ABSTRACT
Environmental humidity has a significanteffect on changes in free 220Rn (thoron) production rate and effective diffusion coefficient of 220Rn in uranium tailings. To understand such changes, a closed cavity containing porous 220Rn media with finite thickness was studied. Based on the 220Rn diffusion migration theory in porous media with finite thickness, a model for calculating the uniform 220Rn activity concentration in a closed container with porous media of finite thickness was established. A laboratory method for concurrently determining free 220Rn production rate and effective diffusion coefficient of 220Rn was proposed and a corresponding experimental setup was made. With samples taken from a uranium tailing impoundment in southern China, water content, free 220Rn production rate, and effective diffusion coefficient of 220Rn in uranium tailings were determined under certain environmental temperature and humidity conditions. Results show that: (1) The method and experimental setup presented in this study can simultaneously determine free 220Rn production rate and effective diffusion coefficient of 220Rn in porous media such as uranium tailing; (2) The free 220Rn production rate in uranium tailings increases linearly with water saturation. Effective diffusion coefficient of 220Rn, on the other hand, decreases exponentially with the increase in water saturation.
