Joining of Ceramic Composites for Nuclear Applications

Ceramic matrix composites, or composites, allow for higher operating temperatures in nuclear reactors and provide improved accident tolerance. However, composites cannot be processed like metals and require joining techniques like brazing to obtain complex three dimensional shapes. Brazing is not the ideal solution, as brazed joint material may not be chemically stable, hermetic, or neutron irradiation tolerant when compared to the base composite material. For example, preferential oxidation can occur due to the lower chemical stability of some brazed joints, resulting in a compromised composite structure. This project will use commercially available arc welding technologies for the joining of silicon carbide based ceramics. Arc welding allows the application of heat at the joint, eliminating the need for large furnaces to heat the entire component being manufactured and joined. Sub- components can be fabricated and joined to form complex three dimensional composite components for next generation nuclear applications. Arc welding parameters will be developed to weld silicon carbide-zirconium diboride-zirconium carbide ceramics. Solidification of the three component weld pool will aid in hindering grain growth compared to two component systems. The shear and flexure strength of the joined materials will be compared with the parent material (not joined), guiding optimization of arc welding parameters and technique. Hardness of the parent material and heat affected zone will also be evaluated to determine the effects of arc welding on the parent material near the fusion zone. Commercial Applications and Other Benefits The high temperature tolerance of ceramic matrix composites could allow power upgrades in commercial reactors of as much as 30%, increasing the capacity of existing plants and saving ~$240 million over the lifetime of a plant. An economical, field-deployable welding method will enable robust joining technology that can be widely deployed for the fabrication of complex, three dimensional, silicon carbide based composites for use in Gen IV nuclear reactors.