Here's an interesting idea that I'm sure we've all thought about - why not use space as our landfill?
Ha, ha. Sure! We could rocket off all the nuclear waste to the moon. Decades later, we'll build a colony on it. And then one day, the nuclear material will become unstable, and the storage pile will act like rocket boosters, and "launch" the moon! (e.g., Space 1999 premise)