Re: Medical waste held for decay

["Radiological Health Unit" <raldrich@emi.com>]

Joelle, you wrote:

>When a medical or research facility holds short-lived nuclides for 10
>half-lives to decay, how much can still be left and still consider the
>material "gone."  I would think that it should be completely gone to be
>gone but isn't this impracticle?  Is this nuclide specific?  

>I'd appreciate answers from different facilities if they differ.  If this
>question has been asked on RadSafe already maybe you can just tell me
>the subject line and I can look through the archives that way.

>Thanks

>Joelle Key
>TN-DRH
>jkey@mail.state.tn.us
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The prescribed procedure is to hold the material for a minimum of 10
half-lives then survey in a low 
background area with all shielding removed using an appropriate survey
meter. If the activity is 
indistinguishable from background it may be disposed without regard to
radioactivity.

After 10 half-lives the activity is reduced by a factor of 1/1024. The
activity remaining, of course 
depends on how much you started with, and could still be quite a lot. It's
never gone. So the condition that the waste activity be indistinguishable
from background is really the most critical. The concern is not that a 
small amount of short lived material is going into a landfill, but that on
the way in it might trip an alarm.

When monitoring DIS waste prior to disposal, you should be thinking about
what the detectors at 
the disposal facility are going to be able to detect. Remember they are
using large scintillators with 
the  alarm set point typically at a few percent above background! (Forget
about 2 sigma!) Once an 
alarm goes off, a train of events will be initiated involving dozens of
people whose time could be 
better spent on other things, but who will now spend the better part of the
day trying to figure out 
what the offending material is, where it came from, and who is going to pay
for it!


************************************************************************
Clayton Bradt	<raldrich@emi.com>        phone: 518/457-1202
Assoc. Radiophysicist                         fax:      518/485-7406
NYS Dept. of Labor
Radiological Health Unit
Blg.12, Rm 134A
State Office Campus
Albany, NY 12240
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