effect of intergranular carbides in the oxidation and stress corrosion behavior of alloy 690 in supercritical water

The nickel base alloy 690, which was designed as a replacement for the nickel base alloy 600, is a material widely used in the nuclear industry due to its optimum behavior to stress corrosion cracking (SCC) under nuclear reactor operating conditions. Because of this superior resistance to some degenerative processes, the alloy 690 has been proposed as a candidate structural material for the Supercritical Water Reactor (SCWR), which is one of the designs of the next generation of nuclear power plants (Gen IV). The presence of intergranular carbides in the alloy 690 plays an important role in the resistance of this alloy to SCC in caustic environments. In spite of this improvement, the mechanism behind it is not yet understood. In addition to this, Arioka et al. observed higher resistance to SCC in specimens without intergranular carbides. Therefore the role of the intergranular carbides in the A690 is still an open question. Considering these results, the aim of this work is to study the oxidation and stress corrosion behavior of alloy 690 with and without intergranular carbides in deareated supercritical water (SCW) at 400 ºC and 500 ºC at 25 MPa in order to gain some insight into the understanding of the effect of these carbides in the resistance of this material. In this presentation preliminary results of an on-going work will be presented