> disasters happen to older plants is not refuted by the observation that lessons learned are applied to the whole fleet.

There was a single nuclear disaster in history that actually caused a lot of damage (Fukushima was of course very costly financially). Both Chernobyl and Fukushima were caused by variables that can be easily controlled, though. Just don't build them in coastal areas were Tsunamis are fairly common and more importantly don't allow Soviet engineers to design and operate your nuclear power plants.