Chernobyl NPP wasn't really dangerous design if run by competent people, many of those kind of NPP reactors are still working decades without a major incident. It was a mistake of the chief of the shift to proceed with unsafe test caused by the failure of the Soviet political system to maintain proper level of understanding and safety in the NPP. The personnel did not have the correct mental model of the device.

Fukushima was a bad plant because they built it in a tsunami zone. Otherwise its design isn't dangerous either. But it got destroyed by unexpected tsunami. People should have expected the tsunami can happen and not build the plant there. People were stupid, NPP design would be fine if built far from tsunamis.