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RE: Questions regarding Appendix B of 10CFR20
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.
For inhalation doses, not only the chemical form, however, is important to
ultimate dose. The particle size is also critical. If the activity median
aerodynamic diameter (AMAD) is 1 micron the lung will receive the inhaled
material to a very significant extent. If the AMAD is 20 microns (boulders
by comparison) most of the material will not get to the deep lung and will
quickly enter the GI track.
In my experience knowing the absolute chemical form isn't absolutely
required but if You don't know any number of other questions may crop up
leading to a high degree of discomfiture. If You do not know the chemical
form, You better use the MOST RESTRICTIVE lung solubility class. If You
use a less restrictive class You need to have good documentation as to the
form that is assumed and valid reasoning for this belief. If processes
change, updated reasoning, testing, etc. needs to be valid and documented.
Ultimately, You need to communicate with your regulator (s) to be sure that
he or she is satisfied with the chosen approach. Also be sure there are no
commitments in your licensing or other documents, regulations etc. that
require a specific degree of quantification and qualification. It may be
that for NESHAPs,NPDES or POTW purposes for example, one must clearly note
the chemical form or forms present.
According to the discussion prior to the tables in Appendix B, "The water
concentrations were derived by taking the most restrictive occupational
stochastic oral ingestion ALI..." The discussion prior to the tables of
Appendix B contain alot of good information worth taking the time to read.
If there are terms that are not clear to You, see 10 CFR 20.1003
(Definitions).
Hope some of this helps-
Let the reader beware, the above clearly represents my experience and
opinions only...
Martin J. Brennan
SNL, Org. 7526
-----Original Message-----
From: k244jsy@pinpoint.kins.re.kr [mailto:k244jsy@pinpoint.kins.re.kr]
Sent: Tuesday, May 25, 1999 11:31 PM
To: Multiple recipients of list
Subject: Questions regarding Appendix B of 10CFR20
Dear Radsafers, May 26, 1999
Could someone please inform me of technical bases on the following
questions ?
According to 10CFR20 appendix B, there are several air effluent
concentration limits based on chemical forms of each radioluclide.
Is it required to identify what chemical form of effluent is or is it
possible to use the more conservative one as a chemical form to be applied
?
According to effluent concentration limits of water effluent, only one
concentration limit is established, although there are several chemical
forms. Is this limit applicable to all chemical forms or is it applicable
to only one type of chemical form per each nuclide ?
Thanks in advance.
Si-Young Jang
Korea Inst. of Nuclear Safety
P.O.B 114, Yusung, Taejon
Korea
(email: k244jsy@kins.re.kr)
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