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Multiphase radon generation and transport in porous materials
1Rogers and Associates Engineering Corporation, Salt Lake City, UT 84110-0330.
Health Physics
|June 1, 1991
Summary
This study presents a unified model for radon transport in porous media, accounting for solid, liquid, and gas phases. The new model accurately predicts radon fluxes and concentrations in various soil moisture conditions.
Area of Science:
- Environmental Science
- Geophysics
- Hydrogeology
Background:
- Radon (Rn) transport in porous materials is complex, involving multiple phases and processes like emanation, diffusion, and advection.
- Existing models often oversimplify moist soil systems, leading to theoretical inconsistencies and calculation biases.
- Accurate modeling of radon transport is crucial for environmental monitoring and risk assessment.
Purpose of the Study:
- To develop a unified theoretical approach for radon transport that integrates solid, liquid, and gas phases.
- To address the limitations of current air-phase models in representing moist soil systems.
- To derive a comprehensive rate balance equation for radon transport, incorporating phase transfer phenomena.
Main Methods:
- Analysis of detailed radon rate balance equations for solid, liquid, and gas phases.
- Combination of phase equations using equilibrium constants to derive a single diffusive-advective rate balance equation.
- Incorporation of phase transfer into emanation, diffusion, and permeability coefficients, with moisture-dependent adsorption and diffusion relationships.
Main Results:
- A unified diffusive-advective rate balance equation for radon transport was derived, with expanded coefficient definitions.
- Radon adsorption was modeled with exponential moisture dependence, and diffusion/permeability constants used established moisture relationships.
- The unified model successfully predicted measured 222Rn fluxes and concentrations in both diffusion- and advection-dominated systems.
Conclusions:
- The developed unified theoretical approach provides a more accurate representation of radon transport in porous media across varying moisture conditions.
- The model's validation with field and laboratory data confirms its reliability for predicting radon behavior.
- This work offers improved theoretical consistency and reduced bias in radon transport calculations for environmental applications.
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