Re: airborne U

[Vincent.King@DOEGJPO.COM (Vincent King)]

     Mike
     
     The DAC values in 10 CFR 835 are based primarily on the methodology 
     and annual limits on intake found in International Commission on 
     Radiological Protection Publication 30.  There are other, more 
     readable sources of information, however (try Internal Radiation 
     Dosimetry, edited by Otto G. Raabe, published by HPS from the 1994 
     Health Physics Summer school). 
     
     In general, you're thinking is correct.  Inhalation of insoluble 
     chemical (e.g., class Y) forms of alpha emitters will result in higher 
     lung doses than will moderately soluble forms (class W).
     
     For both class W and class Y uranium, the lung dose (after applying 
     the ICRP tissue weighting factor) is a more significant contributor to 
     the committed effective dose equivalent (CEDE) to the whole body than 
     is the dose from any other tissue or organ, consequently the CEDE is 
     higher for class Y uranium.
     
     For plutonium, however, the weighted dose to bone surfaces outweighs 
     the lung dose contribution.  And since more soluble forms of plutonium 
     more readily dissolve in body fluids and become available for 
     deposition in the bone, the dose to the whole body increases for the 
     more soluble form (even though the lung dose decreases).   
     
     Note that, while it is correct that chemical toxicity of pure U-238 
     outweighs radiological risks because of it's extremely low specific 
     activity, the radiological dose (at least as far as regulatory limits 
     are concerned) from more insoluble forms of natural uranium and from 
     enriched uranium may outweigh the chemical concerns. It's best to 
     evaluate both risks and determine which limit is more restrictive as 
     solubility decreases and enrichment increases.
     
     Vincent King, CHP
     vincent.king@doegjpo.com
     
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     July 23, 1997
     
     Dear Mike:
     
     Calculation of radiological risks from pure U-238 is meaningless since 
     the actual risk depends on the chemical toxicity of uranium in the 
     kidney not in the bone or lung, although both the bone and lung can be 
     a reservoir of this potentially toxic element.
     
     Otto
     ***************************************************** Prof. Otto G. 
     Raabe, Ph.D., CHP
     [President, Health Physics Society, 1997-1998] Institute of Toxicology 
     & Environmental Health (ITEH)
     (Street address: Old Davis Road)
     University of California, Davis, CA 95616 Phone: 916-752-7754     FAX: 
     916-758-6140 E-Mail: ograabe@ucdavis.edu
     ******************************************************
     
______________________________ Reply Separator _________________________________
Subject: airborne U 
Author:  mcnaught@lanl.gov (Mike McNaughton) at Internet
Date:    7/23/97 12:51


I am comparing the hazards of W and Y class airborne U-238, using the 
derived air concentrations in 10CFR835 appendix A. Can anyone shed some 
light on these?
     
For Pu-239, W class is 3 times as hazardous as Y class, presumably because 
with Y class, some is cleared from the lung before it is deposited on the 
bone.
     
However, for U-238, Y class is 15 times as hazardous as W class. This must 
imply that the critical organ for Y class U-238 is the lung.
     
Is there a document that explains the logic of the derived air 
concentrations in 10CFR835? Thanks, mike
     
"Shlala gashle" (Zulu greeting, meaning "Stay safe") 
mike (mcnaught@LANL.GOV)