About the enthalpy of formation of the UZr2 compound

The U-Zr phase diagram has been the subject of many recent studies, particularly for the development of metallic fuels for future fast reactors. The so-called -UZr2 phase is part of this renewed interest as it is likely to be formed during irradiation of U-Zr10wt% fuel. Although this phase has been the subject of several structural studies, there is a single experimental determination of its enthalpy of formation by dissolution calorimetry. Most of the Calphad and DFT models of this phase rely on this value to support their validation. In this paper, we propose a reinterpretation of this measurement which tends to show that the original interpretation of the authors was probably wrong. However, our reinterpretation leads to a new endothermic estimate of the standard enthalpy of formation of -UZr2 difficult to reconcile with the phase diagram. The need for new heat capacity and formation enthalpy measurements is highlighted. The present work does not invalidate the most recent CALPHAD descriptions.