Bro, THE FUCKING BACKUP DIESEL GENERATORS FOR THE PLANT WERE BELOW SEA LEVEL.
Make it make sense. If those generators had been above sea level, well probably above 100-year tsunami levels, we likely would not have seen the plant catastrophically fail.
You’re right. Not 100% failsafe is failproof.
Another way to put it is 100% failproof is failsafe, by definition.