对冲式止回阀原理及启闭特性分析

压水堆核电站主泵工况变化时,由于止回阀阻止流体逆流,回路会发生程度不同的水击现象.水击严重时不但会产生瞬时超压,危害压力边界,也可能造成止回阀失效.对冲式止回阀是一种新原理止回阀,是为解决传统止回阀关闭时产生的严重水击现象而设计的.分析和实验表明对冲式止回阀能有效地解决回路的水击问题,也能可靠地阻止流体逆流.     

基于耦合程序的流体瞬变流动水锤现象分析

水锤现象严重威胁系统的安全,而设备的启闭是产生水锤现象的重要因素之一。本文针对并联双泵系统建立耦合程序,计算研究泵启动和阀门关闭时的流体瞬变水锤现象。验证过程证明了耦合程序的正确性,并将三维稳态模型计算结果与实验结果进行了对比,二者符合良好。瞬态分析中,动网格技术成功模拟阀门关闭,并获得了闭合时阀内的重要热工水力参数。通过对比泵启动耦合计算结果与传统RELAP5计算结果可知,耦合程序能正确预测水锤压力波和水锤载荷。耦合分析较一维计算能更直观地展现系统中重要设备内的流体瞬变特性。计算获得的三维瞬态特性能对阀门的设计和优化提供重要的参考。     

压水堆核电厂主蒸汽管道汽锤计算分析

通过简化计算的方法求解压水堆核电厂主蒸汽管道汽锤压力。应用PIPENET软件对某百万千瓦级核电厂蒸汽发生器到主蒸汽母管之间的核岛主蒸汽系统进行建模。利用瞬态计算功能模拟汽锤发生及衰减过程,给出最大汽锤压力、管系中最大汽锤载荷、该载荷发生的时间及管道位置。分析了直管段长度及阀门关闭时间对汽锤现象的影响,在其他条件不变的情况下,直管段越短,汽锤能量越低;阀门关闭时间越长,汽锤能量越低。     

止回阀水锤分析

文章分析了止回阀水锤过程,求解了阀板运动微分方程,得到阀门开度无量纲数τ(t)的计算公式。用特征线法计算了止回阀水锤压力波。结果表明,偏置止回阀的水锤压力波最大峰值仅是悬挂式止回阀水锤压力波最大峰值的1/3。增大阀板的转动惯量J、加大限位角Φ_0可以减小水锤压力波峰值并能缓和阀板的振动。分析计算与实验结果符合得较好。     

核电厂RNS止回阀役前试验不合格问题分析和应对措施研究

海阳核电厂的正常余热排出系统(RNS)与一回路冷却剂系统(RCS)的反应堆压力容器直接注入管线(DVI)相连接。在RNS与DVI之间串联两个型式不同的止回阀作为一回路的压力边界,RNS止回阀分为A、B两列,分别为旋启式止回阀V017和截止止回阀V015。RNS止回阀需要定期验证阀门的泄漏和动作性能满足要求。RNS止回阀如果在机组运行期间发生泄漏将会导致一回路压力边界泄漏。在1号机组热态功能试验期间,多次执行RNS止回阀泄漏试验,始终存在泄漏率超标问题。本文主要通过对RNS止回阀在热试期间的四次试验数据进行分析,提出解决RNS止回阀泄漏不合格问题的措施,希望能为此类阀门的在役试验管理工作提供借鉴。     

核级阀门流体阻断试验技术研究

在试验装置上开展了压水堆运行参数范围内动力驱动阀门的流体阻断试验研究和止回阀的动态逆流与静态逆流试验研究。试验结果表明：开展动力驱动阀门流体阻断试验时,在设施能力不足的情况下可将阀门开启度适当减小,也能验证阀门阻断流体的能力;止回阀静态逆流试验相较于动态逆流试验能更苛刻地考验止回阀的阻断性能。本文结果可为开展同类验证试验在试验方法的选取上提供依据。     

核反应堆余热排出过程凝结水击现象实验研究

核反应堆余热排出过程中蒸汽与过冷水在管内发生直接接触凝结,有时会产生严重的凝结水击(CIWH)现象。对水平管内CIWH现象进行了实验研究,研究发现CIWH会引起巨大的压力波动,而且CIWH发生后会周期性出现逐渐衰减的压力峰值信号。分析CIWH发生过程中管路轴向不同位置处压力变化,发现压差的存在诱导了CIWH的产生。120 s内有多个CIWH事件产生,其强度具有高度随机性,最后发现CIWH强度最大值随进汽量的增加而增加,最高可达10 MPa。     

旋启式止回阀关阀水锤优化分析

建立了双泵并联给水系统数学物理模型,针对旋启式止回阀关闭过程中形成的水锤进行编程计算,分析作用在止回阀阀板上的力矩以及阻尼扭簧力矩对关阀水锤的影响。结果表明：在双泵并联给水系统中,旋启式止回阀在关闭时会产生明显水锤,作用在阀板上的力矩对水锤的作用效果有一定影响,选择合适的止回阀阀板材料以及加装合适的弹簧可有效缓解水锤危害。     

某核电止回阀开启过程中的瞬态流动与结构特征

为研究某核电止回阀在开启过程中的流动特征与部件的力学特征，采用商用计算流体动力学软件ANSYS Fluent和用户自定义函数（UDF），模拟了该阀门在高压工况下开启过程中的内部流动。在不同开度条件下采用流固耦合方法对阀门部件的力学行为进行了模拟，分析了阀体及阀芯的应力分布及变形情况。结果表明，随着阀门开度增大，过流断面的喉部与阀门出口出现高速区域；阀门入口段呈现较高的压力梯度；阀体上的最严重变形出现在喉部，变形量随开度变化呈现波动趋势；最大等效应力出现在阀门入口弯管处且最大等效应力随开度增加而减小；阀芯的最大变形量出现在靠近进口的一侧；最大等效应力出现在阀芯与弹簧接触区域，其随开度的增加呈现波动增长趋势。      

核电厂汽轮机甩负荷中调阀阀位反馈与指令偏差超限原因分析

某1000 MW核电机组在快速甩负荷(FCB)试验时,中压调节阀(简称中调阀)不能及时关闭,发生中压调节阀阀位反馈值与指令值偏差超限问题,引发跳机保护动作。分析发现,造成这次问题的原因是调节阀弹簧力矩与阀门气动力矩不匹配。利用FLUENT软件对该汽轮机中调阀内的三维流场进行数值模拟,得到阀门气动力矩和阀门开度的变化关系。结果表明:气动力矩随调节阀开度的增加先增大后减小,开度为30°左右时达到最大值;此时,若弹簧力矩与阀门气动力矩不匹配就会发生中调阀关闭动作迟缓甚至卡涩问题,造成阀位反馈值与指令值偏差超限。     

Numerical simulation and optimization on valve-induced water hammer characteristics for parallel pump feedwater system

In this study, the method of characteristic line (MOC) was adopted to evaluate the valve-induced water hammer phenomena in a parallel pumps feedwater system (PPFS) during the alternate startup process of parallel pumps. Based on closed physical and mathematical equations supplied with reasonable boundary conditions, a code was developed to compute the transient phenomena including the pressure wave vibration, local flow velocity and slamming of the check valve disc, etc. Some interesting results were obtained and it was shown that severe slamming between the valve disc and valve seat occurred during the alternate startup of parallel pumps. The induced maximum pressure vibration amplitude is up to 5.0 MPa, which occurs under the high–high speed startup condition. The scheme of appending a damping torque with the check valve disc was also numerically performed to eliminate the water hammer for the optimum design purpose. The adoption of damping torque slows down the closing speed of the check valve and has been approved to be an effective approach. This work is expected to be instructive for the optimum design of the PPFS in NPPs so as to mitigate the potential damage caused by valve-induced water hammer.     

Mitigating check valve slamming and subsequentwater hammer events for PPFS using MOC

The method of characteristic (MOC) was adopted to analyze the check valve-induced water hammer behaviors for a Parallel Pumps Feedwater System (PPFS) during the alternate startup process. The motion of check valve disc was simulated using inertial valve model. Transient parameters including the pressure oscillation, local flow velocity and slamming of the check valve disc etc. have been obtained. The results showed that severe slamming between the valve disc and valve seat occurred during the alternate startup of parallel pumps. The induced maximum pressure vibration amplitude is up to 5.0 MPa. The scheme of appending a damping torque to slow down the check valve closing speed was also performed to mitigate of water hammer. It has been numerically approved to be an effective approach.     

压水堆核电厂三回路停泵水锤数值模拟

应用停泵水锤的基本理论．建立了压水堆核电厂三回路水泵、泵出口阀、冷凝器和出水虹吸井等边界条件的数学模型．并采用特征线法进行求解结合工程实例计算说明．泵出口阀的关闭程序对水锤压力的影响较大．水泵出口采用两阶段关闭液控蝶阀可以有效减小停泵水锤压力．但其关闭程序应在水锤数值模拟分析的基础上优化确定。     

核反应堆一回路系统水锤数值模拟

采用特征线法,针对核反应堆一回路系统特点建立完整的数学物理方程和边界条件。自主开发WAHAP水锤计算程序,并对含止回阀的4泵并联系统在启动及切换工况下的水锤特性进行模拟计算。计算结果表明,所研究工况中有2个不同阶段存在阀瓣多次剧烈撞击阀座的过程和2种形式的压差震荡。     

Benchmarking analysis of water hammer effects using RELAP5 code and development of RBMK-1500 reactor main circulation circuit model

Correct prediction of water hammer transients is of paramount importance for the safe operation of the plant. Therefore, verification of computer codes capability to simulate water hammer type transients is a very important issue at performing safety analyses for nuclear power plants. Verification of RELAP5/MOD3.3 code capability to simulate water hammer type transients employing the experimental investigations is presented. Experience gained from benchmarking analyses has been used at development of the detail RELAP5 code RBMK-1500 model for simulation of water hammer effects in reactor main circulation circuit. In RBMK-type reactors the water hammers can occur in cases of rapid check valve operation. The performed analysis using RELAP5 code RBMK-1500 model has shown that in general the maximum values of the pressure pulses due to water hammer do not exceed the permissible loads on the pipelines.     

900 MW压水堆一回路系统水锤特性研究

针对压水堆水力过渡过程,建立了三环路900 MW压水堆一回路系统水锤完整的数理模型及边界条件。采用特征线法,开发了FORTRAN水锤仿真程序,并对三泵并联在启动和切换工况下的水锤特性进行了数值研究。研究发现启动和切换过程中,发生2次流量突变、流向逆转、压差突变和振荡;流量突变和逆转均发生在阀门关闭支路,呈振荡衰减的波动趋势,最大倒流流量达1 370 m3/h;压差突变发生在后启动支路,压差振荡最大值达40kPa;并联泵启动方式决定倒流流量和压差突变大小。     

Analysis of the capability of system codes to model cavitation water hammers: Simulation of UMSICHT water hammer experiments with TRACE and RELAP5

The capabilities of the nuclear system transient codes TRACE and RELAP5 to model coupled two-phase flow and pressure wave propagations in a pipe are assessed by analyzing the UMSICHT PPP cavitation water hammer experiments 329 and 135 after valve closure. Time-dependent pressure, flow behaviour, and the generation and collapse of vapor bubbles at the valve and the first bridge are discussed. We show that both codes are able to model the flow behaviour of the water hammer for the high pressure and high temperature case 329 (initially 10–13 bar and 420 K), however condensation heat transfer for the base case needed to be increased in order to accurately model the magnitude of the first pressure excursion. The experimental broadening and damping of the subsequent pressure peaks by Fluid-Structure Interaction (FSI) phenomena arising from the interaction of the flow with the vibrations of the piping structure are not considered in the modeling results. For the lower pressure and temperature case 135 (initially 1–4 bar and 294 K), the TRACE code provides a good approximation of the propagation of the pressure wave and the void fraction behaviour, already with base case conditions, while RELAP5 overpredicts the vapor generation along the pipe and, as a result, considerably underpredicts the pressure amplitudes and overpredicts the water hammer frequency.