Thermal ageing in polymer cables: effect of interfaces on dielectric properties

EPR (ethylene propylene rubber)/CSPE (chlorosulfonated polyethylene) control and safety system cables are used in nuclear plants in France. As part of a continuing plant life assurance program, diagnostic tests for these cables are being developed. In order to evaluate the ageing of plant cables, low frequency (10^-4-10 ⁴ Hz) dielectric measurements have been investigated to probe chemical as well as physical properties of insulation materials. Several artificially aged cable samples with controlled formulations show a shift in the frequency of maximum dielectric absorption with ageing when tested in the laboratory. This effect is shown to be caused by interfacial phenomena between the cable layers and is dominated by the dielectric properties of CSPE whose conductivity drastically increases with thermal ageing. The release of chlorinated species appears to be responsible for this change in conductivity