压水堆燃料棒在轴向流作用下的随机振动响应研究

基于随机振动理论,建立了在轴向流作用下压水堆燃料棒随机响应的纯理论分析方法。将流体力考虑为沿燃料棒轴向位置的脉冲随机荷载,结合模态分析技术,从功率谱分析法推导出燃料棒振动均方根响应的表达式。提供了一套不依赖燃料组件流致振动实验的纯理论分析方法,重点分析了等效流速、湍流强度、相关长度系数等几个主要流场参数对结构均方根响应的影响。结果表明,本文计算模型的精度满足工程分析要求,燃料棒响应随等效流速、湍流强度和相关长度系数的增大而增大;其中响应对于等效流速和相关长度系数的变化较为敏感,而与湍流强度呈线性变化关系;在压水堆运行中的燃料棒均方根幅值约处在μm量级。     

核电厂房三维有限元模型考虑土-结构相互作用的简化方法

为将集总的半无限地基动刚度等效离散给三维厂房结构的筏板基础,借鉴简化的集中质量厂房模型考虑土-结构相互作用(SSI)分析方法,通过力矩等效,推导三维厂房结构考虑SSI的弹簧-阻尼器等效离散模型,并通过模态分析和动力时程分析验证了此等效离散方法的正确性和合理性。这种第一步求解集总的地基动刚度,然后基于通用的有限元软件在三维厂房筏板基础施加弹簧-阻尼器的方法,相对于其他人工边界法更简便易行,便于工程应用。     

反应堆压力容器断裂力学分析中弹塑性有限元方法与工程方法的比较

通过ABAQUS程序对反应堆压力容器简体裂纹进行了弹塑性断裂力学有限元分析,计算了在热冲击(PTS)瞬态作用下裂纹尖端的应力强度因子KI、J积分.同时,与工程方法计算的结果进行了比较,结果表明:工程方法在PTS计算分析时较三维弹塑性断裂力学有限元方法的计算值偏大,计算结果保守.     

半悬臂式燃料元件在间隙限制约束下非线性振动的等效方法研究

半悬臂式燃料元件为上端固定、下端间隙限制的结构形式,该结构可节省使用和安装空间,具有在小型反应堆应用的潜力。相较于传统的两端固定结构,半悬臂式燃料元件下端呈现弱约束特性,在振动工况下存在碰撞接触非线性行为。针对间隙引起的非线性问题,采用弹支梁等效方法,将底端间隙配合等效为弹簧结构。本文将半悬臂式燃料元件的非线性振动过程通过单摆—悬臂梁模型进行等效,推导出半悬臂式燃料元件振动周期公式,结合弹支梁振动方程,可快速准确得到等效弹簧刚度,从而建立半悬臂式燃料元件在间隙限制约束下非线性振动的等效方法。通过半悬臂式燃料元件抗震分析,对本文方法与传统有限元方法进行对比,结果显示：该案例计算时间大幅度减少,本文计算方法所用时间仅为传统有限元方法的1/74;两种方法的结果表明：在关键部位的振动响应基本一致,初步验证了本方法可快速有效求解具有间隙约束的半悬臂式燃料元件振动问题,为小型反应堆提供了快速设计工具。     

一种栅元等效均匀化计算的改进方法及其验证

传统的栅元等效均匀化计算方法一般采用体积-通量权重法,保证了在反射边界条件下各群通量和反应率的守恒,但该方法在边界入射流较强时有一定误差。本文提出了一种改进的等效均匀化方法,该方法以栅元边界入射流与出射流之间的响应等效作为理论基础,认为不需要保证等效前后的平均通量守恒,而应保证入射流与出射流以及各群反应率之间的响应关系守恒。和原有均匀化方法相比,改进方法几乎不增加任何计算量。对带反射层的平板问题及C5G7MOX基准例题分别进行测试计算,结果表明,改进的栅元等效均匀化方法对特征值和棒功率分布的计算精度有明显的改善作用。     

基于粘弹性人工边界的核电工程地基动力阻抗分析

设置人工边界是采用3D有限元技术实现复杂地基抗震分析的有效手段。采用Fortran语言开发大型有限元程序ANSYS的接口程序,实现粘弹性人工边界的设置及等效荷载的施加。采用经典数值算例对粘弹性人工边界及波动输入程序的可用性进行验证,其求解效率和计算精度均较理想。将该方法和程序应用到核电场复杂地基动力阻抗分析中,并将计算结果与成熟的通用程序计算结果进行对比。     

反应堆屏蔽水箱失水过程的水箱表面辐射研究

基于蒙特卡罗方法的MCNP程序,研究了反应堆屏蔽水箱失水过程中的水箱表面辐射剂量的变化情况.在屏蔽计算时为了节省计算时间,运用了堆芯均匀化方法,通过调整均匀化堆芯的核素密度和等效直径,使得均匀化等效堆芯在屏蔽水箱表面的中子和光子注量率与非均匀堆芯近似相同.     

板元件过热熔融物迁移过程的HBI计算方法研究

对比不同函数近似形式在过冷壁面与不同熔融物过热度下与精确解析解间的误差,选取适合计算过冷壁面上过热熔融物凝固问题的函数近似形式。结合准稳态方法研究3层结构下熔融物凝固过程中凝固层厚度随时间的变化。计算结果与数值计算结果、平衡态计算结果以及实验结果符合较好,证明采用准稳态热平衡积分方法求解3层有限结构的过热熔融物凝固问题是可行的。     

压水堆核电厂AFA3G燃料组件径向等效导热率研究

在乏燃料组件的运输和贮存过程中,如何有效地评估组件及承载设施对衰变热的响应是一项重要的工作。由于组件的结构复杂,考虑承载设施后的有限元模型会过于庞大,超过现有计算资源的承受能力。提出的改进方法将燃料组件等效为简单的固体导热模型,利用有限元方法得出AFA3G燃料组件的径向等效导热率,大大减低了计算成本,并与文献报道的国际通用的方法进行了比较。结果表明,在工程设计中,改进方法计算得到的等效导热率更为保守与合理。     

压水堆燃料组件结构搅混格架动态屈曲仿真研究

结构搅混格架作为压水堆燃料组件中的关键部件,由于结构复杂,一直是燃料组件设计的重点和难点。本文采用有限元分析软件建立17×17结构搅混格架有限元分析模型,对其在冲击载荷作用下动态屈曲过程进行了数值模拟研究,得到了不同初速度冲击下的冲击载荷、回弹速度、冲击位移变化曲线,通过以上参量开展格架动态屈曲判定准则的对比验证研究,确定了结构搅混格架动态屈曲的临界载荷。同时基于冲击板作简谐振动的假设,采用周期法计算格架动刚度,基于能量原理建立格架等效阻尼的计算方法。通过与试验结果的分析对比,验证分析方法的合理性,用于指导新型燃料组件格架分析与设计。     

Thermal stresses in rectangular plates: Variational and finite element solutions

This paper deals with the development of an approximate method for the analysis of thermal stresses in rectangular plates (plane stress problem) and an evaluation of the relative accuracy of the finite element method. The stress function is expanded in terms of polynomial coordinate functions which identically satisfy the boundary conditions, and a variational approach is used to determine the expansion coefficients. The results are in good agreement with a finite element approach.     

Stress and fatigue analysis of SNR-300 mixing devices, including optimizations and thermal shock tests on internal structures

Mixing of sodium streams which have different temperatures, causes high frequency random temperature fluctuations and causes, as a consequence together with the other normal transient loadings, fatigue problems. INTERATOM has developed for this purpose and especially for high temperatures a special multi-jet-mixing device for piping systems on the basis of thermohydraulic tests, elastic finite element analyses and fatigue evaluations according to the ASME-code as well as using results of thermal shock tests on internal structures. The dynamic behaviour of gas bubbles in horizontal shock-cavities of internal shell structures gave rise to the incorporation of degasing features. The influence of essential thermohydraulic parameters on the mixing efficiency and on the stresses due to thermal striping as well as on the fatigue is described. Fatigue problems on internal shell structures lead to an optimization of them with respect to thermal stresses. On the basis of similarity considerations three axisymmetric models for the elastic finite element analysis of the external tee-structure are developed and compared between each other with respect to the maximum stresses. The damping characteristic of shock-cavities on temperatures and stresses in the tee-crotch are described. An advanced mixing device is presented, and recommendations for the design and analysis are pooled.     

Soil-structure interaction for transient loads due to safety relief valve discharges

Dynamic responses of BWR Mark II containment structures subjected to axisymmetric transient pressure loadings due to simultaneous safety relief valve discharges were investigated using finite element analysis, including the soil-structure interaction effect. To properly consider the soil-structure interaction effect, a simplified lumped parameter foundation model and an axisymmetric finite element foundation model with viscous boundary impedance are used. Analytical results are presented to demonstrate the effectiveness of the simplified foundation model and to exhibit the dynamic response behavior of the structure as the transient loading frequency and the foundation rigidity vary. The impact of the dynamic structural response due to this type of loading on the equipment design is also discussed.     

快速疲劳分析方法在核电厂疲劳监测系统中的应用

疲劳监测系统通过对一回路易发生热疲劳关键管道和设备进行运行参数采集,采用快速疲劳分析方法对被监测管道和设备进行实时疲劳计算,从而获得真实疲劳损伤情况。该快速疲劳分析方法以格林函数法为基础,通过编制计算程序实现热应力和疲劳使用系数的快速计算。通过与有限元分析结果进行比较,验证了该快速疲劳分析方法具有高效、快速、准确的特点。      

基于虚拟激励法的超多点多维激励下管路简化疲劳寿命分析

针对超多点随机振动边界条件下传统随机振动模块计算规模不适用,且传统疲劳寿命分析方法受建模工作量大制约而无法快速完成疲劳寿命分析的问题,本文基于虚拟激励法提出了一种针对管路系统的超多点多维激励的简化疲劳寿命分析方法。通过对比虚拟激励法和传统随机振动模块计算的结构动力学响应,验证虚拟激励法的适用性,并使用管路简化疲劳寿命分析方法和传统疲劳寿命分析方法分析直管结构和三通连接位置的疲劳寿命。结果表明,虚拟激励法计算的随机振动响应精度与传统随机振动模块一致,说明本文方法可突破传统随机振动模块对振动激励点数和频率点的限制;本文方法无需建立详细有限元模型,直管结构的应力及寿命分析结果与精细模型基本一致,三通连接位置的应力及寿命分析结果相比精细模型更加保守。本文研究可为复杂振动管路系统的快速疲劳寿命分析提供理论指导。      

Structural analysis of a three-dimensional perforated plate by the finite element method with test correlation

An application of the finite element method to a three-dimensional perforated plate structure is presented using a nested modeling technique. Stresses calculated by a general three-dimensional finite element computer program were compared with those obtained from a model test. The structure considered in this analysis is a plenum cover of a pressurized water reactor internal which is a circular perforated plate stiffened with welded cross ribs. This type of structure is common in reactor internals. The nested model analyses consist of two finite element models; one is for the overall structure model and the other for an isolated portion of the structure with refined grid system for more accurate stress calculation. The first model was analyzed to obtain the nodal displacements under the applied loads. Then the second model was run using the displacement boundary conditions obtained from the first model analysis. A fully instrumented Plexiglas model test was conducted to verify this method. Comparison between the test results and the calculated stresses from the second model analysis showed good agreement.     

中国实验快堆堆内构件应力分析与评定

本文是中国实验快堆堆内构件主要部件的应力分析与评定汇总报告.主要构件包括堆内支承结构、堆芯支承结构、堆内热屏蔽等7类设备.堆内各部件采用有限元方法按其特点进行整体分析或部件分析.文章首先建立结构的计算模型,然后,对有限元计算模型进行在自重、流体流动压差、冷却剂流动引起的结构振动和温差载荷条件下的静态分析计算和结构的模态分析以及地震载荷下的动态分析.最后,按规范要求对堆内各结构在承受的各种载荷条件下进行载荷组合与评定.     

The challenges in predicting the fatigue life of dissimilar brazed joints and initial finite element results for a tungsten to EUROFER97 steel brazed joint

This paper summarises the challenges in accurately predicting stress states in dissimilar brazed joints and presents initial results from a finite element analysis of a tungsten to EUROFER97 brazed joint. The residual stresses due to joint manufacture are presented and differences in stress distribution due to thermal and mechanical loading highlighted. The results from this analysis correlate well to experimental results from previous research however further validation is required. The challenges in developing fatigue assessment procedures for dissimilar brazed joints are also discussed. These fatigue assessment procedures are introduced and a validation strategy for such procedures is proposed.     

Some steady and unsteady heat conduction solutions in orthotropic circular cylinders

Simple, approximate solutions are obtained in the case of prescribed axially symmetric boundary conditions. The results are compared in one example with values obtained using a finite element code and good agreement is shown to exist. The problem is of interest in several fields of engineering and applied science, for instance when performing thermal analysis of nuclear fuel elements which in some instances exhibit thermally orthotropic characteristics.     

A comparison between Japanese and French A16 defect assessment procedures for thermal fatigue crack growth

This paper presents the results of a benchmark on thermal fatigue crack growth evaluation for a thick-wall cylinder subjected to cyclic thermal transients. The simplified crack growth evaluation methods of both JNC in JAPAN and A16 procedures proposed by CEA in France are presented. The predictions obtained using both methods are compared with the experimental data. The JNC method, which accounts for the non-linear stress component provides predictions of crack advance in a good agreement with the experimental data. In contrast, significant differences are observed between the A16 predictions and the experimental data. The discrepancies are mainly due to the non-linear stress component which is not accounted for in the A16 method. When using the JNC stress intensity factor solution determined by finite element analysis to account for the non-linear stress component, the A16 method well predicts the thermal fatigue crack growth behavior.