Concentration of Cesium and Strontium Elements Involved in a LiCl Waste Salt by a Melt Crystallization Process

As an alternative to conventional Group I and II separation methods (such as adding a chemical agent and ion exchange), melt crystallization processes, zone freezing, and layer melt crystallization were tested for the separation (or concentration) of cesium and strontium fission products in a LiCl waste salt generated from an electrolytic reduction process of a spent oxide fuel. In these melt crystallization processes, impurities (CsCl and SrCl₂) are concentrated in a small fraction of the LiCl salt by the solubility difference between the melt phase and the crystal phase. As experimental variables, initial molten salt temperature, crucible rising velocity in the zone freezing case, and cooling air flow rate in the layer crystallization case were used. In the zone freezing process, although the operating time is long (1.7 mm/h of crucible rising velocity) when assuming a LiCl salt reuse rate of 90 wt%, >90% separation efficiency for both CsCl and SrCl₂ was shown. In the layer crystallization process, the crystal growth rate strongly affects the crystal structure and therefore the separation efficiency. At a 25 to 30 [script l]/min cooling air flow rate, 700 to 710°C initial molten salt temperature, and <5 g/min crystal growth rate, the separation efficiency of both CsCl and SrCl₂ exceeded 90% by the layer crystallization process, assuming a LiCl salt reuse rate of 90 wt%.