Density-Functional and CALPHAD Studies of U-Zr Alloys

The U-Zr alloy alloys have been recognized as a fuel for liquid-metal fast breeder reactors. First-principles methods are employed to study ground-state properties of U-Zr alloys for the most important phases observed experimentally, namely \textit{$\gamma $} (bcc) and \textit{$\delta $} (C32). Effective interatomic interactions obtained from the screened GPM, incorporating KKR-ASA-CPA, have been applied in MC simulations to derive the \textit{$\gamma $}-phase miscibility gap. EMTO-CPA method has been applied to study properties of the open \textit{$\delta $}-phase. Results of \textit{ab initi}o calculations are compared with experimental data and CALPHAD assessment. Then, the CALPHAD assessed U-Zr phase diagram is contrasted with the one predicted with the input from \textit{ab initio}. This work shows that an overall validity of a combined \textit{ab initio}--CALPHAD approach to thermodynamic properties exists, and that the knowledge and quantitative output gained from quantum mechanics on phase stability and its relation to $f$-bonding, can be used to explore other actinide-based systems, for which experimental data are sparse or lacking. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.