High temperature corrosion of the nickel-base alloy Inconel 617 in helium containing small amounts of impurities

The ANTARES program of AREVA-NP aims at developing a Very High Temperature Reactor (VHTR) system operating within the range of 1000 C degrees in indirect cycle. The corrosion behaviour of Inconel 617, candidate alloy for the heat exchanger, has been investigated in a representative helium containing impurities (CO, H2O, H2 and CH4) in the μbar range. Depending on temperature and gas composition, there is a competition between the formation of protective oxide scales and deleterious carburization or decarburization reactions. The role of each impurity on the corrosion behaviour of the alloy is evaluated in order to define an in-service benign atmosphere. The presence of 20 μbar of methane and 5 μbar of water in the test 6 shows that the alloy does not carburize and does not influence the critical temperature