Assessment of corrosion characteristics and development of remedial technologies in nuclear materials

Main components and structures in nuclear power plants generally use materials having superior resistance to corrosion. Since the damages related to corrosion have become a menace to the safety of NPPs as well as economical loss and the steam generator tubing forming a boundary between the primary and secondary sides of NPPs is one of the main components that are most damaged by corrosion, it is strongly required to verify the mechanisms of the steam generator tubing degradations, to develop remedial techniques for the degradations, to manage the damages, and to develop techniques for the extension of the plant's life. In this study, the PWSCC characteristics of the archived steam generator tube materials in the domestic NPPs were evaluated and the databases of the obtained results were established. Also, the PWSCC characteristics of the welding material, Alloy 182, for Alloy 600, were evaluated. To verify the damage mechanisms of the circumferential SCC occurring in the expansion transition region of the tubes in the Korean standard NPPS, the evaluation technique for the residual stresses in the expanded region was acquired. A procedure of the inhibition technique for the SCC occurring in the secondary side of steam generators and a model for estimating the safety of damaged tubes by the structural leakage were developed, by which the fundamental technologies for the safe operations of NPPs, the management of the damages, and the expansion of the plant life were acquired. The material improvement technique for the integrity enhancement of tubes was developed. Along with the development of the Ni-coating technique the evaluation of the properties such as mechanical and SCC properties of the coated film was performed