Analysis of radionuclide migration in combined fracture/porous media by using stream tube approach

Abstract

Radionuclide migration in geologic media is investigated by using semi-infinite medium Green``s function techniques. In view of critical path to reach the biosphere, a combined fracture/porous media model is introduced to consider the effect of enhanced migration due to thin fracture. The mechanisms for solute transport are assumed to be advection in the fracture, hydrodynamic dispersion in the porous matrix, radioactive decay of the ion species, and sorption on the fracture wall. Stream tube approach is suggested as an efficient method to analyze ground-water hydrology primarily along the fractures. Three-dimensional heterogeneous media may be approximated as network of one-dimensional flow paths (fractures) and the subsurface transport equation can be solved more easily and efficiently by using Green``s function techniques within each stream tubes. And a method of combining these Green``s function to produce an overall Green``s function for the flow path network is developed. Analytical solution with various release mode for heterogeneous media is obtained and numerical calculations are performed for parametric studies. Comparison with other model shows the validity of the present study.