Corrosion-resistant cladding strategies for molten salt reactor components: Ni-based alloys and laser cladding on 316H stainless steel

초록

Structural materials remain a central obstacle to molten salt reactor (MSR) deployment. Hastelloy N, the historical reference alloy for fluoride-salt service, does not have an established Class A design basis under ASME Section III, Division 5, whereas industrially available 316H stainless steel does within the applicable limits but suffers chromium dealloying in halide melts. This mini review examines a bimetallic strategy in which 316H provides the structural function and a thin, corrosion-resistant, Ni-based clad protects salt-wetted surfaces. We summarize corrosion mechanisms in fluoride and chloride salts and compare candidate materials in terms of corrosion performance and the availability of a Division 5 Class A design basis and integrate evidence from three areas: (i) immersion tests showing that electroplated Ni protects 316H in FLiNaK and that deposited Ni clads outperform bare 316H in a molten chloride salt, (ii) weld-overlay and laser-directed-energy-deposition studies defining dilution windows, and (iii) a draft ASME Code Case-compatible design methodology for clad Class A components. Available evidence indicates that clad performance is specific to salt chemistry and operating conditions: electroplated Ni protects 316H in FLiNaK, while weld- and laser-deposited Ni clads outperform bare 316H in NaCl-MgCl2; however, wrought Ni-200 degrades severely in a separate chloride screening. Candidate clads must therefore be validated under the target salt chemistry and operating conditions. We conclude by identifying the main industrialization gaps: irradiation response of clad layers and diluted interfaces, volumetric inspection of anisotropic clad structures, joining at field welds, thermal-expansion mismatch, and specialty-alloy supply chains.

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