Diffusive Transport of Radon in a Column of Moisturized Sand

Abstract

Diffusive transport of radon in a moisturized sand column was investigated under well-defined and controlled conditions using a laboratory facility that consists of a cylindrical vessel (height and diameter 2 m) filled with sand. Equilibrium pore-gas radon-concentration profiles in the sand column were measured as a function of depth for several different levels of the ground-water table. The measurements were performed in the framework of a systematic validation study that also covered experiments with dry sand. The experimental data were compared with results of model calculations. Most parameters in the transport model were obtained from separate experiments on small sand samples. In this manner, the radon diffusion coefficient and emanation coefficient were determined as functions of pore-water content, as well as the water-retention characteristics of the sand. In general, the experimental data are reasonably well reproduced by the calculations with differences of 10%-40%. However, with respect to earlier results with dry sand indicating differences of generally smaller than 10%, the agreement between experiment and model for moisturized sand is clearly worse. The main part of the disagreement probably results from inhomegeneities in the sand column that are not accounted for in the transport model.

Effect of Soil Moisture on Seasonal Variation in Indoor Radon Concentration: Modelling and Measurements in 326 Finnish Houses

“…The agreement with this empirical equation and later tests in moisturised sand is good (21) . The diffusion length (D e /l) 1 2 represents the depth where the soil gas radon concentration has been reduced to 63 % of the deep soil radon concentration.…”

“…Experimental studies confirm that radon transport in moisturised sand is much more complicated than in room-dry sand (21) . The higher complexity is mainly due to partitioning, varying moisture content and diffusion.…”

“…Already small moisture increases of 1-3 volume per cent increase the radon emanation of dry soil. A sharp rise from 0.13 to 0.28 has been observed for sand samples as the pore moisture content increases from zero to only 0.5 % (21) . Markkanen and Arvela as well as Strong and Levins observed a similar rise in the range from 0 to 3 %.…”

“…If only the upper soil layers (e.g. 0-30 cm) are close to saturated with water, the air flows towards the footings may come from greater distances, which increases the radon concentration of sub-foundation air (21) . An increase in the radon emanation factor directly increases the radon concentration in soil pore air.…”

“…l is the radioactive decay constant of 222 Rn, 0.0076 h 21 . A out is the outdoor air radon concentration; in this study, a low value of 5 Bq m 23 has been used.…”