Radiolytic Corrosion of Grain Boundaries onto the UO2 TRISO Particle Surface

Abstract : This work is dealing with the understanding of the corrosion mechanisms at solid/solution interface and taking into account for the 4 He 2+ ions irradiation effects on these mechanisms. These corrosion and 4 He 2+ ions radiolysis phenomena append at solid/solution interface and will be studied at a μmetric scale by the Raman spectroscopy. Moreover, a 4 He 2+ ions irradiation affects a small low volume and allows us to control the irradiated area (solution, solid or interface). For the solid, the chemical species induced by 4 He 2+ ions radiolysis of water are reactive and are involved in classical corrosion mechanisms of UO 2 . Moreover, we want to study the impact of the 4 He 2+ ions radiolysis of water layers physisorbed into the surface onto corrosion mechanisms. That is the reason why we want to use a local irradiation, allowed by the 4 He 2+ ions ion beam provided by the ARRONAX cyclotron (E = 64.7 MeV). In this work an experimental apparatus wi ll be performed in order to characterize solid/solution interface at μmet ric scale by Raman spectroscopy under 4 He 2+ ions irradiation provided by the cyclotron ARRONAX facility. The leaching experiments under irradiation will be performed for a short time in order to study the parameters during the fast instant release step. The grain boundaries effect w ill be studied by the comparison between one TRISO particles set (solids with grain boundari es) and one TRISO par ticles set previously washed by one acid solution (solid wit hout grain boundaries). The role of H 2 will be studied by the comparison between experiments under Ar or Ar/H 2 atmosphere. The dose rate range will be between 0 and 100 Gy/min by using the al pha ion beam which let us control the dose set down into the sample. For all these experiments, measurements will be performed by the in situ Raman spectroscopy during the irra diation in order to follow the formation/consumption of the secondary phase s formed onto the solid. The SEM will be performed in order to characte rize the grain boundaries and th e secondary phases formed by the leaching/irradiation experiments. The μGC is used to measure the P H2 into the irradiation cell to follow the production/c onsumption of this gaseous species formed by the water radiolysis and consumed by the leaching process.