Utilizing high-resolution 3D Voronoi meshing to analyze field data from the Brine Availability Test in Salt (BATS)

Salt is an attractive disposal medium for radioactive waste because intact salt is essentially impermeable and non-porous. However, upon drift or borehole excavation a damaged region develops surrounding the excavation which causes increased permeability and porosity creating potential flow paths for brine. Brine leads to corrosion of waste forms and waste packages and is a possible transport vector for radionuclides, so it is important to better understand the early-time behavior and evolution of brine flow in a salt. As a result, this study is part of Task E of DECOVALEX-2023 which focuses on understanding the evolution of thermal, two-phase hydrological, and mechanical processes in the excavation damaged zone in salt. Field measurements from The Brine Availability Test in Salt (BATS) 1a heater experiment are analyzed by implementing a high-resolution three-dimensional numerical model. This salt heater experiment consists of 28 days of heating and 13 days of cooling in a central borehole within bedded salt at the Waste Isolation Pilot Plant (WIPP). Here, the flow simulator PFLOTRAN is utilized; simulations are run on a Voronoi mesh, with temperature-dependent thermal conductivity, permeability and porosity decay away from excavations. The temperature-dependency of permeability is done to match field measurements. Results from the simulation match temperature measured in the field within + /- 0.1 °C and the total brine inflow over the 41-day experiment. This study illustrates that the accuracy of the temperature evolution within salt is critically important when analyzing and modeling experimental data by simulating three heating scenarios of the BATS 1a experiment showing that temperature has a direct effect on total brine inflow.