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is nuclear fusion impossible to pull off on earth?

S

ShawnTech

Banned
i'm just asking if it is possible to pull off without destroying the entire earth

technically speaking a fusion reaction takes INCREDIBLE heat and force to get started bu then sustains itself by turning hydrogen molecules into helium molecules
if this is the same process that happens on the sun, wouldn't the heat from the reaction burn a hole in the earth then eventualy desintigrate it?
i'm asking because people are researching fusion power and how to get it started but im weery of whether it would completely destroy the earth
the reaction is very efficient and the energy released is E=mc^2. just 1 gram of hydrogen fused all together has the power of like 10 nuclear bombs
 
Considering I work one floor above a fusion reactor, I'd say fusion is possible. 🙂

Fusion is the reaction behind thermonuclear bombs, produced since the 1950s. Controlled fusion reactions has been possible for quite some time using torus plasma reactors (for example, at Princeton and here at UW-Madison) and laser/hydrogen pellet reactors. It's only been in the last decade that the fusion reactors have been able to break even - produce more energy than that is inputted. We can't produce the pressures comparable to the center of a star, so to compensate, much higher temperatures are needed...on the order of about 10 million K, IIRC. The energy needed to reach these temperatures, and the energy needed to sustain powerful magnetic fields (in the case of torus reactors) needed to contain the high-temp plasma is what makes the energy input requirements so high.



<< the reaction is very efficient and the energy released is E=mc^2. just 1 gram of hydrogen fused all together has the power of like 10 nuclear bombs >>

This is a bit high....not all the mass of hydrogen is converted into energy in a fusion reaction. The amount of mass converted to energy will be the difference between the binding energies of the initial and final product...for hydrogen fused into helium, this is about 6 MeV, or about .5% of the total mass of the hydrogen. I believe the fusion of deuterium and tritium (two isotopes of hydrogen) yields roughly 4 times as much energy/unit mass as the fission of uranium-235.
 


<< Considering I work one floor above a fusion reactor, I'd say fusion is possible. >>

What's the location? 🙂
 
i mean controlled nuclear fusion in the thread title actualy, i've known that nuclear bombs worked that way. sorry for misleading on that
 
They're definetly possible. As Sohcan said, the problem is, it's difficult to get them to produce more energy than they require.

Sohcan, that's interesting. I'm curious, do you work on the project? Do you think fusion will be a viable source of energy in, say... 20 years?

-Ice
 


<< What's the location? >>

The University of Wisconsin - Madison....second floor of Chamberlain, on the corner of University and Charter Sts. for anyone who is interested in seeing it...it's pretty cool. 🙂



<< I'm curious, do you work on the project? Do you think fusion will be a viable source of energy in, say... 20 years? >>

Nope, I'm assisting with a different high-energy physics project (building a particle detector for the Large Hadron Collider at CERN in Geneva, Switzerland). I'm not an expert on fusion, but I believe the latest research involves manipulating and fine-tuning the plasma fields so that they produce more energy and require less energy to build and sustain. They're getting incremental improvements, so in my (un)educated opinion, I would think 20-30 years is a viable goal.
 
Since fusion reactions have been implemented in a variety of ways, it's definitely possible. The real question is when/if it will be a viable form of mass power generation. Tokomak/torus reactors work, but they are very far away from a mass generation system that can produce power economically.

One feeling that I seem to be getting from reading various articles is that the industry is moving away from torus reactors and back towards other promising designs - which is a marked shift from a decade again when torus designs were all the rage.
 
Actually, I just checked and I was mistaken....Madison's torus isn't regularly used for fusion experiments. They mostly do high-energy plasma research (at only 5 million degrees C 😉) for other fusion facilities.



<< hey sohcan, can you get me some uranium? >>

Sure, it's for educational purposes, right? 🙂
 
For more information on torus designs, I recommend www.iter.org to visit the biggest of the bunch.

Other ideas for nuclear reactors

There's the Colliding Beam fusion reactor in which beams of boron-11 and hydrogen are generated and sent into a reactor chamber where magnets would cause the beams to bend, causing the nuclei to collide and fuse. The huge advantage of this method over the hydrogen/helium torus designs is that the fusion generates electrons directly, rather than heat energy that then need to be converted into electrical energy via some mechanical process such as a steam generator. The radiation levels are also much lower. On the downside, the scalability of such a reactor are a big question.

There's the Inertial Confinement fusion reactor. From the Inertial Confinement Fusion web page at UC Berkeley:



<< "In inertial confinement fusion, small B-B-size hollow spherical capsules, most likely made of plastic, are filled at high pressure with an equal mixture of deuterium and tritium, and then chilled to cryogenic temperatures, so that the D-T gas freezes as a thin, solid coating on the inside of the capsule wall. Suspended by a thin plastic film at the center of a metal cavity called a hohlraum, these spherical capsules can be injected into the center of a target chamber. There, in a few billionths of a second, lasers, or beams of high-energy heavy ions as pictured in Fig. 1 above, can be used to heat the interior of the hohlraum cavity to temperatures several hundred times the temperature of the sun, vaporizing the surface of the plastic shell into an extremely high pressure plasma. Alternatively, direct-drive targets have no hohlraum, and lasers heat the capsule surface directly.

The capsule, transformed into vaporized plasma, reaches pressures of hundreds of millions of atmospheres. As the plasma expands outward like rocket exhaust, it accelerates the thin layer of D-T radially inward, to velocities of 300 to 400 kilometers per second. The residual D-T gas from the center of the capsule, heated by the denser D-T that surrounds and compresses it, reaches peak temperatures over 100 million degrees Celsius, sufficient to ignite a propagating fusion reaction. Just as a match can light firewood, this hot spot ignites a fusion burn wave that propagates out into the denser D-T. By releasing seventy or more times the energy originally needed to compress and heat the fuel, this dynamic process provides the basis for generating inertial fusion energy. The second chapter of these notes, "How ICF targets work," discusses in greater detail the physical processes that occur in ICF targets, and the issues related to manufacturing inexpensive targets and injecting them with high precision into target chambers. >>



There are alternative forms of magnetic confinement other than the torus/Tokamak design as well. Spherical torus is one different alternative.

What I meant in my post above is that it used to seem (about a decade ago) that progress in fusion reactors meant we were moving upwards in size of torus/Tokamak reactors. ITER was supposed to be the next stepping stone (1TW for 1000 seconds) which would followed by an even bigger one. Then things started getting too expensive and the US got cold feet and the next thing we know ITER is a smaller project, and the US is funding smaller research into other areas such as inertial confinement and colliding beam and magnetic confinement alternatives. It was a rather abrupt shift in policy and it makes me wonder if the fusion program is intended to actually produce real reactors (rather than just keep high-energy physists employed in case the government needs them to work on weapons research in the future), or if there is a fundamental problem with torus designs that are causing people to seek alternatives.
 
i'm sorry, i mislead you guys again

what i meant by this post is perpetual generation without putting more energy in. like the sun. just get it started then let it go nuts on its own.
i was thinkin that the chain reaction would get so hot it would just desintigrate the plant and maybe destroy a significant part of the earth do to the huge energy release.
 
The goal of any power plant is to produce more energy than it requires to generate it. All power plants require energy to run - if only just as much as to run the lights and safety systems. Fusion plants just require more to get started and to run but then they hopefully produce more power than they use. Current reactors actually are past breakeven - theoretically (they measure how much power they could produce, if they were producing it, which they aren't). So current designs could, theoretically, generate more power than they require to ignite.

As far as uncontrolled fusion wiping out the planet... no that's not going to happen unless someone falls asleep on the big red button in NORAD. Most of the earth is composed of materials so heavy that it would require more energy to fuse them than you'd get out of the reaction, so the fusion reaction couldn't be sustained without additional energy. A fusion reaction couldn't run-away and destroy everything on earth. The sun requires high confinement (gravitational confinement in the Sun's case), and a huge supply of hydrogen to maintain the reaction. We don't have either of those on Earth (high gravity or vast amounts of hydrogen in a fusable form).
 


<< just 1 gram of hydrogen fused all together has the power of like 10 nuclear bombs >>



well, 1 gram of H is a whole lot of atoms..

and besides, that requires complete conversion of the H into energy, according to you

--

as for the comment about the sun, we dont really know how much energy was involved in the formation of it, so we can't say =\
 


<< hey sohcan, can you get me some uranium? 😉 >>



You can make your own uranium. You'll need a neutron gun and some thorium.
 
Nope, I'm assisting with a different high-energy physics project (building a particle detector for the Large Hadron Collider at CERN in Geneva, Switzerland).

I've read about that project in Astronomy and Scientific American. I'm excited to see what we'll find.

Nice links pm...reading now.
 


<< i was thinkin that the chain reaction would get so hot it would just desintigrate the plant and maybe destroy a significant part of the earth do to the huge energy release. >>



As PM said this simply cannot happen. In order to sustain a fusion reaction we will have to maintain a very high pressure. In the sun gravitional forces provide that pressure, here we will have to do it artifically. If we loose the pressure the reaction will die. In that sense the fusion reactors will be safer then fission, where we have to activally slow the reaction, and it is possible to lose control.

Further, the most common element in the earths crust is Iron. Iron is a radioactively a very stable element. It is the only element that will not release energy through either the fission or fusion process. Elements lighter can be combined (fusion) to form a bit of energy and a heavier element. Heavier elements can be split (fission) to create two lighter elements and a bit of energy.

Where does Iron come from? In nature all heavy elements can only beformed as the result of a star going Nova or Super Nove. The forces generated by this type of explosion created high enough pressures to force the fusion process into creating the heavy elements.

The implication of this is that every atom on this planet has been burned in a stellar fire. Our sun may be a 3 rd generation star, the fuel it is burning and all of the solar system have been though 2 older stars.

Kinda makes ya think doesn't it!

Now here is a thought, If we can get a good fusion fire going we should be able to burn most anything. Do you suppose we will be able to dispose of our fissiion wastes or will it just make it "hotter". Seems like we could set the temperature and turn out any element we desire. I can see it now, says the fusion foreman "Whats on the list for today, humm, Gold till noon then we shift to Silver in the afternoon, Ok, let crank it up!"

Possible or will any by products be so 'hot" that it is unthinkable?
 


<< Now here is a thought, If we can get a good fusion fire going we should be able to burn most anything. Do you suppose we will be able to dispose of our fissiion wastes or will it just make it "hotter". Seems like we could set the temperature and turn out any element we desire. I can see it now, says the fusion foreman "Whats on the list for today, humm, Gold till noon then we shift to Silver in the afternoon, Ok, let crank it up!"

Possible or will any by products be so 'hot" that it is unthinkable? >>


I dont think it works like that 😉

I mean, we use fusion with hydrogen, and the sun also uses He (probably more stuff to). We use fission to get power from Uranium, Plutonium, etc. The issue is, if you get energy from fissioning uranium, you can't possibly get energy by fusing the two elements that were created. Also, I dont think you'd get energy by fissioning Helium. So, there is somewhere in the middle most likely where you cannot cross and still get energy.

Although maybe you could put in however much energy you need to do it, that would most likely be fairly expensive to do.
 


<< i mean controlled nuclear fusion in the thread title actualy, i've known that nuclear bombs worked that way. sorry for misleading on that >>


controlled reaction? not a problem. Here at the UW (University of Washnington) thve been able to create fusion reactions that produce more energy than is needed to start them. Only problem is making them last longer.
 


<< i'm sorry, i mislead you guys again

what i meant by this post is perpetual generation without putting more energy in. like the sun. just get it started then let it go nuts on its own.
i was thinkin that the chain reaction would get so hot it would just desintigrate the plant and maybe destroy a significant part of the earth do to the huge energy release. >>



theres no such thing as perpetual generation of energy. The sun, like every energy source, will eventually burn all of its fuel.

there are only two kinds of fusion reactors, inertial confinment fusion (icf) and tokamaks (magetic containment). There are two basic problems with fusion reactrors. firstly, the energy generated is less than the energy put in, so basically they dont work. I havnt heard of a fusion reactor that every produced more energy than was put in. And i should have a pretty good idea given i was taught plasma physics by one of the leading fusion researchers in the country last spring at uc berkeley. the second problem is heat transfer, ie how to produce electricity from the heat. fusion reactors are not similar at all to fission reactors (PWR's, BWR's). Actually theres a third problem too, waste. fusion reactions produce large amounts of neutron generations, and neutrons are not contained by the magnetic field. the material surrounding the plasma is thus being bombarded by neutrons, creating radioactive waste.

there are two problems with your post though. firstly E= delta(m) c^2 so you cant simply input the mass of a hydrogen atom or what not. Its the difference of mass between the producs and reactants that is converted to energy. Secondly the amount of energy that is released is proportional to the amount of fuel put in. the reactions that take place in fusion reactors are many many orders of magnitude smaller than even a small nuclear bomb.
 


<< There are two basic problems with fusion reactrors. firstly, the energy generated is less than the energy put in, so basically they dont work. I havnt heard of a fusion reactor that every produced more energy than was put in. >>

Breakeven, the term for a fusion reactor that outputs more than it requires as input, can be defined in a lot of ways (taken from the fusion FAQ, link unknown but you can probably find it fairly easily... I have it saved on my HD):

Commercial: When fusion power can be converted into enough electric power to power the reactor and generate enough electricity to cover the costs of the plant at economically competitive rates.

Engineering: When enough energy can be generated from the fusion power output to supply power for the reactor and generate a surplus; sort of commercial breakeven without the economic considerations.

Scientific: When fusion power = input power; Q=1. (ie. the Lawson Criterion)
A. Extrapolated - projected for actual reactor fuel using an alternative fuel.
B. Actual - determined using the actual fusion fuel to be used in the reactor (typically DT).

No one has come close to the commercial definition since there are no commercial fusion reactors and no one has any current plan to build one. Similarly for the engineering definition. The scientific definition is of far lesser value than the first two, but the "extrapolated scientific" definition was acheived in 1998 by the Japan's Tokamak reactor JT-60U. Since then reactors such as the UK JET reactor have come within 90% of the "actual scientific" definition.


<< the second problem is heat transfer, ie how to produce electricity from the heat. fusion reactors are not similar at all to fission reactors (PWR's, BWR's). >>

The first problem you mentioned is scienfitic - as in we don't know to accomplish a commercially viable fusion reactor. This problem is engineering - and I think it's safe to say that if someone develops a viable reactor method, then the heat could be harnessed effectively. And depending on the fuel used and the type of reactor, this may not even be a problem. As I mentioned in a previous post, fusing boron-11 with hydrogen produces electrons directly.

<< Actually theres a third problem too, waste. fusion reactions produce large amounts of neutron generations, and neutrons are not contained by the magnetic field. the material surrounding the plasma is thus being bombarded by neutrons, creating radioactive waste. >>

This is also a problem that depends on fuel type as well. But I agree current Tokamak schemes using D+D and D+T have this problem. D+He3, D+Li6 and H+B11 don't have this problem - ie. no protons or neutrons are generated by the fusion. (D=deuterium, T=tritium, Li6=Lithium-6, B11=Boron-11, He3=Helium-3)
 
Because of Avagadro's number we can find the number of H molecules. know that 1 gram of H multiplied by 1 mole of H per 2.016g of H (remember that H is a diatomic) is equal to two moles for all practical purposes. Then the number of moles of H multiplied by Avagadro's number (6.02x10^23) tells us that we have somewhere in the neighborhood of 1.204x10^25 molecule of hydrogen.😀
 
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