Evaluation of geochemical conditions favourable for the colloid-mediated uranium migration in a granite fracture

Nairoby Albarran nairoby.albarran@ciemat.es (Environmental Department, CIEMAT, Avda. Complutense 22, Edif. 19, 28040 Madrid, Spain)
Úrsula Alonso
ursula.alonso@ciemat.es (same address as N. Albarran)
Tiziana Missana
tiziana.missana@ciemat.es (same address as N. Albarran)
Miguel Garcia-Gutiérrezmiguel.garcia@ciemat.es (same address as N. Albarran)
Manuel Mingarro
m.mingarro@ciemat.es (same address as N. Albarran)

e-Terra
volume 5 - nº 2 - 2008

e-terra.geopor.pt

Key-words: uranium, colloids, transport, radioactive waste repository, granite.

Abstract: The presence of colloids in groundwater can significantly affect contaminant migration. Therefore, the evaluation of the conditions in which the presence of colloids can favour contaminant migration is one of the most critical tasks for the assessment of the security of radioactive waste repositories. Colloids will be important for radionuclide migration towards the geosphere if they exist in non negligible concentration and if they are stable and mobile. Those aspects are strictly related to the geochemical conditions of the medium, which are of primary importance. In this work, we centred our attention on the uranium migration in a granitic fractured environment. Colloids were shown to be stable over months in low mineralized and alkaline waters (pH=9.7 and ionic strength 1·10-3 M). The transport of uranium in a granite fracture was studied, using a natural groundwater from the Grimsel Test Site (Switzerland) located in a granitic massive, in absence and presence of bentonite colloids. Results showed that the uranium migration was significantly affected by the presence of colloid in the medium.

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