6 ms·

It does seem like fusion research based on tokamak or stellerator designs will yield usable power first.

kersplody 4y ago
And even then, we are decades away from a commercial design due to the large number of engineering challenges needing to be solved. The next major milestone is getting a plasma gain of > 5, where helium-4 interactions become the dominant source of heating and dramatically change the behavior of the plasma. This has been simulated but never experimentally archived. Hopefully ITER will achieve this by 2030. Keep in mind that continuous operation with a Q plasma gain of at least 75 will be required for a commercially viable reactor. ITER will be lucky to hit 15 with upgrades through 2040.
- ncmncm 4y ago
  In other words, there will be no commercial design, ever.
  - binbag 4y ago
    No, that is not the right conclusion.
    - ncmncm 4y ago
      Except, it is. Fusion would necessarily be a lot more expensive than fission. But fission is itself not competitive, and gets less so with each passing day. So, the longer it takes before fusion is actually, technically possible, the less value there is in it.
      - crubier 4y ago
        Why do you think that Fusion would necessarily be a lot more expensive than fission? I don’t see any reason to believe this long term
        simiones 4y ago
        Fusion reactors are more complex in every possible way than fission reactors because of the sheer temperature differentials (super cool magnets next to hot neutron blanket). Plus, they have much more parasitic power loss (running the superconducting magnets and cooling them to keep them superconducting, plus keeping the vaccum in the reactor chamber all require massive power, and they scale with the size of the reactor). You need some extra power to produce hydrogen through electrolysis as well, though that is probably lower. Note that making the magnets stronger to keep the vessel lower (so that everything is more easily cooled) will not get you much more, since we are already nearing the limits of material resistance for the supporting steel structures in the presence of the extreme magnetic forces trying to crush the reactor together - especially given embrittlement. Not to mention, you will always need at least a small fission reactor to breed some tritium, since the fusion reactor will always have some losses. Finally, the much much higher neutron flux that fusion expels (32x or more neutrons, and much higher energy per neutron as well) means that everything close to the reactor becomes brittle in 2-4 years. This means that things like support beams and the magnets themselves need to be constantly replaced. Even worse, they become medium level radioactive waste, which needs to be stored. These are all intrinsic limitations of fusion that fission reactors just don't have.
        binbag 4y ago
        Nice collection of very selective points. To respond to just a few: So if something is complex we shouldn't or can't build it? OK. I hope you aren't an engineer. Energy is needed to perform electrolysis to create hydrogen. What about the energy needed to mine uranium? I think it might require quite a lot of effort, particularly once supplies get harder to reach and extract. The parts get radioactive and need maintenance and storage. The radioactivity is much more short term than fission. Fission fuel needs stored away from all life for 100,000 years. It will be a miracle if we manage to achieve that. I think small scale modular fission is a good option, but your arguements against fusion aren't good.
        ncmncm 4y ago
        The person you are criticizing clearly understands the issues far better than you do. You should read up a bit, instead of just making shit up. https://lvenneri.com/blog/ConFusion https://lvenneri.com/blog/ConFusion
brudgers 4y ago
When I first read that tokamaks were a promising idea, Brezhnev was still alive.
- actually_a_dog 4y ago
  Nuclear fusion has been 30 years away for like 50 years now.
  - Linosaurus 4y ago
    I thought it was always 20 years away, but it seems both have been common.
  - brudgers 4y ago
    When Dad told me the "fusion is always been twenty years away" joke, Brezhnev was still alive then, too.
- binbag 4y ago
  So what? It's been a good idea for a hundred years. That doesn't mean it's simple to engineer in practice, but nor does it mean it's a poor idea that can't be achieved.
  - brudgers 4y ago
    That's holds for transmutation, too. And it has a thousand years of history.
- Trouble_007 4y ago
  Tokamak : https://en.m.wikipedia.org/wiki/Tokamak https://en.m.wikipedia.org/wiki/Tokamak ITER : https://www.iter.org https://www.iter.org

And even then, we are decades away from a commercial design due to the large number of engineering challenges needing to be solved. The next major milestone is getting a plasma gain of > 5, where helium-4 interactions become the dominant source of heating and dramatically change the behavior of the plasma. This has been simulated but never experimentally archived. Hopefully ITER will achieve this by 2030. Keep in mind that continuous operation with a Q plasma gain of at least 75 will be required for a commercially viable reactor. ITER will be lucky to hit 15 with upgrades through 2040.

ncmncm 4y ago
In other words, there will be no commercial design, ever.
- binbag 4y ago
  No, that is not the right conclusion.
  - ncmncm 4y ago
    Except, it is. Fusion would necessarily be a lot more expensive than fission. But fission is itself not competitive, and gets less so with each passing day. So, the longer it takes before fusion is actually, technically possible, the less value there is in it.
    - crubier 4y ago
      Why do you think that Fusion would necessarily be a lot more expensive than fission? I don’t see any reason to believe this long term
      - simiones 4y ago
        Fusion reactors are more complex in every possible way than fission reactors because of the sheer temperature differentials (super cool magnets next to hot neutron blanket). Plus, they have much more parasitic power loss (running the superconducting magnets and cooling them to keep them superconducting, plus keeping the vaccum in the reactor chamber all require massive power, and they scale with the size of the reactor). You need some extra power to produce hydrogen through electrolysis as well, though that is probably lower. Note that making the magnets stronger to keep the vessel lower (so that everything is more easily cooled) will not get you much more, since we are already nearing the limits of material resistance for the supporting steel structures in the presence of the extreme magnetic forces trying to crush the reactor together - especially given embrittlement. Not to mention, you will always need at least a small fission reactor to breed some tritium, since the fusion reactor will always have some losses. Finally, the much much higher neutron flux that fusion expels (32x or more neutrons, and much higher energy per neutron as well) means that everything close to the reactor becomes brittle in 2-4 years. This means that things like support beams and the magnets themselves need to be constantly replaced. Even worse, they become medium level radioactive waste, which needs to be stored. These are all intrinsic limitations of fusion that fission reactors just don't have.
        binbag 4y ago
        Nice collection of very selective points. To respond to just a few: So if something is complex we shouldn't or can't build it? OK. I hope you aren't an engineer. Energy is needed to perform electrolysis to create hydrogen. What about the energy needed to mine uranium? I think it might require quite a lot of effort, particularly once supplies get harder to reach and extract. The parts get radioactive and need maintenance and storage. The radioactivity is much more short term than fission. Fission fuel needs stored away from all life for 100,000 years. It will be a miracle if we manage to achieve that. I think small scale modular fission is a good option, but your arguements against fusion aren't good.
        ncmncm 4y ago
        The person you are criticizing clearly understands the issues far better than you do. You should read up a bit, instead of just making shit up. https://lvenneri.com/blog/ConFusion https://lvenneri.com/blog/ConFusion

brudgers 4y ago

When I first read that tokamaks were a promising idea, Brezhnev was still alive.

actually_a_dog 4y ago
Nuclear fusion has been 30 years away for like 50 years now.
- Linosaurus 4y ago
  I thought it was always 20 years away, but it seems both have been common.
- brudgers 4y ago
  When Dad told me the "fusion is always been twenty years away" joke, Brezhnev was still alive then, too.
binbag 4y ago
So what? It's been a good idea for a hundred years. That doesn't mean it's simple to engineer in practice, but nor does it mean it's a poor idea that can't be achieved.
- brudgers 4y ago
  That's holds for transmutation, too. And it has a thousand years of history.
Trouble_007 4y ago
Tokamak : https://en.m.wikipedia.org/wiki/Tokamak https://en.m.wikipedia.org/wiki/Tokamak ITER : https://www.iter.org https://www.iter.org