Making this argument is a strong indicator that you are extremely under-educated on this subject or motivated to make dishonest arguments.

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.