It's a question of exposure. When the material is encased in solid rock hundreds, if not thousands of feet blow, the exposure risk is very low.
Once you pull it out of the ground - exposure becomes a real problem. They mention that some of the materials must be kept in liquid, so it does not become a dust that can get blown away. At the same time, they need to line the storage pool with a material that will block it from seeping into the groundwater. For centuries.
> At the same time, they need to line the storage pool with a material that will block it from seeping into the groundwater. For centuries.
Not for thorium. The stuff is almost harmless, and is insoluble in water, so tends to just stay put.
Plus, even if you did have to isolate it, centuries would be nothing. It's has a half life of 14 billion years! Just bury it back in the ground and that's all - it's really not very radioactive. (Just deep enough that it won't be dug up by accident and that's all - you don't need to block the radioactivity, since even a piece of paper is enough shielding.)
A little knowledge is a dangerous thing since you are confusing cesium from nuclear reactors and thorium.
Once you pull it out of the ground - exposure becomes a real problem. They mention that some of the materials must be kept in liquid, so it does not become a dust that can get blown away. At the same time, they need to line the storage pool with a material that will block it from seeping into the groundwater. For centuries.