Preliminary Public Dose Evaluation in Support of the Development of
November , 2012
Rare Element Resources, Inc. Bear Lodge Project
8
Table 1.2 lists the average annual dose from natural background radiation in the U.S. (National
Council on Radiation Protection and Measurement[NCRP], 2009).
Table 1.2 Background Doses in the U.S. from Natural Sources
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
mrem y
-1
= millirem per year
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 (US Nuclear Regulatory
Commission [NRC], 2001; International Atomic Energy Agency [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). , Radionuclides can mobilize
during processing and migrate to dust, scales and other process residues, therefore potentially
having relatively higher concentrations of radionuclides than feedstock. This potential increase in
radionuclide concentration can change the magnitude of radiological hazards to the public living
near the REE processing facility. An environmental monitoring program designed to evaluate
potential impacts from REE recovery operations, including public doses, is typically in place
prior to the operation of such facilities.
