Decay Heat Analysis of Non-LWR Spent Fuel Using SCALE

The accurate quantification of decay heat in spent nuclear fuel is essential for ensuring the safety of storage, transportation, and repository systems. Although well-established computational tools effectively predict decay heat for light-water reactors (LWRs), advanced reactors-because of their unique materials, fuel compositions, and design features-require specialized analysis. In the Oak Ridge National Laboratory initiated in 2024 an ongoing study to assess the importance of various nuclides response, in certain advanced reactor spent fuel applications, including those used in molten salt-fueled, sodium-cooled fast, high-temperature gas-cooled, fluoride salt-cooled high-temperature, and heat pipe reactors. This research aims to determine which nuclides are most important to criticality, decay heat, and dose rate across a variety of advanced reactor fuel types, burnups, and decay times. Building on the principles of previous related LWR efforts and using recent modeling and simulation for advanced reactors, the study adapts an existing framework for non-LWR spent fuel applications. Reactor fuel type, burnup, and cooling time were shown to have a significant impact on the relative importance (ranking) of nuclides for their contributions to decay heat. At comparable burnup values, the previous LWR nuclide importance ranking for decay heat was not found to be consistent with that of non-LWR fuel. This underscores the need to supplement LWR decay heat analyses, such as in NUREG/CR-6700, with non-LWR-specific analyses that consider the distinguishing features of these advanced reactor fuels. Additionally, it necessitates investigation into nuclear data needs for high-importance nuclides previously not prioritized by LWR studies of the same kind.