Suppression of Radon Exhalation from Soil by Covering with Clay-mixed Soil

The effectiveness of bentonite-mixed soil as a barrier to radon exhalation from soil is investigated experimentally at a closed uranium mine in Japan. Continuous observations of radon flux from a clay-covered soil surface and a bare soil surface were conducted for a period of 80 days. The mean radon flux from the clay-covered plot was one fifth of that from the bare plot, demonstrating that the clay-mixed soil is effective as a boundary suppressing radon exhalation from the contaminated soil. Numerical analyses using a one-dimensional radon transport model for an unsaturated soil for the dry weather conditions confirmed the effectiveness of the clay-mixed soil cover under a range of weather conditions.