Lol! Duh! Good point! Been a very long day...not thinking too clearly right now. 3AM here.
You know what threw me off was the visualization of the nuke material being carried down with the subducting plate. For some reason, I assumed that is how you meant the material would be safely buried. Of course that would also take a very very long time. So what you are saying then is that it’s simply very deep water at subduction trenches, and that the material would stay at those depths?