Effect Of Zinc Addition On Surface Oxide Film Of PWR Primary Loop Materials

Corrosion of primary loop structure materials greatly affects reactor safety,economical efficiency and lifetime of a nuclear power plant. Primary waterchemistry control prevents or mitigates general corrosion, intergranular corrosionand stress corrosion cracking of reactor components, also prevents deposition ofactivated corrosion products, and therefore reduces radiation dose during refuelingoutages. Zinc injection process, which was firstly used in BWR, has been widelyapplied in foreign PWR plants during recent years due to its remarkable effects oncorrosion and radiation control. Some Chinese PWR plants also have plans toapply zinc injection process, however related researches and knowledges are inblank. This paper researches zinc injection effects on corrosion oxide film in PWRwater chemistry conditions by general corrosion experiments, and means toprovide theory and data for PWR in China.Austenitic stainless steel type316L and304, and nickel-base alloy690wereexposed in a circulating autoclave with zinc addition primary water chemistry. Theexperimental temperature and pressure are320℃and15.2MPa. Corrosion ratewas evaluated by weight gain. Microstructural of oxide film was observed usingScanning Electron Microscope (SEM) and X-ray Photoelectron Spectroscopy(XPS). The experimental results showed that the specimens have higher weight gainrates in the initial stage，and weight gain rate decreases with exposure time.Stainless steel304showed the highest weight gain rate, while alloy690showedthe lowest rate. The weight gain is inversely proportional to the concentration ofZn. With Zinc condition, the size of oxide particles on surface film is in nanometerscale. XPS element concentration depth profile analysis revealed that thecomposition of oxide layer was (ZnxFe1-x) Cr2O4. Zn atom replaced Mn, Fe and Niatoms in tetrahedral site to form more stable zinc-chrome crystal oxides.