There are now more than 450 nuclear reactors throughout the world. If nuclear power is embraced as a rescue technology, there would be many times that number, creating a worldwide chain of nuclear danger zones—a planetary system of potential self-annihilation. To be fearful of such a development is rational. What is irrational is to dismiss this concern, and to insist, after the experience of more than a half-century, that a “fourth generation” of nuclear power will change everything.