It would work. Much like every other sweeping of something under the rug, hiding it elsewhere for it to be a problem later always works for the person throwing it away.

After all, why would we ever wish to extract the remaining U~238~ from the spent fuel? We utilised a full 4%, let's call that square and throw the rest down a hole. Perish the thought we'll ever need to dig near this massive radioactive hole. Or that an undiscovered cycle of nature causes it to come back to bite us. Just throw it down there with the rest of the resources we never want to safely explore, and who cares if there's something valuable within it's sphere of radioactivity.

Apologies for the sarcasm. I consider the idea both wasteful and foolish.

I'm a fan of both Thorium and Molten-Salt Reactors.