You could also just dump it into a deep part of the ocean. Objectively this is safe and effective, but emotionally it's just terrible and people will think I'm trolling for even suggesting it.
Look up the PPM for uranium in ocean water, then multiply that out by how much ocean water there is. The amount of uranium naturally dissolved into the oceans is staggering. Nothing humanity can do will ever come close. Even when you throw the nasty transuranics into the consideration, it's nothing. Dump nuclear reactors straight into the oceans and stop worrying about it.
I don't buy that. Sure, that's true: there's billions of tons of uranium in the ocean and nothing bad happens—but it's *also* true that we added just a few thousand tons of mercury, and there's already fish that are hazardous to human health as a result. There's large chemical differences, in how different things are absorbed by microbes, and bioaccumulate in sea life; it's not an automatic given that everything's as comparatively safe as soluble uranium. (And don't forget: spent nuclear fuel isn't one element—it's about half of the entire periodic table. Many of those transuranics are barely researched, chemically).
This is a question that would need to be extensively researched, before committing to something that's irreversible on a geological timescale. Handwaving arguments aren't enough, for something this important, this consequential.
(There's actually rather a lot of spent nuclear reactors littering the ocean floor, so opportunities to research this question are available right now—if any scientists could be bothered).
It would be safe and effective if we had a mechanism of distributing nuclear waste evenly throughout the entire volume of the Earth's oceans. But we don't have that and that's impossible to build!
Dumping nuclear waste into the ocean will, mathematically, result in a globally acceptable concentration of nuclear waste in ocean water - but it will be locally problematic for wherever we put it, and that's assuming it stays put.
Imo it's bad not for environmental reasons but bc it's wasteful to throw away the waste we could use in the future when breeding reactors or reprocessing plants become mainstream
In the form of U-238? Perhaps too, but look near enrichment plants and you will see yards full of steel cylinders filled with depleted Uranium hexafluoride.
So the spent fuel does not contain valuable energy. Better off removing the requirement to be able to retrieve it and just get on with disposing of it.
Look up the PPM for uranium in ocean water, then multiply that out by how much ocean water there is. The amount of uranium naturally dissolved into the oceans is staggering. Nothing humanity can do will ever come close. Even when you throw the nasty transuranics into the consideration, it's nothing. Dump nuclear reactors straight into the oceans and stop worrying about it.