Given that they already knew this could happen when they built it, what could you plausibly claim has been learned?
There’s nothing very complicated about the EDG buses that supply safety-system components.
Upgrades to such systems, including flex interfaces, has occurred across the US fleet in the years following Fukushima, while exactly zero new reactors have been designed and built.
Sure, there are better designs for EDG siting and support system integration. This is completely besides the point. The point is, even moving the whole safety support system kilometers away is cheaper than designing a new reactor, which I think should be a pretty uncontroversial statement to engineers familiar with the complexity of license approval for power reactors.
Every industry makes severe mistakes early on and eventually irons them out with time. Are you arguing that's not the case?
> However by your logic they had 50 years to take extra safety pre-cautions and improve the structure.
Economically retrofitting an old reactor with safety mechanisms is a much more challenging task than designing new reactors correctly. The industry quickly learned how to build reactors that could handle neglect and abuse, but by then the reactors under the ground were out of their control, and were essentially ticking time-bombs. Everyone in the industry knew it. The IAEA had been complaining about ancient, unsafe reactor designs in the ring of fire for decades when Fukushima happened. So it goes.