State change modal method for numerical simulation of dynamic processes in a nuclear reactor

摘要

Modeling of dynamic processes in nuclear reactors is carried out, mainly, onthe basis of the multigroup diffusion approximation for the neutron flux. Thebasic model includes a multidimensional set of coupled parabolic equations andordinary differential equations. Dynamic processes are modeled by a successivechange of the reactor states, which are characterized by given coefficients ofthe equations. In the modal method, the approximate solution is represented asan expansion on the first eigenfunctions of some spectral problem. Thenumerical-analytical method is based on the use of dominant time-eigenvalues ofa multigroup diffusion model taking into account delayed neutrons. Numericalsimulations of the dynamic process were performed in the framework of thetwo-group approximation for the VVER-1000 reactor test model. The last ischaracterized by the fact that some eigenvalues are complex.