Radiation-Induced Conductivity in Polymeric Insulating Materials Degraded under Specified Conditions

Various polymeric insulating materials for cables were degraded by simulated irradiation and environmental conditions for normal operation and under accident at a nuclear power reactor. Thermally stimulated currents were observed only in the crystalline samples, and the higher thecrystallinity, the larger the amounts of detrapped carriers. The change of fine structure of the degraded sample was investigated by the change of X-ray crystallinity, melting behavior, and glass transition temperature. The radiation-induced conductivity was studied during irradiationand a decay curve was measured after the irradiation. Analysis of the conductivity decay curve enabled us to detect at most four kinds of carriers with different time constants. Long-lived carriers were hardly observed in the non-crystalline samples, while many were seen in the crystalline samples. With the decrease of crystallinity by degradation, only short-lived carriers were observed, indicating the existence of trapping sites for the long-lived carriers in or aroundthe polymer crystallites. Treatment of samples with high temperature steam and chemicals showedno special effect on the samples except for polyimide which dissolved in alkaline solution.