PNNL

Abstract

This paper describes an apparatus used to remove chlorine from chloride-based salt 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. The benefits of removing the Cl from these salts include 37Cl recovery from Cl-based MSR salts, the NH4Cl can be used to make UCl3, and removing Cl from the salts and converting the salt cations to oxides allows 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 5-zone furnace so the temperature of the 4-zone off-gas collection system can be tailored to control the location of NH4Cl condensation on a 4-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 protype system and the batch sizes can be = 2.5-fold higher. In addition, some thermodynamic experiments evaluating the reaction of ADP + KCl as well as pure NH4Cl were performed to assess the temperatures of the decomposition reactions.