Carol;
I was the Project Manager for Duratek, Inc. at a refinery in western
Louisiana that had a melted Ir-192 radiography source. It happened this past
January.
In a nutshell, a 40 Ci (effective) Ir-192 source contacted an energized welding lead inside a acid settling tank that was being repaired. The arc vaporized a good portion of the source, some more stuck to the welding lead, and the rest was cranked back into the projector.
The
vapor seemed to quickly re-condense. Tank ventilation caused discrete particles
to be strewn over the surrounding area and 1,000 meters
downwind.
Here's
some tidbits:
- The particles seemed to be vaporized Ir-192 that condensed onto dust and dirt particles.
- The particles seemed to have a high static charge. They stuck to whatever they deposited on like glue, and stayed there.
- The particles had a very high specific activity
- It was difficult to detect the particles with NaI detectors (e.g. Ludluum 44-10). This is because the beta-to-gamma ration was about 40:1! Seems odd for an industrial radiography source, but true. We could easily find the particles with a HP-210 GM pancake frisker probe, sometimes at 6 feet away!
- This type of source is made up of stacked discs of Ir metal that is irradiated in a Swedish reactor. AEA technologies can give details of the source configuration.
- These sources are rated in "effective" curies. This is because there is significant self-shielding in the source itself. Our source was estimated at 80 curies once it was broken-open and dispersed.
- We had several personnel contaminations. The microscopic nature of the contamination, along with the high specific activity meant that the contamination migrated through standard protective clothing fairly easily. Skin contaminating had to be "sweated-out" because it got into the pores of the skin. We had no significant skin exposures for our event, recovery, remediation, and survey.
- We had zero intakes. No contamination seen in air samples.
- I believe that Ir-192 is also very insoluble. It is a very brittle metal.
In
summary, a Ir-192 RDD might:
- Create a mess, with very high specific activity particles
- Will be a skin contamination and skin exposure problem
- Particles will be easy to detect with standard friskers
- Is not likely to be a significant internal dose contributor
Hope
that this helps.
Respectfully,
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-----Original Message-----
From: Carol S. Marcus [mailto:csmarcus@ucla.edu]
Sent: Friday, September 06, 2002 5:14 PM
To: radsafe@list.vanderbilt.edu
Subject: Chemical state of Ir-192 sources
Dear Radsafers:
I am interested in knowing the chemical state of Ir-192 in sealed sources,
and any thoughts on what would happen chemically to the Ir-192 if it was
exploded as a radiologic dispersion device. I am trying to estimate
biodistribution and kinetics if such Ir-192 were to be inhaled, ingested,
or introduced traumatically (e.g. contaminated shrapnel). Anyone having
any information on biodistribution and kinetics is requested to share it
with me.
The California Statewide Medical and Health Disaster Exercise on Nov 14th
includes an Ir-192 RDD scenario, and I have been asked to critique our
Exercise Guidebook. Ir-192 in an RDD is a reasonable scenario, and I need
to know this anyway.
If, for example, the Ir-192 is chemically just solid metal, and some of it
is converted to insoluble oxide in the explosion, then we would worry about
pulmonary and pulmonary lymph node deposition. Little would ionize and get
into the blood and other organs. Ingested Ir-192 would just pass
through. If, on the other hand, much of it were to be in a soluble form,
the biodistribution and kinetics would be entirely different.
Many thanks for any help you can give me.
Ciao, Carol
Carol S. Marcus, Ph.D., M.D.
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