Syntheses of novel titanate-based waste forms, potentially suitable for
immobilizing Pu(III) and Am(III), have been performed. The dititanate
compounds An2Ti2O7 (An=Pu or Am) were found
to have a monoclinic structure. A series of pyrochlore-type solid solutions
between An2Ti2O7 and the cubic pyrochlore
Ln2Ti2O7 (Ln=Gd, Er, or Lu) has been
established, and limits of solid solubility for
An2Ti2O7 were determined. These limits
were found to increase as the ionic radius of the lanthanide in the host
decreased. Strontium-containing titanate compounds
SrAn2Ti4O12 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 90 Sr. A 2 month leaching study of
Er1.78Pu0.22Ti2O7 and
SrPu2Ti4O12 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.