Occupational Dose Evaluation in Support of the Development of
October, 2012
Rare Element Resources, Inc. Bear Lodge Project
9
Table 1.2 Background Doses in the U.S. from Natural Sources
a
(mrem y
-1
)
a
Source
Mean
(mrem y
-1
)
Standard Deviation
(mrem y
-1
)
Percentiles
2.5
97.5
Cosmic
33
8
20
52
Terrestrial
21
6
12
35
Internal
29
2
23
36
Radon ( includes radon-222
and radon-220)
228
400
9
1110
Composite
311
361
94
1200
a
Adopted from NCRP, 2009
Exposure to radon, primarily indoors, accounts for approximately 73 percent of the dose from
natural sources of background radiation. Background dose rates vary according to factors such as
elevation, radionuclide concentrations in soil and rock, construction materials in residential
buildings, and lifestyle. Background radiation doses in the Mountain West states, including
Wyoming, are higher than the background radiation doses in the west, east and Gulf Coast states.
1.4
Radiological Issues at Rare Earth Facilities
Many ores processed for their mineral content, including REE, contain NORM such as
potassium-40 and the uranium and thorium decay series radionuclides (NRC, 2001; IAEA, 2006;
UNSCEAR, 2000). The minerals used for commercial sources of REE contain elevated
concentrations of radionuclides in the thorium decay series and --to a lesser degree-- the uranium
decay series. These minerals include monazite and bastnasite ores (IAEA, 2006). During
processing operations, radionuclides may mobilize and migrate to dust, scales and other process
residues, leading to the possibility of increased radionuclide concentrations in these materials
when compared to the feedstock. This potential increase in radionuclide concentration can
change the magnitude of radiological hazards to workers involved in the recovery of REE.
Implementing an appropriate radiation protection program (RPP) is a useful way to reduce
worker exposure to radiation to acceptable levels. A RPP typically includes engineering and
administrative controls for important work processes and practices coupled with workplace and
employee monitoring to evaluate the effectiveness of these controls.
SECTION 2
PROJECT DESCRIPTION
The planned scope of the BLP consists of three principal components (RER, 2012):
An open-pit mine operation at Bull Hill and associated support facilities. The proposed
mine operation is located approximately 12 miles north of Sundance, Wyoming.
A PUG for mineral pre-concentration adjacent to the mine.
