The migration of radionuclides in granite: a review based on natural analogues

The characterization of a geological formation for nuclear waste disposal should be carried out on a site by site basis. However, the study of analogous granitic formations, all around the world, gives a few general guidelines for a better understanding of elemental migration processes. In this review, focused on mineralogical, petrological and geochemical phenomena, it is shown that fractures should play a dominant role in transport through granites. Moreover, mineralogical transformations, as well as their textural and petrophysical consequences (e.g. permeability changes), should be reliably predicted. Finally, this review confirms that water-rock interactions do mobilize many elements, including analogues of actinides (U, Th, REE). However, most alteration minerals of granite (e.g. clay minerals, carbonates) exhibit a high capability for efficiently trapping these heavy elements. It is concluded that natural analogues are very useful for specifying the appropriate approach for the characterization of a geological site. They have also proved essential for developing and validating geochemical models of mass transfers around a repository in granite.