6 ms·

I'm not sure about the scale here, but is it really as crazy as the article says to use tritium that is formed from fission? What's the ratio of fusion:fission

I'm not sure about the scale here, but is it really as crazy as the article says to use tritium that is formed from fission? What's the ratio of fusion:fission energy you'd need? I can't imagine even if it was 50% or 25% that it wouldn't be worth doing seeing as you'd just be fuelling a clean energy source from the waste stream of another energy source that doesn't produce CO2.

marcosdumay 4y ago
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.)
- ASalazarMX 4y ago
  > 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?
  - fallingknife 4y ago
    Not really an issue though, as tritium has a half life of 12 years, and the amounts produced would be negligible anyway. You could probably release it into the atmosphere harmlessly (not that regulations would ever allow that, though).
  - adrian_b 4y ago
    The kinds of fusion generators that are considered for the near future produce most of their energy as kinetic energy of neutrons. 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.
    - ncmncm 4y ago
      You could absorb neutron flux in a thousand tons of molten 6Li/7Li, and then try to separate grams of tritium from that thousand tons of molten, extremely inflammable metal, on a continuous basis. Good luck with that. Renewables do not incur such operating expenses. Put renewables and a fusion reactor on the grid, and fusion would never, ever win a bid. "Fusion .. will generate ... less ... than fission"? The whole damn ten-thousand-ton reactor becomes radioactive waste in short order. Fortunately, none will be built, so it is only a theoretical problem.
      - ASalazarMX 4y ago
        I dug more about this because it's an interesting topic. Basically we don't know how long a fusion generator will last before radioactivity forces its decommissioning because none exist yet, but fortunately it's short-life isotopes, about 50-120 years before they become safe. Orders of magnitude better than fission waste. I don't know about fusion vs renewables, because renewables are better, but they need a lot of non-renewables to be manufactured. If a fusion reactor lasted 100 years, it would be a much better option than renewables.
        ncmncm 4y ago
        The reactor would need to be replaced frequently as the chamber walls and molten-lithium pipes weaken from neutron bombardment, every two years, maybe as long as five. By the time they could build one, there might be some way to make it last ten? It needs even bigger containment than a regular nuke because reactive molten lithium bursts into flame on contact with air. The oxidized product is an exploding cloud of vaporized radioactive drain cleaner. A thousand tons of lithium make a lot of drain cleaner. And again, by that time all our power will be cheaply supplied by renewables with no disastrous failure modes, and maintained just by taking bits down and putting up new bits, in shirtsleeves when weather favors it.
        marcosdumay 4y ago
        > Basically we don't know how long a fusion generator will last before radioactivity forces its decommissioning That was one of the main questions the ITER was supposed to answer, wasn't it? AFAIK earlier designs were quite short-lived, but some small changes fixed it. We will know how long they last as soon as we don't have an ITER anymore.
- jszymborski 4y ago
  Wait, so then at _whatever_ cost, the cost of producing Tritium is sorta moot, right? Whether it's building reactors or investing a tonne of energy, the cost of creating the amount of tritium needed is met with theoretically infinite profits?
  - ncmncm 4y ago
    There will never be any marketable fusion power at all, never mind "infinite". Power from Tokamaks necessarily costs at least 10x power from fission, and fission is already not competitive, and gets less so each year.
    - john567 4y ago
      ??? Fission is incredible profitable. It's the only source of reliable electricity we have (with a negligible CO2 impact). The only reason fission isn't more profitable is politics. Politics are making investment and research into fission needlessly costly.
      - ncmncm 4y ago
        You just go on telling yourself that. The rest of the world will do what it does.
        john567 4y ago
        !?!? Lulz. Okay.
      - pfdietz 4y ago
        Fission is grossly uncompetitive. That's why there's never been a single merchant fission power plant built anywhere in the world.
        john567 4y ago
        What county are we talking about here?
perihelions 4y ago
In my sibling comment, I calculate 600:1 fission:fusion, for the heavy water reactors they're talking about. (I think it could be somewhat better if it were a fission reactor optimized for tritium, but I don't know the numbers for that. I think that would entail fast-neutron reactors with enriched ⁶Li blankets -- analagous to what the fusion reactors are planning to do).

marcosdumay 4y ago

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.)

ASalazarMX 4y ago
> 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?
- fallingknife 4y ago
  Not really an issue though, as tritium has a half life of 12 years, and the amounts produced would be negligible anyway. You could probably release it into the atmosphere harmlessly (not that regulations would ever allow that, though).
- adrian_b 4y ago
  The kinds of fusion generators that are considered for the near future produce most of their energy as kinetic energy of neutrons. 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.
  - ncmncm 4y ago
    You could absorb neutron flux in a thousand tons of molten 6Li/7Li, and then try to separate grams of tritium from that thousand tons of molten, extremely inflammable metal, on a continuous basis. Good luck with that. Renewables do not incur such operating expenses. Put renewables and a fusion reactor on the grid, and fusion would never, ever win a bid. "Fusion .. will generate ... less ... than fission"? The whole damn ten-thousand-ton reactor becomes radioactive waste in short order. Fortunately, none will be built, so it is only a theoretical problem.
    - ASalazarMX 4y ago
      I dug more about this because it's an interesting topic. Basically we don't know how long a fusion generator will last before radioactivity forces its decommissioning because none exist yet, but fortunately it's short-life isotopes, about 50-120 years before they become safe. Orders of magnitude better than fission waste. I don't know about fusion vs renewables, because renewables are better, but they need a lot of non-renewables to be manufactured. If a fusion reactor lasted 100 years, it would be a much better option than renewables.
      - ncmncm 4y ago
        The reactor would need to be replaced frequently as the chamber walls and molten-lithium pipes weaken from neutron bombardment, every two years, maybe as long as five. By the time they could build one, there might be some way to make it last ten? It needs even bigger containment than a regular nuke because reactive molten lithium bursts into flame on contact with air. The oxidized product is an exploding cloud of vaporized radioactive drain cleaner. A thousand tons of lithium make a lot of drain cleaner. And again, by that time all our power will be cheaply supplied by renewables with no disastrous failure modes, and maintained just by taking bits down and putting up new bits, in shirtsleeves when weather favors it.
      - marcosdumay 4y ago
        > Basically we don't know how long a fusion generator will last before radioactivity forces its decommissioning That was one of the main questions the ITER was supposed to answer, wasn't it? AFAIK earlier designs were quite short-lived, but some small changes fixed it. We will know how long they last as soon as we don't have an ITER anymore.
jszymborski 4y ago
Wait, so then at _whatever_ cost, the cost of producing Tritium is sorta moot, right? Whether it's building reactors or investing a tonne of energy, the cost of creating the amount of tritium needed is met with theoretically infinite profits?
- ncmncm 4y ago
  There will never be any marketable fusion power at all, never mind "infinite". Power from Tokamaks necessarily costs at least 10x power from fission, and fission is already not competitive, and gets less so each year.
  - john567 4y ago
    ??? Fission is incredible profitable. It's the only source of reliable electricity we have (with a negligible CO2 impact). The only reason fission isn't more profitable is politics. Politics are making investment and research into fission needlessly costly.
    - ncmncm 4y ago
      You just go on telling yourself that. The rest of the world will do what it does.
      - john567 4y ago
        !?!? Lulz. Okay.
    - pfdietz 4y ago
      Fission is grossly uncompetitive. That's why there's never been a single merchant fission power plant built anywhere in the world.
      - john567 4y ago
        What county are we talking about here?

perihelions 4y ago

In my sibling comment, I calculate 600:1 fission:fusion, for the heavy water reactors they're talking about. (I think it could be somewhat better if it were a fission reactor optimized for tritium, but I don't know the numbers for that. I think that would entail fast-neutron reactors with enriched ⁶Li blankets -- analagous to what the fusion reactors are planning to do).