Abstract
Nano-photocatalysts have been widely used for cleaning or self-cleaning applications for the past few decades. This photocatalysis process was adopted to protect the structural components in a boiling water reactor (BWR) from corrosion in recent years. It was found that TiO2 coatings deposited on the surfaces of Type 304 stainless steels were able to mitigate intergranular stress corrosion cracking (IGSCC) in the stainless steels. The principle is to generate sufficient free electrons on the TiO2 coated components upon the absorption of Cherenkov radiation in a BWR. The TiO2 coating bears the n-type semiconductor characteristics, and the induced free electrons would enhance the reduction of the oxidizing species and thus lessen the corrosion of the coated components. Hydrogen water chemistry (HWC) has been the most commonly used techniques for corrosion potential reduction and IGSCC mitigation in BWRs around the world. However, this technique would cause elevated radiation fields when the feedwater hydrogen concentration exceeds 0.5 ppm. A successful application of TiO2 coatings in a BWR is expected to effectively reduce the corrosion potential and the corrosion rate of the structural components even without the presence of HWC. TiO2 nanoparticles were deposited on pre-oxidized Type 304 stainless steel specimens by hydrothermal deposition at 150 oC and 280 oC, and the surface morphologies of the specimens were examined. Electrochemical polarization analyses were conducted to investigate the impact of ultraviolet (UV) radiation on the electrochemical behavior of oxygen and the TiO2 treated specimens in simulated BWR environments. The results showed that the distribution of TiO2 deposited on the specimen surface was not uniform and continuous. It was also observed that the corrosion current densities of the treated specimens and the exchange current densities of the oxygen reduction reactions were comparatively lower in the presence of UV radiation. Without UV radiation, however, no significant differences were observed between the TiO2 treated and untreated specimens. These results indicate that the TiO2 treatment in combination with UV radiation would effectively reduce the corrosion rate of Type 304 stainless steels in high temperature oxygenated environments.