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.

Solid/liquid equilibria in the system UO₂–ZrO₂ are revisited in this work by laser heating coupled with fast optical thermometry. Phase transition points newly measured under inert gas are in fair agreement with the early measurements performed by Wisnyi et al., in 1957, the only study available in the literature on the whole pseudo-binary system. In addition, a minimum melting point is identified here for compositions near (U_0.6Z_r0.4)O_2+y, around 2800 K. The solidus line is rather flat on a broad range of compositions around the minimum. It increases for compositions closer to the pure end members, up to the melting point of pure UO₂ (3130 K) on one side and pure ZrO₂ (2970 K) on the other. Solid state phase transitions (cubic-tetragonal-monoclinic) have also been observed in the ZrO₂-rich compositions X-ray diffraction. Investigations under 0.3 MPa air (0.063 MPa O₂) revealed a significant decrease in the melting points down to 2500 K–2600 K for increasing uranium content (x(UO₂)> 0.2). This was found to be related to further oxidation of uranium dioxide, confirmed by X-ray absorption spectroscopy. For example, a typical oxidised corium composition U_0.6Zr_0.4O_2.13 was observed to solidify at a temperature as low as 2493 K. The current results are important for assessing the thermal stability of the system fuel – cladding in an oxide based nuclear reactor, and for simulating the system behaviour during a hypothetical severe accident.

The enthalpy increment data for the (Th,U)O₂ and (U,Pu)O₂ solid solutions are reviewed and complemented with new experimental data (400–1773 K) and many-body potential model simulations. The results of the review show that from room temperature up to about 2000 K the enthalpy data are in agreement with the additivity rule (Neumann-Kopp) in the whole composition range. Above 2000 K the effect of Oxygen Frenkel Pair (OFP) formation leads to an excess enthalpy (heat capacity) that is modeled using the enthalpy and entropy of OFP formation from the end-members. A good agreement with existing experimental work is observed, and a reasonable agreement with the results of the many-body potential model, which indicate the presence of the diffuse Bredig (superionic) transition that is not found in the experimental enthalpy increment data.