3 ms·

Fusion still has to deal with waste, just not high-level waste. Through the process of neutron activation all of the parts exposed to neutrons eventually become

Fusion still has to deal with waste, just not high-level waste. Through the process of neutron activation all of the parts exposed to neutrons eventually become radioactive enough to be treated as low-level waste. In a reactor large enough to produce energy for the grid these parts could be very large (and expensive) to deal with (not to mention replace).

bbojan 5y ago
https://en.wikipedia.org/wiki/Aneutronic_fusion https://en.wikipedia.org/wiki/Aneutronic_fusion
- EarlKing 5y ago
  ...is even further from breakeven than deuterium+tritium fusion.
- tux3 5y ago
  Yes, though the article consists almost entirely of reasons why aneutronic fusion is really hard ("the conditions required to harness aneutronic fusion are much more extreme than those required for deuterium-tritium fusion being investigated in ITER"). Note that the "Candidate fuels" section is not part of "Technical Challenges", but it might as well be. Helium-3, by far the easiest, is vanishingly rare. Deuterium would not really be aneutronic. Then further down is a list of worse and worse headaches. The leading scenario for acquiring the most convenient fuel candidate is "mining it on the moon". (The alternative scenario being to scale up production of tritium by existing heavy-water reactors from the nuclear weapons program, which decays into helium-3... and defeats the point of researching extremely complex, clean, aneutronic fusion reactors) I want to like aneutronic fusion, but it takes an objective that is several breakthroughs away and plays the game on nightmare mode.
- pfdietz 5y ago
  Anything beyond D-3He or D-D is likely impossible. And any fuel with deuterium will still make enough neutrons to render the reactor inaccessible to hands-on maintenance. So there will still be a waste problem (as well as a huge reliability and maintenance problem). The reactor might not AS MUCH radioactivity, but much of the cost of dealing with it will scale with the mass of the contaminated material, not its activity. And fusion reactors will be very large. The cost of dealing with the activated material might end up higher than the cost of dealing with spent fission reactor fuel.
wrp 5y ago
The main parts of a commercial tokamak would be huge. I read once that due to thermal stresses, replacement might be needed annually. I seem to recall that the STARFIRE project[1] estimated nearly 60 tons of low-grade radioactive waste per year of the operational lifetime. [1] https://www.sciencedirect.com/science/article/abs/pii/0029549381900443 https://www.sciencedirect.com/science/article/abs/pii/002954...
- labawi 5y ago
  Power plant waste: 60T/y for 1200 MWe = 50g / kWe·y = 1.6 mg/MJ Coal energy density: 24 MJ/kg = 0.024 MJ/g -> 42 g/MJ Not perfect, but depending on what the waste is, doesn't seem too bad.
  - chongli 5y ago
    Coal is absolutely the worst so it may not be a fair comparison. How would fusion compare to renewables like solar or wind?

bbojan 5y ago

https://en.wikipedia.org/wiki/Aneutronic_fusion https://en.wikipedia.org/wiki/Aneutronic_fusion

EarlKing 5y ago
...is even further from breakeven than deuterium+tritium fusion.
tux3 5y ago
Yes, though the article consists almost entirely of reasons why aneutronic fusion is really hard ("the conditions required to harness aneutronic fusion are much more extreme than those required for deuterium-tritium fusion being investigated in ITER"). Note that the "Candidate fuels" section is not part of "Technical Challenges", but it might as well be. Helium-3, by far the easiest, is vanishingly rare. Deuterium would not really be aneutronic. Then further down is a list of worse and worse headaches. The leading scenario for acquiring the most convenient fuel candidate is "mining it on the moon". (The alternative scenario being to scale up production of tritium by existing heavy-water reactors from the nuclear weapons program, which decays into helium-3... and defeats the point of researching extremely complex, clean, aneutronic fusion reactors) I want to like aneutronic fusion, but it takes an objective that is several breakthroughs away and plays the game on nightmare mode.
pfdietz 5y ago
Anything beyond D-3He or D-D is likely impossible. And any fuel with deuterium will still make enough neutrons to render the reactor inaccessible to hands-on maintenance. So there will still be a waste problem (as well as a huge reliability and maintenance problem). The reactor might not AS MUCH radioactivity, but much of the cost of dealing with it will scale with the mass of the contaminated material, not its activity. And fusion reactors will be very large. The cost of dealing with the activated material might end up higher than the cost of dealing with spent fission reactor fuel.

wrp 5y ago

The main parts of a commercial tokamak would be huge. I read once that due to thermal stresses, replacement might be needed annually. I seem to recall that the STARFIRE project[1] estimated nearly 60 tons of low-grade radioactive waste per year of the operational lifetime. [1] https://www.sciencedirect.com/science/article/abs/pii/0029549381900443 https://www.sciencedirect.com/science/article/abs/pii/002954...

labawi 5y ago
Power plant waste: 60T/y for 1200 MWe = 50g / kWe·y = 1.6 mg/MJ Coal energy density: 24 MJ/kg = 0.024 MJ/g -> 42 g/MJ Not perfect, but depending on what the waste is, doesn't seem too bad.
- chongli 5y ago
  Coal is absolutely the worst so it may not be a fair comparison. How would fusion compare to renewables like solar or wind?