Underground materials migrate in the groundwater. These materials
interact with various rocks (minerals) during this migration.
The migration behavior depends on the mineral and the properties
of the material. How does a material like uranium behave during
migration?
In JAERI, scientific research on uranium ore deposits has been
conducted in order to examine the future behaviour of materials,
after radioactive wastes have been disposed of into underground.
Research has been conducted at the Koongarra uranium ore deposit
in the northern part of Australia. This ore deposit is about 1,600
million years old, and has been largely stable since. Oxygen containing
groundwater infiltrated about 2 million years ago, and as a result,
some portions of uranium were dissolved in the groundwater, and
it migrated downstream to form a secondary ore deposit; uranium
moved only about 60 m (Fig. 10-3). The radioactivities of rock
samples were measured, and these samples were also examined by
optical microscopy (OM), scanning electron microscopy (SEM) and
transmission electron microscopy (Fig. 10-4, 10-5). As the result,
uranium was found to be concentrated in the iron minerals and
apatite mineral (a mineral with similar characteristics to the
human tooth), which exist in the host rock and weathered rock.
We have also carried out accelerated experiments to clarify the
mechanism. Finally, we have found that uranium is associated with
phosphate, which exists in the groundwater and in minerals. The
interaction of the groundwater with these minerals results in
the formation of a uranium mineral. |