Interim Baseline Radiological Investigation Report
November 14, 2012
Bear Lodge Project, for Rare Element Resources, Ltd.
Rev.1
36
8.1.1 Radioactive Particulates
The resulting concentrations for each radionuclide and high volume sampler were compared to
effluent concentration limits listed in Table 2 of 10 CFR 20 Appendix B and reported in Table 8-
2 as percentages of the respective effluent limits. The most conservative effluent limit was
applied to thorium-230 (3x10
-12
µCi/ml). The Class D and W limits were applied to natural
uranium (3x10
-12
µCi/ml) and radium-226 (9x10
-13
µCi/ml), respectively. There is no 10 CFR 20
limit for natural thorium. A limit for natural thorium (8x10
-15
µCi/ml) was calculated for this
baseline investigation, by assuming equal activities of the constituents of natural thorium (
thorium-228 and thorium-232) and Class W limits for thorium-228 (4x10
-12
µCi/ml) and
thorium-232 (4x10
-15
µCi/ml). The unity rule is 1/(0.5*(4x10
-12
+ 4x10
-15
)) = 8x10
-15
µCi/ml.
On average, the concentrations of radionuclides were on the order of 10
-17
µCi/ml and, with the
exception of radium-226, consistent at each location. The data are summarized in Table 8-3,
according to location, averages, standard deviations and ranges.
Site-wide, the data can be summarized as follows:
•
Natural uranium concentrations ranged from 1.4x10
-17
to 1.7x10
-16
µCi/ml and averaged
2.8x10
-17
µCi/ml.
•
Throium-230 concentrations ranged from 8.9x10
-18
to 2.4x10
-16
µCi/ml and averaged
3.0x10
-17
µCi/ml.
•
Radium-226 concentrations ranged from -2.4x10
-18
to 2.3x10
-16
µCi/ml and averaged
6.4x10
-17
µCi/ml.
•
Natural thorium concentrations ranged from 5.6x10
-18
to 6.7x10
-16
µCi/ml and averaged
5.7x10
-17
µCi/ml.
Other than relative stability in natural uranium and thorium-230 results, there are no clear
temporal or spatial patterns in the radionuclide concentrations. On average, over the course of
monitoring:
•
Natural uranium concentrations at each location were on the order of 10
-17
µCi/ml.
•
Natural thorium concentrations at three of the four locations were on the order of 10
-17
µCi/ml and one order of magnitude higher at AMS-02.
•
Radium-226 concentrations at three of the four locations were on the order of 10
-17
µCi/ml and one order of magnitude higher at AMS-04.
•
Thorium-230 concentrations at three of the four locations were on the order of 10
-17
µCi/ml and one order of magnitude lower at AMS-02.
