3 ms·

Could someone break down the costs of realistic fusion for me like I am 12 please? For example, for fission, my 12 year old understanding is: Stack uranium pla

Could someone break down the costs of realistic fusion for me like I am 12 please? For example, for fission, my 12 year old understanding is: Stack uranium plates until the reaction is self-sustaining, boil water to spin turbine, if reaction gets too fast, cover it with lead / cool it with water. Circulated water is slightly radioactive. Main costs are keeping reaction container / need power to circulate water cooling, disposing of spent fuel is a problem. Power output is 100s or 1000s times more effective than coal / oil once running. In addition to meltdown risk, public opinion is concerned about radioactive cooling water near their community. What's the same tldr for fusion? (and feel free to correct my tldr)

Robotbeat 4y ago
Tiny H-bomb except pure fusion, and instead of a fission bomb as the trigger, you have huge lasers. You’d produce energy the same way, with heat being captured by some sort of spherical shield around the tiny bomb (which could also be breeding some of the fusion fuel out of lithium) and used to produce steam to run turbines. This is the first time that the laser’s photon energy was exceeded by the energy produced by fusion. But this machine isn’t optimized as a power plant, just to demonstrate fusion (mostly to improve modeling of H-bombs, actually). The shots take hours to do, the tiny bombs are currently expensive to make, the chamber for the tiny bombs isn’t designed to capture heat, breed fuel, or even withstand damage from higher yield fusion. Another machine would be needed to demonstrate like 10-100 tiny bombs per second, and the efficiency (and repetition rate) of the lasers would need to be higher and the energy gain also needs to be much higher (but if they got “ignition” where the fusion heat helps sustain the reaction, this may be doable). And need to find a way to make these tiny bombs cheaper.
jokteur 4y ago
Realistic fusion (with the best understood technology): build powerful magnets around a donut shaped chamber, which allows to contain a plasma comprised of Deuterium and Tritium (both Hydrogen isotops) which is then heated by externals sources. Reach very high temperatures such that fusion reactions occur frequently. Some of this energy stays inside the plasma, and some of it escapes under the form of neutrons. Capture these energetic neutrons in a blanket around the chamber, creating fuel (tritium) and heating water pipes that then drive a normal steam turbine. Tritium is radioactive (but has a very short shell life; just wait a couple of decades), and the chamber may be slightly radioactive after decades of neutron bombardment. There are no problems of long term radioactive waste, and the reactor can't do a chain-reaction, so no Fukushima or Tchernobyl. I need to explain what Q is in the context of fusion. Basically, you heat the plasma with some energy (Energy In), and the fusion reactions produces some energy (Energy out). Q is basically the ratio (Energy out)/(Energy In). When Q is bigger than 1, we call it break-even. However, (Energy In) is not the actual cost of energy you need to run the whole facility, it is only the Energy that reaches the plasma. The same goes for (Energy out): this energy cannot be captured 100% efficiently. Some of it will heat the plasma itself, some of it will escape but the conversion back to electricity is not 100% efficient. So in a sense, Q > 1, aka break-even, does not mean commercial fusion, it is only a kind of a psychological barrier to achieve (so this is what the NIF announced; still a major breakthrough). We need at least to achieve (Total Electrical Energy out)/(Total Electrical Energy In) > 1 to achieve commercial fusion. But physicists consider the rest as engineering problems, not physics problems. And great news, there is no theoretical limit on how big Q can be: for example, the sun has a Q of infinity, as there is no required energy input. Current estimates put Q at least 30-40 to achieve commercial fusion (again: there is no physical limit to achieve that, only engineering difficulties). Main costs are: difficult to define, because we haven't commercialized a reactor yet. I would say, for now, everything around it is expensive (magnets, the blanket, the fuel (tritium)). However, once we have sufficiently understood the optimal parameters on how to produce net gain energy, there is no reason why the design of the reactor can't then be simplified to be mass-produced. Note: the technology used by the NIF is very different from what I described for a realistic fusion device: what I described is called magnetic confinement, and what the NIF did is called inertial confinement.
- throw1234651234 4y ago
  Thank you, "Current estimates put Q at least 30-40 to achieve commercial fusion (again: there is no physical limit to achieve that, only engineering difficulties)" is exactly what I was looking for.

Robotbeat 4y ago

Tiny H-bomb except pure fusion, and instead of a fission bomb as the trigger, you have huge lasers. You’d produce energy the same way, with heat being captured by some sort of spherical shield around the tiny bomb (which could also be breeding some of the fusion fuel out of lithium) and used to produce steam to run turbines. This is the first time that the laser’s photon energy was exceeded by the energy produced by fusion. But this machine isn’t optimized as a power plant, just to demonstrate fusion (mostly to improve modeling of H-bombs, actually). The shots take hours to do, the tiny bombs are currently expensive to make, the chamber for the tiny bombs isn’t designed to capture heat, breed fuel, or even withstand damage from higher yield fusion. Another machine would be needed to demonstrate like 10-100 tiny bombs per second, and the efficiency (and repetition rate) of the lasers would need to be higher and the energy gain also needs to be much higher (but if they got “ignition” where the fusion heat helps sustain the reaction, this may be doable). And need to find a way to make these tiny bombs cheaper.

jokteur 4y ago

Realistic fusion (with the best understood technology): build powerful magnets around a donut shaped chamber, which allows to contain a plasma comprised of Deuterium and Tritium (both Hydrogen isotops) which is then heated by externals sources. Reach very high temperatures such that fusion reactions occur frequently. Some of this energy stays inside the plasma, and some of it escapes under the form of neutrons. Capture these energetic neutrons in a blanket around the chamber, creating fuel (tritium) and heating water pipes that then drive a normal steam turbine. Tritium is radioactive (but has a very short shell life; just wait a couple of decades), and the chamber may be slightly radioactive after decades of neutron bombardment. There are no problems of long term radioactive waste, and the reactor can't do a chain-reaction, so no Fukushima or Tchernobyl. I need to explain what Q is in the context of fusion. Basically, you heat the plasma with some energy (Energy In), and the fusion reactions produces some energy (Energy out). Q is basically the ratio (Energy out)/(Energy In). When Q is bigger than 1, we call it break-even. However, (Energy In) is not the actual cost of energy you need to run the whole facility, it is only the Energy that reaches the plasma. The same goes for (Energy out): this energy cannot be captured 100% efficiently. Some of it will heat the plasma itself, some of it will escape but the conversion back to electricity is not 100% efficient. So in a sense, Q > 1, aka break-even, does not mean commercial fusion, it is only a kind of a psychological barrier to achieve (so this is what the NIF announced; still a major breakthrough). We need at least to achieve (Total Electrical Energy out)/(Total Electrical Energy In) > 1 to achieve commercial fusion. But physicists consider the rest as engineering problems, not physics problems. And great news, there is no theoretical limit on how big Q can be: for example, the sun has a Q of infinity, as there is no required energy input. Current estimates put Q at least 30-40 to achieve commercial fusion (again: there is no physical limit to achieve that, only engineering difficulties). Main costs are: difficult to define, because we haven't commercialized a reactor yet. I would say, for now, everything around it is expensive (magnets, the blanket, the fuel (tritium)). However, once we have sufficiently understood the optimal parameters on how to produce net gain energy, there is no reason why the design of the reactor can't then be simplified to be mass-produced. Note: the technology used by the NIF is very different from what I described for a realistic fusion device: what I described is called magnetic confinement, and what the NIF did is called inertial confinement.

throw1234651234 4y ago
Thank you, "Current estimates put Q at least 30-40 to achieve commercial fusion (again: there is no physical limit to achieve that, only engineering difficulties)" is exactly what I was looking for.