Impact of fission products on the microstructural and thermophysical properties of (U,Pu)O2-x

U1-yPuyO2-x mixed oxide fuels with 20% < y < 35% are currently considered the best candidate for Sodium-cooled Fast neutron Reactors. During irradiation, the chemical composition of MOx fuels changes due to the continuous generation of fission products (FPs), resulting in a heterogeneous materials. A key point of reactor safety is to ensure that no local melting can occur during irradiation. However, experimental data on the melting point of (U,Pu)O2-x fuel remain scarce due to the extreme radiotoxicity of these materials. To overcome this challenge, we have developed a strategy based on (U,Pu)O2-x materials doped with 11 non-radioactive FPs (SIMMOx) to replicate both composition and microstructure of spent fuel. Laser-heating experiments, carried out under different atmospheres on SIMMOx samples, have allowed us to determine their melting points. Nevertheless, these results must be correlated with actinide and FPs oxidation states to better assess their impact on thermal properties.