NATURITA, Colo. — The future of nuclear power in America is back on the table, with all its vast implications, as global warming revives the search for energy sources that produce less greenhouse gas. But in this depressed corner of western Colorado — one of the first places in the world that uranium, nuclear energy’s primary fuel, was ever dug from the ground in industrial scale — the debate is both simpler and more complicated. A proposal for a new mill to process uranium ore, which would lead to the opening of long-shuttered mines in Colorado and Utah, has brought...