Originally the simulator was used only for training the operating personnel of the Paks Nuclear Power Plant, but now it is used as a "test bed" for new systems prior their installation on the real plant, too. The first such testing was the replacement of the Reactor Protection System with a new computerized one. For this reason the scope of the models had to be extended to cover the severe accidents, which needed a much more powerful simulator computer than the original one. The outdated control room interface system had to be replaced by a new one, because spare parts became unattainable and its service required very high cost. Only the instructor?s system remained in its original form.

Now the old Instructor's system has been replaced as well. All the old functions were realised by convenient full-graphic Man-Machine Interface tools. The paper describes in detail the newly added functionalities of he Instructor's system, too.