Corrosion and creep studies of candidate in-core materials for Generation IV supercritical water reactor

The High Performance Light Water Reactor (HPLWR) design is one of the concepts chosen for Generation IV reactors; HPLWR uses supercritical water as coolant with design reactor outlet temperature at about 500 °C. The out-of-core material choices can be conveniently adopted e.g. from conventional coal-fired supercritical power plants. However, in the core area radiation sets additional requirements for the construction materials. In addition to resistance to stress corrosion cracking, also oxidation resistance and creep resistance become important. The materials currently under study for application in the HPLWR in-core area can be divided into four categories: ferritic/martensitic steels, oxide dispersion strengthened (ODS) steels, austenitic stainless steels, and nickel-base alloys. This paper discusses the resistance to oxidation, creep and stress corrosion cracking of selected sets of these materials in the temperature range 300 to 650 °C. Based on the material studies done the present candidate materials for the core internals of the European SCWR are austenitic stainless steels, which have a good enough oxidation and creep resistance up to 500 °C or even 550 °C. High chromium austenitic steels and ferritic/martensitic ODS steels are considered, in long term, for the fuel rod cladding because of their good oxidation resistance up to 650 °C.