Dislocation loop evolution in Kr-irradiated ThO2

The early stage of microstructural evolution of ThO2, under krypton irradiation at 600, 800, and 1000 degrees C, was investigated using in situ transmission electron microscopy (TEM). Dislocation loops grew faster, whereas their number density decreased with increasing irradiation temperature. Loop density was found to decrease with ion dose. Interstitial dislocation loops, including Frank loops with Burgers vector of a/3 < 111 & rang; and perfect loops with Burgers vector of a/2 < 110 & rang;, were determined by traditional TEM and atomic resolution-scanning TEM techniques. Atomistic and mesoscale level modeling are performed to interpret experimental observations. The migration energy barriers of defects in ThO2 were calculated using density-functional theory. The energetics of different dislocation loop types were studied using molecular dynamics simulations. Loop density and diameter were analyzed using a kinetic rate theory model that considers stoichiometric loop evolution. This analysis reveals that loop growth is governed by the mobility of cation interstitials, whereas loop nucleation is determined by the mobility of anion defects. Lastly, a rate theory model was used to extract the diffusion coefficients of thorium interstitials, oxygen interstitials, and vacancies.

Automated summary

The early stage of microstructural evolution of ThO2 under krypton irradiation was studied using in situ transmission electron microscopy (TEM). The growth rate and density of dislocation loops were investigated with changing irradiation temperature and ion dose. Different types of dislocation loops were determined using various TEM techniques, and diffusion coefficients of different defects were extracted using a rate theory model.