Paul,paulhunn said:I have managed to find out that waste products from fusion reactions are far less dangerous than those from traditional fission reactions but i cannot find anywhere that states what the waste products actually are. Can somone please tell me what the waste products from a deuterium and a tritium reaction are?
darkar,darkar said:How much Helium will be produce by fusion process in fusion power generator (assuming they are operational)? Will it be a lot?
Astronuc said:... In this sense, fusion does produce waste products in the form of irradiated (and activated) structural materials, which ultimately have to be disposed in some appropriate facility.
...
Not to mention Z(B) = 5, which means fairly high brehmstrahlung losses for a given plasma temperature, and high electron pressures if one tries to fully ionize B, and also recombination and cyclotron rad losses. P-B11 would be great, but for the limitations.mheslep said:Allow me to qualify for benefit of the OP: There are 'aneutronic' reactions, or reactions that do not produce any neutrons; the energy is released instead by alpha particles which can be captured by electromagnetic fields and in general are much less of radiation hazard. Examples include proton + Boron 11. Note that ITER type Tokamaks are not capable of burning these fuels because they require higher reaction energies, hence the reason one doesn't here much discussion of aneutronic fuels. Example ~110keV for P-11B vs ~15KeV for D-T.
Helium is a noble gas. How can it be an asphyxiant? If you breathe it, it just makes you talk funny. CO2, on the other hand, in sufficient concentration (eg. 5%) will interfere chemically with hemoglobin transport of oxygen in the blood. I don't see how Helium can do this. If you breathe nothing but He for long enough, of course, you will die from lack of oxygen.darkar said:How much Helium will be produce by fusion process in fusion power generator (assuming they are operational)? Will it be a lot? Because this might lead to increase concentration in atmosphere after a lot of year of running like CO2. High concentration of helium can be dangerous because helium is a simple asphyxiant(http://en.wikipedia.org/wiki/Asphyxiant) .
What to do with those Helium after they are collected?
Related:
http://en.wikipedia.org/wiki/Helium#Precautions
Andrew,Andrew Mason said:How can it be an asphyxiant? ...
If you breathe nothing but He for long enough, of course, you will die from lack of oxygen.
Astronuc said:Not to mention Z(B) = 5, which means fairly high brehmstrahlung losses for a given plasma temperature, and high electron pressures if one tries to fully ionize B, and also recombination and cyclotron rad losses. P-B11 would be great, but for the limitations.
Another aneutronic reaction D-He3 still has other issues, such as there is still the D-D reaction which does produce He3+n in 50% of reactions and T+p in the other half. T+D would still lead to [tex]\alpha[/tex] + n.
sunday,sunday said:I found this forum looking for info on plasma physics, info that I need to understand a little the works of a IEC fusor of the Bussard type, i.e. a Polywell*. I think that Bussard claims that the Bremsstrahlung losses in the core of the polywell are very low, as the high electron density make the electron cloud (Wiffle Ball) in the center of the device to behave as a diamagnetic medium, and expelling the magnetic field used to create the virtual cathode. As I have formal education on nuke physics and technology, but not on high-energy nor plasma physics, I don't know if that claim is reasonable.
Morbius said:Paul,
We can't really say that right now.
First, the deuterium - tritium or D-T reaction that you are referring to is:
1D2 + 1T3 --> 2He4 + 0n1 + 17.6 MeV
That is deuterium + tritium --> Helium-4 + a neutron + energy.
The direct "waste products" are Helium-4 and the neutron. The Helium-4 is
nothing to be concerned about - it's ordinary stable Helium.
What is of concern is that 14.1 MeV neutron - or more specifically - what
that 14.1 MeV neutron hits. That's where the "waste" of a fusion reactor
is going to come from - the radioactivity induced by the neutron that comes
out ot the reaction. Since the designs aren't finalized - we're still trying to get
the reaction to work - we don't know what will be used to stop that neutron.
So unlike fission - where the waste products are the direct result of the reaction,
in fusion, the waste products are an indirect result of the reaction - so we can't
really say what they will be with 100% certainty as of yet.
Dr. Gregory Greenman
Physicist
ensabah6,ensabah6 said:Could radioactive nuclear waste absorb these neutrons, becoming less radioactive or perhaps even be used as fuel?
Morbius said:You answered your own question. You don't need a chemical reaction to have an
asphyxiant. If the gas just displaces enough oxygen; it will asphyxiate you.
Helium is lighter than air, but would only get to rise to the top of the atmosphere if enough were contained in a balloon or something to displace more than its weight in atmosphere. Released straight into the air, it seems to simply mix with it.Futhermore, helium released to the atmosphere escapes very quickly into space.
GTrax said:Helium is lighter than air, but would only get to rise to the top of the atmosphere if enough were contained in a balloon or something to displace more than its weight in atmosphere. Released straight into the air, it seems to simply mix with it.
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I guess atmospheric gases are lost into space, but I don't think we will run out anytime soon.
mheslep said:Allow me to qualify for benefit of the OP: There are 'aneutronic' reactions, or reactions that do not produce any neutrons; the energy is released instead by alpha particles which can be captured by electromagnetic fields and in general are much less of radiation hazard. Examples include proton + Boron 11.
The p+p->D cross section is extremely low relative to p+11B so we get less than 0.1% residuals, which practically does away w/ the activated first wall problem in D+T, D+D fusion.signerror said:This is not entirely achievable because the components will also react in unwanted, neutronic reactions. For instance, in p+11B, you have p+p->D+e+v and D(n,y)T, hence D+T fusion on the side.
Edit: it seems other side reactions are more important
http://en.wikipedia.org/wiki/Aneutronic_fusion#Residual_radiation_from_a_p.E2.80.9311B_reactor
This may be a dumb question but why would one let the 14.1 MeV neutron be absorbed by a heavy nucleus and create useless/dangerous radioactive elements? Why not surround the reactor with a moderator of light or heavy water the to absorb the 14.1 MeV neutron energy and produce heat and then eventually capture the slowed neutron (to produce deuterium or tritium which can then be used for more fusion)? It should be a zero sum - for each neutron produced from a D-T reaction you can produce another D or T nucleus which can then be fed into the fusion reactor.Astronuc said:From the fusion reaction itself, there are no 'waste' products, in the sense that the products can be used. He (helium) can be collected and the neutrons provide energy in whatever they absorbed.
D + T -> n (14.1 MeV) + He4 (3.5 MeV).
The 14.1 MeV neutrons irradiate the surrounding structure, and when the neutron is ultimately absorbed, the absorbing nuclide generally becomes radioactive In this sense, fusion does produce waste products in the form of irradiated (and activated) structural materials, which ultimately have to be disposed in some appropriate facility.
Two reasons:Andrew Mason said:This may be a dumb question but why would one let the 14.1 MeV neutron be absorbed by a heavy nucleus and create useless/dangerous radioactive elements? Why not surround the reactor with a moderator of light or heavy water the to absorb the 14.1 MeV neutron energy and produce heat and then eventually capture the slowed neutron (to produce deuterium or tritium which can then be used for more fusion)? It should be a zero sum - for each neutron produced from a D-T reaction you can produce another D or T nucleus which can then be fed into the fusion reactor.
AM
That's pretty much it. There needs to be a 'first wall' or structural vessel that encases the plasma, which operates in a vacuum. Water (or similar fluid) would simply evaporate in the vacuum and quench the plasma. And the first wall materials will eventually become activated.mheslep said:Two reasons:
1. Some kind of higher Z wall is required to hold the water/ or whatever.
2. The neutrons must be used to breed tritium to maintain the fuel cycle (as you suggest). Current plan is do this with a lithium blanket behind the wall. I had thought fast neutrons were needed for that, but I don't know.
I can see lithium working because the nuclear mass is low, so it has a moderating effect - converting neutron energy into heat. That was my point. You don't want nuclei that will absorb the fast neutrons. You want to have material inside the first wall that will convert neutron energy to heat.Astronuc said:That's pretty much it. There needs to be a 'first wall' or structural vessel that encases the plasma, which operates in a vacuum. Water (or similar fluid) would simply evaporate in the vacuum and quench the plasma. And the first wall materials will eventually become activated.
Stainless steels are affected by (n,p), (n,α) and the p's and α's accumulate interstially, although H forms metal hydrides. The other effect is clusters of dislocations, which can be annealed out. Ni-58 can undergo an (n,p) reaction which produces Co-58, or Ni-58 absorbs the n, and produces Ni-59 which decays to Co-59, which can absorb a neutron and become Co-60.
There has been a big research project at ORNL on first wall materials, which also has relevancy to traditional steel pressure vessels and core structures of LWRs and fast reactors.
Lithium could actually flow inside the first wall, but that's tricky. The issue is the n(6Li,α)T and the effect of the α on the plasma, which is why it would be necessary to confine it outside the first wall. There's also the issue of confining T, and recovering it. Li-7 can be used as a coolant since it has a lower cross-section for n-absorption.
An aneutronic reaction e.g. d+3He would be ideal, but it's problematic given the cost and low abundance of 3He.
Andrew,Andrew Mason said:I can see lithium working because the nuclear mass is low, so it has a moderating effect - converting neutron energy into heat. That was my point. You don't want nuclei that will absorb the fast neutrons. You want to have material inside the first wall that will convert neutron energy to heat.
There are two possible results from a neutron interaction with a nucleus, either it scatters or it is absorbed. The vast majority of high energy neutrons will scatter, and in doing so, the neutron loses some energy and goes on to his other nuclei. Now the nuclei that get struck are displaced in the metal crystals, and that is the radiation damage that embrittles a metal. We refer to displacements per atom (dpa) as a measure of irradiation damage in a metal, and it is this measurement which is correlated with mechanical behavior and degradation of mechanical properties of metal, particular low temperature embrittlement. The neutron and gamma radiation will certainly heat the first wall, and that is one reason that the material must have high temperature strength and melting point. One deleterious effect of irradiation damage is spalling in which the first wall flakes and falls into the plasma chamber. The objective is to use materials which do not spall.Andrew Mason said:I can see lithium working because the nuclear mass is low, so it has a moderating effect - converting neutron energy into heat. That was my point. You don't want nuclei that will absorb the fast neutrons. You want to have material inside the first wall that will convert neutron energy to heat.
AM
Quite right. But I was thinking more of the efficiency. Neutrons bouncing off heavy nuclei would not impart much energy per collision so one would need many more collisions to absorb that energy - ie. a much thicker wall of heavy nuclei would be needed in order to convert the neutron energy into heat. Perhaps one could put a thick shield of depleted uranium around the core to absorb the fast neutrons - at least then the neutron capture could produce useable plutonium fuel for a fission reactor. But I expect that the DU would not withstand the high temperature.Morbius said:Andrew,
If you absorb the neutron - you are going to get the heat energy. Where else would the energy of the neutron go?
You have a fast moving neutron, and it is absorbed by a nucleus - so now you have just a new compound nucleus. Where did the momentum and kinetic energy of the neutron go?
It has to go to that compound nucleus. The nucleus is going to originally get that energy; and if you have a solid; the new compound nucleus is constrained from moving too far by its neighbors; so the kinetic energy of the nucleus will diffuse to the neighbors, which are also constrained by their neighbors, so the energy diffuses - and all the atoms now have a bit more energy.
That's heat. It's not just light nuclei that give you heat.
The major selling points of fusion over fission include nearly eliminating radioactive waste and little or no weapons proliferation risk. Take that away and as I understand the issue there's little to recommend fusion over fission at all until all the U and Th deplete in, what, 500 years?Andrew Mason said:...Perhaps one could put a thick shield of depleted uranium around the core to absorb the fast neutrons - at least then the neutron capture could produce useable plutonium fuel for a fission reactor. But I expect that the DU would not withstand the high temperature.
AM
At current rates of extraction we have about 30 years supply in known reserves so we probably will have 40-50 years supply before serious shortages occur. That is, unless we start reprocessing fuel - then we have probably 10000 years supply.mheslep said:... until all the U and Th deplete in, what, 500 years?
Andrew,Andrew Mason said:Quite right. But I was thinking more of the efficiency. Neutrons bouncing off heavy nuclei would not impart much energy per collision so one would need many more collisions to absorb that energy
Andrew,Andrew Mason said:Perhaps one could put a thick shield of depleted uranium around the core to absorb the fast neutrons - at least then the neutron capture could produce useable plutonium fuel for a fission reactor.
mheslep,mheslep said:The major selling points of fusion over fission include nearly eliminating radioactive waste and little or no weapons proliferation risk.
IIRC in comparison to spent fuel rods D-T fusion waste from high Z first wall materials is still low rad, short half life material.Morbius said:mheslep,
Actually, if a nation wants to develop nuclear weapons; they can use neutrons from a fusion reactor
to make plutonium every bit as effectively as with a fission reactor.
It is a MYTH that fusion is inherently more proliferation resistant, or waste resistant than fission.
That myth comes from people that look at the byproducts of a fusion reaction and see, for example;
a He-4 and a neutron. They stop thinking right there and say - Helium-4 and neutrons are not long
lived waste nor useful for weapons - therefore fusion is waste-resistant and proliferation-resistant.
However, if you think one more step; whatever that neutron hits will most likely be activated and hence
constitute a radioactive material that needs to be dealt with.
An argument for more aneutronic fusion research? IRC that was Lidsky's argument in the 'The Trouble with Fusion'.Additionally, that neutron can be used to
breed plutonium and hence can be used for nuclear weapons proliferation.
Dr. Gregory Greenman
Physicist
mheslep,mheslep said:I
I don't agree the two, fission and fusion, are equivalent in proliferation risk. Granted one can make Pu by inserting U into a neutron producing fusion reactor (though the practicality is not clear to me). The point is practical weapons production regardless of the process still requires U up front. Fusion power completely eliminates the need for U; thus a country attempting to acquire U is unmistakably stating "I am making a weapon" and can be dealt with accordingly.