Corrosion of Structural Alloys in High-Temperature Molten Fluoride Salts for Applications in Molten Salt Reactors

Abstract

Hastelloy N Ò , a nickel-based alloy, and 316 stainless steel are among the candidate structural materials being considered for the construction of the molten salt reactor (MSR). Most of the proposed MSR concepts use molten fluoride salts as coolant which can be quite corrosive to structural alloys. The results of studies on the corrosion behavior of the two alloys in molten Li 2 BeF 4 (FLiBe) salt at 700°C are discussed. This salt is being considered as the primary coolant for MSR designs featuring solid fuel particles, but the reported results also provide insights into the corrosion in MSR designs where the uranium fuel is dissolved in the molten fluoride salt. Corrosion was observed to occur predominantly by de-alloying of Cr from the alloy surface and into the molten salt, with more pronounced attack occurring along the grain boundaries than in the bulk grains. The magnitude and the mechanisms of corrosion were different for corrosion tests performed in graphite and metallic capsules, a result warranting recognition given the coexistence of structural alloys and graphite in the molten salt medium in the MSR.

Re‐establishing the paradigm for evaluating halide salt compatibility to study commercial chloride salts at 600°C–800°C

“…If there is any question if Equation is applicable and linear extrapolations are incorrect, time series experiments show decreasing mass change or rate with increasing exposure time as the salt becomes saturated . By the same understanding, the decrease in the mass loss with decreasing temperature in Figure b may be attributed to a decrease in the Cr solubility with temperature and the small Cr depletion at 700°C should not be interpreted as proof of compatibility.…”

Enabling chloride salts for thermal energy storage: implications of salt purity

“…[1][2][3][4][5][6][7] Mixed molten salts have high heat-capacity, are chemically stable at elevated temperatures, and exhibit a tailorable melting point through compositional changes. A large body of work has been performed on uoride, nitrate, and carbonate salt mixtures, such as lithium beryllium uoride (FLiBe), [8][9][10][11] sodium potassium nitrate (NaNO 3 -KNO 3 ), 7,[12][13][14] lithium potassium carbonate (LiKCO 3 ), 15,16 and many others. [17][18][19] Chloride-based salt mixtures have several advantages over nitrates, carbonates, and uorides.…”

Corrosion and Thermal Stability of CrMnFeNi High Entropy Alloy in Molten FLiBe Salt

“…Corrosion resistance of alloys in light water reactors (LWRs) and more generally in oxidative environments is achieved by the formation of protective oxide layers that hinder further oxidation. Alloys containing Cr, Al, or Si typically tend to form a compact and self-healing chromia (Cr 2 O 3 ), alumina (Al 2 O 3 ) or silica (SiO 2 ) layers, respectively, which acts as effective diffusion barriers against further oxidation 1–3 . However, in molten fluoride salts (salt of choice for many molten salt reactor concepts, MSRs) these protective oxide layers on structural alloys are unstable which in turn leads to the dissolution of the least noble element in the alloy.…”

“…However, in molten fluoride salts (salt of choice for many molten salt reactor concepts, MSRs) these protective oxide layers on structural alloys are unstable which in turn leads to the dissolution of the least noble element in the alloy. Such a corrosion mechanism can lead to a reduction in components’ wall thickness and eventually the loss of the structural integrity of the reactor components 1,2 . The dissolution products themselves may lead to plate-out in the relatively cooler sections of the system due to the strong sensitivity of solubility of analytes to temperature.…”