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

One might object that there is selection bias in the original claim, due to the slowdown in construction of recent plants, but that is a separate issue. A more thorough investigation of the causes of all events leading to a significant degradation of safety margins would be needed to determine whether and how older designs are inherently more risky and whether that risk can be adequately mitigated given the constraints imposed by their design.

The fact that, prior to Chernobyl, there were several foreshadowing incidents with RBMKs which should have raised serious concerns, suggests that 'lessons learned' isn't much of a reason to be satisfied with the status quo.

Even in case of RBMK where were many lessons learned. There are still to this day 7 operational RBMKs in Russia.

https://en.wikipedia.org/wiki/RBMK

RMBKs are irrelevant to nuclear reactor safety.

You had a good argument up until you went there.

> 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.