| Abstrakt: |
AbstractRecent investigations into the performance and economics of mixed thoria-urania fuel cycles demonstrate potential advantages at high burnup. Initial neutronic and fuel behavior calculations for several ThO2-UO2mixtures being considered for use in commercial nuclear power plants are described.The Monte Carlo N-Particle-Origen2 Coupled Utility Program (MOCUP) was used to analyze the reactivity characteristics and isotopic concentrations of unit fuel pins/cells and lattice/assembly models as a function of burnup and reactivity. Neutronic results for a three-batch 6-yr cycle for each of three proposed ThO2-UO2mixtures with the UO2enriched to 19.5% 235U are presented. Neutronic results show that fuels fabricated from ThO2-UO2mixtures can reach an average discharge burnup of up to 70 MWd/kgHM, which will increase the time between refueling and decrease the production of weapons-grade plutonium by a factor of 3 as compared to all-urania fuel.A version of FRAPCON-3, modified to handle pure thoria and ThO2-UO2mixtures, was used for the fuel performance and behavior calculations. The new version called FRAPCON-3Th includes the updated material property models for thermal conductivity, specific heat capacity, emissivity, thermal expansion, modulus of elasticity, and melting temperature to predict fuel behavior for pure ThO2or ThO2/UO2mixed fuel. For a concentration of 75% ThO2/25% UO2, initial fuel performance parameters (peak centerline temperature, gap conductance, thermal expansion, etc.) predicted operating conditions are better than those of current UO2fuel. A ThO2-ThO2/UO2thermal conductivity model is still in the development stage. For all fuel calculations, an interim model that interpolates between the Belle and Berman predicted thermal conductivity using a correction factor for radiant heat transport and the MATPRO-predicted thermal conductivity for UO2was applied. |
