Performance assessment of I&C cable insulation materials by DSC and SEM for NPP ageing management

Instrumentation and control (I&C) cables used in nuclear power plants (NPPs) are exposed to various deteriorative environmental effects during their operational lifetime. The factors consisting of long-term irradiation (at rather low dose rates, in the presence of oxygen), and enhanced temperature eventually result in insulation degradation. Monitoring of the actual state of the cable insulation and the prediction of their residual service life consist of the measurement of the properties that are directly proportional to the functionality of the cables [usually the elongation at break (EAB) is used as the critical parameter]. Although, there exist several condition monitoring and life estimation techniques, currently there is no any standard methodology or an approach towards incorporating cable ageing effects into probabilistic safety assessment of NPPs. In view of this, accelerated thermal and radiation ageing of I&C cable insulation materials have been carried out and the degradation due to thermal and radiation ageing has been assessed using oxidation induction time and oxidation induction temperature measurements by differential scanning calorimetry (DSC). As EAB is considered to be a benchmark characterization technique for polymeric materials, tensile tests have also been carried out on these cable materials for correlating the DSC findings with EAB. The scanning electron microscopy (SEM) performed on fresh and aged samples support relatively good correlation between thermal and mechanical properties.