Steady-state Rn diffusion through tailings and multiple layers of covering materials

Uranium tailings piles are generally rehabilitated by covering them with a number of layers of earthen materials. This paper derives exact equations for the Rn concentration profile and flux attenuation through any number of covering layers. The equations take account of the distribution of Rn between interstitial air and water. Numerical examples are given to show that approximate methods give rise to significant errors in some circumstances. The flux attenuation factor depends not only on the diffusion coefficient, porosity, moisture content and thickness of each layer but also upon the order of placement. To achieve maximum flux attenuation, the least permeable material should be uppermost.