US EPA

3729551 

Journal Article 

Migration of defect clusters and xenon-vacancy clusters in uranium dioxide 

Chen Dong; Gao Fei; Deng Hui-Qiu; Liu Bo; Hu Wang-Yu; Sun Xin 

2014 

Yes 

International Journal of Modern Physics B
ISSN: 0217-9792 

28 

18 

10.1142/S0217979214501203 

WOS:000336961000009 

The possible transition states, minimum energy paths (MEPs) and migration mechanisms of defect clusters and xenon-vacancy defect clusters in uranium dioxide (UO2) have been investigated using the dimer and the nudged elastic-band (NEB) methods. The nearby O atom can easily hop into the oxygen vacancy position by overcoming a small energy barrier, which is much lower than that for the migration of a uranium vacancy. A simulation for a vacancy cluster consisting of two oxygen vacancies reveals that the energy barrier of the divacancy migration tends to decrease with increasing the separation distance of divacancy. For an oxygen interstitial, the migration barrier for the hopping mechanism is almost three times larger than that for the exchange mechanism. Xe moving between two interstitial sites is unlikely a dominant migration mechanism considering the higher energy barrier. A net migration process of a Xe-vacancy pair containing an oxygen vacancy and a xenon interstitial is identified by the NEB method. We expect the oxygen vacancy-assisted migration mechanism to possibly lead to a long distance migration of the Xe interstitials in UO2. The migration of defect clusters involving Xe substitution indicates that Xe atom migrating away from the uranium vacancy site is difficult. 

Defect clusters; migration mechanism; minimum energy paths; vacancy-assisted mechanism