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 ;-) ).
