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I'd believe Lockheed Martin's CFR claims more if they didn't say things like this: > Energy created through fusion is 3-4 times more powerful than the energy r

by grkvlt 7y ago

I'd believe Lockheed Martin's CFR claims more if they didn't say things like this: > Energy created through fusion is 3-4 times more powerful than the energy released by fission.[0] Which is just confus(ed/ing) on a fundamental level... More Powerful energy? So each Joule from fusion is actually 3-4 times better than each Joule from fission, in some way? I really can't work out what they are trying to say here. 0. https://www.lockheedmartin.com/en-us/products/compact-fusion.html https://www.lockheedmartin.com/en-us/products/compact-fusion...

mikeash 7y ago
I think they’re saying that a single fusion event produces 3-4x more energy than a single fission event.
- wutbrodo 7y ago
  Do you mean a single _fusion_ event?
  - mikeash 7y ago
    Yes, thanks. Brain no function beer well without.
- grkvlt 7y ago
  But even that is pretty vague, since a single Uranium atom fission event releases about 200 MeV of energy, whereas most of the Hydrogen/Deuterium/Tritium/Helium/etc. fusion pathways release around 10% of this per fusion event: D + T -> He fusion gives 17 MeV, 4 p -> He gives 27 MeV, D + D -> He is 12 MeV and so on. Now, the energy released per nucleon greater for fusion, but I'm not convinced that's a useful or intuitive metric?
  - mikeash 7y ago
    How about energy per kilogram?
    - grkvlt 7y ago
      OK, so 235 kg of U_235 has the same number of fissile units (N atoms = 1000 x N_a) as 5 kg of D-T has of fusible units (2N atoms of combined weight 5 amu, or 1000 x N_a pairs) so (ignoring the N_a for now) one kg of U_235 gives 200 MeV / 235 = 0.85 MeV and the D-T fusion gives 17 MeV / 5 = 3.40 MeV So, yeah, that's exactly four times the energy per kilogram. Now, why couldn't they just say THAT on the web page instead of the confusing and meaningless "this energy is 3-4 times more powerful than that energy" nonsense? But, thanks 'mikeash for clearing that up for me!

by grkvlt 7y ago

mikeash 7y ago

I think they’re saying that a single fusion event produces 3-4x more energy than a single fission event.

wutbrodo 7y ago
Do you mean a single _fusion_ event?
- mikeash 7y ago
  Yes, thanks. Brain no function beer well without.
grkvlt 7y ago
But even that is pretty vague, since a single Uranium atom fission event releases about 200 MeV of energy, whereas most of the Hydrogen/Deuterium/Tritium/Helium/etc. fusion pathways release around 10% of this per fusion event: D + T -> He fusion gives 17 MeV, 4 p -> He gives 27 MeV, D + D -> He is 12 MeV and so on. Now, the energy released per nucleon greater for fusion, but I'm not convinced that's a useful or intuitive metric?
- mikeash 7y ago
  How about energy per kilogram?
  - grkvlt 7y ago
    OK, so 235 kg of U_235 has the same number of fissile units (N atoms = 1000 x N_a) as 5 kg of D-T has of fusible units (2N atoms of combined weight 5 amu, or 1000 x N_a pairs) so (ignoring the N_a for now) one kg of U_235 gives 200 MeV / 235 = 0.85 MeV and the D-T fusion gives 17 MeV / 5 = 3.40 MeV So, yeah, that's exactly four times the energy per kilogram. Now, why couldn't they just say THAT on the web page instead of the confusing and meaningless "this energy is 3-4 times more powerful than that energy" nonsense? But, thanks 'mikeash for clearing that up for me!