Colloid Properties in Granitic Groundwater Systems, with Emphasis on the Impact on Safety Assessment of a Radioactive Wa
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COLLOID PROPERTIES IN GRANITIC GROUNDWATER SYSTEMS, WITH EMPHASIS ON THE IMPACT ON SAFETY ASSESSMENT OF A RADIOACTIVE WASTE REPOSITORY
C. DEGUELDRE, Paul Scherrer Institut, CH-5232 Villigen.
ABSTRACT Since colloids are present in all groundwaters, they are studied because of their potential role in the migration of relevant radionuclides in the geosphere. Colloid sampling and characterization campaigns have been carried out in the Grimsel area, Switzerland (Transitgas tunnel, Grimsel Test Site) and in the North Switzerland/Black Forest area (Menzenschwand, Bad Sickingen, Zurzach, Leuggem). On the basis of results obtained for 25 groundwaters a consistent picture is emerging. Colloids in granitic systems are basically composed of components of the aquifer materials (clay, silica). Under the hydrogeochemical conditions existing at depth in crystalline rock systems, colloid concentrations are not expected to exceed 100 ppb. However, under transient conditions when physical and/or chemical changes are occuring (e.g., hydrothermal activity), colloid generation may be enhanced. Colloid concentration of 10 ppm may be observed when the calcium concentration is low enough (
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