承压热冲击对核压力容器强度的影响

主要研究核压力容器承压热冲击（PTS）的瞬态过程,对热应力和机械应力产生的耦合效应进行分析,评价承压热冲击事件对容器强度的影响。利用有限元方法,建立合理的三维计算模型,模拟核压力容器进出口水管附近的承压热冲击的过程和特性。承压热冲击的历程大体在几百秒量级。热冲击产生的应力大压力变化产生的应力,最大应力出现在接管和容器的接口附近,在这些区域产生局部塑性区。     

反应堆压力容器承压热冲击分析研究

依据RCC-M规范和美国NRC 10CFR50.61,对存在假想裂纹的反应堆压力容器堆芯带区进行承压热冲击分析研究.计算核电厂寿期末的基准温度,并采用承压热冲击筛选准则进行评定;计算了承压热冲击瞬态作用下裂纹尖端的应力强度因子,并按RCC-M规范进行评定.     

CRDM承压壳体多故障模式下的动态可靠性分析

为研究控制棒驱动机构（CRDM）的结构可靠性规律，考虑CRDM承压壳体的多失效模式，根据应力强度干涉理论建立与CRDM步跃动作次数相关的结构动态可靠性模型。用顺序统计量描述强度失效模式下应力幅值的动态分布模型，基于Miner累积损伤理论和疲劳等效应力分布模型建立结构疲劳寿命和累积损伤分布与步跃冲击载荷作用次数的关系。研究结果表明，在步跃冲击载荷作用下，承压壳体前期的结构可靠度主要由强度失效模式的可靠度决定，当步跃动作达到一定次数时，疲劳失效模式的失效率开始显著增大；相对于疲劳失效模式，强度失效模式的可靠度对应力均值的变化更加敏感。该结果可对CRDM承压壳体的可靠性设计和维修管理提供参考。     

核主泵主轴机械-热耦合疲劳分析

文章研究机械应力与热应力对核主泵主轴疲劳寿命的影响。机械应力分析表明,在正常工况下,单纯的机械荷载不会导致主轴出现疲劳裂纹。文章深入考察了主轴服役环境下的特殊载荷-热冲击导致的热应力。该主轴服役环境存在着一个十分明显的冷热水混合区域,由于该区域的存在使得主轴热应力发生较大程度的应力波动。研究热分析中关键的参数-对流换热系数的变化范围及规律,重点讨论了影响热应力的几个因素:对流换热系数、外界温度、热冲击时间。在温度场分析的基础上,得到了热应力的分布情况。热应力的波动是疲劳裂纹产生的最主要的原因。文章特别考察了对流换热系数对热应力的影响程度指出在一定范围内,减少对流换热系数可以有效地降低热应力从而提高主轴疲劳寿命。     

LOCA下具有表面裂纹的反应堆压力容器承压热冲击分析

失水事故（LOCA）瞬态下,具有半椭圆形表面裂纹的反应堆压力容器（RPV）承压热冲击（PTS）问题被研究。采用有限元方法计算瞬态过程的热-应力响应;采用影响函数法计算应力强度因子,分别对母材和堆焊层内的应力进行分解,从而解决了由于堆焊层存在造成的应力拟合困难带来的计算偏差。编制了相应的断裂分析程序,对LOCA下RPV的结构完整性进行了分析。结果表明,在研究的LOCA下,整个瞬态过程中RPV应力强度因子均未超过材料断裂韧性,压力容器结构安全。本文研究为RPV在PTS下的结构完整性评估提供理论指导。     

核一级承压设备疲劳分析方法

基于Miner线性累积损伤理论和雨流计数法,得到单载荷历程作用下疲劳分析的方法,并根据核一级承压设备的特点和核承压设备分析规范的要求,给出了一种适用于核一级承压设备疲劳分析的方法;结合设备实际运行情况,提出了瞬态分组组合的优化疲劳分析的方法,并给出一个案例.结果表明,瞬态分组组合使疲劳分析与设备实际运行情况更加接近,计算结果更加精确.     

瞬态过程中闸阀的流场温场及形变分析

闸阀是反应堆一回路系统的重要部件,瞬态过程中流体温场的变化会影响阀体的温场变化,进而影响阀门的密封情况。本文使用计算流体动力学方法对包含部分管路系统的闸阀进行瞬态三维流固耦合分析。通过对闸阀内流体的流场和温场的模拟计算,获得了瞬态过程中闸阀阀体温场的变化以及由于温场变化导致的热变形和热应力;在此基础上对不同边界条件和不同阀门结构进行了计算分析和评价,其结果可供闸阀设计参考。     

船用堆燃料棒包壳疲劳寿命分析

船用堆瞬态变工况下燃料棒包壳温度和冷却剂压力波动较大,引起包壳的疲劳损伤,因此包壳疲劳寿命分析至关重要。本文利用ANSYS软件模拟船用堆瞬态变工况下燃料棒的热机械行为,结合锆包壳疲劳寿命设计曲线,考察包壳温度、冷却剂压力、燃料棒内压以及辐照对船用堆燃料棒包壳疲劳寿命的影响。计算结果表明,瞬态变工况使得包壳疲劳寿命有很大降低;包壳温度变化与冷却剂压力变化相比,前者对包壳疲劳寿命的影响小;辐照会降低包壳疲劳寿命。在不影响核动力船舶机动性的前提下,可采取一些必要的措施来降低包壳的疲劳损伤。     

核一级三通管热疲劳研究

钠冷快堆在启动和停止过程中会产生大的热应力,多次循环之后容易产生热疲劳损伤,特别是在三通管连接区域。本文将研究不同角度对三通管热疲劳性能的影响。通过ANSYS计算不同角度三通管道的热应力,确定三通管道的热疲劳寿命和疲劳损伤系数。给出了疲劳许用强度与三通管角度的函数关系。结果表明,随着角度的减小疲劳强度降低。此结果对核一级管道设计中选取三通管道的角度具有一定的参考价值。     

温度梯度对金属波纹管力学性能影响分析

高温熔盐调节阀中金属波纹管是保证其正常运行的重要部件,波纹管外侧被熔盐介质包围,承受外压、轴向位移及高温载荷,且波纹管轴向存在较大温度梯度,为调节阀中薄弱元件。本文应用有限元软件ANSYS,材料模型选择理想塑性材料模型,计算单元为热固耦合单元,对比分析了U形和V形波纹管在各设计工况下的应力分布,结果表明,位移载荷是两种波纹管失效的主要原因。位移载荷在两种波纹管中引起的应力大小基本一致,但V形波纹管在设计压力、温度载荷作用下的应力显著小于U形,故调节阀中使用波纹管类型选择为V形。此外,对V形波纹管在多工况下的应力分布、塑形应变及极限位移载荷进行了计算,对比分析了设计温度载荷、阀体存在保温层时温度载荷及常温温度载荷对波纹管的影响,结果显示,高温下波纹管极限位移载荷约为常温的三分之一,但阀体外部添加保温层,虽然使得波纹管温度升高,但对波纹管极限压缩载荷影响并不大。     

A Lower Rigid Support Structure for the HT—7U Vacuum Vessel

Vacuum vessel of the HT-7U is a fully welded toroidal structure with a noncircularcross-section nested in the bore of the TF coils. According to the requirement of the physicsdesign, sixteen horizontal ports on outboard mid-plane and thirty-two vertical ports on the topand bottom are designed for diagnostics, plasma heating, current driving, vacuum pumping andgas puffing. Bellows on these port necks are used for flexible components to absorb the relativedisplacement in radial and vertical directions due to external load, thermal expansion or contrac-tion and assembly tolerance, and also used for isolation of mechanical vibration. For the supportsystem of vacuum vessel it should be not only strong enough to withstand forces acting on thevessel interior components and the vessel itself due to the dead weight and electromagnetic inter-actions during plasma disruption, but also sufficiently flexible to be suited to thermal expansionduring baking. In order to solve this contradiction a new kind of low rigid s     

Thermal fatigue strength of type 304 stainless steel in simulated BWR environment

Thin-walled cylindrical carbon steel specimens were thermally fatigued in a pressurized autoclave. Since high and low temperature pure water were alternately supplied into the autoclave, the specimens were subjected to homogeneous thermal stress through the wall thickness. The thermal fatigue life was defined as the number of cycles to crack penetration to the inside of the cylindrical specimen. The thermal fatigue strength was compared with the mechanical fatigue strength performed in air and in high temperature water. Even if taking account of the Higuchi-Iida formula, which considers the effects of strain rate, dissolved oxygen concentration and water temperature on fatigue life, the thermal fatigue lives of carbon steel were found to be slightly shorter than the mechanical fatigue lives.     

Thermal transient simulation tests of a sodium valve

The feasibility of thermal transient testing of sodium components using a fluid other than sodium is considered. Simulation of thermal transient conditions that may exist in the sodium system is considered to be, in general, achievable in a special test fixture, if the thermal and hydraulic conditions of the fluid to be used are properly selected. This feasibility is demonstrated for the 28 in. FFTF hot-leg isolation valve by introducing a high-speed gaseous nitrogen flow into an annulus formed by the valve body and a cylindrical pipe insert. The structural wall temperature distributions were estimated first for the sodium system, and the simulation was established by equating the transient heat transfer rates as a function of time at key locations in both real sodium and simulating nitrogen systems. Remarkably good simulation test results were achieved.     

Structural analysis and optimization for ITER upper ELM coil

ITER ELM coils are used to mitigate or suppress Edge Localized Modes (ELM), which are located between the vacuum vessel (VV) and shielding blanket modules and subject to high radiation levels, high temperature and high magnetic field. These coils shall have high heat transfer performance to avoid high thermal stress, sufficient strength and excellent fatigue to transport and bear the alternating electromagnetic force due to the combination of the high magnetic field and the AC current in the coil. Therefore these coils should be designed and analyzed to confirm the temperature distribution, strength and fatigue performance in the case of conservative assumption. To verify the design structural feasibility of the upper ELM coil under EM and thermal loads, thermal, static and fatigue structural analysis have been performed in detail using ANSYS. In addition, design optimization has been done to enhance the structural performance of the upper ELM coil.     

Experimental study on fluid mixing phenomena in T-pipe junction with upstream elbow

Temperature fluctuation in fluid causes high cycle thermal fatigue in structure materials according to temperature distributions and time variations. A mixing tee is one of typical geometries where temperature fluctuation occurs. In the nuclear reactors and general plants, an elbow is often used near the mixing tee and it brings biased velocity distribution and also the secondary flow. In this study, influences of upstream elbow in the main pipe were studied in a water experiment of mixing tee with the elbow. Temperature distribution in the mixing tee was measured by a movable thermocouple tree and velocity field was measured by a high speed PIV. The temperature fluctuation at the mixing tee with the upstream elbow had the large component at low frequency in comparison with the straight case. The effect of the upstream elbow is significant to evaluate the high cycle thermal fatigue in the mixing tee because of larger importance of low frequency fluctuation on the point of fluid temperature-stress conversion.     

压水堆材料冷却剂环境疲劳修正因子研究

本文对考虑压水堆一回路冷却剂环境对材料疲劳影响的环境疲劳修正因子Fen进行研究，结合核电厂延寿需求，确立基于环境疲劳修正因子的疲劳分析流程。针对典型接管嘴结构，采用考虑瞬态应力时间历程的应变增量方法计算转换应变率和Fen，对比了环境修正对疲劳结果的影响。考虑环境影响后，奥氏体不锈钢的疲劳使用系数增大3.2倍，低合金钢的疲劳使用系数增大8.5倍，冷却剂环境对疲劳寿命的影响显著。将考虑环境影响后的疲劳使用系数与EPRI导则的计算结果进行对比，二者计算结果接近，验证了考虑瞬态组合的环境疲劳修正因子分析计算方法的正确性。     

Numerical Analysis of Fatigue Behavior of ITER-Like Monoblock Divertor Interlayer Under Coupled Heat Loads

High-confinement mode is a very prominent operation style for future fusion device due to its unique advantages. However, the conjuncted edge localized modes (ELMs) are very difficult to control so that divertor plates are very prone to suffer both stationary high heat flux (HHF) loads of long-pulse operating mode and transient shock loads of ELMs. Most previous researches focus on degradation of plasma facing material (PFM), however, as a layer joining PFM and cooling tube, the soft copper interlayer suffers concentrated thermal stress loads due to mismatched thermal expansion of PFM and cooling tube. Its thermal fatigue behavior under such coupled loads is also of great significance to structural safety of divertor component. With such a motivation, the reduction effects on fatigue life time of a typical interlayer of monoblock divertor under series of coupled HHF and ELMs shock loading conditions are investigated. It is found that: (1) The transient shock feature of ELMs loading is propagated into interlayer with less sharp pattern. The increase of damage induced by coupled ELMs loading is limited in single cycle, while the accumulated damage of multiple consecutive coupled loading cycles is increased nonlinearly. (2) Under the coupled HHF and ELMs loading, the fatigue life time of interlayer is generally decreasing. The magnitude of decrease is increasing nonlinearly with the magnitude of ELMs peak and averaged heat flux. (3) For three characteristic parameters of ELMs shock loading such as frequency, duration and peak heat flux, the peak heat flux and frequency are two parameters more sensitive to determine coupled reduction effects on fatigue lifetime of the interlayer, while for high frequency case, time averaged heat flux takes the lead.     

Probabilistic assessment of thermal fatigue in nuclear components

A probabilistic framework is set up to assess the fatigue life of components of nuclear power plants. It intends to incorporate all kinds of uncertainties, such as those appearing in the specimen fatigue strength (number-of-cycles-to-failure of specimens), design margin factors (taking into account the size, surface finish and environmental effects), mechanical model (precisely, the uncertainty on the model input parameters) and the thermal loading. This paper presents the global methodology and details the statistical treatment of the fatigue specimen test data. A first analytical example shows that the reliability of a structure submitted to a periodic stress cycle S changes significantly with respect to the value of S, although the codified (deterministic) design criterion is equally fulfilled. A more comprehensive example involving a mechanical model of a pipe submitted to a deterministic inner temperature loading is finally analysed. The use of the first-order reliability method (FORM) allows to compute the probability of failure as a function of the foreseen lifetime and to rank the input random variables according to their importance in response sensitivity.     

热管反应堆堆芯缩比模块瞬态特性分析

热管堆具有长寿期、高可靠性等优势,是当下空间核反应堆的研究焦点之一。为研究热管堆瞬态过程中的核热耦合现象,本文基于半物理仿真技术,搭建了针对热管反应堆堆芯缩比模块的核热耦合实验平台,通过实验模块测量了堆芯缩比模块的温度分布,在仿真模块中基于点堆模型计算了输出功率随时间的变化情况。通过耦合实验模块和仿真模块,探索了瞬态条件下堆芯缩比模块核热耦合特性,分析了引入不同初始反应性时堆芯温度、加热功率和剩余反应性的瞬态演变过程,揭示了系统热容量造成的温度迟滞变化效应,即热惯性现象。结果表明,堆芯缩比模块的热惯性随引入的初始反应性的增大及初始功率水平的增加而减小,且与基体材料的热扩散率呈反比。