Development of a solute and defect concentration dependant Ising model for the study of transmutation induced segregation in neutron irradiated W–(Re, Os) systems

Abstract

In this study, radiation-induced precipitation of transmutation products is addressed via the development of a new solute and vacancy concentration dependant Ising model for the W–Re–Os system. This new model includes interactions between both Os and Re atoms with vacancies, thus facilitating more representative simulations of transmutation in fusion reactor components. Local solute concentration dependencies are introduced for the W–Re, W–Os and Re–Os pair interactions. The model correctly accounts for the repulsion between small clusters of vacancies and the attraction between larger clusters/voids, via the introduction of local vacancy concentration dependant interaction coefficients between pairs of atoms and vacancies. To parameterise the pair interactions between atoms and/or vacancies, the enthalpy of mixing, ΔH mix, for various configurations and solute/defect concentrations, was calculated using density functional theory, within 6 binary systems: W–Re, W–Os, Re–Os, W–vacancy, Re–vacancy and Os–vacancy. The new energy model was implemented into the SPPARKS Monte Carlo code, and successfully used to predict the formation of voids decorated with Re and Os solute atoms. Analysis suggests that there is a strong thermodynamic tendency for Os to bind to these voids with a comparatively weaker binding from Re atoms. The binding energies of various solute/vacancy clusters were calculated and showed that Re and Os solute atoms tend to stabilise small clusters of vacancies, increasing the attractive binding energy between the constituents.

Parallel simulation via SPPARKS of on-lattice kinetic and Metropolis Monte Carlo models for materials processing

“…In [58] they added a semi-grand canonical MC algorithm to their app to allow the concentration of rhenium (Re) atoms (a radiation-induced transmutation product) in the W matrix to fluctuate. In tandem with diffusion, they observed clustering and precipitation of Re, which has been experimentally observed to embrittle the W. In [59], osmium (Os) atoms (another transmutation product) were included in the KMC model and DFT calculations, and vacancy clustering was observed, with the voids decorated by Re and Os atoms which can stabilize the voids, leading to degradation of the W.…”

“…This allows various interatomic potentials implemented in LAMMPS (a three-body angular dependent potential in their model) to be evaluated and to include off-lattice relaxation effects via energy minimizations of the before and after on-lattice configurations. In [58,59], Lloyd et al modeled radiation effects on tungsten (W), a plasma-facing material proposed for nuclear fusion reactors, using DFT calculations to compute changes in energy due to diffusive events and infer rates for their KMC model. In [58] they added a semi-grand canonical MC algorithm to their app to allow the concentration of rhenium (Re) atoms (a radiation-induced transmutation product) in the W matrix to fluctuate.…”