Heat capacity measurement of gadolinia-doped (7.3 mol%) UO 2 from 310 to 1370 K

Abstract

Uranium–neodymium mixed oxides (U1−yNdy)O2±x (y=0.2–0.85) were prepared by citrate gel-combustion and characterized by XRD. Single phase fluorite structure was observed up to y=0.80. For solid solutions with y>0.80 additional lines pertaining to hexagonal neodymium oxide were observed. Lattice thermal expansion of these samples was investigated by using high temperature X-ray diffraction (HTXRD). The coefficients of thermal expansion for (U1−yNdy)O2±x for y=0.2, 0.4, 0.6, and 0.8 in the temperature range 298–1973 K were found to be 16.46, 16.64, 16.79, and 16.89×10−6 K−1, respectively. Heat capacity and enthalpy increment measurements were carried out by using DSC and drop calorimetry in the temperature range 298–800 K and 800–1800 K respectively. The Cp,m values at 298 K for (U1−yLay)O2±x (y=0.2, 0.4, 0.6, and 0.8) are 63.4, 64.3, 61.8, and 58.9 J K−1 mol−1 respectively.