The PI has access to 6 irradiated samples obtained from SiC-SiC composites irradiated (1.0-1.5 dpa) inside the MITR reactor in PWR conditions. Across the 6 samples, 2 different chemical vapor deposition (CVD) SiC microstructures were irradiated. Two samples from the cladding wall and a cross section of an endcap joint will be extracted from a representative specimen for each microstructure. These samples will then be packaged and shipped to Pacific Northwest National Laboratory (PNNL) and Center for Advanced Energy Studies (CAES) for advanced microscopy investigations. The proposed work will complement the ongoing PIE of the samples including mechanical testing, thermal-physical properties, and other microstructural investigations such as XRD and XCT being conducted at, and being funded by, GA-EMS. Characterization at GA-EMS will capture the macro-scale property changes in the SiC-SiC composites after irradiation such as the hoop strength of material. GA-EMS has the pre-irradiation mechanical data to evaluate the change in properties after irradiation. The proposed advanced microscopic characterization of irradiated SiC-SiC composites utilizing techniques as EBSD, TEM and APT will enable a deeper understanding of the mechanisms driving the observed property changes.

This data would be used to better understand grain and microstructure effects on SiC corrosion response especially if highly localized attack along grain boundaries is observed deeper into the composite from the TEM and APT investigations. The characterization of these specimens will advance the goals of the Department of Energy-Office of Nuclear Energy by advancing SiC composite technology supporting the continued operation of existing United States LWR fleet, enabling the deployment of advanced nuclear reactors and fuel cycles, and maintaining US leadership in nuclear energy technology.

This proposal seeks to utilize the advanced microscopy characterization techniques at NSUF facilities (Pacific Northwest National Laboratory and Center for Advanced Energy Studies) to investigate the corrosion behavior and irradiation damage of SiC-SiC composites irradiated in typical PWR conditions. Data collected from this work will be impactful and help to advance the knowledge of microstructure influences on the corrosion in SiC-SiC composites for in-core performance. The proposed work aims to used advanced microstructure investigations to evaluate the influence of grain boundary corrosion in neutron irradiated SiC-SiC composites and relate those effects on macro-scale changes in SiC-SiC composite properties. The produced data can be used to modify SiC-SiC fabrication approaches for improved performance in LWRs for accident tolerance and high burn up as well as other advanced reactors. Further, the results would supplement the knowledge of the corrosion behavior of SiC-SiC composites, improving the ability to have predictive modeling in the MARMOT-BISON-MOOSE framework (currently being performed at GA-EMS).