Simulations of flow-through experiments using the granite fractures by THMC coupled model considering pH dependence

摘要

When evaluating the stability of the geological disposal system for the high-level radioactive wastes(HLW),it is necessary to estimate the long-term permeability change of rock fractures that control the groundwater flow within natural barrier by numerical simulation.In the previous study,it is indicated that mineral reactions within rock fractures such as pressure dissolution alter fracture permeability over a long duration.In the actual environment where HLW are disposed,mineral reactions may result in the change of chemical property in groundwater such as a change in pH due to the inflow of the highly alkaline cement solution from an artificial barrier.However,numerical models that can simulate the influence of change in pH of groundwater on rock permeability change driven by mineral reactions observed in the experiment have not been developed well.In this study,a THMC coupled model considering multi-mineral reactions depending on pH condition is presented.Then,the proposed model was applied to replicate the results obtained from flow-through experiments using granite samples with a single fracture under the various pH conditions of permeable water.The model predictions could reproduce the permeability change observed in the experiment under neutral conditions,but couldn't simulate well it under alkaline conditions.The predicted effluent element concentrations showed a relatively good agreement with experimental measurements in several elements under both neutral and alkaline conditions.