Historically, the built of multiple Nuclear Power Plants (NPP) at one site has often been stretched over a considerable timespan, with different NPP going into commission many years apart. Therefore, multi-unit sites consisting of different types of NPP exist, e.g. comprising a boiling water reactor and a pressurized water reactor or two pressurized water reactors of consecutive generations, with the newer one more technologically advanced. Consequently, it is to be expected that the oldest NPP on such a multi-unit site will go into shutdown and decommissioning first, with decommissioning measures such as decontamination, removal of components and even demolition of buildings taking place while the other NPP on the site is still in operation. It is reasonable to assume that the altered plant state and the ongoing decommissioning work will influence the operation of the operating NPP on the site.