However the media and the excellent board-posters seem to be assuming that nuclear weapons work like conventional explosives. They do not. I haven't read anything scholarly enough to tell if the experts are making the same mistake in their modeling (and I probably wouldn't understand them, if I did). If their modeling assumes that kilotonnage equivalents of a nuclear weapon will have the same effect as that many kilotons of TNT, then they are on the wrong track.

Convention explosives (and rocket propellant, for that matter) work by including a substance that expands very rapidly.

Nuclear weapons work by producing huge amounts of heat in a very short time. This heat subsequently causes whatever matter that happens to be near (air, water, dirt, buildings, people...) to expand very rapidly. In space there is no matter to cause this effect.