Effect of heating rate up to 300 K/min on high-temperature steam oxidation and degradation of Cr-coated Zry-4

This work focuses on the oxidation performance of chromium-coated Zircaloy cladding under varying heating rates up to 1500 °C. Zircaloy-4 tubes, 12 cm in length and coated with 15 µm PVD-Cr, were tested in the QUENCH-SR facility. Oxidation of the cladding was conducted at heating rates between 5 and 300 K/min in steam. Hydrogen production was measured simultaneously, and post-test examinations included microstructural analysis. Increasing the heating rate primarily affects the microstructure by reducing oxidation time, resulting in thinner oxide layers, a finer eutectic microstructure, and the presence of residual Cr at 300 K/min. Although accelerated oxidation occurs above the eutectic temperature and the oxidation rate increases with heating rate, the total hydrogen production decreases. Under conditions relevant to severe accidents, Cr-coated samples release less hydrogen than uncoated Zircaloy-4.