Nobody has. Nuclear casks need maintenance for their life time. We haven’t invented any kind of nuclear proof forever material that’s immune to entropy. And every single one of these solutions people propose have flaws that render the solution not viable so for now we end up storing it all above ground
Everything in life slowly degrades over time and the longer the life span of something the more it degrades. Especially when that contained is filled with something radioactive.
There are lots of people who are justifiably not comfortable expecting a private company to continue a maintenance cycle that brings in zero profit and all costs for a few thousand years without cutting corners. I don’t like the idea of the Elon musks being the Smaug of nuclear waste