Carbon oxides in fuel particles with uranium dioxide kernels

The present paper considers the determination of the carbon monoxide pressure under the coating of fuel particles using the Homan and Proksch formulas. The thermodynamics of the kernel+buffer model system was investigated. For this model, the pressure of carbon monoxide is an order of magnitude higher than the pressure obtained using the Homan or Proksch phenomenological relations. The equilibrium kernel composition was calculated separately from the buffer layer. Unbound oxygen formed during uranium fission in the kernel model system interacts with uranium dioxide to form U4O9, U3O8, and UO3 compounds, while its diffusion into the buffer layer is suppressed. Oxygen may release into the buffer layer from the surface layer of the fuel kernel by a mechanism similar to the migration of gaseous fission products under the impact of uranium fission fragments.