Laser heating investigation of the high-temperature interaction between zirconium and UO2

The present work aims to improve accuracy of solid/liquid transition temperatures in Zr-rich corner of the U-Zr-O ternary system, where no experimental data are available in literature. A laser heating technique has been used to investigate three compositions close to the section Zr-UO2. A clear melting/solidification thermal arrest has been observed in the Zr-richer (86.4 at% Zr) composition. A double transition has been recorded for the compositions with higher uranium dioxide content (76.8 at% Zr and 65.5 at% Zr, respectively). Interestingly, the lowest temperatures at which the second thermal arrests occur in the latter two compositions are lower than the melting point retained for pure Zr (2125 K approximately). This suggests the presence, in this part of the phase diagram, of a minimum liquefaction point. Emissivity of the investigated samples has been obtained with a multi-wavelength pyrometer within the grey-body assumption: this is reasonable in a narrow wavelength range between the visible and the near infrared spectral domain. However, further investigation on the optical properties of this set of alloys might allow to reduce the uncertainty on the measured transition temperatures.