Multi-scale characterization of the inner surface of as-received steam generator tubes and correlation with the Ni release in primary water

Abstract

The inner surface of two as-received steam generator (SG) tubes made of nickel base alloy 690 was analyzed to explain the differences in nickel release obtained for the tubes in a loop simulating the primary environment of pressurized water reactors. The roughness, microstructure and chemical heterogeneities were characterized; differences that could explain the specific behavior of the two tubes in primary water were noted. In particular, the presence of alumina particles at the surface of SG tubes influences the nickel release: their dissolution in the primary coolant induces a change in roughness and a local breakdown of the passive film.