Thermal diffusion of helium in 238Pu-doped UO2

UO2 samples doped with 0.1 wt.% plutonium oxide have been investigated with the aim to study alpha-damage effects and the behaviour of radiogenic helium in spent nuclear fuel by single effects studies. Characterizations were performed by X-ray diffraction, scanning and transmission electron microscopy. Helium release rate as a function of temperature and total helium quantity were measured using a Knudsen effusion mass spectrometer and a quantitative gas measurement system, respectively. A new model for the simulation of helium release has been developed taking into account single gas atom and bubble motion, trapping, grain and bubble growth. The model, embedded into commercial multiphysics software, provided a good description of the experimental data and correlations for gas-atom and bubble diffusion coefficients have been proposed. Finally, the effect of radiation damage on helium diffusion was assessed by comparing the results of the present study with literature data.