Thanks for your quick response. No need to apologize. Each part, and the whole site could be tagged, but each of them, each type of element with the respective instance type of Wikidata item. 

The reactors in OSM could be tagged with a Wikidata "instance of" "nuclear reactor", and the nuclear power stations in OSM could be tagged with a Wikidata "instance of" "nuclear power plant".

When you select which Wikidata item to "link", you need to check that it is the same type of element, not only that the label/name matches.
In some cases is more easier or direct than others.

E.g. for nuclear power plants, the class is https://www.wikidata.org/wiki/Q134447 which has property P1282 (Openstreetmap tag or key) = https://wiki.openstreetmap.org/wiki/Tag:plant:source=nuclear so, to map an OSM element power=plant + plant:source=nuclear, the Wikidata item you choose has to be an "instance of" "nuclear power plant" (wikidata class Q134447)
