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?
Sorry, never mind. I read what you wrote above and understand (’concrete casks and steel’, until it takes the trip downward millions of years later)
I had a conversation years ago with a nuclear engineer, a coworker at the facility which we both worked. I told him about my idea and he said that the casks (developed by Bechtel Engineering way back in the 1970s) would safely store the waste as it was first buried by tons of sediment, then all of it would eventually be crushed molecule thin as it slid under the tectonic plate.
Keep in mind that the Aleutian Trench is thousands of feet deep and the casks would be under megatons of seawater.
This recycling happens slowly over a very long period time. The main idea is to keep it far from human contact.
I’m sure that some at this post will be saddened to know it is highly unlikely that radioactive worms or monsters will be issuing from the trench. Sorry!