Environmental Engineering Reference
In-Depth Information
TABLE 22.4
Resuspension Factors for U, Th Isotopes and Fallout Pu at
Argonne, IL
Air
Concentration (
μ
Bq m
−1
)
Ground
Deposition (Bq m
−2
)
Resuspension
Factor (m
−1
)
Nuclide
228
Th
0.32
629
5.1 × 10
−10
230
Th
0.54
1036
5.3 × 10
−10
232
Th
0.30
555
5.5 × 10
−10
U
1.55
2516
6.1 × 10
−10
Pu
0.026
37
7.0 × 10
−10
Source:
Adapted from Golchert, N.A. and Sedlet, J., Resuspension studies on fall-
out level plutonium, in Selected Environmental Plutonium Research
Reports of the Nevada Applied Ecology Group, Report NVO-192, 1978.
the Pu in soil was in a relatively steady-state condition. Anspaugh et al. (1975) estimated RFs for 20
year old Pu deposition at the Nevada Test Site to be 3 × 10
−10
and 2 × 10
−9
m
−1
. Golchert and Sedlet
(1978) considered the U and Th representative of the “ultimate aged source and their resuspension
factors, the equilibrium condition.” However, these RF estimates are site speciic and cannot be
taken as the general case. It does suggest that resuspension will be the source of fallout Pu (in the
absence of any atmospheric weapons testing or nuclear accidents) for a long period of time.
22.8 RESPIRABLE CONCENTRATIONS OF U, TH, AND PU
The term TSP refers to particles <500 μm in diameter. The next smaller fraction is called the inhal-
able particulates with sizes of <10 μm in diameter, sometimes designated as PM
10
. Their size per-
mits penetration into the nose and throat. The respirable particulates have diameters of <2.5 μm
(PM
2.5
) and penetrate into the lung. The NCRP has deined the respirable fraction as “the fraction of
airborne material that can be inhaled and possibly deposited in the lung” (NCRP 1988). “Respirable
dust” was deined as the portion of inhaled dust which is deposited in the non-ciliated portions of
the lung (Lippmann and Harris 1962).
Golchert and Sedlet (1978) determined the particle size distribution of U and Pu at the ANL off-
site location. A commercial high-volume cascade impactor was operated for one month to collect a
total air volume of 2.28 × 10
4
m
3
. The summary of their results is shown in Table 22.5. It is worth
noting that the total particulate concentration of 55 μg m
−3
of air is in excellent agreement with the
UNSCEAR (2000a) adopted value of 55 μg m
−3
of air. As expected the Pu-bearing particulates are
very small, 87% of the total activity associated with particle sizes of ≤2 μm. The soil-derived U parti-
cles tend to be much larger with <20% of the total activity in the ≤2 μm fractions. Volchok et al. (1974)
collected air samples with a horizontal elutriator to determine the respirable fraction of Pu in an urban
and a rural setting. The results were the same for the two locations (84% respirable) and in excellent
agreement with the ANL data. With the uncertainties associated with the collections and measure-
ments of these samples, fallout Pu will be considered 100% respirable. Although no measurements
were reported for respirable fraction of Th, it is assumed that it is the same as for U, that is, ≤20%.
22.9 VALUE OF LONG-TERM MONITORING
The work performed and published by Golchert et al. (1973) demonstrates the scientiic signiicance
of long-term monitoring efforts. The measurements of two naturally occurring actinide elements,
Search WWH ::
Custom Search