Influence of Irradiation on the Oxide Film Formed on 316 L Stainless Steel in PWR Primary Water

Oxidation of stainless steel in PWR primary water at 325 A degrees C was studied by investigating the influence of defects created at the alloy subsurface by proton irradiation before corrosion exposure. Corrosion experiments were conducted by sequentially exposing samples, with H (2) (18) O used for the second exposure. The oxide layer, formed in these conditions was studied by SEM and TEM and could be divided in two parts: an external discontinuous layer composed of crystallites rich in iron and an internal continuous layer richer in chromium. Tracer experiments revealed that the growth of this protective scale was due to oxygen diffusion in the grain boundary of the oxide layer. Defects created by irradiation have an effect on the two oxide layers. They are a preferential nucleation site for the external layer and so increase the density of the crystallites. They also induce a slower diffusion of oxygen in the internal layer.