Is Nuclear Waste Really Waste?


Uploaded by GoogleTechTalks on 15.12.2010

Transcript:
>>
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. ??
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