 --> 0:13:12.360 things had gone wrong, but radiation would have been contained. 0:13:12.720 --> 0:13:15.560 In the process of sending it along this chain, some 0:13:15.640 --> 0:13:18.440 of the compressors leaked and some of that gas got 0:13:18.480 --> 0:13:21.439 released into the environment. That gas also had to pass 0:13:21.480 --> 0:13:25.880 through several HEPPA filters, which removed most of the radio newclides, 0:13:26.400 --> 0:13:29.360 so most of the heavier radioactive materials. In fact, all 0:13:29.440 --> 0:13:34.120 the heavy radioactive materials were all caught, but some radioactive 0:13:34.160 --> 0:13:38.800 noble gases passed through those filters. Those gases had radio 0:13:38.840 --> 0:13:41.760 nuclides with a very short half life, and the gases 0:13:41.800 --> 0:13:47.240 themselves were biologically inert, so it wasn't like organisms were 0:13:47.280 --> 0:13:51.880 going to soak up those gases. They didn't interact with them, 0:13:51.960 --> 0:13:55.000 so it wasn't an environmental catastrophe. It's still not great 0:13:55.200 --> 0:14:00.840 to say radioactive gas escaped are our facility, but at 0:14:00.880 --> 0:14:03.800 least you could say, but this radioactive gas does not 0:14:03.960 --> 0:14:07.000 interact with the environment in any way, so we should 0:14:07.040 --> 0:14:10.560 be fine. So in fact, numerous independent health studies and 0:14:10.679 --> 0:14:14.080 environmental studies showed no real evidence of ill effects from 0:14:14.240 --> 0:14:17.280 this incident. So it was a bad accident. It should 0:14:17.320 --> 0:14:20.120 not have happened, but the safety measures that were in 0:14:20.200 --> 0:14:23.280 place in the event of catastrophic failure appeared to hold 0:14:23.360 --> 0:14:27.000 up pretty well. The accident revealed enormous gaps in technology 0:14:27.000 --> 0:14:31.200 and training, but the safety measures managed to hold in place. 0:14:31.880 --> 0:14:34.480 But the communication of the event caused a great deal 0:14:34.480 --> 0:14:39.600 of distress and panic, understandably so, so they clean up 0:14:39.680 --> 0:14:43.560 process for t m I too, because this radiation got 0:14:43.680 --> 0:14:47.160 leaked inside the facility. It took more than a decade 0:14:47.160 --> 0:14:50.960 and cost nearly a billion dollars. While the impact to 0:14:51.000 --> 0:14:54.680 the region around the plant was minimal, inside the plant 0:14:54.720 --> 0:14:56.840 was a different story. You had a lot of services 0:14:56.840 --> 0:14:59.960 that had to be decontaminated. The water in the cyste 0:15:00.040 --> 0:15:04.120 them had to be thoroughly processed and decontaminated. The damaged 0:15:04.120 --> 0:15:07.440 fuel in the reactor had to be retrieved and then stored. 0:15:08.400 --> 0:15:12.680 T m I one, the other reactor, was actually offline 0:15:13.080 --> 0:15:16.040 during this accident. It was shut down. It was undergoing refueling. 0:15:16.520 --> 0:15:19.720 It would end up remaining offline during an investigation led 0:15:19.760 --> 0:15:24.000 by the Nuclear Regulatory Commission and would come back online 0:15:24.040 --> 0:15:27.640 in October. So t m I two was offline but 0:15:27.720 --> 0:15:30.640 t m I one did come back into service, and 0:15:32.160 --> 0:15:38.200 the Exelon Corp Corporation, which then owned Three Mile Island, 0:15:38.440 --> 0:15:41.280 said that without action from the State of Pennsylvania, operations 0:15:41.280 --> 0:15:44.080 at t m I one would end in twenty nineteen, 0:15:44.160 --> 0:15:47.520 So next year, t m I one is licensed to 0:15:47.640 --> 0:15:52.920 operate until twenty four but it is not economically feasible 0:15:53.000 --> 0:15:56.280 to do so under the current climate. According to Exelon Corporation, 0:15:56.800 --> 0:16:00.160 Three Mile Island was the worst nuclear power disaster or 0:16:00.200 --> 0:16:06.000 in US history, but no one died as a result 0:16:06.040 --> 0:16:08.920 of Three Mile Island and there were no harmful effects 0:16:09.000 --> 0:16:14.040 that could be pointed to Three Mile Islands. So while 0:16:14.120 --> 0:16:16.800 it was bad and never should have happened, it could 0:16:16.800 --> 0:16:19.000 have been much worse, and it pales in comparison to 0:16:19.040 --> 0:16:22.800 some of the other disasters. So we're going to look 0:16:22.880 --> 0:16:24.600 at one of those in just a second, But first 0:16:24.640 --> 0:16:35.040 let's take a quick break to thank our sponsor from 0:16:35.120 --> 0:16:39.000 Pennsylvania in nineteen seventy nine. We now travel to the Ukraine. 0:16:39.160 --> 0:16:43.720 In nineteen eighties six, near the border between Ukraine and 0:16:43.800 --> 0:16:48.440 Belarus is Chernobyl, the site of a terrible nuclear disaster. 0:16:49.040 --> 0:16:52.880 The name Chernobyl has become synonymous with concepts like radiation 0:16:53.040 --> 0:16:57.800 and nuclear meltdowns. So what exactly happened at Chernobyl. Well, 0:16:57.800 --> 0:17:01.880 the short answer is that a trained staff working at 0:17:01.880 --> 0:17:05.880 a poorly designed Soviet nuclear power plant caused a massive 0:17:05.920 --> 0:17:09.880 catastrophe in one of the four reactors that directly resulted 0:17:10.119 --> 0:17:13.000 in the deaths of at least thirty people over the 0:17:13.040 --> 0:17:17.040 course of a few weeks. Initially, two thirty seven people 0:17:17.119 --> 0:17:21.399 received a diagnosis of acute radiation syndrome or a r S. 0:17:22.080 --> 0:17:25.320 That number would be reduced to one four once those 0:17:25.320 --> 0:17:28.479 cases were confirmed, But that really doesn't tell us much 0:17:28.480 --> 0:17:32.679 about what actually happened, right, So to understand what happened 0:17:32.680 --> 0:17:36.400 at Chernobyl helps to understand the difference in the design 0:17:36.520 --> 0:17:39.400 of that power plant compared to say, the three Mile 0:17:39.560 --> 0:17:43.359 Island designed. So this design was called the r b 0:17:43.760 --> 0:17:46.399 m K one thousand, and I am not about to 0:17:46.600 --> 0:17:50.080 attempt to pronounce the words that r B m K 0:17:50.320 --> 0:17:53.600 stands for, because my Russian is just as bad as 0:17:54.000 --> 0:17:59.280 all my other pronunciations, which you guys know is uniformly terrible. 0:17:59.800 --> 0:18:03.520 But the meaning in English, if you were to translate 0:18:03.600 --> 0:18:07.720 those Russian words is high power channel reactor and the 0:18:07.880 --> 0:18:11.320 r B M K design used water as a coolant 0:18:11.520 --> 0:18:15.359 and graphite as a moderator, although water was also a moderator, 0:18:15.520 --> 0:18:19.359 so that is the moderators, they help absorb neutrons and 0:18:19.400 --> 0:18:22.960 that controls the rate of nuclear reactions. As I mentioned 0:18:22.960 --> 0:18:25.760 in the previous section, the R and B m K 0:18:26.000 --> 0:18:29.560 also had boron carbide control rods that would do that 0:18:29.600 --> 0:18:32.800 as well. So if you were to insert the boron 0:18:32.920 --> 0:18:37.160 carbide control rods all the way into the UH, into 0:18:37.240 --> 0:18:40.440 the reactor core, you would shut down reactions because you 0:18:40.480 --> 0:18:43.120 would be absorbing all the neutrons that were being given 0:18:43.160 --> 0:18:46.120 off and the reaction would not be able to sustain itself, 0:18:46.160 --> 0:18:50.320 so you would no longer have nuclear power that way. 0:18:50.760 --> 0:18:53.080 But one thing the R B M K design did 0:18:53.080 --> 0:18:56.240 not have was a heat exchanger. It did not have 0:18:56.359 --> 0:19:01.200 these two closed loops like three Mile Island did, so 0:19:01.760 --> 0:19:06.560 instead it used one loop for water. The water that 0:19:06.640 --> 0:19:10.080 was the coolant for the actual reactor core was the 0:19:10.119 --> 0:19:13.320 same water that we get turned into steam, go through 0:19:13.320 --> 0:19:17.720 a steam turbine, go through a cooling process, condensed back 0:19:17.760 --> 0:19:20.560 into water, and go back into the system. So it 0:19:20.600 --> 0:19:23.959 was a very different approach from Three Mile Island UH. 0:19:24.119 --> 0:19:27.879 The water would boil within that reactor design. So you 0:19:27.920 --> 0:19:30.800 remember Three Mile Island that was bad when the cool 0:19:30.880 --> 0:19:33.240 it was boiling off and steam was introduced into the 0:19:33.280 --> 0:19:36.480 system because the cooling pumps had trouble pumping the water 0:19:36.600 --> 0:19:41.760 with steam in it. The Soviet version depended upon having 0:19:42.160 --> 0:19:48.639 steam inside the system, so uh, you needed it to 0:19:48.760 --> 0:19:52.000 work this way to generate power the way the Soviets 0:19:52.040 --> 0:19:54.760 had intended. But it did introduce another problem with the 0:19:54.920 --> 0:19:57.520 r b M K one thousand, which is that you 0:19:57.560 --> 0:20:04.400 have an issue called positive voy coefficient. So water like graphite, 0:20:04.640 --> 0:20:08.080 can absorb neutrons, so it can act as a bit 0:20:08.119 --> 0:20:11.879 of a moderator, not just a coolant. So water it 0:20:11.880 --> 0:20:14.520 can help cool core, but it can also absorb some 0:20:14.640 --> 0:20:17.320 of those neutrons that are being given off and thus 0:20:18.000 --> 0:20:23.040 help with the rate of nuclear reaction. Liquid water does 0:20:23.080 --> 0:20:27.520 this much better than steam does. So the more steam 0:20:27.560 --> 0:20:31.080 you have in your mixture, the less capable the water 0:20:31.280 --> 0:20:36.200 is to absorb those neutrons. And we call the little 0:20:36.240 --> 0:20:41.160 steam bubbles in the water supply voids in the nuclear 0:20:41.200 --> 0:20:44.560 power biz. So as the number of steam bubbles grows, 0:20:44.600 --> 0:20:47.600 the neutron absorbing capability of the water decreases. And since 0:20:47.720 --> 0:20:52.480 sustain nuclear reactions depend upon nuclear fuel absorbing neutrons. That 0:20:52.520 --> 0:20:58.280 means you get more reactions as the positive void coefficient increases. 0:20:58.640 --> 0:21:00.879 So the more steam bubbles are in the water, the 0:21:00.920 --> 0:21:03.680 more neutrons are going to get absorbed by other atoms 0:21:03.680 --> 0:21:07.199 of uranium, and the more reactions you're gonna get as 0:21:07.200 --> 0:21:10.240 a result, and the more heat you get. The Soviet 0:21:10.240 --> 0:21:13.320 design depended upon that process. The control rods could be 0:21:13.320 --> 0:21:17.040 inserted into the pressurized tubes that contain the nuclear fuel 0:21:17.119 --> 0:21:19.600 rods and shut down a reaction if things got out 0:21:19.640 --> 0:21:24.040 of hand, Now it's your noble. The process got out 0:21:24.040 --> 0:21:27.760 of hand big time. So first it became a cycle 0:21:27.880 --> 0:21:32.200 that fed upon itself. The nuclear reactions would heat up 0:21:32.320 --> 0:21:35.119 the coolant water and start to convert some of that 0:21:35.119 --> 0:21:39.639 water into steam. Steam bubbles or voids began to form. 0:21:39.680 --> 0:21:42.439 That reduced the capability of the water in the system 0:21:42.640 --> 0:21:46.880 to absorb neutrons, and that increase the rate of nuclear 0:21:46.880 --> 0:21:49.879 reactions within the core, which meant the core got hotter, 0:21:50.119 --> 0:21:52.680 which meant heated up the water even more, which meant 0:21:52.760 --> 0:21:56.080 it increased the number of voids, which meant that even 0:21:56.200 --> 0:21:58.760 fewer neutrons were absorbed. So you see how this very 0:21:58.880 --> 0:22:04.879 quickly becomes a problem. On a reactor four at the 0:22:04.960 --> 0:22:09.160 Chernobyl facility was beginning to shut down. It was getting 0:22:09.200 --> 0:22:12.680 ready for a scheduled maintenance and refueling. This was totally routine, 0:22:13.640 --> 0:22:16.040 but before it was to shut down, it was going 0:22:16.119 --> 0:22:19.000 to go through a testing procedure on the following day, 0:22:19.000 --> 0:22:23.120 on April uh and that test was to see how 0:22:23.160 --> 0:22:26.240 long the reactor would be able to generate steam and 0:22:26.280 --> 0:22:30.399 thus spin turbines in the event of a main electrical 0:22:30.480 --> 0:22:34.440 power supply loss. So they were going to simulate losing 0:22:34.520 --> 0:22:37.600 power at this facility and they were going to see 0:22:38.680 --> 0:22:44.000 how long can this reactor continue to generate steam and 0:22:44.160 --> 0:22:46.720 turn this turbine even if the power is lost to 0:22:46.960 --> 0:22:50.639 the reactor itself. So to conduct that test on the 0:22:52.080 --> 0:22:56.520 back on the operators started to disable automatic shutdown features. 0:22:58.200 --> 0:23:01.960 And when you hear about shutting down ematic shutdown features, 0:23:02.000 --> 0:23:05.360 that should raise some pretty big alarm flags in your 0:23:05.520 --> 0:23:07.879 in your head, you should be thinking that doesn't sound 0:23:07.880 --> 0:23:10.240 like a good idea, and in fact it wasn't. So 0:23:10.320 --> 0:23:13.440 the operator went to shut down the reactor by instarting 0:23:13.440 --> 0:23:17.240 the control rods into the core, and for some reason 0:23:17.320 --> 0:23:22.359 or another, that action, telling the the control arms too 0:23:22.920 --> 0:23:27.120 insert those control rods caused a power surge, and the 0:23:27.160 --> 0:23:30.920 hot fuel in the reactor began to fragment. Water began 0:23:30.920 --> 0:23:34.480 converting into steam at an accelerated rate, and as I mentioned, 0:23:34.480 --> 0:23:37.119 that meant the water was less efficient at absorbing neutrons. 0:23:37.440 --> 0:23:40.280 So the reaction began to accelerate. The production of steam 0:23:40.320 --> 0:23:44.199 began to increase, and that increased the pressure inside the 0:23:44.240 --> 0:23:49.960 system so much that the pressure actually partially detached the 0:23:50.080 --> 0:23:54.040 steel cover plate on top of the reactor. That steel 0:23:54.160 --> 0:23:58.960 cover plate weighed one thousand tons. That's how much pressure 0:23:59.040 --> 0:24:02.919 was inside this react term enough pressure to displace at 0:24:02.960 --> 0:24:08.479 least partially one thousand tons of steel. Worse, when this 0:24:08.600 --> 0:24:13.480 cover plate became partially dislodged, it it wedged the control 0:24:13.600 --> 0:24:15.960 rods in such a way that they could not insert 0:24:16.160 --> 0:24:20.840 completely into the pressure tubes. So the control rods were stuck. 0:24:20.840 --> 0:24:23.480 They couldn't go all the way in and thus shut 0:24:23.520 --> 0:24:26.879 down the nuclear reaction. They had only reached about the 0:24:26.920 --> 0:24:31.160 halfway mark, so the nuclear reaction was continuing because there 0:24:31.200 --> 0:24:35.040 was the control rods couldn't absorb those extra neutrons. The 0:24:35.080 --> 0:24:38.280 build up of steam reached catastrophic levels, and there was 0:24:38.359 --> 0:24:43.040 an explosive rupture which released nuclear material into the atmosphere. 0:24:43.560 --> 0:24:48.160 Seconds later, another explosion followed, and this one flung out 0:24:48.480 --> 0:24:53.919 superheated graphite and nuclear fuel flying out from the facility. 0:24:54.119 --> 0:24:58.160 The general consensus is that the second explosion happened after 0:24:58.600 --> 0:25:02.520 hydrogen gas, which had been generated from the reactions in 0:25:02.560 --> 0:25:08.520 the core, ignited from those high temperatures. The explosion killed 0:25:08.640 --> 0:25:12.320 two of the workers at Chernobyl outright. The hot material 0:25:12.400 --> 0:25:15.840 started numerous fires in the area because chernobyls in the 0:25:15.880 --> 0:25:19.879 middle of a forest, and so the four started catching fire, 0:25:20.160 --> 0:25:24.280 and that helped distribute radioactive material further into the atmosphere 0:25:24.320 --> 0:25:28.280 and the general environment. And some of the radioactive elements 0:25:28.320 --> 0:25:32.680 included iodine one and ses M one thirty seven. Both 0:25:32.720 --> 0:25:36.600 of those post significant dangers to the public in the region. 0:25:37.080 --> 0:25:41.119 Iodine one one has a relatively short half life of 0:25:41.160 --> 0:25:43.439 just a few days. Caesium one thirty seven is like 0:25:43.480 --> 0:25:46.840 a decade our thirty years rather, so you've got thirty 0:25:46.920 --> 0:25:49.840 years half life or case one thirty seven a few 0:25:49.920 --> 0:25:52.960