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Studies the behavior of uranium (U) in zirconolite, CaZrTi2O7, which is an important constituent of synroc. Study of U in a range of atmospheres; Related pyrochlore-structured titanate phase; Processing atmosphere of solid materials to immobilize multivalent waste ions such as actinides.

Trivalent Pu can be incorporated in the silicate apatite structure to form Ca[sub 2]Pu[sub 8](SiO[sub 4])[sub 6]O[sub 2] 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 Ca[sub 2]Pus(SiO[sub 4])[sub 6]O[sub 2] after firing at 1250°C are given, and the a and c lattice parameters are 0.9561[sub 1] and 0.7028[sub 1] nm, respectively. The respective solid solubility limits of U and Hf in Ca[sub 2]Gd[sub 8-x](U/Hf)[sub x](SiO[sub 4])[sub 6]O[sub 2] apatite samples were 0.3 and 0.2 f.u. [ABSTRACT FROM AUTHOR]