Personally, I think they ought to dump nuclear waste into lava pools.
No--that's no good either--it just keeps being vomited up. You really want it in a subduction zone, right where one plante dives down into another. Dig a trench just in front of a subsea cliff. The next big quake and the plate moves under that cliff--that or wait some number of years for gradual subduction. Seeing how difficult Deepwater Horizon operations were at depth--putting it on the moon is actually easier.