I actually did produce a technical solution: stick it deep in yucca mountain and forget about it. It's safe, and there's more than enough room for the little waste that can't be turned back into fuel.
The time frame we are talking about invalidates the "safety" because the earth's crust moves and warps, which allows water to access that sort of storage
Why dont you suggest what "safe" looks like, and we can discuss your understanding of safety. Its clear to me that the issue is your standards and not actual waste disposal.
My understanding is that this material remains toxic to life for thousands, to tens of thousands of years.
Safe means that it's stored such that there's no harm to the environment for that lifetime.
In all "bury it" scenarios, the place where the waste is buried will be subject to change resulting in water, air, able to interact with that waste when normal tectonic and erosion processes do their thing.
The time frame we are talking about invalidates the "safety" because the earth's crust moves and warps, which allows water to access that sort of storage