RD&D-Programme 2004 - SKB

Uranium series analyses from clay- and hematite-rich fracture fillings from Äspö have been
evaluated together with analyses of uranium-234 and uranium-238. The results support the
interpretation that the current redox front (transition from oxidizing to reducing conditions)
does not reach a greater depth than about 30 metres on Äspö /19-81/.
The prevailing paleohydrogeological picture of the Äspö/Laxemar area is that four different
zones have been distinguished: (1) an upper zone where the redox conditions have varied and
where both calcite dissolutions and precipitation have taken place, then (2) a zone (down to
about 500 metres) with active calcite precipitation under various groundwater regimes (both
marine and meteoric), as a result of which zoned calcites are commonly occurring and old
hydrothermal calcites have been preserved as well. A supply of organic matter creates the
necessary conditions for activity of sulphate-reducing and iron/manganese-reducing bacteria.
(3) Down to about 1,000 metres, potential freshwater carbonates have been found in the
fractures. There are no clear indications of marine carbonates, however. Organic matter
reaches down to these depths, but becomes progressively less abundant with increasing depth.
(4) Below about 1,000 metres conditions are relatively stagnant, and low-temperature calcites
are rare /19-82/.
Programme
Further experiments with weathering of iron-containing fracture-filling minerals are planned
within the coming six-year period. Studies of fracture-filling minerals as indicators of former
groundwater chemistry will continue within the EU project Padamot. A project aimed at
studying Fe(III) oxides on Äspö has been started. The properties of these oxides may be
useful for determining previous redox conditions.
New calculations are planned in preparation for the next safety report to find out how deep a
glacial water can penetrate and how deep oxygenated glacial water can reach before the oxygen
has been consumed. The problem of direct and indirect datings of fracture-filling minerals
has not yet been solved. New developments are being monitored and will be acted on when
appropriate.
19.2.17 Reactions with the rock – sorption of radionuclides
Conclusions in RD&D 2001 and its review
It is stated in RD&D 2001 that experiments with the Chemlab probe will continue, but that no
other major work is planned.
SKI pointed out in the review of RD&D 98 that both a relevant database of K d values and a
good process understanding of sorption are important. This standpoint is repeated in the review
of RD&D 2001. SKI also says that surface complexation models should be developed to support
the K d concept, and that sorption kinetics should be investigated. Furthermore, the authority
would like to see sorption studies of site-specific material.
Newfound knowledge since RD&D 2001
Several projects are aimed at investigating sorption, including the Äspö projects RNR
(Radionuclide Retention) and True (Tracer Retention Understanding Experiments).
In the project RNR Actinide, migration of actinides has been studied in a drill core with a longitudinal
fracture. The core was installed in the borehole laboratory Chemlab-2, which was then
placed in a borehole at a depth of 450 metres in the Äspö HRL. The fracture was equilibrated
with groundwater before a solution of actinides (maximum solubility concentrations of tetravalent
plutonium-244, trivalent americium-243 and pentavalent neptunium-237) was injected into
the fracture from a compartment in Chemlab-2. After the actinide injection, groundwater was
262 RD&D-Programme 2004