You can't "breed" 3He; you have to breed tritium, which
decays to He3 with a half-life of 12 years.
Huh, I didn't know that. Helion directly claim they've "developed [a] complete self-supplied 3He fuel cycle", though. How did they manage that? Are they just massaging the truth, by saying that warehousing the tritium exhaust for a decade, then putting the 3He back in the reactor, still counts as a closed fuel cycle?
I imagine you could produce 3He by hitting deuterium with a proton beam, (or doing something exotic with 4He, or 6Li) at incredible cost per litre of produced 3He, but that's not really a "fuel" cycle, since the power reaction isn't involved in any way...
Fusion reactors are generally made from boron carbide
??? Source? I've never seen a vacuum chamber cast from boron carbide, and you certainly can't make magnets out of it, which have to be centimeters away from the reaction, and therefore get irradiated. Are there any running fusion experiments that use internal boron carbide cladding to shield the vacuum chamber walls?
>Helion directly claim they've "developed [a] complete self-supplied 3He fuel cycle", though. How did they manage that?
I have no idea.
The D-3He reaction is: D + 3He >> p + 4He + 18 MeV. The D-D side-reaction is D + D >> n + 3He. Maybe they're recovering 3He from the side-reaction? But D-D is harder to ignite than D-3He.
This would hardly be aneutronic (you'd have one neutron per two nuclear collisions, instead of roughly per 100 with exogenous 3He), but it does provide a way of making 3He. I should stress that I am only guessing.
>Are there any running fusion experiments that use internal boron carbide cladding to shield the vacuum chamber walls?
Actually, ITER uses beryllium[1]. This has the same high cross-section and low propensity to create dangerous radionuclides as B4C, but is expensive and toxic. It is, however, much easier to make things out of, because it is just a metal. Older projects use tungsten, which does create dangerous radionuclides (181W and 185W). I was mostly aware of research re: B4C, but had been ignorant of beryllium.
So I should have said "modern fusion reactors generally use first-wall materials like boron carbide and beryllium, which do not become radioactive when irradiated". In practice, it's not worth holding up experiments on containment to make safe walls (ITER isn't built to last). In any case, the question of irradiated reactor walls is slowly becoming a solved problem.
According to wikipedia D-D is the second easiest reaction behind D-T. Half the reactions produce 3He directly. The other half produce a proton plus tritium, which decays to 3He with a 12-year half-life.
You'll get some D-T from the tritium you produced, but the pulsed reaction probably helps a lot.
"Assuming complete removal of tritium and recycling of 3He, only 6% of the fusion energy is carried by neutrons."
I imagine you could produce 3He by hitting deuterium with a proton beam, (or doing something exotic with 4He, or 6Li) at incredible cost per litre of produced 3He, but that's not really a "fuel" cycle, since the power reaction isn't involved in any way...
??? Source? I've never seen a vacuum chamber cast from boron carbide, and you certainly can't make magnets out of it, which have to be centimeters away from the reaction, and therefore get irradiated. Are there any running fusion experiments that use internal boron carbide cladding to shield the vacuum chamber walls?