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

The thermal expansion characteristics of polycrystalline (UyTh1-y)O-2 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 (U0.13 Th0.87)O-2, (U0.55Th0.45)O-2 and (U0.91Th0.09)O-2 are 1.033 x 10(-5), 1.083 x 10(-5) and 1.145 x 10(-5) K-1, respectively. The measured thermal expans ion values were compared with those calculated by applying the equations fo r linear thermal expansion of pure urania and thoria. It was shown that the stoichiometric (U, Th)O-2 solid solutions are almost ideal at least up to 2000 K. The binding energies of U 4f(7/2) and Th 4f(7/2) electrons of (U0.1 Th0.9)O-2, (U0.25Th0.75)O-2, (U0.50Th0.50)O-2, (U0.75Th0.25)O-2 and (U0.90T h0.10)O-2 were experimentally determined by X-ray photoelectron spectroscop y. The result showed the presence of only U4+ and Th4+ chemical states in t he stoichiometric urania-thoria solid solutions. (C) 2000 Elsevier Science B.V. All rights reserved.