High-temperature stability of SiO2 oxide film on surface of SiC

SiC, which is a promising accident-tolerant fuel cladding, is a non-oxide, and it is known that passive oxidation occurs, where by a protective oxide film of SiO2 is formed under atmospheric conditions above 900°C. The reaction occurring at this high temperature is important in assessing the soundness of SiC during a severe accident, but the understanding of it is still insufficient. In this study, to evaluate the high-temperature oxidation behavior when SiC cladding is exposed to the atmosphere( 105 Pa) during an accident involving a light-water reactor, an oxidation test was performed for up to 100 h at 1100 to 1500°C. As a result, a SiO2 oxide film was formed on the surface of SiC, but the formation of bubbles originating from impurities and cracks due to a phase transformation was confirmed. In addition, it was observed, for the first time in this research, that a multilayered SiO2 oxide film was formed at 1500°C. Therefore, it was shown that the oxidation reaction of SiC does not stop depending on the surrounding conditions under high temperature and atmospheric conditions. © 2019 Atomic Energy Society of Japan, All Rights Reserved.