Experimental study of the effect of seepage on radon exhalation in circular tubular porous emanation media.

Radium, which is naturally present in many rocks, decays to the radioactive gas radon, which is then exhaled from the surface of underground tunnels and other underground buildings and is a major source of human exposure to radioactivity. A mathematical model for the migration of radon from a circular tubular emanation medium was established based on the seepage–diffusion migration theory for radon in porous emanation media, such as artificial retaining walls and the surrounding rocks in these locations. An analytical solution for the distribution of radon concentrations and the calculation formula for the radon exhalation rate under steady-state conditions were then obtained. An experimental device was designed to determine the radon exhalation rate under different pressure gradients. The theoretical calculation values for the radon exhalation rate and the total amount of radon exhalation are in good agreement with the experimental results. The radon exhalation rate at the low-pressure side increases with an increase in seepage velocity (pressure difference), while the radon exhalation rate at the high-pressure side is on the contrary. The total amount of radon exhalation increased over time with an increase in the seepage velocity and tended towards a maximum value. [ABSTRACT FROM AUTHOR]