核电厂在役检查探讨

在役检查是指核电厂承压边界重要核安全相关部件的定期检查,是核电厂整个寿期内的重要活动之一。本文从核电厂营运单位的角度论述了核电厂在役检查的组织体系、文件体系、不同阶段的重点工作和在役检查人员配置等。     

Requirements related to in-service inspection of reactor vessels

The in-service inspection of nuclear facilities should make it possible to detect all flaws capable of deterioration. The size of a flaw is not normally characteristic of its seriousness: a large, stable defect which is not developing is of no importance for the safety of the facility whereas a small but developing defect may be dangerous and hence of importance for safety. It is essential to detect all defects, so that any development they may be undergoing can be assessed, and to use, for that purpose, a technique with a maximum detection probability; but the main thing is to characterize all developing defects. For the in-service inspection of pressurized-water reactor vessels the “Commissariat à l'Energie Atomique” has conducted studies on inspection methods with a view to ensuring first the best possible detection and secondly the best possible characterization of flaws. Since 1973 many publications have appeared on the subject and this paper will only recall the essentials giving particular attention however to the characterization of defects, which is the principal purpose of the studies currently being conducted.     

Advanced flaw production method for in-service inspection qualification mock-ups

One of the key issues in in-service inspection qualification is the representativeness of the defects used in qualification specimens. The best representativeness is achieved with realistic defects. However, present specimen production techniques have some significant weaknesses, such as unrealistic defects or additional alterations induced in the surrounding material. Specimens manufactured, for example, by weld implantation or with weld solidification defects always result in one or more extra weld interfaces. These interfaces can be detected by NDT. To overcome problems with the current specimens, a new defect manufacturing technique was developed. The new technique produces natural, representative defects without introducing additional weld metal or other unwanted alterations to the specimen.The new method enables artificial production of single, separate fatigue cracks by thermal loading. The method is based on a natural thermal fatigue damage mechanism and enables production of real cracks directly into the samples. Cracks are produced without welding or machining and without any preliminary surface treatment or artificial initiator such as a notch or a precrack. Single crack or a network of cracks can be induced into the base material, welded areas, HAZ, weld claddings, threaded areas, T-joints, etc. The location, orientation and size of produced cracks can be accurately controlled. Produced cracks can be used to simulate different types of service-induced cracks such as thermal fatigue, mechanical fatigue and stress corrosion cracks. It is shown that artificially produced thermal fatigue cracks correspond well with the real, service-induced cracks and overcome the problems of traditional qualification specimen manufacturing techniques.     

Development of a non-destructive specific activity inspection system for mushroom logs

Following the Fukushima Daiichi nuclear disaster, a specific activity inspection system is required to ensure that raw wood used for cultivating shiitake (Lentinus edodes) is safe. Although most radioactive materials adhere to tree bark, as of 2016, the current inspection method measures the specific activity of the whole log. To resolve issues with the current inspection method and contribute to the reconstruction of agriculture and forestry in the disaster area, we developed an inspection system to measure the specific activity of the bark without cutting the tree in the forest. The gamma-ray detector used in this system consisted of four radiation detection modules that could enclose the tree. The external surfaces of the four detectors were covered with lead to block background radiation from the environment. Log samples were analyzed by this system and by an HP-Ge semiconductor detector, and the results were compared. A quantification factor was determined to convert the counts measured by this system into the specific activity of the bark. The field test was conducted in the northern parts of Miyagi and Fukushima prefectures. The results confirmed that the system had reasonable measurement accuracy and could determine the direction from which radiocesium had been transported.     

Quantification of the reliability required of non-destructive inspection of PWR pressure vessels

This paper presents a method of quantifying the reliability required of non-destructive inspections of PWR pressure vessels. It gives a strategy for improving the effectiveness of ultrasonic non-destructive testing in assuring the integrity of a PWR vessel and allows targets of inspection reliability to be set in order to achieve the requisite level of vessel integrity. To do this the failure rate of PWR pressure vessels is predicted on the basis of a probabilistic fracture mechanics model. We use various models of the reliability of non-destructive inspection to discover the minimum level of reliability which is consistent with the desired integrity of the structure and to demonstrate how improvements can be made most effective.The reliability of inspection is usually modelled by a function giving the probability of leaving an unacceptable defect in the vessel. This function B(a) is really the “unreliability” of inspection and so 1 - B(a) gives the usual reliability. A reliable inspection is one which detects and correctly classifies defects according to some criterion usually based on size. A reliable inspection must use a technique which is intrinsically capable of detecting and sizing defects in the required size range and it must be reliably applied in practice.We find that, based on certain stated assumptions, that an inspection reliability of 80% of detecting and correctly sizing a defect of 15 mm through-wall extent yields a predicted failure rate of 10⁻⁷ per vessel year. The failure rate includes a frequency of a major accident such as a large loss of coolant (LOCA) of frequency 10⁻⁴ per vessel year. The predicted failure rate can be reduced to 10⁻⁸ per vessel year if the sizing accuracy of the technique is improved so that the chance of undersizing a 15 mm defect falls from 0.19 to about 0.01. However, the failure rate of the vessel is not predicted to decrease further with any subsequent improvement in sizing accuracy unless there is also an improvement in the asymptote of the reliability of inspection. This asymptote is due to factors beyond the capability of the technique such as, for example, human error.     

Considerations for in-service inspection on pressure vessel of 200MW nuclear heating reactor

The 200MW nuclear heating reactor adopts an integrated arrangement for the primary circuit. It is designed to be operated at lower temperature and lower pressure as compared to large reactors. A steel containment serves a barricade for the reactor pressure vessel. The pressure vessel has some safety characteristics, such as low stress level, low induced integral neutron flux, and high toughness etc. Among them, the most important is its LBB behavior. Based on the safety analysis for the pressure, the requirements and procedures of in-service inspection are layed-out accordingly.     

Special NDT systems applied to the in-service inspection of a BWR nozzle and safe-end welds

The present report refers to various dedicated NDT systems applied at 2 particular areas with a BWR, more specifically the inside of a feedwater nozzle for one and safe-end welds as second. At various instances the operating experiences with BWRs have demonstrated the occurrence of actual cracking phenomena in these particular areas.     

Secondary side corrosion in steam generator tubes: lessons learned in France from the in-service inspection results

Non-destructive testing (NDT) has proved to be very important in the maintenance of steam generator tubing. This is particularly true in the case of secondary side corrosion, because this type of degradation leads to various morphologies which are often complex (intergrranular attack) (IGA), intergranular stress corrosion cracking (IGSCC), or a mixture of both. Their detection and characterization by the usual NDT techniques have been achieved through numerous laboratory studies, which were conducted in order to determine the performance and limitations of NDT. Pulled tube examination in a hot laboratory was very valuable, for both NDT and fracture mechanics aspects. The eddy current bobbin coil probe, used for multipurpose inspection of tubes, allows the detection of IGA-SCC at the tube support plate elevation. In France, the use of rotating probes is not required for that type of degradation, since the repair criterion is based on bobbin coil results only. The bobbin coil is also used for detection of IGSCC occurring in free spans, within sludge deposits. The eddy current rotating probe allows, in that case, characterization of main cracks. Concerning the outer diameter initiated circumferential cracks which occur at the top of the tube sheet, only the rotating probe is used. An ultrasonic (UT) inspection was performed several times, in order to obtain information on UT capabilities. The goal of tube inspection is obviously knowledge of the status of steam generators, but also to follow up degradations and to estimate their revolution, and to verify the beneficial effect of some corrective measures, e.g. boric acid injection.     

Evolution in the design and development of the in-service inspection device for the Indian 500 MWe Fast Breeder Reactor

In-service inspection (ISI) plays a major role in monitoring the condition of nuclear power plant structures and components. Based on the information gathered during inspection and the studies carried out, it is possible to assess the extent of damage and take corrective measures to keep effects of ageing under control. In nuclear power plants comprehensive ISI is dictated by issues of increased safety to personnel and equipment, and efficiently enhances the plant life. A special emphasis has been laid on the development of robotic devices for the ISI of the indigenous Indian 500 MWe Prototype Fast Breeder Reactor (FBR) components. This paper traces the experiments and simulations in the key developments of a robotic device, for the ISI of main vessel and safety vessel of FBRs, carried out at Indira Gandhi Centre for Atomic Research, India.     

Research of in—service sipping test device

Sipping test device is used to identify the tightness of the irradiated fuel assembly during refuelling campaign.The gas is selected as the medium and the xenon-133 as the indicating nuclide,The device consists of the gas system,the γ-activity detection and measurement system,the power supply and signal system,the mechanical components and parts.The device has satisfactory functions,e.g.easy operation,indication in instrumentation,chart record and acoustic alarm,which can meet the operation demand of the nuclear reactor.     

A comparative study of PIXE and XRF corrected by Gamma-Ray Transmission for the non-destructive characterization of a gilded roman railing

Several fragments of a gilded railing were found in the archaeological excavations carried out in Écija (Spain), among the remains of a collapsed temple. The alloy composition and the gilding procedure used for its manufacture are of interest for a complete archaeological knowledge of the artefact. The common use of IBA techniques directly on the objects for their analysis is not possible due to the thick corroded patinas that they exhibit due to the burial environment. However, non-destructive analyses of a few selected fragments have been done using PIXE and XRF techniques in combination with Gamma-Ray Transmission. Indeed, as was previously shown [1], [2], bronze objects can be characterized in a completely non-destructive way using the combination of these techniques. This work, shows the applicability of that method to artefacts made of leaded copper alloy, which is the case of samples studied, for which some problems could arise from the lead segregations present in these kind of alloys. We have found that this railing contains low amounts of Sn and Sb, and that the gilding was most probably obtained using a gold leaf.     

Toward risk-based control of nuclear power plant configurations

This paper presents an analysis of risks associated with component outage configurations during power operation of a nuclear power plant and discusses approaches and strategies for developing a risk-based configuration control system. A configuration, as used here, is a set of component states. The objective of risk-based configuration control is to detect and control plant configurations using a risk perspective.The configuration contributions to core-melt frequency and core-melt probability are studied for two plants. Some equipment configurations can cause large core-melt frequency increases and there are a number of such configurations that are not currently controlled by technical specifications. However, the expected frequency of occurrences of the impacting configurations is small and the actual core-melt probability contributions are also generally small. Effective strategies and criteria for controlling configuration risks are presented. Such control strategies take into consideration the risks associated with configurations, the nature and characteristics of the configuration risks, and also the practical considerations such as adequate repair times and/or options to transfer to low risk configurations. Alternative types of criteria are discussed that are not overly restrictive to result in unnecessary plant shutdown, but rather motivate effective test and maintenance practices that control risk-significant configurations to allow continued operation with an adequate margin to meet challenges to safety.     

Probabilistic non-destructive assay of radioactive waste

Random loading of fissile material in radwaste containers may lead to significant uncertainty in the determination of the fissile content by non-destructive assay. An analytical procedure is developed for evaluating this uncertainty. The procedure is suitable for low fissile density, may be applied to single or multiple measurements and accounts for possible size distribution of the fissile particles. It is shown how the probabilistic interpretation of non-destructive assay depends fundamentally on the response function of the assay apparatus. This relationship is exploited to develop quantitative criteria for the degree of mass-resolution capability of the apparatus. These criteria provide useful guidelines for the optimal design of apparatus for non-destructive assay.     

表面弯曲的古陶瓷样品X射线荧光无损定量分析

常规X荧光分析中对样品表面有较高要求，这大大影响了利用X射线荧光法对古陶瓷无损分析的进行，本文提出了基本参数法和经验系数法中的两种较为简单的处理方法，以满足对不同大小和弯曲形状品分析的需要。     

简便快速的TGC探测器性能检测系统

介绍一个基于USB总线的用于检验薄间隙室TGC的简便快速检测系统,详细叙述了测试原理、系统的结构以及测试结果。     

Probabilistic interpretation of non-destructive assay of nuclear materials

The response of a non-destructive assay system for radioactive-waste containers depends on the spatial distribution of the assayed nuclear materials in the measured container. Therefore, interpretation of measured activity in terms of contained mass will be ambiguous unless the spatial distribution is specified. A probabilistic approach is presented by which the measured activity can be interpreted in terms of a probability distribution of the contained mass. A computationally feasible procedure is formulated for calculating the conditional probability of having a certain mass given a measured value of the activity. The procedure assumes random loading of the assayed material within the container, and accounts for variation of the mass, number and position of assayed items. The procedure is generalized to account for measurement of more than one radiation. A simple explanatory example is discussed.     

Application of gamma ray computed tomography to non-destructive testing

A gamma ray computed tomography (ψ-ray CT) system has been developed for applications to large specimens of high density materials.The system features a wide fan beam of ψ-rays, extendable up to 20 degrees, 20 channel ψ-ray scintillation detectors using bismuth germanate oxide with a counting rate being up to 10⁵ per second for reducing the mechanical scan time. Performance of the ψ-ray CT system is confirmed by measuring a test piece and a stepping motor (diameter: 5 cm; main material component: iron), for instance. It can represent these cross-sectional images with a spatial resolution of 1.5 mm. About 10 min are required to obtain these images using a 100 mCi ¹³⁷Cs source.     

A unit for inspection of materials using differential gamma-ray scattering technique

The main objectives of this research were to develop a prototype unit using the differential gamma-ray scattering technique (DGST) and to demonstrate its possible use in nondestructive inspection of materials. The unit consisted of a 5 mCi (185 MBq) ¹³⁷Cs gamma-ray source positioned perpendicularly to a 5 cm × 5 cm BGO detector. The gamma-ray beam was collimated by a 5 cm thick lead collimator with 1 cm ∅ opening while the detector was only side shielded allowing scattered gamma-rays to reach the detector from different angles. The unit was then tested with 20 cm × 20 cm × 20 cm concrete mortar containing four rebars at its corners. It was found that the integral of the differential spectrum changed corresponding to the size and position of the rebar which was in front of the source and the detector. It was also found that the integral of the differential spectrum increased with increasing degree of corrosion of the rebar. The results indicated that a portable DGST unit could be designed to be used as a tool in nondestructive inspection but the interpretation of the differential spectrum still needs further investigation.     

基于小波变换的图像增强方法在射线无损检测中的应用

基于小波变换的图像增强技术引入射线无损检测(NDT)图像处理中,并通过实验证明该技术对常规的射线NDT图像有很好的降噪效果,其处理后的图像质量明显优于一般常规方法。