Speaker
Description
Long-term safety assessments of radioactive waste repositories in rock salt require the modelling of coupled hydraulic and mechanical processes over geological time scales. One of the key processes is rock convergence – the progressive closure of excavated voids due to the creep of the surrounding salt formation. In voids that have been filled with crushed salt, rock convergence is strongly coupled to the compaction of the backfill material. Compaction reduces pore space, thereby affecting fluid flow and radionuclide transport in the near field.
This poster presents the development and integration of a convergence model into NaTREND, the dedicated near-field module of the RepoTREND code package, which was developed by GRS (Germany) for integrated performance assessment. The model describes the time-dependent volume reduction of repository compartments by expressing the convergence rate as the product of several physically motivated factors. These factors include the effects of fluid pressure, the increasing mechanical resistance of the compacting backfill, local geological variability, temperature and moisture conditions, as well as an explicit time-dependent term that describes the gradual slowdown of convergence.
A particular challenge lies in embedding this boundary-driven process into a grid-based finite-volume framework. Rock convergence is primarily determined by the mechanical interaction between excavated voids and the surrounding salt formation. Consequently, convergence is inherently defined at the scale of repository compartments rather than at the level of individual grid cells. The implemented approach therefore evaluates convergence at the compartment level and maps the resulting changes in geometry and material properties to the computational grid in a consistent way. This mapping explicitly accounts for anisotropy (direction-dependent behaviour) and discretization-related effects, ensuring a physically meaningful representation within the numerical scheme. Mechanical convergence affects not only the effective repository volume but also transport-relevant properties such as porosity, permeability and capillary behavior.
This poster summarises the conceptual model and outlines its numerical implementation within the NaTREND simulation framework.
| Country | Germany |
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