Safeguarding Commercial Breed and Burn Sodium-Cooled Fast Reactors

There is a new class of reactors being developed that use fast neutron spectra and rely on fuel technology advancements to reach a steady-state system where no future enrichment or chemical separation of fissile material is required to sustain or grow the nuclear fleet. To achieve operations without the need for enrichment or chemical separation requires nuclear fuel that can remain in the reactor environment for much longer than current limits and the transfer of partially irradiated fuel as the initial fissile source for new and replacement reactors. Through reducing the need for enrichment and reprocessing to sustain a reactor fleet, this technology would indirectly reduce the burden on IAEA safeguards. However, this complex dynamic system poses new safeguards challenges. Initial deployment will require substantial inventory of enriched uranium including high assay low enriched uranium (HALEU) above 10% but well below 20%. Over time the system evolves to have a substantial in-core inventory of Pu at concentrations near 10% Pu. After the initial inventory, no additional fissile material is required to sustain operations because the required fissile material is bred in situ, referred to as “breed and burn.” For future reactors, the initial fissile material will come from partially irradiated fuel from a reactor that has reached the end of its operating life, or the breed and burn reactors can be designed to produce excess Pu in the form of irradiated fuel above what is needed to sustain operations. This study evaluates safeguards-relevant measures including but not limited to inventory and isotopic evolution of irradiated fuel, the amount of special nuclear material in the core at the end of the reactor life, and the unique challenge of transferring special nuclear material in the form of irradiated nuclear fuel to a new reactor. The overall goal is to identify and quantify the complex dynamic inventories for an example system that will need to be under safeguards from initial deployment to an eventual steady state operation. This presentation outlines modeling results which will be incorporated into the final safeguards assessment of this project.