Ionising radiation changes polymers by scission (breaking chains) and crosslinking. Which effect dominates depends on structure.
Typical tolerance (order of magnitude, dose in kGy)
| Material | Approximate tolerable dose |
|---|---|
| PTFE | Low, about 10 to 50 kGy before strength loss |
| FKM | About 100 to 500 kGy |
| Silicone | About 100 to 300 kGy, softening and hardening varies |
| EPDM (peroxide) | About 1,000 kGy or more with suitable compound |
| Nitrile | About 500 kGy |
| PEEK | About 10,000 kGy |
| Polyimide | About 10,000 kGy and above |
| Polyurethane | Moderate |
These are indicative. Compound formulation, dose rate, temperature and oxygen change results.
Nuclear power seals
- EPDM compounds are standard for reactor primary and containment seals, with strict qualification for radiation, steam and loss-of-coolant accident conditions.
- Standards include IEEE 323 and IEEE 383 (equipment qualification) and ASME Section III (nuclear components); national regulators add rules.
- Compounds are produced with controlled raw materials and full batch traceability under a nuclear quality programme such as ISO 9001 with ASME NQA-1 where required.
Sterilisation
Gamma sterilisation of medical and pharma assemblies typically uses 25 to 50 kGy. PTFE, silicone and some elastomers change under this dose; qualify the real seal after irradiation. E-beam and ethylene oxide are alternatives.
Design hints
- Choose a material with a dose margin of at least a factor of two.
- Peroxide-cured, non-sulphur, low-plasticiser compounds hold up better.
- Specify dose rate, temperature and air or inert atmosphere during test.
- Replace on a schedule.
Documentation
Nuclear and medical buyers audit suppliers. Be ready with material certificates, process control plans, and a change-notification agreement.
About this article. It is original writing prepared from public sources, standards and general industry practice. It is not a copy of any book or standard and it is not engineering advice. Confirm values against the current edition of the standard and test in your own application. Only analyse material you own or are entitled to analyse.
