Candidate materials performance under Supercritical Water Reactor (SCWR) conditions

The High Performance Light Water Reactor (HPLWR) is working at super-critical pressure (25 MPa) and a core coolant temperature up to 500°C. As an evolutionary step this reactor type follows the development path of modern supercritical coal-fired plants. This paper reviews the results on performance of commercial candidate materials for in-core applications focusing on corrosion, stress corrosion cracking (SCC) and creep issues. General corrosion (oxidation) tests with an inlet oxygen concentration of 125-150 ppb have been performed on several iron and nickel alloys at 300 to 650°C and 25 MPa in supercritical water. Stress corrosion cracking (SCC) susceptibility of selected austenitic stainless steels and a high chromium ODS (Oxide Dispersion Strengthened) alloy were also studied in slow strain rate tests (SSRT) in supercritical water at 500°C and 650°C. Furthermore, constant load creep tests have been performed on selected austenitic steels at 500°C and 650°C in supercritical water (25 MPa, 1 ppm O2) and in an inert atmosphere (He, pressure 1 atm). Based on the materials studies, the current candidate materials for the core internals are austenitic steels with sufficient oxidation and creep resistance up to 500-550°C. High chromium austenitic steels and ODS alloys steels are considered for the fuel rod cladding due to their oxidation resistance up to 650°C. However, problems with manufacturing and joining of ODS alloys need to be solved. Alloys with high nickel content were not considered for the SCC or creep studies because of the strong effect of Ni on neutronics of the reactor core.