[ RadSafe ] Salsman RE: Gardner Sellafield cluster

[James Salsman]

John Andrews wrote:

>... I wonder how long this 
> UO3 will stay in the vicinity of the vehicles that were damaged and 
> continue to be an exposure hazard.  If it has a very slow setteling rate 
> (is this true?) then it will disperse with the normal air movement and 
> not be a significant problem because of dilution and dispersion.  

The terminal gravitational settling velocity is given by Stokes law, as:

       W = r*G*d^2/18*n

where r is the particle density (about 8 g/cm^3 for UO3),
       G is the gravitational acceleration constant,
       d is the particle diameter (about 7 Angstroms for UO3),
       n is the dynamic viscosity of the media,

Using the viscosity of air at 25 deg. Celsius, UO3 gas particles settle
out at about 60 cm/year.  However, that understates the rate to the
extent that atmospheric mixing and diffusion results in deposition on
the ground, plants, animals, exposed food, etc.

As for diffusion, that is determined by the diameter of the particle,
so in this case it is a little more volatile than benzene C6H6.

In order to get all this exactly right I am supposed to read
D.L. Ermak in Atmospheric Environment, vol. 11 (1977) pp. 231, which
I have not done yet.

Sincerely,
James Salsman