RD&D-Programme 2004 - SKB

development that has taken place has also been incorporated in the planned strategy for
transport modelling within the site investigation programme /19-101/.
Results from True Block Scale have also been utilized to develop the geological structure and
retention model used in Task 6 within the Äspö Task Force, see under the heading “Model
studies” above.
Programme
Model studies
Within the international Äspö Task Force, Task 6 is continuing with modelling exercises in
a block-scale (200 metres) fracture network. Both experimental time scales and time scales
relevant to the needs of the safety assessment will be analyzed. The main purpose of Task 6 is
to study how models that have been conditioned on the basis of data from field investigations
(on a limited scale) predict transport when extrapolated in both time and space. Not only does
the exercise provide indications of how different model concepts work when extrapolated, it
also provides answers to what kinds of investigation data are useful and decisive in modelling.
Methodology for radionuclide transport is being developed in the ongoing safety assessment
project SR-Can, within integrated modelling for safety assessment. See the planning report
for a description of this development work /19-44/. With regard to transport in the geosphere,
mention can be made here of methodology for analyzing flow and transport through backfilled
tunnels, as well as transport calculations where detailed information from discrete fracture
network models concerning fractures and flows on a canister scale is transferred to the codes
for nuclide transport in the near- and far-field.
Field studies
Both True Block Scale Continuation and True-1 Continuation will continue during parts of
the coming period. Together, these projects comprise a platform where data collected from the
laboratory and the field are utilized to evaluate conceptual and numerical models for radionuclide
transport.
The current phase of the Äspö project True Block Scale Continuation (BS2B) includes
predictions and evaluations of tracer tests in an intermediate structure over distances of up to
30 metres where prediction on the basis of geological information is emphasized. Another goal
is to analyze how background fractures in the fracture network are activated in connection
with tracer tests. In the numerical modelling, microscale fracture heterogeneity is included in
the analysis, along with variability in retention properties perpendicular to the fracture plane
(i.e. variability in the direction for matrix diffusion).
Additional laboratory investigations of sorption will be conducted in the Äspö project True-1
Continuation. Specifically, the purpose is to analyze sorption properties in fine-grained fault
gouge and material in the altered rim zone nearest the fracture. A better understanding of the
sorption properties of these materials is important for predicting tracer tests in the field.
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