Re: Self Shielded Irradiators

[D J Hornsey <bssdjh@bath.ac.uk>]

Dear Kent,
        Our University has such a self-shielded irradiator and like you I
have had to dream up worst case scenarios and write contingency plans for
it. The unit I am thinking of in this case has several hundred curies of
Co-60 and small samples are fed into close proximity to the source on a
piston operated system. When the irradiator was inspected a few years ago,
the first comment that was made was about security. It shows how naive I
was them, because my reaction was "the things weighs 5 tonnes, no-one is
going to steal it" That was not the security he was talking about. If the
piston delivery system wasn't adequately secured then an explosive device
could be pushed into the source and I was left wondering how a bomb
disposal squad would deal with such an event and also how I would assess
what my contingency plans would be. Although the unit it locked, anyone
with a respectable set of bolt cutters could gain access and cause a
considerable amount of mischieve. Like Kent I would be interested in what
contingency plans radsafers have for such, hopefully, extremely rare 
events.   


                                         David Hornsey
 **************************************
 * David J. Hornsey, Radiation Safety.*
 * South Building,                    *
 * University of Bath                 *             
 * Claverton Down,                    * 
 * Bath BA2 7AY. UK.                  *
 *                                    *
 * tel:01225 826540                   *
 * fax:01225 826779                   *  
 * e-mail: d.j.hornsey@bath.ac.uk     *
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On Tue, 31 Mar 1998, Kent N. Lambert wrote:

> Group,
> 
> Those that are familiar with self shielded irradiators are aware of 
> the inherent safety of the devices under normal use.  I was asked 
> about radiological considerations in a disaster.  
> 
> My initial impression is that because the shielding is made of lead, 
> and lead has a low melting point, that one obvious concern is a loss 
> of shielding in a fire.  Presumably the lead is encased in steel such 
> that this is unlikely to occur.  But at what temperature would the 
> structure fail?  Is this temperature likely to be achieved in a 
> serious building fire?  Is the device more suseptible to structural 
> damage at these elevated temperatures?
> 
> Also are there other disasters which might create a major problem - 
> explosions (don't laugh, I'm sure that we are not the only one that 
> has seen the bomb squad at their facility), earthquakes (structural 
> damage to building causing the device to fall tens of feet onto a 
> hard, solid object), tornadoes, thermal shock (e.g., fire followed by 
> water from fire suppression system),  others?  
> 
> So, what sort of disaster could affect the integrity of the shielding 
> or the sources?  Are there written standards that these devices must 
> meet?  Are actual tests performed on prototypes?  I would appreciate 
> references if possible.
> 
> Kent N. Lambert, M.S., CHP
> lambert@auhs.edu
> Allegheny University of the Health Sciences
> Hahnemann Division
> Radiation Physics and Safety, MS 106
> Broad and Vine Streets
> Philadelphia, PA  19102-1192
> 
> 215-762-8768 (voice)
> 215-762-7683 (fax)