The characteristics of fission gas release from uranium dioxide during irradiation

Release rates for the unstable rare gases 88Kr, 87Kr, sup(85m)Kr, 133Xe, 135Xe, 138Xe were measured for samples of polycrystalline and large-grained uranium dioxide in the temperature range 700-15500C. Interpretation is in terms of simple diffusion of gas atoms and their halogen precursors. Derived diffusion coefficients for iodine are compared with those obtained from direct measurements of 133I release from the same experiment and show good agreement. Diffusion coefficients calculated for krypton, xenon and iodine are similar in their magnitude and temperature dependences, but magnitudes for bromine are much (approximately 200 times) higher. (Auth.)