RE: Questions regarding Appendix B of 10CFR20

["Elizabeth M. Brackett" <brackett@bright.net>]

The clearance class is specifically used to describe the clearance of
inhaled radioactive material from the lung; it doesn't describe clearance
from the rest of the body.  Once the material passes from the lung into
body fluids, a single biokinetic model is applied to all forms of an
element (which is why there's no classes given for ingestion intakes). All
forms of uranium making it to various organs are retained with the same
effective half times (the class D ALIs are limited by dose to the bone
surfaces because of this; it clears the lung quickly but then stays in the
bone for a long time).

Liz Brackett
 

At 02:00 PM 5/27/99 -0500, you wrote (in part):
>The chemical form is an essential determinant for how an intake is
>"processed" by the body.  Where it goes, how long it remains, etc.
>determines ultimate committed effective dose equivalent (CEDE).  Lung
>clearance half-times (residence time) for inhalation is typically
>considered in terms of three classes referred to as D,W and Y.  Uranium
>hexafluoride is very soluble (Class D) and so passes through the body in a
>matter of days.  A high fired uranium oxide (Class Y) by contrast, sticks
>around for years.  Remaining in one's body much longer, the CEDE for UO2 is
>much greater for the same intake than for the UF6.  This is reflected in
>the much lower ALI and more restricted DAC for the oxide form.  This is a
>somewhat simplistic discussion, other factors come into play in determining
>CEDE as well.  Be careful not to fall into the trap of thinking that Class
>Y necessarily results in the most restrictive DAC.  For example, many of
>the thorium isotopes have more restrictive DACs for Class W than for Class
>Y material. 

******************************
  Elizabeth M. Brackett, CHP 
     Sr. Health Physicist     
     MJW Corporation, Inc.       
       (330) 644-3757        
  mailto:brackett@bright.net 
******************************
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