Corrosion behaviour of reactor coolant system materials in nuclear power plants

The materials used for the pressure-retaining parts of reactor coolant system components in light water reactor nuclear power plants have to meet special requirements in terms of their mechanical properties, workability and in-service performance. Corrosion issues play an important role in connection with plant operating conditions. While giving consideration to the specific service environment of the reactor whether a pressurized or boiling water reactor - the materials used for the individual components and the water chemistries employed in the various systems are selected such that metal loss due to general corrosion will remain very low. Thus the materials used in light water reactor plants exhibit a high general resistance to corrosion for their specified service conditions, material conditions and mechanical loads. However, under certain operating conditions other corrosion mechanisms may be found to induce damage. This paper uses data from the literature, published results of national and international research programs, information on damage which has actually occurred world-wide and experience gained by Framatome ANP GmbH (former Siemens/KWU) in this field as a basis for discussing these mostly localised corrosion phenomena in terms of "classical" corrosion systems. Aspects associated with irradiation and its effects are not considered. Suitable remedial actions are, however, addressed wherever these are of relevance. The materials considered comprise unalloyed and low-alloy steels, austenitic chromium-nickel steels as well as high-nickel steels and nickel-base alloys which are exposed to the reactor coolant environment of boiling water reactor or pressurized water reactor plants, including materials investigated in corresponding water environments simulated in the laboratory.