To assure the safety of oxide-fuel based nuclear reactors, the knowledge of the atomic-scale properties of U_1−yM_yO_2±x materials is essential. These compounds show complex chemical properties, originating from the fact that actinides and rare earths may occur with different oxidation states. In these mostly ionic materials, aliovalent cationic configurations can induce changes in the oxygen stoichiometry, with dramatic effects on the properties of the fuel. First studies on U_1−yAm_yO_2±x indicated that these materials exhibit particularly complex electronic and local-structure configurations. Here we present an in-depth study of these compounds, over a wide compositional domain, by combining XRD, XAS and Raman spectroscopy. We provide evidences of the co-existence of four different cations (U⁴⁺, U⁵⁺, Am³⁺, Am⁴⁺) in U_1−yM_yO_2±x compounds, which nevertheless maintain the fluorite structure. Indeed, we show that the cationic sublattice is basically unaffected by the extreme multi-valence states, whereas complex defects are present in the oxygen sublattice.

Some example applications are presented, in which the peculiar Raman fingerprint of PuO₂ can be used for the detection of crystalline Pu⁴⁺ with cubic symmetry in an oxide environment in various host materials, like mixed oxide fuels, inert matrices and corium sub-systems. The PuO₂ Raman fingerprint was previously observed to consist of one main T_2g vibrational mode at 478 cm⁻¹ and two crystal electric field transition lines at 2130 cm⁻¹ and 2610 cm⁻¹. This particular use of Raman spectroscopy is promising for applications in nuclear waste management, safety and safeguard.

During rapid high-temperature events, like a terrorist attack with radiological dispersal device, radiological material will be released into the environment. In these scenarios, the ratio between parent and daughter nuclides can be used for nuclear forensic investigations to determine the age of the used radioactive source. We have used fast laser heating to produce aerosols of a material often found in radioisotope thermoelectric generators. To investigate the behaviour of SrTiO₃, we have recreated pure and mixed samples, mimicking several parent-to-daughter ratios. By combining scanning electron microscopy and energy-dispersive X-ray spectroscopy analysis with Raman spectroscopy, we were able to distinguish different elements and phases present in the aerosols. Two types of aerosols have been identified: individual aerosols from a few micrometre to a few tens of micrometre and agglomerates of smaller aerosols from a few hundred nanometre to a few micrometre. The bigger aerosols, formed from mechanically expelled liquefied material, showed a parent-to-daughter ratio that stays close to the value that would be anticipated by the initial composition of the material, but in the agglomerates, formed from vaporised material, the presence of the daughter elements reduces significantly due to differences in the condensation behaviour.