Contamination Dispersion Cs 137

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

Hullo Group,

                I would like to see you 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The rod holding the grub screw was withdrawn over the middle of the hot cell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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