AUTHOR=Williams Thomas , Sanglas Jordi , Trinchero Paolo , Gai Guanqun , Painter Scott L. , Selroos Jan-Olof TITLE=Recovering the Effects of Subgrid Heterogeneity in Simulations of Radionuclide Transport Through Fractured Media JOURNAL=Frontiers in Earth Science VOLUME=8 YEAR=2021 URL=https://www.frontiersin.org/journals/earth-science/articles/10.3389/feart.2020.586247 DOI=10.3389/feart.2020.586247 ISSN=2296-6463 ABSTRACT=

Groundwater flow and contaminant transport through fractured media can be simulated using Discrete Fracture Network (DFN) models which provide a natural description of structural heterogeneity. However, this approach is computationally expensive, with the large number of intersecting fractures necessitated by many real-world applications requiring modeling simplifications to be made for calculations to be tractable. Upscaling methods commonly used for this purpose can result in some loss of local-scale variability in the groundwater flow velocity field, resulting in underestimation of particle travel times, transport resistance and retention in transport calculations. In this paper, a transport downscaling algorithm to recover the transport effects of heterogeneity is tested on a synthetic Brittle Fault Zone model, motivated by the problem of large safety assessment calculations for geological repositories of spent nuclear fuel. We show that the variability in the local-scale velocity field which is lost by upscaling can be recovered by sampling from a library of DFN transport paths, accurately reproducing DFN transport statistic distributions and radionuclide breakthrough curves in an upscaled model.