Sorry but that isn’t true about the amount of high level nuclear waste for the world. An Olympic swimming pool is 2500m3 and the UK alone already has over 2000m3 of high level waste.
Vitrification is useful in making the waste easier to handle but doesn’t remove the radioactivity.
Of course the cost of clean up also includes an awful lot more ILW.
The fact remains that we haven’t fully decommissioned a single reactor, let alone built a long term geological storage facility (capable of lasting for thousands of years) so how can we predict the costs with any certainty? The history of nuclear waste management is littered with massive cost over runs and underestimated budgets!
I’m not saying nuclear can’t be useful but let’s not underestimate the challenges (technical and financial).