Contamination Dispersion Cs 137

["Mike Malaxos" <mike@radiationsafety.com.au>]

>Hullo Group,
                    My second attempt to get the formatting right.
>                I would like to see your comments regarding the dispersion
of contamination from a ceramic bead double encapsulated Cs 137 special form
source. I believe that information  concerning the following experience
would be valuable to many of us. A 5 year old 50 mCi Cs 137, ?? double
encapsulated, X8 approx 6 mm x 8 mm ) source was removed from a density
gauge source container for testing. The source was enclosed in an X 38 (13
mm x19 mm) aluminium outer capsule to fit the cavity in a Density Gauge
source container. The container label identified the enclosed source as 50
mCi 1995.   The thorough wipe of the  X 38 outer aluminium capsule
concentrating on the grub screw end was 2- 3 Bq.  The X 38 capsule was
installed in a holder in a hot cell and the grub screw removed to extract
the source. When the extended hex driver was inserted  into the grub screw
it was found that the grub screw was fully inserted  but only finger tight.
(it would not have compressed the source) As the grub screw was unscrewed
from the capsule  it was noted that the thread contained flakes of white
material(probably a sealing compound).  The rod holding the grub screw was
withdrawn over the middle of the hot cell
>and checked with a thin window GM detector. It was grossly contaminated .
No attempt was made to  measure the activity. It was replaced in the X 38
capsule and the capsule transferred to a holding pig with contaminated
waste. Care was taken to prevent the grub screw and screw holding tool from
touching another surface during the procedure.  The rod holding the screw,
the area over which it passed ( a track 20 cm wide), and a vertical section
of the hot cell wall 20 cm from the centre of the path was contaminated
(probably 2 - 200 kBq in all) . Is it possible internal corrosion may have
generated internal pressure causing tiny particles of contamination to be
blasted out from the cavity when the grub screw was removed or could the
particles of contamination been small enough to disperse over the area (in a
draft free location).  I require information concerning the chemical form of
the Cs 137, the chemical and physical characteristics and retention
capability of the ceramic. I would appreciate any information concerning
previous occurrences of suspected internal pressure build-up due to
corrosion in Cs 137 or Co 60 sources which could spread contamination or
experience of dispersion of microscopic particles in still air.  Is the use
of a fume hood considered mandatory when handling sealed sources.  We now do
an additional wipe test when the source retaining screw has been  unscrewed
about three turns to prevent a re-occurrence of this type of situation.
>
Thanks in advance  for your comments.
>
>Best Regards,
>Mike Malaxos.
>Radiation Safety Services
>Mike@radiationsafety.com.au
>69 Robinson Avenue Belmont Western Australia 6104
>Phone 61 (0)8 94750011 FAX  61 (0)8 94750011
>

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