Spread Spectrum Time Domain Reflectometry for In-situ Monitoring of Cable Insulation

In-situ cable monitoring methods are needed for management of aging cables in nuclear power plants (NPP). The NRC Regulatory Guide 1.218 maintenance rule requires NPPs to establish a cable condition monitoring program. Additional requirements are specified for second license renewal (SLR) through the Aging Management Programs (AMPS). Inaccessible cables, those routed underground through ducts, trenches, conduits, etc. must be tested for insulation degradation. The AMPS call for “Monitoring and Trending” at 6-year intervals to provide information on the rate of cable insulation degradation. Methods used today require the system to be de-energized and cables to be disconnected. We will provide a new type of tester for cable integrity that can be used in-situ while the system is energized, thus enabling better monitoring and trending of cable health and integrity. This system will be capable of long-term or instantaneous monitoring of cable insulation and will both detect and locate degradation across the entire cable, or in localized regions. It can be used on either energized or de-energized cables and will not damage the cable. Once installed, the system will test the cable integrity, insulation integrity, and the electrical health of components directly connected to the cable, without requiring the system to be de- energized or cables / devices to be disconnected / reconnected for testing. The system may also be used to verify the integrity of the cables and electrical interconnect system at the time of installation or after maintenance actions (planned or unplanned). The enabling technology for the EIT is spread spectrum time domain reflectometry (SSTDR), which has been used for fault location on live electrical systems. Initial tests shown that SSTDR can determine the electrical properties and health of cables and their insulation. In Phase I, LiveWire will (1) collect SSTDR signature data on an energized nuclear cabling test bed at PNNL, (2) use this data to evaluate the feasibility of SSTDR insulation integrity evaluation (tan-delta, dielectric constant, etc.), (3) evaluate the maintenance requirements/processes needed to make an embedded product feasible. We will evaluate methods to convert the SSTDR signatures into cable integrity measures (tan-delta, etc.) related to AMPS and NRC maintenance regulations.