Hyperalkaline Cement Leachate-Rock Interaction and Radionuclide Transport in a Fractured Host Rock (HPF Project)
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+\SHUDONDOLQH&HPHQW/HDFKDWH5RFN,QWHUDFWLRQDQG5DGLRQXFOLGH7UDQVSRUWLQD )UDFWXUHG+RVW5RFN +3)3URMHFW Urs Mäder 1, Bernd Frieg 2, Ignasi Puigdomenech 3, Michel Decombarieu 4 and Mikazu Yui 5 1 Geological Sciences, University of Bern, Baltzerstr. 1, CH-3012 Bern, Switzerland 2 Nagra, Hardstrasse 73, CH-5430 Wettingen, Switzerland 3 SKB, Box 5864, SE-102 40 Stockholm, Sweden 4 ANDRA, Parc de la Croix-Blanche, 92 298 Châtenay-Malabry cedex, France 5 JNC, Tokai Works, Tokai, Ibaraki 319 - 1194, Japan $%675$&7 The HPF project (Hyperalkaline Plume in Fractured rock) at the Grimsel Test Site comprises an underground long-term field experiment in a shear zone, in-situ radionuclide transport experiments, two laboratory core infiltration experiments, sophisticated reactive transport modeling exercises, studies on radionuclide stability and solubility, innovative on-line measurement techniques and development of equipment for high-pH conditions (K-Na-Ca-OH, pH = 13.4 at 15 °C). Results to date indicate a decrease in the overall transmissivity of the tested shear zone over a duration of 2 years accompanied by channeling of flow as evidenced by repeat dipole tracer testing with Na-fluorescein, 82Br, 131I, 24Na, and 85Sr. The associated evolution in fluid chemistry indicates the in situ formation of Ca-Si-hydrates. Tracer transport modeling of dipole tests are based either on a heterogeneous porous medium approach or on discrete fracture models. Reactive transport modeling is achieving reasonable agreement with a laboratory core infiltration experiment. Integral to the project are supporting sorption / stability studies, colloid measurements, and development of analytical and measurement techniques. ,1752'8&7,21 The motivation of the HPF project (Hyperalkaline Plume in Fractured rock) at the Grimsel Test Site (GTS) is to understand and predict the effects of hyperalkaline leachates (which are expected to emanate over long time periods from a cementitious repository) on a repository host rock. An important aspect is that even at ambient temperatures, hyperalkaline plumes may induce measurable changes to the hydraulics of fracture-bound flow fields. This situation offers a challenging test case for new developments in implementing porositypermeability feed back in reactive transport computer models. The aims of the project are: • to examine the likely cement EBS (engineered barrier system) / repository host rock interactions in the vicinity of a cementitious repository by means of an in-situ, long-term experiment at ambient temperature • to monitor the chemical, mineralogical, physical and hydraulic changes in the host rock's flow system during high-pH / rock interaction • to link these changes to the transport and retardation properties for select radionuclides by means of dipole tracer tests • to constrain parameters of a complex field situation in terms of structure, mineral alteration, and transport properties as a function of space and time • to test the capabilities of state-of-the-art reactive transport comput
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