As the Problems in Japan have shown. One of the dangers of Nuclear power is the need for power to keep them cool. Lose that power and uh oh. So I had an idea, would this work? Most plants are built near large bodies of water or the ocean. What if you dug down and so that the cores were well below the lake or Sea level they are next to, then built a damn. In the event of a serious problem the dam is opened and the plant flooded with water which will continue to be replaced by the lake or ocean with out the need for pump. Practical?