Re: tritium oxidation rates -Reply -Reply

[MICHAEL S FORD <MFORD@pantex.com>]

Scott, 

When I was discussing you choice of DAC values, I was referring
to your comment below:

>
>Now, if T2 and HTO are both released into an atmosphere and
>measured by bubbler or measuring air conditioner condensate,
>things get a little confused.  In both cases, you are measuring
>HTO, but from which ORIGINAL species did the tritium come? 
>One might argue that it really makes no difference, as the
>biological absorption, and therefore the limits, are similar,..."
>

The last statement is what I took issue with.  The biological
absorption for T2 (gas) and HTO (vapor) are not similar, nor are the
limits.  'Sorry I was not more clear on where the issue was taken.

>
>... but it does make a difference when one is trying to account for
>all the tritium.
>

Your approach might be difficult to defend depending on your point
of measurement.  If you're measuring only at the point of release
and are only looking for HTO, you're not accounting for the T2 that
is later converted to HTO downwind.  Depending on your process,
prevailing meteorological conditions and receptor locations, this
could be negligible.  

If this is cooling water you're dealing with (for steering magnets or
beam stop?), assuming all HTO would be a reasonable approach.

I do agree that, mathematically speaking, your differences in DAC
and sampling efficiency do cancel out.  But you could make a
stronger argument for your approach by characterizing your source
term (which you've probably already have done) and tailoring you
measurements and analyses based on the known source term.

If you know what your T2/HTO mix is and have a reliable HTO
measurement process, you only need to measure for HTO and then
calculate your T2 effluent.  Depending again on the variability of
your process, take confirmatory measurements to make sure your
T2/HTO mix is constant or characterize it for any process (beam
current/beam type?) variability.

v/r
Michael
*************************
Michael S. Ford, CHP
Texas Radiation Advisory Board
Address:
Radiation Safety Department
Battelle Pantex
Amarillo, TX
806.477.5727 phone
806.477.4198 fax
mford@pantex.com
*************************

>>> Scott Schwahn wrote on Mon 8 Jun 98  6:31 >>>
Thanks - the constants appear to be helpful - I'll have to do some
number crunching to see if they're what I'm looking for.  And I
would go back to saying, no, it really _doesn't_ matter.  As I
mentioned in my earlier post, the detection efficiency for T2 is
about 4 orders of magnitude lower than that for HTO.  So if one
assumes that it is all HTO, and uses the DAC for HTO, it essentially
doesn't matter what the mix of chemical species is -
all gaseous, all water, or anywhere in between.  The ratio of
detection effeiciency to DAC cancels each other out.  Would you
not agree on this?

MICHAEL S FORD wrote:

> Since the exposure limits (DAC) are about four orders of
>magnitude lower for HTO than for T2, it really does matter.
> ...
> They obtained a dry air oxidation rate constant of
> 5.6e-4 mL/mCi-hr and 2.9e-3 mL/mCi-hr for moist air.

--

Scott O. Schwahn, CHP
Thomas Jefferson National Accelerator Facility
schwahn@jlab.org