Preliminary Public Dose Evaluation in Support of the Development of
November , 2012
Rare Element Resources, Inc. Bear Lodge Project
3
1.2
Report Objective
The purpose of this report is to:
•
identify potential human exposure pathways to naturally occurring radioactivity
associated with the mining and processing of the Bear Lodge ore and
•
provide a conservative estimate of the magnitude of expected radiation doses to
members of the public (the public) resulting from the proposed actions at the BLP. It
includes a perspective on the significance of this estimate.
NORM —in ore and ore concentrates— poses potential risks to members of the public because it
emits ionizing radiation. The predominant pathway by which the public can receive doses from
the ionizing radiation is inhalation of NORM in dust and exposure to radon gas released from the
BLP. Doses from gamma radiation from sources external to the body are also a potential
pathway but it is expected that the public will be precluded from spending enough time near the
source terms, rendering this pathway an insignificant contributor to the public dose.
Additionally, it is expected that engineering controls will be in place to prevent contamination of
drinking water sources thus mitigating this pathway for public dose. Consequently, this report
only addresses public doses from the inhalation pathway. To help put these potential exposures
in context, regulations applicable to radioactive materials and potentially relevant to NORM are
discussed.
1.3
Naturally Occurring Sources of Radiation and Radioactivity
Relevant characteristics of NORM are described in this section, to assist readers who may be
unfamiliar with the concepts of natural radiation and radioactivity.
1.3.1
Sources of Naturally Occurring Radiation
Radiation is produced from the naturally occurring radionuclides contained in all environmental
media. Natural uranium and thorium and their associated radioactive decay products are major
constituents of NORM and are most important when considering the ore at the BLP. Natural
uranium; i.e., uranium with natural isotopic abundances, consists primarily of uranium-238 and
uranium-234 (based on radioactivity) and to a lesser degree uranium-235. Table 1.1 shows the
natural isotopic abundance of each important uranium isotope based on mass and radioactivity.
Table 1.1 Natural Abundances of Uranium Isotopes
Uranium Isotope
Abundance (%)
a
Mass
Radioactivity
Half-Life (y)
a
Uranium-238
99.28
48.6
4.5 x 10
9
Uranium-235
0.71
2.2
7.0 x 10
8
Uranium-234
0.0058
49.2
2.5 x10
5
a
Adopted from Eisenbud and Gesell, 1997
y = year
