Contaminated Hosp Pipes

["A. Hancock" <a.hancock@s1.cxwms.ac.uk>]

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