Molten fluoride salts are considered as coolants and fuel solvents for use in Gen IV nuclear reactors. However, progress of molten salt reactor technology relies heavily on materials issues related to corrosion of salt-facing components. Molten salts degrade alloys by preferential attack on the less-noble alloying elements such as Mn, Cr, Fe. To minimize the corrosion issues in molten fluoride environments, salt purification is extremely important. The most common purification method for fluoride salts has been the fluorination by a mixture of hydrogen fluoride (HF) and hydrogen. However, due to safety concerns involving the use of HF and its relatively sluggish fluorination thermodynamics, other purification approaches are being investigated. In the present work, we purified LiF-NaF-KF (FLiNaK) salt with NF3 as the fluorinating agent and compared its effectiveness to the conventional HF/H2 purification. As an ultimate test of salt purity, 316H stainless steel coupons were exposed in molten FLiNaK salts purified by both NF3 and HF approaches. To assess the effectiveness of each purification method, the results of these corrosion experiments as well as salt characterizations will be presented.

Use of nitrogen trifluoride (NF3) to purify fluoride salts

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ACS Fall 2022

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