Nuclear power comes from splitting atoms to create heat that can be used to generate electricity. Most nuclear reactors operating today heat water to produce steam that turns a turbine, generating massive amounts of carbon-free electricity. Inside each nuclear reactor are hundreds of miles of electrical cables used for powering equipment, controlling components, and monitoring instruments.
The average nuclear power plant in the United States has now been operating for more than 42 years. Safety-related electrical cables were qualified to perform through 40 years of the initial plant operating license and to withstand exposure to extreme thermal, radiation, and chemical environments that may be present. Many plants have received their first operating license extension, and the efforts to obtain second 20-year license extensions are underway. However, use of existing electrical cables for additional decades requires verification of their continued safe and effective status.
Researchers at Pacific Northwest National Laboratory (PNNL) are supporting the continued safe operation of nuclear plants beyond their initial license periods using the Accelerated Real Time Environmental Nodal Assessment (ARENA) test bed to determine how electrical cables in power plants degrade and how their health can be monitored. The ARENA test bed complements PNNL’s extensive nuclear-focused ultrasound, radiography, and electromagnetic nondestructive examination (NDE) capabilities. ARENA and related PNNL cable aging management capabilities allow scientists to reexamine the assumptions made during initial electrical cable qualification, understand the limits of standard cable testing methods, and develop or validate new NDE testing techniques.
The ARENA test bed is composed of an electrically isolated 480-volt motor controller with a remote starter for personnel safety, a half-horsepower motor, elevated cable trays simulating real power plants, and an in-line oven and water bath allowing extreme environments to artificially age the cable systems. Electrical cables are exposed to elevated temperatures, wet conditions, and cobalt-60 sealed sources for gamma radiation (at PNNL’s nearby Radiological Exposures & Metrology Laboratory). Cable Integrity test instruments can connect near the motor, power supply, or anywhere in between. Parameters including voltages, frequencies, signal treatments, and connection configurations can be easily explored using the physical test and accompanying digital simulation environment.
Having effective ways to test electrical cable conditions and identify degradation keeps nuclear power plants running safely and efficiently. Replacing all cables simply due to their age would be cost prohibitive and could lead to early plant closure. Performance-based testing and understanding of aging cables can give plant operators the ability to target cable replacement before failure—or fix conditions to mitigate further damage while assuring continued safe operation.
“The most promising aspect of ARENA is filling the gap between academic development of new cable assessment technologies and pilot-scaled, in-plant trials. Significant volumes of data need to be obtained and understood to transition new NDE inspection technologies to the field. This test bed can fill that gap, modeling a nuclear power plant environment and leading to a greater chance of promising technology deployment,” said Leo Fifield, PNNL materials scientist and ARENA project manager.
Since ARENA started in 2021, researchers have used frequency domain reflectometry (FDR) and spread-spectrum time domain reflectometry (SSTDR) NDE techniques to detect and locate ground faults, line-to-line faults, moisture exposure, mechanical damage, and thermal aging. Although FDR measurements require cables to be disconnected from a live source to locate damage and assess conditions, SSTDR assessments may be implemented on live cables of up to 1,000 volts and do not require the cable to be disconnected for the measurement. SSTDR has been deployed in the aircraft and rail industries but has not been extensively applied to nuclear power plants. ARENA scientists plan to continue assessments of various cable damage conditions, NDE inspection techniques to improve damage detection and location, and extend the cable management program for damage mitigation and repair to minimize power plant disruption, Fifield said.
Fifield’s materials scientist colleague, Mychal Spencer, along with senior advisor in NDE technologies Bill Glass, are also developing a digital twin, or a digital representation of testing behavior. The simulation model enables better understanding of observed behavior plus prediction of the effect of different test configurations, NDE instrument settings, damage mechanisms, and damage locations. The researchers are targeting online NDE techniques for continuous monitoring of installed nuclear reactor electrical cables. Online monitoring does not require cable systems to be de-energized or for cables to be disconnected. This has significant potential to reduce operating and maintenance costs, and provides real-time electrical cable aging management feedback.
ARENA test bed and NDE capabilities are advancing the technology demonstration and development of online monitoring for future deployment in the nuclear energy industry.
Read more about ARENA in the Department of Energy, Office of Nuclear Energy’s Light Water Reactor Sustainability Program newsletter. ARENA will also be a topic of discussion at the Electric Power Research Institute (EPRI) Cable User Group meeting on June 6–11, 2023, at PNNL in Richland, WA, and the American Nuclear Society’s 13th Nuclear Plant Instrumentation, Control & Human-Machine Interface Technologies Conference on July 15–20, 2023, in Knoxville, TN.