What is the Maximum Achievable Tritium Breeding Rate for a Fusion Engine?

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Discussion Overview

The discussion revolves around the maximum achievable tritium breeding rate for a fusion engine, focusing on the use of Lithium isotopes and neutron multipliers such as lead and beryllium. Participants explore theoretical limits, practical challenges, and the implications of neutron energy on breeding efficiency.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests that only 4% of emitted neutrons at 14 MeV can be utilized for breeding tritium, raising the question of the maximum achievable breeding rate with Lithium-7 and Lithium-6.
  • Another participant mentions theoretical figures for tritium breeding rates, citing a maximum of close to 2, with ITER achieving around 1.6 using beryllium, while a figure of 6 is mentioned but considered hard to believe.
  • Concerns are raised about neutron multiplication being limited due to safety considerations, as unlimited multiplication could lead to nuclear weapon capabilities.
  • A participant notes that achieving high breeding ratios may involve complex reactions, including (n, 2n) and (n, 3n) reactions, which have high energy thresholds and require careful consideration of neutron absorption processes.
  • Discussion includes the potential for combined fusion/fission reactors, though this introduces complications related to radioactive waste management.

Areas of Agreement / Disagreement

Participants express varying opinions on the theoretical limits of tritium breeding rates, with no consensus on the validity of the higher figures mentioned. The discussion remains unresolved regarding the feasibility of achieving these rates and the implications of neutron energy on the breeding process.

Contextual Notes

Participants highlight the need for detailed cross-sectional data and simulations to accurately assess breeding rates. The discussion acknowledges the complexity of neutron interactions and the limitations imposed by energy thresholds and material consumption.

Sebastiaan
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Let say we need to maximize the amount of breeded Tritium next to a fusion engine, but we got only access of 4% of the emitted neutrons at 14 MeV. What would be the maximum achievable tritium breeding rate, using Lithium7, Lithium 6, and any neutron Neutron multipliers like lead and beryllium.
 
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Well I'm trying to figure out what is the theoretical maximum amount of tritium that can be bred. I heard some figures about close to 2, ITER doesn't seem to be able to get higher than 1.6 using Berylium. Another source entirely I heard the figure 6, but this sounds hard to believe.

Either Lead or Berelium is used to increase the amount of neutrons, but the resulting neutron are of lower energy, meaning meutron multiplication is very limited.
 
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That is complicated. You need the cross sections for all relevant processes at all relevant energies, and then some simulation. Neutron multiplication is always limited - otherwise you would have a nuclear weapon. Driving a subcritical fission reactor (multiplication of ~20) with an external neutron source is a concept under study (mainly to burn away transactinides), but that is not a fusion reactor any more. Combined fusion/fission reactors are also a concept, but then you have the radioactive waste issue again.
 
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mfb said:
Neutron multiplication is always limited - otherwise you would have a nuclear weapon.
LOL
 
Sebastiaan said:
Another source entirely I heard the figure 6, but this sounds hard to believe.

what is that figure?
 
ChrisVer said:
what is that figure?
I believe Sebastiaan is referring to a breeding ratio, i.e., for one T consumed, one would obtain 6 T, ostensibly from some spallation reactions with neutrons of an initial energy of 14 MeV. There are a number of (n, 2n) reactions and possibly (n,3n) reactions, but they have high energy thresholds. Then each neutron has to be absorbed in something that produces an (n, t) reaction. Alternatively, if one can use some (n, n't) or (n, n'nt) reactions, it might be feasible, but that might require an exotic blanket.

Also, one has to keep in mind the level of consumption. How much of a blanket will be consumed to produce X kg (or moles) of T.
 

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