Transport of radon in still water.

摘要

A new method was developed to measure the effectiveness of water in reducing the release of radon emanating from 226Ra-bearing sand into air. Fick's law on diffusion was used to model the transport of radon in water including the impact associated with radioactive decay. A multi-region, one-dimensional, steady-state transport model was used to analyze the movement of radon through a sequential column of air, water and air. An effective diffusion coefficient was determined by varying the thickness of the water column to predict the transport of 222Rn through particular thickness of water. A one-region, one-dimensional transient diffusion equation was developed to investigate the build up of radon at the end of the water column until a steady-state, equilibrium condition was achieved. This build up with time is characteristic of the transport rate of radon in water and established the basis for estimating the effective diffusion coefficient for 222 Rn in water. The results suggest that convective forces other than molecular diffusion impact the transport of 222Rn through the water barrier. An effective diffusion coefficient is defined that includes effects of molecular diffusion and convection to describe the transport of radon in water. Several experimental arrangements were evaluated to examine the influence of physical parameters on the radon transport. The effective diffusion coefficients measured in these experiments are 6.8 x 10 -4 +/- 28% and 3.5 x 10-4 +/- 34% cm2 sec-1 for the steady-state and transient diffusion approaches, respectively. Water barriers ranging in thickness from 30--50 cm reduce the amount of radon released from the radium-bearing source material by a factor of 0.3--0.1, respectively.