WEBVTT - How Nuclear Power Plants Work 0:00:04.120 --> 0:00:07.160 Get in touch with technology with tech Stuff from how 0:00:07.200 --> 0:00:13.680 stuff works dot com. Hey there, and welcome to tech Stuff. 0:00:13.720 --> 0:00:16.479 I'm your host, Jonathan Strickland. I'm an executive producer with 0:00:16.520 --> 0:00:20.520 how Stuff Works and I love all things tech, and 0:00:20.640 --> 0:00:25.520 recently I got some requests to talk about some subjects 0:00:25.520 --> 0:00:28.080 related to nuclear power. Specifically, I had a request to 0:00:28.120 --> 0:00:31.720 talk about cold fusion and whether there is any validity 0:00:32.120 --> 0:00:35.519 to cold fusion claims and research, and that's a very 0:00:35.640 --> 0:00:38.960 loaded subject and I will tackle it. But before I 0:00:39.000 --> 0:00:41.479 can handle that topic, I thought we would be good 0:00:41.479 --> 0:00:44.960 to do a couple of episodes about nuclear power to 0:00:45.040 --> 0:00:47.720 lead up to it, and that includes how nuclear power 0:00:47.760 --> 0:00:51.200 plants work today and how nuclear fusion reactors will work 0:00:51.240 --> 0:00:53.159 in the future if we ever suss out how to 0:00:53.200 --> 0:00:55.440 do them in a way that isn't a net loss 0:00:55.480 --> 0:00:59.080 on energy and is sustainable. So today's episode is going 0:00:59.120 --> 0:01:02.640 to be about new clear fission reactors. That's the kind 0:01:02.680 --> 0:01:06.600 that we use today to generate electricity. Their nuclear power 0:01:06.640 --> 0:01:09.400 plants all across the world, and all of the ones 0:01:09.440 --> 0:01:13.640 that are not just pure research facilities are fission based. 0:01:14.120 --> 0:01:16.959 And then fusion is something that is in a research 0:01:17.040 --> 0:01:20.240 stage in various places around the world, and then this 0:01:20.280 --> 0:01:22.560 is actually gonna be a nuclear power week because we're 0:01:22.560 --> 0:01:24.840 going to talk about cold fusion in the third episode. 0:01:24.840 --> 0:01:27.119 In the fourth episode, I think I'm going to take 0:01:27.520 --> 0:01:31.520 a really close look at some of the famous nuclear 0:01:31.560 --> 0:01:37.160 facility disasters, things like Three Mile Island, Chernobyl, and the 0:01:37.160 --> 0:01:40.679 Fukushima reactor and talk about what happened in each of 0:01:40.720 --> 0:01:44.480 those instances and what the consequences were, so that we 0:01:44.520 --> 0:01:47.160 can have a deep understanding. Now, this is not supposed 0:01:47.200 --> 0:01:50.680 to be a series that is meant to scare you 0:01:50.960 --> 0:01:55.840 about nuclear power. I actually believe that nuclear power, if 0:01:56.360 --> 0:02:04.919 performed responsibly, is a good alternative to fossil fuel based power. 0:02:05.560 --> 0:02:10.560 But the responsibly part is absolutely of paramount importance. And 0:02:10.600 --> 0:02:13.560 we'll get into why as I talk about this. But 0:02:14.080 --> 0:02:18.200 this is not an anti nuclear power or even a 0:02:18.280 --> 0:02:22.079 pro nuclear power episode. It's just to kind of give 0:02:22.200 --> 0:02:24.880 us the understanding of what it is, what's going on, 0:02:25.280 --> 0:02:27.960 what are the pros and the cons of it. So, 0:02:28.639 --> 0:02:32.080 fission means they use a process to generate energy that 0:02:32.160 --> 0:02:37.720 involves splitting one heavy atom into lighter atoms, and fusion 0:02:37.800 --> 0:02:40.240 is the opposite. You would take two or more lighter 0:02:40.280 --> 0:02:44.079 atoms and you squish them together real hard to make 0:02:44.120 --> 0:02:48.520 into a heavier atom, and both processes release energy, though 0:02:48.880 --> 0:02:52.040 a fusion reaction would release far more energy than a 0:02:52.080 --> 0:02:56.600 fission reaction. I'll explain how that is in the next episode. 0:02:56.639 --> 0:03:00.840 But first, fission, well, it happens naturally with certain large 0:03:00.960 --> 0:03:05.960 unstable atoms. Uranium, for example, It will spontaneously undergo fission 0:03:06.200 --> 0:03:09.160 uranium two specifically, but it does so at a very 0:03:09.200 --> 0:03:12.679 slow rate. But you can speed that rate up through 0:03:12.720 --> 0:03:17.760 a process called induced fission. And generally speaking, induced fission 0:03:17.880 --> 0:03:21.320 happens when you take a heavy and unstable atom and 0:03:21.360 --> 0:03:26.520 you pelt it really hard with neutrons. You accelerate the 0:03:26.520 --> 0:03:29.920 neutrons and you shoot them at these heavy isotopes, and 0:03:29.960 --> 0:03:34.359 those isotopes break up into smaller components. That process generates 0:03:34.400 --> 0:03:36.400 a lot of energy in the form of heat, and 0:03:36.440 --> 0:03:39.320 you can use that heat to heat up water, preferably 0:03:39.320 --> 0:03:42.440 in a separate, sealed system. Not all nuclear power plants 0:03:42.440 --> 0:03:44.960 work that way, but about two thirds of the US 0:03:45.520 --> 0:03:48.200 nuclear power plants do, And you convert the water into 0:03:48.240 --> 0:03:52.320 steam and use that steam to turn turbines conducted to 0:03:52.400 --> 0:03:57.120 generators to produce electricity. Now, in a way today's nuclear 0:03:57.120 --> 0:04:00.360 power plants are really not all that different from coal 0:04:00.600 --> 0:04:04.720 power plants or thermal plants that use solar power to 0:04:04.760 --> 0:04:08.120 heat up water. And in all these cases, you use 0:04:08.240 --> 0:04:13.600 a process to either generate or harness heat. And you know, 0:04:13.720 --> 0:04:15.840 you can burn cold to do that, you can harness 0:04:15.920 --> 0:04:18.680 solar power to do that, you can use nuclear power 0:04:18.760 --> 0:04:22.080 to do that. Use that heat to boil water, to 0:04:22.160 --> 0:04:26.080 convert water into high pressure steam, and you direct that 0:04:26.120 --> 0:04:31.760 steam to move turbines, and those turbines are electricity generators. Now, 0:04:31.760 --> 0:04:37.760 to be clear, the generators aren't generating energy because energy 0:04:37.800 --> 0:04:41.320 can be neither created nor destroyed. You can convert energy 0:04:41.400 --> 0:04:45.760 from one form to another. You can convert mass into energy, 0:04:45.800 --> 0:04:50.000 but you can't just create energy and of nothing. So 0:04:50.400 --> 0:04:57.120 electricity generators are converting some form of energy into electricity. Uh. 0:04:57.160 --> 0:05:01.359 With steam turbines, we're talking about converting kinetic energy, the 0:05:01.440 --> 0:05:05.040 energy of movement, into electrical energy. And here's how that works. 0:05:05.080 --> 0:05:09.159 In a nutshell. Generators have many parts typically, but a 0:05:09.240 --> 0:05:14.560 really important component is the alternator. And inside the alternator 0:05:14.720 --> 0:05:17.359 you have a statter and you have a rotor. The 0:05:17.440 --> 0:05:21.520 statter stays motionless with respect to the generator. It's remains 0:05:21.520 --> 0:05:26.919 stationary motionless. The rotor, as a name suggests, rotates on 0:05:27.000 --> 0:05:30.960 its axis. So it rotates. Uh. Typically the statter has 0:05:31.000 --> 0:05:34.320 an iron core and you have conductive wire or cable 0:05:34.360 --> 0:05:37.200 wrapped around that iron core. So you think about this, 0:05:37.240 --> 0:05:39.560 it sounds oh, it sounds like an electro magnet. Well, yeah, 0:05:39.720 --> 0:05:44.520 kind of. The rotor typically has permanent magnets or some 0:05:44.720 --> 0:05:48.840 other thing that generates a magnetic field, and as the 0:05:48.960 --> 0:05:54.480 rotor rotates, this magnetic field moves with the rotation. So 0:05:54.520 --> 0:05:58.840 this is essentially a fluctuating magnetic field. And as we know, 0:05:59.040 --> 0:06:02.320 when you have a fluctuation magnetic field and you've got 0:06:02.360 --> 0:06:07.039 a a conductive wire that's wrapped around an iron core, 0:06:07.520 --> 0:06:10.760 that can induce or it does induce a voltage difference 0:06:10.880 --> 0:06:14.880 in that conductive material and that wire, and that voltage 0:06:14.960 --> 0:06:19.600 difference produces alternating current or a c electricity. There are 0:06:19.640 --> 0:06:22.720 tons of different types of generators out there. Some of 0:06:22.760 --> 0:06:27.120 them burn fuel in a in an engine that creates 0:06:27.120 --> 0:06:30.680 the energy needed to move a motor, which in turn 0:06:30.839 --> 0:06:33.280 rotates the rotor. So you can take fuel, you can 0:06:33.320 --> 0:06:35.440 burn it in an engine and use that engine to 0:06:35.520 --> 0:06:38.440 work with a generator to produce electricity, so you just 0:06:38.560 --> 0:06:43.680 refill the uh that the engine whenever the fuel runs out, 0:06:43.760 --> 0:06:46.960 and you can keep on generating electricity this way, or 0:06:47.040 --> 0:06:50.279 you could use turbines that are turned by stuff like 0:06:50.360 --> 0:06:53.960 wind or water. So with a typical steam turbine, you 0:06:54.040 --> 0:06:57.839 have a closed system in which a heat source heats 0:06:57.880 --> 0:07:01.320 up water until it boils and creates high pressure steam. 0:07:01.520 --> 0:07:03.360 That high pressure means the steam has got a lot 0:07:03.360 --> 0:07:07.240 of energy behind it, and the steam encounters the first 0:07:07.320 --> 0:07:13.040 blades of the turbine. Typically turbines consist of multiple blades, 0:07:13.480 --> 0:07:16.120 and they start in a very kind of tight circle, 0:07:16.480 --> 0:07:18.840 and then as you go further into the turbine, the 0:07:18.840 --> 0:07:21.840 circles are getting bigger and bigger because steam expands as 0:07:21.840 --> 0:07:24.760 it's moving through this turbine system, and the fans are 0:07:24.760 --> 0:07:27.560 angled so that the push from the steam creates a 0:07:27.640 --> 0:07:31.040 rotational force on the turbine and it turns the rotor. 0:07:31.480 --> 0:07:33.880 So steam passes through the fan blades, it expands, it 0:07:34.000 --> 0:07:37.160 keeps pushing those next series of fans. This is what 0:07:37.360 --> 0:07:42.080 allows you to create a very efficient steam turbine design, 0:07:42.600 --> 0:07:44.679 and it helps you capture as much of the energy 0:07:44.720 --> 0:07:47.560 from the steam as you can. The turbines shaft, like 0:07:47.560 --> 0:07:49.560 I said, is connected to the rotor of the electrical 0:07:49.600 --> 0:07:52.840 generator that produces the rotational energy that creates the fluctuating 0:07:52.880 --> 0:07:57.000 magnetic field, etcetera, etcetera, etcetera. Now, the steam continues through 0:07:57.000 --> 0:08:00.480 the system after passing through the turbine, and it cools 0:08:00.560 --> 0:08:04.560 down as it does so typically through exposure to some 0:08:04.640 --> 0:08:08.280 other part of this system. And as it cools down, 0:08:08.320 --> 0:08:12.000 it condenses back into water and it flows back into 0:08:12.080 --> 0:08:14.880 the boiler where the whole process can start over again. 0:08:15.520 --> 0:08:20.040 But again, with nuclear power, you're using a different material 0:08:20.120 --> 0:08:23.040 and process to create the heat than you would with 0:08:23.080 --> 0:08:25.680 a coal power plant, and there's a need to make 0:08:25.720 --> 0:08:28.880 sure the systems in a nuclear power plant are secure 0:08:28.960 --> 0:08:32.200 and separate from each other to prevent contamination, or at 0:08:32.280 --> 0:08:36.120 least shielded very very well if you have a full 0:08:36.320 --> 0:08:39.800 implemented system. So if the water is actually passing through 0:08:39.840 --> 0:08:42.199 the reactor and that same water is the water that's 0:08:42.200 --> 0:08:44.800 converted into steam to pass with the turbine, you want 0:08:44.800 --> 0:08:47.840 to make sure that that facility is very well shielded. 0:08:48.720 --> 0:08:52.800 Most nuclear power plants have two water systems. They have 0:08:52.880 --> 0:08:55.400 one that's the coolant uh and then they have a 0:08:55.440 --> 0:08:58.160 secondary one where there's a heat exchanger that sends the 0:08:58.200 --> 0:09:02.320 heat from the coolant into this boiler, which then boils 0:09:02.360 --> 0:09:06.280 off the water and create steam. And the two systems 0:09:06.280 --> 0:09:09.320 are separate. They don't they don't come into direct contact 0:09:09.320 --> 0:09:13.319 with each other, so you don't pass radioactive contaminants from 0:09:13.360 --> 0:09:16.440 the coolant into the steam that you're using to turn 0:09:16.480 --> 0:09:20.720 the turbines. Now, the isotope most commonly associated with nuclear 0:09:20.760 --> 0:09:25.680 power is uranium two thirty five, but plutonium two thirty 0:09:25.760 --> 0:09:28.400 nine is also used in some reactors, and there are 0:09:28.400 --> 0:09:32.160 some nuclear power proponents who really advocate a thorium based 0:09:32.200 --> 0:09:35.840 power plant. More on that later in this episode. And 0:09:35.840 --> 0:09:37.679 I've said the word isotope a few times. Why does 0:09:37.679 --> 0:09:40.800 that actually mean. Well, isotopes are two or more forms 0:09:41.120 --> 0:09:45.360 of the same element, meaning uh, two or more forms 0:09:45.360 --> 0:09:48.040 that all have the same number of protons. Because if 0:09:48.080 --> 0:09:50.679 you have different number of protons and you have different elements, 0:09:51.120 --> 0:09:54.640 so you're looking at two different atoms that represent the 0:09:54.679 --> 0:09:57.120 same element, and they have the same number of protons, 0:09:57.160 --> 0:09:59.760 but they have different numbers of neutrons from each other. 0:10:00.280 --> 0:10:03.960 Neutrons are particles have a neutral charge. You find them 0:10:03.960 --> 0:10:07.440 in the nuclei of atoms. They don't affect the chemical 0:10:07.559 --> 0:10:12.199 properties of the element, but isotopes do have different atomic 0:10:12.320 --> 0:10:17.480 masses relative to one another, so they are chemically identical, 0:10:17.840 --> 0:10:22.679 but from a nuclear process perspective, they are different. So 0:10:22.840 --> 0:10:26.040 uranium two thirty five is as you would imagine an 0:10:26.040 --> 0:10:29.800 isotope of uranium. It is not the most commonly found 0:10:29.880 --> 0:10:33.240 form of uranium in nature. The most common form of 0:10:33.360 --> 0:10:36.920 uranium is uranium two thirty eight. Uranium two thirty eight 0:10:36.960 --> 0:10:41.520 has ninety two protons and one forty six neutrons. Uranium 0:10:41.559 --> 0:10:44.360 two thirty five has ninety two protons and one forty 0:10:44.520 --> 0:10:48.280 three neutrons. Uranium two thirty five makes up less than 0:10:48.360 --> 0:10:52.880 one percent of all naturally occurring uranium in the world, 0:10:53.360 --> 0:10:56.199 and it has a half life of nearly seven hundred 0:10:56.200 --> 0:10:59.880 four million years, which means if you have a qual 0:11:00.080 --> 0:11:04.439 unto ty of uranium to thirty five any given amount. 0:11:04.840 --> 0:11:07.400 Let's say that you have a pound of uranium two 0:11:07.400 --> 0:11:10.240 thirty five. That's an enormous amount of uranium two thirty five. 0:11:10.240 --> 0:11:11.760 But let's say you have a pound of it, it 0:11:11.800 --> 0:11:17.800 would take approximately seven four million years for that uranium 0:11:17.800 --> 0:11:22.040 two thirty five to reduce in half through radioactive decay, 0:11:22.120 --> 0:11:25.000 so you would end up with half a pound on 0:11:25.120 --> 0:11:31.120 average after seven four million years. More or less. This 0:11:31.200 --> 0:11:35.120 is essentially uh the rate of radioactive decay. But I 0:11:35.160 --> 0:11:38.160 think we could actually do a lot better than that 0:11:38.240 --> 0:11:40.120 if we really put our minds to it, And I'll 0:11:40.120 --> 0:11:43.000 explain how in just a second, but first let's take 0:11:43.000 --> 0:11:53.920 a quick break to thank our sponsor. Okay, So, uranium 0:11:53.920 --> 0:11:58.240 two thirty five will spontaneously decay and release energy in 0:11:58.280 --> 0:12:01.520 the process, and when it decay as uranium two thirty 0:12:01.559 --> 0:12:05.240 five will split to create an alpha particle that's technically 0:12:05.240 --> 0:12:09.000 two protons and two neutrons that are bound together. Interestingly, 0:12:09.240 --> 0:12:12.559 there's no standard equation we can use to represent spontaneous 0:12:12.600 --> 0:12:16.800 fission for uranium two thirty five because the results are unpredictable. 0:12:17.080 --> 0:12:19.320 But if you were to trace the chain of decay, 0:12:19.440 --> 0:12:22.959 the chain of decay goes like this. And pardon me, 0:12:23.000 --> 0:12:26.640 because this gets really kind of ridiculous to describe it all, 0:12:26.679 --> 0:12:29.240 but all right, you start with uranium two thirty five, 0:12:29.600 --> 0:12:33.120 and that decays into thorium two thirty one, which decays 0:12:33.160 --> 0:12:38.000 into protact tenium. And I'm sure I'm mispronouncing that two 0:12:38.080 --> 0:12:42.720 thirty one that decays into actinium to twenty seven, which 0:12:42.720 --> 0:12:46.440 decays into thorium to twenty seven, which then decays into 0:12:46.520 --> 0:12:49.720 radium to twenty three, which then decays into rate on 0:12:49.760 --> 0:12:53.680 to nineteen, and then to polonium to fifteen, and then 0:12:53.720 --> 0:12:57.880 to lead to eleven, to bismuth to eleven, to thallium 0:12:57.920 --> 0:13:01.800 two oh seven, and then finally to lead too oh seven. 0:13:02.160 --> 0:13:04.839 Lead to oh seven is a stable atom, so it 0:13:04.880 --> 0:13:09.360 will not decay at least not through any observable time 0:13:09.400 --> 0:13:13.319 frame that we can talk about, so that's a relief. 0:13:13.840 --> 0:13:16.480 But as I mentioned earlier, if uranium two thirty five 0:13:16.720 --> 0:13:20.319 gets hit with a high speed neutron, it can absorb 0:13:20.520 --> 0:13:25.720 that neutron and then undergo fission. So as the uranium 0:13:25.760 --> 0:13:29.120 two thirty five atom splits, it can release two or 0:13:29.280 --> 0:13:32.680 three more neutrons, which is also unpredictable. It all depends 0:13:32.720 --> 0:13:36.080 on how the uranium splits, but we cannot predict how 0:13:36.120 --> 0:13:40.840 many neutrons would be given off by any one reaction. However, 0:13:41.120 --> 0:13:43.959 those two or three neutrons can then go and get 0:13:44.000 --> 0:13:47.560 absorbed by other uranium two thirty five atoms. If you 0:13:47.600 --> 0:13:51.040 have enough uranium two thirty five atoms concentrated in the 0:13:51.080 --> 0:13:55.880 same space, then the decay of one can affect another one, 0:13:56.040 --> 0:13:59.280 and if a neutron from one decaying uranium two thirty 0:13:59.280 --> 0:14:03.600 five atom hits another, then that will prompt another reaction. 0:14:04.120 --> 0:14:06.440 So if you have the right concentration of uranium two 0:14:06.440 --> 0:14:09.680 thirty five, called a critical mass, you can have a 0:14:09.800 --> 0:14:13.959 sustained nuclear reaction. Now there has to be enough uranium 0:14:13.960 --> 0:14:16.760 two thirty five and the neutrons need to be moving 0:14:16.800 --> 0:14:20.320 at the right speed for that to happen. With lower 0:14:20.360 --> 0:14:23.480 concentrations of uranium two thirty five, you actually need to 0:14:23.560 --> 0:14:26.600 slow down the neutrons a bit in order to improve 0:14:26.680 --> 0:14:30.080 the chances that the existing uranium two thirty five atoms 0:14:30.080 --> 0:14:33.880 will absorb that incoming neutron. So you would typically use 0:14:34.000 --> 0:14:38.240 another material like graphite to act like kind of like 0:14:38.280 --> 0:14:41.080 a set of breaks. They slow down the neutrons enough 0:14:41.120 --> 0:14:43.280 for the uranium two thirty five atoms to take them 0:14:43.320 --> 0:14:46.200 in and then split apart. That type of material is 0:14:46.240 --> 0:14:50.080 called a moderator. Use a moderator to moderate the speed 0:14:50.280 --> 0:14:53.840 of the neutrons. That reaction will sustain itself until the 0:14:53.880 --> 0:14:58.360 amount of uranium two thirty five reduces below critical mass. Now, 0:14:58.400 --> 0:15:01.800 one atom of uran two thirty five will release about 0:15:01.840 --> 0:15:06.400 two hundred million electron volts worth of energy, which is 0:15:06.440 --> 0:15:09.560 actually not a very large amount of energy. So an 0:15:09.560 --> 0:15:12.120 electron vault is the amount of energy gained by the 0:15:12.240 --> 0:15:16.520 charge of an electron moved across an electric potential difference 0:15:16.720 --> 0:15:20.400 of one vault. So two hundred million electron volts sounds 0:15:20.400 --> 0:15:22.240 like a lot, because two hundred million is a really 0:15:22.280 --> 0:15:26.200 big number, But a mosquito in flight has the kinetic 0:15:26.360 --> 0:15:31.920 energy of about one trillion electron volts, so it's a 0:15:32.000 --> 0:15:36.280 fraction of the energy of a mosquito flying. However, I 0:15:36.320 --> 0:15:40.760 did say a single decaying atom of uranium two thirty 0:15:40.760 --> 0:15:44.680 five releases two hundred million electron volts. That's just one atom. 0:15:44.720 --> 0:15:47.120 If you've got a significant amount of uranium two thirty five, 0:15:47.160 --> 0:15:50.640 you're talking about billions or trillions of these atoms, and 0:15:50.680 --> 0:15:54.080 that adds up pretty darn fast. So individually the atoms 0:15:54.120 --> 0:15:57.280 don't have that much energy, but collectively they've got a 0:15:57.360 --> 0:16:01.080 whole bunch of it. In fact, in one hound of uranium, 0:16:01.320 --> 0:16:04.920 you have as much energy as three million pounds of coal, 0:16:05.760 --> 0:16:09.520 so very energy dense. When a uranium two thirty five 0:16:09.520 --> 0:16:12.760 atom splits, it also releases energy in the form of 0:16:12.880 --> 0:16:16.400 heat and gamma radiation. It's not just splitting neutrons off, 0:16:16.400 --> 0:16:19.760 it's also releasing heat and gamma radiation, which is a 0:16:19.880 --> 0:16:24.000 high energy photons. In addition, the two new atoms that 0:16:24.040 --> 0:16:28.400 result from the fission of uranium two thirty five will 0:16:28.480 --> 0:16:33.080 undergo beta radiation, which means they release super fast electrons, 0:16:33.160 --> 0:16:36.280 and they also release more gamma radiation. A gamma radiation 0:16:36.360 --> 0:16:38.960 is pretty dangerous stuff. It will not turn you into 0:16:39.000 --> 0:16:42.520 the hook, it will hurt you very badly. So let's 0:16:42.520 --> 0:16:47.800 talk about the innards of a nuclear reactor. So you've 0:16:47.800 --> 0:16:50.960 got to get a source of uranium two thirty five 0:16:51.320 --> 0:16:54.400 enriched uranium two thirty five. That means that there's a 0:16:54.480 --> 0:16:58.920 higher concentration of uranium two thirty five in your amount 0:16:58.960 --> 0:17:01.760 of uranium and you would find in nature. So if 0:17:01.760 --> 0:17:04.320 you went out in nature, you got yourself a pick, 0:17:04.840 --> 0:17:07.560 and you're going to an area that's rich in uranium. 0:17:07.640 --> 0:17:10.280 Can you mind yourself some uranium and you get a 0:17:10.280 --> 0:17:13.600 big chunk of uranium. Most of the atoms of that 0:17:13.760 --> 0:17:16.720 uranium are going to be you two thirty eight, almost 0:17:16.720 --> 0:17:19.760 all of them. Uranium two thirty five would make up 0:17:19.760 --> 0:17:24.199 about point seven two of all the atoms in that 0:17:24.359 --> 0:17:26.879 sample you collected. That is not enough for you to 0:17:26.880 --> 0:17:29.320 be able to hit critical mass. You need to be 0:17:29.440 --> 0:17:33.240 at around two or three percent uranium two thirty five 0:17:33.680 --> 0:17:37.040 in the overall sample in order to have that sustainable 0:17:37.080 --> 0:17:40.480 nuclear reaction, which means you have to have enriched uranium. 0:17:40.640 --> 0:17:43.840 You have to have uranium that has unnaturally high concentrations 0:17:43.880 --> 0:17:47.119 of uranium two thirty five. And you form these samples 0:17:47.200 --> 0:17:51.600 of enriched uranium into pellets. Now, each pellet is a 0:17:51.640 --> 0:17:54.960 cylinder that's about two and a half centimeters long or 0:17:55.000 --> 0:17:57.959 about an inch long, and they have a diameter of 0:17:58.040 --> 0:18:02.560 around eighteen millimeters round points seven inches, so in other words, 0:18:02.600 --> 0:18:06.119 they are about the diameter of a US dime. And 0:18:06.280 --> 0:18:09.720 you take these little cylindrical pellets and you put them 0:18:09.880 --> 0:18:13.840 end to end to form rods, uranium rods. You then 0:18:13.880 --> 0:18:17.760 collect bunches of those rods into what are called bundles. 0:18:18.280 --> 0:18:21.760 The bundles you put into a pressure vessel that's filled 0:18:21.760 --> 0:18:25.280 with water, and the water access you're coolant. These nuclear 0:18:25.280 --> 0:18:28.200 reactions generate a lot of heat, and without a coolant, 0:18:28.520 --> 0:18:30.840 that amount of heat would be high enough to actually 0:18:31.280 --> 0:18:35.000 melt the rods themselves. That rods would overheat through these 0:18:35.000 --> 0:18:38.520 reactions and we get hotter than the melting point for uranium. 0:18:38.520 --> 0:18:40.600 This is what we in the BIZ call a nuclear 0:18:40.640 --> 0:18:43.639 melt down, and it is a bad thing to have happen, 0:18:44.480 --> 0:18:47.400 so you have to have that coolant there. Another preventive 0:18:47.400 --> 0:18:52.200 measure against overheating are the control rods. Control rods are 0:18:52.240 --> 0:18:56.000 made out of a material that can absorb neutrons. Now, remember, 0:18:56.240 --> 0:18:59.920 the sustained nuclear reaction of a nuclear power plant involves 0:19:00.080 --> 0:19:04.199 uranium two thirty five emitting these neutrons and then absorbing 0:19:04.240 --> 0:19:07.640 incoming neutrons, emitting, splitting, and emitting more neutrons, and that's 0:19:07.640 --> 0:19:09.639 what keeps the reaction going. So if you put in 0:19:09.720 --> 0:19:14.280 material that can absorb those neutrons, you're taking away the 0:19:14.280 --> 0:19:18.320 trigger that would continue to allow this nuclear reaction to happen. 0:19:18.760 --> 0:19:22.080 So you can actually use these sort of robotic arms 0:19:22.119 --> 0:19:26.040 to lower or raise the control rods out of the 0:19:26.040 --> 0:19:31.879 bundles of uranium to and by uh by putting them 0:19:31.920 --> 0:19:34.800 into the bundles, you absorb more of those neutrons, so 0:19:34.880 --> 0:19:37.639 you can reduce the rate of nuclear reaction. You can 0:19:37.680 --> 0:19:39.960 even stop it completely if you if you leave it 0:19:39.960 --> 0:19:42.480 in there long enough and you have enough of the 0:19:42.680 --> 0:19:46.520 control rods there, or you can lift it out of 0:19:46.560 --> 0:19:50.160 the bundles to allow more of those reactions to occur, 0:19:50.240 --> 0:19:53.359 to increase the reactions, And it all depends on how 0:19:53.400 --> 0:19:55.960 things are going on in the core at any given time, 0:19:56.560 --> 0:19:59.399 and uh, if the reaction is ramping up too quickly 0:20:00.520 --> 0:20:03.359 lower a rod in the bundle soak up some neutrons 0:20:03.359 --> 0:20:06.000 prevent those YouTube thirty five atoms and the bundles from 0:20:06.040 --> 0:20:08.760 doing it and pushing the reaction even further. Now, in 0:20:08.880 --> 0:20:12.280 some reactors, the coolant isn't water at all, It might 0:20:12.320 --> 0:20:14.560 be something else. There are a few that use gas 0:20:14.600 --> 0:20:19.520 based coolants like carbon dioxide, or they might use liquid 0:20:19.560 --> 0:20:22.840 metals like sodium or potassium. That generally allows you to 0:20:22.880 --> 0:20:26.080 operate at a higher temperature than you would if you 0:20:26.080 --> 0:20:30.680 were using water, but that also could mean that you're 0:20:30.680 --> 0:20:33.439 burning through fuel a lot faster. So in some reactors, 0:20:33.480 --> 0:20:35.600 like the third of the ones that are in the 0:20:35.680 --> 0:20:39.000 United States, the coolant is in fact the water that 0:20:39.040 --> 0:20:43.320 gets converted into steam and eventually pushes a turbine. But 0:20:43.359 --> 0:20:45.640 again that can be risky because that coolant has been 0:20:45.640 --> 0:20:48.879 in direct contact with the radioactive materials. So if that 0:20:49.000 --> 0:20:53.639 steam were to escape him, then that could be a 0:20:53.680 --> 0:21:00.520 potential hazard for the surrounding environment. Generally, most of the 0:21:00.520 --> 0:21:04.800 power plants in the United States use pressurized water reactors 0:21:04.840 --> 0:21:07.640 and a secondary closed system of water for the purposes 0:21:07.800 --> 0:21:11.200 of turning the turbines. Two thirds of the power plants 0:21:11.240 --> 0:21:14.800 the United States use this approach. So you have the 0:21:14.840 --> 0:21:18.240 water the coolant that's inside your nuclear reactor under a 0:21:18.359 --> 0:21:22.560 tremendous amount of pressure, and that pressure prevents the water 0:21:22.640 --> 0:21:26.960 from boiling off. It remains liquid, so it's superheated liquid 0:21:27.560 --> 0:21:30.960 that cannot boil because of that pressure. But that superheated 0:21:31.040 --> 0:21:35.119 liquid is in contact with a heat exchanger, and the 0:21:35.160 --> 0:21:39.480 heat exchanger transfers heat to the water that's inside a boiler, 0:21:39.840 --> 0:21:42.719 and that water can boil off, turn into steam, and 0:21:42.760 --> 0:21:46.560 turn steam turbines, but it's in its own closed, parallel system, 0:21:46.920 --> 0:21:49.960 so the two systems don't actually share any water between 0:21:50.000 --> 0:21:52.360 the two of them, and that way you have one 0:21:52.600 --> 0:21:57.680 relatively clean system of water that's consistently being heated to steam, 0:21:57.720 --> 0:22:00.879 turning turbines, condensing back into water and starting over again, 0:22:01.200 --> 0:22:02.840 and then you have the other one that's acting as 0:22:02.880 --> 0:22:05.480 the coolant for your actual reactor. Two thirds of the 0:22:05.520 --> 0:22:09.000 power plants in the United States use that approach. The 0:22:09.160 --> 0:22:11.840 steam that powers the turbine has to cool off in 0:22:11.960 --> 0:22:15.280 order to condense back into water, so some plants will 0:22:15.400 --> 0:22:18.960 use water from natural resources like lakes or streams to 0:22:19.080 --> 0:22:22.840 cool that steam using another form of heat exchange. So 0:22:22.960 --> 0:22:27.040 the steam exchanges heat, it transfers heat to the water 0:22:27.240 --> 0:22:30.679 from the lake or stream, and then as a result, 0:22:30.720 --> 0:22:33.600 the steam itself starts to cool down because it's pushed 0:22:33.640 --> 0:22:36.560 that heat energy off to a different source and turns 0:22:36.600 --> 0:22:40.000 into water. Other nuclear power plants have those really tall 0:22:40.119 --> 0:22:45.840 cooling towers. Those are those iconic, enormous chimney like structures 0:22:45.840 --> 0:22:48.159 that we tend to associate with nuclear power plants. Like 0:22:48.200 --> 0:22:51.880 if you watch the Simpsons, you see that that iconic 0:22:52.000 --> 0:22:55.680 shape of the cooling towers next to the power plant 0:22:55.760 --> 0:22:59.399 in in Springfield. So for every unit of electricity produced 0:22:59.400 --> 0:23:02.720 by a power plant, it about two units of waste 0:23:02.760 --> 0:23:06.119 heat get transferred to the environment. But that's just heat. 0:23:06.440 --> 0:23:10.760 It's it is heat, but it's not greenhouse gas, so 0:23:10.840 --> 0:23:14.399 it's not something that contributes to climate change on a 0:23:14.440 --> 0:23:20.240 global scale. You get some regionalized heating, but it's temporary, 0:23:20.440 --> 0:23:23.880 So that's good. But nuclear power plants obviously create some 0:23:24.040 --> 0:23:27.399 real challenges. What are those Well, I'll tell you in 0:23:27.480 --> 0:23:29.879 just a second, but first let's take another quick break 0:23:30.080 --> 0:23:40.480 to thank our sponsor. Because the energy from a nuclear 0:23:40.520 --> 0:23:45.240 reactor includes stuff that can really cause harm to humans 0:23:45.240 --> 0:23:48.199 in various ways, the nuclear reactor itself has to be 0:23:48.320 --> 0:23:51.680 heavily shielded to prevent that radiation from getting out into 0:23:51.680 --> 0:23:56.719 the general environment. Typically, the reactor has a concrete liner 0:23:56.880 --> 0:23:59.960 to act as a radiation shield, and around that line 0:24:00.000 --> 0:24:02.280 inner so one layer out. Think of it as an onion. 0:24:02.359 --> 0:24:03.679 So you've got a reactor at the core of the 0:24:03.680 --> 0:24:06.160 onion that you've got a peel of the onion. Layer 0:24:06.160 --> 0:24:08.960 of the onion that is the concrete liner. Then you 0:24:09.000 --> 0:24:12.600 have another layer around that that's a steel containment vessel, 0:24:12.960 --> 0:24:15.200 and then the power plant itself is typically made out 0:24:15.200 --> 0:24:18.240 of very thick concrete that access sort of a final 0:24:18.320 --> 0:24:21.760 layer of protection between the reactor and the surrounding area 0:24:21.880 --> 0:24:26.000 if all else were to fail. In addition, the spent 0:24:26.200 --> 0:24:30.520 fuel in a fission reactor is itself radioactive. It contains 0:24:30.520 --> 0:24:34.640 a lot of different radioactive materials in it of various 0:24:35.280 --> 0:24:38.480 uh half life's so some of those half lives are 0:24:38.640 --> 0:24:41.159 on the matter of days or a couple of years, 0:24:41.200 --> 0:24:46.080