Online monitoring of nuclear cables could provide ongoing confidence in reliable condition, trending information to inform operational considerations, and early signals of concern to enable efficient planned maintenance. Recent developments in instrumentation and advanced data analysis have demonstrated feasibility to monitor the condition of energized cables online using frequency domain reflectometry (FDR) and spread spectrum time domain reflectometry (SSTDR). FDR and SSTDR tests have been applied directly to cable conductors for more than a decade to detect and locate cable damage. These measurements have mostly been performed off-line on de-energized circuits for reasons including that power line voltages can be damaging to diagnostic instruments and that reflectometry response spectra are complex and can require skilled experts for interpretation. These state-of-the-are limitations have resulted in cumbersome and costly sequence of testing events including:
• Scheduling the cable system to be off-line for testing (usually only convenient during one-month refueling outages occurring every one-and-one-half to two years)
• De-energizing and uncoupling the cable from motors and terminals
• Bringing trained experts with specialized test equipment onsite to perform and analyze tests
• Re-connecting and returning to cable service if it passes
• Repairing or replacing and re-testing cable before returning to service if it does not pass.
We will discuss three enabling technology advances funded by the Light Water Reactor Sustainability program that could enable more cost-effective online cable monitoring program to increase confidence in continued use of aging cables and reduce risks associated with unplanned cable or system failure. These include an inductive coupler that allows reflectometry of cables energized above 10kV, a Field Programable Array (FPGA) multiplexing instrument capable of performing FDR and SSTDR in a connected cable, and a machine learning screening code to detect reflectometry responses well in advance of cable failure. These examples of technology to support online monitoring are timely as the industry evolves toward the reliance on verified cable condition for continued confident use of cables with plant life extensions and for implementation in advanced reactors where manual inspections will be more difficult due to long refueling cycles and harsh environments.