2012:67 Technical Note, Hydrogeological modelling of the Forsmark site

A modelling study has been conducted using discrete-fracture network (DFN) models in combination with discrete-feature hydrogeological modelling methods for representation of other potentially conductive features such as the disturbed zone around repository tunnels.

The principal results consist of hydraulic and transport property estimates for discrete-fracture network (DFN) models on block scales of 50 m and 100 m, including blocks containing representative segments of deposition tunnels with deposition holes. These block scales are representative of the discretization used in equivalent continuum porous medium (ECPM) models of the Forsmark site in support of the license application.

Analytical, geometrical, and permeameter simulation methods are used to give multiple methods for estimating effective properties and understanding the significance of results. 

Geometrical estimates of hydraulic conductivity, porosity and wetted surface for 50 m and 100 m block scales are comparable to analytical estimates based on models for fractures of infinite extent. However, the geometrical estimates of these properties, which take into account the finite extent of fractures as well as stochastic variation between blocks, are typically lower than the analytical estimates for the same depth intervals.

Comparison of geometrical estimates with permeameter simulations show that, for the DFN models and block scales, the geometrical estimates of hydraulic conductivity (averaged over the three coordinate directions) tend to be higher than the permeameter estimates by about an order of magnitude for the lower part of the hydraulic conductivity range, but show better agreement for the more conductive blocks.