Can’t you just dump radioactive uranium into the bottom of the ocean? Can’t imagine it would do much damage with all of the water around it.
Just dumping fuel pellets into the deep ocean would be a pretty terrible idea though. All the fission products and impurities that build up as the fuel is burned lead to the pellets starting to crack apart. Any cesium or iodine would leach into the water quickly, it would not be a good day for Shamu.
https://www.latimes.com/environment/story/2021-04-26/ddt-was...
Did I say thousands? Wow.
Don't ever trust anyone that says "We'll just safely dispose of that in the deep ocean.".