Elements with very long half-lives aren't very radioactive. Something with a half life of millions of years is essentially not radioactive at all. Nuclear fuel

Elements with very long half-lives aren't very radioactive. Something with a half life of millions of years is essentially not radioactive at all. Nuclear fuel itself isn't radioactively dangerous, it's dangerous because it's a heavy metal (like lead). After nuclear fuel is reacted, it produces a bunch of nuclear decay products. Some of these decay products have a half-life of 10s of years, which are the problems: they're short enough to be dangerously radioactive, but long enough that they need to be handled carefully for a long time. But not for 10s of thousands of years.