オクロ鉱床によるナチュラル・アナログ研究の現状と展望 (1993年度日本地球化学会奨励賞受賞記念)

抄録

The Oklo uranium ore in the Republic of Gabon is an ideal natural analogue for radioactive waste disposal in geosphere, because it has preserved abudant fissiogenic nuclides for 2 Ga. Isotopic studies of the Oklo fission reactor zones have been carried out to estimate the geochemical behavior of fissiogenic nuclides and to evaluate some nuclear parameneters for the reactor characterization. In a few years, new type of fission reactor zones has been found in the Oklo ore, and interesting information on the behavior of long-lived radionuclides such as ⁹⁰Sr, ⁹⁹Tc, ¹³⁵Cs and ¹³⁷Cs has been obtained. Cooperative isotopic measurements by whole rock analysis (with TIMS and ICP-MS) and by in-situ observation (with SIMS) make possible to clarify the retention and /or migration processes of fissiogenic nuclides over the wide range from μm to m. In this paper, recent studies and perspectives in near future on the behavior of radionuclides expected from Oklo study are reviewed.