Abstract
In pressurized water reactors, the existence of lead contamination can promote the corrosion of Alloy 690TT. During the manufacturing, transportation and assembly processes, Alloy 690TT surface are easily scratched and it’s easily ignored. The effect of added lead on the scratched surface is different from that on unscratched surface. In the present study, Alloy 690TT were treated with mechanical polishing (MP) and electrochemical polishing (EP) to generate scratched and unscratched surfaces. With the addition of lead, the thickness of passive film on the MP sample increases by 8 times, while that on the EP sample only slightly increases. These chemical composition changes of passive films induced by lead result in the drop of their electrical resistivity, and the electrical resistivity of passive film on the MP sample is reduced by two orders of magnitude, while that on the EP sample decreases only 3 times. Nevertheless, the thickness and electrical resistivity of passive film on the MP sample are always greater than those of the EP sample. The toxic effect of lead on the MP sample is more severe than that of the EP sample, which may be closely related to their subsurface microstructure. Therefore, Alloy 690TT should better avoid being scratched in secondary circuit system of pressurized water reactors, as scratched behavior will result in a faster corrosion rate of Alloy 690TT with the presence of lead.
Highlights
Heat transfer tubes, made of nickel-based alloy, are a key component in pressurized water reactors (PWRs), which are used to transfer heat from primary to secondary circuit water system
It can be found that the outer layer of passive film is always a chromium-rich layer, except for the passive film grown on the mechanical polishing (MP) sample in lead-containing solution
The effect of lead on the passive film of Inconel 690TT alloy with MP and electrochemical polishing (EP) treatments in high-temperature and highpressure water has been investigated by auger electron spectroscopy (AES) and current sensing atomic force microscopy (CS-AFM)
Summary
Made of nickel-based alloy, are a key component in pressurized water reactors (PWRs), which are used to transfer heat from primary to secondary circuit water system. Studies suggest that there are many ways to damage the heat transfer tubes, such as primary side stress corrosion cracking (PWSCC), secondary side stress corrosion cracking (SCC), and intergranular corrosion (IGA) (Staehle and Gorman, 2003). These types of corrosions are usually closely related to. The scratching, mechanical polishing (MP) and grinding treatments cause metal to have a high-stress layer with many sub-grains and dislocations on the surface (Meng et al, 2011; Zhang et al, 2011; Wang et al, 2017). Subsurface microstructures with higher grain boundary and dislocation densities will result in higher corrosion rates
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