Some Neutron Physical Consequences of Maximizing the Conversion Ratio of Pressurized Water Reactors Operated in the Uranium-Plutonium Cycle

Maximum conversion ratios of Pu/U mixtures in a pressurized water reactor (PWR)-like open rod lattice core are assessed complying with established data of thermal design, allowing for agreeable discharge burnup values, and utilizing plutonium from PWRs with present time fuel management or with that expected for the near future. Void reactivity, temperature coefficients, and control rod requirements are discussed with respect to their compatibility with the usual PWR design principles. While the temperature coefficients show a completely satisfying behavior, the core control requirements lead to design inconveniences, which nevertheless can be overcome. A crucial constraint, however, is the void reactivity, which limits the specific plutonium content. From the economical point of view, high conversion fuel cycles are penalized by high fissile inventories but promoted by low net consumption of fissile material as well as by low specific reprocessing expenditures.