RE: Decay Storage Requirements

["Michael P. Grissom" <mikeg@SLAC.Stanford.EDU>]

DIS Interested Parties,

There were some General Laboratory licensees, who used only
I-125 labeled RIA materials, that were allowed in their licenses
to process (survey prior to disposal of course) waste after 7
half-lives.

The amount of activity per assay tube was in the typically
in the nCi range (much less after decanting).  Solid waste
(tubes, paper, wipes, etc.) was held for the specified number
of half-lives and then surveyed prior to disposal in normal
trash.  For a time, it was required to send the waste to a
commercial DIS facility (due to the large volume of tests
done by these laboratories, >10,000 per month) for storage
for the specified time.  The commercial DIS facility (in Illinois)
was also required to hold for 10 half-lives and survey prior to
disposal in normal waste streams.

Accumulated liquid waste was surveyed (including aliquot 
sampling with gamma well counting) to indicate no remaining 
activity above prevalent background prior to sanitary sewer 
disposal.

This policy was not uniformly applied to all General Licensees,
however, since some had the 7 half-life rule while others had
the 10 half-life rule.  All labs (that I audited/reviewed in the olden 
days--late 80's early 90's--during RSO peer review visits) had to 
survey after the DIS period to confirm no rad detected above 
prevalent backgrounds using appropriate survey instruments.

S.,

MikeG.


At 12:39 PM 12/5/96 -0600, you wrote:
>I've often wondered this myself. We've had it in our license and have
>been dutifully following it for years. My suspicion is that the
>10-half-life figure was chosen because, after this period of time, the
>original activity has been reduced by slightly more than 1/1000. (A
>round figure that sounds good to regulators but, as stated by others, it
>all depends on how much you start out with.)
>
>Has anyone out there ever successfully gotten the NRC to approve
>disposal of  waste once the levels of contamination are effectively
>background WITHOUT having to go through the decay-in-storage for
>10-half-lives? For waste minimization and conservation of storage space,
>don't we tell users to frisk first before putting a whole benchtop
>blotter in the rad waste? Isn't that the same thing?
>
>...
>
>Jim F. Herrold
>Radiation Safety Officer


-----------------------
Michael P. Grissom
Special Assistant, SLAC
mikeg@slac.stanford.edu
Phone:  (415) 926-2346
Fax:    (415) 926-3030