RD&D-Programme 2004 - SKB

Figure 19-2. Connectflow representation of a discrete fracture network model in a continuum
model.
resaturation of the repository after closure. Other issues of interest in an open repository may
be e.g. the influence on near-surface conditions, such as water levels in wells.
The code DarcyTools has also undergone considerable development over the past three
years. DarcyTools is basically a continuum model, but makes use of a special technique for
generating continuum fields. A discrete fracture network is created, which is then transformed
into a continuum field by a volume-based weighting of permeability properties for individual
structures. For transport of salt and tracers, a multi-rate matrix diffusion model has been
incorporated in DarcyTools. This technique makes it e.g. possible to describe the historic
evolution of salinity in the Baltic Sea in a credible manner, i.e. with realistic parameters for
e.g. rock porosity. DarcyTools has also been equipped with a new numerical equation solver
that makes it possible to simulate models with up to several million fractures and elements.
Connectflow and DarcyTools have both been used in the ongoing site modelling projects
for Forsmark and Oskarshamn /19-13, 19-14/. These studies have entailed that the models
have been tested against each other, and that some functionality such as interfaces has been
developed. Connectflow has also been used to redo the glaciation simulation that was produced
within SR 97 /19-15/.
New process knowledge regarding groundwater flow has been obtained in the super-regional
simulation studies conducted for Northern Uppland /19-16/ and Eastern Småland /19-17/. These
studies show that local flow patterns (flow cells), caused by the ratio between local and regional
gradients, dominate the groundwater flow down to typical repository depths. Since the local
topography strongly determines the local gradients, it is of the utmost importance to have a
good database and numerical resolution of the topography. Furthermore, these studies show that
the presence of saline groundwater at depth may serve as a floor for the groundwater flow and
thereby further reinforce the effects of the local flow cells.
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