Diffusive Transport of Radon in a Homogeneous Column of Dry Sand

Spoel, W.H. van der; Graaf, van der Emiel; Meijer, R.J. de

doi:10.1097/00004032-199705000-00014

Cited by 22 publications

(16 citation statements)

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“…At higher moisture contents, the increasing number of water blockages in the pore space inhibits most of the diffusive transport through air-filled parts, causing a more rapidly decreasing diffusion coefficient. For dry sand, the bulk diffusion coefficient is measured at (2.42 IfI 0.11) X10-6 m2 s-l, in good agreement with the value (2.39 2 0.08)X10-6 m2 s-l inferred from the porosity, tortuosity , and diffusion coefficient in air ( Van der Spoel et al 1997).…”

Section: Radon Diffusion Coefficientsupporting

confidence: 82%

“…Assuming that the sample taken from the largest depth (75 cm) was completely saturated with water, a porosity of 0.365 (estimated uncertainty 0.005) was obtained from volume and mass determinations. This value is 7% larger than the value assumed in all previous model calculations for dry sand ( Van der Spoel et al 1997, 1998a, inferred from the mass increase of a small sand sample due to water saturation. The compaction that was observed during wetting and drying this sand sample apparently did not occur in the same degree in the vessel.…”

Section: Sand Propertiescontrasting

confidence: 53%

“…The laboratory facility has been described in a preceding paper (Van der Spoel et al 1997). In short, the facility consists of a cylindrical stainless steel vessel (height and diameter 2 m; bottom slightly curved for strength) filled with sand and surrounded by a stainless steel moat filled with water, acting as a water seal (Fig.…”

Section: Vessel Experiments With Moisturized Sandmentioning

confidence: 99%

“…Some of the sand properties that are of importance for describing radon transport in dry sand have previously been measured in separate experiments (Van der Spoel et al 1997). These results are presented in Table 1.…”

Section: Sand Propertiesmentioning

confidence: 99%

“…The first and second set of measurements were carried out on diffusive and advective radon transport in dry sand, respectively (Van der Spoel et al 1997, 1998a. In both series, the comparison between experimental results and model calculations, using values of parameters obtained from separate experiments on small sand samples, showed a good correspondence, with maximum differences between model and experiment of less than 10%.…”

Section: Introductionmentioning

confidence: 99%

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Diffusive Transport of Radon in a Column of Moisturized Sand

Spoel¹,

Graaf²,

Meijer³

1999

Health Physics

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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.

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Section: Radon Diffusion Coefficientsupporting

confidence: 82%

Section: Sand Propertiescontrasting

confidence: 53%

Section: Vessel Experiments With Moisturized Sandmentioning

confidence: 99%

Section: Sand Propertiesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Diffusive Transport of Radon in a Column of Moisturized Sand

Spoel¹,

Graaf²,

Meijer³

1999

Health Physics

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Analysis of equivalent thickness of geological media for lab-scale study of radon exhalation

Hong

Yang

Wang

et al. 2021

Environ Sci Pollut Res

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Geological media are widely distributed in nature. Lab-scale tests are frequently employed in radon studies for these media. Thus, it is critical to find the thickness of the medium at an experimental scale that is equivalent to the medium thickness in a real geological system. Based on the diffusion-advection transport of radon, theoretical models of the surface radon exhalation rate for homogeneous semi-infinite and finite-thickness systems were derived (denoted as Jse and Jfi, respectively). Analysis of the equivalency of Jse and Jfi was subsequently carried out by introducing several dimensionless parameters, including the ratio of the exhalation rates for the semi-infinite and finite-thickness models, ε, and the number of diffusion lengths required to achieve a desired ε value, n. The results showed that when radon transport in geological media is dominantly driven by diffusion, if n > 3.6626, then ε > 95% (and if n > 5.9790, then ε > 99.5%).When radon migration is dominantly driven by advection, if n > 2.5002, then ε > 95% (and if n > 4.0152, then ε > 99.5%). Therefore, if the thickness of the geological media (x0) is greater than a certain n times the radon diffusion length of the media (L), the media can be modeled as semi-infinite. To validate the model, a pure radon diffusion experiment (no advection) was developed using uranium mill tailings, laterite, and radium-bearing rocklike material with different thicknesses (x0). The theoretical model was demonstrated to be reliable and valid. This study provides a basis for determining the appropriate thickness of geological media in lab-scale experiments of radon exhalation.

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