(486a) Dissolution of Surrogate U-Zr Fuel Using Alniflex Conditions

Commercial nuclear reactor fuel can be safely and efficiently dissolved using nitric acid (with mercury to catalyze dissolution of aluminum cladding) or with electrolytic dissolution flowsheets. However, some fuel types like uranium-zirconium alloy (U-Zr) and U-Zr alloy with 1- 20 mol % Zr can exhibit explosive exothermic reactions during nitric acid dissolution. One of the preferred methods to dissolve U-Zr fuel is to use fluoride to accelerate the dissolution of zirconium and mitigate the exothermic reaction; however, fluoride will also quickly corrode and compromise dissolution vessels fabricated from iron-based alloys. Alniflex was a flowsheet proposed in the 1960s to mitigate the corrosion of stainless-steel vessels while still efficiently dissolving U-Zr fuel. One challenge is that the Alniflex flowsheet requires a balance of fluoride and acid concentrations while dissolving Al, Zr, and U metals to avoid undesired precipitation reactions and excessive vessel corrosion. This talk will present dissolution and corrosion kinetics and solubility observations of zirconium, aluminum, and stainless steel at several different hydrofluoric and nitric acid concentrations and at 50-90 °C. Uranium was later added to determine its dissolution and solubility behavior within the Alniflex flowsheet.