Résumé
Plutonium oxide nanoparticles constitute a hot topic in modern actinide science due to their past release in the environment (e.g. nuclear tests or accident) but also to their potential contribution in industrial processes (e.g. high burn-up structures, fuel synthesis).[1-3] Nanoparticles and related nanomaterials often exhibit interesting or unexpected properties when shrinking in size due to their increasing surface contribution (S/V ratio). Nevertheless, few results have been described in the literature for actinide nanoparticles. A better description of the speciation and formation mechanisms for these nanoscale objects represent a challenging topic that could contribute in the understanding and predictive modelling of their behaviour and reactivity, particularly useful for environmental purposes.[4-6] This presentation describes the synthesis and relevant synchrotron characterization of PuO2 and ThO2 nanoparticles exhibiting different sizes that were prepared using various approaches. A thorough investigation of these nanomaterials with XRD, HR-TEM and EXAFS spectroscopy evidenced strong similarities for both actinide oxides at the nanoscale. A strong correlation between the size of the nanoparticles and their local structure has been established thus eliminating the potential contribution of other oxidation states in the crystalline structure and evidencing a size-dependent local structural disorder driven by a nanoparticle surface effect.