Experimentally Measured Resuspension Rates cont'd

DOE-HDBK-3010-94

4.0 Solids; Powders

8760 hr/yr and from 0.35% to 35% of the source is depleted per year. The error would not

be significant for short periods of time (e.g., 4E-5 of the source is depleted in one hour at a

resuspension rate of 4E-5/hr). An uncertainty is the possible loss of resuspended materials if

the plume height exceeded the sampling height. Furthermore, it is uncertain which surface

areas are being sampled by the samplers. The material plume spreads as it rises and travels

downwind. The material sample is some cumulative fraction of some unknown upwind area.

Most recently, several researchers have investigated the long-term effects of the radionuclides

deposited from the Chernobyl Nuclear Power Generating Station incident. Garland and

Pigford (1992) investigated the resuspension of the material under a variety of circumstances.

Resuspension factors varied inversely with the amount deposited. Some seasonal variation

was observed and some increase due to traffic. Generally, results support the use of the

lowest resuspension factors. Typical and mean resuspension factors from site with highest

deposition during the initial periods were 5E-9 and 2E-8 and decreased for next periods.

The sampling configurations nor periods were given but they most certainly exceed a second

and are more likely in days. Therefore, even the initial resuspension factors would be less

than the rates measured by Sehmel and Lloyd (1976).

Garger, Gavrilov and Zhukov (1992) modeled the transfer and fallout of radionuclides

deposited from the Chernobyl accident. The airborne concentration and deposition rate of

radionuclides due to resuspension and activities were modeled for normal and unfavorable

steady-state meteorological conditions. Resuspension rates of 1E-9/s at 5 m/s and 2E-7/s at

15 m/s were calculated based on air sampling.

Based upon the information on resuspension factors and rates found in the two reviews, the

experimentally measured rates tend to indicate that the long-term resuspension rate bound

determined by Sehmel and Lloyd (1976), 4E-5/hr, is reasonable. Although the rates appear

to decrease with time (and even higher rates are probably possible for short periods of time

during the initial phases of the aerodynamic entrainment), using the initial, higher rates

would be conservative. The value is derived for the continuous phase of the aerodynamic

entrainment and does not represent the instantaneous airborne release from puffs. Caution is

advised in evaluating results that are treated as instantaneous release values for nonreactor

conditions. Furthermore, in an operational facility with a effluent exhaust system, the

airflow was present during the release and materials deposited have already experienced the

flow during transit. The fraction released with time is for MAR that may be difficult to

define and decreases with depletion by the entrainment and other phenomena such as burial,

cover by debris deposited on the surface, etc. The resuspension tends to fluctuate as the

level of stress fluctuates and the surface conditions respond to the previous stresses. After

an event, the powder released may be exposed to primarily aerodynamic stresses within the

facility or remnants of the facility until remedial action can be taken. The time interval of

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