Decomissionning is a made-up issue: no other industrial activity is expected to return clean nature after they stopped operating, even mundane things like business offices real estate or highways wouldn't be economically viable if they had to provision for decommissioning.
You could clean up the high activity thing and let the buildings and their asbestos in place and nuclear decommissioning would still be more environmentally friendly than every other heavy industry.
You could clean up the high activity thing and let the buildings and their asbestos in place and nuclear decommissioning would still be more environmentally friendly than every other heavy industry.