Nuclear power plants emit no carbon dioxide and have been statistically safer than every competing energy industry, including wind turbines. And at last, more than seventy years after the technology’s inception, engineers were finally developing reactors with design priorities that lay not in making bombs but in generating electricity. In principle, these fourth-generation reactors would be cheaper, safer, smaller, more efficient, and less poisonous than their predecessors and could yet prove to be the technology that saves the world.