Studies on thermal expansion and XPS of urania-thoria solid solutions

The thermal expansion characteristics of polycrystalline (UyTh1-y)O2 solid solutions with y=0.13, 0.55 and 0.91 were determined in the temperature range from 298 to 1973 K by means of X-ray diffraction technique. For these temperatures, the average linear thermal expansion coefficients for (U0.13Th0.87)O2, (U0.55Th0.45)O2 and (U0.91Th0.09)O2 are 1.033x10-5, 1.083x10-5 and 1.145x10-5 K-1, respectively. The measured thermal expansion values were compared with those calculated by applying the equations for linear thermal expansion of pure urania and thoria. It was shown that the stoichiometric (U, Th)O2 solid solutions are almost ideal at least up to 2000 K. The binding energies of U 4f7/2 and Th 4f7/2 electrons of (U0.1Th0.9)O2, (U0.25Th0.75)O2, (U0.50Th0.50)O2, (U0.75Th0.25)O2 and (U0.90Th0.10)O2 were experimentally determined by X-ray photoelectron spectroscopy. The result showed the presence of only U4+ and Th4+ chemical states in the stoichiometric urania-thoria solid solutions