Diffusion of plutonium and uranium in irradiated mixed-oxide fuel

Abstract

Interdiffusion coefficients have been measured in two uniquely fabricated slightly hypostoichiometric (U, Pu)O 2 fuel rods. The measured results can be expressed as D ̃ = 1× 10 −5 exp(−61000/RT) and D ̃ = 1 × 10 −5 exp (− 53 000/RT) for the fuel with burnups of 3.5 and 10 at %, respectively. No radiation enhancement of the diffusion coefficients was observed between ∼ 1000 and ∼ 2000°C. Effects of fission-product impurities and oxygen concentration gradients, which are discussed in terms of the Lidiard model for lattice disorder, are thought to be partially responsible for the observed low activation energies. Effects of diffusion short circuiting are also important. The diffusion measurements were made in fuels irradiated under typical fast-breeder reactor conditions, and the results are directly applicable to a description of processes that affect fast-breeder reactor fuel performance.