Multipoint Kinetics Model with Power Reactivity Effect for the Axial Offset Control in the VVER-1200 Nuclear Reactor in the Load-Following Mode

In this work, a multipoint kinetics model for a VVER-1200 nuclear reactor consisting of a diverse (two-point, four-point, six-point, eight-point, and ten-point) set of point kinetics models in the axial direction that are coupled to each other by coefficients determined in the diffusion approximation is proposed and simulated in MATLAB environment. For a more precise description of the dynamic modes of the reactor, the model is provided with power reactivity feedback determined by temperature effects of reactivity and Mann’s approach to describing thermal-hydraulic processes in which it is assumed that two coolant nodes are adjacent to a single fuel node. The effect of different numbers of delayed neutron groups on the accuracy and speed of simulation of transient processes in the load-following mode is tested on the model with four axial points. In addition, a new mathematical model of control rods (CRs) is proposed that uses a combination of sign functions to sequentially influence all nodes during insertion or withdrawal. The results of numerical simulation show that the statistical accuracy of the proposed model is satisfactory, and general assumptions about transients are consistent with their physical definitions. This research contributes to the advancement of point nuclear reactor models for improving the synthesis of an automatic power controller.