4 ms·

Speaking of solar it would be nice if we could just plate the inside of a reactor with photoelectrics instead of blowing all the budget on a clusterfuck of a st

Speaking of solar it would be nice if we could just plate the inside of a reactor with photoelectrics instead of blowing all the budget on a clusterfuck of a steam system. Too bad silicon doesn't like 100M degrees... Actually thinking about it figuring that out would make fission a lot more tenable too

u320 4y ago
Fusion produces neutrons, not photons.
- DFHippie 4y ago
  I'm pretty sure it produces both.
- fy20 4y ago
  Is there an equivalent of the photoelectric effect for neutrons?
  - ncmncm 4y ago
    None. Hot neutrons are the lowest-grade sort of energy.
    - blincoln 4y ago
      Maybe a dumb question, but could one use bricks of depleted fission fuel as the neutron shield in a fusion reactor, and swap them back into a fission reactor every time they become fuel-grade again?
      - ncmncm 4y ago
        It would be an overwhelmingly smarter and better use of money to burn uranium in an ordinary fission plant, and maybe breed up extra fuel there. But we already know that fission, too, is uncompetitive, moreso each day as costs for renewables and storage continue relentlessly downward. Fusion has no chance of ever catching up.
        blincoln 4y ago
        Sorry, maybe I was unclear. I wasn't asking about using the fusion reactor just to produce fission fuel. I was asking "if the fusion reactor produces a bunch of extra neutrons as a side effect, is this a way to use them to produce more energy later instead of throwing away that energy, or letting the neutrons actively damage the fusion reactor?" i.e. one needs to prevent the neutrons from escaping or degrading the material the reactor is made out of, so instead of just adding a throwaway shielding layer, would it work to use something that is not only super dense, but is currently a waste product[1], and also becomes more valuable in the process of being used as the shield? Seems like it would be vaguely equivalent to a photoelectric collector for neutrons, but I am not a physicist or reactor engineer. [1] I do think it's a shame that we stopped building breeder reactors, but that's a separate discussion.
        ncmncm 4y ago
        Breeder reactors are not used because refining the bred fuel costs more than processing mined uranium. The overarching requirement on fusion neutron absorption material, besides delivery of heat to process steam, is that it needs to produce more tritium to burn. You don't get that if the neutrons are absorbed in something other than lithium.
- scarmig 4y ago
  Fusion covers a lot of different types of processes, some of which release most of their energy in charged particles and photons. Though you'd need something very different from existing photovoltaics to capture the energy from those x-rays.
  - ncmncm 4y ago
    The fusion they are working on emits hot neutrons. It will never produce so much as one kWh of commercial power.
- ben_w 4y ago
  Anything hot produces photons, and a working reactor would necessarily produce a lot of heat. These photons can’t usefully be converted directly into electricity with the photoelectric effect, but they sure could be converted indirectly via the same mechanism that the fusion in the core of the sun is reduced to the band that current PV runs at. Not sure if it’s worth doing that (may well be such a diffuser would be so large it would be easier to do something completely different), but that’s very different thing to your dismissal.
MobiusHorizons 4y ago
Are you honestly suggesting that we place photovoltaics (which perform worse when they get hot, and can only absorb a narrow spectrum of the energy emitted by the reactor) inside a fusion reactor instead of using a very well understood and efficient heat -> electricity technology (steam)? I'm pretty certain they would just simply melt at the temperatures that a tokamak is subjected to, even if there weren't other issues with efficiency.
- lightedman 4y ago
  This is nothing more than an engineering challenge, looking at it seriously. Cooling? an IR barrier in the reactor to stop IR from reaching the cells should solve about 80% of the issue - assuming you can make something transparent at the right wavelengths for the cells - and capable of withstanding the heat of the reactor. The other 20% is already doable with current technology, and we do it from large-scale solar farms to single-family homes - water tubing on the backs of the devices to a radiator or storage tank. Hell, while using them to harvest light energy, that water loop can be used to harvest heat energy, thus improving the overall system efficiency!
  - ben_w 4y ago
    IR as in infrared? Nonono, at 100 million kelvin, if I’ve done the maths right, a blackbody spectrum peaks somewhere around the x-ray band, and about one part in a trillion of the energy is in the IR band or lower.

u320 4y ago

Fusion produces neutrons, not photons.

DFHippie 4y ago
I'm pretty sure it produces both.
fy20 4y ago
Is there an equivalent of the photoelectric effect for neutrons?
- ncmncm 4y ago
  None. Hot neutrons are the lowest-grade sort of energy.
  - blincoln 4y ago
    Maybe a dumb question, but could one use bricks of depleted fission fuel as the neutron shield in a fusion reactor, and swap them back into a fission reactor every time they become fuel-grade again?
    - ncmncm 4y ago
      It would be an overwhelmingly smarter and better use of money to burn uranium in an ordinary fission plant, and maybe breed up extra fuel there. But we already know that fission, too, is uncompetitive, moreso each day as costs for renewables and storage continue relentlessly downward. Fusion has no chance of ever catching up.
      - blincoln 4y ago
        Sorry, maybe I was unclear. I wasn't asking about using the fusion reactor just to produce fission fuel. I was asking "if the fusion reactor produces a bunch of extra neutrons as a side effect, is this a way to use them to produce more energy later instead of throwing away that energy, or letting the neutrons actively damage the fusion reactor?" i.e. one needs to prevent the neutrons from escaping or degrading the material the reactor is made out of, so instead of just adding a throwaway shielding layer, would it work to use something that is not only super dense, but is currently a waste product[1], and also becomes more valuable in the process of being used as the shield? Seems like it would be vaguely equivalent to a photoelectric collector for neutrons, but I am not a physicist or reactor engineer. [1] I do think it's a shame that we stopped building breeder reactors, but that's a separate discussion.
        ncmncm 4y ago
        Breeder reactors are not used because refining the bred fuel costs more than processing mined uranium. The overarching requirement on fusion neutron absorption material, besides delivery of heat to process steam, is that it needs to produce more tritium to burn. You don't get that if the neutrons are absorbed in something other than lithium.
scarmig 4y ago
Fusion covers a lot of different types of processes, some of which release most of their energy in charged particles and photons. Though you'd need something very different from existing photovoltaics to capture the energy from those x-rays.
- ncmncm 4y ago
  The fusion they are working on emits hot neutrons. It will never produce so much as one kWh of commercial power.
ben_w 4y ago
Anything hot produces photons, and a working reactor would necessarily produce a lot of heat. These photons can’t usefully be converted directly into electricity with the photoelectric effect, but they sure could be converted indirectly via the same mechanism that the fusion in the core of the sun is reduced to the band that current PV runs at. Not sure if it’s worth doing that (may well be such a diffuser would be so large it would be easier to do something completely different), but that’s very different thing to your dismissal.

MobiusHorizons 4y ago

Are you honestly suggesting that we place photovoltaics (which perform worse when they get hot, and can only absorb a narrow spectrum of the energy emitted by the reactor) inside a fusion reactor instead of using a very well understood and efficient heat -> electricity technology (steam)? I'm pretty certain they would just simply melt at the temperatures that a tokamak is subjected to, even if there weren't other issues with efficiency.

lightedman 4y ago
This is nothing more than an engineering challenge, looking at it seriously. Cooling? an IR barrier in the reactor to stop IR from reaching the cells should solve about 80% of the issue - assuming you can make something transparent at the right wavelengths for the cells - and capable of withstanding the heat of the reactor. The other 20% is already doable with current technology, and we do it from large-scale solar farms to single-family homes - water tubing on the backs of the devices to a radiator or storage tank. Hell, while using them to harvest light energy, that water loop can be used to harvest heat energy, thus improving the overall system efficiency!
- ben_w 4y ago
  IR as in infrared? Nonono, at 100 million kelvin, if I’ve done the maths right, a blackbody spectrum peaks somewhere around the x-ray band, and about one part in a trillion of the energy is in the IR band or lower.