Application of Vacuum Salt Distillation Technology for the Removal of Fluoride and Chloride from Legacy Fissile Materials

Between September 2009 and January 2011, the Savannah River National Laboratory (SRNL) and the Savannah River Site (SRS) HB-Line Facility designed, developed, tested, and successfully deployed a production-scale system for the distillation of sodium chloride (NaCl) and potassium chloride (KCl) from plutonium oxide (PuO₂) scrap. Subsequent efforts adapted the vacuum salt distillation (VSD) technology for the removal of chloride and fluoride from less-volatile halide salts at the same process temperature and vacuum. Calcium chloride (CaCl₂), calcium fluoride (CaF₂), and plutonium trifluoride (PuF₃) were of particular concern. To enable the use of the same operating conditions for the distillation process, SRNL employed in situ exchange reactions with alkali metal hydroxides (e.g., potassium hydroxide) to convert the less-volatile halide salts to volatile compounds that facilitated the distillation of halide without removal of plutonium. SRNL demonstrated the removal of halide from CaCl₂, CaF₂, and PuF₃ below 1000°C using VSD technology.