Patent ID: 8582713

Claim:
A method for improving the energy generating output of a nuclear reactor while satisfying a maximum subcritical banked withdrawal position (MSBWP) reactivity limit, comprising: ranking enrichments of individual fuel rods by evaluating an uranium enrichment of fuel rods at a two top-most nodes of each fuel rod of a fuel bundle, a highest ranked fuel rod being a fuel rod with the lowest enrichment of uranium at said two top-most nodes, the evaluation of the two top-most nodes being performed by discounting existence of any natural uranium blanket, replacing a highest ranked fuel rod with a fuel rod containing natural uranium in either the top node, or the two top-most nodes, performing a core simulation to determine whether there is any margin to a MSBWP reactivity limit, repeating the replacing and performing function for each lower ranked fuel rod until no fuel rods violate the MSBWP reactivity limit, so as to achieve a desired lattice design for the top of the fuel bundle, and operating the core of the reactor having fuel bundles configured with the desired lattice design at the top of the fuel bundle.