Impact of nickel and iron on PWR zirconium alloy surface CRUD formation and boron precipitation

Abstract

BackgroundCorrosion products will deposit on the surfaces of PWR (pressurized water reactor) zirconium alloy to form CRUD (chalk rivers unidentified deposit), the precipitated boron will cause axial power distribution anomaly and affect the core safety.PurposeThis study aims to investigate the impact of nickel and iron on PWR zirconium alloy surface CRUD formation and boron precipitation using an artificial CRUD experiment setup.MethodThe experimental loop of high temperature and high pressure hydrodynamic circulation was utilized to carry out simulation study of CRUD formation and boron precipitation. The impact mechanism of nickel and iron on CRUD formation and boron was analyzed by X-ray photoelectric spectroscopy (XPS) and scanning electric microscope (SEM) methods. The measurement data were obtained by adjusting the injection sequence of nickel-iron and DH (dissolved hydrogen) concentrations.ResultsExperimental results show that maximum CRUD thickness are 5 μm and 15 μm, respectively, under 40 cm3·kg-1 and 0 cm3·kg-1 DH concentrations; boron mole fraction inside CRUD are 19.8%, 4.5% and 0.3%, respectively, corresponding to 1.06, 0.48 and 0.11 of nickel-iron ratios. The morphology of deposited iron is spinel whilst the morphology of the mixed nickel-iron deposit is porous.ConclusionsThese results indicate that iron is easier to deposit on the clean zirconium alloy surface, and the iron can enhance the deposition of nickel. Elevating the CRUD nickel-iron ratio could cause the boron precipitation while the relatively low nickel-iron ratio has little impact on boron precipitation.

Keywords

• pwr
• zirconium alloy
• crud
• boron precipitation
• nickel-iron ratios