I recall reading some proposal for dumping nuclear waste in the Marianas Trench. The rational had something to do with tectonic shifting eventually pushing the waste into the Earth's mantle.
The subduction zone off Vancouver, BC is also a place for this, and off Chile is even better.
The problem is the subduction zones are very slow -- on the order of 25 meters per 100 years, at most. The waste isn't particularly threatening past 10-20k years.
I still believe in reprocessing as the best solution.
