Have you seen the nuclear plant disasters that need a thousand years to clean up? Two of them so far and it hasn’t even been a century
There are a variety of commercial reactor design families that CANNOT melt down. Literally impossible for have a Chernobyl or Fukushima from the designs. These are not new. There is no reason anyone feeling like they know enough to contribute to this sort of discussion should be unaware. HTGRs, MSRs, SMRs, LMRs, SFRs...
"Sometimes nuclear plants melt down and cause widespread problems for very long timescales" is a nonsense argument to use against "We should build new reactors" when the new reactor designs we would be building can't melt down.