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 (NHHPO or ADP) at temperatures up to 600 °C to produce NHCl as a byproduct. The benefits of removing the Cl from these salts include Cl recovery from Cl-based MSR salts, formation of UCl from the NHCl, 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 NHCl 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 NHCl condensation on a four-piece fused quartz off-gas system. Both ADP and NHCl decomposition reactions include the production of NH and acids (i.e., HPO and HCl, respectively), so careful temperature control is needed during the ADP-salt reactions to maximize the NHCl production and minimize NHCl decomposition. In two sets of experiments run in the generation-1 and generation-2 apparatuses, NHCl 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 NHCl were performed to assess the temperatures of the reactions and identify off-gas products.