Multipoint kinetics model with power reactivity defect for the axial offset control in the VVER-1200 nuclear reactor during the load following mode of operation

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This article proposes the multipoint kinetics model consisting with different number of point kinetics model (two points, four points, six points, eight points, ten points) in the axial direction for the VVER-1200 nuclear reactor. Each node is coupled with others through the coupling coefficients determined from the diffusion approach. For more precise description of the dynamical modes of the reactor operation, the proposed model integrates the power reactivity feedback derived from temperature reactivity coefficients and Mann’s thermal hydraulic model which assumes one fuel node adjacent to two coolant nodes. On the model with four axial points, additionally was tested the influence of the different number of delayed neutrons groups on the accuracy results and model running time during the load-following mode of operation. Moreover, the novel model of the control rods is introduced, utilizing a combination of sign functions to sequentially influence all nodes during insertion or withdrawal. The computational results show that the accuracy of the proposed model is satisfactory, and general assumptions about transients align with their physical definitions. This research contributes to the advancement of the point-like nuclear reactor modeling for improvement of the automatic power controller synthesis.