Effect of Irradiation on Long Term Alteration of Oxides and Metals in Aqueous Solutions

The production of radiolytic species in aqueous solutions under irradiation is dependent on the nature and energy of the irradiating particles. A study is reported of the effects of gamma (⁶⁰Co) and light ion (H⁺) radiolysis on corrosion. The ⁶⁰Co source irradiates platinum, carbon steel and copper electrodes immersed in clay water (synthetic).The H⁺ ion beam delivered by a cyclotron irradiates a platinum/sodium sulfate interface. The open circuit potentials of the electrodes are measured as a function of irradiation time. The concentrations of radiolytic hydrogen peroxide (H₂O₂) and hydroxonium (H₃O⁺) ions are measured in the solutions after irradiation. The mass loss rates of the carbon steel and copper electrodes are also measured. The results show that an oxidation process accelerates copper dissolution when the gamma source irradiates the clay water at a dose rate of 0.8±0.2 kGy/h. Carbon steel corrosion is totally unaffected in the same conditions. The Pt open circuit potential reaches a steady-value that is about 0.2-0.3 V higher for the sodium sulfate solution under proton irradiation than for the clay water under ⁶⁰Co gamma irradiation. A difference is observed although both type of irradiations produce comparable amounts of H₂O₂, (1-2) 10^-4 m in the solutions. Furthermore, the open circuit potentials respond rapidly, in a time scale of the order of minutes, to the switching on and off of both types of irradiations. These properties suggest that, in addition to stable species, short-living radiolytic species, as radicals, control the potentials under irradiation. Modelling of the solution radiolysis as a function of irradiation time shows that the concentrations of the radiolytic species reach steady-state values. This behaviour is consistent with the experimental evolution of the open circuit potentials of the electrodes.