Development of Non-Destructive Condition Monitoring Techniques for Low-Voltage Cables

Abstract

Nuclear power plants contain more than one thousand kilometres of electrical cables. A large majority of these cables are dedicated to Instrumentation and Control (I&C) functions. I&C cables are key components of a nuclear power station because they link measuring and control equipment to the instrumentation used to monitor and control the plant. Research data and operational experience show that nuclear power plant cable materials gradually become brittle and may crack, thereby resulting in loss of dielectric strength and increased leakage current. The main stressors causing age-related degradation are elevated temperatures and ionising radiation. Most cables installed at the CANDU® stations were initially qualified for a 30-40 year service life. As station personnel now face the prospect of plant life extension, the focus is on assessing the remaining life of the cables (including Design Basis Event (DBE) survivability) beyond the 30-40 year period. The number of techniques available for on-site monitoring is limited because of the strong requirement from station personnel to use non-destructive and non-intrusive techniques. As a result, a CANDU Owners Group (COG) R&D project was initiated to develop new non-destructive and non-invasive techniques for on-site condition monitoring and help the station users assess the remaining life of installed cables. This paper summarizes the results obtained to date using three non-destructive techniques: the measurement of cable indentation and post-indentation parameters, the measurement of electrical dissipation factors at low frequencies, and the measurement of sound velocity using laser-ultrasound.