Quite naturally all the critters will read the signs and avoid the area. And so the entire ocean food chain begins to die off.
Several nuke subs (with build-in containment features) do not equal the shear mega-tonnage of waste that would end up on the bottom in little more than concrete filled 50 gal barrels. A little bit, but not a deluge, nature can handle.
Besides there are technologies to recycle the ‘waste’. Not a new or cleaver idea. Plus your ocean biology sucks; I’m sure you can find dozens of peer reviewed papers on the subject.
“I’m sure you can find dozens of peer reviewed papers on the subject.”
I’ve looked around a bit and haven’t found much. If you have a pointer, please share. Recycling versus deep sea disposal is not either/or. Recycle as much as makes economic and public safety sense. Permanently dispose in miles deep water. If you’re really worried, put it into an active subduction zone where it will be pulled into the Earth’s interior. The only thing that radioactive atoms can emit are energetic particles and photons. Water absorbs all the energy of these emissions very well.