Sealed sources: extension of recommended working life

["Dahlskog, Leif" <Leif.Dahlskog@health.wa.gov.au>]

Dear radsafers

I am seeking comments on extending the recommended working life (RWL) for
sealed sources approaching or having completed their RWL.  

A source manufacturer lists a recommended working life (RWL) of 10 years for
their Pu-238 sealed disc sources with a beryllium window.  The period of the
RWL is based on:
-toxicity of nuclide,
-total initial activity,
-source construction,
-half life,
-typical application environments,
-operational experience
-test performance data, etc

Consider that it is often difficult to obtain a working history for the
sources, or knowledge of adverse environments or extremes of temperatures
that may have been experienced.

If sources are to be used past their RWL, what criteria should be considered
?.
If, to extend the RWL, a source capsule should be tested, would a
satisfactory test involving a visual inspection, a wipe test and immersion
test be considered sufficient to extend the working life ?
What frequency should the tests be performed ?

How have other regulators dealt with this issue ? 

I am hoping to receive a response specifically from:
a) other regulators.
b) those involved in source manufacture.
c) those with experience in testing source capsules.
d) anyone who may have experience on this matter.

Please respond to me personally unless you consider this a worthy subject of
discussion on radsafe.

Regards

Leif Dahlskog
Scientific Officer
Radiation Health Section
Health Department of Western Australia

email:   leif.dahlskog@health.wa.gov.au