Charcoal Filters and HEPA Filters ... II.

[mirolies@nbnet.nb.ca (Miroslav Lieskovsk\})]

Hi again,
I just want to add some more info re. my previous posting (I was just about
to miss my carpool):

"Dear Radsafers,

We are currently looking for charccoal loaded HEPA filters for industrial
use.  These filters are requested for a certain work to be undertaken in a
very near future, and as it stands now, the only manufacturer we were able
to locate is in Switzerland. Their delivery times are quite long.

As a matter of fact, I also wanted to ask for an info from (but not only)
nuclear power plants staff about some experience with antimony family in the
air (specificaly, Sb-124 and/or 125) and their "alleged" passing through the
normal HEPA Filters.  Is there anybody to contact who could give us a thought.  

Thank you very much in advance."

The job I was talking about is a mechanical (dry) cleaning on the primary
side of our steam generator (SG) tubes.  This cleaning (called "Vacu-blast")
has been developed by Siemens in Germany. In principle, the cleaning is
carried out by air driven metal shots inside the SG tubes in a leak-tight
closed loop (hopefully) and remove (i.e., clean) virtually any deposited or
plated out materials (mainly magnetites, [Fe,Ni,Cr](x)O(y)) from the inner
surface of tubes and without any damage to the tubes itself(!).  In the
matrix of magnetites there are activation products such as Co-60, Zr/Nb-95,
Fe-55,59, Ni-63, Sb-124,125, Sn-113, etc. (We do not have iodines there - no
damage on fuel sheets,and further, they are all "decayed". The unit is down
for more than 3 months now.) The cleaning process creates particulates with
approximately 2-3 micrometers in diameter.  
Well, as it sounds and (I'm afraid) as it is, this process could turn into
airborne contamination problem.  To avoid this and eventually to contain any
leaks during the cleaning, we are building additional tents to enclose the
Siemen's cleaning systems and the SGs. The air inside these areas will be
filtered with a separate industrial air-cleaning equipment (high capacity
ventilation units, 470 L/s ~ 1000 cfm) with build-in HEPA filters.  As we
hear from Siemens' specialists, these filters are, however, not efficient
for antimony, because it is released during the cleaning "almost as a gas",
passing through the ordinary HEPA Filters, and, because of this, charcoal
filters are needed.  It is (for me) hard to believe, that this is a case,
but we do not want to take any chance, and we want to equip our ventilation
units with charcoal loaded (or beds) HEPA filters.  The size that fits our
units the best: 24"x24"x11.5".

The personnel protection aspects are to us a lesser problem, since the
cleaning process is  automatic, and, if necessary, our staff can be
protected using plastic suits with own airlines. 

Hope this helps to outline the problem.

Looking forward for your help.  It is greatly appreciated. 

Thanks.        


     Miroslav

PS. Standard disclaimers apply.
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If I had an opinion, it sure wouldn't be mine... or my employer's!
Nazory nemusia v ziadnom pripade vyjadrovat postoj mojho zamestnavatela, 
ba niekedy ani moje vlastne.
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Miroslav Lieskovsky                               Health Physics Department
mirolies@nbnet.nb.ca                       Point Lepreau Generating Station
Phone  bus: (506) 659 2220 ext. 7421                    New Brunswick Power
Fax    bus: (506) 659 2003                             P.O. Box 10, Hwy 790
Phone  res: (506) 636 7629                                    Lepreau, N.B.
e-mail res: miroslav@mi.net                                 Canada, E0G 2H0