The Flow and Diffusion of Radon Isotopes in Fractured Porous Media: Part 1, Finite Slabs

Abstract

Abstract In the conventional equations used to describe gaseous transport of radon isotopes through fractured porous media the two processes responsible for radon movement are diffusion and pressure-driven flow (advection). Fractures in a porous medium can be especially effective for pressure-driven transport but lateral diffusion can be a strong mitigating influence. The interplay of diffusion and flow is examined for a fractured concrete slab and a fractured, high-diffusivity layer between a house and an underlying radium-rich medium. For underpressures common in houses, fractures only a fraction of a millimetre wide in concrete are important and often big enough to ensure flow transport of radon with small diffusive loss. In contrast, fractures several millimetres wide through high-diffusivity layers several metres thick such as sand may be unimportant for radon transport due to large lateral diffusive losses.