Field and modeling study of windblown particles from a uranium mill tailings pile. Interim report Page: 5 of 136

                                
ABSTRACT
Progress on a research study sponsored by the U.S. Nuclear Regulatory
Commission is presented. The objective of this study is to develop an
understanding of the nature and transport of solid particles from a uranium
mill tailings pile. The intent is to develop and verify suspension and
transport models that may be useful when applied more generically to similar
spoil piles of uranium extraction tailings. A field study is reported,
showing that for a carbonate-leach-process mill tailings pile in the Grants,
New Mexico region much of the residual radioactive constituents in the
tailings is found associated with particles 7 um in diameter and smaller.
As the tailings material dries, particle attachment and aggregation occurs
with the result that radioactive constituents become associated more with
larger particles. Soil samples taken at surface and subsurface on radial
lines extending from the tailings pile for 5 miles showed the distribution
of radium-226 and other radionuclides in the soil. After corrections for
background were made, it was shown that the 226Ra deposited on the soil
was distributed in such a manner that about 1.6 Ci of radon-??? per day
enters the atmosphere from this secondary source.
The suspension and transport of particles were studied using an array
of sampling towers and wind speed and velocity instrumentation that signaled
designated samplers at upwind and downwind locations to operate when wind
direction and speed criteria were satisfied. Flux of particles in various
size ranges was determined as a function of wind speed. The radionuclide
content of airborne particles as a function of particle size was measured
for some samplers. A general conclusion was reached that a significant
fraction of airborne radioactive material is associated with respirable
particles. Additional field experiments are continuing.
Suspension and transport models and their application to this problem
are under investigation. Several curves are presented to show how
deposition and downwind concentration are related to wind speed, distance
downwind, and particle mass or size. Continuing study will apply site

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