Reactive Transport of Chemicals in Compacted Bentonite under Nonisothermal Water Infiltration

Abstract

This paper presents an investigation of coupled thermal, hydraulic, and chemical behavior of a compacted bentonite buffer under the heating and hydration conditions of geological disposal of high-level nuclear waste. The study presented provides further insight into the evolution of hydro-geochemistry of the compacted bentonite and the clay microstructure effects through a numerical modelling development of the reactive transport of multicomponent chemicals. The application/validation case study is based on a series of laboratory tests on heating and hydration of compacted bentonite for a period of 0.5-7.6 years reported in the literature. The effects of microstructure evolution during hydration and dehydration on the transport phenomena are included via a new approach that links the geochemistry of clay hydration/dehydration with the transport properties. The analysis results related to the moisture flow and chloride transport demonstrate close correlation with the experimental results by the inclusion of the effects of microstructure evolution in the transport phenomena. The results of numerical analysis of reactive transport of chemicals highlight the importance of accessory minerals present in bentonite on the distribution of some anionic species. The behavior of major cationic species is shown to be mainly governed by the transport processes. Further insights into the chemically driven processes in clay buffer due to coupled hydraulic and thermal effects are presented and discussed that are captured from the results of modeling the clay-water-chemical system.