Transuranic and Tracer Simulant 

 Resuspension 



G. A. SEHMEL 



Plutonium resuspension results are summarized for experiments conducted at Rocky 

 Flats, on site on the Han ford reservation, and for winds blowing from off site onto the 

 Hanford reservation near the Prosser barricade boundary. In each case plutonium 

 resuspension was shown by increased airborne plutonium concentrations as a function of 

 either wind speed or as compared with fallout levels. All measured airborne concentra- 

 tions were below maximum permissible concentrations. 



Both plutonium and cesium concentrations on airborne soil were normalized by the 

 quantity of airborne soil sampled. Airborne radionuclide concentrations (in microcuries 

 per gram) were related to published values for radionuclide concentrations on surface 

 soils. For this ratio of radionuclide concentration per gram on airborne soil divided by 

 that for ground-surface soil, there are seven orders of magnitude uncertainty from 10"^ 

 to 10^ . This uncertainty in the equality between plutonium concentrations per gram on 

 airborne and surface soils is caused by only a fraction of the collected airborne soil being 

 transported from off site rather than all being resuspended from each study site and also 

 by the great variabilities in surface contamination. 



Horizontal plutonium fluxes on airborne nonrespirable soils at all three sites were 

 bracketed within the same three to four orders of magnitude from 10~'^ to 10~^ iiCim" ^ 

 day~^ for ^^^Pu and 10'^ to 10~^ idCi m~^ day~^ for ^^^Pu. These represent the 

 entire experimental base for nonrespirable airborne plutonium transport. 



Airborne respirable ^^^Pu concentrations increased with wind speed for a southwest 

 wind direction coming from off site near the Hanford reservation Prosser barricade. 

 Airborne plutonium fluxes on nonrespirable particles had isotopic ratios, 

 ^^ ^Pu/^ ^ ^ ^'^^Pu, similar to weapons-grade plutonium rather than to fallout plutonium. 



Resuspension rates were summarized for controlled inert-particle-tracer simulant 

 experiments. Wind resuspension rates for tracers increased with wind speed to about the 

 fifth power. This wind-speed dependency is comparable to that measured for off-site 

 plutonium resuspension near the Prosser barricade However, plutonium resuspension 

 data near the U-Pond Area showed an air concentration dependency on wind speed to the 

 1.5 power. There is still uncertainty in the wind-speed dependency of airborne 

 concentrations at different sites. 



The weathering half-life is the average time required for airborne concentrations from 

 resuspension sites to decrease by one-half when airborne concentrations are averaged over 

 all meteorological conditions. Airborne plutonium and cesium concentrations measured 

 at Hanford as well as tracer resuspension experiments show that the weathering half-life is 

 much greater than that usually reported in the literature: 5 months or much longer rather 

 than only 35 to 45 days 



Resuspension rates for local mechanical resuspension of inert tracer particles caused 

 by vehicular and pedestrian traffic are summarized. 



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