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.
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.