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I have no idea if nuclear fusion is feasible in the near future, or what kind of timeline is required, but I don't see any downside to spending money on project

I have no idea if nuclear fusion is feasible in the near future, or what kind of timeline is required, but I don't see any downside to spending money on projects like this. Pure scientific pursuits seem to be fund able at relatively low prices, with massive upsides and no obvious downsides, other than the opportunity cost of the money being spent.

pfdietz 8y ago
Fusion absolutely will not be feasible in the near future. We don't even have the materials that would be needed to build them. In any other field of engineering, lack of materials is a showstopper, and new material development is always painful and slow. And if you examine any of the designs with a skeptical eye none of them seem promising, and all involve lots of handwaving.
- dwaltrip 8y ago
  You are saying that ITER will fail?
  - pfdietz 8y ago
    ITER cannot lead to an economically competitive reactor, even if it achieves every one of its stated operational goals. It's a massive dead end waste of money.
    - dwaltrip 8y ago
      Although I happen to disagree, that is a different, more reasonable critique than your original comment.
      - pfdietz 8y ago
        My original comment is entirely reasonable. Fusion faces generic obstacles that are likely unsolvable, and certainly unsolvable in the near term. Consider the problem of tritium breeding. Fusion reactors have to make their own tritium -- T from fission reactors would be far too expensive -- but tritium breeding blankets cannot be tested without a working fusion reactor. And the requirements for the breeding blankets are seriously constraining. They must achieve some neutron multiplication (from (n,2n) reactions of energetic fusion neutrons) to offset losses, not lose too many neutrons to penetrates/parasitic capture, and be able to give up the produced tritium fairly quickly. And there are very strict limits on how much tritium can be lost to permeation into reactor materials (or lost from the reactor exhaust, since ~99% of the injected tritium doesn't fuse). No one knows how to do this, or if it can be done economically, or even if it can be done at all. And I repeat: testing it is going to require a working fusion reactor! This circular dependency in development will be painful to run around, and won't happen quickly. Then there's the matter of materials that can withstand prolonged exposure to fusion neutrons. These materials have not been developed, in part because this again requires something close to a working fusion reactor (at least, something with Q at least ~0.1), and much painful rebuilding as that reactor, built with less adequate materials, destroys itself over time. This material development will not be fast, so we will not have working, practicl fusion reactors soon. Even when all that is solved, the fundamental problem of fusion -- low volumetric power density -- remains. That alone seems insurmountable. When you see a fusion reactor design, ask what this power density is. For ITER, it's 0.05 MW/m^3. For ARC or Lockheed's design, it's around 0.5 MW/m^3. These are very bad compared to fission reactors. A final point: the complexity of the irradiated part of a fusion reactor (the part that's too radioactive for hands-on maintenance) will be MUCH higher than that of the similar part of a fission reactor. Reliability is going to be an enormous problem. Making fusion reactors reliable enough for them to be practically interesting, even if all other problems were solved, will take much experience and time.
robertAngst 8y ago
>I don't see any downside to spending money on projects like this. Would you rather spend billions of dollars on unproven energy solutions OR anti-cancer research for poor children? Ask questions like this, resources need to be allocated. Although, given the US government, probably spent on the military.
gregw2 8y ago
The downside is that the public will spend 10s of billions only for some billionaire "startup" to hire away the physics expertise and the public ends up paying a monopolistic/oligopolistic premium. Now theres nothing new about that.. but when talking about throwing tons of public money at something it's important to control the terms on which the public money is spent and who absorbs the risks/rewards.

pfdietz 8y ago

Fusion absolutely will not be feasible in the near future. We don't even have the materials that would be needed to build them. In any other field of engineering, lack of materials is a showstopper, and new material development is always painful and slow. And if you examine any of the designs with a skeptical eye none of them seem promising, and all involve lots of handwaving.

dwaltrip 8y ago
You are saying that ITER will fail?
- pfdietz 8y ago
  ITER cannot lead to an economically competitive reactor, even if it achieves every one of its stated operational goals. It's a massive dead end waste of money.
  - dwaltrip 8y ago
    Although I happen to disagree, that is a different, more reasonable critique than your original comment.
    - pfdietz 8y ago
      My original comment is entirely reasonable. Fusion faces generic obstacles that are likely unsolvable, and certainly unsolvable in the near term. Consider the problem of tritium breeding. Fusion reactors have to make their own tritium -- T from fission reactors would be far too expensive -- but tritium breeding blankets cannot be tested without a working fusion reactor. And the requirements for the breeding blankets are seriously constraining. They must achieve some neutron multiplication (from (n,2n) reactions of energetic fusion neutrons) to offset losses, not lose too many neutrons to penetrates/parasitic capture, and be able to give up the produced tritium fairly quickly. And there are very strict limits on how much tritium can be lost to permeation into reactor materials (or lost from the reactor exhaust, since ~99% of the injected tritium doesn't fuse). No one knows how to do this, or if it can be done economically, or even if it can be done at all. And I repeat: testing it is going to require a working fusion reactor! This circular dependency in development will be painful to run around, and won't happen quickly. Then there's the matter of materials that can withstand prolonged exposure to fusion neutrons. These materials have not been developed, in part because this again requires something close to a working fusion reactor (at least, something with Q at least ~0.1), and much painful rebuilding as that reactor, built with less adequate materials, destroys itself over time. This material development will not be fast, so we will not have working, practicl fusion reactors soon. Even when all that is solved, the fundamental problem of fusion -- low volumetric power density -- remains. That alone seems insurmountable. When you see a fusion reactor design, ask what this power density is. For ITER, it's 0.05 MW/m^3. For ARC or Lockheed's design, it's around 0.5 MW/m^3. These are very bad compared to fission reactors. A final point: the complexity of the irradiated part of a fusion reactor (the part that's too radioactive for hands-on maintenance) will be MUCH higher than that of the similar part of a fission reactor. Reliability is going to be an enormous problem. Making fusion reactors reliable enough for them to be practically interesting, even if all other problems were solved, will take much experience and time.

robertAngst 8y ago

>I don't see any downside to spending money on projects like this. Would you rather spend billions of dollars on unproven energy solutions OR anti-cancer research for poor children? Ask questions like this, resources need to be allocated. Although, given the US government, probably spent on the military.

gregw2 8y ago

The downside is that the public will spend 10s of billions only for some billionaire "startup" to hire away the physics expertise and the public ends up paying a monopolistic/oligopolistic premium. Now theres nothing new about that.. but when talking about throwing tons of public money at something it's important to control the terms on which the public money is spent and who absorbs the risks/rewards.