Investigation into the spatial reactivity effects of NPP power reactors

Method of numerical calculation of differential efficiency of PWR control rods is considered with regard to spatial distribution of neutron flux over reactor volume and possibility of its application for other types of reactors. Power reactors of the USSR are taken as examples to show that application of single in-core or the group of out-of-core neutron detectors for reactivity measurement can result to considerable errors in evaluation of control rod worth due to spatial distribution of neutron flux density (NFD). NFD spatial effect is especially significant for indications of reactivity meters when disturbing rod is located in the plane of out-of-core detectors. It was established experimentally that application of the optimal number of in-core detectors located over the volume of large power reactors decreases sufficiently the contribution of spatial effect and the effect of detector shielding by control members