Determining Remaining Useful Life of Aging Cables in Nuclear Power Plants ? Interim Study FY13

Abstract

Executive SummaryThe motivation for this study stems from the need to address the aging management of incontainment cables at nuclear power plants (NPPs). The most important criterion for cable performance is its ability to withstand a design-basis accident. With nearly 1000 km of power, control, instrumentation, and other cables typically found in a NPP, it would be a significant undertaking to inspect all of the cables. Degradation of the cable jacket, electrical insulation, and other cable components is a key issue that is likely to affect the ability of the currently installed cables to operate safely and reliably for another 20 to 40 years beyond the initial operating life. The development of one or more nondestructive evaluation (NDE) techniques and supporting models that could assist in determining the remaining life expectancy of cables or their current degradation state would be of significant interest. The ability to nondestructively determine material and electrical properties of cable jackets and insulation without disturbing the cables or connections has been deemed essential.Currently, the only technique accepted by industry to measure cable elasticity (the gold standard for determining cable insulation degradation) is the indentation measurement. All other NDE techniques are used to find flaws in the cable and do not provide information to determine the current health or life expectancy.There is no single NDE technique that can satisfy all of the requirements needed for making a lifeexpectancy determination, but a wide range of methods have been evaluated for use in NPPs as part of a continuous evaluation program. The commonly used methods are indentation and visual inspection, but these are only suitable for easily accessible cables. Several NDE methodologies using electrical techniques are in use today for flaw detection but there are none that can predict the life of a cable.There are, however, several physical and chemical property changes in cable insulation as a result of thermal and radiation damage. In principle, these properties may be targets for advanced NDE methods to provide early warning of aging and degradation. Examples of such key indicators include changes in chemical structure, mechanical modulus, and dielectric permittivity. While some of these indicators are the basis of currently used technologies, there is a need to increase the volume of cable that may be inspected with a single measurement, and if possible, to develop techniques for in-situ inspection (i.e., while the cable is in operation). This is the focus of the present report.Several approaches to nondestructively measuring key indicators of cable aging and degradation may be available, and could include chemical, mechanical, and electrical measurements. Electrical and acoustic measurements are potential alternative NDE approaches that may be capable of providing in-situ assessments of cable condition and remaining useful life.Measurement studies were conducted with samples of aged ethylene propylene rubber (EPR) cabl...

Life assessment of marine ethylene propylene rubber power cables based on hardness retention rate

“…According to Equation 4 and the activation energy, the lifetime of cable insulation under different temperatures as well as end levels as shown in Table 4. It can be seen that the errors between EAB% and the hardness retention rate at different temperatures and end levels were very small.…”

“…Commonly used analytical techniques for mechanical property changes include elongation at break (EAB), indenter modulus (IM), dynamic mechanical analysis (DMA) and ultrasonic measurements (UM) [4]. Chemical property changes include differential scanning calorimeter (DSC), thermo-gravimetric analysis (TGA) and Fourier transform infrared spectrometer (FTIR).…”

Principal Component Analysis (PCA) as a Statistical Tool for Identifying Key Indicators of Nuclear Power Plant Cable Insulation Degradation

“…Therefore, when considering the aged cables, we need to take the whole spectrum of aging cables in to consideration. [3,4]…”

Degradation Assessment of Polyethylene-Based Material Through Electrical and Chemical-Physical Analyses

“…On the contrary, temperature and mechanical stresses could be predominant for LV cables and, depending on the application, humidity and radiation could also be significant. This latter, particularly gamma radiation, may remarkably affect the cable insulation used in nuclear power plants (NPPs) and aircraft/aerospace applications [1][2][3][4][5]. In general, however, all degradation phenomena occurring in electrical insulation As mentioned in the introduction, polymers for electrical application are filled with different kinds and concentrations of additives.…”