Colloid properties in granitic groundwater systems, with emphasis on the impact on safety assessment of a radioactive waste repository

Conference · Fri Dec 31 04:00:00 EST 1993

OSTI ID:62272

Degueldre, C ^[1]

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1. Paul Scherrer Institut, Villigen (Switzerland)

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 Saeckingen, 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 concentration are not expected to exceed 100 ppb. However, under transient conditions when physical and/or chemical changes are occurring (e.g. hydrothermal activity), colloid generation may be enhanced. Colloid concentration of 10 ppm may be observed when the calcium concentration is low enough (<5 ppm). Whereas reversible sorption on the host rock leads to conservative predictions for radionuclide migration rates, the reverse is true for sorption onto colloids. The most conservative assumptions are therefore reversible nuclide sorption and colloid attachment on the rock and irreversible sorption on colloids. For calcium concentrations larger than 5 ppm, and sorption capacities at the nM level, their presence in granitic aquifer can be neglected in safety analysis when reversible sorption onto colloids is considered. This situation could change when sorption is followed by aggregation on incrustation processes. This study shows that for the colloid conservative size distributions found and for the granitic water conducting fissures considered, sorption-agglomeration reactions are unlikely to take place. Therefore, irreversible sorption by this mechanism is improbable.

• OSTI ID: 62272
• Report Number(s): CONF-921101--Vol.294
• Country of Publication: United States
• Language: English

Related Subjects

05 NUCLEAR FUELS
54 ENVIRONMENTAL SCIENCES
CHEMICAL ANALYSIS
COLLOIDS
GRANITES
GROUND WATER
RADIOACTIVE WASTE FACILITIES
RADIOACTIVE WASTES
RADIONUCLIDE MIGRATION
SAFETY ANALYSIS
SORPTIVE PROPERTIES
UNDERGROUND DISPOSAL