Dielectric and Mechanical Behavior of Thermally Aged EPR/CPE Cable Materials

Power and instrumentation cables play a crucial role in the safe operation of Nuclear Power Plants (NPPs). Thermal and other stressors present in the reactor environment cause the cable materials to degrade. In this work, dielectric and mechanical properties of cable insulation and jacket materials are studied as they are thermally aged, supporting development of non-destructive evaluation sensors for monitoring cable aging. Materials selected for this study are found in certain types of single-core unshielded power cables. These utilize ethylene propylene rubber (EPR)-based insulation material and chlorinated polyethylene (CPE)-based jacket material. Flat mats of these materials were obtained from the cable manufacturer and thermally aged at 140 °C in an air-circulating oven. Elongation-at-break was measured on tensile specimens stamped from the aged mats, and dielectric properties were measured from 100 Hz to 100 kHz using a parallel plate capacitor and precision LCR meter. In the case of aged EPR-based materials, rapid decrease in elongation at break indicating end of useful life was accompanied by a significant increase in dissipation factor, D, measured at 100 kHz. Capacitive measurement of D shows promise, therefore, as a non-destructive indicator of corresponding mechanical property changes in thermally-aged EPR-based insulation materials.