Selection and corrosion evaluation tests of candidate SCWR fuel cladding materials

Supercritical water cooled reactor (SCWR) is a promising Gen IV high performance reactor which can be developed for future large capacity electric power plants. However, the material selection for fuel cladding still remains one of the key issues. For a typical prototype SCWR design with outlet coolant temperature of 510 °C and pressure of 25 MPa, the hot spot temperature on fuel cladding exceeds 600 °C at normal operation conditions, and will be much higher during transients. Materials for fuel cladding should have good mechanical properties to meet the harsh working conditions in order to keep the integrity of fuel rod under normal and abnormal operational conditions, while corrosion in supercritical water and neutron irradiation damage will not lead to significant loss of strength and ductility, or lead to unacceptable deformation during service life. Materials for ultra-supercritical fossil fire plants, fast breeder reactor and jet air engines etc., are proposed as the candidate materials for SCWR fuel cladding. This paper reports the results based on corrosion screening tests of candidate materials exposed in supercritical water up to 650 °C. Results show that their corrosion rates increase significantly with the increase of temperature, and the protective oxide films of most candidate materials turn to be unstable above temperature of 600 °C. According to the present knowledge available, austenitic stainless steels with high Cr concentration show better performance and are more potential to be the references for developing the SCWR fuel cladding material.

► General technical requirements of fuel cladding materials for SCWR are proposed.
► We report corrosion behaviors of candidate cladding materials in supercritical water up to 650 °C.
► Corrosion rate of ferritic/martensitic steels is too high to meet the requirements.
► Austenitic stainless steels with high Cr or Al content show very low corrosion rate.
► Addition of alloy elements to maintain the protective oxide film is important.