Tried and tested units are very safe....we put people in them and have done so for years. Experimental systems are just that and wouldn't be used for this purpose....spent fuel rods could be safely enclosed in containers and launched into oblivion....burying it in a mountainside somewhere insures that it will threaten the Earth for a thousand years.
I watched the space program all the way from the 1960s to the present time. My brother just retired from from the Kennedy Space Center. I've watched from up close. Those "very safe" rockets blow up a lot more frequently than you think.
Man-qualified rockets cost a great deal more than the containers that are buried in the desert. Radioactive waste cannot be handled outside of those containers because it is too radioactive. A single exposed waste rod will kill a man from the distance of fifty yards. The waste would have to transported and then loaded onto the rockets in those containers. Rockets would have a hard time boosting those containers because they are large and massive.
Just one accident would poison a big chunk of our planet.