Resumo (PT):
Abstract (EN):
Radon emissions from uranium mill tailings may constitute a major source of
environmental contamination and consequently a potential health hazard to the nearby
population. Radon-222 gas is generated from the radioactive decay of 226Ra present in
the particles. When it is formed, radon is free to diffuse along the pores of the residues
to the surface and escape to the atmosphere. A major concern in waste management and
long term stabilization is to reduce radon emissions to near background levels. The
common theoretical approach is to calculate the cover thickness that results in a radon
flux lower than a stipulated and accepted value. The conceptual model is based on the
principle of diffusion across a porous medium, which allows the mathematical description
of the radon transport through the waste and the cover. The basic diffusion
equations are used for estimating the theoretical values of the radon flux formed from
the decay of the 226Ra content in the waste material. The algorithm incorporates the
radon attenuation with an arbitrary cover system placed over the radioactive waste.
Alternatively, the thickness can be estimated for a cover that allows a lower radon flux.
Once the radon is released into the atmosphere it is available for atmospheric transport
by the wind. Radon atmospheric dispersion is modelled using a modified Gaussian
plume equation that estimates the average dispersion of radon released from a point
source representative of one or more uniform area sources. The model considers the
median release point between all the areas contaminated. The concentration available
for the dispersion is calculated from the total flux released. The dispersion can be
simulated for different wind directions, with different wind velocities, as well as in the
dominant wind direction.
Language:
English
Type (Professor's evaluation):
Scientific
Contact:
mldinis@fe.up.pt
No. of pages:
8