Discrete fracture network (DFN) modelling of a high-level radioactive waste repository host rock and the effects on its hydrogeological behaviour

Fracture network modelling and a hydrological evaluation were performed in a well more than 900 m deep that penetrated the Boda Claystone Formation, a potential host rock for high-level nuclear waste disposal facilities in Hungary. The fracture network geometry was generated with a discrete fracture network algorithm, in which the permeability and porosity of the system can be calculated if the aperture of the fractures is known. The hy-drological aperture of the fractures was estimated via an aperture calibration based on a comparison of the measured and modelled permeability values. Flow zone indices were calculated for numerous sections along the well, designating hydraulic units, in which the fluid flow-controlling properties are internally even.Based on the fracture network geometry and the hydraulic flow units, most parts of the well behave uniformly, while three narrow zones differ significantly. The first zone is located in the upper 100 m of the well probably formed due to weathering. The second zone is located at approximately 400 m, where a large-scale structural boundary is presumed. In the third zone at 700 m, a lithological change greatly affects the hydrological prop-erties, but the influence of tectonic processes cannot be ruled out.