Method for Evaluating the Local Variation of the Neutron Flux

Abstract

One method of evaluating the local variation of the neutron flux is described. By regarding the variations in nuclear reactors such as control rod motion, fuel shuffling and refueling as disturbances added to the material buckling, a one-group diffusion equation is solved using the perturbation theory in one-dimensional geometry. This method is applied to an inhomogeneous reactor, which has already been disturbed, where the disturbances are approximated by a number of square pulses small enough for the method to be applicable. Good results are obtained with this method for disturbances equivalent to a reactivity of several percent. Discussion based on several examples are presented on the errors introduced by larger disturbances.