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Fusion Gets Closer With Magnetic Field Correction
jparadise writes: "Seems folks over at the
the U.S. National Fusion Facility in San Diego have figured out a way
to fiddle with magnets to contain plasma and make their scale-model fusion generator produce energy significantly in excess of what they're putting in. It's not the final answer, doesn't look like, but it seems (maybe? hopefully?) like a step in the right direction ..."
So it looks technically feasible after all. Since the first experiments most people have been thinking you can't get more out of fusion than you put into it. It's interesting since the physical laws behind fusion power aren't exactly known and thus it isn't really possible to prove how much is the theoretical maximum that fusion can deliver. We can look at the sun for one example, but you can't have a power plant that big on Earth. (The same goes for superconductivity, no one knows whether it's possible to achieve under room temperature)
Maybe now the scientists can get some real funding out of their governments... after the cold war projects that require huge amounts of effort like the creation of the nuclear bomb and moon travel have been kinda gone. I wonder what the world would be like if the soviet union hadn't collapsed and flexing of the superpower's muscles had poured in the same amounts of money into science that they did 50 years ago...
Exactly how would clustering fusion reactors that don't give out more energy than is put in help? Power plants in general are more efficient the bigger they are.
For instance, people keep whining about electric cars with the argument that the energy must be produced elsewhere and that makes pollution - but the power that is lost in transmission of the energy is easily gained by the increase of efficiency when using huge power plants instead of a small one in every car.
Energy production just isn't the same as computer power. Computers become less effective when they get hot, power plants get more effective :) This is a fundamental law of thermodynamics.
Are there any fusion protest groups yet?
Against the National Ignition Facility
"Friends of the Earth" Europe say: "The commercial use of nuclear fusion is pure fantasy. Already 25 years ago the same people had predicted that in 50 years fusion would be a viable energy resource, but it seems like we are always 50 years away from fusion becoming economic. The European Council has to stop this waste of millions of taxpayers money."
Green groups say Fusion is a Scam
"Friends" of the Earth wants to "Terminate existing tokamak reactors, cancel construction of the similar spherical torus reactor, and adhere to a withdrawal from the International Thermonuclear Experimental Reactor (ITER) program."
Sierra Club The dangers posed by the probable releases of tritium used by fusion plants, the problems with decommissioning these plants, and their high costs lead the Sierra Club to believe that the development of fusion reactors to generate electricity should not be pursued at this time.
Pretty interesting idea. But that patch of empty sky is actually full of a lot of air. The heat has to pass through a lot of air before it gets free in space. Since conduction and convection are much more effective than radiation at transmitting heat, wouldn't you just end up making your local chunk of the atmosphere very warm?
:). As you raise the temperature, radiative cooling starts to dominate (transfer by conduction goes up linearly with the temperature difference).
Heat lost by radiation goes up as the fourth power of temperature - this is why you'd have the coolant hot enough to glow orange
If I understand correctly, the atmosphere's pretty good at blocking light in the thermal IR band, but you can see by example that visible and near-visible passes through quite easily - most of the sunlight shining on earth reaches the ground.
Heat the coolant up to a thousand degrees centigrade or so, and most of its emission will be in visible and near-IR (thermal IR is the band that objects at room temperature shine in).
Now, a week of cloudy days would make this system less effective, but you could get around that by using a nearby lake for heat storage until the sky clears again (though that won't be very nice for the inhabitants of the lake).
Bottom line, if someone can come up with a cheap/light way to store electricity (either through a flywheel or through a superconducting coil), we'll still keep boosting my Exxon stock. And we'll do it by drilling in your backyard.
Fuel cells for cell phones should be appearing within the next 2-5 years or so. Prototypes already exist, and energy density is almost as good as a chemical fuel.
Fuel cells at present are a pain for things like cars because storing the hydrogen they use is very annoying (it's nowhere near as dense as a liquid). However, fuel cells that can process methanol are buildable, and will IMO probably be what brings fuel cell cars into the real world. Or you could just pump methanol into an interal combustion engine made of ceramics or otherwise made corrosion-resistant.
Methanol can't be easily produced by "recharging" fuel cells (unlike hydrogen), but you can make it by fermenting plants or by direct synthesis (burn CO2 incompletely in a hydrogen atmosphere and use fractional distillation on the combustion products).
In summary, power storage won't be a problem for long.
anyone with a tenth of an IQ point knows that fusion is clean and safe, unlike fission.
Fusion is certainly safer than fission from a high-level waste point of view, but how exactly do you propose to prevent the reactor vessel from becoming radioactive? Even "relatively few" neutrons is enough to cause major headaches for disposal of replaced parts for a multi-gigawatt reactor.
Claiming that it's perfectly clean will only make backlash worse when the public finally clues in. Remember when fission power was supposed to be safe and clean?
What about the supply of deuterium? It's not perpetual...
It's close enough to perpetual that it makes no difference.
About 1 hydrogen atom in 7000 is deuterium. Hydrogen accounts for 1/9th the mass of water, which means that the mass of deuterium we could extract from the oceans is about 1/63000th the mass of the oceans.
Assuming an average depth of about 3km and a coverage of 2/3 of the Earth's surface, you have about 1e18 tonnes of water on the planet. Let's say 1e-5 of that is deuterium that you can easily extract, and you get 1e13 tonnes of deuterium.
Fusion is about 1% efficient at turning mass into energy. Let's say that your fusion reactor is 0.01% efficient in total (pessimistic estimate). This gives about 1e13 J/kg, or 1e16 J/tonne.
The total amount of energy we could extract from fusing the oceans' deuterium with these fairly inefficient fusion plants is about 1e29 J.
If we want our fuel supply to last a million years, that gives a world power consumption of 3e15 watts. Far, far more than we consume now.
If, within the next million years, we build reactors good enough to fuse light hydrogen, we'll have enough fuel to last us until the sun burns out (several billion years). Or we could just ship in deuterium from elsewhere in the solar system. Either way, barring a *huge* population expansion, we won't run out of power - ever.
In other words, either we get cheap, clean, nearly free unlimited energy, or our future is gonna look uncomfortably like those Mad Max movies.
Actually, what would be more likely to happen is a slow and painful shift to renewable forms of energy and a lifestyle that consumes less power.
Fossil fuels won't run out all at once - they'll get incrementally more expensive as they become scarcer and more difficult to extract. As price climbs, people will out of necessity start using less power, and alternative forms of power generation will become cost-competitive (even if their own cost doesn't change).
You'll see more houses with photocell shingles. You'll see a mirror-based heat plant or a wind farm next to most cities. More people will take public transit, because it's cheaper than driving. House design will depend more on passive heating/cooling and good insulation than on furnaces and air conditioners (they'll still be used; just on lower settings). People will have to hang-dry their clothes instead of tossing them in the drier. And so forth.
A Mad Max style catastrophy would only happen if energy supplies ran out all at once. A nuclear war or an asteroid strike could cause this, but I doubt fossil fuel problems will.
ok, so you have this plasma "floating" in the bottle at 12 gazillion degrees. the power goes out. doesn't your ball of plasma just eat it's way through anything it touches and head towards the center of the earth?
The plasma is very hot, but also very tenuous. You might have a few thousanths of a gram of matter in the reactor. As soon as this touches the reactor wall, it cools down to room temperature. Your reactor wall gets warm. That's about it.
Also, as your plasma is much less dense than air, if anything, a ball of plasma would rise.
You'd never get a ball. What happens is that as the containment field weakens, the donut-shaped mass of plasma expands until it touches the side of the container. In theory, if you had a "hole" in the containment field instead of the whole thing weakening, you could get a jet of what looks like flame, but this is next to impossible to do even if you're _trying_. The natural shape of the field is more-or-less uniform.
Plasma is just a hot, conducting gas. It follows gas law like everything else.
This site gives a general overview of current fusion studies.
For the more technically inclined, you can check out the journal Fusion Engineering and Design (Sorry - if the link doesn't work for you, it's probably a pay-per-access journal and your business/school/self isn't a subscriber). Anyway, it's full of juicy fusion engineering and design details.
The downsides are that the D/He-3 reaction has a higher energy threshold, so it requires a better confined plasma to make D/He-3 energy production plausible. Also, the supplies of He-3 on Earth are limited. Of course this disadvantages leads to a interesting convergence of interest between fusion research and space exploration. There's plenty of He-3 (deposited from the solar wind) on the moon. So He-3 mining could be powerful reason to maintain a base on the moon.
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I hope we shall crush in its birth the aristocracy of our monied corporations
And I'd be a Libertarian, if they weren't all a bunch of tax-dodging professional whiners.
Berke Breathed
Why the hell are we working on making our own self contained fusion reactions when we have the solar system's largest self sustaining fusion reaction going on not 93 million miles away?
99.99999% of the sun's energy output flows, wasted, into the interstellar depths. A tiny fraction of this energy falls on our planet's surface and is used by us (either in stored form as fossil fuels, or more or less directly as solar, wind, etc...)
Ultimately the only real solution to our energy woes lies in figuring out how to catch just a little extra sunlight, convert it into usable forms of energy and move it to the Earth's surface.
Solar satellites are the answer. We have the technology now. We know how to make it work now. People have been designing complete, workable systems that use nothing more than existing technology for the last quarter century. Why aren't we funding them instead of this pie in the sky "always another two decades off" technology.
Certainly our skills in manipulating hot plasmas will eventually reach the point where a Fusion plant will become feasible. But by that time we could have built and launched an entire fleet of solar satellites, or paved over every major desert with solar tiles or reflecting concentrators.
-josh
I just copied the (nuclear) plant we have now. Then, I added some fins to lower wind resistance. And this racing stripe here I feel is pretty sharp.
--Homer Simpson
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"Outlook not so good." That magic 8-ball knows everything! I'll ask about Exchange Server next.
So how would you convert the energy produced into electricity?
Steam turbines might seem archaic, but they're still used for the simple reasons that they're a well-proven technology and high pressure steam contains a *lot* more energy per unit volume than pretty much anything else in routine use. (After whatever heats the water in the first place, of course!)
Remember, the plume of vapor over your tea kettle on the stove is not steam. It's water vapor condensed from a very small amount of steam. Steam is invisible, and tends to do things like fling heavy fighter aircraft off of flight decks or instantly cut people in half if they walk in front of a pinhole leak.
For every complex problem there is an answer that is clear, simple, and wrong. -- H L Mencken
I post this as a former fusion researcher and a former project manager for the Office of Fusion Energy (OFE) of the Department of Energy (DOE)
Many decades ago the international fusion community put all of its chips on the Tokamak. It has been a disaster.
Even if a Tokamak could produce break-even fusion ( getting more energy out than you put in) the engineering obstacles to creating an economically successful reactor are daunting.
Many years ago, the OFE sponsored a study, Project Aries, of the costs of a Tokamak reactor. Even using the usual optimistic assumptions, the cost came in way above solar and wind power, let alone fossil fuels.
Another symptom of the problem is that three times in a row, projects to build larger Tokamak have collapsed in the design stage. That is, even before anything was build, none could come up with a working design. The International Thermonuclear Experimental Reactor (ITER), the latest attempt, collapsed as the price tag spiraled above $20 billion (US)
The whole OFE degenerated into a "you scratch my back and I'll scratch yours" process where the lab directories divvied up the pie. All non-Tokamak ideas were cut off, including the one I worked on.( more below).Congress cut the OFE budget almost in half a few years ago in response to this.
That being said, I respect the findings of the DIII-D team. The DIII-D is very well run research project, the their accomplishment is to be applauded. Now for a blatant plug. In the 70s I worked on a small project at the University of Miami, the Trisops project, which was defunded. The amount of money was not an issues ( our request was quite small), but the non-Tokamak nature, and the nerve of the principal investigator, Dan Wells, to point out that the Tokamac was unworkable.
The Trisops machine was recently moved from the University of Miami, to Lanham Md, with a small NASA grant, but there is not money to run it. You can see a report on it.
Another interesting project, the Plasmak(TM) project that is being run by Paul Koloc ( out of his garage!!).
The holy grail on fusion research is a stable plasma structure. The Trisops project achieved it one way. Paul has noted that ball lightning, which has been known for millennia, is a stable plasma structure. He has machine that produces ball lightning, and is measuring it. He gets no DOE funding of course.
I work at princeton plasma physics laboratory in the computational plasma physics group. Politics have jack shit to do with why we don't have fusion working. The fact that plasmas are goddamned hard to model and understand and maintain stably ARE why we haven't gotten fusion energy yet. We get PILES of USDOE funding every year and pour it into more and more innovative research. No one is standing out picketing plasma research labs because anyone with a tenth of an IQ point knows that fusion is clean and safe, unlike fission. In summary: pull your foot out of your mouth and your head out of your ass, and talk about something you know.
At first I thought I might agree, but then I thought about what the reaction "products" were. IIRC, you get fast neutrons (high kinetic energy) and high-energy photons (gamma radiation). There is a kind of amusing simplicity in the strategy of letting these slam into some object, raising the average kinetic energy of the object's molecules (hence it's temperature), then extracting that energy from the other side. As others have pointed out, steam turbines are surprisingly efficient.
Are there materials that could be used for the gamma-ray equivalent of a photocell?
Given that neutrons have no electrical charge, is there any way to extract the kinetic energy other than smacking them into something?
Does a significant amount of the reaction output show up as "fast" helium? Is that any easier to deal with than neutrons?
I assume that you mean the actual containing field, rather than the shaping fields discussed in the article. Presumably, the power would come from the reactor itself, so that if the magnetic fields collapsed, it would indicate that the reaction had ceased. That would not necessarily mean that there wouldn't be plasma leakage. Most likely, though, there would be redundant generated power for critical systems (as there is at nuclear plants). For example, several reactors in the same complex could each power the others. In other words, that particular problem shouldn't be too likely.
If magnetic containment were to fail, you would have a very hot stream of plasma shooting in a straight line from the reactor. The pressure of the stream would drop so rapidly that there could not be a sustained reaction (i.e., no boom). The walls in the way of the stream would likely be melted. I'm not sure what they would do for secondary containment - most likely a shell similar to what is done with fission reactors, but using different design to account for the different hazards. You'd probably get a huge puddle of (non-radioactive) water to clean up, too.
-- Two men say they're Jesus. One of them must be wrong. - Dire Straits
I know it is theoretically the perfect power source, and that it shouldn't produce environmental problems like nuclear waste or dirty emission - but I also know as-sure-as-eggs-is-eggs that there is going to be a protest movement against it, regardless. Which leads me to my question...
Are there any fusion protest groups yet? I'm always late to join protest movements so I get crappy seating at rallies and never get to talk to the news media about my important opinions on the subject.
If you know of any, please post. If it helps, I am SINCERELY against the late 60's musical movement by the same name.
(signed, someone who genuinely wants to make a difference, as long as others are watching...)
(Then our next problem will be heat pollution)
Perhaps... Heat Pollution would become a problem, but hopefully that would be worse than greenhouse-effect causing gasses that we release by Fossile fuels, if such gasses do in fact cause global warming (of which I'm not fully convinced.)
A higher dependency on Solar Cells and heat-energy-converting/trapping devices could also help lower the amount of heat we have to deal with.
And of course Trees help quite a bit, too. If would could just stop cutting them down.
"Everything you know is wrong. (And stupid.)"
"Everything you know is wrong. (And stupid.)"
Moderation Totals: Wrong=2, Stupid=3, Total=5.
Well, here's a little calculation that might help convince you about the greenhouse effect. I'm too lazy to look up the numbers and everything right now, but if you look in any basic astronomy book and this calculation should be there.
Take the luminosity of the sun and using the cross-sectional area of Earth and knowing Earth's distance from the sun, and accounting for it rotating for a more-even heat distribution, you can find the average solar power striking Earth.
Now assuming the Earth is in thermal equilibrium with it's surroundings, it will thermally radiate at this same power rate. Assuming Earth is a simple blackbody, what is the temperature that it radiates at? In other words, what is the temperature of the surface of Earth, as determined by the power of the sun and the distance from that sun?
The answer comes out to roughly (it's either a few degrees above or below this value) 0 degrees celcius. That is, around the freezing point of water. Granted some parts of Earth are frozen, but most parts are able to easily maintain liquid water, often at substantially higher temperatures than 0-degrees C. What accounts for Earth to be this warm? It's the greenhouse effect!
Most scientists will readily argue that the greenhouse effect is real, and in fact necessary, for life on the planet. So I hope that answers your question about the effects of greenhouse gases and global warming.
The real question, though, comes about when we consider how would the surface temperature change as we adjust the CO2 levels from what they were a hundred years ago. That's the harder question to answer.
I do believe that as a species, through engine emissions and other means, we are starting to significantly alter the planet's ecosystem. Probably through increased population alone will the effects start to manifest themselves. .V / _` (_-<_-<
.\_/\_/\__,_/__/__/
__ __ ____ _ ______
\ V
make world, not war
IANAP, so I am talking out my ass here, but it seems to me that the interior surface of the container of a reaction might just somehow be able to more directly collect energy, similar to the way solar-panels collect light. Of course, I have no idea what kind material might be used to accomplish this. How do solar-panels work? Silicon? Is it just dumb luck that the elements of a solar panel happen to convert light to energy, or is it a man-made composite, built specifically for that purpose?
... fusion reactor vessels will likely not be cheap).
... collisions ...). By that time, all that the sun radiates is a near perfect blackbody radiation spectrum.
Yes, you are talking out of your ass.
Note: I did my Ph.D work in plasma physics but now I work in quantum and optical electronics. I am probably one of the better qualified people here to answer your question.
Conventional fusion reactors fuse deuterium and tritium. Or, if you breed tritium from a lithium blanket surrounding the reaction, you can do fusion using deutrium-deutrium full burn (this is tougher to do than D-T reactions).
However, the by-products of D-T and D-D fusion are mostly high energy neutrons (and some gamma rays and neutrinos and alpha particles...). High energy neutrons are not easy to convert into electricity because neutrons are not charged. In fact, the neutron flux of a large fusion reactor would be deadly and thus a fusion reactor needs to be heavily shielded while operating. (Watch "Chain Reaction" and laugh as Keanu and his advisor walk around the operating reactor after it stabilizes.)
A typical approach for the conversion consists of letting your neutron flux heat a block of lead (or other material) and then running a standard steam cycle.
This sucks on many levels.
First, you end up throwing away much of your power from the inefficiency of the steam cycle. That is the theoretical thermodynamic efficiency of a fusion reactor which can somehow do direct conversion is effectively 100% (hot reservior at millions of degrees, cold reservior at room temp) while a steam cycle is limited by how hot you can heat your materials (hot reservior at thousands of degrees, cold reservior at room temp).
Second, the neutron flux will activate (i.e. make weakly radioactive) the walls of your reactor and steadily degrade the structural integrity of your vessel. As a result, current estimates are that the core of a fusion power plant will need to be replaced every couple of years (which makes energy providers frown
Other approaches are to use fusion reactors as breaders for fission plants (i.e. use fusion neutrons to enrich fission reactor fuel). Many estimates already put current reactor technology beyond breakeven for this type of design. However:
- Design is not politically feasible (some alternative fission fuel cycles might be possible). Fission suffers from NIMBY and fusion-fission breeders have a massive proliferation risk.
- Fuel for fission reactors is not particularly rare and running a fusion plant will likely not be cheap. Thus, economically, currently there is no compelling reason.
Solar cells on the other hand rely on photons exciting electron-hole pairs in a semiconductor. The light from the sun partially consists of photons in the visible and near infrared range which are suitable for conversion by a solar cell.
You might be wondering why fusion reactions produce high energy neutrons and gamma rays and other generally nasty things while our sun shines a whole lot of light. You should remember that the sun is big and the products of a fusion in the sun take hundreds of thousands of years to reach the surface (random walk
Because it's not yet possible I wonder if anyone has thought about this before -- would it be less expensive to "cluster" smaller fusion reactors together to achieve energy output, or is building one large reactor the "best" way? I just look at the progression of things: Room-sized computers->high-end workstations->desktops->distributed computing ... maybe power generation can follow a similar model? We've already scaled up -- moved from small output steam generators.. is it time to start scaling down again?
Now, a more appropriate question is whether we could approach the scale of Earth-impacting solar energy with our own heat producing energy sources like fusion, fission and fossil fuels. I admit I have no idea of their relative magnitude.
I would have had no idea of their relative magnitude, either, except that I'm a Slashdot Reader.
The recent solar car race article included references that suggests solar energy flux is of the order of 1 kW/m2. With a radius around 6.3e6 meters, the cross sectional capture is around 1.2e14 m2, suggesting the solar input radiation is around 1.2e17 Watts. (Which also could suggest why CO2 emissions that affect solar gains and losses don't have to do much to cause an observable effect on the planet's temperature. But I digress.)
All the recent hubbub surrounding the California electrical generation capacity crunch has bandied about figures for big power plants that generate, oh, like 5 GigaWatts. Looks like there's a factor of about 1e8 before terrestrial generation gets anywhere close to Sol's warmth.
Given those magnitudes, I doubt man-made heat generation would be a problem. It is much more likely the problem would turn out to be some much more prosaic, like worrying about liquid Lithium being in short supply, or finding a way to deal with the irradiated equipment and byproducts of fusion reaction.
"Provided by the management for your protection."
"In this house we OBEY THE LAWS OF THERMODYNAMICS!" -- Homer Simpson
--- Brent Rockwood, Development Lead
BRENT ROCKWOOD, EST'd 1975
The best way to prevent this from happening is complete disclosure of all knowledge pertaining to fusion, and large-scale mirroring of that information all over the world.
A higher dependency on Solar Cells and heat-energy-converting/trapping devices could also help lower the amount of heat we have to deal with.
umm, these devices, which allow you to store heat energy only take heat out of the system until you actually use them, at which point they return all the heat they took originally.
Sure fusion may allow us to have access to alot more heat, but the stuff is quite willing to radiate off the planet with minimal fuss (Given proper atomospheric conditions).
Now turning our planet into a solar greenhouse or toxic waste dump- those are potential problems. "Heat Pollution" is a non-issue.
Right now, there are some severe issues with getting it to work at all.
But, let's assume that tomorrow there is a breakthrough and it all magically works perfectly.
The problem is that most of the energy of the fusion reaction comes out in the form of neutrinos, which you can't practically stop, some heat, but mostly fast neutrons.
The fast neutrons don't dump their energy into heat energy very easily at all. The best scheme I heard for doing that was lining the inside of the fusion reactor with lithium, transmute that for a bit and then stuff the lithium into a conventional fission reaction and use THAT to make steam.
And that's the most realistic scheme I am aware of. The fission reactors, and the disposal issues of all the elements that are getting irradiated make this very far from being a clean process. Fusion power is never going to be clean.
-WolfWithoutAClause
"Gravity is only a theory, not a fact!"(Slaps Forehead)
Your absolutely right. My bad.
In this setup plasma particles align themselves with the MAGNETIC field, which is threated through the magnetic rings (duh). The Electric field is generated in the center and radiated outward toward the edge of the bottle.
For more information on this containment theory please visit my professor's web page at: Centrifugally Confined Plasmas
You can also get a good scematic of the design at: This link
I apologize for the confusion.
The tokamak reactor design uses a torus (donut) shaped ring to confine the plasma. Another design is one my (former) physics professor and the group he is in are currently working on. Basicaly the design consists of two magnetic rings, one above one another. The electric field is threaded through the bottom one and through the top one. The electric field bulges out between the two rings making a sort of "coat hanger" cross section between the rings. This forms the shape of the magnetic bottle.
Classical EM shows that the plasma particles will be confined to the electric field lines and helix around them. If there were no magnetic fields the particles would "escape" this system through the top and bottom of the E-fields.
The neat part is that when the magnetic fields change, the system imparts an angular momentum onto the plasma particles. The result is that the plasma spins (in the same plane as the magetic rings). Since the electric fields are in a bent, the centripetal force will push the plasma into the middle of the "bottle" and away from the top and bottom. The anaolgy he gave was take a bead and put it on the bent wire of a coat hanger. Now spin the hanger around its long axis. The centripetal force will push the bead to the "bulge" of the hanger. Similarly, the plasma should be pushed to the "bulge" of the magnetic bottle. Hopefully when enough energy is added to the system the plasma will fuse.
Last I heard the group this professor works in was trying to get funding to program a model of the reactor, so no working model is on the way soon. He claims that thoeretically this setup should be able to cross the energy in-energy out threashhold. Of course only time (and money) will tell.
that the only way we have invented to caputre the energy of a nuclear reaction was by superheating water and using steam pressure to turn turbines. That always seemed like a hack way to collect the energy. Anyone know if the energy collected from this thing is more direct than heat+water=turbine-power?
Well, your fingers weave quick minarets; Speak in secret alphabets;
std::disclaimer<std::legalese> sig=new std::disclaimer; sig->dump(); delete sig;
In the meantime, why are we wasting time drilling for oil and chasing cold fusion pipe dreams when we should be pushing forward in the direction of the infinite improbability drive.
Paladium fuel is incredibly expensive and rare. But all you need for the IID is a bit of fairie cake and a cup of tea.
Wait- you're turning into a pengin. Stop it.
From itercanada.com:
What about the risk of an explosion or meltdown? Is this possible with Iter?
No, the fusion process in Iter can only be achieved under precise, controlled operating conditions. If conditions in the Iter machine are not ideal, the process just stops - it cannot escalate out of control. Therefore, there is no possibility of a massive energy release-or a "core melt" accident-from the Iter Tokamak.
Basically, in order to keep the plasma going, it needs to be constantly controlled by the magnetic containment field. If this field fails, there's no explosion; the plasma effectively loses state, and the whole reactor shuts down of it's own accord.
In a nutshell, fusion energy is safer than breathing.
Obliteracy: Words with explosions
A fission reactor is much more dangerous because all the control rods stop (if they work) is the chain reaction. The chain reaction basically splits U235 nuclei up into random sized pieces, mostly highly radioactive, and most of the heat comes from the decay of those fragments. So when they drop the control rods, the fission tank continues to heat up for several hours. To prevent a melt-down, you have to keep the cooling water circulating. Of course this can be powered by the heat you are removing, but if the problem is a blockage in the cooling system... E.g., at THree Mile Island they had a cooling valve closed and didn't realize that for several hours. Secondary cooling kept the reactor well below melt-down, but it did get hot enough that pressure had to be let out, allowing a negligible amount of radiative gas to escape. Note that this was the "worst" accident in commercially-operated nuclear power anywhere in the world (Chernobyl wasn't commercially operated), and fusion would be safer.
There are two dangers in a fusion reactor. One is that one of the fuels might be tritium, a radioactive form of hydrogen, which is remarkably good at finding leaks. Due to the smaller fuel quantities required there is less overall danger of radioactive leakage than fission. It just requires good managment... The other is that fusion reactions release neutrons, which tend to turn other materials radioactive. In other words, unless you very carefully select materials not subject to this effect, and make them extremely pure, after 30 years or so the plant structure itself will be radioactive. Fission also releases neutrons...
Actually, if you are quite close to the reactor when it fails, you are in some serious trouble. The plasma inside the Torus is at a very high temperature (I thought it approached Solar temps, but cannot confirm this). If it spills all over you, you are dead. I assume any commercial reactor would be contained in some way to prevent accidents of this sort.
You are right about the temperature, but containment is exactly the wrong solution. What you want is something that breaks away (in a controlled direction, say "up" would be nice). Remember that the quickest way to cool something really hot is to let it expand. (The second quickest way is of course to get venture capital.)
This applies to pretty much any concentration of free energy. You can burn gun powder safely in a small metal dish, but the same quantity in a small metal pipe makes a rocket or a bomb (or both) depending on how the ends are capped. With the plasma from a just-failed fussion reactor you're looking at something on the order of a lightning bolt. Set free, you have a big flash, a loud bang!, and a lot of people saying "What the fuck was that!?!?!"
Try to contain it, and you have a much louder boom, and a somewhat reduced number of people crying "Oh, the humanity!"
-- MarkusQ
It is a problem with deuterium-detuerium reactions, though, but no worries, there are oceans of helium-3 in Jupiter... we just gotta extract it.
Also, fusion will be MUCH cheaper than gasoline. Consider the fact that the fuel supply for fossil fuels is limited, wheras deuterium is found EVERYWHERE. We have oceans of it here... It is a very good long term solution for any technological civilization, just in terms of fuel supply. Burning old dinosaur bones will only last so long.