Helium and point defect accumulation: (ii) kinetic modelling

The EU programme for modelling radiation effects in fusion reactor materials: An overview of recent advances and future goals

“…Simulations described in Ref. [68] suggest that impurities have a significant effect on the evolution of helium clusters and on the rate of desorption of He from the material. For example, the effective energy for migration of a vacancy had to be increased from 0.67 eV to 0.83 eV and the binding energies of He-V and He-V 2 clusters had to be reduced from 2.3 eV and 0.78 eV to 1.78 eV and 0.54 eV respectively to match the experimentally observed He desorption curves.…”

“…Helium atoms formed by transmutation rapidly diffuse through the lattice and fill the vacant lattice sites, creating substitutional He atoms, which can also be treated as He-V binary complexes. The calculated binding energy of a He-V complex is 2.3 eV [68]. This He-V complex grows by absorbing migrating helium atoms and vacancies, resulting in the formation of a small and fairly stable mesoscopic helium-vacancy cluster.…”

“…A quantitative kinetic Monte Carlo model for the growth of a small helium-vacancy cluster based on ab-initio calculations of energy barriers for the attachment/detachment of individual vacancies and helium atoms is described in Ref. [68]. Simulations described in Ref.…”

Modeling Microstructure and Irradiation Effects

“…The same reasoning is applied to the dissociation events, and efforts are then concentrated on the binding energies. The parameterization can be done with the help of ab-initio calculations [272,273] for small object sizes, with MD for larger cluster sizes or the help of well-defined experiments such as isochronal annealing experiments following simple irradiations such as He implantation desorption [274] or electron irradiation. [275] At the moment, the coarse-grained KMC methods have been mostly used to investigate the annealing of the primary damage, as in References 276 or 24, or the effect of temperature change in the damage accumulation, [277] Fig.…”

“…[281] They were used also to model as well as re-examine simple experiments such as He desorption in W [272] or in Fe [273] as well as the influence of C in isochronal annealing experiments. Figure 6 represents the evolution of the total number of defects in an OKMC simulation of below threshold energy He implantation in W performed by Soltan et al [274] The OKMC simulation, as the experiments, consists of two parts: the implantation sequence followed by isochronal annealing.…”