Sampathkumar Chrisolite Vanithakumari

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 °C. The corrosion rate of the Zr-4 sample, immersed in nitric acid with formaldehyde for two weeks at 80 °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.

Modified 9Cr-1Mo steel is used as steam generator material in prototype fast breeder reactors, owing to its good corrosion resistance, creep, and thermal conductivity characteristics. In the present study, the corrosion behavior of modified 9Cr-1Mo steel in aqueous environments containing various corrosive ions at potentiodynamic polarization conditions is reported. In chloride-exposed samples, randomly distributed dense shallow pits were seen, whereas mixed anions (, Cl−, and ) in fresh water resulted in deeper pits uniformly distributed on the entire surface. Laser Raman spectroscopy studies revealed the formation of Fe-oxides/hydroxides and Cr(VI) species, except in alkaline solution. A very thin film of only Fe-oxides (Fe3O4, γ-Fe2O3, and α-Fe2O3) was identified in an OH– ion-dominated solution. X-ray photoelectron spectroscopy results confirm the corroded surfaces comprised of Fe, Cr, and Mo-oxides of varying composition and enrichment of Mo-oxides in alkaline solution. Chloride ions present in the corroded layer influenced the pitting corrosion in neutral chloride and fresh water solutions. Field emission scanning electron microscopy images revealed abundant crystalline lepidocrocite with laminar morphology and doughnut-type magnetite together with pits on the samples exposed in neutral chloride and fresh water media.

In this work superhydrophobic coating with self cleaning property is fabricated on 304L SS samples directly using a simple one step electrospinning process followed by silane treatment by using polyvinyl alcohol (PVA) and tetraethyl orthosilicate solution. A maximum water contact angle of 169.2° ± 2.1° is obtained at an electrospinning potential of 15 kV for 2 h, with a distance of 18 cm between the collector and needle. The hierarchical nanostructures thus formed on 304L SS composed of poly(vinyl alcohol)‐silica microbeads and nanofibers. The surface morphologies are optimized by varying the electrospinning voltage, time, distance between needle and the collector and aging duration of the precursors. Attenuated total reflectance‐infrared spectroscopy studies at different stages of preparation confirmed the presence of PVA/SiO₂composite nanofibers deposited on the 304L SS surface. The reaction of SiO₂nanofibers with hexamethyl disilazane resulted in the formation of SiOSi bonds that provided water repellent property. The developed SHP surface coating on 304L SS sample showed dynamic bouncing of water droplets and excellent self cleaning performance. The sample retained the SHP behavior in chloride solutions with different ionic strengths and pH.