Pu, U, and Hf Incorporation in Gd Silicate Apatite

Trivalent Pu can be incorporated in the silicate apatite structure to form Ca₂Pu₈(SiO₄)₆O₂ by sintering under reducing conditions, while the incorporation of tetravalent Pu in the Ca/rare earth sites in oxidizing or neutral conditions is limited to only 0.6 formula units (f.u.). The d -spacings and intensities of the X-ray pattern of hexagonally structured Ca₂Pu₈(SiO₄)₆O₂ after firing at 1250°C are given, and the a and c lattice parameters are 0.9561₁ and 0.7028₁ nm, respectively. The respective solid solubility limits of U and Hf in Ca₂Gd_{8– x} (U/Hf) _x (SiO₄)₆O₂ apatite samples were 0.3 and 0.2 f.u.