A discussion on the impact of flow accelerated corrosion on the operation and maintenance of nuclear power plants

FAC (Flow Accelerated Corrosion) is a type of chemical dissolution of carbon steel in high temperature water under reducing atmosphere, accelerated by fast flow. Enhanced mass transfer of ferrous ions through the diffusion layer at the oxide-water interface is the mechanism of the accelerating effect of flow. FAC impacts operation and maintenance of nuclear power plants significantly. Typical examples are wall thinning of secondary side piping, ingress of sludge into the steam generators, and wall thinning of feeder pipes and increase in reactor inlet header temperature in CANDU plants. Significance of those impacts is reviewed, and current status of plant management program is discussed. Development of a reliable FAC model to predict feeder wall thinning should be a major target of research activities in the future. Development of mitigation measures including water chemistry optimization is another topic to be challenged. (author)