>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 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?
Germany's new stellarator, Wendelstein 7-X: http://www.sciencedirect.com/science/article/pii/S0022311504...
[1] http://www.sciencedirect.com/science/article/pii/S0920379697...
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.
http://en.wikipedia.org/wiki/Plasma-facing_material
http://en.wikipedia.org/wiki/International_Fusion_Materials_...