Thermodynamic assessment of the Fe-U, U-Zr and Fe-U-Zr systems

In an attempt to understand the phase formation mechanism at the interface of metal fuel and cladding, the isothermal phase diagrams and chemical potential diagrams of the Fe-U-Zr ternary system were calculated using the optimized interaction parameters of three binary subsystems. The Gibbs energies of solution phases and compounds in the Fe-U and U-Zr systems were calculated through an optimization procedure based on both the experimental thermochemical and phase diagram data. The obtained ternary phase diagrams were consistent with the experimental data, when the Gibbs energies of formation of ternary compounds; Fe0.06U0.71Zr0.23 and Fe0.3U0.3Zr0.4, were assumed to be - 3.7 similar to - 4.3 and - 16 similar to - 17.5 kJ per g-atom, respectively. The calculated chemical potential diagrams described satisfactorily the experimental diffusion path for the U0.8Zr0.2/Fe couple at 923 K. (C) 1998 Elsevier Science S.A.