This paper deals with the effect of a long storage time after thermal and radiation aging on electrical and mechanical properties of insulating materials used in nuclear power plant cables. Strong post-irradiation effects were found on XLPE cable insulation years after irradiation. In particular, a dramatic reduction of mechanical properties was observed, suggesting insulation crosslinking and/or oxidation, as well as an increase of the imaginary permittivity values, particularly in the low frequency range where interfacial phenomena are active. This latter could be associated likely to the increase of interface between amorphous and crystalline regions, thus supporting the evidence that post-irradiation effects may provide mostly polymer crosslinking during storage time at room temperature.

Influence of temperature on low-density polyethylene (LDPE) has been analyzed in this paper. Commercial LDPE films with different thickness were stressed at high temperature (110 °C) and characterized using different test methods such as: impedance spectroscopy, tensile testing and chemical measurements. Thermal treatment has been carried out both in air and under vacuum in order to single out the oxidation contribution on polymer degradation. As a result of these tests we obtained a good correlation between mechanical and electrical properties, which could lead to developing a nondestructive technique (NDT) for polymer diagnostics.

Influence of temperature on low-density polyethylene (LDPE) has been analyzed in this paper. Commercial LDPE films with different thickness were stressed at high temperature (110 °C) and characterized using different test methods such as: impedance spectroscopy, tensile testing and chemical measurements. Thermal treatment has been carried out both in air and under vacuum in order to single out the oxidation contribution on polymer degradation. As a result of these tests we obtained a good correlation between mechanical and electrical properties, which could lead to developing a nondestructive technique (NDT) for polymer diagnostics.

This paper focuses on the electrical and mechanical properties of irradiated and thermallystressed NPP cables used for instrumentation and control (I&C). These cables show some noteworthy changes after few years of uncontrolled environment conditions due to a phenomenon called post-irradiation effect. Strong post-irradiation effects, e.g. reduction of mechanical properties, raise of crosslinking and oxidation grade, were found on XLPE cable insulation years after irradiation. These degradation mechanisms can be correlated with electrical measurements in which imaginary permittivity values raise, in particular at low-frequencies where interfacial phenomena take place. This behavior can be linked to the increase of interfacial area between amorphous and crystalline region of polymer, supporting the evidence that postirradiation effects can lead to polymer crosslinking during a storage period even at room temperature.