Project information

Transport of radionuclides in a natural flow system at Palmottu

Financing institution: CE-FI4W-CT95-0010

Participating institutions: Geological Survey of Finland (GTK), Id. Sweden (SKB), BRGM., ENRESA

Duration: 1996-1999

Project description

Key words

Natural analogue, uraninite, granite, Scandinavian, migration, reactive transport

Setting

Fig 1. Uraninite vein enclosed in granite. Hydrogeological sketch including the flow line and the sampling points

Hypothesis

Fig. 2. Conceptual model: The source of uranium is the dissolution of uranophane (U6+)
in the weathered zone and the dissoltion of uraninite in the deeper zones

Results

Fig. 3. Mass of uranophane and uraninte dissolved after 10,000 years.
The uranophane does not supply more uranium because it does not have more contact with the water.
The uraninite does not dissolve more because the pore solution reaches equilibrium.

Fig. 4. The dissolution of calcite in the weathered zone controls the pH of the entire system.
The dissolution of silicates and the pair Fe2+ - Fe(OH)3 control the Eh values in the shallower part of the system.
The dissolution of uraninite and the pair UO2 - U6+ controls the Eh in the deeper part of the system

Fig. 5. The model also matches the main solute concentration.

Adsorption

The U concentration in equilibrium with U⁶⁺ species sorbed on the Fe(OH)₃(am) surface is close to that measured in boreholes. However, unreasonably high amounts of Fe(OH)₃(am) would be required for adsorption to control the U concentration in solution during a period of time longer than 10 years.
 

Figure 6: Distribution of the U concentration in solution in equilibrium with species sorbed on Fe(OH)₃ (am) surface after 1 and 10 years of meteoric water infiltration