The two direct deaths where from an insufficient sea wall not the reactor design. Saying future reactor designs fix the problem is a mistake. Because again it was not the reactor design that caused their deaths.
So again, saying some hypothetical perfect design exists and it would obviously have a large enough see wall, and that is what your defending is a true Scotsman argument.
PS: Remember, future designs also have future defects.
When people think of the Fukushima disaster the two direct and unfortunate deaths caused by the insufficient sea wall are not what come to mind. The meltdown of the reactor is the primary concern. If a meltdown had never occurred the Fukushima incident would have never been mentioned on this thread or in any other conversation about the safety issues with nuclear power. So I'm sorry but bringing up the inadequate sea wall is a complete straw man argument when talking about safety issues from nuclear power.
Now, back on topic, the nuclear reactor meltdown at Fukushima was caused by a faulty reactor design. Really it was a poorly designed safety system. The Tsunami that came after the initial earthquake took out the backup power generators at the plant. These backup generators were responsible for powering the cooling pumps that are supposed to prevent a meltdown. This is the main fault in the design and one that is not present in modern reactor designs. Modern reactors now have passive safety systems, i.e. if the power fails the safety measures will be triggered automatically and will not depend on outside power to complete their task. One example of this is using an elevated water tower to store the cooling water with a valve that is kept shut electronically. In the case of a power failure the valve would automatically open (since that is where it's in a stable equilibrium) and gravity would 'pump' the cooling water onto the reactor preventing a meltdown.
Without the damage from the tidal wave Fukushima would have been far less of an issue. With a proper wall there would not have been significant issues with the Tsunami, thus making that wall a critical safety feature that failed.
As to passive safety systems, many modern designs can't be left unattended for a month. Because they are not passively safe only being able to go longer without issues.
Anyway this is all abstract pick a design that would have been safe without a sea wall or direct intervention after the fact. While being both proven and cost effective.
PS: On second thought as you said modern design, the worst plant built in the last 10 years is still a 'modern design' and close to where many people live.
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.
