Safety Assessment of SiC Cladding Oxidation Under Loss-of-Coolant Accident Conditions in Light Water Reactors

An experimental assessment was conducted of the silicon carbide (SiC) cladding oxidation rate in steam under conditions that are representative of loss-of-coolant accidents in light water reactors (LWRs). SiC oxidation tests were performed with monolithic alpha-phase tubular samples at atmospheric pressure for steam temperatures of 1140°C and 1500°C and a Reynolds number range of 40 to 330. Linear weight loss of SiC samples due to boundary layer controlled reaction of silica scale (SiO₂ volatilization) was experimentally observed. The weight loss rate increased with increasing steam flow rate and temperature. Over the range of test conditions, SiC oxidation rates were shown to be about three orders of magnitude lower than the oxidation rates of Zircaloy-4. This underlines a weaker interplay between oxidation and mechanical property degradation in comparison with Zircaloy. SiC volatilization correlations for developing laminar flow in a vertical channel were formulated for LWR accident modeling.