Traditionally metal oxides are used as fuel since they have a high melting point. However, urania, used conventionally, has a very low thermal conductivity, which degrades with increasing stoichiometry deviation.
Thoria has been considered as an alternative fuel with a high melting point and higher thermal conductivity . It also has higher retention of fission products (FP) and does not oxidise. We have compared FP diffusion in stoichiometric thoria and urania using first principles molecular dynamics. Thoria has desirable properties as our calculation also confirm onset of a significantly higher oxygen diffusion in urania at lower temperatures than in thoria.
Thoria fuels would not only be safer, due to a higher thermal conductivity, thus lowering the centerline fuel temperature, but especially composites would have higher longevity due to reduced thermal stress.
1. B. Szpunar, J.A. Szpunar, Ki-Seob Sim, J. Phys. and Chem. Solids, 90, 114 (2016).