Preliminary Public Dose Evaluation in Support of the Development of the
November 2012
Rare Element Resources Bear Lodge Project
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SECTION 4
PUBLIC 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 public doses from radiation and radioactivity based on measured values are
not available and must be estimated using conservative estimates of source terms coupled with
computer modeling. The selection of the most appropriate model is based on likely exposure
pathways.
Radiation exposure (i.e., dose) to the public 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. Given that the public is not allowed
uncontrolled access to the source term areas, the most likely receptor will be a
significant distance away from sources of NORM. Thus, the external dose
pathway is not considered to be an important pathway for public dose estimates,
particularly when compared to the inhalation of NORM.
•
Internal Doses from Particulate Inhalation: An important pathway for internal
doses to the public 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.
•
Inhalation of radon (both radon-222 and radon-220) and their short-lived decay
products is another potential pathway for internal dose at the BLP.
•
Another potential pathway for internal doses —but less important than
inhalation— is the unintended ingestion of dust containing thorium and uranium
and their decay products. Due to the insoluble nature of the NORM at the BLP, it
