We conducted an analysis of the safe loading and power maneuvering areas for both existing VVER-1000 power units and prospective AP-1000 power units. Mathematical models were developed to represent these areas accurately. These proposed models offer a comprehensive assessment of the potential operating conditions for Nuclear Power Plant units within the context of evolving energy systems, which are increasingly reliant on renewable energy sources. By adequately accounting for the limitations and constraints associated with safe power output maneuvering, these models facilitate informed decision-making processes regarding the integration and operation of VVER-1000 and AP-1000 nuclear power units alongside wind and solar power plants in electric power systems. This ensures the safe and efficient operation of NPP units while accommodating the growing penetration of renewable energy sources in the overall energy mix.