Time-varying reactivity reconstruction via Walsh functions

The problem of computing and reconstructing the time-varying reactivity input of nuclear reactor systems by using neutron level data records is considered. The integral equation representation of the nuclear reactor is used, and an expansion of the reactivity in a Walsh function series is made. The method provides simple formulas for computing the coefficients of this series. By using these coefficients and the Walsh functions provided by existing generators the time-varying reactivity can be easily reconstructed in a step-like form. A simple example shows the effectiveness of the method.