Enhanced Lifetime of SiC-SiC Joints

The Department of Energy seeks state-of-the-art methods and processes to improve the design and fabrication methods used to join SiC-SiC composites within Generation IV liquid fluoride salt-cooled reactors. These new methods must improve the system durability while reducing cost and providing compatibility for use as a fuel cladding. The inherent corrosion and durability challenges that results with the adoption of Molten Salt Reactor systems lies within the high operation temperatures ≤850°C), the use of molten fluoride salts as the coolant, and the potential to be exposure to high pressure steam. These anticipated operating conditions directly influence the future design of bonding techniques utilized in SiC joints and will require the development of processes that improve the functionality of materials used within these systems such that they can supersede existing standard codes for durability and lifetime during operation. Therefore, state of the art molten salt reactors require validation and testing of new SiC-SiC material joining systems that can enhance component structures robustness and enable them to withstand these corrosive environments. The overall objective of the Phase I and II programs is to develop and demonstrate a low-cost technique to locally apply corrosion resistant coatings on the SiC-SiC end-plug joint used within Molten Salt Nuclear Reactor, such that the corrosion resistance and lifetime of components can be enhanced. Additionally, we will evaluate the effectiveness of combining standard brazing fillers with newly developed electrodeposited coatings that can be locally applied to the joint and improve bonding and corrosion resistance during state-of-the-art molten fluoride salt test. Phase I will demonstrate the potential to braze SiC end-plugs to SiC tubes, then apply a NiMo coating to the metallic braze joint line by utilizing a state-of-the-art no-drip brush electroplating process, and then validate the material’s corrosion performance within a molten fluoride salt environment. The braze and brush plating preparation procedures will be optimized to improve environmental resistance by evaluating the mechanical and thermal expansion properties of the joint after each trial. After optimization, a limited number of the best joints will be produced for corrosion evaluation using a state-of-the-art molten fluoride salt reactor. A preliminary economic and scalability assessment will ensure the cost effectiveness of the approach. In Phase II, the brazing and brush plating processes will be scaled to prepare full size SiC end plugs for beta scale mechanical and performance testing. This approach could be used to apply low cost high value corrosion resistant coatings to the metallic braze joint used to bind the SiC end-plug and the tubes SiC materials used in nuclear reactors. These coatings could provide a low-cost solution that could locally improve the environmental resistance of this system when subjected to molten fluoride salts or high- pressure steam. This approach could also be used on metallic braze joints in other systems like concentrated solar cell systems, supercritical carbon dioxide systems, and many others.