Speciation and Chemical Behavior of Mo in UO2 Samples Prepared by Hydroxide Coprecipitation

Of all the fission products, molybdenum has a very special chemistry in irradiated uranium oxide fuels. The Mo presence is expected to influence the spent
fuel dissolution during reprocessing. This impact may be more or less significant, depending on the speciation of the Mo element in the uranium dioxide. The
aim of this experiment will be to determine the nature of the molybdenum nanoprecipitates formed in several UO2 compounds prepared under oxygen pressure conditions sufficiently different to vary the nature of Mo phase. Given the size of the nanoprecipitates and the expected Mo content in the UO2 (less than or equal to 6 at%), the nature of the phases incorporating molybdenum cannot be determined by XRD in the laboratory. Additionnaly, XANES experiment performed on the same set of samples at Mo edge allow to evidence the valence ste of Mo in the different Mo precipitates.