SiC for Nuclear Parts

Generation IV Gas-Cooled Reactors require advanced structural materials capable of resisting extreme conditions of radiation exposure, high heat flux, corrosive environments and thermo- mechanical stresses. Metallic alloys such as stainless steel and Zircaloy used in fabricating fuel assembly grids, nozzles, strainers and spacers for generation IV Gas-Cooled Reactors, run the risk of melting when exposed to high temperatures in the event of an accident such as that which occurred in Fukushima. Silicon carbide is useful in such applications because of its high melting point (2730 C), low specific weight (3.21 g/cm3), excellent mechanical strength ( & gt;600 MPa) and elastic modulus ( & gt;400 GPa), and a high thermal conductivity (490 W/m-K). Monolithic silicon carbide faces the disadvantage of being inherently brittle while SiC fiber-reinforced SiC composites have the capability to enhance the fracture toughness of the material. MMI has developed a low cost process for producing SiC nanofiber mats from preceramic polymer precursors which will be used to produce the SiC(f)-SiC composites. MMIs will use its plasma pressure compaction process to consolidate these composites to full densities. Phase I research will involve fabrication of the SiC(f)-SiC composites and testing of its thermal, mechanical and radiation resistance properties. In the Phase II effort, selective architectures will be scaled up for fabricating specific Gen IV reactor applications such as assembly grids, nozzles, strainers and spacers. We have already initiated discussions with Westinghouse who have expressed a keen interest in working with several parts for their reactors. Commercial Applications and Other Benefits: The use of SiC/SiC composites in fabricating nuclear power plant parts and equipment such as Fuel Assembly Grids, Nozzles, strainers and Spacers will improve the operational safety under conditions that may arise from an unexpected accident. Silicon Carbide composites have exceptional advantages over conventional silicon-based semiconductors and electronics and are therefore being considered for semiconductor applications. SiC composites will also find use in several high temperature structural applications used for heat treating of metals and alloys.