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.