Characterization by XPS and AES of oxide films formed on stainless steel 304 under various PWR conditions

Abstract

AbstractIncorporation of 60Co during growth of oxide films on alloys in PWR primary coolant circuits give rise to a significant radiological hazard. These oxide films have a duplex structure consisting of a thin inner layer and an outer layer of crystallites. XPS and AES techniques have been used to examine the oxide layers produced under a variety of controlled PWR coolant conditions. The elemental ratios obtained by the various techniques can be correlated with the extent to which the surfaces are covered with crystallites. The surfaces of coupons with thick outer layers of crystals were depleted in chromium with respect to the base metal composition, while examination of a specimen from which the outer layer had been removed chemically showed a significant enrichment of chromium.The relative differences between the oxides were analysed easily by these surface techniques. However, the absolute accuracy of the elemental composition was in some doubt owing to the lack of suitable, rigorously computed sensitivity factors for use in the quantitative analysis of spectra. An attempt has been made to refine the method for producing sensitivity factors appropriate to these materials.