An investigation of 222Rn exhalation rates from backfill mill tailings influenced by the different parameters in underground uranium mines

Abstract

222Rn surface exhalation and mass exhalation rates measured from the backfill mill tailings using a new method comprising the smart-radon-monitor system and accumulation chamber in underground uranium mines are presented in this paper. The range values of 222Rn surface and mass exhalation rates were 0.6–4 Bq m−2 s−1 and 28–71 Bq kg−1 h−1, respectively. Further, Multivariate regression models involving radium content, porosity, moisture saturation and surface area to fit the 222Rn surface and mass exhalation of the backfill materials were developed in this paper. The curve fitting results showed that multivariate models could explain 86% of the variation of surface exhalation rate and 69% of the variation of mass exhalation rate from the backfill materials. This study also revealed that the 222Rn surface exhalation rate calculated based on the method of concentration gradient of 222Rn in soil, found to be about two times more than that of the measured surface exhalation rate. However, the theoretical 222Rn exhalation rate was prone to various uncertainties including a variation of moisture saturation, the occurrence of adsorption and advection in the backfill mill tailings. Therefore, the values of the 222Rn exhalation rate measured inside underground uranium mines are more realistic.