As I understand it (AIUI), the stuff that will still be around in 10,000 won't be that (relatively) dangerous: you would have to either eat the pellets or grind

As I understand it (AIUI), the stuff that will still be around in 10,000 won't be that (relatively) dangerous: you would have to either eat the pellets or grind them up and snort them like cocaine for them to have major health effects. It's mostly alpha (α) radiation (helium) that's being thrown off at that point, which can be stopped by even paper; and some beta (β) radiation (electrons/positrons), which can be stopped by thin metal. If things are encased in (e.g.) concrete and rebar there isn't much escaping. It's generally the 'hot' stuff early on (right out of the reactor, and sits in the water tanks for a few decades) throwing off gamma (γ) radiation that will really get you.