Effects of Fracture Transmissivity Relationship on Repository Performance Characteristics

Abstract

Abstract When simulating flow and transport through sparsely fractured rocks in Earth’s subsurface, discrete fracture network (DFN) modeling has become the alternative approach to continuum approaches. In this work, DFNs are generated using dfnWorks, a parallelized computational suite developed by Los Alamos National Laboratory. The DFNs are then mapped to an equivalent continuous porous medium (ECPM) to allow for nuclear waste repository performance assessment simulations. To this end, reactive flow and transport calculations are performed in PFLOTRAN, a parallel multiphase flow and reactive transport code. For this study, the application problem is a crystalline repository reference case based on the Forsmark site in Sweden. When converting the fracture networks into ECPMs, fracture transmissivity is used to determine the continuum permeability field. New capabilities in dfnWorks have enabled the use of the depth-dependent correlated relationship. To understand the effect of adding the depth-dependent relationship, this study compares repository performance quantities of interest and ECPM permeabilities from the same DFN where the only change is the transmissivity relationship. It was found that although the permeabilities for the varying transmissivity relationships were significantly different, this did not strongly influence the quantities of interest.