"Even Fukushima didn't fail until a tsunami destroyed some backup power systems that were incorrectly placed, and even THEN no one died."
You severely underestimate how close this was to total disaster. "Incorrectly placed" - Yes, the power plant was placed close to the sea, and not in the mountains as engineers 40 years earlier had planned. But still way higher than any presumed tsunami. Then a double (two geological faults) whammy happened at the same time and you got an unprecedented tsunami. So yes, the diesel engines were drowned. As to "no one died" - you forgot to include those who died within as close to two years later, from cancer. People who went into highly radioactive areas, preparing to die.
So what happened then? People had to go in ("go" as in very difficult) to manually turn on and off valves (where not even protective "space suits" could stop the radiation), in an effort to lead high pressure out through a water filtration system to avoid pouring radioactivity straight into the surrounding air. Due to the failing power pressure increased rapidly inside every building, soon going way above the limit and buildings started to explode, despite manually pumping water in to try to cool the reactors.
So, what happened in the end was that at one point they couldn't prevent pressure going up in one particular building, it went twice as high as the design limit and hadn't yet blown (unlike the previous ones which blew at a lower pressure), and at that point this was game over, if that happened it would be Chernobyl all over again just ten (10) times worse, the plant would have gone into total meltdown. They didn't see any way out of that and looked at evacuating 50 million people, all of east Japan including Tokyo, and as far south as Nagoya. An impossibility.
Then a kind of miracle happened. One single plate in the building blew out, and the pressure aired itself out (spewing radioactivity into the air), and prevented the failure. Something which they couldn't actually do manually. To this day nobody understand how or why, but that incident saved all of Japan as we know it at the very last moment.
So, I then told my wife (who is Japanese, and absolutely horrified by what the government is doing right now) that "Fukushima was more than 40 years old, nuclear plants are not meant to be that old, of course there's better safety in newer plants, and they get decommissioned after 25 years I'm sure, or at least 30 years, they should never get that old". And then this comes up. 60 years? That's insane.
When I learned what really happened at Fukushima, and how insanely necessary it is to actively control a standard nuclear reactor at all times to prevent meltdown, I firmly believe that the only type of future nuclear reactors allowed should be ones where you actively have to run the fission, e.g. Thorium reactors. The ones where, if you do nothing (e.g. turns of the electricity), it simply stops. Not the other way around, as in Fukushima, Chernobyl, Three Mile Island. If a fraction of the effort which was put into the research which achieved today's reactors (which were, after all, a particular design choice made because it could produce plutonium for military purposes), then Thorium reactors can surely be developed.
If you want to learn what really happened at Fukushima I recommend the film "Fukushima", which gives a fairly good overview (though with a tight focus on a few aspects of this).