Is there such a thing as safe nuclear power?

With the continuing nuclear threat caused by the Japanese earthquake and tsunami I am wondering about this. Japan built their entire nuclear infrastructure with a very clear understanding of the potential for major devastation yet here they are with reactors throughout the country threatening to melt down, evacuating residents and moving a million miles an hour trying to prevent all out nuclear disaster. These seems to point to the reality that there is really no such thing as preparing for all potential threats.