Re: Question on Specific Activity

[Keith Welch <welch@CEBAF.GOV>]

Subject: Re: Question on Specific Activity

Tim Paul wrote:
> 
> Hello,
> 
> I have a question regarding the definition of Radioacive material in 49 CFR
> Part 173.403.  If the specific activity is greater than 2 nCi/g, then it is
> radioactive.
> 
> When determining specific activity, what can you average this over?  Is it
> just the source/sources inside or the entire contents and container?

Jim Williams responded:

	For DOT (not NRC, disposal site classifications, etc.) purposes, you
avergage over the gross weight of the "package". In most cases, unless
you are using an "overpack", this means the same drum, box, etc. that
you put the markings and labelings on. I have seen this question asked
many times, but the answer is always the same.

	Assume that you had a 100 uCi check source. You place the the check
source in cardboard box and the gross weight is now 2000 grams. In this
case, the specific activity of the "package" is 50 nCi/gram, thus it is
radioactive per DOT.

	If the same check source were placed in a metal drum and the gross
weight was 100,000 grams (~200 pounds) the package would not be
radioactive per DOT. Classification as radioactive in this case would
violate 49 CFR 171.2(f)(2).

	It is common for radioactive waste disposal and processing facilities
to receive radwaste that is not a hazardous material per DOT. In fact, I
once shipped a non-DOT regulated package that required disposal as Class
C waste!

	This only applies to the DOT clasification. In most, but not all, other
situations you do not include the weight of the empty packaging(s).

Jim Williams
-----------------
This is interesting because it is not what I gathered from the training
that I received recently.  I had the same basic question, and if I remember
correctly, the expert opinion of the instructors was that you should use a
great deal of caution when determining the specific activity.  No mention
of taking credit for the weight of the package was mentioned - and in fact,
the prevailing wisdom was that even a single solid item that had a small
spot of radioactivity may not be allowable for averaging purposes.  The
reasoning was that the activity needed to be relatively evenly distributed
in the material.  So for instance if you have a 200 pound piece of steel
plate with a 1" hot spot on it, you better be careful about trying to
average the activity over the entire piece.  So a button source had to be
considered a single entity, and if it was boxed in a 100 lb crate, that
didn't matter.

I know that Jim is an expert shipper, so this is confusing.  Does anyone
have any specific regulatory guidance from DOT that answers this question -
some kind of position statement that could be referenced.


Keith Welch
Thomas Jefferson National Accelerator Facility
Newport News VA
welch@cebaf.gov
Ph: (757)269-7212
FAX:(757)269-5048