Abstract

In Pressurized Water Reactor (PWR) power plants, Alloy 600, a Ni-Cr-Fe alloy, is used for steam generator tube materials. However, these tubes have experienced a lot of corrosion problems during their operation times. Several chemicals have been investigated for inhibitors of stress corrosion cracking (SCC) in the tube materials. Titanium dioxide (TiO₂), which is sonochemically treated in water, was tested to evaluate the inhibition effect of SCC using a reverse U-bend specimen of alloy 600 under the condition of a 10% NaOH solution and a temperature of 315^oC. The TiO₂ particle size was reduced by ultrasonic power, and the morphology of the TiO₂ powder was observed by a transmission electron microscope (TEM) based on the ultrasonic processing times. The particle size of TiO₂ affects the SCC rate of the tube materials, and shows an improvement in resistance on SCC when decreasing the particle size of TiO₂. When the nano-sized inhibitor is applied, the property of the oxide layer is changed to a more dense composition. The chemical composition in the oxide layer was analyzed using an X-ray photoelectron spectroscope (XPS) with a variation in the ultrasonic process times, and the difference in the Ti-compound structure between the oxide surface and inner layer of oxide was compared using XPS data.

Keywords: Corrosion inhibitor, nanoparticle, sonochemistry, steam generator tube, stress corrosion cracking (SCC), titanium dioxide (TiO₂).