Spectrum Shifting as a Mechanism to Improve Performance of VHTRs with Advanced Actinide Fuels

Reprocessing of spent LWR fuel is an intrinsic part of the closed fuel cycle. While current technologies treat recovered minor actinides as high level wastes, the primary objective of one of the U.S. DOE Nuclear Energy Research Initiative (NERI) projects is to assess the possibility, advantages and limitations of designing a single-batch (no-refueling) very high temperature reactor (VHTR) configuration that utilizes transuranic nuclides (TRU) as a fuel component. Since both VHTR core design concepts, pebble bed and prismatic block assembly, permit flexibility in component configuration, fuel utilization and management, it is possible to improve fissile properties by neutron spectrum shifting through configuration adjustments. The presented analysis is focused on the TRU-impact on the single-batch mode (no-refueling) VHTR core lifetime. As a result of the analysis, promising performance characteristics have been demonstrated. The TRU-core configurations are expected to be suitable for long-term autonomous operation without intermediate refueling.