字幕列表 影片播放 列印英文字幕 Everybody who likes drain tanks, this is a drain tank. The big goal of this machine here is to simulate how decay heat is removed from this design when there's a shutdown. That is correct. In January 2015, Kirk Sorensen of Flibe Energy toured UC Berkeley's Compact Integral Effects Test for Pebble and Molten Salt Fueled Reactors. Kirk also presented at UC Berkeley... We're going to talk mostly about the chemical processing and a little bit about the power conversion system as well. ...and the University of Utah. The chemical processing of this reactor... Those two presentations are combined in this video. We're in a situation in our country where we're retiring a lot of power generation right now. This is actually happening particularly in the Eastern US where I live. You can almost trace the outline of rivers like the Tennessee and the Ohio based on where these retirements are taking place. Now, there are things we don't like about coal, and there are things we do like about coal. We like the fact that is a reliable energy source. We don't like the fact that it emits a lot of pollution, and it's not a resource that's going to last forever. There are also new regulations that are coming out that are accelerating this change, so we've got a big job to do. We don't really have a great deal of time to do it. We need a source that mimics all of the benefits of coal-fired power, and tries to eliminate the drawbacks. A number of us are convinced that this energy source is going to be nuclear in origin. The reason for that is, the energies of the nuclear are about two million times greater than the energies of the electron cloud -- the energies of chemical energy, the energies that powers a combustion digestion, all the processes we're used to. Yet, out there in the universe, the universe is powered by the energies of the nucleus, changing nuclear states, fusion and fission and nuclear decay. Humanity has only realized this in about the last 70 or 80 years until we've taken our first steps into a nuclear-powered world. I'm convinced that if we are going to be able to enjoy the industrial society that we have, enjoy reliable energy and improve its cleanliness, we're going to have to make this leap, too. We're going to have to make the leap to nuclear energy. I kind of feel bad when I hear that nuclear reactors are being retired. Even though I know that they're not as efficient as they could be, they're still a whole lot better for the environment than spewing dirty coal into the air. What I'd really like to see is the United States building new nuclear resources to replace our reactors that are being retired, the uranium style reactors, and also to be able to replace coal and fossil fuels. The Department of Energy has put the responsibility for these new nuclear reactors though, squarely in the lap of industry. This is a big deal, because for decades in this country after the war, the Atomic Energy Commission made all the decisions about what was going to happen. It wasn't like industry got to say, "Oh, we want to try this, or we want to try They said, "We're going to do this, or you're going to do that, and you'll submit a proposal." But it was not in industry's court to go and make decisions like this, and now it is. This is a relatively new development, and I think it's going to lead to entrepreneurialism because they've squarely put the onus on us to say how nuclear is going to go forward. Make your business case. Make your argument. If you want a nuclear power plant, say why it's better. What kind of nuclear energy then becomes a logical question. We are blessed on this world with nuclear resources, three forms of nuclear fuel, two forms of uranium, and one of thorium. Thorium is about three times more common than uranium, but the uranium we're using today is only a tiny, tiny, tiny fraction of natural uranium. It's what's called naturally fissile uranium, uranium-235. This is what we're consuming right now for nuclear energy. If you want to make nuclear energy a sustainable enterprise, then you need to go and be using the remainder of these fuels. Thorium has the advantage of abundance. There is an awful lot it, but it doesn't have any naturally fissile thorium. There is no little sliver here that we can point to and say, "This is thorium we can use to start a nuclear reaction." This is one of the reasons why thorium has not been favored for nuclear energy in the early days, but now we've reached a more mature stage, where I think it is time to go ahead and look at implementing thorium as a nuclear fuel. Both thorium and uranium-238 can become nuclear fuels by absorbing a neutron, and this happens inside a nuclear reactor. This is what Glenn Seaborg figured out right here, at Berkeley 70 years ago. Wasn't this was possible? Glenn Seaborg, what a guy. Read all you can about him. If thorium absorbs a neutron, becomes uranium-233, that is now a nuclear fuel. It can fission. It can split, and release energy. Uranium-233, when it's fissioned by a thermal neutron, will produce about 2.3 neutrons net. That's important, because we need a two right here to make this happen in the first place. You've got to have more than two to keep this going. The same thing can happen with uranium-238, which is the common form of uranium, the abundant form of uranium. If it absorbs the neutron, it becomes plutonium-239, and then that can fission, and also release energy. In both ways you can turn these abundant nuclear resources into energy sources. What is the advantage of thorium then? Why think about thorium? Uranium-238 is converted to plutonium through a neutron, but that's thermally fissioned. On that, you only get about 1.9, so you're below two. You're below that threshold. That's why we can't build plutonium breeder reactors in thermal spectrum reactors, just can't do it. There are not enough neutrons. Really, plutonium kicks out enough neutrons. It's just plutonium has a real propensity to eat neutrons, too. If we want to use plutonium efficiently, we really have to go to a fast spectrum, because what happens in fast spectrum is fast neutrons have a much higher probability of fissioning the plutonium without being absorbed. Now, because they have a higher probability of doing that though, they don't have a higher probability of the fission happening in the first place. This is what plutonium looks like to a slowed downed neutron. The blue is the probability that it will fission, and the red is the probability that it will simply absorb the neutron. Each one of these guys is what plutonium looks like to a fast neutron. Every one of those is a better quality hit. You're not going to get an absorption, but you need a lot of it. If you want to have the same amount of cross-section probability, and fast as thermal, you've got to have a lot of fuel, a lot of fuel. This is an advantage of thermal spectrum, because you need a lot less fuel, but because you can't breed in thermal spectrum, the interest has always been for plutonium breeding to go to the fast spectrum. I bring this up because thorium doesn't have this issue. Thorium can go ahead and be used as a nuclear fuel in a reactor with slowed down neutrons. It's called thermalized neutrons. There are a few steps thorium goes through on this way. It first absorbs the neutron and becomes thorium-233, going from 232 to 233. See, the math is not so hard, just plus one. Then that thorium-233 will decay over a period of about a half-an-hour into another element. Protactinium-233. Protactinium is a naturally occurring material. It's part of the decay chain of uranium-235, but protactinium-231, it's got something like, a 172,000-year half-life. This stuff, protactinium-233, has a much shorter half-life, about 30 days. Still, in terms of reactors, that's pretty long. It drives a lot of what I'm going to talk about today with the chemical processing. But ultimately it will decay to uranium-233, as long as it doesn't absorb a neutron, and it has a very quality fission. About 91 percent of the time, it's going to fission rather than absorb, and that makes U-233 the best fuel in the thermal spectrum. It outperforms everything else, and it's one of the reasons we really get a kick out of thorium. There are three options. We can keep bringing U-235, and without getting into issues about seawater uranium, it's just we're using a very small amount, and we're not using a whole bunch of uranium. We can go with the fast freezers I saw yesterday at INL with EVR2, or we can potentially take this tack of a thermal breeder with thorium. The path that we want to go is the thorium, because of its abundance, and because of the fact that we can use it with slowed down neutrons. That makes the reactor design simpler, and quite possibly safer. If you can operate a thorium reactor without any uranium-238 present in the fuel, then you can really reduce the amount of transuranic waste you're going to generate. The reason for that is the thorium absorbing the neutron. Each one of these vertical steps is a neutron absorption. The thorium absorbing the neutron, 90 percent of the time, will be fissioned by the next neutron. At 10 percent of the time, it will go to U-234, which will absorb another neutron, go into U-235. Think of these as like off-ramps off the freeway. If 90 percent of the cars exit the freeway on the first off-ramp, and 85 percent of the cars that are leftover exit the freeway on the next off-ramp, how many are there to make your first transuranic? It's only one-and-a-half percent. With the thorium cycle, you could potentially get down to one-and-a-half percent of the long-lived wastes production of the uranium cycle, and that's a big advantage. On the other hand, when you've got a fuel, like a uranium reactor, it's got a lot of U-238 in it, then it's only one neutron away from its first transuranic. The reason I bring up transuranics is they govern, in large part, our waste disposition strategy. In fact, actinides in general, govern our waste disposition strategy, because they have long half-lives. They have complicated K chains. Our waste disposition strategy is in great part about actinides. Got one of the members of the Blue Ribbon Commission here, so stop me at any time if I screw up here. Here's what we're doing now. This is the red line on a log-log chart. Any line on a log-log chart, tread lightly. This is how long it takes our spent fuel to reach the same rate activities as natural uranium. It's about 300,000 years. If you can keep all the actinides out of the waste stream, then you can really shorten that to about 300 years. One of the goals in the chemical processing system we're going to talk about today is how to keep the actinides out of the waste stream. I hate to even call this stuff that is made by the thorium cycle, waste. Neptunian-237 is actually used to produce the material that NASA uses for batteries in their deep space probes. Have you ever heard of the Curiosity Rover on Mars? Anybody heard of that or followed it? That's being powered by plutonium-238, which comes from this neptunium. Anybody following the New Horizons' mission to Pluto, keeping track of that? That's also powered by this stuff, so even our waste, so to speak isn't even really waste. It's something that we could go and make very useful products out of. Like I said, I was at NASA, so I'm really into this kind of stuff. By the way, 2015 is going to be a really exciting year for NASA, because we're going to see Pluto for the first time, and we're going to see the largest asteroid in the solar system, Ceres, for the first time. Cool stuff coming up this year. If you use thorium with this kind of efficiency, something really amazing becomes possible. This was realized almost immediately by Glenn Seaborg. He thought every cubic meter of the Earth has got a certain amount of uranium and thorium in it. It's about two cubic centimeters of thorium and half a cubic centimeter of uranium. If you can use thorium to the kind of efficiencies that we're talking about today, the energy equivalent of these two cubic centimeters, so imagine two little sugar cubes. Think of two little sugar cubes of thorium metal. Milan, can you hold that in your hand, two cc's of thorium? Is that going to hurt you?