Corrosion is a form of surface degradation of metallic materials via electrochemical means. Corrosion properties are not always an intrinsic property of the material since it is influenced by the chemical environment in which the material or the materials system exists. Corrosion is regarded as a life-limiting issue for nuclear reactor components that remain in contact with some kind of fluid for a long dura­tion of time. For example, in LWRs, the core materials remain submerged under the coolant (pressurized water in PWRs or water plus steam environment in BWRs). In modern reactors, coolant chemistry is carefully controlled in order to cause minimum disruption coming from corrosion. However, corrosion is a natu­ral process in a harsh environment such as a nuclear reactor. The cost of corrosion runs into several billions of dollars in the United States in the form of both direct and indirect costs. Note that although until 1960s corrosion was exclusively consid­ered for surface degradation of metallic materials, the corrosion is now generically applied to describe environmental attacks on a wide variety of materials, including ceramics, polymers, composites, and semiconductors.

5.3.1