RE: Question re Radiolytic Breakdown of Plastics

["NIXON, Grant (Kanata)" <GNIXON@MDS.Nordion.com>]

This is not an easy question. There has been a lot of work done in this

area.



There are a number of good references on degradation effects of polymers.

One such book is:



"Irradiation Effects on Polymers", D.W. Clegg and A.A. Collyer (eds.),

Elsevier Applied Science, New York (1991).



A more comprehensive volume is:



The Effects of Sterilization Methods On Plastics And Elastomers", Plastics

design Library (PDL), PDL Handbook Series (1994) ISBN 1-8842

07-10-3.



Those plastics with aromatic rings (pi-clouds) tend to be more

radiation-resistant while those with double-bonds are most susceptible to

cross-linking. One of the most susceptible plastics to radiation degradation

is Teflon (decomposes into powder at only about 2000-3000 rads). 



Generally though, you can usually irradiate plastics into the kilogray range

(10^5 rads) before mechanical properties show appreciable change (say, 10%

or more). 



However, there are also delayed aging effects due to the diffusion of

free-radicals that continue to cause degradation long after the radiation

source has been removed. Mechanical strength may actually increase before

the polymer becomes brittle.



Generally, you need to look-up the measured properties vis-a-vis radiation

dose. This varies not only the plastic type but also from manufacturer to

manufacturer because of the different chemical recipes used (plasticizers,

fillers, extenders, etc.). That is why a specilialized handbook (or the

manufacturer) should be consulted.



Best regards,



Grant





-----Original Message-----

From: JOHN.RICH@sargentlundy.com [mailto:JOHN.RICH@sargentlundy.com]

Sent: Wednesday, August 20, 2003 2:43 PM

To: Estabrooks, Bates (IHK)

Cc: owner-radsafe@list.vanderbilt.edu; 'radsafe@list.vanderbilt.edu'

Subject: Re: Question re Radiolytic Breakdown of Plastics







There were a few reports on organic degradation due to radiation that came

out shortly after TMI.  One that seemed particularly helpfull was from

EPRI; EPRI NP-2129, "Radiation Effects on Organic Materials in Nuclear

Plants."



The basic mechanisms were cross-linking and damage from free radicals.  If

I remember correctly, the first property to go was flexibility.  But most

of the organics were good to about 1E5 rads before they exhibited

appreciable degradation.



hope this helps.



All opinions are mine.  My management doesn't even know I have an opnion.

john rich





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