Novel lattice models for porous media

Several barriers in a nuclear waste repository, such as waste immobilisers, backfills and host rock are porous. Predicting the changes in their permeability over the repository lifetime is critical to the assessment of radionuclide transport. Pore network models used in petrology offer an advantageous way for such predictions, because they can be linked elegantly to physical mechanisms that could lead to pore structure changes, e.g. mechanical damage, gas generation, or irradiation. The existing models are based on cubic lattices, where pores residing on lattice sites are connected by throats to neighbouring pores. The need to increase the pore coordination beyond the closest six neighbours has lead to topologically permissible but physically unrealistic networks with intersecting throats. This work proposes novel network models based on two non-cubic lattices with rhombic dodecahedral and truncated octahedral cells. They offer coordination of 12 and 14, respectively, without compromising the network's physical realism. The use of the models to predict fluid transport under various conditions, including internal gas pressure, is demonstrated and compared to existing models' predictions. The coupling with mechanical damage using dual networks representing the solid phase is also described.