Changes in electrical insulation resistance of EPR insulator irradiated in water

The electrical insulating properties of cable-insulators in an environment where radiation and water vapor coexist. Ethylene propylene rubber (EPR) is irradiated in oxygen-free or oxygen-containing water, and changes in volume resistivity and swell are observed. Irradiation is also performed in water vapor, as well as in water, at high temperatures. It is revealed that changes in volume resistivity in such environments are basically different from those of material which is exposed alternately to radiation and vapor. In particular, volume resistivity is decreased in a high temperature range even when oxygen does not exist. No difference is observed between irradiation in vapor and water. In the case where oxygen exist, on the other hand, volume resistivity is found to decrease greatly in a low temperature range from room temperature to 70 deg C. It is demonstrated that such changes in volume resistivity are closely related with those in swell. (Nogami, K.)