So instead, it needs to be safely buried in a place like Yucca Mountain under extremely stringent criteria (must survive 10k years with no maintenance, etc).
In France (and other places), the leftover fuel/waste is actually a valuable resource. They recycle it and get new nuclear fuel. Some of the waste products are used as radiation sources in medicine.
In a power plant near its operational life span end you only have those waste products with long lifespans of radioactivity which no one has figured out how to do a reasonable cost decommission of as remember the plan infrastructure of the reactor vessel, etc also contains those long lifespan radioactive elements form being bombarded for 40+ years.