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AIRBORNE no"Py CONCENTRATION, aCi!m
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{ALL WINDS. SITE AB)
FIGURE 3.
FIGURE 2. Airborne °9pu Concentration at Site AB
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239
Airborne
Pu Concentrations from Impactor
2.0 um Stage Collections
as a Function of Impactor Collection
Site
The general trend of the complete airborne plutonium-239 concentration data
1s a decrease in concentration with increasing distance eastward from site
A {Sehmel and Lloyd, 7976a).
As might be expected, this decrease in concen-
trations corresponded to increasing distance from the original oi! storage
area, which was the principal source of ground contamination. However,
significant deviations did occur in the concentration profiles of airborne
plutonium-239 with both distance and height. These deviatfons might be
attributed to sampling "hot" soil particles which contain relatively more
Plutonium than average. These increases in average airborne plutonium-239
concentrations were present at both sites AB and B,
As indicated in Figure 3 for site AB, “hot" particles may have been present
in the 2.0-um size range. In this case, the concentration at the 1-m height
of site AB is 1 to 2 orders of magnitude greater than at other heights for
this site. More important to the "hot" particle concept is the concentration at the 10-m height of B. This concentration of 230 aCi/m? was the
Jargest plutonium-239 concentration for 2-um particles measured at any location. This relatively high concentration was unexpected since this sampling
location was the most remote from both the ground and the original oi)
storage area. This Suggests that other relatively "hot" particles could
also be escaping from the plant boundaries; however, due caution is indicated
in interpreting this "hot" particle cgncept. The total of 6 dis/min collected on the 2-ym stage or 230 aCi/m? is much less than the maximum per-
missible air concentration of 2 x 106 aCi/m3 (occupational).
It is con-
ceivable that the majority of this "hot" plutonium might have been attached
to one soil particle.
188
Even with the limited plutonium data collected in this experiment, it was
evident that airborne plutonium-239 concentrations increased with an increase
in wind speed.
In Figure 4, total airborne concentrations are shown for air
sampled at al? wind Speeds (average wind speed of 0.9 m/sec), at wind speeds
from 4.1 to 6.3 m/sec, and at wind speeds from 6.3 to 9.8 m/sec. Airborne
plutonium-239 concentrations at wind speeds from 4.1 to 6.3 m/sec are
definitely larger than average airborne concentrations for continuous air
sampling. However, the 2c radiochemical counting statistics error limits
are too targe to determine the wind speed dependency. Nevertheless, an
attempt to approximate airborne plutonium-239 concentrations and consequently the resuspension rate dependency upon wind speed was made for the
7-um-diameter particles. This was for the 0.3-m height at sampling site AB.
For the three data points taken at the 0.3-m height, plutonium-239 concentrations tended to increase as the 5.9th power of wind speed.
This July 1973 plutonium resuspension experiment at Rocky Flats showed
resuspension of both plutonium-238 and plutonium-239. However, all airborne
plutonium concentrations were significantly below maximum permissible concentrations in air. Since plutonium-239 was collected on each particle
cascade impactor stage, the suggestion is that most plutonium was attached
to soil particles when the plutonium was resuspended,