Tritium Decon

[/I=J/S=PRESLEY/O=AECB.CCEA@mhs-atomcon.attmail.com]

     In answer to Les' call for Canadian Help.
     
     I used to work at the Darlington Tritium Removal Facility
     and can offer my condolences to anyone trying to decon
     tritium contaminated materials.
     
     There is only one way that we found which would effectively
     remove tritium from material and that is, as Les suggested,
     heating it.
     Typically, we're talking 250-300 C.
     A Vacuum furnace can be used if it is available and large enough.
     Heating tape or similar heating attachments can be applied to surfaces
     to raise their temperature substantially.
     
     The problem with surface decon is that the "dissolved" tritium will
     continue to migrate to the surface (driven by the concentration 
     gradient) after surface cleaning.
     This process seems to equilibrate after about 24 hours and the only 
     way to prevent it is to remove all of the tritium from the bulk of the 
     material by heating it and "boiling" it off.
     
     Something else to consider, the tritium comes off the material almost 
     exclusively in the oxide form. This makes it a much more serious 
     inhalation hazard than tritium gas. Depending on your materials and 
     heating rates, high "puff" concentrations are possible.
     
     Other than that, if you can't heat the item to decon it, and it is 
     porous material you might try soaking it in water, but that just gives 
     you a whole new set of problems !! I would recommend sending it 
     straight to rad waste !
     
     Hope this helps.
     
     James Presley
     Health Physicist 
     Atomic Energy Control Board
     ATOMCON/I=J/S=PRESLEY/O=AECB.CCEA@MHS.ATTMAIL.COM
     
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Date:         Fri, 23 Feb 96  09:28:12 EST
From: "Les Slaback, Health Physics" <SLABACK@micf.nist.gov>
Subject:      tritium decon

In reponse to Mike Grissom's horn blowing I have to plead excess exhalation
on his part.  My negative experience with tritium decon consists of an
effort (as a test) to decon the steel shell of a vac-ion pump off a
neutron generator.  The pump had contained in excess of 50 Ci of tritium and
released mCi amounts when brought to atmospheric pressure.  As I recall my
estimate of the 'apparent' burden (by turning the shell into an ion chamber)
was half a curie.  Acid washes, repeated heating, ultrasonic washing all
remove
d activity but did not appear to reduce the 'apparent' activity.  From folks
who study hydrogen 'solubility' in metals this is not unexpected.

I have had similar negative results with aluminum tritium contamination, but
have not done such extensive brute force efforts.  I did find that tritium
leaves tungsten very readily via heating.


Take care not to do a contamination test immediately after surface decon

procedures.  More tritium will bleed to the surface.
My conclusion is that the economical route is simply disposal, or controlled
usage if the item will remain in use.

Our local materials expert indicated the maximum hydrogen to iron atom ratio
would be 1:1e6.  If anyone knows of a definitive reference for this I
would appreciate the source.

If you have airborne tritium, e.g., like at heavy water reactors, concrete
walls can be a reservoir that retains it.

If you have asbestos around, be aware it is hydroscopic and hence will suck
up airborne tritium.[mixed waste?]

I suspect the canadians must have a pile of info on this topic given there
operating experience with the heavy water CANDU facilities.  Perhaps we can
get input from someone up north before golf season starts (couldn't resist
mentioning that topic that bothers some folks).

SLABACK@MICF.NIST.GOV  [NBSR Health Physics Group]
    ...a little risk, like a bit of spice, adds flavor to life

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