David N. Miller

Transcription

>> Okay, so we have Kirk Sorensen who founded the energyfromthorium website and is a passionate proponent of using thorium to cure the words--world's energy ills. He was at NASA and the U.S. Army for several years and now he's at University of Tennessee. >> SORENSEN: As a student. >> As a student--PhD student in Nuclear Engineering, teaching courses there and is working--is the Chief Nuclear Technologist at Teledyne Brown Engineering. And he's here at Google exploring ways to improve the environment with nuclear energy. And he's got--done elementary analysis recently on the composition of nuclear waste or the nuclear resource of spent reactor fuel and he's going to tell you about his simulations about what's in waste, how it changes versus time, and how there might be some value to be collected there. Kirk Sorensen. >> SORENSEN: Thank you. [Pause] Thank you everybody, I hope I earned that. My name's Kirk Sorensen. Like I was saying, I'm here from Teledyne Brown Engineering in Huntsville, Alabama and we're very interested in nuclear energy as possibilities for the future. We've been involved in nuclear work for a number of years and also with the U.S. Space Program and we see this as a growth opportunity. And so I have been spending a number of weeks and months trying to learn a lot more about--well, what the heck is a--what the heck is in spent nuclear fuel or nuclear waste, as it's sometimes called. So we'll start out about what the heck goes on in a nuclear reactor when a fission takes place. So you have a heavy nuclei, uranium typically, and you hit it with a neutron and it splits into two fission products, so one's kind of bigger and one's kind of smaller and also several additional neutrons come off and enable you to continue the reaction. Now what's really significant about this is a kilogram of fissile material will release as much energy as, like, 13,000 barrels of oil. So this is--you know, if you remember that at the notes, this is why we care. This is why nuclear energy matters is because it's a very, very energy dense way to go about producing energy. So when you talk to people about nuclear energy, a lot of times they say, "Okay, but what about the waste? Is that a real problem? And you now, what's involved?" So this is really getting back to this process. Why do we have waste? Well, the reason why nuclear waste is generated and why it's radioactive is because the fissile material has a particular neutron or proton balance that keeps it semi-stable. This is why this stuff's been around for billions and billions of years, is because it's pretty close to being stable, it's not as radioactive, but it's pretty close. And then if you go and take this stuff that's at such and such a balance of protons and neutrons, about 1.53 to 1.56 and you split it in half, all of a sudden, you got two pieces and they retain that neutron-proton balance, but it's all wrong for how big they are. They want stable neutron-proton ratios of about 1.25 to 1.46, so what they've got is they have too many neutrons. They inherit too many neutrons from their birth, from when they get started, and they will go ahead and they will change this. They'll change a situation by a very simple process, radioactive decay, specifically beta decay. And beta decay is how nature takes care of this imbalance of neutron and protons. Nature will go and turn neutrons into protons and it will do it by--there's a simple way to think about it, and I'm sure this is wrong, but as you could essentially think about them, say, you bust a neutron into two pieces, you bust it into a proton and an electron and charge is conserved and you know nature is happy. The beta particle, which is an electron, gets kicked out of the nucleus and the proton stays put. Now if you recall, the electron doesn't hardly weigh anything. The proton on the other hand, weighs about the same amount as a neutron. So what beta decay does is it changes the chemical composition of a material without changing its mass. So once a fission product is born, it pretty much stays at whatever mass it is, it doesn't--it doesn't change. But what it will do is it'll undergo changes in its chemistry, it'll undergo changes in what it--which element it is. It'll go from being cesium to being--oh, shoot! Now I have to think what the next thing on the periodic table--barium or something. And so essentially, beta decay changes one element into another without changing its mass. So the next thing I wanted about was, well, okay, what do we make out of nuclear fission? If we go and we fission a bunch of fissile material and we go and look what comes out, what do we see? And you kind of see this double hump distribution. This is--I'm showing this on a--on a normal plot and then here it is again on a log plot, you kind of see this double hump distribution. And where this comes from is you got a big piece and you got a little piece and you'd think that fission would split things right in half, but it doesn't. It--for whatever reason again, beyond me, this is how things come out. And so if you look at it on the periodic table, a bunch of people will say, "Okay. Well, fission makes everything in the periodic table." And so I got curious and I went and started looking at that, does it really do that? Well, it turns out, no it doesn't really. It creates a lot of stuff on periodic table but it's a finite number. It creates about 35 different elements are created through fission and at different amounts. So I then got really curious about what was in fission, what was being made. So I wrote a simulation and this is the part I really kind of want to show you guys and I'll probably spent most of this talk talking about. I'm going to about--I'm going to shoot for going about 20 minutes and no longer so we can have questions, because Chris told me yesterday that people stop watching Tech Talk videos after 10 minutes. So I figured 20 where I'm one standard deviation, I better not push our luck beyond that. Okay. So, took a typical white water reactor, typical uranium fuel, and I took my computer code and I burned it. I burned it for a typical amount of time which is, in nuclear terms, this was a 39,000 megawatt day burn, and that's probably a little bit on the high end of what you'd normally get out of fuel. So this is kind of higher performance fuel. You know, this is taking advantage of the latest technologies and then you go and you essentially drop all this stuff in the computer and you say, "Okay, what's there?" Now let me talk just really quickly about radioactivity and what radioactivity means. This is a word that actually has a rigorous definition. Activity is defined as the number of disintegrations per second, so how many times is something disintegrating? Let's say you have two samples and each of them are disintegrating, they're having a thousand disintegrations a second, a thousand decays. Both of them have the same level of radioactivity, okay? Now what else is really interesting is because different materials have a natural--what's called a decay constant, they have different decay constants; radioactivity and the amount of mass you have are interchangeable concepts. So if I say I have a sample that has one curie of activity, you know exactly how many grams of whatever it is you've got as long as you know what the sample is, but those two numbers can be very different. So if I have a sample of iodine 131 and I have one curie of iodine 131, and I have one curie of uranium 238, I go, "Wow!" both of these have the same level of radioactivity, but you're going to find out that that sample of iodine 131 is like a microgram and that sample of uranium 238 is probably like the size of my car or something like that. So I mean it's just that you get very, very different amounts of materials. So that's kind of level one, the activity; how fast or thick--how radioactive is something, how fast is something radioactively decaying? Another rule of thumb is to remember that--and this is going to sound really obvious, but if you have a nuclide and it's radioactive, that means all of it is radioactive. In other words, there's no fraction of it that's not radioactive and there's some fraction that is. All of it is radioactive and it will all decay away, because it will decay into something else. It will never become--you'll never have stable uranium 238 because uranium 238 will decay into something else. So that kind of helps us understand if we got a sample of something, it's going to go away over time. Things decay overtime and the more radioactive they are, the faster they decay and the more dangerous they are. The most dangerous radionuclides are the ones that have the shortest half-lives, okay? That's another thing to remember, too. The longer the half-life, the less active it is, typically, the less dangerous it is. Okay, so we show up at our reactor in this simulation and we come at, you know, one day after shutting it down. And what I'm going to take you through is about 30,000 years of decay of this nuclear material. So we're not going to do anything to it. We're just going to watch it. We're just going to imagine we can just follow for 30,000 years. And we're going to see through--we're going to see roughly four eras in this--in this fuel. The first era is going to be we're going to have lots and lots of radioactivity right off the bat and then we're going to go through a period of about 10 or 20 years of moderate radio activity, and then we're going to drop to a period of lower radioactivity. And then finally, all the fission products are basically going to be gone and then we're going to go on to an era where it's just dominated by that stuff that didn't burn the first time. Okay, so I'm going to try to start running this simulation and we're going to have to follow this. The circle size is dictated by the total radioactivity in this sample, and this is a--this is a megacuries per metric ton of uranium. So we're going to follow this from one day and this is a log scale on the bottom as you might imagine, so we're going to follow it and the first thing we see is, okay, most of the radioactivity is neptunium 239. What's that? Well, that's uranium that's about to become plutonium which is potentially future fuel. Neptunium 239 always has a two-day half-life so it's going away pretty quick. So by about a month into things, we've already moved out of that first era and to the second era and our radioactivity have fallen by about a level of four from where we started. So then, we start moving into this era where we see a number of different fission products, and they're so many; it's kind of hard to tell what the heck is going on. So we keep running the simulation more and more, and this list is going to get smaller and smaller and smaller. Now we're going out to about a year. And now we've got a more manageable set of stuff to look at. One of the things we see is we see plutonium, plutonium 241 which is not an isotope we normally think a lot about; that's actually a more rare form of plutonium. We see promethium, praseodymium, cerium, cesium, and barium. Now these two turn out to be related. Cesium decays into barium, so that's--keep your eye on those guys because they're going to turn out to be important. And then look for another one right here, strontium and neutrium, that's another one that'll turn out to be important, but you can see they're not really the big ones at a year. We got a lot of other stuff, so let's take it forward a little further in the future. Let's take it out to about 10 years. Okay, so now we've dropped to less than a megacurie. We're at half a megacurie now and we can see that as a fraction of our total radioactivity, the plutonium is a whole lot larger. Now, really, you can see strontium and neutrium are a big chunk, and cesium and barium are another big chunk. So I'll take it out a little bit further, I'll take it out to about 20 years. Now, 20 years is a timeframe where we have lots of spent nuclear fuel that's 20 years old, that's been sitting in fuel pools or dry cask for 20 years. And this is essentially from a radio--from a radioactivity standpoint, this is what it looks like. All right, so first order, you can say it's really basic. You got three main things in it, it's got strontium and neutrium, and you can ignore the neutrium because it comes from strontium. So it's got strontium 90, its got cesium 137, and barium 137m comes from cesium 137. So it's one, two and then the third thing you've got is the stuff that didn't burn in the reactor, the americium and the plutonium. And you can really see the plutonium rally dominates that scenario. So then let's take it out even further beyond this and I'm just going to sort of hit play and let it go for a minute. Okay, now it's really moving in a log scale. So now we're taking it out to about 100 years. Okay. Now, both strontium and cesium have 30-year half-life so at 100 years, we've gone through three half-lives of them and now we're down to about 1-100th the rate--no, I'm sorry about--1-1000th radioactivity we started with. And let's keep following it further and further into time, and we see strontium and cesium decaying away to--by about 300 years, they're going to be essentially gone entirely. And why 300 years? Well, a good rule of thumb is 10 half-lives and it's gone, so if you got a 30-year half-life on strontium and cesium, 10 to those is 300 years and then it's gone. So by the time we get to three or four hundred years, you can see that the radioactivity problem essentially is entirely the stuff that didn't burn. Everything that did burn is pretty much gone and it's the stuff that didn't burn. And then we can let the sim run out through a couple of thousand years and it's just shifts between plutonium and americium without a--without a terribly big difference. So here we go, thousands of years. I will stop it real quick at 10,000 years. And the significance of 10,000 years is the Yucca Mountain Waste Repository was intended for a 10,000-year operation or--I'm sorry, for a 10,000-year isolation. So what do you got 10,000 years? Well, you got a bunch of plutonium, basically. So the reason I think that's something to note is plutonium is fuel. You know, we can burn it up in reactors and we can make energy from it and putting it in a waste stream is a good way to kind of loose track of it over time because of all these protecting radioisotopes will burn away. Okay, so and then you take it out even further and further and further in the future and you essentially end up with a mass of plutonium. Okay, so that's radioactivity, and let me go kind of reset the whole thing again. The next aspect to think about is decay heat, and that's when you have an activity, when you have a disintegration, you release a certain amount of heat. And not all of these guys release the same amount of heat; some release a lot more than others. So in this simulation, I've set it up so that you can go and you can switch everything to decay heat instead of to radioactivity, and you can look at how things change. And one of the things it changes--you know, it's some broad changes but not super different. So, we know that there's a certain amount of energy that comes from the decay of radionuclides; but then we want to worry about what's the danger, you know. People are scared of radiation and they think, "Okay, what is it about spent nuclear fuel that it could harm me?" Well, there are three kinds of nuclide decay: there's alpha, beta and gamma decay. And of those three, gamma is by far and away the most penetrating part of decay. That's really what you have to design shielding and casks and so much for is gamma decay, because gamma's particles will get out of the nuclear material and you stop it with a bunch of concrete; this is essentially what we do. So I went and I took activity times decay heat times the fraction of the material that was being released as gammas and I found something that really, really surprised me. So, let me reset the simulation here and show you what I found that surprised me so much. I'll set it to gamma power, and I'll take it out about 15 years. And here's what I found that surprised me so much is that from about five to fifteen years, almost all of this gamma energy is coming off from two radio nuclides; one of them is cesium 134 and the other one is barium 137m. Barium 137m comes from cesium 137, so, if you went into spent nuclear fuel and you extracted only one thing, one element, cesium. Okay, so you went in there and said, "I'm taking this out," you would remove most of the gamma energy from the spent nuclear fuel. And that was a big surprise to me because I've never read that before in the literature or anywhere else. I don't--maybe I made a mistake, you know, my code is open and you can certainly go and see if I made a calculational error. But it seems to imply to me that we could address spent nuclear fuel in a very different way from what we we're doing now, and potentially reduce the risks substantially by taking exactly one thing out of the spent nuclear fuel, and that is cesium. So, kind of an intriguing result. Okay, so I've showed you that and I want to jump back and talk about some of the things that are in spent nuclear fuel. We have a variety of things. Now, what I showed you was all the things that were radioactive. But most of the things that show up in spent nuclear fuel are not radioactive because they're stabilizing very quickly. And there's essentially about six categories here of things in spent nuclear fuel that I thought were interesting and worth looking at. One of them is high-value, rapidly stabilizing fission products. And the two of these that are--that are really of interest are xenon and neodymium. Now, xenon is a noble gas and we use it--at NASA, we use it in ion engines, and you can use it in light bulbs, and you can use it in energy-efficient windows. Well, this is the number one fission product that comes out of fission and also, it's the very first one to stabilize, it stabilizes in just a few months. So you could go and extract all the xenon from spent nuclear fuel, and it is completely non-radioactive and it would have, you know, a fairly substantial amount of mass. This is not--this is not, you know, super expensive stuff but it's not super cheap either. So this would be kind of the low-hanging fruit of something that you could economically recover from spent nuclear fuels, the xenon gas. It is not radioactive at all after a few months; it is completely stabilized. It's got a typical value about $1,200 per kilogram, and so, a metric ton of uranium could have about $7,700 worth of xenon in it. The next most common fission product is neodymium. Now, I would wager to say a number of you have already--this morning had neodymium in your ears. Raise your hand if you know what I'm talking about. Okay. If you've had little earbud earphones in your--in your ears today, you've had neodymium in your ears today. So this is--this is a great thing because in the '80s, we discovered how to make super strong magnets from neodymium. So this is the number two thing that comes out of spent nuclear fuel; and the other great about it is it stabilizes really quickly too. Its longest lived half-life only has an ele--its longest-lived radionuclide only has an 11-day half-life. And so wait a few months and this stuff is not radioactive at all. So, I think it's interesting that the first two things out of spent nuclear fuel have potential economic value. Okay. Then there's another category of stuff you might be able to get, and these are high-value, medium-stabilizing fission products that have--that take about 10 to 15 years to reach a level of a no-radioactivity. Ruthenium, rhodium and palladium; all of these are potential catalysts and they have much higher valuations than neodymium or xenon. Ruthenium is worth about $6,300 a kilogram and rhodium's worth $90,000 a kilogram and that number fluctuates but these are very valuable materials. They're--some are just using catalyst and other things. Palladium is also very valuable, although we do have one really, really long-lived radionuclide in palladium. But it's got a half-life of six and half million years, which means its radioactivity levels are exceptionally low. We may be able to just go ahead and live with that and use palladium. I mean, it's a very weak beta-emitter and it's really doesn't pose any radiological risks, so even the palladium may be able to be recovered at economic value. Okay. Now ironically, some of the most valuable things in spent nuclear fuel, if it could be reprocessed quickly, are the things that are really radioactive and don't hang around very long. One of them is molybdenum-99 and that is used in medical treatments. It's used to create technetium-99 which people ingest and it gives off a gamma ray signature that's very close to an X-ray, so people are able to use this for diagnostic procedures. I was talking to an elderly crowd a couple of months ago, and I said, "Raise your hand if you've drunk tech-99m." And I would say about half the people in the room raised their hand and said, "Yeah, I've drunk it," you know. So, this is something that we use to save lives all the time. Another one is iodine-131 which is used to--iodine will bioconcentrate in the thyroid. In fact, it represents probably the major hazard in an inadvertent radiological release from an accident; but it's also used for medical treatments. It doesn't last very long; it has an 8-day half-life. So if you want it, you got to get it and use it pretty quickly. So, if we could reprocess spent nuclear fuel quickly, we could actually obstruct--obtain some of these materials. Then, there's also medium-lifetime products like strontium and cesium which have enough radioactivity to last for a while. But because of that, you know, I'm thinking like a NASA guy, we could use these for radioisotope heat sources for deep-space probes. We could also use cesium-134, 137. Remember that strong gamma power I talked about? We could use that to irradiate food and to destroy pathogens. Food irradiation is a process that does not induce radiation in food, it does not lead to residual risk; but what it will do is it will destroy some very difficult pathogens and enable us to heal a group of people who are killed by E.coli each year. So I think it's on the order of several thousand people die each year from E. coli; that's something that we cold stop with widespread use of food irradiation. So, even these very radioactive radioisotopes may be valuable. And then, there's also the uranium and the transuranic elements. Okay. I'm running out of time so I'm going to jump right to the good stuff. Okay. How does this all add up? And what I did is a benchmark that said, "The Nuclear Regulatory Commission will charge you a dollar per megawatt hour for every megawatt hour of electricity you make from nuclear power." So if you got a nuclear power plant and you're making electricity, you're paying a dollar and a tax, and they use that money--the thought was you're going to use it to build Yucca Mountain. Well, Yucca Mountain has been cancelled so we got $25,000,000,000 sitting in this fund. So I got curious, I thought, "Could we make enough money from the fission products to pay back that dollar that we're spending on the waste fund?" So I kind of racked and stacked these different things: xenon, neodymium. I took the price per kilogram. I took how many kilograms we could expect from a ton of uranium and then, I hit it with a value coefficient because some of these really have very, very low value. And so then I extracted a value. And these are not in order; but you can see some of these have rather high valuations. The number one on the list was palladium and I wasn't sure if I should use a value coefficient to one there or not because of the palladium 107. Rhodium was also very high, ruthenium. So, when you go and say, "Which ones are worse than money?" Those are the three that rise to the top of the list. So then I assessed it as a percentage of the nuclear waste fee. Okay, did this--does this get to the point where it would potentially payback the money you've paid in the fee? The answer was no. So, if you went and summed all the fission products, you really didn't get there. You got to about, you know, maybe a third of the waste fee. Then, if you draw it down and you looked at saying, "Okay, I was going to recover the uranium," which is most of to the spent nuclear fuel, that got you to about a quarter of the fee. But the really interesting one in my mind was the plutonium. If you could recover the plutonium and burn it up for energy--and I just assessed, you know, assuming the plutonium was going to be completely fissioned and the electricity was going to be sold at such and such a kilowatt hour, how much money would I make? And you could see that of all the ones to go and recover, it was the plutonium was the one that had the best chance of making money in the future by being burned up in a reactor for electricity. So, what I took from all this was is nuclear waste really waste? Well, I would say no. I don't think it's waste. I think there's a lot of very useful things in it. And I think, in a culture that values the idea of reduce, reuse, recycle, it behooves us to look carefully at these. Is there enough value in the stuff that's in there now in the way we do nuclear now to recover the money paid in the spent fuel fee? It does not appear that there is enough value there, but there is non-trivial amounts of value, about maybe 40% of your--of your fee. On the other hand, if you recover unburned fuel and you go burn it, there is a substantial amount of value in that. So, the upshot from all this would seem to be, let's go and take the spent nuclear fuel and let's go burn up the stuff that's going to last for a long time if we don't burn it, and make money selling the electricity from it. So, I hope that's a takeaway. Thank you very much. All right. Yes, sir. >> Nice presentation. Thank you. I have a question about the--not the price but the cost of reprocessing purification. There's a--there's a presumption that these values are--they're based on pure material. And, like for example, to put a neodymium iron borate magnet in my ear, I want to make sure that it doesn't have any trace radioactive elements that are going to irradiate my brain. >> SORENSEN: Yes. That seems a logical desire. >> Yes. So, the cost of reprocessing boiling nitric acid is just the beginning, then there is a whole series of separation steps that have to occur. Have you looked at the cost of separating these elements into pure enough forms that they can be safely used? >> SORENSEN: That--that's a very good question and it's definitely one that underpins the whole thing here that I wonder about. I mean, I don't know, it's beyond the scope of this rather cursory examination, but I hear what you're saying. And in order to go and extract all 35 fission products and along with five or six uranics and transuranics, you're looking ideally right off the bat at 40 separation steps. So if you had a perfect separation, it would be a process that had 40 separation processes in it. That's probably too many. So we can say right about, "Oh, that's probably going to make sense." So the next layer is you go, "Okay, what is in the valuation scheme that may be worth recovering?" And that's why I broke some of these out. The easiest one of all to get out and the one you have the best chance of getting the highest purity is xenon. Because it will come out of the spent fuel as a gas, it will come out with krypton; and those two can be distilled cryogenically from one another with a high separation factor. So, xenon, to answer that part of question, has an excellent prospect. Neodymium, I'm not a (inaudible) chemist and I don't pretend to be; I know there is some challenges getting that. But neodymium would most likely be compounded with praseodymium. If you look at neodymium on Wikipedia, you find out that those two took a long time to separate. Praseodymium actually also stabilizes very quickly, so that's kind of woosh on that one. So, even if you had some residual praseodymium, it's probably not going to represent a real problem for you. But, you know, all of them, nth of a kind, I don't know. And it all--this is a--this is a valuation at which to go and measure against your processing scheme go. Okay. If I have a processing scheme that costs $1,500 a kilogram, am I going to make money doing this? Maybe not. If I have a processing scheme that will do it for $100 a kilogram, no, maybe a whole different story. So, I think what you've asked is really the going in question to the next layer of analysis, which is to say--go ahead, Chris. >> And it's very unlikely that you're going to use boiling nitric acid. You know, that was a technique for extracting pure plutonium for making bombs. It wasn't designed to do this. You'd probably use some kind of electroseparation with molten salt or something like that to get a lot of these things out in high purity at low cost. >> SORENSEN: Yeah. But that nitric acid is definitely what a lot of people have--it's the basis of the PUREX and the other aqueous processes. Yes, what I use today. But what we use today has sort of dubious economics. And certainly for fission product recovery, it's very dubious, so. Any other questions? Okay. Right yeah. >> So, your chart showed the radioactivity of plutonium dominated after, I don't know, 50 years or something. >> KIRK SORENSEN: Yes, yes. >> It was four or five orders of magnitude less than the start, so I take it the embodied energy in plutonium is different from the radioactivity. >> SORENSEN: Yes, yes. Yes. >> Right. >> SORENSEN: The embodied energy in the plutonium through fission is the real value. In fact, I mean you didn't even see uranium 235 on that and there's still a substantial amount of uranium 235 in the fuel but its radioactivity is so incredibly low that even after 30,000 years it still doesn't even show up on our chart. >> Did you do any pie charts that show the embodied energy that you could get out of reprocessing the fuel to use as a nuclear fuel? >> SORENSEN: I didn't do that because I was primarily interested in the fission products. I knew they have no--they have no additional energy to give me as a--through fission. Although the decay heat which is a chart--that was sort of the number two idea was to show the decay heat if you are pulling out like strontium 90 and cesium, you may be--probably not so much cesium but more strontium 90, that may be interesting to you as a radionuclide for decay heat purposes. And there is a, you know, modest amount of decay heat that you could get especially if you needed a long-lived heat source in a very remote environment like we look at for space probes. It could be a really good source for that. So, but, yes, most of the energy that's in the plutonium through fission is not being manifested in the activity. >> Sir, could you give us a sense what the masses of the, I guess, the two main things, uranium and plutonium that can still be used as nuclear fuel again? >> SORENSEN: Let me throw up a chart. I should have put--I think will help understand this. This chart shows composition rather than radioactivity and you start out with fuel that is essentially unburned at the beginning and you see that it's about 3% enriched, it's all uranium, about 3% U235, the rest of it, uranium 238. And this shows the process as that fuel burns up over about three years in the reactor and then gives you a snapshot. So that bar on the very end is essentially equivalent to the beginning of the simulation that I showed and let me--what you see is you see the uranium 235 burning up and you see those fission products generated and then you see some plutonium generated from uranium 238 and then some of that plutonium is also burning up through fission as well and it's creating also some of those fission products. And then you see xenon, zirconium, neodymium, molybdenum; you see those main fission processes, so this is by mass, this is not by radioactivity. By the time you get done, your uranium 235 is back at about natural levels of concentration about 0.7% and you have roughly 1% of plutonium 239, 242, 241, the so-called transunranic. So that's enough--that's not enough to keep this kind of reactor going, but you could introduce that into another reactor that would consume that plutonium and I really think in the long run, the thing to do is to burn up that plutonium. And some, you know, my interest in throwing, I think we should burn it up and make U233 and run thorium reactors off it. But leaving it in the ground for a long period of time is kind of just dumb on a number of fronts. For one thing, it has a long-lived radioactivity. Its radioactivity is going up very, very slightly. The other thing too is it has economic value. You know, it's not a good thing to leave around, so. Dan, go ahead. >> DAN: There really are three big reasons why we haven't pursued reprocessing in this country at least on the commercial side. One is obviously the security-related issues extracting these fissile materials and all the non-proliferation aspects of that might be useful for you to comment on. The second is that for a long time and I think looking ahead, the economics don't really justify it. The issue with the future of nuclear power in this country is not the cost of fuel; it's the capital cost of new reactors. All the projections for the cost of uranium fuel don't have it as a major factor in the stumbling block that existed for new nuclear reactor. So, being able to pull fuel out of this doesn't seem, from an economic perspective, to be all that compelling, and then, of course, there are the environmental end--the environmental side of this. Reprocessing, as you know well, produces a lot of waste that themselves that have to be dealt with and have caused a number of issues that we've had to address in at least on the nuclear weapons side of that. >> SORENSEN: Well, let me tackle--can I tackle those too? Let me make sure I got this right. Number one was the cost of reprocessing? >> Number one there are proliferation issues. >> SORENSEN: Okay, I'm sorry, proliferation of reprocessing. Number two was the cost of fuel and number three was the cost of reprocessing? >> Cost of the reactor. >> SORENSEN: Cost--I'm sorry, you're right, the cost of reactors. Okay. >> [INDISTINCT]. >> SORENSEN: Yes, good point, good point. >> The waste products... >> SORENSEN: Okay. >> ...from the reprocessing themselves have to be addressed. >> SORENSEN: And would I be accurate in stating when you say reprocessing, you're talking about conventional PUREX, you know, nitric acid, aqueous base reprocessing? >> You tell me what we were talking about because... >> SORENSEN: Okay. >> ...traditional has been what--it is what we have used and it continues to be what we do use. >> SORENSEN: Yes, that's traditionally what we've used. When I say reprocessing up here, I'm literally talking in the utter abstract. I'm talking about a process where we just separate things. Now, then you go like what you asked to the next level go, "Okay, how do you actually do this?" You know, "What are the costs involved?" As Chris has mentioned, I am much more interested in salt-based approaches through reprocessing because the first thing that they do is they don't inflate the waste stream like an aqueous based reprocessing approach does. The other thing they let you do is they let you handle very, very radioactive fuel in a form where it's impervious--the salts are impervious to radiation damage; whereas the aqueous based processes, you have to be very careful with your solvents like tributyl phosphate and kerosene as far as not having too much radioactivity in the fuel. Okay, so right about--let's talk about--let's talk about proliferation. In plutonium, it's really the question mark there, because our nuclear process now makes plutonium and for various reasons, we do not separate out the plutonium and we say, "Okay, we're leaving the spent fuel where it's 'self-protecting.'" Well, one of my real surprises here was to do the analysis and finding out that, guess what, there's one thing in the spent--in the fuel that's essentially doing all that, and that's the cesium, so. As long as plutonium is chemically separable from spent nuclear fuel, I don't really think that our approach today is particularly safer or better than any other approach, because nations around the world pursue reprocessing kind of irrespective of what we do. So, I guess I just--I look at this and say, "Okay, how can we go and get a basic fissile currency that is much less susceptible to proliferation in the first place?" And that's why I think we want to get off the plutonium. I think the plutonium is stuff that is a whole lot more suited for proliferation purposes than the uranium-233. The uranium-233 has a natural built-in barrier against proliferation, the contamination of uranium-232. So I'm in favor of saying, you know, let's move from the kind of world we have now to the world where fission is based on uranium-233 and thorium. That would kill two things: we would get rid of the plutonium inventory and we would also eliminate the need for enrichment which are the two main paths to proliferation purposes. Would that--would you agree with that? >> You've jumped over a big step which is you're going to be pulling plutonium out of vast amounts of nuclear spent fuel... >> SORENSEN: Yes. >> ...which is, in and of itself, a serious concern from a proliferation standpoint. >> SORENSEN: I guess I see that as an inevitable step that we have to take. If we leave in the spent fuel indefinitely, the fission process will decay away and you'll have--you'll have essentially plutonium mines. So, I kind of see it. If we don't do a plutonium separation step at some point, how can we really address this in the long run? >> Address what? >> KIRK SORENSEN: Address the existence of the plutonium in the inventory. I mean, we have this amount in our spent fuel now, and it's like, do we leave it or do we get rid of it? To get rid of it, we need to take it out and burn it up. So, that-,-I guess that's... >> The U.S.--the U.S. decision for decades has been you don't separate it on the civilian side and you find an adequate place to put it underground geologically. >> KIRK SORENSEN: Yes, and I just--I think in the long run, that's not a good strategy because eventually, we'll reach a point where you've got plutonium that doesn't have any fission product protection around it, and you just go get it. So, I think--I think we got to get past that. I mean, just my opinion, so. The second one was one that I think was a really important which you talked about, the capital cost. You know, all these fuel costs, they're really not significant. I had my students do an exercise a few weeks ago, and you realize that fuel costs even today, as poorly as we use nuclear fuel, is still not very much. It's--the calculation there was about one seventh of the cost of the energy we were going to make. So, if we recover this and burn it up, have we really saved a lot of money? No, not probably. The bigger deal is reducing the capital costs of nuclear reactors. How do we do that? Well, I got a few ideas, one of them is go to a low-pressure system, a system doesn't require 9-inch thick steel and big containments and steam turbines and all that kind of stuff. And that's another talk if you want to watch one of my older ones. You go to a system that has a lot higher levels of inherent safety. You take on capital cost, because capital cost fundamentally are the thing--the barrier between here and a--and a nuclear future. And Dan is absolutely right, that is the number one problem and it has to be tackled. And that's why I think, in some ways, our nuclear renaissance now is--if it happens it's--you know, I want to see us get rid of carbon production from fossil fuels. I don't think it's going to happen with our nuclear technologies now; but I think it can happen with nuclear technology in general if a better nuclear technology is employed. And even better if we can use this spent nuclear fuel as the bridge to getting to that nuclear future. If we can destroy these long-lived waste products, while the same time generating material that will help us get to that. The third point you made was--was it cost or si...? >> The environmental footprint. >> SORENSEN: Oh, the environmental question. Okay. The environmental question--and that had to do, I think, a lot with the aqueous reprocessing steps. What they tend to do--and I didn't get into it here--is they will inflate the waste stream and they're designed to extract a very high purity uranium and plutonium, primarily the PUREX processes. Everything else essentially goes into an inflated waste stream and then it has to be vitrified. It's a whole lot bigger and so you start out and you go, "You now, if it's not worth it to pull the uranium and plutonium out, then it's really not worth it to go inflate this waste stream by a factor of a hundred and then try to turn around and vitrify it in glass." And so again, this has to get right back to you want to look at reprocessing scheme that does not inflate the waste stream. And that's why I think this--the salt base reprocessing schemes have the potential to do that very effectively to through fluorination. But it's very different what we've done before, so it's going to require research and development. Okay, any other questions? >> Just a question. So in the spent fuel, all these isotopes are mixed together and you're calculating the decay period and the--what they fission into over time. Does that--is that different whether the chemicals are in isolation or all mixed together? In other words, do they influence each other? >> SORENSEN: oh, okay, okay. Let me back up to what you said. You said as they decay and fission. When I start that simulation, we're assuming fission is over. So fission is done and this is strictly radioactive decay, so nothing else happens. And the answer to your question is it makes absolutely no difference whatsoever if they're separated from one another or they're all together, because to a radionuclide, it lives in its own little world. It doesn't see anything. It doesn't care about anything. There's nothing you can do to affect radioactive decay rates. It's kind of interesting. H. G. Wells actually wrote a book 100 years ago called The World Set Free, where it was all based on the idea that you could change radioactive decay rates. We have never ever figured out how to do that, and there's little prospect we will ever figure out how to do it because it's so fundamental to the properties of a radionuclide. So it doesn't matter if we separate them or have them together, everything will proceed the same, so. >> Going back to your simulations, have you correlated these with actual reactors, the waste products, like the starting stage and as well as several decades down the road? >> SORENSEN: Well, the code that was used to run the simulation is called Origin, and that's pretty much an industry standard code to model the depletion and decay of spent nuclear fuels. So essentially, all my java code is just a graphical front end to this big stream of data that comes out of this industry standard code. So they're pretty much using the same code to get the data, I'm just trying to make it into a prettier picture. >> Well have you heard about the [INDISTINCT] so they have compared to the actual waste products? >> SORENSEN: Yes, they--Origin has been validated against spent nuclear fuel extensively, you know, and essentially, what I showed you is just a graphical front end to this origin code. >> Thank you. >> SORENSEN: Any other questions? All right, thank you so much for your time, hope you had a great time. ?? ?? ?? ??