Waveguide ultrasonic liquid level transducer for nuclear power plant steam generator

This paper deals with the development and utilization of a new acoustic method to control the level of the coolant in industrial power-generating equipment. The development research was carried out on the basis of the method of acoustic impedance, based on measuring attenuation of a longitudinal ultrasonic wave in a waveguide sensing element. Ultrasonic attenuation is determined by the degree of submergence of the sensing element in liquid. For this purpose waveguide ultrasonic transducers are used, made with specially designed technology (waveguide acoustic transducers—WAT-technology). The transducers are adapted for operation under extreme conditions in the water coolant with temperatures up to 350°C and pressure up to 20 MPa. The paper tackles: principle of operation of transducers, methods of testing under laboratory conditions, design and results of calibration in a thermophysical test facility, results of the operational trial of the level transducer at the nuclear power plant in Zaporozhye.     

The newest two-phase flow control devices in LWR equipment based on ultrasonic and WAT-technology

This paper deals with new acoustic methods of two-phase flow diagnostics used to carry out research in the fields of nuclear power thermophysics and nuclear power plant (NPP) technologies equipment control. All the designs are to be used under extreme conditions, characteristic for water coolant, with temperature up to 350°C and pressure 20 MPa. All the safety and reliability requirements are met. The methods use waveguide ultrasonic transducers for longitudinal and bending waves, made according to specially designed technology (waveguide acoustic transducers — WAT technology). This paper deals with the operating principles of transducers and processing device physical models as well as some results on the practical use of this equipment. The method of acoustic impedance is based on measuring attenuation of a longitudinal or bending ultrasonic wave in a thin-walled tube diameter vapour fraction or the level of the coolant in the tank. The waveguide transducers, designed by the centre, use bending waves of a surface type. They enable us to carry out diagnostics of the liquid film on the inner surface of the tube or discover gas inclusions in the liquid flow. The paper touches upon the method of acoustic emission for measuring moisture content in a steam flow.     

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.     

Development of an ultrasonic inspection system using array transducers

A new ultrasonic inspection system was developed to obtain ultrasonic images of defects. This system adopts an electronic beam control method using array transducers. The beam control modes are a compound scanning mode and a linear scanning mode. Both modes are performed by timing control of ultrasonic wave transmission and reception at each transducer element.In the focal beam, the refraction of the ultrasonic wave at the boundary between water and metal in immersion testing is utilized to improve the lateral resolution of the ultrasonic beam. In steel, the improvement is a maximum of 25% for focal lengths from 5 to 35 mm as compared to lateral resolution not utilizing refraction.This system successfully imaged two side drilled holes in a steel block.     

蒸汽发生器换热管电磁超声纵向导波换能器设计与优化

高温气冷堆蒸汽发生器换热管特殊的螺旋结构导致传统外置型电磁超声导波换能器难以进行有效检测。本文针对蒸汽发生器不锈钢换热管的缺陷检测,开发了一种新型内置型电磁超声纵向导波换能器,建立了有限元多物理场耦合模型,研究了换能器铁磁结构的静态磁场分布,并对换能器激励出的纵向导波进行了时域仿真。结果表明：采用挤压聚磁的换能器结构可保证线圈附近的垂直方向磁场远大于水平方向磁场,能高效地在管道内部激励单一模式的纵向导波;优化后的探头可检测直径为5 mm的通孔缺陷和长×宽×深为20 mm×1.5 mm×1.2 mm的环向槽缺陷。因此,新型电磁超声纵向导波换能器可有效激励纵向导波,并有望应用于高温气冷堆蒸汽发生器换热管的在役缺陷检测。     

Detection Method of Fatigue Damage in Carbon Steel Using Laser Ultrasonics

Ultrasonic attenuation was measured by the laser ultrasonic technique among the carbon steel specimens which were subjected to five stages of fatigue damage by constant cyclic tensile stress amplitude. Irradiation of a Q-switched laser was used for ultrasonic generation, and a laser interferometer which consists of a frequency-doubled continuous wave laser and a Fabry-Perot etalon was used for detection of ultrasonic vibration on the specimen surface. From the comparison of the broadband ultrasonic waveforms among five stages of fatigue damage, the attenuation coefficient of the longitudinal wave by the intrinsic material attenuation increased progressively with increasing the number of fatigue cycle. Ultrasonic attenuation at 2.5, 5.0, 7.5 and 10.0MHz were also calculated by Fourier transformation in order to compare the decay of the longitudinal wave among these frequency components. From the results, ultrasonic attenuation increased as the number of fatigue cycle increased, in both broadband and narrowband frequency components. Therefore, the measurement of broadband and narrowband ultrasonic wave obtained by the laser ultrasonic technique would be effective as the detection method of fatigue damage in nuclear power plant components.     

Profiling a reactor component using ultrasonics

Nuclear reactors have many components within the reactor vessel. During the life of a reactor it is possible for these components to be displaced or deformed because of the thermal cycles to which they are subject. Also, these components are handled during refuellings and reconfigurations of the core. During these operations, damage is possible. Inspection of these components in situ therefore becomes important for the upkeep of the reactor. However, high radiation levels make it difficult to monitor using optical methods. This paper describes an ultrasonic method which was successfully employed in profiling a deformed guide tube of a reactor. The method uses the well-known ultrasonic ranging technique. However, the speciality of the method is the use of air transducers at 40 kHz to overcome the inherent divergence problems and the difficulties associated with high temperatures inherent in a sodium cooled reactor     

Development of an ultra sonic phased array system for nondestructive tests of nuclear power plant components

A phased array ultrasonic inspection (PAULI) system is being developed to obtain electronically scanned ultrasonic images of the inside of nuclear power plant components for nondestructive evaluation. The development strategy of PAULI system was the modification of a medical ultrasound imaging system that had 64 individual transceiver channels. Optimization of array transducers has been also pursued based on the systematic investigation of the radiation beam field simulated by the use of the boundary diffraction wave models. 7.5 MHz phased array transducers was, then, fabricated and tested with the carbon steel specimen having side-drilled holes. For the nondestructive tests on power plant component, a sample mockup of turbine blade root with EDM notches was fabricated and the detection capability was demonstrated. The developed system can provide electronically scanned ultrasonic images in real time fashion and greatly enhance the efficiency and reliability in the flaw detection and location in comparison with the classical ultrasonic testing (UT) using A-scan signals. For the flaw classification, the analysis of the electronically scanned ultrasonic images was not sufficient at this moment but analysis of features obtained from A-scan signals of flaws at the various steering angles showed the potential capability.     

Prototype EMAT system for tube inspection with guided ultrasonic waves

A prototype system with full computer support for ultrasonic inspection of ferritic tubes using guided waves is described. The ultrasonic waves are launched and received with the aid of electromagnetic acoustic transducers which are layed out as linear phased arrays. The array structure provides a good axial directivity for the transducers so that the probe can be positioned anywhere along the tube length sequentially transmitting ultrasonic pulses in the foreward and backward directions. While the probe is fixed at one axial position during inspection the tube length is measured by the system and flaws are detected from returning ultrasonic echos. Results of the inspection of tubes with natural flaws are given and the wavelength-spectrum of the ultrasonic mode used for the inspection is discussed with respect to flaw depth sizing.     

Remove Welding Residual Stress for CFETR Vacuum Vessel by Trailing Ultrasonic Impact Treatment

The China fusion engineering test reactor (CFETR) vacuum vessel is welded by narrow gap TIG (NG-TIG) welding, and the welding residual stress of the CFETR vacuum vessel can be redistributed by trailing welding ultrasonic impact treatment. In order to investigate the feasibility of the residual stress removing scheme, and to obtain the optimal trailing ultrasonic impact treatment technological parameters in the process of removing welding residual stress, a welding model that similar to vacuum vessel welding seam is established by using ABAQUS software, a NG-TIG welding heat source subroutine which is written in FORTRAN language used to simulate NG-TIG welding. According to the welding simulation results, a trailing welding ultrasonic impact treatment model is established, and the effects of the impact pin number, the impact method, the impact pin diameter and the impact frequency on welding residual stress are studied. The results show that the longitudinal residual stress in welding seam and its adjacent area and the lateral residual stress in the whole region have been obviously decreased by different trailing welding ultrasonic impact processes, and have made the tensile stress in the welding seam and its adjacent area has been changed into compressive stress, which can provide theoretical guidance and reference for actual production.     

A novel encoding water level monitor system during and after LOCAs in a nuclear heating reactor

The water level in a nuclear reactor vessel is an important parameter during and after LOCAs. Nuclear safety specifications can not be carried out when the water level is measured using a pressurizer which does show the level in the vessel. It is difficult to monitor the water level in the vessel of a Daqing 200MW Nuclear Heating Reactor (NHR-200) using the present differential pressure transducers. Based on the heat transfer differences between water (or liquid) and steam (or gas), a novel level detector, which includes encoding heating shell thermocouples, has been developed and verified for use experimentally under pressures of 0.15–3.0 MPa. A novel encoding water level monitoring system was designed, made up of an assembly that contains several detectors, a signal encoder and an intelligent processor. Analysis and experiments have shown that the new system is correct in principle, reliable and feasible in structure for monitoring the water level in the NHR-200 reactor.     

Flaw density examinations of a clad boiling water reactor pressure vessel segment

As part of the Oak Ridge National Laboratory's Heavy-Section Steel Technology Program, studies have been conducted to determine flaw density in a section of reactor pressure vessel cut from the Hope Creek Unit 2 vessel. This boiling water reactor vessel was never in service. One objective was to evaluate the approximate 0.7- by 3-m (2- by 10-ft) segment of the vessel provided using ultrasonic flaw detection methods performed with both ASME Code techniques and supplemental ultrasonic methods. A second objective was to evaluate the inner surface stainless steel cladding for cracks with a high sensitivity penetrant examination. Both objectives were successfully completed. Five Code-recordable indications were detected ultrasonically; however, all were found to be anomalies associated with the cladding. One flaw was detected by the supplemental ultrasonic tests, and it was analyzed destructively. This flaw was pipelike indication, about 20 mm (0.8 in.) long extending along the length of the longitudinal weld in which it was located and was about 20 mm below the cladding surface. The flaw had a through-wall dimension (or length) of about 6 mm (0.24 in.) for an approximate 3-mm (0.1-in.) distance along the 20-mm major length. No flaws were detected by the penetrant examination of the cladding surface.     

Wave propagation visualization in an experimental model for a control rod drive mechanism assembly

Nondestructive inspection techniques such as ultrasonic testing, eddy current testing, and visual testing are being developed to detect primary water stress corrosion cracks in control rod drive mechanism (CRDM) assemblies of nuclear power plants. A unit CRDM assembly consists of a reactor upper head including cladding, a penetration nozzle, and J-groove dissimilar metal welds with buttering. In this study, we fabricated a full-scale CRDM assembly mock-up. An ultrasonic propagation imaging (UPI) method using a scanning laser ultrasonic generator is proposed to visualize and simulate ultrasonic wave propagation around the thick and complex CRDM assembly. First, the proposed laser UPI system was validated for a simple aluminium plate by comparing the ultrasonic wave propagation movie (UWPM) obtained using the system with numerical simulation results reported in the literature. Lamb wave mode identification and damage detectability, depending on the ultrasonic frequency, were also included in the UWPM analysis. A CRDM assembly mock-up was fabricated in full-size and its vertical cross section was scanned using the laser UPI system to investigate the propagation characteristics of the longitudinal and Rayleigh waves in the complex structure. The ultrasonic source location and frequency were easily simulated by changing the sensor location and the band pass filtering zone, respectively. The ultrasonic propagation patterns before and after cracks in the weld and nozzle of the CRDM assembly were also analyzed. Since this visualization method is not limited in the flat cross section, it will be useful in developing ultrasound-based structural health monitoring technologies, advanced nondestructive methods, and numerical models. In addition, the proposed laser UPI system could be a useful tool in optimizing the receiver and transmitter locations, the ultrasonic path, and the ultrasonic frequency.     

Inspection procedure assessment using modelling capabilities

Before carrying out inspections on technical components, criteria have to be met to qualify the inspection procedure. The inspection qualification can be performed by technical justification or performance demonstration. The qualification of non-destructive testing methods can be checked on full scale mock-ups where real or realistic defects are implemented. To minimize costs it will become mandatory to model the inspection procedure. In the case of ultrasonic testing, the modelling includes the ultrasonic probe, the pulse-defect interaction and the probe geometry. The applied modelling code is the elastodynamic finite integration technique (EFIT) which includes mode conversion effects. The results of the code are either wave fields, A-scans at different probe positions or complete r.f. data fields. Examples demonstrate the efficiency in modelling angle beam probes which transmit both pressure, shear and subsurface longitudinal waves. These waves are scattered by horizontal or surface breaking cracks. The modelled r.f. data fields are used within the synthetic aperture focusing approach to predict the ultrasonic image which would be obtained in performing the experiment. In addition it will be shown that the EFIT wave fronts for anisotropic homogeneous media are explicitly related to the group velocity in these media.     

铅铋快堆一回路充排系统可靠性分析

铅铋快堆属于第四代反应堆,其一回路采用液态铅铋合金冷却.铅铋快堆一回路充排系统可以调节反应堆主容器内液态金属液位,该系统充满含有放射性物质的液态金属,其可靠性水平对反应堆运行及安全有重要影响.本文以中国科学院核能安全技术研究所·FDS团队自主设计的铅铋快堆一回路充排系统为研究对象,运用故障树分析方法对该系统进行可靠性分...     

Assessment of an Ultrasonic Sensor and a Capacitance Probe for Measurement of Two-phase Mixture Level

We perform a comparison of two-phase mixture levels measured by an ultrasonic sensor and a two-wire type capacitance probe with visual data under the same experimental conditions. A series of experiments are performed with various combinations of airflow and initial water level using a test vessel with a height of 2 m and an inner diameter of 0.3 m under atmospheric pressure and room temperature. The ultrasonic sensor measures the two-phase mixture level with a maximum error of 1.77% with respect to the visual data. The capacitance probe severely under-predicts the level data in the high void fraction region. The cause of the error is identified as the change of the dielectric constant as the void fraction changes when the probe is applied to the measurement of the two-phase mixture levels. A correction method for the capacitance probe is proposed by correcting the change of the dielectric constant of the two-phase mixture. The correction method for the capacitance probe produces a r.m.s. error of 5.4%.     

Models for the computation of ultrasonic fields and their interaction with defects in realistic NDT configurations

Developments in quantitative ultrasonic non-destructive testing (subsequently denoted by NDT) require simulation tools for cost-effective research and engineering works. The present paper reviews the two models developed for several years at the French Atomic Energy Commission (CEA) for this purpose. The first one is dedicated to the computation of the ultrasonic field radiated by arbitrary transducers into pieces under examination. The second simulates actual testing configurations, that is, includes beam/defect interaction as well as the transducer scan over the piece so as to synthesise images typical of those actually measured in NDT experiments. Examples of their application in the context of nuclear engineering are given. They demonstrate the usefulness of such modelling tools in ultrasonic NDT either to study and optimise testing configurations, including transducer design or to help NDT-experts to interpret actual data, possibly by means of model-based automatic data inversion.     

UT digitized data processing for in service inspection of pressurized water reactor vessels

Pressurized reactor vessels in France have been examined from the inside with ultrasonic focused transducers since the very first inspection (Gagnor and Levy, 1993, Proc. 7th Asian-Pacific Conference on Nondestructive Testing, Shangaï, China, 867 pp.). The developments carried out in collaboration with the French Atomic Energy Commission (CEA) to improve the characterization of flaws detected in the body of the vessels or in the nozzles, in the vicinity of the inner or the outer surfaces now have application throughout the CIVAMIS software. The processing modules of CIVAMIS, which are implemented on site since 1994 and used by INTERCONTROLE during the in service inspections of the French PWR vessels, allow full characterization of these specific flaws. The first module is devoted to the characterization of defects located near the outer surface of the vessel or the bottom head welds (OSD module). It includes the modeling software MEPHISTOMIS which predicts the echoes coming from the interaction between the ultrasonic beam and the defects. The second module of CIVAMIS (inner surface defect module called ISD), applied to the analysis of flaws expected near the inner surface of the vessels, has been used during performance demonstration exercises on qualification mock-ups, and also on-site in five expert appraisals since its qualification in 1995. The third module available on the system has been developed and qualified for the analysis of flaws likely to appear near the inner surface of the nozzles. This module, named ‘Undercladding Crack Defect' (UCD) module, provides the operators with a set of pre-defined processing configurations well adapted to the characteristics of the transducers and of the digital acquisitions triggered in this examination case. The last new module (SAFE-END module) has been developed for the evaluation of defects located close to the bimetallic weld in the nozzles. The capacity of CIVAMIS to be adapted to each examination area and the characterization tools included in the different modules are developed in the present paper.     

Visualization of the ultrasound-induced behaviour of gas pockets entrapped on a patterned surface. Application to inspection of sodium-cooled fast reactors

The presence of microscopic gas pockets trapped on a non-wetting solid/liquid interface induces a significant decrease of the transmitted ultrasonic energy. This phenomenon can reduce the performance of ultrasonic inspection in sodium-cooled fast reactors (SFR) for instance. To explain this event, a hypothesis was formulated in a previous study: under the effect of ultrasound, the gas pockets could coalesce, forming a gas film which would prevent the passage of the ultrasound. This coalescence hypothesis can be studied by visual observation of the phenomenon. This paper is presenting an original experiment which simulates this phenomenon in water. This experiment consists in observing the ultrasound-induced behaviour of gas pockets over various time scales. The results allow dismissing the coalescence hypothesis. Our conclusion indicates how future works are reoriented to improve the design of ultrasonic transducers dedicated to SFR inspection.     

Effect of prestress force on longitudinal vibration of bonded tendons embedded in a nuclear containment

In this paper, evaluation of tensile force on bonded seven-wire strand embedded in nuclear reactor containments has been nondestructively investigated. For this purpose, a total of eight prestressed concrete beam specimens with different tension force levels have been fabricated and tested in terms of using an impact pulse at one end of the strand. Subsequently, various longitudinal vibration characteristics excited by the pulse have been analyzed in detailed. In short, the present study has demonstrated that longitudinal frequency, elastic wave velocity, and elastic modulus are nonlinearly increased as the tensile force level is increased. It is thus postulated that the longitudinal vibration characteristics of the existing bonded tendons can be of promising indicators for the inspection of a tensile force loss.