ABSTRACTUraninites from the Bangombé natural fission reactor (RZB) and “normal”
uranium-ore occur as fine veins in the sandstone host-rock as well as
altered, broken, and slightly displaced grains in an illitic matrix, and in
nodules and veins of solid bitumen. Inclusions of galena, (Y,Gd)-rich
phosphates, a Pb-oxide and a Ti-oxide? were observed. Uraninites just below
RZB were partially altered to a uranyl-sulfate. Three generations of
uraninite were identified based on their PbO-contents of 8–11.06 wt%, 6 wt%
(the largest population), and a younger generation with 3 wt%. The high
Pb-uraninites may be the precursor to the low Pb-uraninites. Diffusional
loss of Pb is indicated by the presence of a Pb-oxide at the interface to
the uraninites. The behaviour of the metallic fission products, incompatible
with the uraninite structure, may mimic the behaviour of Pb in these
uraninites. The averaged impurity-content ranges from 4.29 to 6.89 wt%, and
consists mainly of SiO2, TiO2, ZrO2, FeO,
CaO, Al2O3 and P2O5. The
averaged content of Y2O3 and the Ln's is less than
0.78 wt% and there is a scattered positive correlation with
P2O5. The content of Y + Ln's is generally highest
in the uraninites from RZB. Uraninite hydration and the formation of
“uranopelite/zippeite” have caused complete loss of Y and the Ln's. These
elements seems also to be partially lost by weak phosphatian
coffinitization. The analytical results indicate that Y and the Ln's, which
are high yield fission products, may be released from uraninite during
alteration in the presence of P.
Depleted Uranium Oxides and Silicates as Spent Nuclear Fuel
Waste Package Fill Materials