Bimetallic Refractory High-Entropy Thick Alloy Coatings for Corrosion-Resistant Liquid-Cooled High-Temperature Reactor Components

Advanced high temperature nuclear reactors such as liquid salt cooled reactors (fixed fuel or dissolved fuel) and lead-bismuth cooled reactors, experience serious corrosion problems. Although the structural components are made out of corrosion resistant steels such as SS 316 or 800H alloys, (per ASME Section III Division 5 guidance), they do not provide enough protection. Hence, there is a need for developing surface protection interface that will inhibit corrosion. The Department of Energy (DOE) seeks novel solutions for advanced nuclear reactors, including high temperature Molten Salt Reactors (MSRs) and molten metal reactors (MMRs). The innovative MSR designs include chloride- and fluoride-based molten salt reactors. Consequently, the materials used in the structural components of the reactor primary loop where the molten salt circulates must not only be corrosion-resistant but must also be compatible with the reactor components. Presently, weld overlay cladding, roll bonding etc. are used but do not provide extended life span. In this phase I STTR, we propose that the usage of bimetallic RHEAs, in the form of thick surface layers with proper pre- and post-processing, can provide long-term corrosion resistance for liquid-cooled, high-temperature reactor components. In this Phase I STTR, we propose to develop novel, thick-surface layer processes and components based on proven, bimetallic corrosion-resistant refractory high-entropy alloys (RHEAs) coatings with enhanced corrosion and wear protection. The proposed thermal spray process has the capability to provide highly bonded thick coatings that are resistant to peeling, spalling, scratching, and debonding etc. We are focusing on the development of corrosion resistant RHEA thick coatings to protect the high temperature reactor components by using plasma spray and HVOF techniques. The selected RHEAs, formed from well-known, reactor-compatible elements, such as hafnium, zirconium, niobium, chromium, rhenium, vanadium, and molybdenum, will be synthesized in bulk and powder form suitable as feedstock for a thermal spray coating (Air Plasma Spray and High Velocity Oxygen Fuel), as well as solid components using spark plasma sintering. The coated substrates will subsequently be characterized and validated experimentally for their corrosion resistance, structural strength and mechanical properties. Thick bimetallic RHEA coatings will provide significant near- and long-term corrosion & oxidation solutions along with high temperature capability for reactors; and fortunately, these solutions also serve other advanced reactors designs, high-efficiency power conversion units (e.g., liquid cooled reactors, CO2 Recompression Closed Brayton Cycles), high-temperature combustion cycles (e.g., Allam Cycles), concentrated solar power, and aerospace applications. The benefits of this endeavor will result in reactors that operate at increasingly higher temperatures, for improved power-generating performance, reduced maintenance cost, and lower CO2 footprint. In addition, by leveraging recent SNL patents and recent advances at DRS and SNL, we will demonstrate low-cost, near-term solutions for high-temperature applications. In particular, we will validate the application of various bimetallic RHEA compositions for industrial-grade nuclear reactor applications within two years. These advantages will inevitably result in more favorable economics for the RHEA-based SMRs and provide tremendous marketing opportunities at the domestic and international level.