CORROSION BEHAVIOR OF ALLOY-800 IN HIGH-TEMPERATURE AQUEOUS-SOLUTIONS- LONG-TERM AUTOCLAVE STUDIES

Generalized corrosion of Alloy 800 under primary coolant conditions wa s investigated by measuring the average thickness of oxide layers grow n after long isothermal exposures in the autoclaves located out of cor e in the Embalse Nuclear Power Plant and shorter exposures in laborato ry static autoclaves. The films exhibited the familiar double layer st ructure but after long exposures the inner layer was found to be hidde n by the formation of overlayers and/or by the deposition of species i nevitably present in high temperature coolant. The samples exposed to the primary coolant showed greater average oxide thickness than those in the static autoclave studies, indicating the deposition of corrosio n products from the coolant. Analysis of the films grown in static aut oclaves showed the presence of hydrated species at the oxide/solution interface and spinel structures inside the film. Oxidized nickel was f ound only within few nanometers in the outermost layer of the films wh ereas elementary nickel predominated in the rest of the oxide.