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The Ruprechtov natural analogue site has been studied extensively for several years [1]. The site is
located in the North West part of the Czech Republic. It is underlain by granitic basement, covered
by kaolin layers of various thicknesses. The interface between the kaolin layers and the upper formation
(montmorillonite clays of Tertiary pyroclastic origin) in 20 to 50 m depth is composed by
the so-called clay/lignite layer of few meter thickness with high content of SOC and local uranium
enrichment (up to 600 ppm). Granite of Calsbad type with higher content of U is proposed as a primary
uranium source [1].
2. Methodology and approach
The project scientific activities in RTDC5 followed a scheme that can be assigned as “a puzzle system”
proceeding from investigation of “single puzzle pieces” (e.g. characterisation of natural organic
matter, characterisation of the U immobile phases combining sophisticated analytical methods,
etc.) to a more integral investigation and characterisation of a complex natural system, integrating
results e.g. from single uranium and natural organic matter investigations. Finally a complete
picture puzzle was assembled, i.e. the evaluation of hydrological, geochemical and environmental
data was used to characterize the hydrogeological flow pattern, the geochemical evolution of the
system and in particular the uranium enrichment scenario at the site.
Methodologies and analytical methods used were discribed elsewhere e.g. [2,7,13,14]. Direct combination
of classical methods (sequential extraction), radioanalytical methods (U(IV)/U(VI) separation)
and modern spectroscopical methods was implemented for the first time [4,11,13].
3. Results
The scientific results of the activities that had been performed within RTDC 5 were described in
more detail in [4].
In the first level of the project the single-task scientific topics were dealt with, e.g. sedimentary organic
matter (SOM) behaviour or uranium immobilisation as a smallest puzzle pieces. Organic matter
on the site was found having significant influence neither on U complexation and mobilization
by dissolved organic species in groundwater nor on U direct sorption on organic SOM [2,3,5].
Fe As U
As(V)
As
As(0)
Fe
U
150 μm, 4 μm step
504
150 μm, 2 μm step
Figure 2 : μ-XRF distribution maps for a
150*150 μm 2 area of a thin section of a
sample from NA5. The distribution of the
total As, Fe and U measured with Eexcite =
18 keV and its corresponding Red-Blue-
Green (Fe, As, and U, respectively) image,
as well as the arsenic chemical state
distributions for As(V) and As(0) are
shown. [5]
The application of macroscopic and microscopic methods provided a detailed insight into the U enrichment
processes at the Ruprechtov site. Confocal μ-XRF and μ-XANES identified U in the