4 ms·

Nuclear fusion as an energy source has major unsolved problems. Off the top of my head: * The super conducting metals required for confinement randomly stop

by ryao 1y ago

Nuclear fusion as an energy source has major unsolved problems. Off the top of my head: * The super conducting metals required for confinement randomly stop superconducting. * The fuels produce absurd amounts of radiation and the Helium-3 solution for that might as well be fairy dust, since even if we convert the energy global economy to helium-3 production, we will not have enough by orders of magnitude to power hypothetical fusion reactors that would handle our needs. Strip mining the moon for it is supposedly a way to get it, but defacing the surface of the moon for minuscule amounts of Helium-3 per acre is unlikely to ever be profitable. * The amount of radioactive materials produced from the experiments are many times those produced in fission reactors. This is just off the top of my head. Until recently, I would have included the inability to produce more energy than we put into it on this list, but LLNL’s breakthrough a few years ago seems to have solved that. I suspect that someone with time to look into the practical issues involved in building a fusion reactor would find other issues (such as the design not being practical to use in a production power plant and thus further research being needed to make one that is). I wonder if the only reason countries fund nuclear fusion research is to keep nuclear scientists from finding employment in the production of nuclear weapons.

physix 1y ago
I'd love to see some references on those three claims. None of them make sense to me.
- ryao 1y ago
  There is a very well researched youtube video that explains a couple of these things: https://www.youtube.com/watch?v=FrUWoywZRt8 https://www.youtube.com/watch?v=FrUWoywZRt8 I do not recall where I heard about the helium-3 situation, but I recall hearing some figures and the prospect of having enough to run fusion reactors was not good. Doing a search suggests that I had been only slightly mislead about the scarcity of helium-3. It is still extremely rare, but the US reportedly has used up to 70,000 liters of it per year: https://en.wikipedia.org/wiki/Helium-3#Human_production https://en.wikipedia.org/wiki/Helium-3#Human_production The density of Helium-3 at STP is presumably 0.1338 g/L, based on Helium-4's 0.1784 g/L. That suggests that the total annual US industrial demand is ~9 kg. This is definitely not as bad as I had thought, but it is still fairly dire. As per wikipedia, a single 1GW nuclear fusion reactor that is 100% efficient at converting helium-3 into electricity would need 52.5 kilograms per year. 6.7 metric tons per year would be needed to power the entire US. https://en.wikipedia.org/wiki/Helium-3 https://en.wikipedia.org/wiki/Helium-3 That assumes 100% efficiency, and if the conversion efficiency is anything like a nuclear fission plant, we would be lucky to see 3% efficiency, but we could be optimistic and assume something higher. Either way, it does not change the conclusion. With an annual supply of ~9 kg, practical helium-3 fueled nuclear fusion reactors are not happening. Maybe the supply would be higher if you include other countries, and maybe we could get it somewhat higher if we try, but the reality is that helium-3 is an extremely rare isotope and the idea of using it as a practical fuel for a nuclear fusion reactor is a pipe dream unless the supply problem is solved and people figure out how to actually build a reactor that generates power using it, without encountering any of the other known problems that make this unlikely. The difficulty in scaling supply is why are people discussing wild ideas like mining the moon, or even mining Jupiter. The supply situation is so constrained that the US government is reportedly buying 3 liters of it from a company that promises that it will strip-mine the surface of the moon for it with delivery by April 2029: https://www.morningstar.com/news/pr-newswire/20250507sf81778/us-department-of-energy-buys-helium-3-from-us-space-resources-company-interlune-in-historic-agreement https://www.morningstar.com/news/pr-newswire/20250507sf81778... I fully expect them to fail to deliver. That said, the fairy dust remark was probably inaccurate, but the idea that our supply is short by orders of magnitude is correct according to mathematics.
fallingknife 1y ago
> The super conducting metals required for confinement randomly stop superconducting. Yeah, that doesn't happen > The amount of radioactive materials produced from the experiments are many times those produced in fission reactors. And neither does this
- ryao 1y ago
  Fermilab would disagree with you on the quenching problem: https://lss.fnal.gov/archive/2023/slides/fermilab-slides-23-088-td.pdf https://lss.fnal.gov/archive/2023/slides/fermilab-slides-23-... As for the amount of radioactive material, the experimental reactors are several times the size of fission reactors. It is obvious that they irradiate far more material. There is a very well researched youtube video that goes over these things: https://www.youtube.com/watch?v=FrUWoywZRt8 https://www.youtube.com/watch?v=FrUWoywZRt8
  - fallingknife 1y ago
    Quenching isn't random. The waste has a half life of 10 years. You can use an idiotic unit like total mass of material without taking into account level of radioactivity or half life, but that's not even worth discussing.
    - ryao 1y ago
      "Quenching isn't random" is a big change from "it doesn't happen". Quenching is random for all intents and purpose, which is why test fusion reactors have systems in place to try to detect and respond to it before very bad things happen. If they knew when it would happen, they would not need such detectors. As for the waste, you are still going to have to pay per unit to clean it up, just like you would with waste from a nuclear fission reactor. You have far more of it since the volume being irradiated is far higher. Although it is by volume rather than by weight, a decomissioned MH-1A PWR power plant produced 89 m^3 of solid radioactive waste and 363 m^3 of liquid waste: https://world-nuclear.org/information-library/nuclear-fuel-cycle/nuclear-waste/decommissioning-nuclear-facilities https://world-nuclear.org/information-library/nuclear-fuel-c... The youtube video stated that the cleanup effort for the Joint European Torus was projected to produce 3000m^3 of waste, and the ITER reactor would be 10 times its size. Neither of them produced or will produce useful energy, yet they produced / will produce orders of magnitude more waste when it is time to decommission them than a decommissioned fission reactor did. It also does not matter if the half lives are lower. It is still not going to be safe to be around that stuff long after both of us are dead and buried. The costs are effectively the same, since they will both be disposed in the same way.

by ryao 1y ago

physix 1y ago

I'd love to see some references on those three claims. None of them make sense to me.

ryao 1y ago
There is a very well researched youtube video that explains a couple of these things: https://www.youtube.com/watch?v=FrUWoywZRt8 https://www.youtube.com/watch?v=FrUWoywZRt8 I do not recall where I heard about the helium-3 situation, but I recall hearing some figures and the prospect of having enough to run fusion reactors was not good. Doing a search suggests that I had been only slightly mislead about the scarcity of helium-3. It is still extremely rare, but the US reportedly has used up to 70,000 liters of it per year: https://en.wikipedia.org/wiki/Helium-3#Human_production https://en.wikipedia.org/wiki/Helium-3#Human_production The density of Helium-3 at STP is presumably 0.1338 g/L, based on Helium-4's 0.1784 g/L. That suggests that the total annual US industrial demand is ~9 kg. This is definitely not as bad as I had thought, but it is still fairly dire. As per wikipedia, a single 1GW nuclear fusion reactor that is 100% efficient at converting helium-3 into electricity would need 52.5 kilograms per year. 6.7 metric tons per year would be needed to power the entire US. https://en.wikipedia.org/wiki/Helium-3 https://en.wikipedia.org/wiki/Helium-3 That assumes 100% efficiency, and if the conversion efficiency is anything like a nuclear fission plant, we would be lucky to see 3% efficiency, but we could be optimistic and assume something higher. Either way, it does not change the conclusion. With an annual supply of ~9 kg, practical helium-3 fueled nuclear fusion reactors are not happening. Maybe the supply would be higher if you include other countries, and maybe we could get it somewhat higher if we try, but the reality is that helium-3 is an extremely rare isotope and the idea of using it as a practical fuel for a nuclear fusion reactor is a pipe dream unless the supply problem is solved and people figure out how to actually build a reactor that generates power using it, without encountering any of the other known problems that make this unlikely. The difficulty in scaling supply is why are people discussing wild ideas like mining the moon, or even mining Jupiter. The supply situation is so constrained that the US government is reportedly buying 3 liters of it from a company that promises that it will strip-mine the surface of the moon for it with delivery by April 2029: https://www.morningstar.com/news/pr-newswire/20250507sf81778/us-department-of-energy-buys-helium-3-from-us-space-resources-company-interlune-in-historic-agreement https://www.morningstar.com/news/pr-newswire/20250507sf81778... I fully expect them to fail to deliver. That said, the fairy dust remark was probably inaccurate, but the idea that our supply is short by orders of magnitude is correct according to mathematics.

fallingknife 1y ago

> The super conducting metals required for confinement randomly stop superconducting. Yeah, that doesn't happen > The amount of radioactive materials produced from the experiments are many times those produced in fission reactors. And neither does this

ryao 1y ago
Fermilab would disagree with you on the quenching problem: https://lss.fnal.gov/archive/2023/slides/fermilab-slides-23-088-td.pdf https://lss.fnal.gov/archive/2023/slides/fermilab-slides-23-... As for the amount of radioactive material, the experimental reactors are several times the size of fission reactors. It is obvious that they irradiate far more material. There is a very well researched youtube video that goes over these things: https://www.youtube.com/watch?v=FrUWoywZRt8 https://www.youtube.com/watch?v=FrUWoywZRt8
- fallingknife 1y ago
  Quenching isn't random. The waste has a half life of 10 years. You can use an idiotic unit like total mass of material without taking into account level of radioactivity or half life, but that's not even worth discussing.
  - ryao 1y ago
    "Quenching isn't random" is a big change from "it doesn't happen". Quenching is random for all intents and purpose, which is why test fusion reactors have systems in place to try to detect and respond to it before very bad things happen. If they knew when it would happen, they would not need such detectors. As for the waste, you are still going to have to pay per unit to clean it up, just like you would with waste from a nuclear fission reactor. You have far more of it since the volume being irradiated is far higher. Although it is by volume rather than by weight, a decomissioned MH-1A PWR power plant produced 89 m^3 of solid radioactive waste and 363 m^3 of liquid waste: https://world-nuclear.org/information-library/nuclear-fuel-cycle/nuclear-waste/decommissioning-nuclear-facilities https://world-nuclear.org/information-library/nuclear-fuel-c... The youtube video stated that the cleanup effort for the Joint European Torus was projected to produce 3000m^3 of waste, and the ITER reactor would be 10 times its size. Neither of them produced or will produce useful energy, yet they produced / will produce orders of magnitude more waste when it is time to decommission them than a decommissioned fission reactor did. It also does not matter if the half lives are lower. It is still not going to be safe to be around that stuff long after both of us are dead and buried. The costs are effectively the same, since they will both be disposed in the same way.