EVOLUTION OF ETHYLENE-PROPYLENE COPOLYMERS PROPERTIES DURING AGING

Ageing of Ethylene Propylene copolymer used as joints for electrical m ateriels in nuclear power plants has been studied in EDF (Electricite de France). The objective was to determine the elastomer service lifet ime in normal and accidental conditions. This material is thermally st able up to 130 degrees C for long term service and it can be used unti l a radiation dose of at least 60 kGy. If the probability to have no m ore waterproofness in normal conditions during 30-50 years at 40 degre es C and at 0.01 Gy/h is low, it could be quite different in accidenta l conditions where the temperature could be higher than 150 degrees C. That is why we first studied the thermal ageing of this material at c onstant temperatures from 90 degrees C to 150 degrees C. During ethyle ne propylene copolymer ageing, we examined the evolution of mechanical properties and morphology. Mechanical properties such as elongation a t break and tensile strengh allowed us to appreciate the material serv ice lifetime according to IEC 544-2 (Guide for determining the effects of ionizing radiation on insulating materials). Besides, the evolutio n of morphology including density and oxidation was examined in order to determine whether crosslinking or chain scission was predominant at high temperatures. The lifetime prediction of ethylene propylene in a ccidental thermal conditions was estimated by applying a kinetic model where the constant depends on the Arrhenius law. In a second step, we proceeded to a radiation ageing on non-aged ethylene propylene copoly mer samples according to normal and accidental conditions. The prelimi nary results obtained under gamma radiation are presented.