Technical Report NTB 89-28

Numerical modelling of gas migration at a potential repository for low- and intermediate-level nuclear wastes at Oberbauenstock, Switzerland

Hydrologic impacts of corrosive gas release from a hypothetical L/lLW nuclear waste repository at Oberbauenstock are explored by means of numerical simulation. A schematic two-dimensional vertical section through the mountain is modeled with the simulator TOUGH, which describes two-phase flow of water and gas in porous and fractured media, Two reference cases are considered which represent the formations as a porous and as a fractured-porous (dual permeability) medium, respectively. Both cases predict similar and rather modest pressure increases, from ambient 10 bars to near 25 bars at the repository level. These results are to be considered preliminary because important parameters affecting two-phase flow, such as relative permeabilities of a fractured medium, are not well known at present.