Effects of oxides produced during welding on oxidation behavior of the 304L welded joint in simulated primary circuit solution of PWR

•The type and thickness of the welding oxide film affect the atomic diffusion.•Cr oxide in Cr-rich welding oxide film was insoluble in high temperature water.•Fe oxide in welding oxide film partially dissolved in high temperature water.•Welding oxide film, dissolved Fe oxide, new formed oxide film cumulated the result.•Diffusion of dissolution in dissolution-reaction-precipitation limit to micron. In order to study the effect of welding oxide film on high temperature water oxidation, welded joint samples with welding oxide film were immersed in simulated primary loop solution of pressurized water reactor for 90 days. Both the type and thickness of the welding oxide film affect the atomic diffusion process of the high temperature water oxidation reaction, thus affecting the oxide type and oxidation rate. The chromium oxide in the chromium-rich welding oxide film was basically insoluble in high temperature water. The matrix metal atoms dissolved after passing through the film. The dissolved ions participated in the oxidation reaction and precipitate to form a new oxide film. The iron oxide in the chromium-poor welding oxide film and metal atoms in the matrix partially dissolved in high temperature water. The dissolved ions participated in the oxidation reaction and precipitated to form a new oxide film as well. The experimental results showed that the diffusion range of the dissolution process in the dissolution-reaction-precipitation mechanism was confined to the micron range.