Study of the oxide layer formed on the alloy 182 in a simulated pressurized water reactor environment

The alloy 182 is a nickel-base alloy commonly applied as weld in Pressurized Water Reactor (PWR). The corrosion behavior of this alloy is a crucial matter due to economic and safety reasons. The present work describes a study of the oxide layer formed on the alloy 182 before and after exposure in simulated PWR environment by X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM) equipped with an Energy Dispersive Spectroscopy (EDS), and Atomic Force Microscopy (AFM). Samples with two different surfaces treatment - with the surface mechanically and electrochemically polished - were exposed during four weeks in autoclave. The results show great effects of the surface treatment on the growth of the oxide layer. We observed oxide layers with different thicknesses and chemical compositions in the depth profile obtained by XPS coupled with Argon ion sputtering cycles. Furthermore, the morphologies of oxide layers formed on electrochemically and mechanically polished surfaces are different even though deposited particles seem to be present on both of them. The XPS analyses and AFM images of the samples before exposure showed that the electrochemical polishing stimulated the growth of an oxide layer relatively iron-depleted and chromium-rich which plays an important role in the corrosion.