[@MetalLover]Well, pure fusion nukes won't leave behind radiation. At least not in the classical sense of things. Typical nukes use nuclear fission which works by splitting the radioactive heavy atoms to smaller elements and the difference in energy is radiated out in the process. The split atoms are generally still radioactive elements and these decay slowly while releasing dangerous radiation at a constant rate.
Theoretically fusion doesn't have this drawback because the resulting element is stable. In effect currently we use fission nuke to produce the conditions for the fusion to occur so it's the same deal. Yet there are alternatives. One of them is to use an array of sufficiently focused and powerful lasers to heat up the fusion material. This method was already tested but unfortunatelly with current technology it's too cumbersome to be a viable alternative (for now). Granted in a setting with railguns we should have the technology to make the laser array far more compact. Another and perhaps more realistic alternative is the antimatter. Using the energy of pair-annihilation it'd be relatively easy to produce the heat for fusion reactions and thus we can build ridiculously compact nukes of practically any yield.

Both of the latter variations on fusion nukes can be called as "pure fusion" because they don't generate nuclear fallout. Sure, there'll be a burst of neutrons, x-rays and gamma rays but those come and go. Technically there shouldn't be any radioactive material spread by the explosion (unlike with fission nukes).


Anyways, I want nukes to be used with a bit of frequency during the war to change the world's view on nuclear power. It'd be interesting to play in such environment.