<br/>Molten fluoride salts can serve as a fuel medium or heat-transfer fluid in molten salt reactors. The tendency of a molten salt to oxidize containment materials can be mitigated through initial purification of the salt via the hydrofluorination process, which involves sparging the molten fluoride salt with a combination of hydrogen and anhydrous hydrogen fluoride gases. Due to its toxicity, anhydrous hydrogen fluoride must be carefully handled and stored, which makes the hydrofluorination process challenging to implement and often cost-prohibitive for small-scale purification. Solid sodium bifluoride produces hydrogen fluoride gas and solid sodium fluoride upon heating and as such can be used as a controllable source of hydrogen fluoride for salt purification. The kinetics of hydrogen fluoride production from the thermal degradation of sodium bifluoride has been studied as a function of temperature and salt-layering depth and this analysis has been used to design a novel HF-production vessel. The salt depth and temperature are optimized to release hydrogen fluoride at a rate that is most efficient for downstream salt purification without compromising the salt purification vessel or sparger integrity. The HF-production vessel can be loaded with sodium bifluoride at specified layering depths and heated to release hydrogen fluoride to be subsequently mixed with hydrogen gas and sparged through a molten eutectic mixture of sodium, lithium and potassium fluoride (FLiNaK). This purification strategy will be compared to a traditional hydrofluorination process (using anhydrous hydrogen fluoride) with the purified salt from each treatment being analyzed by inductively-coupled plasma mass spectrometry.

Sodium bifluoride as a hydrogen fluoride source for hydrofluorination of molten fluoride salts

ACS Fall 2021

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