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Granite /Nuclear reaction analysis /Radwaste disposal /Rutherford backscattering/Sorption/Transuranium elements SummarySorption experiments have been carried out with polished sections of vitreous silica and granite constituents and aqueous solutions of transuranium analogues (U,Th and REE). The sorption is evaluated through the near-surface analysis of solids with MeV ion beam techniques (RBS and RNRA). Two retention mechanisms have been found, namely incorporation within hydrosilicates and precipitation of secondary crystalline phases. Implications for the disposal of radwaste in a geological formation are discussed.

Samples from a new natural reactor of Oklo (zone 10) have been investigated with the aim of specifying possible elemental migrations into its close surroundings. The mineralogy demonstrates the occurrence of a redox front at the boundary of the reactor. We show first that significant migration of rare earths and uranium took place on a decimetric scale around the reactor and that secondary phases (both clay minerals, carbonates filling fissures and accessory minerals such as zircon) are responsible for their subsequent immobilization within the rock.

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