Nuclides Important for Shielding Analyses of Non-LWR Spent Fuel Storage and Transportation Configurations

Advanced reactors present a broader range of fuel forms, fuel initial enrichments and discharge burnups, and neutron spectra than those of traditional light water reactors (LWRs). The detailed characterization of radiation sources in advanced reactor spent fuel is essential for its safe management, including its transfer, storage, and transportation. The study described in this paper evaluated the contributions of nuclides in a variety of irradiated non-LWR spent fuel compositions to the external dose rates of generic non-LWR spent fuel transfer, dry storage, and transportation cask configurations. The study also identified high-impact nuclides that are major contributors to external cask dose rates.The radiation characteristics of spent nuclear fuel from representative high-temperature gas-cooled reactor, fluoride salt–cooled high-temperature reactor, solid-fueled heat pipe reactor, molten salt reactor, and sodium-cooled fast reactor concepts were analyzed. The nuclide inventories and radiation source terms were calculated using SCALE/TRITON/ORIGEN and the external cask dose rates were computed with SCALE/MAVRIC for three generic cask designs with different shielding materials.This study identified 24 individual nuclides and parent-daughter nuclide pairs with relative dose rate contributions greater than 1% across all the combinations of cask types, fuel types, fuel burnups, and cooling times evaluated. Of these nuclides, 14 had relative dose rate contributions greater than 10%, and 9 were the highest dose rate contributors for at least one combination of cask type, fuel type, fuel burnup, and cooling time.Nuclides with major contributions to the external gamma dose rates include fission products with high cumulative fission yields (i.e. 95Zr/95Nb, 144Ce/144Pr, 90Sr/90Y, 137Cs/137mBa), nuclides that are primarily produced from neutron capture in fission products with high fission yields (i.e. 134Cs and 154Eu), and activation products (i.e. 60Co). Actinides with significant spontaneous fission neutron and/or α-particle emissions (i.e. 244Cm and 241Am) were major contributors to the external neutron dose rate for spent fuel with high burnup values and long cooling times.These findings provide guidance for prioritizing nuclides in shielding safety analyses and support the development of licensing frameworks for advanced reactor spent fuel management.