Electrochemical Behavior of Corrosion at Normal Temperature of Three Typical Metals in Coast Nuclear Power Plants

The corrosion behavior in three solutions at 30 ℃ of three typical important structural materials used in coastal pressurized water reactor (PWR) nuclear power plants were studied by electrochemical methods. The effects of solution and material factors were analyzed. The three materials were low alloy steel 16MND5, stainless steel weld metal 308L and stainless steel base metal Z2CND18-12N. And the three solution were simulated PWR primary water, simulated PWR pninary water with 10 mg/L Cl- and 3.5% NaCl solution. The results showed that, in simulated PWR primary water, three materials exhibited passivity and the minimum corrosion susceptibility as compared with in other solutions. When the primary water was added with 10 mg/L Cl-, corrosion behaviors of the two stainless steels had little change, while the corrosion rate of 16MND5 increased significantly and exhibited active dissolution controlled by polarization. Maximum corrosion susceptibilities of three materials were exhibited in 3.5% NaCl solution. 16MND5 showed the highest rate of general corrosion. The passivity zones of the two stainless steels were relatively narrow, indicating high susceptibility to pitting. The pitting resistance of weld metal 308L with different orientations was similar and lower significantly than that of Z2CND18-12N. Exposing the test solutions to air caused increase of corrosion susceptibility of the three materials, especially the low alloy steel, due to high content of dissolved oxygen in solutions.