Release of fission products (Xe, Kr, I, Cs) implanted in polycrystalline UO2

Under irradiations in nuclear reactors, the microstructure of oxide nuclear fuel changes. To improve the modeling of the UO2 fuel behavior under irradiation, it is necessary to understand the elementary mechanisms of fission products diffusion. Among them, rare gas Xenon and Krypton represent 30% of created elements and fission products such as Iodine and Caesium are corrosive for the clad. Our experimental work consists in the measurement of the fission products release kinetics by Knudsen cell mass spectrometry. For that, 8mm diameter-1 mm height fresh polycrystalline UO2 pellets are implanted with different concentrations in 129Xe, 83Kr, 127I, 133Cs to understand the effect of the fission products density on the diffusion. The release kinetics is studied either during the heating at a given rate from room temperature to about 2050DC (Figure) or during isothermal annealing every 100 DC from 100 to 1600 DC.