Abstract
Molten fluorides of alkali metals are considered a technological medium for molten salt reactors (MSRs). However, these media are known to be extremely corrosive. The successful implementation of high-temperature technological devices using molten alkali metal fluorides requires the selection of such structural materials that have high corrosion resistance in melts with compositional characteristic of MSRs. In this research, the corrosion behavior of 12Cr18Ni10Ti steel, the alloy Ni60Cr20Mo15, and the alloy Monel 404 (Ni50Cu50) was investigated in the LiF–NaF–KF eutectic melt, containing additions of CeF3 and NdF3 from 0 to 5 wt.% as imitator fluorides of actinides in an inert argon atmosphere at 550 °C for 100 h. Gravimetry, energy-dispersive X-ray (EDX) microanalysis of surfaces and cross-section of samples, and ICP-MS were used to establish the corrosion behavior of the investigated alloys. Corrosion resistance of the studied materials was found to decrease in a row from Monel 404 > Hastelloy C2000 > 12Cr18Ni10Ti. The addition of cerium fluoride into the melt resulted in the additional etching of the alloy surface. The addition of neodymium fluoride resulted in the formation of the point/inter-crystalline corrosion damages in the sample bulk. The samples of steel 12Cr18Ni10Ti were subjected to local cracking corrosion. The austenitic nickel-based alloys suffered specific local corrosion with formation of subsurface voids. Excellent corrosion resistance of the Monel alloy under the test conditions was found.
Highlights
Molten alkali metal halogenides are promising coolants, allowing for the expansion of the operating temperature range of power plants by hundreds of degrees, including nuclear reactors, to ensure efficient heat transfer from the hot zones of high-temperature devices.Due to the thermal and radiation resistance in the temperature range from the melting point to the boiling point, halogenides compare favorably with water and organic heat carriers
Corrosion resistance of the studied materials was found to decrease in a row from Monel 404 > Hastelloy C2000 > 12Cr18Ni10Ti
The addition of neodymium fluoride resulted in the formation of the point/inter-crystalline corrosion damages in the sample bulk
Summary
Molten alkali metal halogenides are promising coolants, allowing for the expansion of the operating temperature range of power plants by hundreds of degrees, including nuclear reactors, to ensure efficient heat transfer from the hot zones of high-temperature devices.Due to the thermal and radiation resistance in the temperature range from the melting point to the boiling point, halogenides compare favorably with water and organic heat carriers. Molten alkali metal halogenides are promising coolants, allowing for the expansion of the operating temperature range of power plants by hundreds of degrees, including nuclear reactors, to ensure efficient heat transfer from the hot zones of high-temperature devices. For example, in the case of damage or destruction to the pipeline or to the housing of the heat transfer device, they do not form explosive gas mixtures when interacting with water or a humid atmosphere. These properties, as well as basic thermophysical characteristics, make molten fluorides and chlorides of alkali metals attractive and competitive coolants, components of fuel mixtures, and regenerative media of new-generation nuclear reactors. The significant aggressive action of alkali metal halide melts requires selection of resistant materials, development of methods of corrosion protection in molten salts, a detailed study of corrosion behavior, and the mechanism of destruction of materials
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