Nuclear Power Plant Cables Research Articles

원전 케이블용 절연재료의 열분석과 등가수명

The activation energy of a material is an important factor that significantly affects the lifetime and can be used to develop a degradation model. In this study, a thermal analysis was carried out to evaluate and collect quantitative data on the degradation of insulation materials like EPR and CSP used for nuclear power plant cables. The activation energy was determined from the relationship between log and 1/T based on the Flynn.Wall.Ozawa method, by a TGA test. The activation energy was also derived from the relationship between ln(t) and 1/T based on isothermal analysis, by an OIT test. The activation energy of EPR derived from thermal analysis was used to calculate the accelerated aging time corresponding to the number of years of use, employing the Arrhenius equation, and determine the elongation corresponding to the accelerated aging time.

Frequency domain reflectometry for remaining useful life estimation of instrumentation and control cables

As the existing fleets of nuclear power plants age, a greater emphasis has been placed on technologies to quantify the remaining useful life of safety-critical components and to ensure that these systems will operate as intended when called upon, especially in emergency situations. Some of the most important, yet often overlooked components, are the cables that provide the signal paths for instrumentation and control systems used to ensure safe and efficient operation of nuclear power plants. Instrumentation and control cable aging, in particular, is primarily concerned with degradation of the polymer material by thermal oxidation while exposed to heat, humidity, radiation, and other environmental stressors. Consequently, as the polymer becomes embrittled, it cracks and becomes susceptible to moisture intrusion that can cause shorts and shunts in the cable circuits. This article describes the development of two prognostic models to estimate the remaining useful life of nuclear power plant cables. The first model uses data compiled in an existing polymer aging database as background for introducing the remaining useful life model development methodology. The second model uses data generated from accelerated cable aging experiments performed by the authors and explores the use of in situ electrical measurements such as frequency domain reflectometry for predicting the remaining useful life of instrumentation and control cables typically found in nuclear power plants.

Diagnosis of Medium Voltage Cables for Nuclear Power Plant

Most accidents of medium-voltage cables installed in nuclear power plants result from the initial defect of internal insulators or the initial failure due to poor construction. However, as the service years of plants increase, the possibility of cable accidents is also rapidly increases. This is primarily caused by electric, mechanical, thermal, and radiation stresses. Recently, much attention is paid to the study of cable diagnoses. To date, partial discharge and Tanδ measurements are known as reliable methods to diagnose the aging of medium-voltage cables. High frequency partial discharge measurement techniques have been widely used to diagnose cables in transmission and distribution systems. However, the on-line high frequency partial discharge technique has not been used in the nuclear power plants because of the plant shutdown risk, degraded measurement sensitivity, and application problems. In this paper, the partial discharge measurement with a portable device was tried to evaluate the integrity of the 4.16kV and 13.8kV cable lines. The test results show that the high detection sensitivity can be achieved by the high frequency partial discharge technique. The present technique is highly attractive to diagnose medium voltage cables in nuclear power plants.

Methods for testing nuclear power plant cables

Nearly all of the operating U.S. commercial nuclear power plants (NPPs) are seeking, or have already received, license renewal from the Nuclear Regulatory Commission (NRC). As such, the nuclear industry is directing increased attention toward ensuring the safe and reliable operation of the various working components in NPPs, including the thousands of miles of power and signal cables that tie together complex plant systems. Because wholesale cable replacement is not an affordable option for aging NPPs, in-situ techniques for assessing the condition of installed cables are of critical importance. The goal of the research presented in this report is to refine existing techniques and to develop novel cable monitoring and testing methods for new and aging NPPs in the U.S. and worldwide.

Diagnosis of cables in nuclear power plants using joint time-frequency domain reflectometry

In this paper, a new methodology which is referred as joint time-frequency domain reflectometry (JTFDR) is proposed to detect and to locate faults of control and instrumental cables in nuclear power plants. Since this method considers information both in time and frequency domain at the same time, we use a linearly increasing Gaussian envelope chirp reference signal as an incident signal which has a adjustable time duration and frequency bandwidth together. After calculating the time-frequency cross-correlation function with two distribution signals, we can determine the fault distance using time delay between the peak of the incident and reflected signals in the cross-correlation. The usefulness of the proposed method in nuclear power plants is verified by the experiments. Experimental results show that JTFDR can be the reliable method for diagnosis of control and instrumentation cables in the nuclear power plants.

Diagnosis of MV Power Cables for Nuclear Power Plants

The diagnosis of MV (Medium Voltage) cable used in NPPs (Nuclear Power Plants) has become one of the most urgent issues. In accordance with PSR (Periodic Safety Review) results, continuous condition monitoring of cables is also continuously required. In this paper, HFPD (High Frequency Partial Discharge) measurement and an infrared imaging thermography test were performed to check the status of 13.8 and 4.16 kV MV cables installed in the domestic power plant. The diagnosis was found to be good for the target cable. The on-line diagnostic technology to assess the condition of MV cables during the operation of a power plant will contribute to enhance the safety of NPPs. In the future, these latest technologies will be applied to perform condition monitoring of HV (High Voltage) cables in NPPs.

Remaining life prediction of I&C cables for reliability assessment of NPP systems

Abstract Instrumentation and control (I&C) cables are one of the most important components in nuclear power plants (NPPs) because they provide power to safety-related equipment and also to transmit signals to and from various controllers to perform safety operations. I&C cables in NPP are subjected to a variety of aging and degradation stressors that can produce immediate degradation or aging-related mechanisms causing the degradation of cable components over time. Although, there exits several life estimation techniques, currently there is no any standard methodology or an approach toward estimating the time dependent reliability of I&C cables that can be directly used in probabilistic safety assessment (PSA) applications. Hence, the objective of this study is to develop an approach to estimate and confirm the continued acceptable margin in cable insulation life over time subjected to aging. This paper presents a framework based on the structural reliability theory to quantify the life time of I&C cable subjecting to thermal aging. Since cross-linked polyethylene (XLPE) cables are extensively being used in Indian NPPs, the remaining life time evaluations have been carried out for a typical XLPE cable. However, the methodology can be extended to other cables such as polyvinyl chloride (PVC), ethylene propylene rubber (EPR), etc.

Life-assessment technique for nuclear power plant cables

The condition of polymer-based cable material can be best characterized by measuring elongation at break of its insulating materials. However, it is not often possible to take sufficiently large samples for measurement with the tensile testing machine. The problem has been conveniently solved by utilizing differential scanning calorimetry technique. From the tested cable, several microsamples are taken and the oxidation induction time (OIT) is determined. For each cable which is subject to the assessment of the lifetime, the correlation of OIT with elongation at break and the correlation of elongation at break with the cable service time has to be performed. A reliable assessment of the cable lifetime depends on accuracy of these correlations. Consequently, synergistic effects well known at this time - dose rate effects and effects resulting from the different sequence of applying radiation and elevated temperature must be taken into account.

Reduction of seismic loads in cable tray hangers

A study has been conducted to partially assess the feasibility of using flexible rather than rigid support systems for carrying electrical and control cables in nuclear power plants. Using analytical and experimental studies, it was found that a flexible hanger design with appropriate stiffness and damping characteristics could be used to isolate trays from hanger vibration and significantly reduce hanger loads during seismic events if the connectors could be adequately tuned to account for system variables. Finite element techniques were used to select a flexible connector for a specified base hanger system. Tests were conducted on one-third-scale models to establish values for some of the parameters and to partially verify the analytical methods. For the hanger systems considered, introduction of the flexible connector allowed support-hanger loads and hanger displacements to be reduced greatly while satisfying tray displacement constraints. It appears that a flexible-connector system can provide better dynamic response than the conventional type system using rigid connectors. This conclusion is valid for all variations in system parameters studied. Although the flexible-connector concept looks very promising based on this study, substantial work, including full-scale testing, must be completed before this concept can be validated for actual plant designs.