Weerd H van de ,
Leijnse A ,
Hassanizadeh SM ,
Richardson-van der Poel MA
88 p
in Dutch
1994
Toon Nederlands
English Abstract A study of uranium transport in one of the best studied
"natural analogue sites", the Koongarra site of Alligator Rivers uranium
deposit (Australia), is carried out. The purpose of this research is to
test the simulation package METROPOL, developed at RIVM to simulate
transport of radionuclide, over large time scales. At the Koongarra site
secondary uranium mineralization and dispersed uranium, is present from the
surface down to the base of weathering, some 25 meters deep. In the
Koongarra uranium deposit, the transport processes have been going on for a
few (1-3) million years, and during this period many climatological,
hydrological and geological changes have taken place. Field data show that
three layers can be distinguished in the Koongarra area: i) a top layer
which is fully weathered, ii) an intermediate layer which is partially
weathered (the transition zone) and iii) a lower layer which is unweathered.
The groundwater velocities are largest in the transition zone which has been
moving downward as the weathering process proceeds. The transport of
uranium in the transition zone is simulated with the finite element code
METROPOL. It has been adapted to account for the movement of the transition
zone and to describe the dissolution of uranium in the orebody by a
non-equilibrium relation. In the simulations a qualitatively reasonable
agreement between calculated and measured soluble uranium concentration in
the present transition zone is achieved. In this study was shown that over
large timescales geologic processes may have a large impact on the transport
of radionuclides ; over large timescales, the movement of the transition
zone will have a large impact on the uranium concentration distribution.
The simulation results in this study are stongly influenced by the
parameters values, which are difficult to estimate for a period of some
million years. The largest uncertainties are associated with the boundary
conditions.
