Migration of radioelements around the new nuclear reactors at Oklo: petrological and geochemical results

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. (author). 2 refs., 1 fig., 3 tabs