Experimental study of the diffusion of Xe and Kr implanted at low concentrations in UO2 and determination of their trapping mechanisms

The fission of uranium dioxide produces gaseous elements degrading nuclear fuel properties. A thorough understanding of the transport and release of gaseous products is thus essential. The present work focuses on xenon and krypton migration mechanism in uranium dioxide. Desorption experiments on ion implanted UO2 were performed at 1300°C. Xe and Kr releases were simulated using a mesoscale model that was developed taking into account single gas atom diffusion and defect traps. We showed that the defects have a high influence on Xe and Kr migration mechanisms and therefore have to be considered to accurately determine diffusion coefficients. We evaluated the diffusion coefficient of Xe and Kr at (1.73 ± 0.15)x10−20 m2/s at 1300°C and we showed that the diffusion of rare gases is subjected to two trapping mechanisms. The first occurs during the ion implantation and the second during high-temperature annealings. The nature of the trapping sites is discussed in the light of the literature on radiation induced defects. This study also consolidates the use of non activated UO2 implanted with heavy ions as a less-hazardeous substitute for irradiated UO2.