Isn't the idea of npp decommissioning to leave the area as it was before npp?
Environmental impact of different techs was described in UNECE report I think
Uneconomical. The best way to dispose of things like the weakly radioactive reactor hulls is often to simply leave them when they are.
They aren't particularly dangerous, and they don't leach contaminants. So you just bury them so no one can access them too easily. But it does require leaving the sealed reactor buildings in place - even if you can reuse the rest of the land and the exclusion area.
I think it's still done as full dismantling (but maybe not all countries?). French superphenix will be basically erased. Something similar is happening to german plants like Isar 2
Some countries may have postponed decommissioning because it's cheaper to wait a bit
Some countries allow recycling of some stuff, even concrete, like Italy
