Corrosion of intermediate VHTR heat exchanger alloys: Achievements of the US-France I-NERI program

A concerted 3-year R&D program has been completed in France and in the US on materials for heat exchangers of next generation nuclear gas-cooled reactors. The scope was to gain data on the mechanical and corrosion behavior of candidate heat exchanger alloys in the range of service conditions expected for a Very High Temperature Reactor (VHTR), specifically the temperature, the load and cycling, and the chemical environment. As far as corrosion was concerned, the main objectives of the program were to compare the performances of materials and to improve the understanding of their properties. Oxidation, carburization and decarburization modes were evidenced depending on the coolant impurity content. A special emphasis was placed on the consequences of corrosion on alloy properties: microstructure, ductility, tensile strength. Next step will involve the study of the environmental effect on fatigue and creep-fatigue life. This paper presents the main achievements on corrosion of the R&D program.