Fission product speciation across a UO2 spent nuclear fuel

This article presents the preparation, the realization and the results of the first X-ray absorption spectroscopy analysis of a bulky irradiated UO ₂ sample. The studied sample was taken from a high burnup fuel rod irradiated for 5 years in a nuclear reactor. HERFD-XANES spectra at the K edge of molybdenum and at the L ₃ edge of cæsium were measured at different radial positions of the original pellet. Important information on the chemical forms of Mo in the spent fuel could be obtained: Mo is mainly in the form of two metallic phases, or in solution in UO ₂, the nature of these “dissolved” species is discussed in details. At the Cs L ₃ edge, several experimental difficulties were encountered for this first experiment, and the data obtained, although promising, are more difficult to interpret. They show, nonetheless, that the cæsium is in the same chemical form(s) in the center and on the periphery of the pellet, probably predominantly dissolved in UO ₂.