The problem is that there a major, major shortage of one of the isotopes needed to re-enrich weapons grade uranium (pu 238). Thats before you get to the vast energy inefficiency of doing it which isn’t a problem, if you’re just decommissioning them anyway and you don’t care about energy consumption. However, in this instance, you would need to worry about energy consumption as well as the isotope there won’t be enough of to convert even a fraction of it.
Again, even if you had 100 years, there aren’t enough of the specialist minerals needed for hydro storage and renewables.