About electrical and mechanical behaviour of low-voltage I&C cables used in nuclear power plants

Abstract

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.