Euradwaste '08 - EU Bookshop - Europa

Investigation of far-field processes in sedimentary formations
at a natural analogue site - Ruprechtov
Ulrich Noseck 1 , Vaclavá Havlová 2 , Radek Cervinka 2 , Juhani Suksi 3 , Melissa Denecke 4 , Wolfgang
Hauser 4
Summary
1 GRS, Germany
2 NRI, Czech Republic
3 University of Helsinki, Finland
4 FZK-INE, Germany
The analogue study at Rurpechtov site aimed at in-depth understanding of the behaviour of
uranium and organic matter in a natural sedimentary system similar to overlying strata of salt
domes but also other host rock formations for radwaste disposal. By application of a set of different
microscopic and macroscopic analytical methods the complex immobilisation mechanism
for uranium and the long-term stability of the immobile U(IV) phases were shown.
Sedimentary organic carbon (SOC) is microbially degraded in the lignite rich layers, but DOC
concentrations are relativley low, since only a very small fraction of SOC seems to be accessible.
Beside increase of process understanding another important contribution of this study to
the Safety Case consists in further development and testing of methods for colloid analysis,
sample characterisation on μ-scale, and evaluation of environmental isotope signatures.
1. Introduction
In component RTDC5 of the integrated EC project FUNMIG the far field of the host rock formation
salt is subject of the investigations. In contrast to the two other host-rock components RTDC3
(clay) and RTDC4 (granite) RTDC5 is a natural analogue study. The study is performed at Ruprechtov
site in Czech Republic and represents an analogue for potential migration processes in a
similarly structured overburden of a salt dome but also in other geological formations, which are
foreseen as potential host rocks for radioactive waste repositories.
Results from site characterisation were already available before this study, e.g. [1]. Within the
FUNMIG project specific questions have been addressed, to receive an in-depth understanding of
the evolution of the natural system and the key processes involved in uranium immobilisation as
well as the behaviour of organic matter. Emphasis was put into characterisation of the immobile
uranium phases, their long-term stability and the processes controlling mobility of uranium in the
system. The second major issue comprised the behaviour of colloids and organic matter in the system,
i.e. to better understand the interrelation between sedimentary organic carbon (SOC) and dissolved
organic carbon (DOC) and its impact on the mobility of uranium.
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