High temperature oxidation and microstructural evolution of SiC layer of TRISO particles in the presence of NaCl

Abstract

With the different types of advanced nuclear fission reactors, the reliability of the SiC layer in tristructural-isotropic (TRISO) particles exposed to different corrosive environments is of vital important. In the present work, the oxidation behaviors of the SiC layer of TRISO particles exposed in NaCl salts with the concentrations of 0.2–2 wt% at 800–1400 °C were investigated. The effects of NaCl concentration and oxidation temperature on phase composition, microstructure, and chemical composition of the TRISO particle samples were systematically investigated. The results show that, with the increase of oxidation temperature and NaCl concentration, the oxidation rate of SiC layer in TRISO particles was accelerated. However, the effect of NaCl concentration alone on the oxidation rate of SiC layer was not significant. This could be attributed to the volatility of NaCl at high temperature. In addition, just like other halogen salts, NaCl salts also reacted with the oxide layer to form silicate compounds, such as Na2SiO3, which provided a channel for both oxygen and fluoride ions to diffuse into the inner SiC layer. The results obtained in the present work can provide a guide for the application of TRISO particles in molten salt stacks of chlorine salt.