Impact of small defects and dislocation loops on phonon scattering and thermal transport in ThO2

•The impact of small defects and dislocation loops on thermal transport is quantified.•Phonon scattering parameters for all the defects considered are extracted.•Given a fixed dose, defect clustering assists thermal conductivity recovery. Radiation damage can significantly degrade the thermal conductivity of ThO2 due to enhanced phonon-defect scattering. To quantify the effect of radiation-induced defects on thermal transport, we employ non-equilibrium molecular dynamics simulations to estimate the thermal conductivity in the presence of various types of defects. For each defect species, the phonon-defect scattering cross-section is extracted based on analytical models. In addition, the impact from two types of experimentally-observed dislocation loops (perfect and faulted) on thermal transport is examined with respect to the loop size and orientation. Notably, simulation cell size effects are analytically and quantitatively addressed via a phonon-mean-free-path-resolved analysis. It can be concluded that, for a given total number of defect sites per unit volume, agglomerating defects into larger clusters improves thermal conductivity compared to isolated defects. Importantly, this work provides quantitative information towards the defect-specific thermal conductivity, and phonon-defect scattering cross-sections, which can serve as inputs to large-scale transport models to quantify the evolution of overall thermal conductivity of ThO2 under irradiation.