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esults and integrated to develop a conceptual model for the geological development of the site with
respect to the uranium immobilisation scenario.
The following major steps comprise the uranium imobilization scenario [13, 14]:
o detrital input of U bearing minerals from underlaying granite
o granite kaolinisation
o major volcanic activity deposition of tuffaceous material
o granite alteration + tuff argillitization
o microbial activity in clay/organic rich horizon reduction of dissolved sulphate formation
of pyrite nodules
o sorption of As and subsequent formation of arsenopyrite on pyrite nodules
o CO2-rich water likely initiated U release from accessory minerals in the granite soluble
uranyl-carbonate complexes formed
o U transported to clay/organic rich layers reduced on arsenopyrite layers
o secondary uraninite might have formed at later stages of the geological history at conditions
where phosphate concentration might have decreased.
4. Contribution to the SAFETY CASE
The assembled picture puzzle of the real Ruprechtov system analyses gave a clear message: the
sedimentary rock can provide under certain circumstance a strong barrier function for radionuclide,
in this case for uranium. The key parameter is presence of organic matter that contributed to maintaining
reducing conditions in the clay/lignite layers. Its oxidation provided degradation products
(phosphates) that than took part in uranium mineral formation (ningyoite). Moreover, the results
showed that the presence of organic matter does not naturally mean increased mobilization of radionuclide
due to organic ligand complexation or organic colloid formation. On the contrary, there
are no indications for significant uranium release during the last million years within reducing conditions
of clay/lignite layers.
5. Acknowledgements
This project has been co-funded by the European Commission and performed as part of the sixth
Euratom Framework Programme for nuclear research and training activities (2002-2006) under contract
FI6W-CT-2004-516514, by the German Federal Ministry of Economics and Technology
(BMWi) under contract No. 02 E9995, and by RAWRA and Czech Ministry of Trade and Industry
(Pokrok 1H-PK25).
References
[1] Noseck, U., Brasser, Th., 2006. Radionuclide transport and retention in natural rock formations
– Ruprechtov site. Gesellschaft für Anlagen- und Reaktorsicherheit, GRS-218, Köln.
[2] Cervinka, R., Havlova, V.; Noseck, U.; Brasser, Th.; Stamberg, K., (2007). Characterisation
of organic matter and natural humic substances extracted from real clay environment. Annual
Workshop Proceedings of the IP Project FUNMIG”. Edinburgh 26.-29.November 2007.
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