Nuclear fuel cladding integrity is critical for reactor safety, yet detecting breakage defects in densely packed fuel assemblies remains challenging due to extreme operational environments and inefficient conventional inspection techniques. This study introduces a novel multi-channel ultrasonic testing system integrated with machine learning for precise, efficient cladding defect detection in nuclear fuel assemblies. By leveraging time-division multiplexing, the system expands the number of channels of commercial ultrasonic flaw detectors from 8 to 32, reducing inspection time for a 17x17 assembly from over 40 minutes to under 10 minutes. Hilbert transform is employed to extract robust envelope features from dispersive Lamb wave signals, suppressing environmental interference while quantifying acoustic impedance changes caused by coolant leakage. Addressing the "scarce defective samples, abundant normal samples" challenge, a One-Class SVM is used to build an anomaly detection model with only normal samples. Experimental results show 100% defect detection rate (no misses) and <3% false positive rate in simulations. The algorithm screens 264 fuel rods per assembly in under 3 minutes, cutting manual review time by 66.7% (from 1.5 hours to 30 minutes). This solution overcomes traditional ultrasonic testing bottlenecks, providing a robust automated framework for in-service inspection and significantly enhancing nuclear power maintenance efficiency.

Pressurized water reactors (PWRs) are the predominant type of nuclear power plant globally, with their reactor pressure vessels (RPVs) subject to stringent in-service inspection (ISI) requirements as mandated by regulatory standards. However, the complex curved surface of the reinforcement part presents challenges for ultrasonic testing in the outlet nozzle-to-shell weld areas, resulting in inaccessible zones that lack practical quantitative analysis methods for volume coverage. This study systematically parameterized the geometric features of the outlet nozzle reinforcement part, including the cone, fillet, and ellipse. It introduced seven categories of ultrasonic beam tangent segmentation algorithms based on spatial curves. Using Pro/E software, we developed a 3D ultrasonic beamline model of inaccessible zones and validated its accuracy against two-dimensional data obtained from AutoCAD. Building on this foundation, a fully parametric simulation model and discrete volume data were employed to plot the continuous curves of inaccessible zones' volume on the side of the typical outlet nozzle reinforcement part as a function of ultrasonic incidence angles, elucidating the nonlinear, multi-stage superimposed impact of complex surface characteristics on the volume of inaccessible zones. This research provides vital theoretical support and a methodological basis for optimizing ultrasonic testing processes and quantitative evaluation of volume coverage in nozzle areas with complex surfaces, particularly saddle-like profiles.

Regular ultrasonic full-coverage inspection of reactor pressure vessels (RPVs) is critical to ensuring the safe operation of nuclear power plants. However, due to the extreme operating conditions and complex internal geometry of RPVs, most existing inspection technologies face significant challenges in achieving convenient and efficient full-coverage traversal detection. To address these limitations, this study proposes a novel nondestructive inspection robot equipped with four symmetrically arranged inspection arms for comprehensive RPV ultrasonic inspection. By considering the structural symmetry and motion characteristics of the inspection arms, a corresponding kinematic analysis is conducted, resulting in a precise kinematic model that enables real-time computation of both forward and inverse kinematic solutions with high accuracy. Furthermore, an adaptive full-coverage inspection method is developed by leveraging the vessel’s axisymmetric geometry and by partitioning the RPV into seven distinct detection zones, allowing the four inspection arms to independently complete inspections across the maximum number of zones, thereby significantly enhancing both detection coverage and operational efficiency. Experiments demonstrated the practical feasibility of the proposed robotic system and validated the effectiveness of the full-coverage inspection method.

The traditional microstructure detecting methods such as metallography and electron backscatter diffraction are destructive to the sample and time-consuming and they cannot meet the needs of rapid online inspection. In this paper, a random forest regression microstructure characterization method based on a laser ultrasound technique is investigated for evaluating the microstructure of a titanium alloy (Ti-6Al-4V). Based on the high correlation between the longitudinal wave velocity of ultrasonic waves, the average grain size of the primary α phase, and the volume fraction of the transformed β matrix of the titanium alloy, and with the longitudinal wave velocity as the input feature and the average grain size of the primary α phase and the volume fraction of the transformed β matrix as the output features, prediction models for the average grain size of the primary α phase and the volume fraction of the transformed β matrix were developed based on a random forest regression. The results show that the mean values of the mean relative errors of the predicted mean grain size of the native α phase and the volume fraction of the transformed β matrix for the six samples in the two prediction models were 11.55% and 10.19%, respectively, and the RMSE and MAE obtained from both prediction models were relatively small, which indicates that the two established random forest regression models have a high prediction accuracy.

中广核集团核电站在役检查技术研发中心(简称集团在役检查研发中心),2022年度在无损检测技术研究、先进仪器及传感器研发、智能检测系统装备开发、无损检测信号处理等方面开展多项研发工作.具体进展包括高性能阵列涡流仪、水下三维测绘技术、基于机器学习的传热管涡流智能信号识别、控制棒驱动机构热套磨损测量技术、凝汽器新型示踪检漏技术、核电用超薄超声检测传感器及光热电站智能清洗装备等方面.

This paper introduces the current situation, advantages and disadvantages of the design of large-diameter pipeline inspection mechanism at home and abroad. Based on the typical characteristics of the main coolant line of nuclear power plant and the requirement of minimizing the personnel residence time, a new type of pipe inspection mechanism with high load, lightweight and multi-function is developed. The stress model of the lightweight gear ring in various statuses is established with detailed stress conditions of the gear ring are calculated, and then the maximum deformation and stress are simulated. By comparing the vertical deviation principle of prototype and new rigid structures, the coupling optimization method of probe is explained. Through the practical application in the nuclear power plant, the overall performance and lightweight effect of the system are verified.

This paper investigated a mean grain size characterization method base on laser ultrasonic. The 316L stainless steel samples with different mean grain size were conducted with different heat treatments and times, and each sample was observed by SEM and tested by laser ultrasonic. Due to the state of the sample surface, complexity of equipment and environment, the ultrasonic signal contain a lot of noise. Proposes a method to calculate the ultrasonic attenuation coefficient based on the signal after wavelet threshold denoising. Using db3 as the wavelet basis function, the signal is decomposed and denoised 5 times and then recombined. The attenuation coefficients of the amplitudes in the time domain and frequency domain of the original signal and the denoised signal are calculated. The results show that wavelet threshold denoising can improve the signal-to-noise ratio of the signal and the calculation accuracy of the average grain size.

Defects or discontinuities are inevitable during the melting and consolidation process of metal additive manufacturing. Online inspection of microdefects during the processing of layer-by-layer fusion is urgently needed for quality control. In this study, the laser ultrasonic C-scan imaging system is established to detect the surface defects of selective laser melting (SLM) samples that have a different surface roughness. An autosizing method based on the maximum correlation coefficient and lag time is proposed to accurately measure the defect length. The influences of the surface roughness on the laser ultrasound signal-to-noise ratio distribution and defect sizing accuracy are also studied. The results indicate that the proposed system can detect notches with a depth of 50 µm and holes with a diameter of 50 µm, comparable in size to raw powder particles. The average error for the length measurement can reach 1.5% if the notch is larger than 2 mm. Meanwhile, the sizing error of a 1 mm length notch is about 9%. In addition, there is no need to remove the rough surface of the as-built SLM samples during the detection process. Hence, we propose that the laser ultrasonic imaging system is a potential method for online inspection of metal additive manufacturing.

European Pressurized Reactor (EPR) nuclear power plant is now under construction in China. One of the biggest changes in the EPR reactor pressure vessel (RPV) is the nozzle to shell welds are designed as "set-on" principle instead of "set-in" principle in the CPR1000 units. The nozzle to shell welds of the EPR pressure vessel must be inspected according to the RSE-M code. This is necessary in order to guarantee the integrity of the primary circuit. The In-Service Inspection (ISI) program of EPR nuclear power plant demands the automatic ultrasonic inspection of the nozzle to shell welds from nozzle inner surface. This paper presents the technical characteristics of the EPR reactor vessel, and analyzes the in-service examination requirements of nozzle to shell welds. Technical solutions have been designed to perform the examination of the component. The qualification process of the ultrasonic examination of the nozzle to shell welds is also presented.

The Main Coolant Line (MCL) is the pressure boundary of the reactor coolant loop in the pressurized reactor nuclear power plant, and the weld quality determines the integrity of the pressure boundary. Nowadays, the narrow gap gas tungsten arc welding (GTAW) technology has taken place of the shield metal arc welding (SMAW) technology in the installation of the main pipeline. The Ultrasonic testing is one of the main methods to test the quality of the narrow gap welds. Due to the space and location limit, the specific manipulator is designed to perform ultrasonic inspections from the external surface of the Main Coolant Line welds. Techniques have been developed using conventional ultrasonic duel element focusing techniques for the inspection of thick section austenitic stainless steel. In this paper, the validation of this technique on mock-up has been performed. The qualification result shows that the selected ultrasonic technology and specific designed scanner demonstrate excellently in the mock-up and block with artificial flaws.

This paper introduces the structure of the control rod drive mechanism pressure housings welds (CRDM)of the third generation CEPR unit.In view of the material and microstructure of the weld,the requirement of the lower weld of the control rod drive mechanism for ultrasonic testing technology was put forward and experiment to verify the technology was designed.The results showed that the ultrasonic testing method could detect a defect of its height being equal to or greater than 3 mm.

Reactor pressure vessels, as the most important security barrier for nuclear power plant safety, are the only part of nuclear power plant that cannot be replaced during the whole life. The security of the vessels is very important for the safety of nuclear power. The nuclear reactor pressure vessels NDT robots are very important equipments. The detection process for these pressure vessels using the robots requires absolute safety, so it is necessary to simulate the nuclear reactor pressure vessel NDT robot and verify the feasibility. In this paper, physical modeling, the D-H rule modeling, kinematics modeling and simulation for the nuclear reactor pressure vessel NDT robots are implemented and verified with joint simulation and MATLAB.

The opening width of fatigue crack was very small, and conventional Bobbin probe was very difficult to detect it in steam generator tubes. Different sizes of 8 fatigue cracks were inspected using bobbin probe rotating probe. The analysis results showed that, bobbin probe was not sensitive for fatigue crack even for small through wall crack mixed with denting signal. On the other hand, the rotating probe was easily to detect all cracks. Finally, the OD phase to depth curve for fatigue crack using rotating probe was established and the results agreed very well with the true crack size.

The invention relates to an ultrasonic automatic scanning device for a large-aperture pipeline in a nuclear power plant. The ultrasonic automatic scanning device comprises a mechanical scanning part, an electric control part and a pipeline part, wherein the mechanical scanning part comprises a circumferential guide rail part, a circumferential moving module and an axial moving module; the circumferential guide rail part comprises an annular body and a plurality of supporting legs which are mounted on the inner side of the annular body and are capable of moving along the radial direction of the annular body; the circumferential moving module comprises a circumferential guide rail fixed on the annular body, an arc-shaped fixed plate which is detachably mounted on the circumferential guide rail and is capable of moving along the circumferential guide rail, and a circumferential driving motor which is fixed at one end of the arc-shaped fixed plate and is meshed with the circumferential guide rail; the axial moving module comprises an arc-shaped frame detachably mounted on the arc-shaped fixed plate, a probe disk which is parallel to the arc-shaped fixed plate, can slide in the arc-shaped frame and is used for fixing ultrasonic probes, an axial driving motor fixed on the arc-shaped frame, and a transmission mechanism which is connected with the axial driving motor and is used for driving the probe disk. On one hand, the mechanical scanning part is modularized, so that the occupation space can be effectively reduced, and the mechanical scanning part can conveniently move and be mounted in the narrow space of the nuclear power plant; on the other hand, the mechanical scanning part is in a detachable quick connection locking mode, so that the mounting time is shortened.

The first Chinese Evolutionary Pressurized Reactor (CEPR) nuclear power plant is being built on the Taishan site, Guangdong Province. The regulation of application imposes a rule to perform the Pre-Service Inspections on the components of the main primary system with qualified Non-Destructive systems.

The present invention discloses a non-destructive testing method of detecting robot and its nuclear reactor pressure vessel. Comprising: a column assembly; a plurality of support legs, each support leg one end fixedly connected to said upright assembly, and the other end detachably connected to the column assembly and pressure vessel axis and the axis line coincides with the pressure vessel ; a first robot arm provided with a first scanning probe assembly for the pressure vessel cylinder; the second arm, which is provided with a second probe assembly for scanning the lower head of the pressure vessel; a third arm , which is provided with a third scanning probe assembly for the pressure vessel portion of the nozzle; and a fourth robotic arm, which is provided with a threaded bolt hole fourth probe assembly for scanning and pressure vessel flange for scanning the pressure vessel the fifth probe assembly ligament area of ​​the bolt hole of the flange; main rotary joint, which is rotatable about the axial direction of the post assembly pivotally connected to the lower portion of the upright assembly, said second arm by a pivot joint about a perpendicular an axial direction of the upright assembly rotatably connected to the main rotating joint, the other robot arm is detachably connected to the main pivot joint.

反应堆压力容器检查机的支撑腿结构起定位和支撑作用,其结构的合理性对反应堆压力容器检查机的定位精度和可靠性具有重要影响.针对第三代核电站EPR堆型核反应堆压力容器结构,设计了具有自动定心功能的支撑腿结构.采用有限元方法分析了支撑腿结构的可靠性,并进行了验证力学试验.试验结果印证了相关理论分析结果,证明该支撑腿结构的设计是合理可行的.

反应堆压力容器主螺栓在核电厂以及核动力装置系统中起着至关重要的作用,RESM标准中对其也有着严格的检验要求.综合考虑机械、电气控制、超声仪器等参数,为实现无损检测的目标,设计了超声检查设备控制系统,实现了自动化的超声检查.机械设备部分的设计保证了超声仪器探头可在主螺栓内部进行轴向和周向运动.电气控制系统运动控制器采用数字运动卡及其互联模块实现伺服闭环控制,为检查所需的高精度要求提供保障.与之配套的软件设计大大降低人为失误造成的损失,提高了安全性和实用性.该控制系统已用于核电站的役前和在役检查之中,达到了良好的效果.

The history of in-service inspection qualification in the worldwide nuclear power plants was described. The characteristics and applications of two methods both ASME qualification and ENIQ qualification methodology were analysed.Finally,the status of in-service inspection qualification in China was introduced and the domestic qualification work in future was also suggested.

The research on reliability of foreign non-destructive testing(NDT) were described,focusing on the reliability parameters such as defect inspection rate,probability of false alarm,reliability of quantification and receiver operation characteristics.Two common calculation models of defect inspection rate were given.Three conventional calculation methods on NDT reliability evaluation were summarized.The advantages and disadvantages between the three methods were compared.The engineering applications of NDT reliability research were introduced.The difference of NDT reliability research between China and advanced countries were given.The results can provide a reference for the NDT reliability research and engineering application of China.