Disposing Of Nuclear Waste As Nuclear Fuel 76
Saige writes "Nuclear waste has been a contentious issue, recently culminating with fights in the government over Yucca Mountain in Nevada as a proposed storage site. Well, perhaps there's a better way to deal with nuclear waste -by using it in nuclear reactors. A nuclear scientist at the University of Maryland, has come up with CAESAR, a reactor that runs not on the standard U-235, but on U-238. U-238 makes up most of the fuel rods in current reactors, but doesn't contribute to the reaction, and ends up currently as waste." The Yahoo! story linked from this article doesn't seem to open, but here's a story at The Economist.
So what does the waste turn into? (Score:2)
I'm not trying to sound ignorant, I just know nothing of nuclear physics.
Re:So what does the waste turn into? (Score:1)
Re:So what does the waste turn into? (Score:3, Interesting)
So... there is less waste for the same amount of electricity, this is the advantage...
Re:So what does the waste turn into? (Score:2)
Re:So what does the waste turn into? (Score:3)
Re:So what does the waste turn into? (Score:4, Informative)
The point is not "more uranium". It is about putting U-238 (which is normally considered useless) to a productive use, instead of its more appreciated U-235 brother, which is much less common (0.7%). This way, instead of having to be disposed of as waste, it is used (and at the end of the process you have less waste than you started with).
In nuclear processes, Uranium does not produce more uranium
(apart from the other, naturally-occurring radioactive behaviour of uranium: it emits an alpha particle, becoming Thorium, which then becomes Radium, which becomes Polonium, which finally becomes Lead (not radioactive - it doesn't become anything else)).
Re:So what does the waste turn into? (Score:2, Interesting)
you dont start out with Pure U-235, only about 4%,
(they get the percentage this high be making a Uranium gas, puting it in a large column, and skimming the lighter U-235 off the top)
So, they still have lots of other stuff, including other types of Uranium.
(only 9.7% of natural Uranium is U-235)
only the U-235 is broken down by the neutrons that the current moderator, water, creating other radioactive elements such as Ba-141 and Kr-92 plus 3 more neutrons, or Xe-140 and Sr-94 plus 2 neutrons.
There is still alot of Uranium in the fission fuel, just not the right kind
(the "235" in U-235 represents its atomic weight, all Uranium has 92 protons in its nucleus)
(you subtract 92 from 235 to find the number of Neutrons in a U-235 atom)
(in order to get Plutonium, you start with U-238, add a neutron going the right speed, then you get U-239*[*=excited], which then beta decays, making a beta particle, a Np-239* and a neutrino. The Np-239* then beta decays and you get Pu-239, a beta particle and a neutrino. This is called "breeding" and is how nuclear bomb fuel is created)
Re:So what does the waste turn into? (Score:3, Informative)
The energy release would modify the steam, but only it's temperature or, if it is at the right temp... it's water fraction, but this would probably not effect the moderation greatly since the mass of the steam is unaffected by temperature...
That was three questions (Score:5, Informative)
Fission products are lighter nuclei which result from the fission of heavier ones. Some fission products are themselves radioactive, some are not. Pretty much all of them are useless as nuclear fuel.
Radiolysis is the radiation-induced breakdown of chemical compounds. A gamma ray or a fast neutron has more than enough energy to smash a water molecule apart, and this process will produce free radicals such as hydrogen and hydroxyl ions. If those radicals get together, you can get products such as hydrogen gas and hydrogen peroxide, and hydrogen peroxide decomposes pretty quickly to oxygen and water again.
You'd be better off reading an intro on the web, but I hope this whets your appetite for more learning.
Nuclear rocket idea (Score:1)
In a reactor, the by-products would be ( probably automatically ) chemically seperated from the gas maybe as a solid ( idunno what substituting a barium/krypton/thorium/whatever in a UF6 molecule would yield: hopefully not fluorine gas but prolly Krypton+Fluorine is not a molecule. Maybe Krypton will decay into something more reactive fast enough to take up the excess flourine or maybe one of the other byproducts will be able to do it.)
In a rocket, why couldn't you just shoot the ( superhot ) crap out the ass end?
Re:Nuclear rocket idea (Score:2)
Darn links... (Score:3, Informative)
If anyone cares, the link to Plastic wasn't what was intended and can be safely ignored.
Re:Darn links... (Score:2)
Cool, but isn't the real problem... (Score:5, Insightful)
Isn't the real "nuclear waste problem" not just the fuel rods, but the kilotons of contaminated building materials, protective clothing, screwdrivers, air ducts, semi-trailer trucks, topsoil, reactor coolant, baseball caps, human remains...
I'm sure this is a great advance for many reasons, but it's barely gonna scratch the surface of how to deal with contaminated material - or am I wrong?
Re:Cool, but isn't the real problem... (Score:5, Informative)
It's fairly hard to make something radioative by exposure. The LLWR is largely stuff that has come into contact with radioactive material, as in processing, hence comtamination.
The biggest problem with LLRW is political -- people don't want it in their back yard. And I don't blame them -- given a choice of your yard or mine, I'd pick yours.
Re:Cool, but isn't the real problem... (Score:2, Interesting)
Half Lives:
U-235 = 7.037 x 10^8 years
U-238 = 4.468 x 10^9 years
U-239 = 23.47 minutes
Th-90 (from U-234) = 7.5 x 10^4 years
Ra-88 (from above) = 1.6 x 10^3 years
Strontium:
90 - 28.5 years
94 - 1.235 seconds
Here is a picture similar to to the one in my Physics book on the decay of Uranium(its life forever until its stable)http://www.physics.umd.edu/deptinfo/facili
From this Page
http://www.physics.umd.edu/deptinfo/facilities/le
Re:Cool, but isn't the real problem... (Score:1)
Re:Cool, but isn't the real problem... (Score:2)
Check out http://www-formal.stanford.edu/jmc/progress/anti-
The interesting part is that we aren't talking about the half-life of Uranium. We are mostly talking about the half-life of what happens when Uranium splits. Which does NOT have a particularly long half-life.
So, really, what you are looking at is 500 years before it is less radioactive than the ore it came from, and a few thousand years before it is truly safe. Not the millions and millions of years that people always talk about.
Of course, a few thousand years is still quite some time.
Weapons (Score:5, Interesting)
All reactors IIRC produce some plutonium, from bombarded U-238 (virtually all Pu is manmade). Breeders produce a lot. The "waste" which is U-235 depleted but plutonium enriched must be further processed to produce weapons-grade material. For 25 years we have banned reprocessing even to the level needed for use as fuel because of the concern is could be stolen and further enriched. Some countries like France and Japan disagree and do reprocess. The scare in Japan last week illustrates the risk. Most people here would agree there' no such thing as perfect security, esp. with the universal hazards of corruption, accident, and incompetence.
Even if the thieves were unable to purify the material, it would make excellent "dirty bomb" material. Pu is not especially radioactive, absent heavy chain reaction, but it is very toxic and dangerous to ingest or inhale where it might lodge and expose sensitive tissue to prolonged damage.
It's a shame nuclear policy is so constrained by weapons issues.
Re:Weapons (Score:1)
BTW, 60 Minutes is populist shit. I hope they someday do a piece on something you really know, like your hometown, or something, then you'll see. They will distort the truth just to make whatever they are talking about sound interresting. I saw a piece on Finland where they (for real) explained that Finns don't do anything but dance tango. No exceptions, just tango, in all of their spare time, because Finns can't speak to eachother due to pathological shyness. So bollocks to their NK-piece.
What crap.
Re:Weapons (Score:1)
The striking and non-interpretive thing did was simply a space photo of the Korean peninsula at night -- all dark above the border and bright cities to the south. Relevant here was the fact that without Russian aid they are quite desperate, something that has been reported widely and should be accounted for in the eventual negotiated settlement we will need unless we really want to make them a colony. N. Korea I *do* know something about and I didn't detect anything horribly wrong with their report.
Finland -- I agree, that was pretty silly! I think it was intended to be "fluff." I tend to assume all media reports could be totally off the mark, but think 60 Minutes does OK for TV journalism.
Re:Weapons (Score:5, Interesting)
Re:Weapons (Score:1)
For purposes of monitoring -- and unless we are going to ban all distrusted powers from using nuclear energu, monitoring will be required -- should be easier here. Knowing nothing about reactor design, this one included, I don't know was kind of tamper-proofing could be used. I'm picturing a great big seal.... Anyway, I suspect it would be a lot easier than what we've been doing with cameras and stuff, and less invasive, too.
Re:Weapons (Score:3, Insightful)
I agree that it would probably be easier to detect tampering with a sealed reactor, if only because they'd need a fair amount of time & equipment to crack it, and you could build some of the detectors inside the sealed part where they'd be hard to defeat. The solution N Korea used - throw out the inspectors, shut off the cameras, ignore the griping until you've accomplished what you want to do - does, though, make me a tad nervous re the viability of any preventive measures that have to be carried out on foreign soil. Personally I'd have preferred we built the nukes in S. Korea, and ran a big power line across the DMZ.
Re:Weapons (Score:2, Insightful)
I like your idea of delivering power from SK. It's probably practical -- power in the U.S. is sold over very long distances. The problem is that NK would not accept it, not least because it would give us a big on/off switch to push them around with.
Re:Weapons (Score:2)
Also, you wrote parenthetically: "virtually all Pu is manmade". All plutonium is manmade. All the natural plutonium on the Earth decayed long ago.
Re:Nitpicker plus (Score:1)
On the second, there is a natural reactor [pu.org] in Africa that years ago produced some plutonium. I included "virtually" to avoid nitpickers who know this, but forgot about the nitpickers who do not.
The pu.org site has other interesting info about, guess what, Pu.
Re:Nitpicker plus (Score:2)
Although, I haven't yet found any good information on how much Pu is left at Aklo. But it's also the case that there's trace amounts of Pu to be found--some is generated from spontaneous fissioning of U-238 with subsequent reabsorption of a neutron.
Enough with the misconceptions already! (Score:5, Informative)
This is all-important for making a bomb. U-235 has a half-life of around 700 million years, and making a bomb with it is easy: squeeze together a prompt-supercritical mass, and wait a few milliseconds. Pu-239 is tricky, because its half-life is only about 25000 years and you have very little time to get it into a prompt-supercritical configuration before a spontaneous fission starts the reaction going. If the reaction starts too soon, the bomb blows itself apart into a sub-critical configuration before releasing much energy and all you have is a fizzle. Now imagine dealing with a substantial fraction of Pu-240 (half-life 6564 years [jaeri.go.jp] or Pu-241 (half-life 14 years [jaeri.go.jp]).
Bomb-grade material is made in special reactors which allow the fuel to be irradiated relatively briefly at a low level, and then removed and processed to remove the plutonium. This is specifically to avoid the production of enough higher isotopes of plutonium to be a problem. The stuff coming out of a power reactor after a full fuel cycle is dirty as hell, but amateur proliferators are not going to be able to make a serious bomb (as opposed to dirty weapon) out of it. This is why we had few objections to building pressurized-water reactors for North Korea; they are essentially proliferation-proof.
I doubt that it's quite that simple. The real problem is that the plant required to refine fuel-grade Pu from spent power reactor fuel uses the exact same chemical processes as the plant which refines bomb-grade Pu from depleted uranium rods held briefly in a neutron flux for transmutation purposes. If you have a world full of people reprocessing it would be very hard to put a finger on the ones who are making weapons, so the US decided we had enough uranium to put the kibosh on all reprocessing just to set a good example.I think we should have gone with the Integral Fast Reactor [berkeley.edu], but it seems to have succumbed to the fundamentalist anti-nukes (who probably couldn't figure out that there are medical and explosive grades of nitroglycerine either...).
Re:But misconceptions fuel great arguments! (Score:4, Informative)
My understanding from many sources is that a breeder can produce material of 20-30% Pu. Yes, it "can breed more fissionable fuel than it burns" but that new fuel is (as I understand it) exactly the Pu-239 we fear. All Pu comes from reactors, anyway, it's just a question of technique, esp. removing the material after a brief bombardment by appropriate-speed neutrons.
Bombarded Pu-rich reactor fuel is not the only problem, there's also the fuel-grade Pu after reprocessing. I've seen a couple of accounts of fuel-grade Pu bombs [ccnr.org] detonated, and I assume if one had the facilities to purify the fuel it would be even easier.
There are serious technical hurdles to engineering the actual bomb, but here we want to deny them even the fuel. Plenty of countries have surmounted the techincal end, anyway, such as Pakistan [fas.org]. Even a sloppy detonation would be bad enough. BTW, I'm not thinking about terrorists, unless they somehow stole a complete weapon. They'd take the surer low-tech path of a dirty bomb or flying a plane into a building, etc. Terrorists with nukes are a Hollywood thing for now.
On policy, here [nei.org] is a rather different account of why we don't reprocess -- economics. According to this account, Reagan vacated the Carter order in 1981. Truth?
Re:But misconceptions fuel great arguments! (Score:2)
Re:But misconceptions fuel great arguments! (Score:1)
~ excerpted from the US Department of Energy Publication ~
Nonproliferation and Arms Control Assessment
of Weapons-Usable Fissile Material Storage
and Excess Plutonium Disposition Alternatives
It's an excerpt of a Lawrence Livermore publication, and believe me *they* ("the bomb factory") are not anti-nuclear. Anyway, what it says is in accord with what I've read elsewhere, and the critical bit of data is the feasibility of a fuel-grade Pu detonation, that is, the proliferation risk.
Re:But misconceptions fuel great arguments! (Score:2)
Re:Enough with the misconceptions already! (Score:2)
Uranium bombs are a different beast. Without highly (isotopically) enriched uranium, it is flat out impossible to produce a useful explosion.
With chemically separated plutonium, you can build an inefficient bomb. With chemically separated uranium--you can warm your toes.
All that said, a terrorist group would still be better off leaving plutonium or uranium dust in the streets or in a major building. Much bigger fear factor for the masses.
Bombs, uranium and otherwise (Score:2)
I'd almost be inclined to let the most determined of the bastards get some spent fuel and try. The most likely outcome is that they'd kill a lot of their people from the radiation without producing anything useful (to them), whether their aim was a nuclear explosive or just a "dirty bomb". Their activities would not be that easy to hide; gamma detectors, xenon sniffers and such would make them much easier to find than people making anthrax or VX.
Use neutron irradiation to breed thorium-232 into uranium-233, then separate chemically. Bingo, you've got a highly purified fissionable isotope (but another bugger of a problem with short half-lives, not terribly much better than plutonium). If that uranium comes from a thorium breeder, you can do both.BTW, I got a nuclear physicist to weigh in on the plausibility of the parent article. He says that it pins his bogosity meter (my words, not his).
Has Nobody Heard Of Fast Breeder Reactors? (Score:1)
There have been a few test reactors - notably at Douneray in scotland and an experiment in Japan.
Has this guy come up with a hitherto unknown reaction for power generation? Or does nobody on Slashdot remember their basic nuclear physics.
Oh I get it (Score:2)
Re:Has Nobody Heard Of Fast Breeder Reactors? (Score:2)
BTW. I think it is an alpha particle for getting Pu...
Sorry for the pun (Score:2, Funny)
Great idea! (Score:5, Insightful)
Well.... (Score:4, Interesting)
Stolen reprocessed plutonium would be very useful for a dirty bomb. It would have to be enriched before making a bomb, but it would be a headstart and obviate a nucleare reactor to make the Pu.
I don't think the problem is that we're overflowing in nuclear waste. The problem is we've had so much trouble confronting where exactly to put the stuff because of political opposition. Countries like Japan and France have far less oil, and this desperation makes the nuclear power sacrifices less daunting.
Old nuclear fuel is sequestered in ceramics and buried. There is not that much need to guard it. Nuclear fuel grade uranium is only 2-3% enriched U-235 to begin with, so its a -long- way from being particularly useful. Old weapons-grade Pu is mixed with material like U-238 to make it useless. With Iraq or N. Korea, the big challenge they face is not getting material, but purifying it.
So
One Problem: (Score:2)
Separating plutonium is not remotely comparable (Score:3, Informative)
Separating plutonium from U238 in spent reactor fuel is much easier. Plutonium and uranium are different chemical elements and can be separated by chemical processes. It's not something you can do in your kitchen, but atom bomb designer Ted Taylor, in John McPhee's excellent book The Curve of Binding Energy, compares its difficulty to that of building, say, a large scale drug lab.
We know perfectly well that criminal organizations manage enough chemical engineering to produce refined heroin and cocaine by tens of tons even without any governments supporting or protecting them. Separating Pu from U in quantities of only a few kilograms, as an official project of the local rogue government, appears quite achievable in the face of that knowledge.
Elements v. Isotopes (Score:2)
Isotopes are a different problem, and I didn't make this clear. Pu isotopes have different fission properties. [ieer.org] For a weapons, the Pu-239 alone is desirable; the other isotopes, particularly Pu-240, tend to spew neutrons that cause pre-ignition of the reaction, resulting is a "dirty" nuclear explosion and inefficient conversion of plutonium. Non-Pu-239 isotopes also make the material harder to handle because of spontaneous decay.
A commercial reactor, esp. light-water, produces a significant proportion of the "undesirable" isotopes. Separating isotopes, as with U, is a lot of work; it's better just to produce the Pu right in the first place, that is, get the right reactor in the right configuration, and run it correctly for the purpose. But if you're a hard-up tinpot dictator and can settle for a 1-kt boom, or at least poison a water supply, and your real goal is to extort aid or concessions from other countries, then several kilos of dirty Pu will tide you over.
I'd like to know what kind of efficiency the Indian and Pakistani bombs have. I read somewhere that the device to approach 100% fission would be a very large H-bomb, and so the small "neutron bomb" of the 80's was pitched misleadingly.
Don't forget that 1 kt boom (Score:2)
Pakistani fusion bomb? I don't think so. (Score:1)
Wow. (Score:5, Informative)
The dark side of all this is, of course, that a lowered cost of entry makes it just that much easier for "nuclear club" wannabe countries to produce plutonium for less benign applications. The author of the Economist article notes that countries could seal their CAESAR reactors (thus, I assume, burning the created plutonium for power alongside the U238) "to show that their nuclear intentions were entirely peaceful." Yeah, right. I'm sure Saddam Hussein and Kim Jong would be perfectly content to have their CAESARs crank out power, with nary a thought to the goodies sealed therein.
Yet another two-edged sword, but a damned intriguing one.
Re:Wow. (Score:1)
Re:Wow. (Score:2)
Re:Wow. (Score:2)
Sounds like it's hard to breed in this reactor... (Score:1)
Building a Reactor Using U-238 Is No Big Deal (Score:4, Interesting)
At any rate, Fermi's reactor in Chicago (the first) used natural uranium (almost all U-238) as fuel. There wasn't any other choice. Enrichening U-238 to higher quantities of U-235 is a really big deal. Natural uranium contains only about one half of one percent U-235. Fermi's design used highly purified graphite in a honeycomb pattern as the moderator. The Russians, before they got the plans for our reactor, looked at a U-238 design that used heavy water as the moderator (the Germans were going that way, too). Anyway, as this guy has shown, it's all about finding the correct moderator in the right configuration.
Actually, it is a very big deal (Score:5, Informative)
There are ways to get energy directly from fission of U-238, but they require very fast neutrons such as are created in a deuterium-tritium fusion reaction [iadfw.net].
Then the Canadians must be smarter than the Russians, because the Canadians actually did it [carleton.ca].Re:Actually, it is a very big deal (Score:2)
Precisely (Score:2, Interesting)
Re:Precisely (Score:2)
As I understood the article, the idea is that neutrons from other unstable fission products in the 'spent' fuel rods are to be moderated so that they can cause U238 fission (and so produce more fission products).
Since we currently just store the spent fuel rods, this is a great idea if it works, we can 'store' them in a reactor and generate power.
Of course, I'm not a nuclear physicist.
Re:Actually, it is a very big deal (Score:2)
Re:Building a Reactor Using U-238 Is No Big Deal (Score:1)
Just ask the Russians about how good it burns as well
Safer too (Score:4, Interesting)
It seems that this design not only allows the complete removal of the whole enriching process, and the elimination of a good percentage of nuclear waste, but it seems safer too.
The fission is only sustainable when the neutrons are just the right speed, which in turn can only happen when the steam is at just the right density. If anything goes wrong (e.g. steam escapes, etc.) the density changes and the whole chain reaction fissles pretty much to a halt.
However when a good percentage of the U-238 has formed Pu-239, would this level of control still hold? (Thinking that Pu-239 undergoes fission with a wider range of neutron energies.)
Better than the Integral Fast Reactor? (Score:1)
Seems like a lot of trouble (Score:3, Funny)
Re:I don't pretend to understand how... (Score:1)
and the waste problems of fission power generation would be lessed, though not eliminated perhaps, by a combination of responsible management and recycling waste.
and in any case folks, there are natural fission reactors here on earth anyway.
and if i'm not mistaken, nuclear fission keeps the earth's core nice and hot
Re:I don't pretend to understand how... (Score:1)
Amazing thing
[curtin.edu.au]
Here[Oklo]
Re:I don't pretend to understand how... (Score:3, Informative)
Probably not. It's likely responsible for heat in the mantle though. This [sciam.com] Scientific American article gives more detail.
The core is hot because... it hasn't cooled down yet. The earth is a very poor conductor of heat, so it takes a very long time for the heat at the core to radiate out to space. I remember doing the math as an excerise to show that the 4Gy age of the earth was not great enough to account for a significant radiative transfer of heat from the core---which is why volcanos and such have to get their energy from somewhere else. Friction and fission being the most likely candidates.
As to safety, well, let us rather look at cost effectiveness, for total lifetime cost. Against the value of the energy produced, set the cost of:
The last three items are not usually significant with 'conventional' energy sources. Or rather, it's not nearly as expensive to render acceptable the output of an oil-fired generator as it is radioactive isotopes with ky half-lives.
So, which is cheaper? Note, I don't know. There is so much mis- and dis-information on both sides it's tough to decide.
Similar to Boiling Water CANDU (Score:3, Interesting)
IAANP, and from what I can tell from the article, the design looks similar in concept to the boiling water CANDU, which didn't quite live up to its promise.
There are a couple of problems with steam-moderated designs:
The first problem is a polite way of saying there may be reactor stability issues. If CAESAR uses super-heated steam this may be less of an issue, but otherwise the ratio of steam to liquid in the cooling circuit is a function of pressure and temperature in ways that can create problems if there is an unexpected excursion.
The second problem is a major issue, especially when coupled with the long-term affects of radiation on materials. Intense neutron bombardment is a good way to introduce defects in metallic lattices. Defects are a good place for corrosion, cracking and other bad things to start. Ergo, the odds of a sealed reactor lasting for more than a decade or so are not good. Retubing of reactors is an ongoing maintenance problem even in conventional designs.
Nuclear power is an option that we may in the end decide we have to go with, and it's good that advanced reactor designs continue to get consideration, but the engineering challenges are still severe and the proliferation potential is large.
--Tom
Re:Similar to Boiling Water CANDU (Score:1)
CAESAR page at U of M (Score:3, Informative)
Here's the U of Maryland page on the CAESAR project.
http://www.caesar.umd.edu/ [umd.edu]