Historical experience providing bases for predicting corrosion and stress corrosion in emerging supercritical water nuclear technology: Part 3-review

This review assesses past experiences from superheated fossil plants, supercritical fossil plants, superheated nuclear plants, and light water reactors from the late 1940s until the present. Data from the development and operation of these plants are directly applicable to supercritical water reactor (SCWR) plants being developed currently. This past work can be applied to the development of current designs in the choice of materials, temperature dependencies, effects of stress, and effects of environments on materials. Some of the past data from light water reactor (LWR) technology can be extrapolated into the present SCWR regimes. The past data are in good agreement among the various previous investigators. These past data are considered with respect to specific components in SCWR: fuel cladding, reactor structurals, reactor vessels, and feed water heaters. Choosing materials for the SCWR applications must recognize that the materials at nominal outlet temperatures are in a dynamic thermal range, i.e., in the nuclear superheat and fossil superheat range, the atomic structures of materials change significantly and change properties such as ductility. It is also possible that compositions and structures of grain boundaries can change, for example, the susceptibility to SCC. The surface temperatures on fuel cladding will be significantly higher than the outlet temperature, and both temperatures will exceed, substantially, the outlet temperatures of present water-cooled plants. Past isothermal data directed toward core structures may not be relevant to the same alloy as fuel cladding. The outlet temperature is useful for considering core structural materials but not for fuel elements, owing to an inevitably high film drop. SCW environments are expected to produce extensive SCC, which differs from past experience. Finally, past data were reanalyzed and additional useful insights were obtained.