Remaining antioxidant and thermal-radiation degradation in ethylene-propylene-diene rubber

We have evaluated the thermal and radiation degradation of flame-retardant ethylene-propylene rubber (EPR) insulators used for safety cables in nuclear power plants. Accelerated degradation of EPR sheets was conducted under conditions of (1) simultaneous thermal-radiation aging (100 °C and 1.0 kGy/h), (2) radiation aging (room temperature and 1.0 kGy/h), and (3) thermal aging (100 °C or 200 °C, and 0 kGy/h). The degraded samples were analyzed by infrared spectroscopy, elongation at break, and oxidation induction time. The infrared measurements were not well suited for estimating the oxidation of EPR samples. The mechanical properties and induction time measurements show that the samples exposed to conditions (1) and (2) showed similar degradation behavior and the cross-linking reaction might be the main cause of the degradation.