基于数值模拟的核级管系中阻尼器削减

针对核级管系中减少使用或不使用阻尼器的问题,以管道力学计算专业有限元分析软件为平台,采用数值模拟计算方法,对核级管道系统进行了大量的数值模拟计算,得到了管道应力、节点位移和支吊架反力。对比分析了阻尼器削减前后的计算结果,并根据计算结果改变部分支架的功能类型、调整支架布置位置以及用刚性支架代替阻尼器,使阻尼器削减后的管系力学性能仍然满足设计规范要求。     

核级管道的应力分析

管道是核反应堆中重要的部件。本文介绍了核电站管道系统应力分析评定过程,即利用管道系统应力分析程序SYSPIPE,对管道承受的自重、内压、热膨胀、地震等载荷进行计算,根据RCC-M规范进行应力分析和评定。核级管道的应力分析不仅可以保证管道、支架、设备的安全,且可以优化设计,在核电站建造和运行中起到很重要的作用。     

核级工艺管道支吊架系列的研制

核级工艺管道支吊架是核电站一回路工艺系统核级管道的一个重要组成部分,它直接影响核电站的运行可靠性,影响核电站的建设周期和投资。按ASME-ⅢNF篇规定进行设计、研制出能满足核级管道设计要求的支吊架系列,在PC工程(巴基斯坦CHASNUPP核电站)设计中是一项必不可少的工作,也是我国今后核电事业发展中必须解决的一项重要设计。经两年多的工作,已建立起拥有57种型式、2460多种规格的部件所组成的核级工艺管道支吊架,系列完善,能满足核电站核级管道施工设计的需要。核级工艺管道支吊架主要用于安全1、2、3级工艺管道,也用于其他核级管道和有抗震要求的非核级管道。     

核级工艺管道支吊架系列的研制

核级工艺管道支吊架是核电站一回路工艺系统核级管道的一个重要组成部分,它直接影响核电站的运行可靠性,影响核电站的建设周期和投资。按ASME-ⅢNF篇规定进行设计、研制出能满足核级管道设计要求的支吊架系列,在PC工程(巴基斯坦CHASNUPP核电站)设计中是一项必不可少的工作,也是我国今后核电事业发展中必须解决的一项重要     

秦山核电厂OLE项目特殊管道支吊架改造方案研究与应用

“核2、3级管道支吊架改造”是秦山核电厂运行许可证延续（OLE）工程改造中的一项。项目中有2类较为普遍的但改造难度较大的特殊支吊架：一类是与管道轴线不垂直的刚性支撑杆支架，另一类是使用“导向支架底板”的导向支架。为了满足改造设计要求和相关法规标准，设计了2种新的标准支吊架部件，并实现了标准化和系列化，与已有的标准系列部件配合可满足改造要求。2种改造设计方案解决了项目改造的难题，同时具有改造方便、普适性强、便于推广的优点。     

CEFR事故余热排放系统部分管道应力分析

本文通过Pipestress软件计算事故余热排放系统有关管道,合理布置管道支吊架系统.使管道系统在各种预期的载荷工况下,均能满足ASME设计规范规定的应力限值,并满足机械设计和现场安装的要求.     

高温气冷堆支承冷却系统管道应力分析

本文采用管道有限元方法对高温气冷堆反应堆压力容器承重支承的冷却系统进行了管道应力分析,分析了管道的特征及应力分布特点,讨论了关键点支吊架的设置方案对应力计算结果的影响,提出了管道支吊架布置的优化方案。分析结果表明,该管道的应力计算结果满足ASME标准。     

二代改进型核电站管道系统应力分析与评定

管道是核电站中的重要部件。为了使管道满足规范要求,需要对管道进行应力分析与评定。本文分析了二代改进型核电站1级和2级管道应力分析与评定过程,论述了不同载荷下管道应力的计算方法,并分析了RCC-M规范版本的变化对管道应力分析结果的影响。最后,以岭澳核电站二期工程安全注入系统为例,对管道进行了应力分析与评定,满足了RCC-M规范的设计要求,并输出了支撑载荷、接管载荷、管道位移等接口参数。本文可以为二代改进型核电站管道系统应力分析与评定提供帮助。     

某核电厂主蒸汽管道应力分析

本文研究了某核电厂中主蒸汽系统管道的计算和评定等典型内容。此系统管道运行中承受的载荷工况多样,管道应力状态复杂。为了保证系统管道能够正常运行,在设计上需保证该系统管道的应力能够满足相关规范要求。分析采用管道力学分析软件PIPESTRESS进行,计算模型包括主回路、主蒸汽系统及相关的管道和阀门,分析包含静力和动力计算等。对计算结果依据美国机械工程师学会的ASME及相关规范进行了应力评定,并包含了LBB评定,保证了回路运行的安全。     

CEFR事故余热排放系统优化设计

为提高快堆管道设计的经济性,根据支吊架优化原则,对事故余热排放系统进行优化设计,使管道系统在各种预期的载荷工况下,都能满足ASME设计规范规定的应力限值,并减少阻尼器、弹簧支吊架的使用量。通过对CEFR的事故余热排放系统的优化设计,积累了高温管道支吊架的布置经验,为以后快堆的管道设计打下基础。     

CARR二次水管道系统应力分析与评定

使用PIPSTRESS软件对中国先进研究堆(CARR)二次水管道系统进行分析计算,针对管道系统及所连接设备的不同特点,采取不同的措施,对支吊架类型、安放位置和方向等进行了优化配置,得到适当的管道系统应力数值和接管载荷数值。结果表明,二次水系统的应力分析与评定符合规范要求。     

中国先进研究堆主回路进堆管系接管载荷优化

在已完成的中国先进研究堆(CARR)主回路系统进堆管道计算中,换热器管嘴载荷超值,需对支吊架设置进行优化.结合管道布置特点,利用PIPESTRESS软件的强大功能,找到接管载荷超值的主要原因,采用先静载荷后动载荷的方法合理调整支架,经反复对比分析,得到工程可实现的约束方案,使管嘴载荷满足了要求,从而保护了设备,提高了系统安全性能.为保护设备,管嘴附近的承重架应距设备尽可能地远,并应兼顾地震和热胀载荷对支架设置的不同要求,结合管嘴载荷、支架反力及现场安装等因素设置支架.     

Enhanced seismic criteria for piping

In situ or laboratory experiments have shown that piping systems exhibit satisfactory seismic behavior. Seismic motion is not severe enough to significantly damage piping systems unless large differential motions of anchorage are imposed. Nevertheless, present design criteria for piping are very severe and require a large number of supports, which creates overly rigid piping systems. CEA, in collaboration with EDF, FRAMATOME and IRSN, has launched a large R&D program on enhanced design methods which will be less severe, but still conservative, and compatible with defect justification during operation. This paper presents the background of the R&D work on this matter, and CEA proposed equations.Our approach is based on the difference between the real behavior (or the best estimated computed one) with the one supposed by codified methods. Codified criteria are applied on an elastically calculated behavior that can be significantly different from the real one: the effect of plasticity may be very meaningful, even with low incursion in the plastic domain. Moreover, and particularly in piping systems, the elastic follow-up effect affects stress distribution for both seismic and thermal loads.For seismic load, we have proposed to modify the elastic moment limitation, based on the interpretation of experimental results on piping systems. The methods have been validated on more industrial cases, and some of the consequences of the changes have been studied: modification of the drawings and of the number of supports, global displacements, forces in the supports, stability of potential defects, etc.The basic aim of the studies undertaken is to make a decision on the stress classification problem, one that is not limited to seismic induced stresses, and to propose simplified methods for its solution.     

蒸汽发生器非线性支承系统的抗震能力分析

计算核电厂设备的高置信度低失效概率(HCLPF)抗震能力是地震概率安全评价、地震裕度评价的一个重要步骤。以蒸汽发生器支承为研究对象,建立其详细的非线性有限单元模型,通过逐步增大地面运动水平,反复计算系统的响应,最后得到蒸汽发生器支承的抗震能力,并与通过确定性失效裕度法得到的HCLPF进行比较。结果表明,两者的计算结果差别较大。本文建议对于非线性较强的设备需采用非线性时程分析方法计算设备的HCLPF。     

Impact of structural steel flexibility and restraints gaps on the dynamic behaviour of piping

The effect of gaps present in the seismic supports of nuclear piping systems and of the flexibility of the steel structure to which intermediate supports are attached, is studied in this paper. An actual piping system is used to investigate the impact of structural steel and mechanical snubber gaps on the dynamic behaviour of piping. An evaluation is thus performed of the finite element modeling techniques employed by the designers in the dynamic analysis of piping systems.     

核安全一级高温管道系统结构分析与安全评估方法研究

为解决复杂核安全一级高温管道系统结构分析与评定工程问题，在管道分析软件与核级高温评定规范ASME-NH之间建立了一座桥梁。首先，对管道结构（直管及弯管）在不同载荷作用下的应力状态解析解进行了详细推导分析，并且与有限元数值解进行了误差分析。结果显示，给出的直管及弯管结构应力状态解析解具有很好的准确性。随后，将一维管线力学分析模型与截面三维应力状态解析解相结合，给出了高温管道系统结构分析、评定方法及应用步骤，将ASME-NH-3650规范内容明确化。      

Pipe-anchor discontinuity analysis utilizing power series solutions, Bessel functions, and Fourier series

One of the paradigmatic classes of problems that frequently arise in piping stress analysis discipline is the effect of local stresses created by supports and restraints attachments. Over the past 20 years, concerns have been identified by both regulatory agencies in the nuclear power industry and others in the process and chemicals industries concerning the effect of various stiff clamping arrangements on the expected life of the pipe and its various piping components. In many of the commonly utilized geometries and arrangements of pipe clamps, the elasticity problem becomes the axisymmetric stress and deformation determination in a hollow cylinder (pipe) subjected to the appropriate boundary conditions and respective loads per se. One of the geometries that serve as a pipe anchor is comprised of two pipe clamps that are bolted tightly to the pipe and affixed to a modified shoe-type arrangement. The shoe is employed for the purpose of providing an immovable base that can be easily attached either by bolting or welding to a structural steel pipe rack.Over the past 50 years, the computational tools available to the piping analyst have changed dramatically and thereby have caused the implementation of solutions to the basic problems of elasticity to change likewise. The need to obtain closed form elasticity solutions, however, has always been a driving force in engineering. The employment of symbolic calculus that is currently available through numerous software packages makes closed form solutions very economical. This paper briefly traces the solutions over the past 50 years to a variety of axisymmetric stress problems involving hollow circular cylinders employing a Fourier series representation. In the present example, a properly chosen Fourier series represent the mathematical simulation of the imposed axial displacements on the outside diametrical surface. A general solution technique is introduced for the axisymmetric discontinuity stresses resulting from an anchor restraint on a selected of pipe geometry. These solutions can be economically implemented on today's symbolic calculus software packages with no loss in solution accuracy when compared to often more expensive techniques such as the finite element method. Verification of the axisymmetric solution technique is illustrated by the comparison of results for the closed form solutions versus those approximated by the finite element technique. Extensions of the general axisymmetric solution technique to other geometries and applied loads are also discussed while the numerical and graphical results are tendered.     

Simplified seismic analysis methods in Belgium

Seismic design and analysis of nuclear plant systems, structures and components have requested huge effort and tremendous costs in the past two decades. The extended use of sophisticated, linear response type methods (modal analysis, spectral response) and the associated conservatism are responsible for the significant stiffening of the piping systems and the multiplication of supports and snubbers. The remedy used against the seismic risk seems worse than the pain itself, and safety might be impaired rather than improved. Indeed, system stiffening increases the average load level in normal operation (stresses, fatigue, nozzle loads, etc.); supports do not behave ideally as assumed (friction, rust, etc.) and snubbers are remarkably unreliable. On the other hand, experience with actual earthquakes shows that industrial facilities designed using very simplistic seismic techniques, or even no seismic requirement at all, suffer essentially no damage, even in the case of a large earthquake. This paradox challenges the traditional seismic design techniques, and appeals for revised seismic qualification methods of piping systems. When the assumption of the occurrence of an earthquake event is made in a plant in operation, which has not been designed against seismic criteria, the use of the standard seismic qualification techniques is still more questionable; simplified (quasi-static) techniques offer in this case a valuable and economically justified alternative. The paper describes the application of the quasi-static “modified load coefficient method” to the seismic assessment of the piping in a nuclear plant in operation, designed during the pre-seismic era.     

Reliability analysis for stiff versus flexible piping

The overall objective of this research project is to develop a technical basis for flexible piping designs which will improve piping reliability and minimize the use of pipe supports, snubbers, and pipe whip restraints. The current study was conducted to establish the necessary groundwork based on the piping reliability analysis.A confirmatory piping reliability assessment indicated that removing rigid supports and snubbers tends to either improve or affect very little the piping reliability. We then investigated a couple of changes to be implemented in Regulatory Guide (RG) 1.61 and RG 1.122 aimed at more flexible piping design. We concluded that these changes substantially reduce calculated piping responses and allows piping redesigns with significant reduction in number of supports and snubbers without violating ASME code requirements. Furthermore, the more flexible piping redesigns are capable of exhibiting reliability levels equal to or higher than the original stiffer design.An investigation of the malfunction of pipe whip restraints confirmed that the malfunction introduced higher thermal stresses and tended to reduce the overall piping reliability. Finally, support and component reliabilities were evaluated based on available fragility data. Our result indicated that the support reliability usually exhibits a moderate decrease as the piping flexibility increases. Most on-line pumps and valves showed an insignificant reduction in reliability for a more flexible piping design.     

Probability of crack-induced failure in BWR recirculation piping

The Lawrence Livermore National Laboratory (LLNL) has estimated the probability of double-ended guillotine break (DEGB) in the reactor coolant piping of Mark I boiling water reactor (BWR) plants. Two causes of pipe break are considered: crack growth at welded joints and the seismically-induced failure of component supports. For the former a probabilistic fracture mechanics model is used, for the latter a probabilistic support reliability model. This paper describes a probabilistic model developed to account for effects of intergranular stress corrosion cracking (IGSCC). The IGSCC model, based on experimental and field data compiled from several sources, correlates times to crack initiation and crack growth rates for Types 304 and 316NG stainless steel against material-specific ‘damage parameters’ which consilidate the separate effects of coolant environment (temperature, dissolved oxygen content, level of impurities), stress (including residual stress), and degree of sensitization. Application of this model to actual BWR recirculation piping shows that IGSCC clearly dominates the probability of failure in 304SS piping, mainly due to cracks that initiate within a few years after plant operation has begun. Replacing Type 304 piping with 316NG reduces failure probabilities by several orders of magnitude.