Multiphase Radon Generation and Transport in Porous Materials

Abstract

Radon generation and transport in porous materials involve solid, liquid, and gas phases in the processes of emanation, diffusion, advection, absorption, and adsorption. Oversimplifications, such as representing moist soil systems by air-phase emanation and transport models, cause theoretical inconsistencies and biases in resulting calculations. Detailed Rn rate balance equations for solid, liquid, and gas phases were analyzed and combined using phase equilibrium constants to derive a single diffusive-advective rate balance equation in the traditional form. The emanation, diffusion, and permeability coefficients in the new equation have expanded definitions and interpretations to include Rn phase transfer. Radon adsorption was characterized by an exponential moisture dependence, and diffusion and permeability constants utilized previous moisture relationships. Correct boundary and interface conditions were defined, and the unified theoretical approach was applied to field data from a diffusion-dominated system and to laboratory data from an advection-dominated system. Measured 222Rn fluxes and concentrations validated the modeled values within the measurement variability in both applications.

Preliminary Study on a Regional Radon Concentration in Surface Soil Prediction Method

“…If only diffusion effect is considered, the steady-state radon transport in the soil is governed by (x vertical axis, directed downward on the ground side) 1) (1) Where N 1 is the radon concentration (Bq·m -3 ). D 1 is the pore average radon diffusion coefficient (m 2 ·s -1 ).…”

“…The specific activity of radium C Ra , the soil density and porosity were measured in the experiment. The measured C Ra varied from 21.9Bq·kg 1 up to 70.6Bq·kg 1 . Other parameters, such as radon emanation coefficient and the diffusion coefficient, were assigned based on the reference 5) .…”

“…It is a feasible way to predict the regional radon distribution quickly and efficiently by combining these data with radon migration theory. Based on a steady-state radon transport model in porous materials 1) , combined with the local geological and pedological parameters, several methodologies were also developed for predicting a regional radon concentration [2][3][4] .…”

User's manual for RESRAD-BUILD version 3.

“…The diffusion coefficient is also affected to a lesser degree by particle shape and size; packing; and changes in the composition, temperature, and pressure of the gas-filled pore space and those for the liquid occupying the remaining pore volume. Further information can be found in Stranden and Berteg (1980) and Rogers and Nielson (1991). In general, the effective diffusion coefficient approaches its upper limit for fibrous insulation material and its lower limit for relatively impermeable materials or membranes, such as metals or sealants.…”

“…Additional information on the radon emanation fraction can be found in documents by Tanner (1964Tanner ( , 1980; Barretto et al (1972); Pensko et al (1972);Wilkening (1974);Periera (1980);Ingersoll (1983); Schery et al (1984); Damkjaer and Korsbech (1985); Van der Lugt and Scholten (1985); Schery and Whittlestone (1989); Rogers and Nielson (1991); Markkanen and Arvela (1992);and Rood et al (1998).…”