The flow and diffusion of radon isotopes in fractured porous media: Pt. 1

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. (author)