Design of NPP (nuclear power plant) safety important systems (relating to a critical information infrastructure) is basing on observing the regulatory documents and proving reliable plant performance during all its life-cycle. An aspect of the increased requirements for reliable and safe NPP APCS (automated process control system) performance is the necessity of perfecting NPP operator information support systems. An approach is considering, under which a core of the operator information support system is a flexible modeling software package that can be used as a digital shadow or digital twin in the dependence of solved tasks. This approach applies to a wide range of tasks of upper-level systems of NPP APCS.