  Thermal recovery of irradiated uranium dioxide lattice have been investigated
by experimental groups and defects related to each recovery stages are
estimated based on the indirect observations like activation energies. In this
study, thermal recovery mechanisms of both neutron and alpha-particle
irradiated uranium dioxide lattice is investigated by atomistic simulation
methods. Isochronal and isothermal annealing have been applied to the
irradiated samples. Following the same procedures of the experimental groups,
activation energies are calculated with molecular dynamics simulations and
compared with empirical data which show a good agreement. Migration energy
barrier and the recovery energies of the obstruction type defects are
calculated with molecular dynamics simulation and density functional theory.
Recovery stages of the irradiated crystals are discussed however unlike the
predictions of the most experimental groups, it is shown that neutron and
alpha-particle irradiated crystal structures do not thermally recover for the
same reason. All three recovery stages of neutron irradiated uranium dioxide
crystal is attributed to oxygen interstitials while the three recovery stages
of the alpha-particle irradiated crystals is considered to the oxygen -
uranium, uranium and uranium interstitial defects respectively. Finally, the
reason and the main driving force of thermal recovery of irradiated crystals is
the obstruction type defects which give a lead to all other types of defects
recover with themselves in each lattice recovery stages.
