Abstract
The Oklo uranium deposit at the Republic of Gabon, central Africa, had partly functioned as natural fission reac-tors. Many elements of the Oklo reactor zones and the related samples show the variations in the isotopic compo-sition caused by a combination of nuclear fission, neutron capture, and radioactive decay. Isotopic studies provide useful information to estimate reactor conditions and to understand behavior of radionuclides in geological media. In my recent work, in-situ REE, Pb, and U isotopic analyses of individual tiny minerals in and around reactor zones have been performed using a Sensitive High Resolution Ion Micro-Probe (SHRIMP). The data suggest the adsorption property of apatite in trapping fissiogenic LREE and Pu migrated from the reactor zone, and distribution of fissiogenic REE under oxidizing atmosphere.
