Dechlorination Apparatus for Treating Chloride Salt Wastes: System Evaluation and Scale-Up

This paper describes an apparatus used to remove chlorine from chloride salt-based nuclear wastes from electrochemical reprocessing and/or chloride-based molten salt reactors (MSRs) through dechlorination by reacting the salts with ammonium dihydrogen phosphate (NH₄H₂PO₄ or ADP) at temperatures up to 600 °C to produce NH₄Cl as a byproduct. The benefits of removing the Cl from these salts include ³⁷Cl recovery from Cl-based MSR salts, formation of UCl₃ from the NH₄Cl, as well as removal of Cl from the salts and conversion of the salt cations to oxides to allow for immobilization in a chemically durable iron phosphate waste form. This generation-2 system is an improvement over the generation-1 system and provides a means for scaling up salt throughput as well as NH₄Cl recovery. The generation-2 system includes a five-zone furnace so the temperature of the four-zone gradient furnace can be tailored to control the location of NH₄Cl condensation on a four-piece fused quartz off-gas system. Both ADP and NH₄Cl decomposition reactions include the production of NH₃ and acids (i.e., H₃PO₄ and HCl, respectively), so careful temperature control is needed during the ADP-salt reactions to maximize the NH₄Cl production and minimize NH₄Cl decomposition. In two sets of experiments run in the generation-1 and generation-2 apparatuses, NH₄Cl yields were ≥5.5-fold higher for the new system compared to the original prototype system and the batch sizes can be ≥2.5-fold higher. In addition, some thermodynamic experiments evaluating the reactions of ADP + KCl as well as decomposition of pure NH₄Cl were performed to assess the temperatures of the reactions and identify off-gas products.