Studies on the Corrosion Performance of CP-Ti and Zr-4 in Hot Nitric Acid with Formaldehyde for Aqueous Reprocessing Applications

The robust performance of components within nuclear fuel reprocessing plants, especially in environments characterized by hostility, corrosion, and radioactivity, is imperative for ensuring seamless plant operations. Nitric acid serves as the primary process medium in the complex chemical processes involved in reprocessing spent fuel. While 304L SS is conventionally employed for nitric acid service in these plants, there is an ongoing exploration of alternative candidates such as titanium (Ti), zirconium (Zr) and their alloys. This study focuses on assessing the performance of commercially pure titanium (CP-Ti) and zirconium alloy (Zr-4) in nitric acid with formaldehyde at 80 degrees C. The corrosion rate of the Zr-4 sample, immersed in nitric acid with formaldehyde for two weeks at 80 degrees C, was negligible when compared to the commercially pure titanium (CP-Ti) sample under the same conditions. Comprehensive characterization of the oxide film formed on the surface of CP-Ti and Zr-4 samples was achieved through field emission scanning electron microscopy (FE-SEM) coupled with energy dispersive x-ray spectroscopy (EDS), as well as x-ray photoelectron spectroscopy (XPS). The corrosion behavior of both Ti and Zr-4 samples in nitric acid containing formaldehyde was systematically evaluated using potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS). The results revealed enhanced corrosion resistance for both CP-Ti and Zr-4 samples. Consequently, this study suggests that titanium and zirconium may be considered as suitable candidates for the process equipments handling hot nitric acid with formaldehyde in the aqueous reprocessing of spent fuel.