And DT fusion neutrons are even worse than fission neutrons, since they are much more energetic (and because only 3% of the energy in a fission reactor is released in neutrons.) The 14 MeV DT neutrons are above the threshold for (n,p) and (n,alpha) reactions, which cause gas to accumulate in reactor materials. The helium produced by (n,alpha) reactions accumulates in tiny bubbles that would reach extreme pressures and rip materials apart.
