Water Chemistry Effect on Corrosion of Nuclear Fuel Cladding Material, Zircaloy-4 (Zr-4)

Effect of lithium and boron on waterside corrosion rate of the nuclear fuel cladding material, Zircaloy-4 (Zr-4), was measured through Tafel calculations using cyclic polarization technique at room temperature. In addition, passivity of ZrO2 film was discussed through cyclic potentiodynamic polarization curves. After the corrosion experiments, the surface of the formed oxides were characterized by SEM. Lithium concentration in water covered the range 2.2 to 7000 ppm Li ions as lithium hydroxide (LiOH). At 100 ppm lithium in aqueous solution, boron added at 10 up to 4000 ppm as boric acid (H3BO3). Results showed that the corrosion of Zircaloy-4 is accelerated at high concentration of LiOH not in the diluted solutions. From the presented work, it is suggested that the enhancement of corrosion is caused by porosity generation through the oxide film. Below a critical LiOH concentration, only superficial porosity was developed in these short-duration experiments. At this critical concentration (which lies between 0.5 and 1.0 M LiOH for Zircaloy-4 at room temperature) porosity develop throughout the whole oxide layer and corrosion rates are enhanced. Boric acid has ameliorating effect on the degradation of Zircaloy-4 corrosion resistance caused by LiOH. PH effect and blocking mechanism can be proposed as inhibition mechanism.