The Influence of Energy Group Structure and Nonlinearities on the Calculation of Xenon-Induced Flux Oscillations

A nonlinear model is developed for the xenon-induced flux oscillation problem that occurs in nuclear power plants. The model is based on Galerkin's method of weighted residuals applied to multigroup diffusion theory. A similar linear model is developed by the same methods in order to consider the effects of the nonlinearities of the system. The effects of multi- and single-energy group considerations are also examined. The one- and three-energy group models give substantial differences in results for a 0.25% perturbation in the absorption cross section in various regions of the core. The effect of the number of profiles describing the flux distribution has an effect on the accuracy of the simulation. The minimum number of profiles is one higher than the number of regions into which the reactor is divided for a one-dimensional calculation. The use of additional profiles causes a small increase in the accuracy of the results at the expense of a dramatic increase in computational time.