Role of paleohydrogeological studies from the perspective of the natural analogue study of the Tono uranium deposit

Sasao, Eiji   ; Iwatsuki, Teruki  ; Amano, Yuki   

In the Tono uranium deposit, most of the uranium has been preserved, even though the deposit has been subjected to the effects of several cycles of uplift, erosion and subsidence since its formation. In order to enhance confidence in the demonstration of long-term safety of a geological disposal system for high-level radioactive waste in a geologically active area such as the Japanese Islands, it is necessary to understand how geological phenomena have affected deep geological environments. To contribute the studies of the Tono uranium deposit to paleohydrogeology, it is important to determine any long-term changes and to evaluate the stability of the geological environments. Because the deep geological environment is affected by many factors such as groundwater flow, microbes, water-rock interaction and so on, a paleohydrogeological approach is essential to know the state of ancient, deep geological environments which might influence the the preservation or mobilization of uranium.