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exists as a stable mineral phase in oxidation state IV. Most uranium in all samples is U(IV), with
contents between 50 and 90 wt.%. The highest U(IV) fraction is found in NA6-37.
Table 1. Amount of uranium and 234 U/ 238 U-activity ratios (ARs) in the different phases from uranium
separation [4]
sample U [ppm]
U(IV) U(VI) U(res, IV) U(IV) total
[%]
234 238
U/ U [%]
234 238
U/ U [%]
234 238
U/ U [%]
NA6 35a 356 7 28.7 0.54 0.01 41.9 1.42 0.02 29.5 0.65 0.01 58.1
NA6 35b 468 9 45.9 0.56 0.01 33.3 1.69 0.03 20.7 0.64 0.02 66.7
NA6 35c 369 8 23.3 0.47 0.01 47.4 1.16 0.02 29.3 0.67 0.01 52.6
NA6 37a 37.3 2 73.7 0.79 0.03 15.7 2.66 0.07 10.6 0.73 0.01 84.3
NA6 37b 47.5 1,5 66.2 0.52 0.01 9.0 3.37 0.15 24.8 0.86 0.02 91.0
NA6 37c 35.7 2 51.3 0.58 0.01 19.8 2.56 0.08 28.9 0.71 0.04 80.2
NA11 a 52.5 2,2 4.2 0.44 0.02 34.1 0.94 0.01 61.7 0.55 0.02 65.9
NA11 b 53.6 2,5 6.1 0.39 0.02 49.6 0.94 0.02 44.3 0.67 0.02 50.4
NA12 a 27.2 1,4 3.9 0.26 0.02 47.5 1.31 0.04 48.6 1.22 0.03 52.5
NA12 b 31.4 2,1 4.2 0.13 0.02 57.4 1.25 0.04 38.4 1.04 0.03 42.6
NA13 a 216 7 5.4 0.53 0.02 46.8 1.15 0.02 47.8 0.55 0.01 53.2
NA13 b 230 9 1.6 0.58 0.03 46.2 1.15 0.02 52.2 0.53 0.01 53.8
NA14 b 317 10 13.3 0.87 0.02 68.8 1.28 0.02 18.0 0.44 0.01 31.2
NA14 c 354 11 25.4 0.88 0.02 39.6 1.11 0.01 41.5 0.54 0.01 58.5
That U(res) and U(IV) exhibit in nearly all samples an AR below one is a strong indicator for their
long-term stability. AR values significantly below unity are caused by the preferential release of
234 U, which is facilitated by �-recoil process and subsequent 234 U oxidation. In order to attain low
AR values of approx. 0.2 in the U(IV) phase, it must have been stable for a sufficiently long time,
i.e. no significant release of bulk uranium has occurred during the last million years. This is in good
agreement with the hypothesis that the major uranium input into the clay/lignite horizon occurred
during Tertiary, more than 10 My ago [10].
3.3 Real system analysis
One part of the work comprised the re-evaluation of existing, and the evaluation of new hydrological,
geochemical and environmental isotope data from groundwater wells at Ruprechtov site to
characterise the hydrogeological flow regime and the carbon chemistry in the system. The existing
idea about the flow system in the tertiary sediments was confirmed. Additionally, the complexity of
the system was demonstrated [2]. Differences in stable isotope signatures in the northern part of the
site indicate very local connections of the flow systems with the flow system in the underlying
granite via fault zones.
The chemical conditions of the site are characterised by low mineralised waters with ionic strengths
in the range from 0.003 to 0.02 mol/l. The pH-values vary in a range of 6.2 to 8, the Eh-values from
435 mV to -280 mV. More oxidising conditions with lower pH-values are found in the near-surface
granite waters of the infiltration area. In the clay/lignite horizon the conditions are strongly reducing
with Eh-values as low as -280 mV. The Eh-values measured directly by in-situ probe are significantly
lower than those measured on-site in pumped water. The latter method is more susceptible
to disturbances by the contact with atmosphere, which is probably responsible for these differences.
In order to understand the carbon chemistry and the interrelation between SOC and DOC iso-
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