HIGH-TEMPERATURE STEAM OXIDATION KINETICS AND MECHANISM OF SCWR FUEL CLADDING CANDIDATE MATERIALS

Effects of temperature, dissolved oxygen (DO), and degree of cold work (CW) on the oxidation kinetics of supercritical-water-cooled reactor (SCWR) fuel cladding candidate materials, including three types of 15Cr-20Ni austenitic stainless steels (1520 SSs), in superheated steam have been investigated assuming power-law kinetics. Characteristics of oxide layers and its relation to oxidation behaviors are also discussed. The effect of DO on the weight .gain behavior in superheated steam at 700 degrees C was minor for all specimens at least up to 200 ppb DO. The tube-shaped specimens of 1520 SSs showed very good oxidation resistance at 700-780 degrees C. There was no clear difference in the oxidation kinetics among the three investigated types of 1520 SSs. The degree of CW is a significant parameter to mitigate oxidation in superheated steam. It has been suggested that the tube specimens showed a very slow oxidation kinetics since Cr diffusion in the outside surface of the tubes is accelerated as a result of an increase of dislocation density and/or grain refinement by a high degree of CW.