I remember going to see the Nautilus in Groton. It was the same... In one door, walk to the control room the out again. They wouldn't even let us see the reactors!
Reactors are still classified as top secret. It is common sense, the basic reactor design haven't changed much over the years, but all the equipment have.
Let us say an tourist take very good quality picture of an reactor. he could use those pictures to help him with designing his own reactor...
Nah a reactor is classified as top secret but also closed off for you'r safety. mainly due to that even after an reactor have been shut down, it have to stay like that for a very long time before they can consider removing it. Just look at reactors closed down in the 60-70's.. first now 40-50-60 years later they start to remove the reactor an it's equipment.
Remember when a reactor operator say they have stopped a reactor... in reality they have only slowed down the reaction in the reactor, enough for it to start to cool down and fuel from a reactor that are removed have to stay in a cooling pond up to a 100 days (+-), before they can safely be taken out and placed in special made containers (containers that are designed to withstand anything), for then stay on the reactor site for a long time, before it is safe enough to be moved to a permanently storage place or as in some countrys in Europa, send it to a lab, where they recycle it. For then be used in an partial Thorium reactors or similar.