压水堆核电厂稳压器波动管热分层现象数值分析

为分析评价压水堆核电厂稳压器波动管热分层现象对波动管结构完整性的影响,采用计算流体力学(CFD)分析方法,对稳压器波动管热分层现象进行了数值模拟.研究了波动管内的流体流动,得到了稳压器波动管的传热特性、流体流场和温度分布,分析了稳压器波动管波动热分层现象与波动流速之间的关系.研究结果表明:波动流速在一定范围内变化时,管道最大截面温差随着波动流速的增大而增大.并且得到了不同波动流速下管道最大截面温差及其出现的位置,指出了热分层现象发生时波动管的薄弱环节.     

稳压器波动管不同布置方式对热分层现象的影响

通过改变波动管的倾角建立了两种不同布置方式的波动管模型,采用计算流体力学(CFD)分析方法,分别对这两种模型的热分层现象进行数值模拟分析,比较不同流量下两种模型热分层现象的特点,并对两种模型热分层现象差异产生的原因进行分析。结果表明:两种模型热分层现象产生的位置和热分层覆盖范围不同,引起这些差异的原因主要是由于不同模型的波动管内流体流动不同。本研究能为优化波动管布置达到减弱热分层效应提供参考。     

稳压器波动管热分层应力及疲劳分析

稳压器波动管内流体的温度分层引起管壁温度分层,从而在管道截面产生整体弯曲应力、局部热应力以及管道系统超过预期的位移和支撑载荷.将稳压器波动管的热分层这种复杂的三维应力分析问题简化为一维和二维组合问题,利用SYSTUS程序和ROCOCO程序对秦山核电二期扩建工程稳压器波动管热分层的应力及疲劳进行了分析研究,计算了考虑热分...     

压水堆稳压器波动管热分层的分析研究

热分层是管道水平管段中相对滞止或缓慢流动的冷、热流体因缺少混合而产生的不均匀温度分布现象.通过稳压器波动管热分层现象产生的原因和机理分析,并对稳压器波动管热分层现象进行数值模拟,建立了不同稳压器内部不同截面的热分层瞬态.     

核电厂稳压器波动管内热分层效应分析

利用CFD方法对核电厂稳压器波动管以及与之相连接主管道内反应堆冷却剂进行流固耦合共轭流动传热计算,获得在升温瞬态条件下稳压器波动管内冷却剂的温度场分布,证实在水平段内可产生明显的热分层结构。在此基础上,利用有限元分析软件,结合波动管的结构特征,建立稳压器波动管的热分层应力计算模型,并对稳压器波动管的应力水平进行计算分析,给出稳压器波动管中的应力场分布特性。     

管型对波动管热分层现象的影响分析

为分析评价压水堆核电厂稳压器波动管管型对热分层现象的影响,提出采用螺纹管来减弱热分层的措施。利用计算流体力学（CFD）分析方法,对升温、升压阶段波动管原型和改进模型的热分层现象进行数值模拟,得到两种模型不同波动流速下沿波动管轴线方向的截面最大温差分布以及流场分布。对比分析结果表明：波动管结构由光管改为螺纹管后流场紊动加强并出现涡流,冷热流体间的混合增强,与原型相比可使波动管的截面温差减小约1/3,从而有效地减弱热分层的影响。     

升功率工况下波动管热分层数值分析

以CPR1000稳压器波动管为研究对象,采用CFD方法,使用FLUENT软件,对反应堆功率增加瞬态工况下波动管热分层现象进行数值模拟研究,得到了波动管内热分层流体的流场和温度场分布,探讨了涡流效应对热分层分布的影响。结果表明：瞬态工况下波动管热分层与传统观念下的稳态热分层相比有很大不同,最显著的是T型三通区域,由于受到涡流效应的影响,流体热分层呈环形左右分布,而不再是稳态热分层的上下分布。本研究得到的瞬态工况下的温度分布结果可作为瞬态热应力分析的温度载荷,为后续的力学分析和疲劳分析奠定了基础。     

布置方式对波动管热分层现象的影响分析

为分析评价压水堆核电厂稳压器波动管的布置方式对热分层现象的影响,提出增加准水平段的倾角和在与主管道相连处增加一段竖直管段2种方案共6种布置方式.利用计算流体力学( CFD)分析方法,对采取不同布置方式的波动管的热分层现象进行数值模拟,得到每种布置方式的波动管在不同波动流速下的准水平段管道截面最大温差分布.对比分析结果表...     

稳压器波动管热分层应力强度可靠性分析

稳压器波动管热分层现象可能影响核电厂的安全运行。为了充分研究稳压器波动管几何、材料和热分层现象的随机性,准确地对波动管进行可靠性评估,将ANSYS程序和蒙特卡罗程序相结合的方法引入波动管热分层模型的计算中。以概率论为基础,利用ANSYS程序中的可靠性模块对波动管模型进行随机抽样分析,求出在一定置信度下的可靠度曲线,幵对输出随机变量的灵敏度和抽样过程进行了分析,求得对结果影响最大的因素。结果表明,计算模型可以有效地反映波动管热分层的实际情况,为波动管结构可靠性分析提供参考。     

稳压器波动管内热纹振荡现象数值模拟研究

对波动管内热纹振荡现象展开研究,获得波动管内热纹振荡现象的产生原因以及启堆升功率工况下热纹振荡现象造成波动管内壁面温度振荡的幅值和频率。采用计算流体力学(CFD)方法中的动态Smagorinsky涡粘模型对波动管内热纹振荡现象进行了数值模拟。结果表明:波动管内产生热振荡现象的原因是冷热流体相对流动所产生的涡状流使得冷热交界面产生上下振荡;波动管内的热纹振荡现象使得波动管内壁面温度的振荡幅值在4~20℃范围内,频率低于5 Hz。     

Fluid-structure interaction analysis for pressurizer surge line subjected to thermal stratification

Serious mechanical damages such as cracks and plastic deformations due to excessive thermal stress caused by thermal stratification have been experienced in several nuclear power plants. In particular, the thermal stratification in the pressurizer surge line has been addressed as one of the significant safety and technical issues. In this study, a detailed unsteady computational fluid dynamics (CFD) analysis involving conjugate heat transfer analysis is performed to obtain the transient temperature distributions in the wall of the pressurizer surge line subjected to stratified internal flows either during out-surge or in-surge operation. The thermal loads from CFD calculations are transferred to the structural analysis code which is employed for the thermal stress analysis to investigate the response characteristics, and the fatigue analysis is ultimately performed. In addition, the thermal stress and fatigue analysis results obtained by applying the realistic temperature distributions from CFD calculations are compared with those by assuming the simplified temperature distributions to identify some requirements for a realistic and conservative thermal stress analysis from a safety point of view.     

基于运行数据的船用堆波动管热分层现象研究

基于运行数据将船用堆波动管热分层划分为升功率、降功率、变工况、小喷淋流量4类典型瞬态,对4类典型瞬态分别进行无量纲里查德森数（Ri）分析、瞬态工况数值模拟计算,得到波动管在4类典型瞬态下水平管段的热分层区间长度、持续时间和最大温差。结果表明,升功率和降功率瞬态热分层仅单次贯穿波动管,升功率瞬态的接头部位循环的热波动以及小喷淋流量瞬态水平段的长区间、长时间、大温差的热分层现象和变工况导致的热应力波动可能影响到波动管的安全。本文提出的基于运行数据的波动管热分层现象研究方法为后续热应力和热疲劳分析奠定了基础,同时可以为其他容积设备热分层研究提供参考。      

稳压器波动管热分层分析

为评价热分层对稳压器波动管结构完整性的影响,从理论上分析了稳压器波动管热分层发生的条件.以百万千瓦级三环路压水堆核电厂核反应堆启堆为例,建立了热分层瞬态,研究了热分层应力计算方法,从理论上将一个复杂的三维应力分析问题简化为一维和二维组合问题.结合ANSYS程序功能,提出了波动管热分层应力计算的工程方法.     

Stress analysis of a 900 MW pressurizer surge line including stratification effects

Following temperature monitoring programmes performed on 900 MW pressurized water reactor pressurizer surge lines, it has been reported that those lines are stratified in steady state, owing to their geometry. The highest temperature difference occurs during reactor heat-up and cool-down, reaching 110°C. Obviously, this phenomenon was not considered in nuclear steam supply system (NSSS) design transients and stress reports.Based on Electricité de France and FRAMATOME experiences, such as temperature measurements on site and mock-up, and thermal hydraulic computations, NSSS transients are updated. Stratification conditions are defined in different cross-sections of the line, using pressurizer temperature, hot leg temperature and flow rate, through the Froude number. A complete stress analysis of surge lines is performed including the updated transients and bending moment increase due to stratification. First of all different sensibility studies are carried out in order to simplify assumptions.Using a two-dimensional-one-dimensional method developed by FRAMATOME, the usage factor is then computed in different cross-sections, distinguishing upper and lower parts. In the presence of stratification, the surge line is subjected to thermal stresses following thermal shocks and to bending moment variation. These two load types are studied vs. time in order to reduce conservatism present in usual analyses.     

Numerical prediction of stratified pipe flows in PWRs

The phenomenon of thermal stratification has been analysed on the l'EXPRESS experimental facility representing the pressurizer surge line of a Framatome PWR. This experimental approach has allowed to characterize flow regimes for different operating conditions. A numerical simulation approach has been performed by the TRIO code. The measured fluid temperatures have been compared to calculated values. A first validation of the numerical simulation was realized by comparing steady state results to experimental values, the second one by comparing transient conditions. Also the stratification onset has been estimated and compared to the experiment. The numerical simulation has allowed to obtain a good prediction of the quantities representative of the thermal loading.