Preliminary Public Dose Evaluation in Support of the Development of the
November 2012
Rare Element Resources Bear Lodge Project
22
4.2.1
Radon Emission Estimates
Radon flux from all sources is estimated using the following expression from
Sources and
Effects of Ionizing Radiation, Annex B
(UNSCEAR, 2000):
=
(1 − )( ⁄ )
0.5
1000
Where:
J
D
= the radon flux (pCi m
-2
s
-1
) for radon-220 or radon-222
C
Ra
= the activity concentration (pCi g
-1
) of radium-226 or radium-224 in the
case of radon-222 and radon-220, respectively
λ
Rn
= the decay constant of radon-222 (2.1x10
-6
s
-1
) or
radon-220 (1.26 x 10
-2
s
-1
)
f
= the emanation fraction for earth material (assumed at 0.2 [UNSCEAR,
2000] )
ρ
= soil or rock density (2700 kg m
-3
for the BHM and LGOS and 3400 kg
m
-3
for the TSF [RER, 2012b])
ε
= porosity of dry earth material (assumed at 0.25 [UNSCEAR, 1993])
D
e
= radon diffusion coefficient (assumed at 2 x 10
-6
m
2
s
-1
[UNSCEAR,
2000] ), and
1000 = a factor to convert g to kg
The above expression is valid only for dry soil or rock. The presence of water in soil affects
radon emanation and diffusion coefficients and reduces the radon flux from the material surface.
It is a conservative estimate of radon flux since soil or rock material contains moisture, resulting
in an over-estimate of actual radon flux. Radium-226 and radium-224 were assumed to be in
secular equilibrium with uranium-238 and thorium-232, respectively.
The radionuclide concentrations in Table 4.1 were used to estimate the radon flux from each of
the three sources. For the purpose of modeling with AERMOD, the estimated radon flux
expressed in units of activity (pCi) were converted to units of mass (g) by dividing the flux (pCi
m
2
s
-1
) by the specific activities of radon-220 (9.22 x 10
20
pCi g
-1
) and radon-222 (1.54 x 10
17
pCi g
-1
). Table 4.4 lists the radon emission from each source.
