In case of severe accident conditions in a nuclear reactor, corium a complex material coming from the melting of the core at a very high temperature (2500-2800 K), will be formed. The cooling process of this material from the liquid state can be rapid in the case of contact with water (from a few milliseconds to a few seconds for the so-called Fuel Coolant Interaction (FCI)), or slow in the case of contact with concrete (from a few minutes to a few hours for the so-called Molten Core Concrete Interaction (MCCI)). Both the solidification mechanism and the structure of the obtained solid state phases are strongly dependent of the cooling process involved during accident progression. Studies were carried out on prototypical corium obtained Fuel Coolant Interaction experiments performed in the KROTOS facility at CEA Cadarache. The fragmented or exploded corium debris under consideration are corresponding to a ternary compound according to the U1-x ZrxO2y solid solution. Powder particles of a typical size of 200 µm or less than 50 µm have been studied to determine their microstructure, elemental composition and structural state. Electron Probe MicroAnalysis (EPMA) was used to determine with high accuracy the local variation of the composition. A specific methodology will be presented and results will be compared with global elemental composition obtained through Rietveld refinement of both X rays and neutrons diffraction patterns. The high-resolution diffraction pattern were recorded at the Mars beamline at the SOLEIL synchrotron while neutrons diffraction experiments were done at the D2B of the Institute Laue Langevin. Moreover, micro texture analyses were performed through SEM/EBSD observations and Laue microdiffraction experiments done on the BM32 beamline at the ESRF synchrotron. We clearly evidenced intra-crystalline local cationic composition variations in a large able to be associated to the different cooling process and the particles sizes.