液压下压力管线活动缺陷声发射信号研究

在液压试验装置上,对含预制裂纹的压力管开展了缺陷扩展声发射信号试验研究.全程不间断监测压力管道疲劳裂纹扩展的声发射信号,并对采集到的信号进行分析处理.结果表明:管道缺陷声发射信号的幅度和能量随加载时间逐步增大,可以用于鉴别管道是否存在活动缺陷;在缺陷贯穿前,声发射信号的幅度、能量和计数急剧增加,可以预报管道缺陷的贯穿泄漏.     

A study of the characteristics of the acoustic emission signals for condition monitoring of check valves in nuclear power plants

The objective of this study is to demonstrate that a condition-monitoring system based on acoustic emission (AE) detection can provide timely detection of check valve degradation and service aging so that maintenance or replacement can be preformed prior to the loss of safety function. This research is focused on the investigation and understanding of the capability of the acoustic emission technique to provide diagnostic information on check valve failures.AE testing for a check valve under controlled flow loop conditions was performed to detect and valve degradation such as wear and leakage due to foreign object interference. It is clearly demonstrated that the distinction of different types of failure were successful by systematically analyzing the characteristics of various AE parameters.     

燃料棒破损超声检测技术研究

研制了单探头和双晶片探头两种类型超声探头,通过对模拟燃料棒破损前后超声信号变化规律的研究,确定了超声检测探头的型式及检测方法。研究结果表明,可通过15~20mm声程范围内超声回波幅度的差异来判定燃料棒是否破损;与单探头相比,所研制的双晶片探头更适用于燃料棒破损超声检测,该双晶片探头能有效分辨的燃料棒内的最小水量为0.2mL。     

An assessment of acoustic emission for nuclear pressure vessel monitoring

Recent research has greatly improved our understanding of the basic mechanisms of deformation and fracture that generate detectable acoustic emission signals in structural steels. A critical review of the application of acoustic emission (AE) to the fabrication, proof testing and in-service monitoring of nuclear pressure vessels is presented in the light of this improved understanding. The detectability of deformation and fracture processes in pressure vessel steels is discussed, and recommendations made for improving source location accuracy and the development of quantitative source assessment techniques.

Published data suggest that AE can make an important contribution to weld fabrication monitoring, and to the detection of defects in lower toughness materials during vessel proof testing. In high toughness materials, however, the signals generated during ductile crack growth may frequently be too weak for reliable detection. The feasibility of AE for continuous monitoring has not yet been adequately demonstrated because of high background noise levels and uncertainty about AE signal strengths from the defect growth processes that occur in service. In-service leak detection by AE shows considerable promise.

It is recommended that further tests are carried out with realistic defects, and under realistic conditions of loading (including thermal shock and fatigue) and of environment.     

Acoustic emission monitoring of ZB-1 intermediate scale vessel test

A program to develop the use of acoustic emission (AE) flaw detection methods for continuous surveillance of reactor pressure boundaries is in process in the United States. Evaluation of laboratory developed relationships for data verification and interpretation was performed by participation in a German intermediate scale vessel (ZB-1) test. The test sequence consisted of repeated blocks of a hydrostatic test followed by two sets of cyclic loading at different R-ratios. Testing was performed in cooperation with the German Materialprüfungsanstalt at the Grosskraftwerk facility in Mannheim, West Germany. This paper discusses preliminary results obtained during the first half of the test which was performed at 70°C. The AE system detected crack growth from machined flaws and also spontaneous crack growth in a fabrication weld. AE signals from cracking were consistently high amplitude and occurred at or near peak load. Crack growth rates estimated from AE data were consistent with values derived from crackopening-displacement gauges. The test produced unique and important data needed to develop reliable application of AE methods for continuous monitoring of reactor pressure systems.     

基于波形采样的PPAC数据处理

数字化波形采样技术在实验核物理中得到了广泛的应用,选取合适的采样频率非常重要。本文使用脉冲幅度甄别定时方法和恒比定时方法对采样频率为100 MHz~5 GHz的平行板雪崩计数器(PPAC)信号进行了模拟分析,采样频率为250~500 MHz时,使用脉冲幅度甄别定时方法可得到比较精确的位置信息,与传统获取系统定位的位置分辨的差别Sigma小于0.15 mm,采样频率低于100 MHz时信号定位误差较大。使用高速采样数字化仪可对信号幅度小于20 mV的信号进行定时分析,与传统的PPAC获取系统相比,探测效率提升了4.3%。     

基于6LiF/ZnS(Ag)和闪烁光纤的宽能谱中子探测技术研究

为了解决传统中子探测器在狭窄空间、强电磁干扰、远距离传输等复杂环境下探测中子时存在的不足,本研究将6LiF/ZnS(Ag)混合材料和闪烁光纤相结合,设计了一种可用于宽能谱中子测量的新型闪烁体光纤中子探测器。基于蒙特卡罗粒子输运计算程序FLUKA对该新型光纤中子探测器的中子探测性能进行了模拟研究,完成了闪烁体光纤探头的优化设计。结果表明,当入射中子的能量在0.01~10 eV和0.5~10 MeV范围时,该新型中子探测器具有较高的中子探测效率,可用于热中子-快中子宽能谱范围中子的探测;通过对比脉冲幅度的差异,该新型中子探测器能够实现n-γ信号的甄别。      

A New Non-destructive Technique for Hydrogen Level Assessment in Zirconium Alloys using EMAR Method

In order to study the applicability of EMAR (electromagnetic acoustic resonance) method to non-destructive hydrogen level assessment in fuel spacer bands at pool side, an ultrasonic transmitter and receiver together with an EMAT (electromagnetic transducer) were used. Unirradiated Zircaloy-2 thin plates were hydrogen charged for the measurements. An irradiated fuel cladding tube was also used to examine the detection sensitivity of the resonance spectrum of the irradiated material. The following results were obtained. Acoustic anisotropy Δf, defined by using two resonance frequencies for shear waves with different polarization, was adopted as a parameter to express the ultrasonic resonance property. A hydrogen concentration dependence of Δf was observed in the range up to 1,200 ppm. Specimen thickness and oxide thickness were found to have negligible effect, on Δf, and liftoff of the sensor up to 1mm did not affect the Δf value. The acoustic anisotropy proposed in this paper was not sensitive to any of specimen dimension, surface condition, or sensor liftoff.     

反应堆安全壳超声波无线通信技术研究

为解决传统的无线传感信号无法实现反应堆安全壳内外的信息传输问题,研究设计了通过超声波将无线信号传输到安全壳外的超声通信系统。超声通信系统的发射单元将信号加载于40 kHz的超声波上,超声通信单元将接收到的信号通过超声换能器穿过安全壳传输到接收单元,接收单元通过三级放大、检波、滤波、比较电路,最终实现信号由安全壳内到安全壳外的传输。系统在模拟安全壳工况下试验,试验结果表明:信号能够低功耗、稳定传输,且误码率低于10~(-6)。     

Progress for on-line acoustic emission monitoring of cracks in reactor systems

This paper reviews accomplishments and planned tasks for the NRC-sponsored research program concerned with “Acoustic Emission/Flaw Relationships for Inservice Monitoring of Nuclear Reactor Pressure Boundaries”. The objective of the acoustic emission (AE) monitoring program is to develop and validate the use of AE methods for continuous surveillance of reactor pressure boundaries to detect flaw growth. Topics discussed include testing AE monitoring on reactors, refinement of an AE signal identification relationship, study of slow crack growth rate effects on AE generation, and activity to produce an ASTM standard for AE monitoring and to gain ASME code acceptance of AE monitoring.     

Measurements of the acoustic field on austenitic welds: a way to higher reliability in ultrasonic tests

In nuclear power plants many of the welds in austenitic tubes have to be inspected by means of ultrasonic techniques. If component-identical test pieces are available, they are used to qualify the ultrasonic test technology. Acoustic field measurements on such test blocks give information whether the beam of the ultrasonic transducer reaches all critical parts of the weld region and which transducer type is best suited. Acoustic fields have been measured at a bimetallic, a V-shaped and a narrow gap weld in test pieces of wall thickness 33, 25 and 17 mm, respectively. Compression wave transducers 45, 60 and 70° and 45° shear wave transducers have been included in the investigation. The results are presented: (1) as acoustic C-scans for one definite probe position, (2) as series of C-scans for the probe moving on a track perpendicular to the weld, (3) as scan along the weld and (4) as effective beam profile. The influence of the scanning electrodynamic probe is also discussed.     

基于轮转电极的多电极电容式棒位测量传感器静态特性研究

电容式棒位测量传感器是200 MW低温核供热堆控制棒水压驱动系统的关键测量部件,其精度和可靠性直接关系到反应堆的安全性。本文基于有限元方法建立了电容式棒位测量传感器的理论模型,对两电极电容式棒位测量传感器检测场的灵敏度分布特性进行了分析。结果表明,在检测场内存在一个特定区域,被测杆向该区域偏移时偏心误差较小。基于该特性提出了多电极电容式棒位测量传感器的设计方案和轮转电极的电容检测方法,针对该传感器,利用有限元模型进行了传感器结构优化和被测杆偏心误差分析,完成了传感器静态特性实验并验证了模型计算结果。分析结果表明,多电极电容式棒位测量传感器与轮转电极的电容检测方法能有效利用检测场的灵敏度分布特性,优化后传感器的偏心误差能达到棒位测量不失步的要求。研究成果为电容式棒位测量传感器的设计和优化提供了新的方向。     

Development of localization system using ultrasonic sensor for an underwater robot to survey narrow environment

This paper describes a localization system for a swimming robot to survey underwater narrow environments. In that environment, external sensors cannot be set up to localize the robot position, as there are many structures and the robot moves three-dimensionally. Therefore, the position needs to be calculated only by internal sensors. In this work, a new localization method based on map-matching is proposed, referring to cross-sectional shape data cut from a three-dimensional computer-aided design (CAD) data as an environmental map and structural shapes measured by a range sensor. As a range sensor, an ultrasonic sensor which is two-dimensional scanning-type was developed. The reflected signals of the ultrasonic sensor have some noise. Only structural shape data are extracted from the reflected signals. The image correlation is used as the matching method. Experiments to evaluate the performance of the proposed system were implemented at a mock-up environment. As a result, it was confirmed that the position was detected with an accuracy of 100 mm. The error is mainly caused by measurement error of the ultrasonic sensor that is used to calculate structural shapes. We concluded to improve the measurement accuracy of the ultrasonic sensor to reduce localization error.     

An overview of development and application of acoustic emission methods in the United States

Beneficial uses being made of acoustic emission (AE) technology for flaw or fault detection both inside of and outside of the nuclear industry tend to be obscured by some of the earlier disappointing efforts to utilize the technology. The objective of this paper is to counter that tendency by providing an overview of a variety of AE applications being made in the United States. In addition to nuclear power applications, the paper discusses applications in other nuclear areas, fossil power plant applications, and other industrial uses including aircraft monitoring. Major AE research and development programs in progress in the United States are also summarized.     

反应堆控制棒组件超声检测探头的研制

为了检测核电站反应堆控制棒组件,保障核电站在役检查顺利实施、降低检测成本。对反应堆控制棒组件（RCCA）检测用超声探头进行自主研制,本文详细介绍了15MHz-Φ4mm-FP8 mm RCCA超声探头制作流程,通过对压电晶片、声透镜、背衬3方面详细介绍探头制作工艺。通过对超声探头进行性能测试,测试脉冲周期数为1.5周,频带宽度为105%,在高温环境下仍能保持优良性能。对超声探头进行模拟检验测试,缺陷测试结果清晰可见,满足检验需求,可完全实现国产化替代进口产品。       

Development of Acoustic Leak Detection and Localization Methods for Inlet Piping of Fugen Nuclear Power Plant

The development work carried out on Fugen NPP is focused on detection of a small leakage on the reactor's inlet feeder pipes at an early stage by an acoustic leak detection method with usage of high-temperature resistant microphones. Specifically, the leak rate of 0.046 m³/h has been chosen as a target detection capability for this system. A cross-correlation technique has been studied for leak detection under low signal-noise ratios. The study shows that the sound diffusion on piping causes distortion of leak signals that results in their low correlation. A leak-location estimator and multi-channel correlation value, associated with estimated leak position, have been employed to detect such low-correlated leak signals. A method based on cross-correlation of signal spectral components has been proposed to deal with non-stationary leak signals. Joint-Time-Frequency-Analysis has been applied to analyze such signals, whilst a Wavelet decomposition technique has been used to extract their short-term spectral fluctuations. Since the spectral components are less affected by signal distortion, they provide higher correlation value and can be applied for leak detection under lower signal-noise ratios. The possibility of detecting and locating a small leakage by the methods proposed has been demonstrated by a number of simulation tests conducted on the Fugen NPP site.     

The development of techniques for the surveillance of LMFBRs

The development of surveillance techniques of LMFBRs is determined by the interaction of three factors: the specification of requirements, improvements in technique and the physical analysis of the processes involved. The specification of requirements, which sets the structure for the discussion, is mainly concerned with public safety. Two main divisions are identified: those concerned with thermal events in the nuclear core and those concerned directly or indirectly with the mechanical integrity of components. The necessary developments are then discussed in terms of the signal analysis techniques to anticipate various modes of failures. The importance of an adequate understanding of the failure mode is emphasised in optimising the surveillance technique.

Core surveillance may be achieved by monitoring individual sub-assemblies or by monitoring bulk conditions. The important features of sub-assembly monitoring are discussed and the advantages of temperature analysis explained. The specification of the temperature-monitoring systems is identified and the conflicting requirements for the reactor sensor discussed, viz adequate band width as against a robust and reliable construction. A theoretical treatment using Monte Carlo techniques allows a full examination of the choice of method of temperature analysis. This shows that, although a filtered rms value has been the preferred choice for detecting either local blockage or sodium boiling, it may be possible to distinguish the temperature signals of blockages from those of power gradients by an amplitude probability density plot. The advantages of acoustic monitoring using the noise of boiling sodium to detect overheating, leading to core damage, are examined. An important consideration is the thermal-acoustic process of sodium boiling, and evidence is submitted from a range of out-of-pile experiments involving local sub-cooled boiling and bulk boiling in discussing the merits of pulse analysis and power spectral density techniques. An important factor in discriminating background from signal is the extent of cavitation in reactor components. Experiments are mentioned in which pulse techniques have been used to locate boiling sources by spatial correlation. The interpretation of reactor signals requires a detailed knowledge of the transmission of acoustic waves in reactor pools and structures and the effect of gas bubbles. Measurements in PFR and sodium loops have helped to lead to a more quantitative assessment of the sensitivity of the acoustic techniques.

Structural integrity depends on detecting failure modes, particularly those arising from crack propagation. Manufacturing defects or pre-existing cracks may be identified by ultrasonic inspection or by stress-wave emission. On-line monitoring for stress-loaded cracks by a stress-wave emission is seen as intrinsically difficult because of low signal strength and high attenuation but initial experiments have indicated possibilities for detecting stress-corrosion cracking. Mechanical failure from fatigue may be anticipated from a understanding of the vibrational modes of the sodium and its coupling with the structure. A one-eighth scale model of a LMFBR design has recently demonstrated the likely vibrational modes. A major handicap in supervising mechanical operation in sodium systems is the opacity of the sodium. Visualisation techniques of the major parts of the core structure are being developed. An important aspect is the study of the information processing required to present an image easy for the reactor operator to understand. Advances may be made using transform methods to improve object boundaries by modifying the spatial frequencies of the display or record.     

Pulsed high-current discharge in water: adiabatic model of expanding plasma channel and acoustic wave

This paper presents the results of a theoretical and experimental study of the use of a pulsed discharge in water to obtain a strong acoustic wave in a liquid medium. A discharge with a current amplitude of 10 kA, a duration of 400 ns, and an amplitude pulsed power of 280 MW in water at atmospheric pressure created an expanding acoustic wave with an amplitude of more than 100 MPa. To describe the formation of the discharge channel, an isothermal plasma model has been developed, which made it possible to calculate both the expansion dynamics of a high-current channel and the strong acoustic wave generated by it. Our calculations show that the number density of plasma in the channel reaches 10²⁰ cm^–3, while the degree of water vapor ionization is about 10%, and the channel wall extends with a velocity of 500 m s−1. The calculations for the acoustic wave are in good agreement with measurements.     

核电厂主螺栓超声检测与信号分析

依据RSE-M标准需要定期对核电厂反应堆压力容器（RPV）主螺栓进行超声检测,为了保证主螺栓螺纹区及光杆区不同深度刻槽的超声检测灵敏度,本文对检测工艺进行声场仿真计算,分析与判断数据采集中的相关信号与非相关信号,并重点分析裂纹信号的特征,验证了超声工艺的可靠性。结合现场实施案例,通过45°横波端角反射率高的特性,综合其他检测方法如涡流和渗透检测对缺陷性质进行判定,可有效确定异常信号。      

Performance demonstration for an automated ultrasonic testing system for piping welds

This paper addresses the implementation of an automated ultrasonic testing (AUT) system qualification by performance demonstration (PD) as imposed by the ASME Boiler and Pressure Vessel Code Section XI. To improve the reliability of the ultrasonic testing results for nuclear power plant (NPP) components, almost all engineering codes related to NPP inspection require the ultrasonic inspection systems to be qualified by passing a PD examination. In this study, an AUT system developed to inspect pipe welding parts in NPPs is introduced. To acquire a Korean Performance Demonstration (KPD) qualification, the developed system had a KPD. System obtained the qualification for flaw detection, length, and depth sizing from KPD.