Integrated experimental assessment and validation of oxidation with real-scale SiC fuel compact in HTGR

Air ingress is a critical accident in HTGR design, caused by a rupture in the coolant pipe. It leads to the oxidation of hot graphite at high temperatures, resulting in mechanical degradation of graphite structures. To address this issue, the authors propose a novel approach of substituting graphite fuel compacts with polycrystalline reaction-sintered SiC (RS-SiC) fuel compacts due to their superior oxidation resistance. The adoption of SiC based fuel compact will eliminate the graphite sleeves currently used in the pin-in-block type HTGR designs. It will also make it possible to achieve the high-power density due to the absence of graphite sleeves. There is limited understanding of the oxidation kinetics and transition behavior in RS-SiC. To address this knowledge gap, integrated experiments are conducted to investigate the thermal and oxidation behavior of SiC under varying oxygen concentrations. These experiments aim to provide insights into SiC's performance in HTGR environments using similar temperature and flow velocity conditions. Experimental data obtained will be utilized to develop a numerical model for enhanced understanding. In this study, both experimental and computational fluid dy-namics (CFD) analyses were performed to compare the temperatures obtained from simulations with experi-mental measurements. The results demonstrated good agreement between experimental and numerical data. Passive oxidation was observed in real scale SiC fuel compacts at both 900 degrees C and 1100 degrees C, with slightly lower weight gain at the higher temperature. This suggests the possibility of damage to the SiO2 oxide layer at elevated temperatures. These results are important as the experiments are done in an integrated test facility using the air ingress accident boundary conditions of HTGR with the SiC fuel compact of real scale. These experiments validate the earlier findings from thermogravimetry differential thermal analysis (TG/DTA) conducted in a smaller-scale facility. They play a role in extending our understanding of SiC oxidation behavior, thereby assisting in the advancement of HTGR designs for enhanced safety and performance.