Multinodal Dynamics Model of the VVER-1200 Nuclear Reactor for Synthesis of an Automatic Control System

In this paper, a multinodal model composed different sets of axial nodes determined within the approach of Avery coupled reactors in the axial direction was proposed and implemented in the MATLAB environment for the dynamics of the VVER-1200 nuclear reactor. The number of considered nodes was varied from 2 to 20. To provide a more precise description of dynamic modes of reactor operation, the model was extended by the thermohydraulic Mann’s model, implying that one fuel node is adjacent to two sequential coolant nodes. To model daily maneuvering modes, spatial xenon oscillations were taken into account, and the parameter “axial xenon oscillation index” was introduced. In this paper, a new mathematical multinodal model derived from the model of change in the boric acid concentration in channel geometry was also proposed to reflect the influence of boric acid. This model is coupled to the model of thermohydraulic processes through the mass coolant flow rate. The results of numerical simulation in two experiments with a change in the position of the 12th group of Control and Protection Systems Control Rods (CPS CR) and in the liquid absorbent concentration in the coolant of the primary circuit show that the statistical precision of the proposed model is more than satisfactory as compared to a multifunctional simulator, and the general form of transient processes agrees with physical representations. The submitted work is a contribution to the further development of multipoint models of a nuclear reactor to improve the synthesis of the automatic power controller.