Fission product release in high-burn-up UO2 oxidized to U3O8

Results of oxidation experiments on high-burn-up UO2 are presented where fission-product vaporisation and release rates have been measured by on-line mass spectrometry as a function of time/temperature during thermal annealing treatments in a Knudsen cell under controlled oxygen atmosphere. Fractional release curves of fission gas and other less volatile fission products in the temperature range 800–2000 K were obtained from BWR fuel samples of 65 GWd t−1 burn-up and oxidized to U3O8 at low temperature. The diffusion enthalpy of gaseous fission products and helium in different structures of U3O8 was determined.