Please explain how people in the midst of a nuclear winter aren’t going to be aware of what a radiation hazard is? Come on, just think for a moment before you say something.
Loss of knowledge in disasters so wide is not something which is hard to imagine. How come you have so much trouble with it? And nuclear winter is just one catastrophic scenario. Will you come for every one I list?
Nuclear winter would be caused by a nuclear war so there would be a lot of effort put into surviving the effects of radioactive fallout, it would be the first thing on everyone’s minds and would be an ongoing concern. In that case there would be many other sources of radiation to deal with. There’d be plenty of other hazards leftover too in any disaster of similar scale. Those aren’t reasons to not use potentially hazardous materials, the best thing to focus effort on is preventing those worst case scenarios in the first place and having a plan to deal with them if they do happen.
....and then nuclear winter ends, generations after generations despise everything about nuclear. later they forget about it, more generations, more generations and meanwhile the stuff is still there and still dangerous.