Re: Tritium Adsorption

[Jim Williams <NARM@postoffice.worldnet.att.net>]

I have been involved in the decontamination and decommissioning
 of five H-3 contaminated facilities in the last three years and the one
 pattern that I have seen is that there is no pattern.
 
         There are many variables that affect sorption, including
 exposure time, time since exposure, relative humidity, atmospheric
 pressure, original concentration at exposure, air turnover rate, etc.
 
         In addition, there doesn't seem to be any definable 
relationship between fixed contamination and loose surface 
contamination. In one facility, one area of a wall had 1K dpm loose and 
75K dpm fixed. One foot away, the wall had 25K loose but only 5K fixed. 
Both areas were well away from the "source".
 
       Since the H-3 molecule is so small, it can easily penetrate the
 interstitial spaces of large molecules. However, like most nuclides, it
 tends to penetrate deeper into more porous materials.
 
         You will also notice that the timing of your surveys is
 important. If, for example, you wipe down a surface and immediately
 collect a swipe, the area may be "clean". If you resurvey the same spot
 one hour or one day later, the results will likely be higher. This can
 definitely get you in trouble during release surveys if you aren't  
aware of it.
 
         Although I have never tried it, I have always thought that you
 could decontaminate a room by adjusting the relative humudity. The
 procedure would be to bring the humidity up to 100%, then down as low
 as possible (with a desicant), then repeat.
 
         There are some reference papers by DOE on H-3 sorption rates,
 but I think that you will find them of limited use in the real world.
 
         Standard Disclaimers.

	Jim Williams
	Thomas Gray & Assosciates, Inc.
	5227 Blossom
	Houston, Texas 77007
	713-869-0018
	713-869-0070 (fax)