H2O2 and γ-radiation induced corrosion of 304L stainless steel in aqueous systems

Abstract

In light-water reactors the water used as neutron moderator and coolant is subjected to a constant radiation field which leads to the formation of a number of oxidizing and reducing species. In this work, the reactivity of the radiolysis product H2O2 towards the 304L alloy, commonly used for structural materials in nuclear power plants, was investigated as well as oxidative dissolution of steel components as a consequence of γ-radiation and chemically added H2O2. The concentration of hydrogen peroxide as a function of time was monitored in the presence of different amounts of steel powder, and the second order reaction rate constant was determined to k2 = (1.8 ± 0.2) × 10−10 m s−1. In the case of catalytic decomposition of hydrogen peroxide, hydroxyl radicals are formed which can be scavenged by methanol. In this reaction formaldehyde is formed, which can be detected spectroscopically. A high yield of formaldehyde was observed, indicating that catalytic decomposition is the main reaction path of H2O2 in the current system. A significant contribution of the homogeneous Fenton reaction to both the reaction rate constant and the formaldehyde formation must however be considered, as Fe(II) will be released from the oxide layer in solution. In the case of γ-irradiation, an increased nickel content in solution compared to background experiments is seen. When the steel is subjected to chemically added hydrogen peroxide on the other hand, the chromium content in solution is increased. This indicates that the different types of exposure will impact different parts of the oxide layer characterized by different composition.