I guess he was talking about higher walls around the (few) nuclear plants, not the whole country. That would not make the country "a jail where the only place I can see the ocean is from on top of a mountain".
The water will just go around the wall. I think people don't quite understand the logistics involved. You have this massive wave travelling at 300 km/h. The seawall will break up the wave, but you have to have it long enough to prevent the water from reaching the bits that you want to protect before it retreats (often 20-30 minutes later).
Do a google search for "tetrapod japan images" to see what the beaches around here already look like. The Japanese government is not trying to avoid money on reducing the damage of tsunami. It seems like there should be a simple solution, but there isn't.
Thank you for suggesting the image search -- I had been imagining a castle-like wall, and seeing the stacked tetrapods [0] was really eye-opening. (Apparently it helps dissipate the wave energy.)
However, you have to ask yourself, "Why are virtually all the nuclear power plants in Japan next to the sea?" You could answer that with "Because engineers are stupid" or you could look for a more likely answer ;-)
I am not a nuclear engineer and I don't have enough background to really say what the answer is. My guess is that they are set up right next to the sea so that they can do exactly what they did in Fukushima -- pump sea water into the reactor.
Naturally higher ground is actually hard to find near the sea (because the mountains are usually set back by about a kilometre from the sea). Also, if you perch yourself on a cliff next to the sea, then you are at a more serious risk of landslides during the many 6-7 magnitude earthquakes we have in Japan each year. With artificially higher ground, I suspect you would be at even more risk.
The other main reason for not putting a nuclear reactor on high ground is that in the event of a containment breach, the contaminated water will run downhill (in indescriminate directions). The placement in low ground next to the ocean may be the best place, environmentally, in the case of a disaster.
Again, I'm only guessing, but I'm sure if you ask someone who is trained in the field they can give you better answers.
I'm hoping that Japan will transition away from nuclear reactors in the middle term. There is enough geothermal potential to provide base load (though protecting the environment with all the earthquakes we have here is not trivial in that case either). Since Fukushima, the amount of solar panels being installed in my area is insane, so I'm hopeful that things will improve over the next 50 years or so.
(Having said all that, Hamaoka power plant, which is just down the road from me, is perched up on top of a cliff overlooking the sea ;-) ).
Not an expert in the matter, but I'm guessing the pressure on such a wall would be too great. One of the things that caused the death of many people in the big tsunami after the Tokoku earthquake was the assumption that if you just went up to the roof of your apartment building you would be safe. Unfortunately, the wave just wiped out everything. Huge concrete buildings were just flattened.
To be honest, I have often wondered how the powerplant survived at all. I guess it was high enough up and that only the generators got clobbered, but I haven't looked into it in detail.
