The scope of this paper is the investigation of the control-strategy-design problem. The digital-control system of a model of a nuclear boiling-water reactor power plant of 500-MW electrical output is considered. The proposed approach, i.e., a system partitioning approach, is applied to the case where there are different kinds of interactions inside the system and where the state-vector representation is used to describe the unsteady states of the reactor. The overall control system is investigated for different sampling periods of digital controllers, and for the case where constraints are imposed on the reactivity controller signals. The influence of the real-noise disturbances upon the overall dynamics of a large power reactor is investigated for the case where the control strategy is determined for the ideal white-noise type of disturbance.