Transmutation of Long-lived Fission Products in a Sodium-cooled Atw System

To devise an optimal strategy for transmuting long-lived fission products (LLFPs) in fast systems, various design studies have been performed for a sodium-cooled Accelerator Transmutation of Waste system. For Tc and I target assemblies loaded with metallic Tc and CaI2 targets and ZrH2 moderator, assembly design studies were first performed, focused on the optimisation of neutron spectrum and the reduction of local power peaking in neighbouring fuel assemblies caused by moderation in the target assembly. Then, using optimised LLFP target assembly designs, full core depletion calculations were carried out to find optimum loading options. The result shows that loading of moderated target assemblies in the core periphery (reflector region) is preferable from the viewpoint of neutron economy and safety. By a simultaneous loading of twelve Tc and twelve I target assemblies in the reflector region, Tc and I are consumed with a support ratio equal to the transuranic support ratio (~3.2) at the cost of a 10% increase in fuel inventory. Consumption fractions of ~29% and ~37% are achieved at discharge for Tc and I target assemblies with a ~5-year irradiation period. 1. Korea Atomic Energy Research Institute, Republic of Korea.