but that type accounts for about 3% of all nuclear waste and is currently being safely disposed of in deep-level purpose-built facilities.
Sorry, but that is just false. The only european country, that is on the track to build and operate such a facility is Finland. Their facility will be finished in a hundred years and only contain the waste of a single Nuclear power plant of a country of 5 million people. Also it is sheduled to cost around a billion Euro. https://en.wikipedia.org/wiki/Onkalo_spent_nuclear_fuel_repository
In Germany there is the plan to designate a spot to build a facility by 2040, but it is entirely uncertain, as the most likely feasible geological formations for that are in Bavaria. The state that is a strong proponent of nucelar power, but rejects to store any of its waste. It is NIMBYism by the pro nuclear faction par excellence. So we dont know, if by 2040 we will just have found a spot for a facility and can begin the planning process for it.
All storage facilities in Germany that were supposed to be long term, have been subject to deterioation, unsafe handling of nuclear waste and water entry with the potential to leak nuclear waste into the groundwater.
In central Europe, where 200 Million people are living in one of the most densely populated regions of the globe the issue of storing the radioactive waste is neither solved politically, nor technologically, nor is the funding secured with certainty.
It is still very much hypothetical, if, when and how the radioactive waste, that is waiting in "intermediate" storage facilities since 50 years will actually end up in a feasible permanent storage. Proponents of nuclear energy and in this case you specifically distort the facts tremendously, by saying the issue of storage is solved or even close to being solved
Also it is absurd, to claim to know the costs and challenges would be less than for other industrial wastes, because the fucking technology doesn't exist in any larger scale implementation