Freeze-casting SiC-SiC Composites

Silicon carbide fiber-reinforced silicon carbide composites SiC/SiC) have become a leading candidate material in Generation IV reactor designs, due to predicted favorable corrosion and radiation tolerance over legacy metal alloy materials. However, the material is very expensive and challenging to produce to the required design allowables, and performance data under realistic operating conditions is limited. Liquid fluoride salt and liquid lead-cooled reactor designs offer high levels of efficiency and inherent safety since they operate at near ambient pressure, in comparison to the current fleet of water-cooled reactors. A major technology gap exists with the primary coolant pumping components that can withstand the harsh corrosive and erosive conditions within the core, as these components are some of the least mature parts of the design. Adoption and qualification of SiC-SiC materials by reactor designers can offer a solution to this technology gap, but significant advances in lowering the material availability costs are required. Stoichiometric SiC fibers are very costly, and the further matrix formation and densification steps using chemical vapor infiltration is prohibitively expensive and presents scalability issues. MillenniTEK proposes to produce a SiC-SiC composite material using a unique freeze-casting process to create a unique preform microstructure that can be densified at low-cost using melt infiltration. Further, a SiC coating process to limit free silicon exposure to the molten coolants will be investigated and characterized. This new SiC-SiC composite can be produced by an inexpensive synthesis process that can produce material exhibiting an attractive combination of high thermal conductivity, excellent thermomechanical stability, and corrosion resistance. Irradiation resistance is unknown, but published research into related system compounds shows promising tolerance to the high neutron fluence environments of the GEN IV reactor designs. During the project, MillenniTEK will initially produce representative material samples using this process and collaborate with Virginia Tech researchers to characterize the corrosion and erosion resistance in both high temperature liquid fluoride salt and liquid lead. After the initial material studies are completed, a complex geometry primary coolant pump impeller and pipe section will be fabricated and tested in the flowing coolants for extended performance. This data, along with the inclusion of a major nuclear reactor plant designer in this project seek to shorten the timeframe to qualify this SiC-SiC material for this application. In addition to the nuclear applications supporting development of this new class of material, there are other significant potential areas where the material could be commercialized including high temperature, oxidation-resistant composites for aerospace, defense, and industrial applications.