Fundamental study on a diagnostic technology for degradations of cable insulation materials due to radiation exposure and aging

Age-related degradations of various cables used in nuclear power plants have been of constant concern. In general, many types of polymer material are selected for cable insulators because of their high insulating performance. However, they are degraded in not only their mechanical performance but also their electric performance by radiation exposure. Since current inspection methods, such as measuring the insulation resistance, require substantially high costs and workloads, simpli fi ed nondestructive methods will be useful. We have developed a digital hammering inspection system with an AE ( acoustic emission ) sensor. This system detects the degradations of cable insulators due to radiation exposure and aging by assessing the frequency distributions obtained by FFT ( fast Fourier transform ) analysis of measured signals. In this study, we evaluated the relationship between the natural frequency obtained by the digital hammering system and the breaking elongation measured by the tensile testing of the insulating materials after electron beam irradiations of up to a maximum of 2,000kGy for cables including those used in a nuclear power plant for about 30 years.