Current Integration Method as a Reliable Tool for Diagnosing Flame-retardant EPDM Cables Removed from Nuclear Power Plants

For obtaining knowledge about the changes in electrical insulation behavior of a cable during the normal operation of a nuclear power plant (NPP), two cables insulated with the same flame-retardant ethylene-propylene-diene rubber were removed from two NPPs. A new cable insulated with the same rubber was also subjected to the experiment as it is and after a severe aging treatment. It has become clear that the new cable and the two removed ones have the highest and lowest electrical conductivity, respectively, among these four cables. The suppression of the carrier transport is likely caused by the hardening of the rubber induced by the heating and irradiation with gamma rays. This result, in turn, indicates that no serious concerns are needed about the degradation of insulation as long as similar cables are used in similar environments. The severity of two artificial aging treatments to simulate two types of serious accidents in NPP is also discussed.