Extended defect change in UO2 during in situ TEM annealing

Abstract

Predicting the nuclear fuel microstructure at each moment of its irradiation cycle (nominal, power transient, accidental conditions) is a significant nuclear safety issue. For that, it is necessary to understand the impact of irradiation parameters on the microstructure. This study provides insight about the temperature effect on dislocations. In situ thermal annealing up to 1400°C on pre-irradiated polycrystalline UO2 thin foils was performed inside a TEM for the first time. The aim of the current study is to establish the kinetic and the mechanisms of thermal recovery of extended defects induced by irradiation.Whatever the initial irradiation conditions, extended defect recovery was observed around 1000-1100°C, in good agreement with literature data. Dislocation line disappear mainly by climb and dislocation loops move by pencil glide along the <110> Burger vector directions. Defect growth by coalescence of dislocation loops is also observed.