AGE special report: Activity build-up and corrosion

Due to the exposure to the aqueous coolant, the components of the primary circuit in a nuclear power plant oxidise, resulting both in the formation of an oxide film on the component surfaces and in the release of soluble metal ions. The properties of the oxide films are likely to have a significant effect on the corrosion susceptibility as well as on the rate at which radioactive nuclei are incorporated on the component surfaces from the coolant. The latter phenomenon has a marked effect on the occupational dose rates, especially during annual outages. This work aims at understanding the properties and behaviour of oxide films in different coolant conditions and thus at predicting the risks for corrosion and activity build-up. The approach chosen is to investigate and model separately the phenomena taking place at the film/solution interface, in the outer, porous part of the oxide film and in the inner, compact part of the film. In addition, a significant contribution is paid to the development of electrochemical techniques capable of operating in high-temperature environments with even extremely low conductivity. This report summarises the progress made during the first two years of the project.