Investigation of the effect of biotite distribution on anion diffusion in crystalline rock

深津 勇太; 舘 幸男

no journal, , 

Matrix diffusion in crystalline rocks is a key process for the retardation of radionuclide transport for geological disposal. Crystalline rocks mainly consist of quartz and alkaline feldspar grains and phyllosilicate minerals such as biotite. The biotite, randomly or regularly, distributed in the rock (foliation) could influence the diffusion of anion radionuclides due to the anion exclusion effect caused by its negatively charged surface. However, there is little information available about the effect of the content and distribution of biotite on anion exclusion in the matrix. In this study, through-diffusion tests with tritiated water (HTO) and anions (Cl or I), together with micro X-ray CT analysis, were conducted on crystalline rocks containing biotite to obtain their effective diffusion coefficient (D) and determine the biotite content and distribution. The anion exclusion effect was evaluated by the ratio of D of anion and HTO.