Diffusion of cerium in uranium-zirconium solid solutions

Abstract

Two types of diffusion couples, U-23 mol%Zr with U-23 mol%Zr-1.3 mol%Ce and U-95 mol%Zr with U-23 mol%Zr-1.3 mol%Ce, were annealed isothermally at 1123 K and 1023 K in order to provide basic data o Ce diffusion in U-Zr alloys, which are the fuel forms for advanced nuclear reactors. Because the Ce solubility in the U-23 mol%Zr alloy is less than 1 mol% in this temperature range, Ce-rich precipitates were formed and dispersed in the U-23 mol%Zr-1.3 mol%Ce alloy. The concentration profiles of Ce in the U-23 mol%Zr/U-23 mol%Zr-1.3 mol%Ce couples were analyzed based on the theoretical solutions of the one-dimensional diffusion equation for the semi-infinite diffusion couple, either side of which is supersaturated with the diffusing substance. From this analysis, the diffusion coefficients of Ce in the U-23 mol%Zr solid solution (γ-U, β-Zr) were estimated to be ̃2 × 10-13 m2/s at 1123 K and ∼6 × 10-14 m2/s at 1023 K, which are between the values extrapolated from the reported self-diffusion coefficients of γ-U and β-Zr. In the U-95 mol%Zr/U-23mol%Zr-1.3 mol%Ce couples annealed at 1123 K and 1023 K, the concentration profiles showed up-hill diffusion of Ce. The interdiffusion coefficients in this quasi-binary U-Zr system containing Ce were obtained from the U or Zr concentration profile and compared with the reported interdiffusion coefficients in the binary U-Zr system without Ce. The result indicated that Ce does not have significant influence on interdiffusion in the U-Zr solid solutions.