Application of signature analysis for determining the operational readiness of motor-operated valves under blowdown test conditions

In support of the NRC-funded Nuclear Plant Aging Research (NPAR) program, Oak Ridge National Laboratory (ORNL) has carried out a comprehensive aging assessment of motor-operated valves (MOVs).As part of this work, ORNL participated in the gate valve flow interruption blowdown (GVFJB) tests carried out in Huntsville, Alabama, The tests provided an excellent opportunity to evaluate signature analysis methods for determining the operability of MOVs under accident conditions.ORNL acquired motor current and torque switch shaft angular position signauresnon two test MOVs during several GVFIB tests. The reduction in operating “margin” of both MOVs due to the presence of additional value running loads imposed by high flow was clearly observed in motor current and troque switch angular signatures. In addition, the effects of differential pressure, fluid temperature, and line voltage on MOV operations were observed and more clearly understood as a result of utilizing the signature analysis techniques.     

A study on a characteristic of stem friction coefficient for motor operated flexible wedge gate valve

Stem friction coefficient is a coefficient that represents friction between thread leads of the stem and stem nut. It is an important factor to determine output thrust delivered from the actuator to the valve stem in assessing performance of motor operated valves. This study analyzes the effects of changes in differential pressure on stem friction coefficient, and determines the bounding value of stem friction coefficient. A dynamic test was conducted on multiple flexible wedge gate valves in various differential pressure conditions, and the test data was statistically analyzed to determine the bounding value. The results show that stem friction coefficient in middle and high differential pressure is influenced by fluid pressure, while stem friction coefficient in low differential pressure is almost not affected by fluid pressure. In addition, it is found that the bounding value of stem friction coefficient is higher in a closing stroke than in an opening stroke.     

An analytical study of the dynamics and stability of a spring loaded safety valve

Spring loaded self-actuating safety valves are employed as part of the overpressure protection systems in various industrial applications. In order to design and predict their performance it is necessary to study the dynamic behavior of the valve over a range of fluid and system conditions. A one-dimensional model has been developed to study the effects of different valve parameters such as the spring-mass characteristics, geometry of internal parts, adjustment ring settings, bellows etc. which influence the dynamic behavior and stability of the valve. Analytical results for steam flow conditions are presented to demonstrate the relative effects of these parameters on the valve opening time, maximum lift, blowdown (upstream pressure differential between the valve opening and closing) and any oscillations of the valve stem. If the valve is not properly backpressure compensated, it may become unstable as the stagnation pressure at the valve inlet decreases. Lowering of the guide adjustment ring position or raising the nozzle adjustment ring generally results in improved stability, shorter valve opening time, higher lift and longer blowdown. The effect of damping on the valve stability is also demonstrated. The model can be used to evaluate the design of safety valves and damping devices to eliminate unstable valve dynamic behavior.     

基于Markov/CCMT方法的数字化紧急停堆系统可靠性分析

传统的可靠性分析方法在数字化仪控系统的可靠性应用中受到较多制约，需要探索新的可靠性分析方法。以数字化紧急停堆系统为研究对象，选取Markov/CCMT方法完成系统的失效建模，得到紧急停堆系统的定性分析结果；在此基础上进行定量分析以获得系统的失效率。结果表明，Markov/CCMT方法分析得到的数字化紧急停堆系统的失效率为1.3×10?6 h?1；Markov/CCMT方法在数字化仪控系统的可靠性分析中具备一定的适用性，相较于传统的可靠性分析方法对系统动态特性的表达更为全面。      

TXRIS007试验监督要求准则的流量判定

为解决某核电基地多机组安注箱逆止阀功能验证试验(TXRIS007)在大多数情况下不满足验收准则的问题,采用一维流体仿真软件(Flowmaster)建立试验模型开展不同配置的瞬态计算,并结合历史数据进行理论分析。研究表明,仅考虑试验管道内径和测量仪表的合理偏差,其他试验影响因素正常,初始流量为2.37～5.70 m³/h,处于合理范围;阀门阻力特性较大改变、管道实际内径和管壁粗糙度等设备性能差异以及共用环路严重的堵塞都会导致流量出现较大的变化;当设置统一的最小流量时,可能无法识别出部分基准流量较高的环路阀门性能的变化,建议电厂结合计算结果针对不同机组在相同的试验条件下标定基准流量,并做好试验时的记录和归纳整理工作。     

一种阀门排放分析验证方法的研究

以稳压器快速卸压截止阀为例,研究一种饱和蒸汽下阀门排放量的分析验证方法。将小开度、低压差下的阀门排放试验数值与理论计算数值对比,表明偏差在可接受范围内;将此试验数值带入推导公式,得到全开度、全压差下的阀门排放量;与ANSYS分析的全开度下排放量对比,发现实际推导排量与理论计算排量偏差为2.73%。研究结果表明,在试验能力不足情况下,可以采用小开度低压差的排放试验结合理论推导的方式分析阀门饱和蒸汽下的排量。      

Analysis of potential waterhammer at the Ignalina NPP using thermal–hydraulic and structural analysis codes

The RBMK (Russian acronym for ‘channeled large power reactor’)-1500 reactors at the Ignalina nuclear power plant (NPP) have a series of check valves in the main circulation circuit (MCC) that serve the coolant distribution in the fuel channels. In the case of a hypothetical guillotine break of pipelines upstream of the group distribution headers (GDH), the check valves and adjusted piping integrity is a key issue for the reactor safety during the rapid closure of check valve. An analysis of the waterhammer effect (i.e. the pressure pulse generated by the valves slamming closed) is needed. The thermal–hydraulic and structural analysis of waterhammer effects following the guillotine break of pipelines at the Ignalina NPP with RBMK-1500 reactors was conducted by employing the RELAP5 and PipePlus codes. Results of the analysis demonstrated that the maximum values of the pressure pulses generated by the check valve closure following the hypothetical accidents remain far below the value of pressure of the hydraulic tests, which are performed at the NPP and the risk of failure of the check valves or associated pipelines is low. Sensitivity analysis of pressure pulse dependencies on calculation time step and check valve closure time was performed. Results of RELAP5 calculations are benchmarked against waterhammer transient data obtained by employing structural mechanics code BOS fluids.     

Analysis of flow induced valve operation and pressure wave propagation for single and two-phase flow conditions

The flow induced valve operation is calculated for single and two-phase flow conditions by the fluiddynamic computer code DYVRO and results are compared to experimental data. The analysis show that the operational behaviour of the valves is not only dependent on the condition of the induced flow, but also the pipe flow can cause a feedback as a result of the induced pressure waves. For the calculation of pressure wave propagation in pipes of which the operation of flow induced valves has a considerable influence it is therefore necessary to have a coupled analysis of the pressure wave propagation and the operational behaviour of the valves.The analyses of the fast transient transfer from steam to two-phase flow show a good agreement with experimental data. Hence even these very high loads on pipes resulting from such fluiddynamic transients can be calculated realistically.     

中国实验快堆典型钠阀温度分布研究

中国实验快堆典型钠阀作为系统重要的涉钠设备,直接影响着反应堆系统的安全运行。中国实验快堆工程在调试和运行阶段面临着钠阀门带来的一系列问题。本文应用CFD软件计算了两种运行工况下典型钠阀稳态温度场分布,分析了保温层厚度一定、高度不同的情况下,钠阀门的温度场分布结果,并与实验结果进行了对比,证明结果是合理的有意义的。     

Investigation on two-phase critical flow for loss-of-coolant accident of pressurized water reactor

The previous investigations were mainly conducted under the condition of low pressure,however,the steam-water specific volume and the interphase evaporation rate in high pressure are much different from those in low pressure,Therefore,the new experimental and theoretical investigation are performed in Xi‘an Jiaotong University.The investigation results could be directly applied to the analysis of loss-of -coolant accident for pressurized water reacor.The system transition characteristics of cold leg and hot leg break loss-of -coolant tests are described for convective circulation test loop.Two types of loss-of-coolant accident are identified for :hot leg” break,while three types for “cold leg”break and the effect parameters on the break geometries.Tests indicate that the mass flow rate with convergent-divergent nozzle reaches the maximum value among the different break sections at the same inlet fluid condition because the fluid separation does not occur.A wall surface cavity nucleation model is developed for prediction of the critical mass flow rate with water flowing in convergentdivergent nozzles.     

高频地震激励对核级阀门危害性分析

利用试验和修正后的集中质量有限元模型预测安装在管道中阀门在不同频率成分地震激励下的响应,研究高频地震激励对管道中质量较大核级阀门的危害性。研究结果表明：高频地震激励对核级阀门的危害在于使阀门以其自身固有振型发生共振,此时阀门顶部取代阀门与管道连接位置成为阀门中响应最大的位置,这会导致安装于阀门顶端的驱动机构遭受苛刻的地震工况。增加管道阻尼和阀门刚度能有效降低高频激励对阀门的危害,但增加阀门刚度会导致管道响应增大。利用等效静力法对阀门进行抗震鉴定时,分析结果对阀体水平部位内力估计不足,对阀体垂直部分、阀盖等阀门上部构件的内力估计结果具有较大裕度。     

Hazard Analysis of Nuclear Safety Class Valve Induced by High Frequency Seismic Excitation

The test and the updated lumped mass finite element model were used to predict the response of the valve installed in the pipeline under the seismic excitation of different frequency components, and the hazard of high frequency seismic excitation to large-mass nuclear safety class valves in the pipeline was studied. The results show that the high frequency seismic excitation causes the nuclear safety class valve to resonate with its own mode of vibration. At this moment, the top of the valve replaces the position where the valve is connected to the pipe to become the position with the largest response amplitude in the valve, which causes the drive mechanism installed on the top of the valve to suffer severe seismic conditions. Increasing the pipe damping and valve stiffness can effectively reduce the hazard of high frequency excitation to the valves, but increasing the valve stiffness will lead to the increase of the pipe response amplitude. When the equivalent static method is used for seismic identification of the valve, the analysis result is insufficient to estimate the internal force of the horizontal part of the valve body, and has a large margin to estimate the internal force of the vertical part of the valve body, the valve cover and other upper parts of the valve.     

核一级低压差旋启式止回阀研制

为了实现核电站关键阀门的国产化,研制了核一级低压差旋启式止回阀。本文介绍了该阀门的技术参数及其研制过程和型式试验的情况。经过各种测试,各种性能指标均达到设计要求。     

核电厂一回路压力边界止回阀在线密封性能测试

320 MW压水堆一回路压力边界止回阀为核Ⅰ级关键设备,严密性要求非常高,直接关系到主系统的内泄漏率.焊接式止回阀维修后常采用密封面色印检查的方式,对其密封性能进行判断.如果管道内有存水或者湿热水汽,会影响到色印检查的准确度.针对在线止回阀密封性试验的特殊性,有的核电厂采用水压压降法试验设计过在线检测装置,但存在一些缺点和使用上的限制.文章采用低压气密封试验流量测定法,设计出可靠、便携的试验装置,对压力边界止回阀检修后密封性做出准确、定量的判断.     

10 MW高温堆热气联箱气流混合模拟的相似律

１０ＭＷ高温气冷实验堆芯出口需设置热气联箱,以使氦气得到充分的热混合。使用两流体方程无量纳化分析方法导出相似准则,得到了热气联箱在缩小模型比例的系统上以常压小温差空气代替主压大温差氦气进行热工水力学模拟试验研究时应遵循的模拟准则,即几何准则、流动准则和传热准则。     

不同初因事件下的两相排放过程热工水力特性研究

本文针对稳压器安全阀开启后的复杂两相热工水力过程进行研究,确定不同初因事件下的稳压器安全阀两相排放特性。采用自主化系统分析程序ARSAC对稳压器安全阀的上下游进行建模分析,选取三种典型的阀门排放过程,包括稳压器安全阀误开启事故、导致一个或多个稳压器安全阀开启的主蒸汽流量完全丧失事故、以及低温超压保护条件下导致的稳压器安全阀间歇性开启的安注泵误启动事故,研究稳压器安全阀开启后水封及蒸汽（或水）排放过程中涉及的复杂两相热工水力特性,结果表明：ARSAC程序能够捕捉两相排放过程中管道内部的流型变化;水封通过下游管道会形成明显的流量峰值,且不同的上游初始条件下排放过程对于下游管道造成的流量峰值及时间特性不同。通过本文的研究可以为载荷分析、安全评价及设计优化提供指导性建议。     

Analysis of the effect of lubrication performance on motor operated valve actuator output thrust

In this study, we performed theoretical analysis and test to identify an effect that lubricant performance has on actuator output thrust of MOV. Particularly, we introduced Stem Friction Coefficient (SFC) concept that means friction coefficient between a stem nut and a stem screw. By using SFC concept, an effect of lubricant performance on the actuator output thrust was analyzed quantitatively. The first phase test was performed to compare the lubrication performance between new lubricant and old lubricant and the second phase test was performed to compare the lubrication performance for the three kinds of representative lubricants (EP0, EP1, EP2) being used in Korea nuclear power plants. According to the test results, SFC value of old lubricant appeared higher than that of new lubricant and a old lubricant at TST point generated lower thrust value than a new lubricant at the same torque value. We can verify that the effect of lubrication performance has on power generated in an actuator was very large and SFC was a very useful variable in analyzing lubrication performance quantitatively.     

Safety Relief Valve Performance for Two-Phase Flow

The performance of main steam safety relief valve has been evaluated with respect only to the steam. In the present study, two-phase flow and subcooled water blow-out tests with model valves were performed in order to evaluate the valve's characteristics and performance. From the test results, it was made clear that not only for the steam but also for the two-phase flow the measurement data were hardly affected by scaling and also that the reaction force of the fluid to the valve stem was hardly dependent upon the void fraction. Analytical study was performed using the two-phase flow model in the valve. The results of the analysis showed good agreement with the test data. It was shown from the test and analysis results that the reaction force of the two-phase flow and subcooled water to the valve stem was almost as much as that of the steam flow, and the integrity of the safety relief valve could be maintained.     

对冲式止回阀局部流动特性仿真模拟

当压水堆核电站主泵工况变化时,回路会发生程度不同的水击现象,严重时不仅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型止回阀,其新型的导流结构设计可很好地减轻水击现象,提高核电站运行的安全性。本工作基于FLUENT流体仿真软件,利用动网格及UDF(用户自定义函数)技术,更真实地模拟了阀门关闭过程中冲压管喉部及其联接腔体内的流场与压力分布。模拟结果表明,虽然几何形状的变化会导致关闭过程中局部流速高于其他部位的,但对阀门关闭过程的稳定性影响很小。另外,通过对流场分析发现,阀门关闭过程可分为3个阶段,每一阶段均有其独立特征,为以后阀门结构的改进及可靠性分析提供了依据。     

汽轮机调节系统二次脉动油压异常分析

针对田湾核电站汽轮机夏季运行工况时出现调节系统二次脉动油压高且波动问题,采用两台机组汽轮机调节系统静态试验曲线以及热力系统参数对比分析的方法,阐述了循环冷却水温度、二次脉动油压拐点、调节阀空行程对二次脉动油压的影响。根据研究结果,通过提高二次脉动油压拐点及减小高压调节阀油动机空行程的纠正措施,有效解决了此问题,提高了调节系统的稳定性。对机组的运行和维修具有一定的借鉴意义。