Numerical modelling of nuclear waste repositories frequently requires the representation of complex geological features and engineering in a computational mesh. Crystalline host rocks present particular challenges because simulation of THMC processes often necessitates the creation of both volumetric meshes (continuous porous media) and discrete fracture networks (fractured media), or hybrid meshes in which separate parts of the domain are represented as different media.

Here, we present near-field THMC simulations enabled by new meshing workflows for generating unstructured CPM, DFN and hybrid meshes around an illustrative facility for spent nuclear fuel. We demonstrate how the LaGriT meshing toolkit, together with DFN meshing algorithms from the combination of FracMan and dfnWorks, can be applied to create a flexible set of medium representations. In the case study, the resulting meshes represent backfilled repository tunnels using surface-conforming 3D tetrahedral cells, whilst the fractured rock sections of the model are represented by either a DFN or CPM mesh depending on the physics to be simulated.

Using the developed meshes, example THMC simulations are undertaken in PFLOTRAN and FracMan. The results demonstrate how the integrated workflow can be used to create high quality, realistic model inputs which result in improved convergence and accuracy in numerical simulations.

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