Refractory Composites for Reactor Applications (PSI-7266-290)

Next generation nuclear reactor cores will operate at temperatures near 1000ºC to increase fuel utilization efficiency. However, the Martensitic steels, which are traditionally used in reactor construction, and the Alloy 800H, planned for the Next Generation Nuclear Plant demonstrator, do not possess the mechanical strength or oxidation resistance to reliably and safely function in systems that operate at these temperatures. Carbon-carbon and silicon carbide ceramic composite structural materials, now under consideration for in-core structural applications, have high strength at high temperature, but do not perform well under off-normal high temperature (emergency) oxidation conditions. In this project, fiber-reinforced ceramic composites will be modified with refractory metals to substantially increase their oxidation resistance and retain high temperature strength. Phase I demonstrated carbon-fiber-reinforced refractory-enhanced silicon carbide composites that retained strength of more than 140 MPa after rapid oxidation at 1000ºC. The helium erosion resistance of the composites was comparable to state-of-the-art SiC/SiC materials, and the composites retained thermal conductivities in excess of 10 W/m-K. In Phase II, post oxidation strength will be increased to more than 140 MPa, and thermal conductivity will be maintained at 10 W/m-K, after helium aging at 1000°C for up to 3000 hours. The composite fabrication process will be scaled up to demonstrate that successful compositions can be fabricated with properties that vary by no more than 10%. Prototype control rod guides and sheaths, fabricated from the best compositions, will be the deliverable. Commercial Applications and Other Benefits as described by the awardee: High temperature, oxidation resistant refractory composites should enable the full-scale commercialization of Next Generation Nuclear Plants. Additional commercial applications include ducting for high temperature exhaust systems, including catalytic converters and incinerators; high temperature catalytic converters for diesel engine systems, which would reduce particulate emissions and help maintain clean air standards; and high temperature exhaust ducting in incinerators, which would allow more complete combustion of waste products and minimize toxic emissions.