控制棒驱动机构的步跃冲击响应分析

基于柔性多体系统动力学理论建立了控制棒驱动机构(CRDM)三维实体有限元离散的刚-柔耦合动力学模型,用于计算CRDM在步跃冲击载荷下的响应。模型的方程采用模态缩减方法降低变形坐标维数,可以比非线性有限元方法更为高效地计算CRDM的运动曲线、冲击载荷和应力响应。此外,模型采用三维实体有限单元离散比杆单元离散方法具有更高的计算精度,不仅能准确地计算出大范围运动结果,而且可用于分析CRDM各部件的应力分布,找出局部应力偏大的部位。     

基于失效物理的核电厂旋转滤网驱动齿轮可靠性研究

基于失效物理可靠性理论,利用瞬态动力学方法仿真旋转滤网驱动齿轮三种运行工况下受力情况,识别齿轮应力薄弱位置为齿根位置,三种工况下齿根等效应力基本相同,基于应力-强度干涉理论的可靠度疲劳寿命计算方法,计算驱动齿轮的可靠寿命,运用Miner线性损伤累积理论建立可靠运行工况与周期计算的约束方程,为设备预防性更换周期制定提供输入。结果表明可靠度为0.95时,齿轮2个换料周期更换合理安全,可延长至4个换料周期,齿轮的疲劳损伤与转速正相关,应严格监控齿轮中高速运行时间。     

考虑应力松弛和辐照影响的堆内构件压紧弹簧疲劳可靠性评估方法

针对反应堆堆内构件压紧弹簧疲劳失效模式,在考虑应力松弛和辐照影响的条件下基于仿真方法开展可靠性评估。首先结合疲劳模型和平均应力松弛Landgraf模型,考虑辐照对疲劳参数的影响,构建了压紧弹簧疲劳寿命模型。在压紧弹簧疲劳寿命模型基础上,根据广义应力-强度干涉模型定义压紧弹簧可靠度并开展灵敏度分析。以非能动压水堆AP1000压紧弹簧为例进行案例分析,在95%置信度水平下,分别计算了可靠度为95%和50%时对应的疲劳寿命。结果表明,若不考虑应力松弛,压紧弹簧总疲劳寿命下降88.3%;从经济性角度考虑寿命预测结果较为保守。通过灵敏度分析发现对可靠度影响较大的设计变量是弹性模量和疲劳强度系数,在一定可靠度下可以通过调整设计变量对压紧弹簧的疲劳可靠性评估进行优化。      

控制棒驱动机构步跃动作运动分析

控制棒驱动机构是核电厂中的重要安全设备。其步跃动作的运行参数包括提升负荷、步距、步速等都是其核心设计指标。本文考虑重力、电磁力、水阻力和弹簧力载荷,建立了步跃运动方程。分别使用有限元方法和解析方法对步跃动作进行了动态模拟分析,获得了包括提升力、速度等时程变化曲线在内的结果,同时讨论了这些结果对设备设计的积极意义。     

核电厂机械设备可靠度计算方法探索

目前核电厂可靠性数据多是针对设备类的统计数据,针对特定设备的可靠性数据较少。使用设计数据计算特定设备的可靠度,可丰富可靠性数据库。本文在机械产品可靠度计算步骤的基础上,研究了机械产品可靠度计算常用的强度-应力干涉模型,推导出不同分布函数对应的可靠度计算公式,计算了某核电厂的钩爪零件在断裂失效模式下的可靠度。研究结果表明：使用机械设备可靠度分析计算的一般步骤对核电厂机械设备进行可靠性分析计算是适合的;使用强度 应力干涉模型计算设备的可靠度是有效的。     

快堆中心柱低周疲劳可靠性评价

采用蒙特卡罗方法对中心柱设计过程中的主要影响因素--低周疲劳进行可靠性评价,为中心柱包覆层设计提供设计依据和可靠性支撑。使用ANSYS软件对中心柱进行热分析和结构分析,利用ASME规范对其累积疲劳损伤进行评价,采用拉丁超立方抽样方法对其进行可靠性计算。计算结果表明：中心柱低周疲劳可靠度为0.808,在2.5%的显著水平下中心柱低周疲劳破坏的敏感因素为紧急停堆次数、焊缝、中子辐照,建议在中心柱外侧增加包覆层。     

压水堆控制棒驱动线的冷态步跃试验

本文采用 7T17S 信号处理机的幅值分析程序和迈因纳线性损伤理论,对驱动轴在步跃时撞击载荷下的高应力部位进行了疲劳分析。     

旋转机械转子可靠性设计分析

本文在查阅了有关旋转机械转子大量试验数据的基础上,从设计角度分析了旋转机械转子系统的各种失效模式及其影响;首次引入了可靠性设计方法对旋转机械转子零部件主要失效模式的初始可靠度及失效率进行了计算,解决了定量可靠性分析中所需参数很难确定的问题,对旋转机械转子系统进行了定量的危害性分析,得出了旋转机械转子系统可靠性设计中初始可靠度最低的失效模式是转子振动过大,危害度最高的失效模式是转子强度破损,这为旋转机械转子系统的可靠性试验与寿命试验的开展指出了方向.     

CIS投用时RPV的承压热冲击分析研究

华龙一号堆腔注水冷却系统(CIS)投入时,反应堆压力容器(RPV)外壁将经历剧烈的温度波动并同时承受较高的内压载荷。为了保证RPV在这种工况下的结构完整性,采用断裂力学有限元方法进行了RPV承压热冲击(PTS)计算及评定,通过疲劳裂纹扩展计算获得了堆芯筒体和下封头区域寿期末的最终裂纹尺寸。PTS瞬态载荷作用下的应力强度因子修正值与相应限值的最大比值约为0.874,满足RCC-M规范要求。研究结果表明,RPV在CIS投用时不会出现断裂失效。     

核级承压设备密封结构的有限元分析

在AP1000反应堆系统中,很多设备具有承压的功能,其密封性能直接关系到系统能否正常运行,因而密封失效是较之弹塑性失效、疲劳失效等更为基本的失效形式。在ASME规范中采用的密封结构设计方法是华脱尔斯法,此方法采用了一些保守的经验和假设,无法对密封结构处的变形和应力进行细致的计算。本文采用ANSYS有限元分析软件对核承压设备典型的密封结构进行了建模计算,提出了在有限元模型中螺栓预紧力和垫片的等效处理方法,能够对密封结构处垫片的回弹量、法兰的变形及应力分布进行预测。模型分析了采用华脱尔斯法进行密封设计时的设计余量,得到了垫片回弹量与设备内压之间的关系,对于核级承压设备密封结构的设计具有一定的借鉴意义。     

Some aspects of the reliability-based design of reactor containment structures

A rational procedure for the design of reactor containment structures is carried out within a probabilistic framework. Various risk concepts such as the return period, non-encounter probability and the reliability function are discussed. Internal load conditions caused by system failure such as LOCA pressure loads, and external load conditions caused, for instance, by impact due to aircraft crashes, external pressure waves and natural hazards such as earthquakes and severe storms, are described by extreme value distributions of the largest values of the Fisher-Tippett types. Statistical and physical arguments are given to support their application. The occurrence of these rare events with respect to time is modeled by a Poisson process. The ultimate strength of a PWR containment structure for the steel (liner) shell is also modeled by an extreme value distribution (of the smallest values). As a good approximation the load action of the shell structure is determined by linear elastic analysis. The failure criterion considered here is that of reaching the ultimate tensile strength at one point of the structure. A numerical example of the reliability analysis of a steel shell structure under internal overpressure is carried out.     

Investigation on the Fatigue Characteristic in Support Structure of HL-2M Tokamak

In order to obtain enhanced plasma parameters a complete new tokamak HL-2M is now under construction in Southwestern Institute of Physics. To assure the structural safety of the device for the entire operation cycle, one of the most important issues is the lifetime-limiting effects due to the pulsed operation mode. Fatigue is one of the major failure modes to be considered in mechanical design, and pulsed operation imposes stress with significant alternating components on the support structure （SS）. Therefore, the reliability of the whole device is strongly affected by the stress and fatigue characteristic of the SS as the interface structure. This article introduces the SS design and details the fatigue life calculation methods based on the different characteristics of the sub-structures. The fatigue life in hazardous areas of the toroidal field coils anti-torque structure （TFCs-ATs） has been determined by non-linear analysis results. And with the stress- time history data of the vacuum vessel ＆ poloidal field coils support structure （VV＆PFCs SS）, the fatigue analysis of the hot spots has been completed based on rain-flow counting method and linear cumulative damage method. The calculated minimum fatigue life on TFCs-ATs and VVSzPFCs SS is 4.743E＋05 and 1.805E＋06 cycles, respectively. And the calculated fatigue life on sub-structures can meet the required life for HL-2M tokamak： 1.0E＋05 cycles.     

Behaviour of materials subjected to an impact force and new evaluation method for impact strength

The size dependence of the amplitude of a stress pulse produced in a rod subjected to an impact force is theoretically considered. Impact fatigue experiments were performed to see the size dependence of the strength of structural materials. According to these results, impact fatigue life of a short specimen was shorter than that of a long one. Based on these considerations, it is shown that the superposition of stress waves with reversed phase is effective to improve the impact fatigue life. In addition, a new method is proposed to evaluate the impact strength of materials with stress unit. By this method, influences of strain rate on the impact tensile strength I_m,t and impact bending strength I_m,b are investigated for carbon steel, aluminium alloy and PMMA using their dynamic stress strain relations which are measured directly on each specimen.     

Probabilistic fracture mechanics

This paper develops the methodology for probabilistic fracture mechanics analysis (PFM) of structural components with crack-like imperfections. Details are given for the development and application of both a simple nomographic method and a basic numerical tool for PFM applications. The tool is a computer program that uses Monte-Carlo simulation to predict the probability distribution of a structural performance parameter from known distributions of input parameters used to model the problem. The structural performance parameter might be the strength margin (strength minus stress), the life ratio (actual fatigue life divided by design fatigue life), or any other relevant model of the failure modes. Two illustrative applications based on linear elastic fracture mechanics are included to demonstrate the utility of PFM to problems of interest to the electric power generation industry.The first example selects the mean yield strength of an alloy in order to minimize the probability of failure for a hypothetical component with two failure modes, yielding and brittle fracture. The example shows that no single value of mean yield stress or of yield-related safety factor, such as specified as part of conventional engineering practice, suffices to minimize failure for all combinations of working stress and flaw size distribution. PFM analysis is required to compute the optimum value of mean yield stress for a given working stress and material quality (flaw size distribution). A second example is presented for which the residual life of a turbine rotor is assumed to be related to three parameters. The parameters are applied stress, material crack growth rate, and initial flaw size. Known variations of the input parameters are translated into variations in residual life. The residual life distribution is required to formulate improved fatigue design criteria. The effects on the turbine life distribution of mutual interdependence of the input random variables and of finite crack initiation life are examined. The second example points out the need for and current unavailability of required input data. It is recommended that data collection efforts be increased to quantify the variational characteristics of the required input parameters, as well as mean, typical, or worst-case values.     

Probability-based assessment and maintenance of welded joints damaged by fatigue

This paper presents a probabilistic reliability assessment procedure for steel components damaged by fatigue. The study combines the structural reliability theory with a maintenance strategy. The fatigue assessment model is based on a modelisation of the fatigue phenomenon issued from the principles of fracture mechanics theory. The safety margin includes the crack growth propagation and allows to treat fatigue damage in a general manner. Damaging cycles and non damaging cycles are distinguished. The sensitivity study of the different parameters shows that some variables can be taken as deterministic. Applications are made on a welded joint ‘stiffener/bottom-plate' of a typical steel bridge. The model is then used for taking into account inspection results. Non destructive inspection (NDI) techniques are also used for updating failure probabilities. The results show their ability to be inserted in a maintenance strategy for optimizing the next inspection time. This has led to define cost functions related to the total maintenance cost; this cost is then minimized for determining the optimal next inspection time. An example of welded joint cracked by fatigue highlights the different concepts. The approach presented in the paper is not only restrained to fatigue problems, but can be applied to a wide variety of degrading phenomena.     

ACP100集成式堆顶结构可压缩气体对流传热数值模拟

反应堆集成式堆顶结构的功能之一是通过冷却气体的对流传热为控制棒驱动机构提供冷却。针对ACP100反应堆集成式堆顶结构建立完整的模型并划分流场网格,基于ANSYS/CFX软件分别对可压缩气体和不可压缩气体进行计算,并严格对比分析了其结果,重点研究气体可压缩性对对流传热计算结果的影响。计算结果表明,气体可压缩性对速度、温度分布和压降有较大影响,忽略气体可压缩性所预测的控制棒驱动机构表面最高温度偏低,控制棒驱动机构间隙气体最大流速和压降也偏低。     

贯穿件J形坡口焊接残余应力分析

核电站反应堆压力容器（RPV）顶盖控制棒驱动机构（CRDM）管座J形坡口焊缝在一回路高温高压水环境下存在应力腐蚀开裂（SCC）的风险，而焊接残余应力是SCC的主要驱动力。使用二维轴对称模型有限元方法对CRDM中心管座J形坡口进行焊接残余应力分析。为了探索一种简单、高效和保守的方法，研究了热源简化、焊缝形状简化、屈服强度、相变和强化行为对焊接残余应力的影响。结果表明:双椭球热源与均匀热源得到的残余应力结果基本一致；焊缝形状由鱼鳞状简化为方块模型对焊接残余应力结果影响不大，但是与合并焊道的结果相差较大；采用低屈服强度得到的残余应力结果并不保守；在ANSYS软件中，固液相变对残余应力结果影响不大；等向强化模型的结果比随动强化模型的结果保守；在工程上，建议采用均匀热源、方块焊道模型和等向强化模型进行焊接模拟。      

Creep-fatigue evaluation of normalized and tempered modified 9Cr---1Mo

Creep-fatigue is a fatal failure mode of the high temperature structural materials of liquid metal fast breeder reactors (LMFBRs). In this report, two important issues are discussed for creep-fatigue evaluation of normalized and tempered modified 9Cr---1Mo (modified 9Cr---1Mo(NT)) steel which is a promising structural material for the steam generator of large-scale LMFBRs in Japan. Several evaluation methods based on the ductility exhaustion concept are discussed for the prediction of tension strain hold creep-fatigue damage of this material. A time-fraction type of linear damage summation concept based on a new ductility exhaustion theory is proposed from the point of view of its appropriate conservatism for time extrapolation and its simplicity.Also, a life reduction mechanism of low cycle fatigue with strain hold at the compression side is discussed, based on the data observed by a scanning type electron microscope. Creep damage or the tension mean stress caused by compression strain hold hardly reduce the low cycle fatigue life of this material. A new concept based on the location of oxidation on the test specimen surface can explain the reduction in low cycle fatigue life of modified 9Cr-1Mo(NT) steel.     

Optimal design of the positions of the hoops for a hydraulic pipelines system

This paper focuses on decreasing the vibration and improving the dynamics performances for a hydraulic pipelines system. The parametric model of the hydraulic pipelines system under the random excitations is constructed and the dynamics characteristics are obtained by the finite element analysis, then an optimization model is presented to reduce the vibration by rationally designing the positions of the hoops in the pipelines system. The dimensions determining the locations of the hoops are defined as design variables, and the dynamics performances, such as the maximum displacement, the maximum axial stress, the maximum shear stress, the maximum axial strain, the maximum hoop strain, the maximum shear strain and the failure probability of the first passage are regarded as nonlinear constraints whereas the failure probability of cumulative fatigue damage is viewed as an optimization objective. The results show that the dynamics performances of the hydraulic pipelines system are distinctly improved by the optimization procedure, such as, the maximum displacement and velocity are reduced by 67.5% and 58.6%, respectively, and the maximum axial stress and strain are both decreased by 61.5% while the maximum shear stress and strain are reduced by 66.1%, and the failure probability of the first passage and cumulative fatigue damage are allayed by more than 99%, etc.