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The effect of simultaneous thermal and gamma irradiation ageing on the mechanical and physicochemical properties of industrial EPDM was investigated. Accelerated ageing, covering a wide range of dose rates, doses and temperatures, was preformed in stagnant air on EPDM polymer samples extracted from the cables in use in the Belgian nuclear power plants. The mechanical properties, ultimate tensile stress and elongation at break, are found to exhibit the strong dependence on the dose, ageing temperature and dose rate. The thermal decomposition of aged polymer is observed to be the dose dependent when thermogravimetry test is performed under air atmosphere. No dose dependence is observed when thermal decomposition is performed under nitrogen atmosphere. The thermal decomposition rates are found to fully mimic the reduction of elongation at break for all dose rates and ageing temperatures. This effect is argued to be the result of thermal and radiation mediated oxidation degradation process.

The mechanical properties of EPDM polymers, degraded as a result of extensive thermal and radiochemical aging treatment, are studied. The focus is given to dose rate effects in polymer insulation materials extracted from industrial cables in use in Belgian nuclear power plants. All studied mechanical characteristics such as the ultimate tensile stress, the Young's modulus, and the total elongation (or elongation at break) are found to be strongly affected by the irradiation dose. The ultimate tensile stress and Young's modulus are clearly exhibiting the dose rate effect, which originated from oxidation mediated interplay of polymer cross-linking and chain scission processes. The change of crossover between these two processes is found to be gradual, without critical dose rate or temperature values. On the contrary, the total elongation is observed not to be sensitive neither to irradiation temperature nor to the dose rate. Both cross-linking and chain scission seem to affect the total elongation in a similar way by reducing the average polymers chain length. This idea is confirmed by the model which shows that all total elongation data as a function of irradiation time can be reproduced by varying a single parameter, the pre-exponential factor of the irradiation rate constant.

The mechanical properties of industrial and neat Ethylene Propylene Diene Monomer (EPDM) polymers, aged under γ-irradiation at different temperatures, are studied. The focus is given to the dose rate effects in polymer insulation materials, so the ageing is performed in the wide range of dose rates, doses and temperatures. Industrial EPDM samples are extracted from the cables in use in Belgian Nuclear Power Plants (NPP), and the neat EPDM samples are produced in the laboratory. The mechanical tests of non-aged and aged polymers are performed, and the methodology of estimating the polymer life time is discussed. The ultimate tensile stress and elongation at break are found to be strongly affected by both irradiation condition and temperature. The ultimate tensile stress clearly exhibits the dose rate effect observed through the shift of the crossover between cross-linking to chain scission process as a function of the dose. This crossover shifts to high dose for large dose rates, while the opposite is observed by increasing the temperature. Dose rate effect is less evident in the elongation at break data, probably because both cross-linking and chain scission affect the elongation at break in the same way, by decreasing it. In comparison to industrial EPDM aged under the same conditions, the cross-linking to chain scission crossover appears at lower dose in neat polymer and the elongation at break decreases faster by increasing the dose. In addition, the elongation at break experimental results can be modeled by changing single parameter, namely pre-exponential factor of the irradiation rate constant. This confirms that both aging processes, cross-linking and chain scission affect the elongation at break in a similar way, by deteriorating network structure responsible for polymer elastic properties. Irradiation rate constant is found to follow the square root dependence for industrial EPDM, while the linear dependence is observed for the neat EPDM. This indicates the existence of different degradation processes in these two polymers.

The quality of the external semi-conductive (SC) layer of separable deadbreak connectors designed for MV was assessed with a view to use them in outdoor applications. EPDM and SIR based connectors were exposed during 1000 hours to an artificial accelerated weathering. The external SC layers were characterized and evaluated by means of chemical, material, mechanical and electrical analyses before and after weathering. There is no clear advantage of using SIR rather than EPDM as matrix. However, according to this study, connector 2 (EPDM) showed the best behavior, followed by connector 5 (SIR) and connector 1 (EPDM). Connector 3 (SIR) and 4 (EPDM) are not advised for outdoor application. (4 pages)