Several Generation IV nuclear reactor concepts feature molten fluoride salt coolants. Selecting these coolants over superheated water or high temperature inert gases obviates the need for high pressure containment and promises passive safety for lower cost. However, corrosion of structural alloys in molten fluorides remains a challenge. Due to the solubility of oxides in the molten fluoride, oxide films cannot be relied upon to retard corrosion of structural alloys. Therefore, corrosion is most dependent on the alloy composition and salt chemistry, as found by previous studies. To better understand these factors, static exposure tests of nickel-based alloys UNS N10003, UNS N10244, UNS N06230, and austenitic stainless steels UNS S31603, UNS S30403, UNS S34700, and UNS S32100 were conducted in the molten fluoride salt known as FLiNaK. Pure elements Ni, Mo, Fe, and Cr were also tested for comparison. Lower alloy Cr content was associated with better corrosion performance in the FLiNaK environment. Low carbon versions of austenitic stainless steels experienced severe grain boundary attack, whereas Ti or Nb stabilized versions experienced mild grain boundary attack.

Subject
Scanning electron microscopy, Energy dispersive X-ray spectroscopy, Corrosion resistant alloys, Stainless alloys, Salts, Fluorides, Nickel based alloys, Molybdenum alloys, Corrosion attacks, Corrosion resistance, Stainless steel, Grain boundary, Voids
Keywords:
MSR, FHR, molten salt, UNS N10003, molten fluoride, FLiNaK
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2017
Association for Materials Protection and Performance (AMPP)
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