2006 Volume 12 Issue Supplement2 Pages 171-176
The GESPER coupled geochemical reaction-mass transport analysis code was improved for application to complex regions, e.g. engineered barriers and the surrounding rock regions in radioactive waste disposal systems. To investigate the role of a bentonite buffer in systems with cementitious materials as a component, typical phenomena considered in the interaction of cement leaching water and a typical Japanese sodium-type bentonite were analyzed by code under various conditions. Bentonite calcification, calcite precipitation, and pH-dependent protonation of the edge sites of smectite were examined. Cation-exchange characteristics of the bentonite may maintain the expected performance of sodium-type bentonite under conditions of sodium concentration higher than about 0.01 M in the pore water. A bentonite buffer layer of 1 m thickness may reduce pH in the pore water for several hundred years. Phenomena in the bentonite and surrounding rock were calculated simultaneously using a multimedia model, to be discussed.
