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I'm just a telecommunications engineer, so my strengths in physics are basically electrodynamics, but recently I have been reading a bit about nuclear physics and nuclear fusion for power production.

I have read that the DT fuel is the best fusion fuel because it has the largest fusion cross section at 5 barns and it is at the lowest energy (65 keV) of any potential fusion fuel. But tritium isn't very common, so an alternative would be useful. Such alternative could be helium-3, because it may be in somewhat considerable quantities in the lunar regolith (statement that I found a bit controversial but after reading a paper on the subject I finally decided in its favor). The problem with using helium-3 in fusion fuels (either 3He-3He or D-3He), as far as I know, is that it requires to heat the plasma even more, while only yielding an energy output assimilable to the DT's, and the same goes for other easier to obtain fuels like D-D (which also chains D-3He and D-T reactions).

I have also found that in fusion reactors it is planned to coat the interior of the reactor with lithium which, through neutron capture, would decay intro tritium, but lithium isn't exactly an abundant element on Earth (although I guess that asteroid mining could help with that).

Getting to the point of the question: Recently I learnt about breeder reactors too. Knowing that 3He may absorb a thermal neutron and break into a proton and tritium (used in neutron detectors), I guessed that maybe thermal breeder reactors could produce tritium from helium-3. I also wonder if they could be used to produce tritium from lithium too. So the question is basically the one in the title, would this work?

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  • $\begingroup$ Hey welcome, as your already guessed is better to just do one question per "question" if you could trim it down to one you'll get better answers faster. $\endgroup$
    – Kuhlambo
    Aug 9, 2022 at 9:32

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I also wonder if they could be used to produce tritium from lithium too.

Yes.

Most of the tritium used in nuclear weapons was produced through the heavy water reaction, where the neutrons from fission would sometimes be captured by the D in the D2O. The cross section is quite small so this is "expensive".

The US operated a fleet of such reactors but shut them down, so now the primary source is the CANDU fleet. Each CANDU makes about 130 g per year. This is sold strictly into the civilian market.

For weapons production, the current method is to infuse normal control rods with lithium-6. The tritium can then be extracted when the reactor is offline for refuelling and the control rods can be removed.

I don't know of anyone that's used the He-3 reaction in this way, but that's likely just because D is so common in comparison, I don't know if there is a physics reason.

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