Understanding of Corrosion Mechanisms after Irradiation: Effect of Ion Irradiation of the Oxide Layers on the Corrosion Rate of M5

International audienceIrradiation damage in fuel cladding material is mainly caused by the neutron flux that results from fission reactions occurring in the fuel. To avoid the constraints inherent in handling radioactive material, the irradiation effects on the corrosion resistance of zirconium alloys can be studied by irradiating the materials with ions. We performed an original experiment using ion irradiation to more specifically study the influence of irradiation damage in the oxide on the corrosion rate of M5®. It has been established that irradiation with a 1.3-MeV helium ion at a fluence of 1017 cm−2 results in significant modifications of oxide properties, oxygen diffusion flux, and oxidation kinetics, as evidenced by Raman spectroscopy, secondary ion mass spectrometry (SIMS) analyses, and measurements of mass gains. A newly identified Raman vibration band at 712 cm−1 was linked to the presence of irradiation defects and allowed the evolution of their concentrations to be followed. The oxygen diffusion flux was significantly reduced after irradiation partly due to a surface concentration decrease of oxygen. The defects remained present in the oxide after 100 days of annealing in pressurized water reactor (PWR) conditions and were thus very stable in PWR conditions, which probably means that these defects would be stable in the reactor. According to the kinetics and in agreement with the results obtained by SIMS analyses, the oxidation rate was significantly reduced after ion irradiation, and this effect remained beyond 100 days in agreement with the high stability of irradiation defects in PWR conditions. An original model described quite well the oxidation kinetic results