Development and verification of a reactive transport model for long-term alteration of bentonite–cement–seawater systems

It is important to assess long-term alteration of engineered barrier composed of bentonite and cement for the safety assessment of radioactive waste disposal. A mineral model for bentonite–cement–seawater systems and a hydraulic conductivity model for bentonite buffer materials were developed and verified by comparing results of the model calculations with experimental observations. Changes in mineralogy of bentonite buffer materials and accompanying changes in the hydraulic conductivity over 10,000 y were calculated to identify key issues in the long-term alteration analysis. The calculation showed that the temperature, the slow kinetics of the dissolution of montmorillonite, the diffusive mass transfer and the initial (∼1000 y) mineralogical changes were identified as the key issues. The salinity of the groundwater was identifies as another key issue, which has both positive and negative effects on the hydraulic conductivity.