Key Considerations in the Packaging and Disposition of Non-Aluminum Spent Nuclear Fuel (SNF) at SRS - 21273

A technical assessment of the repackaging considerations and options for the non-aluminum clad spent nuclear fuel (NASNF) in SRS's L-Basin was conducted. The assessment included evaluation of the processing risk to support dissolution of the NASNF (Non-Aluminum Spent Nuclear Fuel) in the SRS Electrolytic Dissolver. The NASNF inventory at SRS is comprised of five core fuel types containing slightly over 20 MTHM (Metric Tons of Heavy Metal) currently in 395 bundles. The five fuel type cores are UO₂, MOX, Refractory ThO₂ and UO₂-BeO, UZr metallic fuel with 2-5% Zr, and a group of more difficult fuels containing high levels of Zr, ZrO₂, or BeO, with greater potential for uranium losses to sludge, slow dissolution, and high corrosion. While the electrolytic dissolution of over 33 MTHM stainless-clad UO₂-core fuel has been well demonstrated between 1969 and 1980, the dissolution of the more-diverse fuel types presents many challenges that need to be considered. First, most of the fuels are zirconium clad and currently in 5'' diameter or larger bundles, which are wider than previously demonstrated. Hence, demonstration is needed to validate that the 5'' bundles of Zr clad spent fuel can be dissolved and that the large quantities of ZrO₂ sludge can be removed from the dissolver and dispositioned. Second, dissolution of the MOX and refractory oxide pellets requires the use of nitric acid with KF at near boiling to completely dissolve, with slow dissolution rates and significant corrosion. Third, as much as 0.5 M fluoride must be present to prevent an explosion and to avoid high uranium losses when dissolving UZr alloys. At these fluoride levels, minimizing corrosion and avoiding precipitation of uranium, zirconium, potassium, and neuron poisons is challenging. Fourth, the fuels with higher levels of zirconium, ZrO₂, and BeO likely will require new flowsheets or higher fluoride levels. Fifth, much of the metallic uranium core fuel has corroded and is in oversized cans. These will require characterization and repackaging to avoid adverse reactions and hydrogen generation to stay within safety bounds and to avoid excessively contaminating the basin. Sixth, to address these concerns and balance the complex tradeoffs between processing rate and corrosion, a technology development and maturation plan has been developed with ten key tasks to ensure adequate understanding and demonstration to support processing safely and on schedule. The paper will review the key considerations and challenges and the technology roadmap for the effective disposition of the NASNF. (authors)