Degradation of flame-retardant ethylene-propylene-diene rubber by radiation and steam

Safety-related cables in nuclear power plants must be functional even during the occurrence of a severe accident. In this regard, flame-retardant ethylene-propylene-diene rubber (FR-EPR) widely used for electrical insulation in safety-related cables was aged under several simulated severe accident conditions. Namely, ⁶⁰Co gamma rays were irradiated at two different dose rates to sheets of FR-EPR at room temperature or 100°C. After that, saturated or superheated steam was exposed to several sheets at a constant temperature of 155 or 220°C, or at six stepwise elevating temperatures from 120 to 220°C. Various mechanical properties and complex permittivity were measured for these sheets. As a result, the effects of heat, gamma-ray irradiation, and steam exposure on the degradation of FR-EPR were clarified.