Abstract: To compare the effectiveness of radon suppression with the addition of different proportions of bentonite or lime powder in soil, a standard module (35 cm×35 cm×12 cm) with a stable radon exhalation rate as the source term and a height adjustable experiment box with cross section of 30 cm×30 cm were used. The soil moisture content and degree of compaction were kept consistent during the experiment. The results showed the better suppression effect of radon with increasing proportions of bentonite or lime powder, while bentonite more effective in radon suppression than lime powder. The fitting lines showed the logarithmic relationship between radon suppression effect and covering thickness with different proportions of bentonite or lime powder. The logarithmic equation was obtained and the corresponding diffusion coefficient of radon was calculated. The relationship between the radon exhalation rate before covering and the thickness of covered soil has been deduced to meet the required management limit of 0.74 Bq·m^-2·s^-1, which could provide a conservative calculation for the covering thickness for the required surface radon exhalation rate. The economic comparison analysis showed that the cost for adding lower proportions of materials would be higher than the original soil, and vice versa. The cost would decrease with the increasing proportions of materials.

Key words: bentonite, lime powder, radon exhalation rate