anon you can just shut it off and let it sit there basically forever like any other building. even the actual demolition isn't actually particularly expensive. buildings are demolished in large cities every day without turning into massive dust clouds and in the case of properly designed reactors you have a shield pre-built around it so you could actually just turn it into a dust cloud and then wait for it to settle. the only functional difference is that you take the concrete and steel and you put it into big barrels instead of square containers and then pour concrete over it to seal it in place, then dump it in an old mine instead of on garbage mountain.
Denmark