ob, i'm transferring reply over here so as not to upset folks who think party balloons are somehow more relevant to biotech investing than what i posted on that board.
the answer to your question is water. Nuke plants require vast quantities of water so plants are always adjacent to large lakes, rivers, or oceans. Not many people were considering tsunami's as significant threats. I think Japan is stuck with nuclear power because they don't have significant quantities of coal, oil, or gas and other "alternative" energy sources are both much more expensive (now debatable) and incapable of providing sufficient power. If the Japanese had Mr. Peabody's Wayback machine they would probably limit nuke power plant construction to their western coasts.
A few years ago Mitsubishi was working on some interesting, although extremely challenging, technology which linked nuclear power production with non-hydrocarbon based processes for power production (c.f. http://en.wikipedia.org/wiki/Sulfur-iodine_cycle). I doubt that the latter process will be implemented but contrary to popular opinion i think nuke companies will be doing more business in Japan rather than less. Charlie