Helium-3 is a whole 'nother kettle of fish. Deuterium/Tritium is a lot easier to fuse and is what pretty much everybody working on the problem is looking at. If, later, we were able to get get helium-3/deuterium fusion working that would be great because then there wouldn't be any neutrons created reducing the already modest fusion nuclear waste problem to zero. But that's still a ways off.
Well, the gamma rays produced by fusion can still photo-desintegrate various elements which in turn leads to secondary neutron radiation and unstable isotopes. I don't know what the cross sections of those interactions are but it's not quite zero.
As I understand it, if you have conditions that allow deuterium-helium3 fusion you will always get some deuterium-deuterium fusion. So the number of neutrons produced is way less than D-T or pure D-D fusion, but it is still a significant problem.
Agreed about He3, but it's not just D/T; there's at least a bit of money going onto p/B11, as a way of sidestepping the problems of neutron embrittlement. I think TAE is working on it?
