Hydrogen production by anoxic corrosion of steel under gamma radiation

The present thesis work reports an investigation of the impact of gamma radiation on carbon steel anoxic corrosion process and the resultant hydrogen gas production. The multi-barriers concept associated to the French HL-ILW waste deep geological disposal project implies the use of large amount of metallic elements. These metallic elements, exposed to ionizing radiations originating from nuclear waste, will be progressively submitted to anoxic corrosion under irradiation processes. In addition to the fact that neoformed radiolytic species are prone to modify the corrosion processes, both anoxic corrosion and water radiolysis phenomena generate hydrogen gas whose accumulation may significantly affect mid- and long-term safety of the disposal facility. To contribute to the long-term safety assessment of such underground installation, this work aimed to develop an experimental setup allowing to distinguish between the H₂ production related to water radiolysis and the one related to anoxic corrosion. By measuring continuously the hydrogen gas production corresponding to three important stages (pre-irradiation, irradiation and post-irradiation phases), we were able to estimate corrosion rate values evolution occurring before, during and after gamma-irradiation for carbon steel samples immersed in different solutions. The obtained experimental results, associated to the corresponding liquid and solid samples post mortem characterisations, indicate that: (i) both the presence of solute and/or higher pH conditions induce a decrease of radiolytic hydrogen production, (ii) initial chemical composition of the solution impacts directly the pre-irradiation phase corrosion rate values, (iii) gamma irradiation does not induce any significant increase of the corrosion rate values, (iv) progressive alteration of magnetite layer caused by radiolytic induced redox variations could cause structural modifications that may impact both growth and passivating properties associated to mid and long term evolution of the oxide film formed on the metallic surface and (v) modelling can help to predict the concentration evolution associated to key radiolytic species prone to impact anoxic corrosion under irradiation processes. (author)