Effect of surface roughness on corrosion behavior of Alloy 690TT in simulated primary coolant of PWRs

The corrosion products transported into the primary coolant may be activated in the core or re-deposited on the surface of components in primary coolant system including fuel cladding. Nickel cations released from the steam generator tubes cause the serious problems in PWRs, for instance, radiation exposure during maintenance operation, occurrence of axial offset anomaly (AOA) and reduction in plant operation. Some studies have been carried out to characterize the oxide layer grown on a Ni-base alloy in primary water chemical condition, especially on morphology and chemical composition. The oxide layer was deemed to a duplex structure composed to an inner Cr rich layer and an outer spinel layer rich in iron or nickel. The composition and morphology of oxide layer are affected by surface finish, operating condition, and water chemistry. Above all, surface roughness, which is one of the commercial requirements for steam generator tube of PWRs, is extremely important in terms of corrosion degradation and corrosion products. In this study, we report the effect of surface roughness on corrosion behavior in simulated primary water at 330 .deg. C and at 150 bar. The surface roughness was controlled to evaluate its difference in corrosion property using mechanical grinding and polishing method. It was measured using a surface profiler and morphology of oxide layer was investigated with FESEM. The corrosion rate of Alloy 690TT samples was calculated by descale-gravimetric analysis. We investigate the effect of surface roughness on corrosion behavior of Alloy 690TT in the simulated primary coolant environments of a pressurized water reactor. Surface roughness of samples were controlled from 716 nm to 25 nm to evaluate for the effect of surface roughness on corrosion behavior Polyhedral oxide particles were formed on the grounded surfaces, whereas the mixed oxides of polyhedral and needle-like structure formed on the polished surface. The corrosion rate of samples was declined approximately 160% as RMS values decreased from about 450 to 150 nm