71–80 of 167 posts
>in, … 12.3 years…, half of the tritium available today will have decayed into helium-3. When I saw this, I thought that sounded odd, shouldn’t the atomic number go down with radioactive decay? but it turns out that in this case what happens is one of the neutrons splits into a proton, an electron and an electron neutrino so the atomic number goes up by one (unlike the more familiar fission reactions of the heavier e…
I thought the end game was aneutronic fusion using lithium and deuterium anyway creating only charged particles instead of high energy neutrons that are dangerous and damaging to the reactor. If nuclear fusion ever wants to be commercially viable, it must not depend on tritium.
Earlier quoted context omitted.
It seems like every fusion post is bound to have at least one commenter point out that the sun is a working fusion reactor, as if literally anyone in these threads will learn something from this observation.
Roughly $50 billion has been spent globally on fusion research since the 1950s with nothing material to show for the effort; at what point do you stop throwing good money after bad? This strikes me as the learning from these posts.
Title is extremely misleading. > "Right now, the tritium used in fusion experiments like ITER, and the smaller JET tokamak in the UK, comes from a very specific type of nuclear fission reactor called a heavy-water moderated reactor." You litterally just need to make more of these heavy-water moderated reactors, which are rare and approaching end of life, but certainly you can build more of them if it was the differen…
>in, … 12.3 years…, half of the tritium available today will have decayed into helium-3. When I saw this, I thought that sounded odd, shouldn’t the atomic number go down with radioactive decay? but it turns out that in this case what happens is one of the neutrons splits into a proton, an electron and an electron neutrino so the atomic number goes up by one (unlike the more familiar fission reactions of the heavier e…
For every A (the number of nucleons in a nucleus) there is a ratio between (A-Z) and Z (i.e. between the number of neutrons and the number of protons) for which the mass of the nucleus is minimum.
Any other isobaric nuclei have an excess of mass over the nucleus with the optimal neutron/proton ratio, so they will decay towards it. The nuclei with too many protons will capture electrons or emit positrons, while the nuclei with too many neutrons will emit electrons, increasing the number of protons with each emitted electron, until the optimal neutron/proton ratio.
For the decay products of uranium and thorium, there are always too many neutrons, so the normal beta decay is what always happens.
It is possible to artificially produce nuclei with too many protons, and there are a few such unstable isotopes that are produced naturally, which decay by the reverse beta decay (electron capture or positron emission), where Z decreases by 1 for every captured electron / emitted positron.
For A = 3, the nucleus with minimal mass is helium-3. Tritium has too many neutrons in comparison with helium-3, and it must get rid of them by emitting an electron.
> “It would be an absurdity to use dirty fission reactors to fuel ‘clean’ fusion reactors,” This seems like a non-sequitur. If we need to keep around (or even build) a few heavy-water fission plants to enable the fusion industry, what's the problem? The simple phrasing of fission as "dirty" really shows the quotee's biases. You could easily envision a stable energy mix with a few percent of fission, the rest fusion a…
There's a lot of bad thinking in that one sentence. All or nothing. We must have completely clean power or it has no value. Not using comparison. How does it compare to other sources of energy, (including solar which is built in facilities using coal power).
> “It would be an absurdity to use dirty fission reactors to fuel ‘clean’ fusion reactors,” This seems like a non-sequitur. If we need to keep around (or even build) a few heavy-water fission plants to enable the fusion industry, what's the problem? The simple phrasing of fission as "dirty" really shows the quotee's biases. You could easily envision a stable energy mix with a few percent of fission, the rest fusion a…
There's a lot of bad thinking in that one sentence. All or nothing. We must have completely clean power or it has no value. Not using comparison. How does it compare to other sources of energy, (including solar which is built in facilities using coal power).
In a way, that last (...) is also a very black and white way of viewing things.
Earlier quoted context omitted.
The reaction is supposed to be self-sustaining. The reactor walls are supposed to emit more than enough tritium to satisfy your needs. Whatever you bring from outside is just to bootstrap it once you turn it on. (I imagine they are not collecting the tritium between runs, but it's something you are expected to do.)
> The reactor walls are supposed to emit more than enough tritium to satisfy your needs. Didn't know that fusion generators produced its own fuel! If it produces more than enough, then the excess tritium is considered radioactive waste?
The energy of the neutrons is transformed into heat by adsorbing them into some shielding walls. The materials for those walls will be chosen to minimize the quantity of radioactive waste that is produced by the extremely intense neutron irradiation, but it is impossible to avoid completely the production of radioactive waste.
So all the fusion generators planned for the near future will generate radioactive waste, but in significantly less quantities than fission reactors of the same power.
Because they produce an intense neutron flux, like the fission reactors, the fusion reactors can also be used for element transmutation by neutron capture, e.g. for producing tritium or for producing lightly-doped silicon crystals for the high-voltage electronic devices (by transmuting silicon into phosphorus).
However, such transmutation applications usually also need the use of a neutron moderator, to slow the neutrons down to whatever speed is optimal for producing the desired isotope, e.g. tritium. For tritium, heavy water can play both roles, of the neutron moderator and of the target containing the element to be transmuted.
> “It would be an absurdity to use dirty fission reactors to fuel ‘clean’ fusion reactors,” This seems like a non-sequitur. If we need to keep around (or even build) a few heavy-water fission plants to enable the fusion industry, what's the problem? The simple phrasing of fission as "dirty" really shows the quotee's biases. You could easily envision a stable energy mix with a few percent of fission, the rest fusion a…
It's actually tilted very far in the opposite direction. The ratio is something like 600:1 heavy-water fission to fusion. A mix of 99.8% fission and 0.2% fusion, if your fusion is relying on that as its sole source of tritium.
- "Small quantities of tritium are also produced by CANDU-type nuclear reactors—on the order of 100 grams per year for a 600 MW reactor,"
You'd need 60 kg/year for a 600 MW D+T fusion reactor.
I'd love if it fusion became commercially viable but I'm doubtful it ever will. At the least the kind involving fusion atoms in a plasma for all the documented reasons, most notably plasma turbulence and the power loss and container damage from neutron escapes.
I'm not that concerned about a shortage of tritium. That's a solvable problem. In fact we probably need a variety of breeder reactors for things like this and producing plutonium for deep space probes anyway.
Fusion is a trap for many because it seems so easy. I mean the Sun is doing a lot of it. But the Sun is relatively inefficient (which is compensated for by mass) and it solves the containment problem with gravity.