Re: Sealed sources: extension of recommended working life

["Mike Malaxos" <rss@arach.net.au>]

The following comments relate generally to high energy sealed gamma sources
such as Cs 137 and Co 60.

It seems amazing that the question of extending the life of sources seems
to be made more on an emotional basis than a technical basis. The following
may be examples of this.

The comment:
  
" I see this problem very much as a liability issue.  Is the savings
generated by non-replacement worth the potential liability of capsule 
failure?"

The fact that:
Some regulatory organisations may insist that the source be removed and
tested every 5 years.

The reality of the situation is:
Sources which are discarded after 10 or 15 years must be stored pending
disposal and new ones produced doubling or trebling the number of sources
every 30 years.

There are many instances where sources in their containers have been
improperly disposed of entering the waste stream causing very expensive
clean-up operations. (The contamination of reinforcing rods in buildings in
Tiawan, the San Jurez incident are just two recent ones).

These incidents were not the result of leaking capsules, they were the
result of improper disposal due to the negative value of the source.( the
high cost of disposal). These instances may not have happened   
if the sources had some value because they would have been sold, not thrown
away.

When considering liability surely those organisations which produce source
containers in which the sources are not enclosed in a sealed cavity and
authorities which approve their use must bear some responsibility. In this
situation the source capsule can be exposed to an almost infinite cocktail
of corrosive vapours which the manufacturer cannot predict. The fact that
the capsule is sealed and meets all the appropriate tests must help to
absolve the manufacturer from further responsibility.  

The possibility of leaking sources becomes a non-issue if we assume that
all sources will leak.
We assume this because we examine and test more than 100 sources per year.
We will not load a source into an industrial gauge container unless the
source is sealed inside a cavity with a stainless steel grub screw.

In this situation the possibility of a leaking source is no longer an
issue.  If the source leaks the contamination is sealed inside the cavity. 
Before the grub screw is removed it is wiped and tested down to a few Bq.
If clean the grub screw is removed and checked down to a few Bq. If clean 
the source is removed and immersion tested.

If the grub screw is contaminated it is replaced and the whole container or
source rod is sealed in a steel tombe for burial.

If those removing the source are not qualified enough to follow these
procedures they are likely to burn or break open a non-leaking source when
removing it and spread contamination anyway.

Contamination, if controlled, is not an issue. Any source which becomes
uncontrolled can easily be damaged causing widespread contamination.

When sources are sealed in this way and the source holder is checked
routinely for external contamination it can only occurr when the sealing
grub screw is removed.

The 5 year periodic testing of the source actually increases the risk of
contamination when the source capsule is removed from the sealed cavity or
thw capsule is damaged during the removal procedure.



Best Regards
M.Malaxos
Radiation Safety Services
69-71 Robinson Avenue Belmont
Western Australia.  6104 
Fax 61 89 475 0165
P 61 89 475 0099  a/h 089 255 1214
email rss@arach.net.au
 

----------
> From: Fred Axmacher <axmacher@ix.netcom.com>
> To: Multiple recipients of list <radsafe@romulus.ehs.uiuc.edu>
> Subject: Re: Sealed sources: extension of recommended working  life
> Date: Saturday, 7 March 1998 10:52
> 
> I see this problem very much as a liability issue.  Is the savings
> generated by non-replacement worth the potential liability of capsule
> failure?
> 
> The capsule manufacturer has already limited his exposure by
> conservatively calculating the durability of the capsule in years on the
> basis of what he knows -
>     1) The ductility of the casing material and sealed joints
> (welded/brazed) that undergo potential  volume changes and radiation
> hardening due to decay processes,
>     2) The ability of the nuclide in its chemical form to be removed by
> leaching.
>     3) Operational testing performed as per ISO 2918 (?) that typify the
> capsule by five testable criterea.
> And by what he doesn't know but can recomend for -
>     1) The operational environment.
> What doesn't seem to be a factor is the half-life nor the activity
> level.
> And what particularly doesn't seem to be a factor is real world
> experience!
> 
> My experience with source manufacturers is that they will gladly
> recertify the capsule based on a microscopic visual exam and a leach
> test, but only for five years...!
> 
> By the way, I find it funny that an Australian should bring up this
> question of recertification, in that your government has declared what
> the operational life of a sealed source shall be.
>