Release of fission products (Xe, I, Te, Cs, Mo and Tc) from polycrystalline UO2

The release of xenon, iodine, tellurium, cesium, molybdenum and technetium from lightly-irradiated, polycrystalline UO2 has been studied in post-irradiation anneal experiments. The effective diffusion coefficients for cesium were found to be comparable to those for xenon and roughly an order of magnitude smaller than those for iodine and tellurium over the temperature range studied. Activation energies for diffusion of the more volatile elements as derived from analysis within the Booth model were 156 ± 45 (Xe), 122 ± 33 (I), 115 ± 11 (Te) and 99 ± 11 (Cs) kcal/mol. The activation energies for Mo and Tc found by a similar treatment were 353 ± 24 and 205 ± 42 kcal/mol, respectively, and are indicative of a fairly complex mechanism for release of these elements. The soluble ionic species Np4+, Zr4+, La3+, and Nd3+ were completely retained in the UO2. (orig.)