Occupational Dose Evaluation in Support of the Development of the
October, 2012
Rare Element Resources, Inc. Bear Lodge Project
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External dose rate and removable contamination levels
SECTION 4
OCCUPATIONAL WORKER DOSE ASSESSMENT
This section is intended to provide an overview of the kinds and magnitudes of potential
radiological issues associated with the proposed BLP. At this stage of project development,
specific estimates of worker exposures to radiation and radioactivity based on measured values
are not available. Based on data in Table 2.1, the concentrations of NORM in ore, intermediate
concentrates, and tailings are low although there is potential for some workers to receive a
radiation dose more than 100 mrem in a year, resulting in a need to develop and implement a
RPP to control worker exposure to ionizing radiation to levels that are below regulatory limits
(OSHA or NRC occupational dose limits described in Section 3) and as low as is reasonably
achievable.
Radiation exposure (i.e., dose) can occur from being exposed to gamma radiation from sources
outside of the body and also through radiation that is taken into the body through inhalation or
ingestion. The following general comments apply with respect to possible pathways of exposure
at the BLP.
External Doses: As discussed previously, gamma emitting radionuclides are
present in both the uranium and thorium decay series. An external dose can be
received from the gamma radiation generated from these radionuclides. The
magnitude of the external dose is directly related to the amounts of uranium
and/or thorium in the material being processed and inversely related to the
distance from the material or source. If external gamma levels are unacceptably
elevated, external doses can be reduced using administrative controls (e.g.,
increasing distance from source and/or reducing time near source) or engineering
controls such as shielding.
Internal Doses from Particulate Inhalation: An important pathway for internal
doses is inhalation. The processes at the BLP have the potential to create dust
containing radionuclides in the thorium and uranium decay series. Engineering
controls such as water sprays will be used to control dust in the mine area and
haul roads. Scrubbers and bag houses will be located at key points in the PUG and
Hydromet, and active ventilation of process buildings will occur. The BHM is an
open pit so unlike underground mining, natural ventilation will also mitigate the
concentration of dust in the mine area.
