(GRS 199) Modelling the re-saturation of bentonite in final repositories in crystalline rock

Bentonite plays an important role in the design of underground repositories for toxic and radioactive waste. The hydrophilic properties of bentonite appear to be ideally suited for minimising any contact of water with the waste. However, the behaviour of bentonite at changing water contents is a very complex phenomenon which may be influenced by hydraulic, mechanical, thermal and chemical processes. Therefore, the prediction of the resaturation process requires a numerical model. The investigations documented here aim at a re-saturation model in the context of long-term safety analyses. For this reason, such models has to be as simple as possible.
 
A comprehensive discussion of the microstructure of bentonite as well as the processes which might be relevant to re-saturation forms a base for providing a sound conceptual model. Applying these fundamentals to the already existing models reveals some severe deficiencies. In particular, they do not contain the central process of hydration of the clay minerals and they do not account for the hydration of water vapour in the pore space. Thus, new conceptual models are developed for the re-saturation via liquid water as well as via water vapour.