Abstracts

samples from the Upper Silurian, the D e
values (iodide tracer) are 10 -12 m 2 /s or lower. The
D e
values obtained with tritiated water (HTO) tracer are on average 1.9 times greater
(range 0.8 to 4.9) than measured with iodide due to anion exclusion. The sample-scale
anisotropy ratios (D e
parallel versus D e
normal to bedding) are 0.9 to 4.9 for iodide and
1.1 to 7.0 for HTO. Diffusion measurements were conducted with confining pressure up
to 17.4 MPa. For measurements with HTO tracer, increasing confining pressure results
in decreases in D e
up to -34%, and with iodide tracer the decreases were as large as -44%.
Comparison of numerical simulations to measured depth profiles for naturally occurring
porewater tracers allowed for assessment of diffusion coefficients at the formation scale.
Using best available estimates for boundary and initial conditions, simulated tracer profiles
do not match the measured profiles unless the diffusion coefficients are decreased relative
to the laboratory-measured values by a factor between five and ten for chloride, and between
one and three for 18 O. Future efforts will focus on measurement of diffusion coefficients
for dissolved gases (e.g. CH 4
, CO 2
and He) and refinement of the RI methods to
improve tracer detection so that the method can be applied to rocks with very low porosity,
and to expand the range of tracers for both conservative and reactive transport.
273 - Coupled Groundwater Flow and Reactive Transport
Simulations of the Evolution of Groundwater Chemistry for a Deep
Geologic Repository in Shield Rocks
Lee Hartley, Steve Joyce, & Hannah Woollard
Amec Foster Wheeler, Harwell Oxford, Didcot, Oxfordshire, United Kingdom
Niko Marsic, & Magnus Sidborn
Kemakta Konsult AB, Stockholm, Sweden
Björn Gylling & Ignasi Puigdomenech
Svensk Kärnbränslehantering AB, Stockholm, Sweden
Lasse Koskinen
Posiva Oy, Olkiluoto, Eurajoki, Finland
SKB, Swedish Nuclear Fuel and Waste Management Company, has submitted a license
application for a spent nuclear fuel repository at Forsmark sited in crystalline rocks of the
Fennoscandian shield. In support of this application various quantitative assessments were
made to demonstrate the long-term safety of the proposed repository. One such assessment
involved simulation of the long-term evolution of groundwater chemistry as a factor
affecting performance of the disposal system, since this requires geochemical conditions
are maintained within specified limits, specifically relating to salinity, pH and redox conditions.
In the reference case the current temperate period lasts until 12,000 AD. A case of
prolonged meteoric infiltration to 60,000 AD is also considered resulting from e.g. global
warming. This is to fulfil a regulatory request to assess whether extended dilute water
infiltration might lead to a rise in redox potential and also to an increase in erosion of the
bentonite barrier due to formation of colloids. In order to simulate long-term transient
groundwater flow and solute transport with water-solute-rock interactions in 3D regional
equivalent porous medium models, new tools have been developed to closely couple
geochemical, groundwater flow and transport calculations, and perform these efficiently
50 IAH-CNC 2015 WATERLOO CONFERENCE