[SY-B9] Atomistic modelling of point defect clusters in zirconium and impact on the microstructure evolution and crystal growth under irradiation
Zirconium alloys are used to manufacture fuel cladding as well as fuel assemblies of pressurized water nuclear reactors. Under irradiation, they show a dimensional change commonly called growth. Experimental observations have shown that above a threshold dose, these alloys are subject to accelerated growth called "breakaway". It has been well established that the irradiation formation of and <c> dislocation loops is directly responsible for the growth of irradiated zirconium alloys and that the appearance of <c> loops is correlated with this growth acceleration. However, the nucleation mechanisms of the <c> loops are still poorly understood. In order to improve our understanding, atomic-scale calculations based on the density functional theory (DFT) and empirical potentials are used to determine the properties of clusters of point defects (vacancies as well as self-interstitials) in terms of formation energy, binding energy and eigenstrain, of prime importance to assess their influence on the deformation of the material. In particular, DFT simulations of dislocation loops in large supercells allow to revisit their energies used as input parameters of mesoscale models (Object KMC), resulting in prediction of growth and its acceleration. Moreover, pyramids of stacking faults are studied in more detail and their characterization sheds light on their plausible role in the nucleation sequence of <c> loop, which allows to propose an original scenario for their appearance.