Uranium Content, ²³⁴U/²³⁸U Activity Ratio and Watar Quality of Seepage Water in the Tsukuba Tunnel, Ibaraki, Japan

Abstract

Uranium content, ²³⁴U/²³⁸U activity ratio and chemical component of seepage water have been examined in the Tsukuba Tunnel, Ibaraki, northeast Japan. Quality of fracture water through granodiorite was varied from calcium carbonate type to alkali carbonate type in accordance with the distance from the adit mouth. Uranium content in fracture water through gabbro was less than that through granodiorite. ²³⁴U/²³⁸U activity ratio was higher than 1.0 because of the recoil effect of ²³⁴Th. The maximum value was 3.9. Uranium content of such a sample was high, even though the water was in reducing condition. It is concluded that this sample has been recharged by stagnant deep water that had been confined into rock fractures for a long time and led to have large amount of HCO₃^-.