4 ms·

No, that is not the right conclusion.

by binbag 4y ago

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
      - simiones 4y ago
        > So if something is complex we shouldn't or can't build it? We were discussing why fusion plants are necessarily more expensive than fission plants - not whether they can (or even should) in principle be built. > 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. I listed many other energy costs - including some uranium to breed tritium. > The radioactivity is much more short term than fission. Sure, but that still means decades for tritium and centuries for the neutron-bombarded materials - more than enough to make it as big of a problem in our lifetimes per kg, just with many more kg of waste from fusion.
      - pfdietz 4y ago
        He didn't list the worst part (for DT): the volumetric power density of the reactors will suck compared to fission reactors. So not only will the reactors be much more complex than fission reactors, they will also be far larger. How can this possibly be a cheaper source of heat? Fusion's going to have to go with advanced fuels to have a chance. For that and various related reasons, I consider Helion the least dubious of the fusion efforts.

No, that is not the right conclusion.

by binbag 4y ago

No, that is not the right conclusion.

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
    - simiones 4y ago
      > So if something is complex we shouldn't or can't build it? We were discussing why fusion plants are necessarily more expensive than fission plants - not whether they can (or even should) in principle be built. > 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. I listed many other energy costs - including some uranium to breed tritium. > The radioactivity is much more short term than fission. Sure, but that still means decades for tritium and centuries for the neutron-bombarded materials - more than enough to make it as big of a problem in our lifetimes per kg, just with many more kg of waste from fusion.
    - pfdietz 4y ago
      He didn't list the worst part (for DT): the volumetric power density of the reactors will suck compared to fission reactors. So not only will the reactors be much more complex than fission reactors, they will also be far larger. How can this possibly be a cheaper source of heat? Fusion's going to have to go with advanced fuels to have a chance. For that and various related reasons, I consider Helion the least dubious of the fusion efforts.