Nukes don’t cause long therm radiation as the nuclear material is almost entirely used up for the explosion, the remaining radiation goes to unproblematic levels within a few weeks.

This is of course if the Nuke is used correctly, if its used with a impact fuse the dirt around the explosion will be radioactive for longer, however also not that much.

Nukes aren’t Dirty bombs (and strictly speaking Ukraine has already a gigantic dumping sight for radioactive material… No offense but Chernobyl can be seen as that)