Thermal degradation and multi-performance aging assessment of low voltage nuclear cable

• Investigating the thermal aging impact on XLPE-based low-voltage nuclear cables using destructive and non-destructive condition monitoring • Introducing Degradation Index ( DI ) and Degradation Rate ( DR ) as novel degradation quantification metrics • Analyzing the role of anti-oxidant during thermo-oxidative degradation with the help of Anti-oxidant Depletion Factor (ADF) • Demonstrating DI as a novel aging marker along with tanδ at 100 kHz • Establishing dielectric spectroscopy as a viable condition monitoring technique Low-voltage (LV) I&C cables have high significance in Nuclear Power Plants (NPPs) and are considered irreplaceable, whereas they endure radiation and thermal stresses during service. The thermal stress in the presence of oxygen may cause the cable to fail after its insulation undergoes physicochemical changes. Hence, for gaining a better understanding of the insulation degradation process, condition monitoring of these cables is essential for upholding the reliability of the NPPs. In this study, the behavior of the XLPE insulation of LV NPPs’ cable is investigated when subjected to thermal stress for 5 different aging cycles. The performance of the cable insulation was studied through non-destructive dielectric spectroscopy and hardness techniques, along with destructive techniques such as oxidation induction time (OIT) and elongation at break (EaB). Moreover, an evaluation technique that made use of three parameters, antioxidant depletion factor ( ADF ), degradation index ( DI ), and degradation rate ( DR ), provided a thorough representation of the state of degradation of cable insulation. It was observed that the presence of antioxidants deeply influenced XLPE degradation, slowing down the degradation process in the initial phases of aging. The cable gradually reached its end-of-life criterion, the 50 % value of EaB, which was also observed by the DI and DR trends. The dielectric dissipation factor (tanδ) and DI correlated highly with the chemical and mechanical parameters under study, establishing them as reliable aging indicators of NPP cables, and demonstrating the effectiveness of dielectric spectroscopy as a viable non-destructive condition monitoring technique.