This work describes the phenomena of the electrochemical coupling between stainless steel (304L) and platinum group metal particles in the environment of the recycling of burned nuclear fuels. The main goals of this work are to prove the acceleration of the corrosion by these deposits, the comprehension of the mechanisms and the development of a corrosion model. First the corrosion phenomena are evidenced for steel in contact with noble particles ((RuO2,xH2O and Ru(0)). Their accelerating effect on the corrosion process is quantified in 8 mol∙L-1 HNO3. Second a local approach on the reduction process is performed using Scanning ElectroChemical Microscopy (SECM). The reduction reaction is investigated for microelectrodes and for different substrates (Ru, Pt, bare steel and steel with deposit). This approach clearly showed the catalytic effect of the noble particles on the reduction process of nitrate. Most probably the limiting step of the reduction process, the chemical formation of NO2, is catalyzed by these particles. Third a reduction scheme is developed for different materials which can describe the experimental results. Simulation results were in agreement with the experimental results. This demonstrates the validity of the assumptions for the model. Finally a model was developed for the bare steel as well as the covered steel, taking into account the dissolution step. It is shown that the most important parameter, that governs the whole corrosion process is the concentration of N(III) species. It can be concluded that, due to the presence of the deposits, the concentration of these species is higher in the vicinity of the steel substrate.
Phenomena of the coupling between steel 304L and platinum group metal paticles in the environment of the dissolution of burned nuclear fuels