Post-irradiation anneal experiments have been used to determine the release of iodine and tellurium from lightly irradiated UO2 samples maintained at stoichiometry. The applicability of the equivalent-sphere model of diffusion to release of fission gases has been tested. Diffusion coefficients and activation energies have been evaluated. The diffusion coefficient of 132Te at 1400°C was found to be of an order-of-magnitude larger than that of 131I. This result may be of importance for an understanding of the pellet-cladding interaction and for a better evaluation of the source term for fission-product release under accident conditions. Qualitatively, the influence of the stoichiometry on the release of 133Xe, 131I, and 132Te has been established.

In our experiments, post-irradiation anneal of lightly-irradiated UO2 was used to measure the release kinetics of the volatile fission products Xe, I, and Te. The fraction of a particular fission product retained in a specimen was measured by gamma-ray spectroscopy before and following an anneal.