Slashdot Mirror
Combining New/Old Approaches for Nuclear Fusion
L2 writes "Sandia National Labs are looking at some old military tech for a shortcut to nuclear fusion. Still the odd little detail to be worked out, such as how to keep the fuel from melting everything during the reaction. " Interesting approach. While much of the recent fusion work seems to have centered around tokamak reacters, from what I've seen, this one harkens back to a different school of thought. The bottomline, IMHO, is that the sooner we have fusion - or another cheap, environmentally clean energy source, the less likely we are to destroy the rest of this planet and hence ourselves.
plants, would the waste production be higher or lower?
Sure.
In fact, it's easy to show that fission produces _less_ waste - the question is how much less.
DISCLAIMER: I AM MAKING LIBERAL USE OF "FERMI" ESTIMATES. NUMBERS QUOTED SHOULD BE WITHIN AN ORDER OF MAGNITUDE OF REALITY, BUT THAT'S ABOUT IT. THIS IS NOT A DETAILED ESTIMATE.
Both fission and fusion produce secondary waste, in the form of the reactor housing, which becomes radioactive. The housing won't last forever - pieces wear out, as with any device. Let's assume as a rough approximation that the entire thing has to be replaced once every 20 years, and that it is all filed as low-level radioactive waste.
Let's assume that we have a moderate-sized reactor core - a 10m cube (30 feet for the American audience). This isn't a solid structure; in a fission plant, it's a framework holding reactor rods, and either a containment vessel (American reactors) or a network of pipes (Canaadian reactors), with ample amounts of radiation shielding. Let's say it's equivalent to a shell 2m thick. This gives us a volume of about (10^3 - 6^3) = around 800 cubic metres. Assuming a density of around 5 (metal, concrete, and lead), we get about 4000 tonnes of waste every 20 years, or an average of 200 tonnes of waste per year (1 tonne = 1000 kg = about 2200 pounds, so about the same as a US ton, before you object to my spelling).
Now, a fission reactor also produces a fair bit of high-level waste in the form of spent fuel rods. This represents extra waste that a fusion reactor doesn't produce. We have to see how much it is compared to the (roughly) 200 tonnes produced on average per year by our hypothetical reactor.
Let's assume that a reactor with a core of the quoted size produces about 500 MW of power. Let's assume that this represents about 2% of the fuel in the reactor (typical of fission reactors that don't use reprocessed fuels). Let's assume that this fuel converts mass to energy at an efficiency of about 0.1% (typical for fission reactions, IIRC). 500 MW over one year gives us about 1.5e16 joules of energy produced per year. At 100% efficiency, this would correspond to about 0.17 kg of fuel. We're operating at 0.1% efficiency, which means about 170 kg of fuel burned. This represents about 2% of the total amount of fuel, which means about 8.5 tonnes of fuel burned in the reactor per year. This fuel is filed as high-level waste when its finished burning.
So, we find that, unless I'm off by _more_ than a factor of 10 in computing the _relative_ amounts of each type of waste, and assuming that you consider high-level and low-level waste equally bad, both fusion and fission produce about the same amount of waste, most of which is just parts of the reactor that wear out and have to be stored safely.
CAVEATS:
A few notes about fission, that might be confusing people:
A conventional fission reactor has two fuel sources; U235, which is present from the start, and Pu239, which is bred from U238 within the reactor (any reactor containing U238 does this whether you want it to or not). Both of these fission to produce many light byproducts. These byproducts occasionally absorb neutrons, and almost never give them out. After you've left a rod in the reactor for a while, enough of these byproducts accumulate that reactions are not self-sustaining within the fuel rod anymore. It is absorbing neutrons without contributing much energy. This is after somewhere around 2% of its mass has been fissioned. At this point, you can either throw it away or send it to a reprocessing plant, which strips out the light, absorbing components so that you can use the rod again. Nowadays, we throw the rods away and lose 98% of its mass.
Reprocessing isn't done any more because it involves running what amounts to high-level waste through a chemical processing plant. Despite precautions, this resulted in unacceptably high exposure to radiation for people working in the plant. Neutron radiation from the waste also transmuted anything that the waste was in contact with (including whatever you dissolve it in for processing, and so forth), producing a lot of low-level waste. The result of all of this is that reprocessing fuel rods safely is a hassle of monumental proportions. There's enough uranium lying around that we can afford to throw away 98% of it, so we do.
The discussion of the "symmetry problem"---i.e. how to guarantee uniform compression of the fusion fuel---is a common meme in popular discussion of fusion.
What's interesting is that much of this confusion has to be intentional misinformation.
Why? Because it was the solution to the symmetry problem which was the key to the H-bomb. The complete discussion of the concept remained officially classified for decades after the H-bomb was invented. In contrast, the basic physics and outline of the engineering behind the A-bomb was made public in the 1940's already.
Some details had leaked out in one way or another by various 'exposes' but nothing really got it right. I believe it was finally declassified in about 1994 or so---I remember the article in the New York Times. By that point, intertial confinement fusion civilian researchers had already figured it out.
The trick is 'radiation driven implosion'.
The soft x-rays from a fission explosion are diverted down to a hollow tube (hohlraum {hollow room} in the German used by the early researchers). There is in fact a barrier, usually
of tungsten or some other heavy material directly in between the fission primary and the fusion secondary. This is to prevent the explosion of the fission material itself (the stuff) from getting to the fusion part and ruining it. You just want the photons, and if you block the shrapnel, the photons get there first.
The primary is basically many spherical layers---the secondary is a long cylinder with a few coincentric layers, with a gap near the outermost layer for the photons to flow into.
This form a 'photon gas'---but this fluid equilibrates at the speed of light and not the speed of sound, like normal fluids. Which means that the density and energy of the photons gets very uniform quickly. Although you don't normally feel it in every day life, photons carry momentum and can exert a pressure.
The A-bomb uses chemical explosives to precisely compress the fission fuel, but that isn't powerful and even and fast enough to work with fusion. The description in the article, putting the fusion fuel in the center of the bomb, is mostly incorrect. There is a little bit of fusion fuel in the middle of the a-bomb section but it does not make the really big BANG of the true H-bomb, it is just a booster to make more neutrons to make more fission from a given amount of plutonium or uranium.
Back to the photon fluid. This photon gas has enough energy to very very evenly and violently compress the fusion fuel. This is basically a 3-layered hot dog. The outermost layer is a heavy 'tamper' of lead or U-238 or something else. The middle layer is the fusion fuel. Then, there is a rod in the center with fission fuel like U-235 or Pu-239. The photon gas ablates the material on the tamper---the pressure from the photons and momentum from the ablation compress the fusion tube very severely. At the same time, it is magically arranged for just enough neutrons from the primary fission explosion to start a chain reaction in the fission stuff inside the fusion fuel, known as the 'spark plug'. Thus the fusion fuel is compressed from the outside by the photon gas and ablation and squeezed from the inside from the second fission explosion. This is how much work you need to do to get fusion. The fission material, normally very light, is compressed to a density near that of a white-dwarf star, where it reaches quantum mechanical Fermi degeneracy. That is really really really compressed. Not quite a neutron star (that is even more dense, being a giant atomic nucleus) but still thousands of times more dense than any conventional material.
Then, Boom.
The symmetrical lasers in the Livermore fusion experiments do NOT directly shine on the fusion pellet. That would not make sufficiently even compression. They shine on an outer metallic sphere which ionizes and releases X-rays, and these X-rays equilibrate inside the metallic shell (even though it's now totally vaporized it's still heavy compared to photons) and this compresses the fusion fuel.
This is why the intertially confined fusion program is always more classified than the magnetic fusion, because it is in large measure H-bomb technology. The "national ignition facility" being built for the DOE in the United States is yet another really big ICF project. Unfortuantely for political reasons it is being designed entirely from the point of view of military bomb research and not for any energy research. I think that's a shocking waste but there's a gazillion dollars to test the most obscure things about nukes when we already have thousands of bombs that work way way too well for our planet's and species' good.
The lasers are very power inefficient, but better for getting clean data for bomb research. Ion beams, and probably this Sandia machine are much more power efficient and the likely technology for a power plant, but less is known about them because it doesn't fit in the military application as well.
In any case, it is almost certain that this Sandia machine described in the article uses "indirect drive" {as the x-ray compression method is known} instead of "direct drive" and that is how they plan to work on the symmetry problem. So they probably do have an idea what to do about it, contrary to what the article says. It is still a very challenging problem, but not hope is lost.
The best information on the web about Big Bombs is Carey Sublette's archive. Just about everybody who Really Knows what's going on {and I'm not one of them} has said that the technical details are accurate. In fact, some of the information about the W88 warhead that the Chinese supposedly stole can be found on this website, and the Chinese showed this in their defense.
High energy weapons archive
I am a physicist, but not a nuclear physicist or involved in fusion research in any way whatsoever.
The official Department of Energy (DOE) Fusion program is in real trouble - trouble it deserves. Fifty years ago usable controlled thermonuclear fusion was 25 years in the future. Now it is 40 years in the future. They brought it on themselves.
A short bit of history. The Princeton University research team always dominated the program. They area brilliant but stubborn group. No idea that wasn't invented by them had a snowball's chance in hell. The problem is very tricky, heating a plasma (ionized gas) to tens on millions of degrees, and confining it with a magnetic field - as no material could withstand the heat. The Princeton Plasma Lab (PPL) came up with the concept of a Stellarator, a figure-8 shaped magnetic confinement field. This never worked. In the sixties it was scrapped in favor or the Tokamak. - a doughnut shaped field. While this was not invented at Princeton, it was accepted there because it came out of the Soviet Union, not from a rival US group.
The Tokamak was a great advance, and it has been the center of the US, European and Japanese programs for the last four decades. In spite of its improvement it is fatally flawed for a number of engineering reasons. Note that the last three Tokamak projects have been scrapped as unworkable in the design stage, the latest being the ITER project mentioned in the Fresno Bee article ).
The prime damage the Tokamak has done over the decades, besides eating billions of dollars, has been the suppression of research into alternative fusion technology. I can comment on this from two points of view. First I did some of the alternative research before we were de-funded. Second, I was later a Program Manager at the Department of Energy's Office of Fusion Energy for a year before I was let go as part of the massive cutback of the Fusion program.
During the 70's , after receiving my degree, I assisted Dr. Daniel Wells in his TRISOPS project at the University of Miami. The TRISOPS concept was that instead of trying to confine a hot plasma in a magnetic field (which is the mathematical equivalent of confining a ball of angry Jell-O in a cage of rubber bands), we should let the plasma form its own stable vortex structure and then compress it. An example of a stable vortex structure is a smoke ring. The equipment, by fusion standards, was simple. The lab was the size of a small suburban house. We were getting impressive results. See refs (1) at the bottom for a summary. Our funding was cut off because we were out of the mainstream. Also, Dan Wells, the principal investigator, was not good at the politics of science. I understand that the Wells' equipment has been recently moved to Lahnam MD where the experiment is being re-tried (by John Brandenberg under NASA funding - not DOE). I do not what results he has reached.
Another alternative project is being done by Paul Koloc (pmk@plasmak.com ), a plasma physicist formerly at the University of Maryland. He is looking into another stable plasma structure, ball lightning . Ball lightning has been witnessed for millennia, can sometimes last for minutes, and has killed people. Paul creates and measures ball lightning in a lab in a garage in his back yard ( no kidding ). The stable plasma structure lasts several milliseconds (It's is small so it has a short lifetime). He plans later to heat the plasma to fusion temperatures by compressing the atmosphere around the ball. His work is self-funded, with surplus equipment from the national labs, and some volunteer help from scientists there. He has presented several papers, the most recent at the 6th International Symposium on Ball Lightning. It has a small chance of working out, but at least as big a chance of the multi-hundred-million dollar DOE program. The abstracts are at http://home.wxs.nl/~icblsec/pg_abstracts.html under Koloc 1 and Koloc 2 You can write to Paul for the papers themselves.
I have described two alternative research schemes that I know of directly, I'm sure there are many others going on. Now that I have left physics to become an Internet geek, I no longer follow the field carefully. For I time I tracked Cold Fusion, until that fizzled out. As a final note: I do not believe that fusion energy of any sort will be able to compete economically with wind or solar power. There are many good comments and questions on fusion in this Slashdot thread that I will be glad to address on or of line if requested.
Ref (1) "High Temperature, High Density Plasma Production by Vortex Ring Compression" D. Wells (with others), Physical Review Letters, v 41 #3, p166, 1978. "The Interaction between Two Force Free Plasma Vortices in the TRISOPS III Machine" J. Davidson (with others), Physics of Fluids, v 22, p379, 1979.
> article seems like the only way to go right now.
> Once they lick the symmetricity problem -
> possibly by setting up some positive feedback in
> the plasma to keep the reaction shape spherical
> in the crucial nanoseconds - there should be
> more progress.
It turns out that symmetry is extremely difficult to achieve.
This approach to fusion has been tried before - there is a whole class of fusion reactor that tries to induce fusion by running strong electric currents through a plasma (which is what this is - you just get your plasma by zapping a pellet).
From the first approximation, this looks very good - the magnetic fields created by the current flow act to compress the plasma, bringing it closer to satisfying the Lawson criterion. The problem is that variations in the current and in the density of the plasma/pellet cause assymetries, which tend to magnify themselves (the electric and magnetic effects of turbulence cause more turbulence). Because of the way that plasma behaves, there is no magical way to elminate this.
All fusion approaches encounter this problem. One approach to solutions - the one that it looks like they're using here - is brute force. It takes more time for turbulence to muck up a larger volume of plasma, which means that a larger device can come closer to satisfying the Lawson criterion. Also, dumping more energy into the plasma can help; fusion in conventional reactors occurs only among the hottest particles at the tail-end of the temperature distribution. Greater average energy means more particles of sufficient energy to cause fusion.
A second approach is to modify the design of the reactor to either reduce turbulence or to be less sensitive to turbulence. For magnetic confinement reactors, a lot of study has gone into different field geometries that stifle certain types of turbulence. For electrical discharge reactors - like the one described in the article - different electrode geometries have been tried. However, in the case of electrical reactors, this hasn't been enough to match the capabilities of magnetic confinement and inertial confinement (laser) fusion.
A hybrid reactor was recently built that used an electrical discharge to produce a hot plasma that was used as an X-ray source, which in turn was used to heat a fuel pellet in a chamber that reflected X-rays. This proved to be a very promising approach; for details, check back issues of (I think) Scientific American. This does not appear to be the approach described in this article, however.
Laser fusion's main problems aren't turbulence, which is why I haven't mentioned it much in this response.
Does the military already have fusion?
The military has thousands of fusion devices, mounted at the top of ICBMs.
The corrolary(sp?) is that the military never declassifies something until it has developed a countermeasure for it.
As Robert A. Heinlein said, the only defense against a nuclear bomb is not to be there when it goes off.
dragonhawk@iname.microsoft.com
I do not like Microsoft. Remove them from my email address.
The bottomline, IMHO, is that the sooner we have fusion - or another cheap, environmentally clean energy source, the less likely we are to destroy the rest of this planet and hence ourselves.
Yeah, right. And computers will lead to a paperless office hence saving the rainforest.
Cheap power will only lead to increased production capacity and will intensify the demand for raw materials.
People will be able to live in places where it is currently uneconimical to live. The use of said power will also generate a lot of waste heat.
The government will build huge roving automatons with fusion reactors in their bellies to control the population.
All life will be consumed by nanobots which will turn the entire surface of the planet into grey goo which resembles an as yet uninvented flavor of McDonald's shake.
Or something.
I don't profess to know a great deal about Fission or Fusion, but every time someone says "limitless supply of energy" I get skeptical.
Wasn't Nuclear energy supposed to be that? Until we realized there was no place to put the radioactive waste generated.
They are working on this new technology, and while there are still some bugs to work out, I believe human inginuity will prevail, and we will see this technology working within my lifetime (before 2050).
I predict however that there will be unforseen problems, such as disposal of waste... weird kind of pollution generated by the explosions... things that can't be accounted for until a working model is built. Of course when the working model is built, all will bow down before the solution to all the world's energy problems, and nobody will think to listen to anyone with a negative word to say.
Just a thought... might not happen.
Weren't cars, phones, computers, _____ (fill in the blank) supposed to solve all our problems?
I don't think the worlds problems will be solved until there is a significant change in the organization of authority and government in the world. That probably *won't* happen in my lifetime.
Reality has a liberal bias
Here's a quick plasma physics demostration that you can do at home:
Take a wooden splint, like one of those things used to stir coffee.
Stick it into something that will stand it up, say a pencil eraser, or a piece of bread.
Light the tip and stick it into the microwave. Nuke for 1 minute.
Voila. what you will witness is a plasma being formed at the flame. A redox reaction is occuring, with atmospheric oxygen oxidizing the wood. The microwave energy is somehow disrupting the flow of the ionized particles (electrons and all) and forming your plasma.
Now, generating this plasma is one thing (Try it! It doesn't damage the microwave) but controlling this plamsa is a totally different story. Think you can accelerate this plasma down a tube and aim it at some target, a la plasma rifle from Quake? If you can do that, gimme a call 8-)
This demo illustrates the precise nature of fusion research. While generating a fusion reaction isn't difficult, it's controlling the reaction that's being a pain in the arse...
-=- SiKnight
Hey, thanks for calling me an idiot. A random insult from an AC; I'm mortally wounded. Okay, so I might not know everything about what I talk about, and sometimes tend to run at the mouth about certain things. Those posts rarely get moderated up. It's the other things I post where I do know what I'm talking about which do. Of course, it doesn't help that you phrased your previous message (assuming this is the same AC) in such a way that I'd be unable to make a kindly response. Generally when someone points out I'm wrong, I accept that I'm wrong, and try to act civilly about it. It's just rather hard to do that when someone insults me for being wrong.
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"'Is not a quine' is not a quine" is a quine.
"'Is not a quine' is not a quine" is a quine.
Quine "quine?
AFAIK (I'm not a fusion expert) fusion is easier to do if you fuse deuterium and tritium, and that reaction does indeed give off a neutron: 2H + 3H -> 5He -> 4He + 1n (or something very similar to that).
:)
As for making deuterium with fission reactors, most fission reactors are surrounded by water, but hydrogen has such a low neutron capture cross section you don't get any significant quantity of deuterium (If hydrogen did have a large capture cross section, you wouldn't want to surround a reactor with it because it would soak up all the neutrons, upon which the fission chain reaction depends). I work at a research reactor; it's a 250kW reactor sitting at the bottom of a 25ft deep pool of water. That water's been there for 30 years (reactor was installed in 1968), and it's still just regular old water
Actually, modern weapons are all fission-fusion hybrids. Your basic "H-bomb", more technically a fission-fusion bomb, has a fission trigger (that normally uses plutonium) that results in a fusion reaction from the stored hydrogen. It's a relatively "clean" weapon, in that there is a big explosion but not a whole lot of fallout.
But things don't stop there. There are fission-fusion-fission bombs that start out like a fission-fusion bomb, but the fusion reaction is used to create another fission reaction in a sheath of material on the outside of the bomb. Typically, this sheath is made of common U-238, as opposed to the U-235 that is used in uranium based fission bombs and nuclear reactors. U-238 actually has more destructive potential than U-235, but it wasn't used in earlier bombs because it's simply impossible to start a fission reaction in it under normal circumstances. That's why you need that fusion trigger. Fission-fusion-fission bombs are basically the most destructive weapons in existence, and unlike fission-fusion bombs they result in a lot of fallout as well. They are nasty things.
Here's an interesting fact: a lot of modern warheads can be converted between fission-fusion and fission-fusion-fission quite easily. Since the U-238 is typically a sheath surrounding the bomb it can be replaced with a simple lead sheath quite easily. It's nice to have versitile nuclear weapons, isn't it. If you want to blow something up, use the lead sheath. If you want to REALLY blow something up and have no intention of taking over the land you blew up anytime in the near future, use the U-238 sheath.
Want to hear about some even nastier weapons? Sometimes called "hemisphere bombs", cobalt-salted nuclear weapons have the ability to, well, kill everything on a hemisphere. They don't do this with a really big explosion, but rather with intentional and very lethal fallout. If I remember correctly, they use a sheath of cobalt-59. The cobalt-59 is changed to cobalt-60 when the bomb blows up. Cobalt-60 is special because it is very radioactive with a half-life perfect for totally annihalating your enemy. It's half-life is 5 years, which is short enough to be fatal if you are simply exposed to it, rather than just causing cancer which might shorten your life-span in the long-run, yet long enough to make waiting it out in some underground bunker rather impractical. Your cobalt-salted bomb is detonated in the upper atmosphere to spead the cobalt-60 all over your enemy, at which point they are as good as dead.
In case any of you find my fascination with nuclear weapons a little sick, I'll tell you in advance: I don't care. Nukes are fun!
I am not an idiot. Please use my name to email me.
"That's right, I'm quoting myself."
-Upsilon
Er, no, not quite. Usually I post either because I think I have something to say or because I'm horribly bored and want to contribute my two cents. I don't care about my karma, except that I was explaining why my post's score was 2. You might want to look at my user info and notice how in general, I have a high number of posts on certain threads and almost none on most others. You might also notice that I have very few upwards moderations within the last few weeks; if people are being fooled, there sure aren't that many of them.
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"'Is not a quine' is not a quine" is a quine.
"'Is not a quine' is not a quine" is a quine.
Quine "quine?