Uranium-doped britholites CaxLay (SiO4)6-u(PO4)uOt:U synthesis, characterization and preliminary study of uranium diffusion

Natural apatitic phosphosilicates, generally called "britholites", were found to contain certain amounts of radioactive elements or fission products. Thus, britholites have been the object of a great interest because of their potential application as typical matrices for the conditioning of nuclear wastes. In the present report, uranium-doped oxy-silicophosphates CaxLay(SiO4)(6-u)(PO4)(u)O-t/U were synthesized by high-temperature solid-state reaction. The prepared compounds were characterized by X-ray diffraction method, Raman diffusion spectroscopy and X-ray microprobe. The uranium solubility in such compounds was studied. The uranium thermal diffusion in the britholite with the theoretical formula Ca5La5(SiO4)(3)(PO4)(3)O-2 was estimated. The bands present in the Raman spectra were identified and assigned to the corresponding vibration modes of SiO4 and PO4 anions. The diffusion coefficient of uranium in the studied apatite was found close to that calculated for europium and lanthanum in some other apatites. (C) 2004 Elsevier B.V. All rights reserved.