AbstractA method was developed for determining the optimum fuel utilization for the Plum Brook Reactor (PBR). The method used available PBR criticality data to incorporate the effects of neutron leakage and nonuniformity of burnup in a point model of the core. This allowed the model to predict the performance of the core as a function of new element weight and number of uses per element. A graphical model was devised to determine the optimum. The article shows the derivation of the model and its application for a typical PBR configuration.