Occupational Dose Evaluation in Support of the Development of the
October, 2012
Rare Element Resources, Inc. Bear Lodge Project
25
The dose estimates in Table 4.4 demonstrate two key points. First, a conservative dose estimate
using the MSHA TLV for nuisance dust is below the regulatory limit for occupational radiation
doses and national and international guidance for radiation dose limits for workers. RER will be
required to keep occupational dust levels below the TLV, thus radiation doses will be below
occupational dose standards. Secondly, a conservative dose estimate of 321 mrem y
-1
--using a
more typical dust concentration-- is near the national average background radiation dose from
natural sources. The dose estimate of 321 mrem y
-1
is consistent with dose estimates for the rare
earth industry that are summarized in NUREG-1717
Systematic Radiological Assessment of
Exemptions for Source and Byproduct Materials
(NRC, 2001) and in Safety Reports Series No
68
Radiation Protection and NORM Residue Management in the Production of Rare Earths from
Thorium Containing Minerals
(IAEA, 2001).
SECTION 5
SUMMARY
The proposed BLP is intended to recover and process REE from RER-owned deposits located in
the northeast Wyoming. The project facilities will be at two site locations: the BHM and PUG
near Sundance, Wyoming and a Hydromet plant near Upton, Wyoming.
In addition to the rare earth metals, the BLP ore also contains NORM. The NORM consists of
naturally occurring thorium and uranium and associated radioactive decay products. The thorium
and uranium concentration in the BLP ore is variable but averages approximately 0.036 and 0.01
percent by weight, respectively, which is above typical US background levels of about 1 to 10
ppm in rocks and soils. The presence of NORM in rare earth deposits is not unusual as NORM
occurs in most other rare earth deposits and in many resource industries around the world.
However, the presence of NORM in the BLP ore suggests the need to address potential
radiological exposures to workers arising from its mining and processing.
Potential radiological exposures of workers at the proposed BLP would arise from external
gamma radiation and also through inhalation and ingestion of NORM in the workplace. Based on
the information currently available, the largest source of worker exposure at the proposed BLP is
anticipated to be inhalation of NORM in dust generated from the mining and processing
activities. This dose component is estimated to account for between 35 and 84 percent of the
dose under the assumptions used in the dose calculations. External dose from the mining process
is expected to contribute between 15 and 61 percent of the occupational dose. Radon and its
decay products are anticipated to be controlled to acceptable levels through ambient dispersion in
open areas and active ventilation in process buildings. The estimated radiation dose to workers
ranged from 320 mrem y
-1
using typical dust level assumptions to 1300 mrem y
-1
assuming a
worst-case dust scenario equal to the MSHA enforceable TLV for nuisance dust. This estimated
range is consistent with measured doses in the rare earth recovery industry and is below
