Re: Contaminated Hosp Pipes

["David W. Lee" <lee_david_w@lanl.gov>]

	While I was never explicitly taught this in my formal, didactic radiation
safety training which was drenched in the LNT hypothesis, my experience
over the years has imparted to me the seemingly obvious lesson that mere
"detectability does not necessarily mandate or logically guarantee that a
personnel radiation safety HAZARD actually exists."  For example, one can
swipe a lab bench top for H-3 and count say 200,000 dpm/100 cm^2, but if
so, does that necessarily constitute a personnel health hazard?  The point
is that many more things must be considered in addition to mere
radiological detectability before a given unique situation can be
considered to constitute a radiation safety "hazard."

	It is noted that you have measured low-level external dose rates of 5
microgray (0.5 mrad) per hour and 30 microgray (3 mrad) per hour from a
relatively short half-life radionuclide.  If workers are actually being
exposed to a 0.5 mR/hr radiation field, how long per day are they being so
exposed, are the SAME workers always exposed to the field in the room each
day, is the exposure rate relatively constant, do they sustain an annual
external dose equivalent exceeding the standard for a "member of the
public" (which in the U.S. is 100 mrem/yr), or are they "radiation workers"
with a much higher annual permissible dose, etc.

	I don't think it is possible to offer considered advice until the
existence/magnitude of the  potential personnel radiation safety "hazard"
is described in a bit more detail.

REGARDS David W. Lee, Los Alamos National Laboratory (lee_david_w@lanl.gov). 






At 08:28 AM 18-06-97 -0500, you wrote:
>ANY THOUGHTS ON THIS PLEASE:
>
>Patients receive up to 7.4GBq (200mCi) I-131 for Ca-thyroid radionuclide 
>therapy. This is administered on the 6th floor of our hospital. 
>
>Excreted I-131 from these patients passes through cast iron waste pipes 
>down the building to the main drain. 90% of the administered activity is 
>lost via this waste stream. The pipes pass through occupied work areas to 
>reach the main drain.
>
>Careful monitoring of these pipes, in their associated ducting cupboards, 
>has indicated that significant internal contamination builds up within 
>the pipes which remains fixed irrespective of the additional flow of 
>non-active fluid down the pipes. External doserates in the work areas the 
>pipes pass through can exceed 5uGy/hr, and in the direct vicinity of the 
>pipes, up to 30uGy/hr, two days after administration of the iodine dose. 
>Subsequently these doserates only fall via radioactive decay over the 
>following days/weeks.
>
>What can we do ?
>
>One school of thought is that the iodine is being bound to "crud" which 
>builds up and lines the pipes.
>
>Another school of thought is that the pipes are internally corroded and 
>that the iodine is binding to the corrosion sites.
>
>We have decided to internally purge one of the pipes, and reassess. If 
>the crud theory is correct we may have an answer. If the corrosion theory 
>is correct we may only expose more corrosion sites by cleaning, and 
>therefore make the matter worse!
>
>What do you (out there) suggest? N.B. There is no money to replace these 
>pipes in the immediate future, or so I'm told.
>
>FROM: 
>Andy H
>a.hancock@cxwms.ac.uk
>Radiation Protection Adviser
>Charing Cross Hosp
>London UK
>
>
David W. Lee
Los Alamos National Laboratory
Radiation Protection Services Group (ESH-12)
PO Box 1663, MS K483
Los Alamos, NM  87545
PH:   (505) 667-8085
FAX:  (505) 667-9726
lee_david_w@lanl.gov