Modeling of Radon Concentration in Air
and Dose from Measured Radon
Emissions from a Defined Area
Oscar Paulson – Kennecott Uranium Company
Modeling Performed by Randy Whicker - ERG
May 2016
Sweetwater Uranium Project
The Sweetwater Uranium Project is located
approximately 42 miles Northwest of Rawlins, Wyoming
in the Great Divide Basin in Sweetwater County,
Wyoming
Sweetwater Uranium Project
Radon Source
• The Sweetwater Uranium Project has a single measured source
of Radon-222.
• This source is the tailings impoundment.
• Radon-222 emissions from this source are measured annually as
part of currently required (40 CFR Part 61 Subpart W) testing.
• Data from the calendar year 2014 Method 115 Test is provided
below:
Area Description
Exposed tailings
Water covered
areas
Total
Area
(square meters)
64,640.5
92,808.2
157,448.7
Radon-222 Flux
(pCi/m2-sec)
21.85
0
8.97 (average)
The total area of 11(e).2 byproduct material of 157,448.7 square meters has an
average flux rate of 8.97 pCi/m2 –sec. This equates to a total annual Radon-222
release from the impoundment of:
2
(8.97 pCi/m –sec) (157,448.7 square meters) (365 days/year) (24 hours/day) (60
minutes/hour) (60 seconds/minute) = 4.45 E+ 13 pCi = 44.5 curies of Radon-222 per
year.
Tailings Impoundment
The impoundment is shown below:
Image: Google Earth – June 8, 2014
Modeling
The spatial distribution of Rn-222 air concentrations and corresponding
doses to a hypothetical receptor at any given location in the general vicinity
of the Mill were modeled for 3,723 individual receptor points on a 100 ×
100 meter grid covering approximately 8,900 acres using MILDOS with the
impoundment situated at the center of the grid
MILDOS modeling grid (receptor locations on 100-m centers).
Meteorological Data
Four data sets were considered as follows:
Models were run using data from Rawlins, Wyoming and the Sweetwater
Mill from 1983 to 1987
Concentration Modeling Results – Rawlins, Wyoming Wind Data
Modeled Spatial Distribution of Rn-222 Concentrations in Air in the
Vicinity of the Sweetwater Mill Due to Effluents from the
Impoundment.
Dose Modeling Results – Rawlins, Wyoming Wind Data
Modeled Spatial Distribution of Radiological Doses to a Hypothetical
Receptor Located Anywhere in the Vicinity of the Sweetwater Mill Due to
Rn-222 Effluents from the Impoundment.
Concentration Modeling Results – Sweetwater Mill Wind Data
Modeled Spatial Distribution of Rn-222 Concentrations in Air in the
Vicinity of the Sweetwater Mill Due to Effluents from the
Impoundment.
Dose Modeling Results – Sweetwater Mill Wind Data
Modeled Spatial Distribution of Radiological Doses to a Hypothetical
Receptor Located Anywhere in the Vicinity of the Sweetwater Mill
Due to Rn-222 Effluents from the Impoundment.
Measurements
A single quarterly measurement set exists and is as follows:
Location
Start
Date
End
Date
Measurement
pCi/L
Southwest Corner –
(Upwind Corner) of
the Impoundment
Northeast Corner –
(Downwind Corner)
of the Impoundment
Error
1/14/16 4/5/16
2.5
pCi/L
+/- 0.12
1/5/16
2.6
+/- 0.11
4/5/16
Lower Limit of
Detection
pCi/L
0.06
0.06
Each reading falls within the range of the other given the error estimates
of the readings.
Questions?