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 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, they do not provide enough protection. Hence, there is a need for developing surface protection interface that will inhibit corrosion. The Department of Energy seeks novel solutions for advanced nuclear reactors, including high temperature Molten Salt Reactors (MSRs) and molten metal reactors (MMRs). Presently, weld overlay cladding, roll bonding etc. are used but do not provide extended life span. In this phase II STTR, we propose the usage of bimetallic RHEAs, in the form of thick surface layers with proper pre- and post-processing, that can provide long-term corrosion and wear protection for liquid-cooled, high-temperature reactor components. In this Phase I STTR, we focused on the development of corrosion resistant RHEA thick coatings by using plasma spray technique. The selected RHEAs, formed from refractory elements, such as niobium, chromium, tungsten, vanadium, and Tantalum, were synthesized in powder form suitable as feedstock for a thermal spray coating. The coated substrates were subsequently characterized and validated experimentally for their corrosion resistance, structural strength, and mechanical properties. In Phase I program, we successfully demonstrated the reduction of corrosion at elevated temperature under MSR conditions at Sandia National Lab test facility. In Phase II, we will focus on the further development of the RHEA thick layer, its corrosion barrier characteristics, post processing treatments and component level testing. DRS will refine and optimize the process development to apply the APS, HVOF and cold spray techniques to deposit robust, highly adhesive thick RHEA coatings. 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. Component testing with industry & research partners such as Flibe Energy, NGC and AFRL will further validate the application of RHEA coatings on actual components.