温度・pHを制御したフロースルー溶解試験による花崗岩溶解速度定数式の提案とその妥当性の検討

抄録

When considering a geological isolation of high level radioactive wastes, the evolutions of the mechanical, hydraulic, and transport properties of the targeted rocks should be evaluated in advance because those may be degraded by the coupled thermal, hydraulic, mechanical, and chemical effects induced by the emplacement of the wastes. Chemical reactions such as mineral dissolution and precipitation that is dependent on temperature and pH conditions, may be one of the key issues that may trigger off the degradation. Therefore, the dissolution mechanism of the targeted rocks should be thoroughly examined under various temperature and pH conditions.
In this work, a suit of flow-through experiments in granite has been conducted at temperatures of 30, 50, and 70°C, and at pHs of 6, 9, and13, to examine the granite dissolution behavior. An apparent dissolution rate equation of the granite is defined under arbitrary temperature and pH conditions. The acquired dissolution rates are compatible to those evaluated in the literature. Utilizing the dissolution rates, the evolution of the element concentrations measured in the permeability experiments on the granite fracture is replicated. The predicted concentrations follow the experimental measurements both qualitatively and quantitatively. Although showing in a good agreement with the experimental measurements, the predictions slightly underestimate the actual. This is attributed likely to the unaccounted effects of mineral dissolution at the contacting asperities, indicating that a more sophisticated dissolution equation should be achieved by considering such a dissolution mechanism.