Atomistically-informed modeling of point defect clustering and evolution in irradiated ThO2

TL;DR

This paper introduces a detailed cluster dynamics model for understanding point defect clustering and evolution in irradiated ThO2, incorporating atomistic insights and matching experimental data.

Contribution

It presents a novel atomistically-informed cluster dynamics model that accounts for defect off-stoichiometry, diffusivities, and binding energies in irradiated ThO2.

Findings

Predicted loop density and size agree with experiments.

Void evolution is suppressed due to sluggish cation vacancy kinetics.

Model explains absence of voids at low irradiation temperatures.

Abstract

A cluster dynamics (CD) model has been developed to investigate the nucleation and growth of point defect clusters, i.e., interstitial prismatic loops and nanoscale and sub-nanoscale voids, in ThO2 during irradiation by energetic particles. The model considers cluster off-stoichiometry due to the asymmetry of point defect generation on the O and Th sublattices under irradiation, as well as the point defect diffusivities and the defect binding energies to clusters. The energies were established using detailed molecular dynamics simulations considering the statistical variability of cluster configuration. A high-order adaptive time-integration has been used to solve the model. The predicted loop density and their average size is in good agreement with reported experimental observations for proton irradiated ThO2 at 600oC. The model did not predict void evolution due to the sluggish kinetics of cation vacancies, explaining the absence of voids in proton irradiated ThO2 (and other oxides) at relatively low temperatures.