Joining of Ceramic Composites for Nuclear Applications (18-RD-986)

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.How the Problem is AddressedThis project uses 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.What was Done in Phase IArc welding parameters were developed to weld a silicon carbide-zirconium diboride-zirconium carbide ceramic, and solidification of the weld pool was analyzed. The flexure strength of the joined ceramics were shown to be comparable to current ceramic joining technologies, like brazing. Once arc welding parameters were established, arc welding was used to join flat plates to make a monolithic channel box. Arc welding of monolithics was then transferred to composites, fusion welding of ceramic composites was demonstrated.What is Planned for Phase IIArc welding of ceramics is a relatively foreign concept. In Phase II, the understanding of what can be done and how it can be accomplished will be increased through the welding of new ceramic compositions; weld behavior analysis, such as strength and corrosion resistance; to the modelling of the ceramic arc welding process. Moreover, the development of an autonomous ceramic welding system will increase precision and reliability. Ultimately, for successful acceptance and transition, joining of composites via arc welding techniques will continue to be developed, demonstrated, and refined.Commercial Applications and Other BenefitsThe 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.