Abstract
Advanced ceramics and ceramic matrix composite assemblies based on silicon carbide (SiC) are being considered as candidate material systems for nuclear fuel cladding in light water reactors (LWRs). This is due to the high strength, high thermal conductivity, and low chemical reactivity at high temperatures that SiC offers compared to traditionally used zirconium alloys such as zircaloy. Based on these properties, it is expected that SiC composite assemblies could act as nuclear fuel cladding which would remain intact and safe during and after long periods of time at very high temperatures, such as what is seen in loss-of-cooling accident (LOCA) events at nuclear reactors or spent fuel pools. Additionally, the low chemical reactivity of SiC also prevents oxidizing reactions that break down water molecules into explosive free hydrogen gas, and that embrittle tubes (such as the formation of zirconium oxide in zirconium alloys).
The specific structures of interest consist of a monolithic SiC cylinder surrounded by carbon-coated SiC fibers woven into a tubular form and infiltrated (by chemical vapor deposition) with SiC. Additional SiC coatings on the outermost surface of the assembly are also being considered to prevent hydrothermal corrosion of the fibrous structure . The inner monolithic cylinder is expected to provide a hermetic seal to contain the fuel pellets and fission products. The composite structure is expected to display high strength, stiffness, and toughness as the ceramic matrix transfers stress to the fibers, while the carbon interface layer on the fibers provides a mechanism for crack deflection to enable a graceful mode of failure.