The Effects Of Zinc Injection On Corrosion Behaviors Of PWR Primary Loop Structural Materials

Corrosion of primary loop structure materials greatly affects reactor safety, economical efficiency and lifetime of a nuclear power plant. Primary water chemistry control prevents or mitigates general corrosion, intergranular corrosion and stress corrosion cracking of reactor components, also prevents deposition of activated corrosion products, and therefore reduces radiation dose during refueling outages. Zinc injection process, which was firstly used in BWR, has been widely applied in foreign PWR plants during recent years due to its remarkable effects on corrosion and radiation control. Some Chinese PWR plants also have plans to apply zinc injection process, however related researches and knowledges are in blank. This paper researches zinc injection effects on corrosion oxide film in PWR water chemistry conditions by general corrosion experiments, and provides theory and data for PWR plants in China.We researched on Austenitic Stainless Steel 316L, Austenitic Stainless Steel 304, Nickel-base Alloy 690 and Incoloy 800 in static autoclave solutions. After zinc and cobalt injection experiments in 315℃simulated PWR primary coolant water chemistry condition, we used Weighing, Scanning Electron Microscope (SEM), Energy-dispersive X-ray Spectroscopy (EDS) and X-ray Photoelectron Spectroscopy (XPS) to analyze the surface morphology, microstructure and element distribution of materials.The experimental results showed that corrosion weight gains of specimens were decreased more or less but few influences were found on surface oxide morphology after 1500h. XPS deep analysis revealed the composition of inner oxide layer was (Mn_zNi_yFe_1-y-z)Cr₂O₄ without zinc injection and (ZnwMn_zNi_yFe_1-y-z-w)Corrosion of primary loop structure materials greatly affects reactor safety, economical efficiency and lifetime of a nuclear power plant. Primary water chemistry control prevents or mitigates general corrosion, intergranular corrosion and stress corrosion cracking of reactor components, also prevents deposition of activated corrosion products, and therefore reduces radiation dose during refueling outages. Zinc injection process, which was firstly used in BWR, has been widely applied in foreign PWR plants during recent years due to its remarkable effects on corrosion and radiation control. Some Chinese PWR plants also have plans to apply zinc injection process, however related researches and knowledges are in blank. This paper researches zinc injection effects on corrosion oxide film in PWR water chemistry conditions by general corrosion experiments, and provides theory and data for PWR plants in China.We researched on Austenitic Stainless Steel 316L, Austenitic Stainless Steel 304, Nickel-base Alloy 690 and Incoloy 800 in static autoclave solutions. After zinc and cobalt injection experiments in 315℃simulated PWR primary coolant water chemistry condition, we used Weighing, Scanning Electron Microscope (SEM), Energy-dispersive X-ray Spectroscopy (EDS) and X-ray Photoelectron Spectroscopy (XPS) to analyze the surface morphology, microstructure and element distribution of materials.The experimental results showed that corrosion weight gains of specimens were decreased more or less but few influences were found on surface oxide morphology after 1500h. XPS deep analysis revealed the composition of inner oxide layer was (Mn_zNi_yFe_1-y-z)Cr₂O₄ without zinc injection and (Zn_wMn_zNi_yFe_1-y-z-w)Cr₂O₄ with zinc injection. Zn replaced Mn, Fe and Ni in tetrahedral site to form more stable zinc-chrome crystal oxides. The cobalt injection experimental results showed Zn incorporated in oxides did not prevent Co from deposition while Co incorporated in oxides could be replaced by Zn. with zinc injection. Zn replaced Mn, Fe and Ni in tetrahedral site to form more stable zinc-chrome crystal oxides.The cobalt injection experimental results showed Zn incorporated in oxides did not prevent Co from deposition while Co incorporated in oxides could be replaced by Zn. In conclusion, zinc injection restrained general corrosion of experimental materials to a certain extent. In the double-layer oxides with outer layer rich in Fe and Ni and inner layer rich in Cr, Zn²⁺ replaced Fe²⁺, Ni²⁺, Mn²⁺ and Co²⁺ in tetrahedral site of inner layer to form stable zinc-chrome crystal oxides. The conclusions above provide data for zinc injection process in Chinese PWR plants.