A feasibility study on fast reactor with low-enriched uranium fuel at Kyoto University Critical Assembly

Research with fast reactors has drawn interest in the investigation of their characteristics, their applications involving fast neutrons, and such. In this study, to examine the feasibility of the fast core design with the use of three low-enriched uranium (LEU) fuels (Al-alloy LEU, Metal-LEU and U10Mo) at the Kyoto University Critical Assembly (KUCA), numerical simulations with the MCNP6.1 code are conducted with 3-D assembly model of one fuel assembly in the infinite lattice of fuel assemblies to determine 1) performance of the candidate LEU fuels; 2) effect of reflectors and 3) combination of fuel and other plates in the fuel region. Based on the results, the reactor characteristics are analyzed through the full 3-D core model. Consequently, the fast reactor meeting the safety regulations at KUCA is found feasible with the use of the Metal-LEU fuel together with graphite and lead plates, while the other LEU fuels present difficulty in achieving criticality in the designed fast reactor. Finally, the design analyses could offer basic data for onward plans and operation of the KUCA core for fast reactor experiments.