Molecular dynamics study of mixed oxide fuels : issues and perspectives

Economically motivated extension of burnup limits of Light Water Reactor (LWR) fuel cycles based on the use of UO2 fuel and civil MOX causes at the same time the necessity to study further primary effects in highly disturbed polycrystalline lattices which may cause dramatic degradation of physical, chemical and mechanical properties of fuel materials. Apart of "standard" fuels there is vital necessity to evaluate burnup/exposure dependent properties of new candidate fuels for advanced LWR systems or fast reactor concepts. Molecular Dynamics (MD) simulations were proven to be a successful technique in order to understand the physicochemical properties of standard LWR fuels (UO2, MOX) and innovative fuels (U-free fuels, inert matrix fuels). Even though MD is today limited to simulation of nanoscale properties, it can be used to investigate beyond what can be measured experimentally, but it needs robust interatomic potentials. This exercise will focus on basic properties of UO2, including lattice thermal expansion, heat capacity, Young modulus, cohesive energy and defects energies. We will discuss the completeness of experimental data and further experimental effort that might address observed shortcomings.