Thermal Recovery Mechanisms of UO2 Lattices

TL;DR

This study uses atomistic simulations to investigate the thermal recovery mechanisms of irradiated UO2 lattices, revealing different defect recovery processes for neutron and alpha-particle irradiation.

Contribution

It provides a detailed atomistic simulation analysis of defect recovery stages in irradiated UO2, contrasting neutron and alpha-particle effects, and aligns simulation results with experimental data.

Findings

Neutron and alpha-particle irradiated UO2 recover via different defect mechanisms.

Simulation results agree well with experimental activation energies.

Obstruction type defects drive the thermal recovery process.

Abstract

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.