Syntheses of titanate-based hosts for the immobilization of Pu(III)and Am(III)

摘要

Syntheses of novel titanate-based waste forms, potentially suitable for immobilizing Pu (III) and Am (III), have been performed. The dititanate compounds An_2Ti_2O_7(An=Pu or Am) were found to have a monoclinic structure. A series of pyrochlore-type solid solutions between An_2Ti-2O_7 and the cubic pyrochlore Ln_2Ti_2O_7(Ln=Gd,Er,or Lu) has been established, and limite of solid solubility for An_2Ti_2O_7 were determined. These limits were found to increase as the ionic radius of hte lanthanide in the host decreased. Strontium-containing titanate compounds SrAn_2Ti_4O_12 were also prepared and were characterized as exhibiting a perovskite-type structure. Such compounds could serve as waste hosts for the immobilization of not only the actinide but also ~90Sr. A 2 month leaching study of er_1.78 Pu_0.22Ti_2O_7 and SrPu_2Ti_4O_12 by WIPP "A" brine was performed. Very low amounts (< 1 ppm) of Pu(III) were leached. Although the ionic radius of Np(III) is similar to that of Pu (III) and Am(III), analogous Np compounds could not be prepared in any of the titanate systems investigated.