Recent Assessments of Existing Transportation Packages for Use with HALEU Material

Reactor operators, designers, and fuel vendors are pursuing increased ²³⁵U enrichments to low-enriched uranium+ (LEU+) (enrichment between 5 and 10 wt% ²³⁵U) and high-assay low-enriched uranium (HALEU) (enrichments between 10 and 20 wt% ²³⁵U). These advancements will necessitate the ability to transport LEU+ and/or HALEU fuel materials. However, there is uncertainty as to whether subcriticality requirements can be satisfied with existing package designs and whether existing benchmark data are sufficient to support code validation for these applications. This paper presents studies performed to assess the usability of currently licensed transportation packages for the transportation of increased enrichment unirradiated U fuel forms. Package designs were selected that represent each of the following five categories: (1) pressurized water reactor (PWR) fuel assemblies, PWR and boiling water reactor (BWR) fuel pins, (2) UO2 powder and pellets, (3) U-metal/tristructural isotropic (TRISO) particles, (4) BWR fuel assemblies, and (5) UF6. Results obtained from each package evaluation include enrichment and packaging limits (e.g., maximum transportation array sizes) and a brief summary of benchmarks applicability. Results indicate that there are viable means for increasing enrichments into the LEU+ and/or HALEU ranges for the fuel forms, with differing challenges for different packages. Sources of margin to offset enrichment increases include reduced transportation array size, reduced fissile mass, burnable absorber credit, and safety analysis margin harvesting. A sufficient number of existing critical benchmark experiments were identified for validation of all packages except the UF6 container.