The main objective of this project is the determination of hardness, elastic constants and creep properties of a metallic fuel exploratory alloy (U-Mo-Ti-Zr) for sodium cooled fast reactor using in-situ small-scale mechanical testing, specifically nanoindentation. Moreover, Scanning Electron Microscopy (SEM), Electron Back Scatter Diffraction (EBSD), and Energy Dispersive X-ray Spectroscopy (EDX) will be employed for the sample microstructural characterization in order to determine grain morphology, orientation and composition of eventual fission product precipitates at the measurement locations and elemental concentration in the different strata of the Fuel-Cladding Chemical Interaction (FCCI) region. This unique metallic alloy was irradiated in ATR at higher than desirable peak inner cladding temperature (PICT) and developing some degree of FCCI layers. The characterization of the FCCI region, the collection of data on the development of FCCI “front” and identification of any potential low temperature melting phases will be of paramount importance for the future development of this new metallic alloy.The study will be the first ever application of in-situ small-scale mechanical tests (and also at high temperature) on a metallic fuel alloy, providing unique data. Since nanoindentation samples a small volume of material it allows for evaluating the change in mechanical properties over the radius of the pellet. Thus, this technique would allow the first measurements on the FCCI layer at in the operating temperature range. The employment of state-of-the-art in-situ mechanical testing techniques would allow to tackle fuel microstructural heterogeneities, thus capturing irradiation-induced property changes at a local level. Data regarding the irradiated fuel mechanical properties and their correlation to the local microstructure are fundamental input to mesoscale modeling and are needed to quantify physical property changes that have impact on the overall fuel performance and safety.