What is the Most Efficient Fuel for Fusion Reactors: T-D, D-D, or D+He-3?

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Discussion Overview

The discussion centers around the efficiency of different fuel types for fusion reactors, specifically comparing tritium-deuterium (T-D), deuterium-deuterium (D-D), and deuterium-helium-3 (D+He-3) fusion. Participants explore energy output, temperature requirements, and potential reactions associated with each fuel type.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants inquire whether T-D or D-D fusion releases more energy, considering the higher temperature requirements for D-D fusion.
  • One participant asserts that deuterium-tritium fusion produces significantly more energy compared to other fusion types.
  • Another participant provides detailed calculations showing that D-D fusion can yield a total energy output of approximately 14.4 MeV when considering subsequent reactions involving tritium and helium-3, although this is contingent on the availability of tritium.
  • It is noted that D+He-3 fusion requires even higher temperatures for effective reactions compared to D-D fusion.
  • Some participants suggest that if tritium is not needed, the neutrons produced in D-D fusion could be utilized for other exothermic reactions, including potential fusion-fission hybrids.

Areas of Agreement / Disagreement

Participants express differing views on the energy efficiency of T-D versus D-D fusion, with no consensus reached on which is definitively more efficient. The discussion remains unresolved regarding the optimal fuel choice for fusion reactors.

Contextual Notes

Participants mention various assumptions regarding the availability of tritium and the complexities of fusion reactions, which may affect the calculations and conclusions drawn.

Basil Currie
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Hi,
Does a T-D or a D-D fusion release more energy? Even if D-D needs higher temperatures, would it produce more energy in a fusion reactor?
 
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In one way the deuterium tritium fusion generates 17.6MeV
D+T=2He4+n +17.6MeV

In the other way the D+D fusion is more complex:
D+D->T+p +4.03MeV (a 50% of the reactions)
D+D->He3+n +3.27MeV (a 50% of the reactions)
But tritium fuses very quickly with deuterons as cross section is much larger than D+D fusion and D+T generates 17.6MeV as said before
Also happens with the Helium-3 that fuses again more easily with deuterons giving 18.3MeV, so if the reactor fuses also helium-3 at the end you should have:
D+D+D->He4+n+p+ (4.03+17.6)*50%
D+D+D->n+p+He4+ (3.27+18.3)*50%
So:
D+D+D->He+n+p+21.6MeV

So D+D =2/3*21.6MeV=14.4MeV that is less than 17.6MeV.
But that is not the exact account as long as Tritium does not exists so it is generated using the generated neutron again lithium target to generate tritium releasing more energy that I did not took in account
 
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D+He-3 needs even higher temperatures for a relevant cross section than D+D.
If you don't need tritium as fuel you can use the neutrons for some exothermic reactions - even fission has been proposed (fusion-fission hybrid).
 

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