Ageing State Analysis of Insulation of Safety-related Low Voltage Cables for Nuclear Power Plants

Abstract

Safety-related low voltage cables of nuclear power plants are required to perform their safety functions under anticipated environmental conditions over their service life. Elongation-at-break (EAB) has been used as an indicator for evaluating the degradation level of the polymeric insulation of the cables. This paper describes results of measurement of gel fraction, crystallinity from differential scanning calorimetry and infrared absorbance from attenuated total reflectance Fourier transform infrared spectroscopy for commonly used cable insulation types, cross-linked polyethylene, flame-retardant cross-linked polyethylene and flame-retardant ethylene propylene diene rubber, to investigate the correlation between polymeric molecular structure and EAB. The measurements were conducted following accelerated thermal ageing or concurrent thermal and radiation ageing for each insulation type. As a result, infrared absorbance of carboxylic acid for the concurrently aged insulation showed a clear correlation with EAB while gel content and crystallinity were not clearly related.