Experimental investigation of Kr diffusion in UO2+x: Slight deviations from stoichiometry, significant effects on diffusion kinetics and mechanisms

Thermo-Desorption Spectrometry (TDS) was employed to study the release of fission gases from a Kr implanted UO2+x during 1050–1300 °C isotherms. The stoichiometry of the sample has been regularly increased by O2 additions in the vacuum setup to cover an hyperstoichiometry x range from ∼1  ×  10−6 to ∼0.1. We used an analytical model based on Fick's second law to determine krypton diffusion kinetics (DKr) from the Kr cumulated release profiles. We demonstrate that even little x deviations from stoichiometric UO2 down to the 10−6 order are sufficient to quantitatively enhance fission gas diffusion. This likely explains a fair amount of data scatter in literature for experimental fission gases diffusion rates in (supposedly) perfectly stoichiometric UO2. A model was developed from the experimental results and well-accepted data for UO2 to estimate DKr (and DXe equivalently) as a function of T and x in the ranges of the present study.