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A Capacitive Sensor for Nuclear Power Plant Cable Monitoring

A capacitive sensor was designed and tested for the purpose of monitoring nuclear power plant (NPP) cable degradation. The sensor was designed as two copper interdigital electrodes printed on a polymer substrate. Two types of NPP industriallyrelevant cable jacket materials, ethylene propylene rubber (EPR) and cross-linked polyolefin (XLPO), were studied in this research. Accelerated thermal aging was conducted on EPR and XLPO jacket materials by heating them for various durations up to 15 weeks (2520 h), at 408 K (135 °C). Thermal analysis of aged samples reveals degradation of both cable jackets by the decrease of polymer weight and crystalline regions. Scanning electron microscopy and energy dispersive spectrometry identified the dispersion and constituents of inorganic additives in the jacket materials. A large decrease of elongation at break (EAB) of aged samples as a function of increasing aging duration, observed by tensile testing, provided an effective benchmark against which to evaluate the effectiveness of the capacitive sensor. The capacitance of the sensor in contact with the samples was measured and correlated with EAB as a function of aging time. Values of sensor capacitance measured at 1 kHz correlated well (correlation magnitude ~0.85) with EAB of the tested materials.

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