An improved reduced order model for nonlinear stability analysis of spatial xenon oscillations

Abstract

In this paper, an improved reduced order model for studying spatial xenon oscillations has been developed which can be utilized for stability analysis (linear as well as nonlinear). The model presented in this paper has been developed to overcome situations of unphysical results which were obtained by earlier models which used quasi static assumption when the system moves away from the equilibrium point. The earlier model consisted of multipoint neutron kinetics equations including xenon and iodine feedback. In order to eliminate unphysical behaviour in the earlier model, the quasi-static approach is discarded and the total power control is represented by an ordinary differential equation. It represents the action of a reactivity device governed by the deviation of the total power from the steady state power level. In the current approach, a PHWR is modelled by dividing it into two regions. The linear and nonlinear stability analysis was carried out using the new model and compared with the older results. Linear stability maps were constructed in different parameter planes and were found to be identical. However, there was a change in the nonlinear characteristics of the system and the results are presented in this paper. Moreover, the effect of control device on the system behaviour especially on total power variation is studied through numerical simulations.