  Unfaulting of Frank loops in irradiated fluoride oxides are of significance
to microstructural evolution. However, the mechanisms have not been directly
observed. To this end, we utilize molecular dynamics to reveal the atomistic
details related to the unfaulting process of interstitial Frank loop in
ThO$_2$, which involve nucleation of single or multiple Shockley partial pairs
at the loop circumference. The unfaulting is achieved via a synchronous shear
of the partial pairs to remove the extrinsic stacking fault in the cation
sublattice and the intrinsic stacking fault in the anion sublattice. The strong
oxygen motion at the dislocation core may reduce the activation barriers of
dislocation nucleation and migration. These findings provide a fundamental
understanding of the transformation of faulted loops in irradiated ThO$_2$, and
could be transferable to other fluorite systems.
