I will admit that had there been a better sea wall the Fukushima incident would have much less severe. But I still think it's beside the point.
As to your point about passive safety systems only working for a finite period of time before causing issues, would you mind providing some sources for this claim? As far as I know this is completely false. The very nature of 'passive' safety system is that the laws of physics provide a negative feedback loop that stop a chain reaction and dissipate heat away from the core. This isn't the case for every reactor design of the past few decades, but that's not my argument, I'm simply stating that there are reactor designs out there that are completely passively safe (in terms of preventing a meltdown). You will still be left with the radioactive remnants of the (non-active) core but this can be easily shielded by water for an indefinite period of time.
A nuclear battery can be 100% passively safe for decades but they don't produce a lot of power. A pure passive system that's producing 1GW of electric power is producing 2.5GW worth of heat. Which is really hard to dump into the environment passively without connections to external systems. In the event of a tidal wave your pipes to and from the sea are likely blocked which means there is some pool that is going to boil.
Even cooling tower designs often actively cool the tower through the use of water curtains. It's not needed but significantly reduces costs. Now, that that is building up the internal passive designs starts to reduce power. But thus only operates over a range. Further it is going to produce as close to 2.5 GW of heat as it can.
So, now there is no external pool or connection to the sea and here is where you see problems.
PS: Which all comes back to passive designs costing more and being less efficient. Sure, it 100% passive is possible physically just not economically viable.
As to your point about passive safety systems only working for a finite period of time before causing issues, would you mind providing some sources for this claim? As far as I know this is completely false. The very nature of 'passive' safety system is that the laws of physics provide a negative feedback loop that stop a chain reaction and dissipate heat away from the core. This isn't the case for every reactor design of the past few decades, but that's not my argument, I'm simply stating that there are reactor designs out there that are completely passively safe (in terms of preventing a meltdown). You will still be left with the radioactive remnants of the (non-active) core but this can be easily shielded by water for an indefinite period of time.