Improved models of melting temperature and thermal conductivity for mixed oxide fuels doped with low minor actinide contents

Recycling and burning minor actinides (MA, e.g., americium, neptunium) in mixed-oxide (MOX) nuclear fuel is a strategic option for fast reactor concepts of Generation IV to improve the sustainability of nuclear energy by reducing ultimate radioactive waste and improving the exploitation of fuel resources. Thermal conductivity and melting temperature are fundamental properties of nuclear fuels, since they determine the fuel temperature profile and the melting safety margin, respectively and affect the overall fuel performance under irradiation. The available literature on thermal properties of Am or Np- containing MOX, both experimental data and models, is currently scarce. Moreover, state-of-the-art fuel performance codes (FPCs), e.g., GERMINAL and TRANSURANUS, do not account for the effects of minor actinides on MOX fuel properties. This deliverable presents the development and validation of original correlations for the thermal conductivity and melting temperature of minor actinide-bearing MOX (U,Pu,Am,Np)O2-x based on available literature data. These correlations are derived by extending those obtained in the project for U-Pu MOX fuels with the inclusion of the effect of Am and Np content, while preserving the physically- grounded formulation depending on the most relevant parameters. Ways to improve these correlations further in the future are also discussed.