压水堆核电厂二回路系统管道热效率的影响因素分析

在压水堆核电厂热经济性分析中,管道热效率的分析往往不被研究者所重视。首先从管道热效率的定义出发,给出了管道热效率的计算表达式,以及各种管道损失的计算方法。然后针对某些影响管道热效率的因素,同时也对蒸汽动力转换系统循环热效率产生影响的问题,分析了影响管道热效率的因素变化对蒸汽动力转换系统循环热效率和压水堆核电厂全厂热效率的影响。最后,以某990MW核电机组为例,通过计算分析了如主蒸汽管道疏水门泄漏蒸汽、厂用蒸汽、主蒸汽管道散热、蒸汽发生器排污等对管道热效率、蒸汽动力转换系统循环热效率及全厂热效率的影响。结果表明,上述因素变化均导致管道热效率降低和全厂热效率的降低,但不同因素变化对全厂热效率的影响机理却存在较大的差别。     

核电站高中能管道断管影响探讨

在设计核电站时,须对安全壳内外的高能与中能管道进行发生假想性断管事件及其后续效应的设计分析。这些管道一旦发生破裂,泄漏的高能量流体将对管道施加很大的横向力,使管道产生高速运动,即管道甩动。这种高速运动的管道可能会对周围结构造成严重破坏,因而引起世界上各主要发展核电国家的重视,并开展了大量的研究工作。详细叙述常规岛侧高中能管道断管位置的判定准则、假想破口的类型、断管的后续影响及其防护等。还进一步介绍有关管道断裂甩动问题的各种计算方法,如力矩平衡法、能量平衡法、有限元法等。     

Leak-before-break application in US light water reactor balance-of-plant piping

This paper describes the criteria and methodology for a leak-before-break (LBB) program for high energy balance-of-plant (BOP) nuclear piping in the United States. LBB, the analytical demonstration that high toughness piping will leak detectably before catastrophic failure, can be applied to any operational or pre-operational light water reactor plant to minimize pipe rupture hardware and to discount pipe rupture dynamic effects.

The general methodology described herein, encompasses applicable US NRC regulatory requirements and incorporates experience gained in the licensing process of actual LBB programs. First, candidate piping systems must be carefully screened to verify that they are not subject to failure by phenomena that would adversely affect the accurate evaluation of flaws. Next, pipe stresses, material properties, and leak detection capabilities are gathered for the fracture mechanics and fluid mechanics analyses. At the piping locations which have the least favorable combination of material properties and stress, a crack is postulated which is of sufficient size that the resulting leakage will be detected by installed leak detection systems. Finally, LBB is demonstrated if the postulated crack remains stable even if a seismic event takes place before the crack is discovered and repaired. An LBB example is presented in this paper for a generic pressurizer surge line, and reflects the consideration of flow stratification on LBB analyses.     

某核电堆型主蒸汽系统汽锤研究

以某核电堆型核岛主蒸汽系统为研究对象,研究主蒸汽隔离阀快关引起的汽锤现象。采用PIPENET软件进行建模和计算,给出管系中不同管段的最大载荷及出现时间。结果表明关阀瞬间的载荷最大,并且主蒸汽隔离阀后的载荷比隔离阀前的载荷大,主要是因为隔离阀前设置了卸压装置。同时对卸压装置的开启和流量特性进行了模拟。此外,分析了卸压管线的变化以及主蒸汽管道增加支管的情况对汽锤的影响。以上研究结果可应用于系统设计和管道力学应力计算分析,优化管道的布置,对提高主蒸汽系统和电厂的安全性具有重要的意义。     

柴油机管道振动处理

作为转动设备的柴油机,振动普遍存在,柴油机本体的振动与其功率、频率有关,与柴油机本体相连的辅助系统设计上应考虑减振或隔振措施,将振动控制在较低的水平。国内核电站应急柴油机的功率都在兆瓦级别,其所配备的辅助系统体积庞大,辅助系统与柴油机本体相连接部位问题频发。国内某核电站的应急柴油机冷却水系统在日常期间发现管道出现疲劳裂纹,导致冷却水泄漏,影响柴油发电机组的可用性。诊断发现,该管道结构设计不合理,导致管道振动应力较高。电站通过变更管道结构,显著改善了其应力水平。     

Vibration analysis of a 3-dimensional piping system conveying fluid by wave approach

Vibration analysis of a piping system conveying fluid is investigated by employing the wave approach. In this paper, the inviscid fluid-dynamic forces acting on a pipe due to internal fluid flow are approximated by the plug-flow model with the slender-body theory. The straight pipe elements conveying fluid are formulated using a dynamic stiffness matrix in the frequency domain. The curved pipe sections are treated with a single curved pipe element utilizing the mixed methodology of the dynamic stiffness method and the transfer matrix method. The present approach is applied to the frequency response analysis of the 3-dimensional piping system conveying fluid which is composed of straight and curved pipe sections and is compared to the results from the finite-element formulations.     

Pressure wave damping in branched pipes with arbitrary angles

Strong pressure waves may occur frequently as undesired phenomena leading to high loading on piping systems of nuclear power plants and chemical industries. This is occasionally observed when piping systems of different pressures are suddenly and unforeseenly connected together producing pressure or even shock waves. For an unsymmetrical branched channel, as a simple geometrical model of a complete piping system, the attenuation of shock waves is calculated. This calculation is based on the fluid-in-cell method for an unsteady, two-dimensional flow. The results agree with experiments and serve as a check for the applicability of earlier models.     

Preliminary evaluation of seismic isolation effects in a Generation IV reactor

This paper deals with the treatment of methods for a preliminary safety assessment of next generation nuclear power plant (of Liquid Metal cooled Fast Reactor types) structures. As an example, it was considered the European Lead-cooled System (ELSY) international project response under a reference design basis earthquake (Safe Shutdown Earthquake-SSE) excitation, taking into account also the main isolating device effects in order to increase the reactor safety.This study is intended to analyze the structural effects of a reference SSE by means of an appropriate dynamic FEM code, for possible geometries of both not isolated and isolated ELSY containment building foundation cases.A great attention should be focused too on the arisen hydrodynamic forces and coupling effects between fluid and structures (sloshing phenomenon) that may impair the structures resistance and/or operating capabilities.The obtained numerical results were critically analysed with the intent also to contribute to a step of the safety optimization of the mentioned systems.     

压水堆核电机组稳压器比例喷雾阀选型分析

[目的]稳压器比例喷雾阀是压水堆核电机组的关键阀门之一,是电站系统中唯一的核安全1级控制阀,掌握该阀门的技术特点对于工程实践和该阀门的自主化研发具有指导意义.[方法]基于国内压水堆核电机组所用的两种典型结构——气动V型球芯式比例喷雾阀和电磁驱动角式比例喷雾阀,从结构设计、工作原理及运行维护等方面进行对比分析.[结果]经...     

Comments on probabilities of leaks and breaks of safety-related piping in PWR plants

Leaks or failures with a safety significance in Cl 1 or Cl 2 piping of nuclear power plants (NPP) in Germany are very rare events. This excellent record in operating experience is matched by many NPPs in other countries.

The advances achieved in the understanding of fracture behaviour, in the methods of non-destructive testing and surveillance, together with operating experiences, can be used in the re-evaluation of piping systems that have been designed and manufactured to the standards given at the time of construction.

Comments and examples are presented for determining the probability of leaks and breaks in the whole range of Cl 1 and Cl 2 piping systems.     

Some design aspects related to stresses and strains in high temperature piping

This paper is concerned with the differences which exist between piping design procedures for normal temperature usage and those for high temperatures. Some additional modes of failure must be considered in high temperature design, such as creep and creep ratchet, creep relaxation and elastic follow up.The paper discusses possibilities of calculating the influence of the high temperature effects in relation to the analysis of stresses and strains in piping systems. Stress categories and strain limits are developed with respect to typical systems in a sodium-cooled reactor and to steam piping in a gas-cooled high temperature power plant. Rules for dealing with high temperature piping are proposed, the intention being to ensure that these provide the same level of safety as that provided for class 1 piping in water-cooled reactors.     

Optimum X-plate dampers for seismic response control of piping systems

In a vibrating system, the most effective mechanism to dissipate energy is the inelastic strain of supplemental metallic elements with plastic deforming characteristics. An X-plate damper (XPD) is one device that is capable of sustaining many cycles of stable yielding deformation resulting in a high level of energy dissipation or damping. The present paper focuses on a numerical study to investigate the seismic effectiveness of an XPD for piping systems in industrial units (e.g. chemical and petrochemical industries) and utilities such as thermal and nuclear power plants. The seismic performance of piping systems is investigated under important parametric variations of the damper properties (i.e. height, width and thickness of the XPD) under arbitrary ground motions. Investigations are reported for an industrial piping system equipped with an XPD and the response quantities of interest are the relative displacements, absolute accelerations and support reactions of the piping system. The response quantities of the controlled (with XPD) piping system are compared with the corresponding uncontrolled (without XPD) piping systems, to establish the seismic effectiveness of the XPD. Seismic energy dissipation in the piping system, which is represented by the hysteretic energy of the XPD, is also evaluated and compared. It is observed that the XPDs are very effective in reducing the seismic response of piping systems. Moreover, for a given piping system and ground motion, it is difficult to arrive at the optimum properties of an XPD from the parametric variation of the properties of the XPD and by monitoring the responses of the piping system. Therefore, use of hysteretic energy dissipation by an XPD is proposed to obtain the optimum properties of the XPD. Furthermore, the effects of the properties of an XPD on the free vibration characteristics of the piping system are also presented, which is crucial for the design of piping systems with XPDs.     

基于3KEYMASTER软件的核电站汽轮机数学模型与仿真

以福建宁德1000 MW核电机组汽轮机为研究对象,经过系统划分和对具体物理设备进行合理简化和假设后,建立了汽轮机组的动态数学模型。在3KEYMASTER仿真平台上进行了论证,经测试该模型能够正确反映核电站汽轮机的动态特性。     

Application of leak-before-break to primary loop piping to eliminate pipe whip restraints in a Spanish nuclear power plant

The Spanish plant described in this study is a 982 MWe PWR plant with a three-loop primary circuit of piping made from centrifugally-cast stainless steel SA351 CF8A.

The licensee requested an exemption to GDC-4, from CSN, so as to avoid the postulation of guillotine rupture of the primary loop piping. The request was based on the generic work performed for a US PWR plant group to have such exemption to GDC-4. As the piping material in the Spanish plant is different from that in the plants included in the generic work, CSN performed a review of the applicability of the generic results to the Spanish plant. Also, aspects such as fatigue evaluation, net section collapse, crack growth and leak detection, specifically analyzed for the Spanish plant, were reviewed.

CSN found that fracture toughness test results from generic work are applicable to the Spanish plant; sufficient margin exists against unstable crack extension, and adequate leak detection capability exists with the leakage detection systems available in the plant.

Exemption to GDC-4 was approved and CSN authorized the licensee to remove protection devices against dynamic loads from guillotine breaks in the primary coolant loops.     

用于动力设备的纳米镍基合金微观结构及耐磨性研究

阀门是核电站应用最多的一种设备,因材料耐磨性不足导致阀门失效是核电站事故的主要原因之一。文中提出在阀门零件的关键密封表面镀上一层纳米镍基合金,可以大大提高阀门的耐磨性,是减少核电站事故的有力手段。应用X射线衍射、TEM研究了纳米镍基合金的组织结构及相结构,陈述了这种结构为什么具有优异耐磨性的机理。     

Experimental and numerical analysis of spring stiffness on flow and valve core movement in pilot control globe valve

Valves are widely used for fluid flow control, not only for conventional fluid like water, gas and oil, but also for hydrogen under high pressure and so forth. Under these new conditions, the response time and energy consumption of valves are closely related to the whole performance of the piping system. Pilot-control globe valve (PCGV) is a novel quick response valve, which can utilize the pressure difference before and after the valve core to control the open/close states of the main valve. In this paper, the effects of spring stiffness inside PCGV on the flow and the valve core movement are carried out, respectively. To begin with, the experimental setup is introduces and the 3D numerical model is established. The simulation is carried out in software FLUENT with RNG k-ε turbulence model, User Defined Function method and dynamic mesh regeneration methods under transmit state. Then, a comparison of steady valve core displacements between experiment and simulation is carried out. After that, the effects of spring stiffness on flow characteristics, valve core movement and response times during opening and closing periods are presented. Finally, a spring chosen correction equation is proposed. This work can benefit the further design work of PCGVs or similar valves with springs, and it can be also referred by someone dealing with novel control valves design or flow control issues.     

Lubrication aspects in an axisymmetric magneto nanofluid flow with radiated chemical reaction

This paper addresses the effects of axisymmetric magnetohydrodynamic stagnation point flow of nanofluid through the lubrication of power‐law fluid by taking the general slip at the interfacial condition. The impacts of radiated chemical reaction, thermophoresis, and Brownian motions are further accounted. The fluid is impinging orthogonally on the surface via power‐law slim coating liquid lubrication. The partial differential system is governed for both the lubricant and the base fluid. Using dimensional analysis, the arisen partial differential system is modified to ordinary differential systems subject to nonlinear boundary conditions. An implicit numerical technique namely the Keller‐Box method is executed to formulate the solution of developed nonlinear expressions. The influence of different involved constraints on quantities of interest are sketched and discussed. The effects of the skin friction coefficient, heat transfer, and concentration rate at the surface are given and analyzed. The condition from full slip to the no‐slip can be achieved from the present solution. The obtained solutions are matched through the existing data and observed good agreement.     

三偏心快关阀的液压系统设计与动态特性仿真

大型三偏心蝶阀作为紧急切断系统逐步推广应用到燃气发电机组进气保安系统中,其液压控制系统的动态响应特性及可靠性对电站安全运行至关重要。针对三偏心蝶阀作为紧急切断阀系统的功能要求,设计出满足紧急切断要求的液压控制方案。建立液压控制系统的仿真模型,对开阀及关阀过程进行系统的动态特性仿真,并对研制的紧急切断阀系统的动态响应进行了试验,全开过程中执行机构活塞实测最大位移比仿真结果大0.2mm,快关阀全开和紧急关闭实测最长时间都比仿真结果多0.01s。证明在设计过程中采用仿真技术能够准确地预测设计的三偏心蝶阀系统的动态响应特性和优化设计方案。     

The effect of size on efficiency: Power plants and vascular designs

In this paper we use thermodynamics to show why larger flow systems are more efficient than smaller flow systems. This trend is visible across the board, from power generation and refrigeration, to vascular design and animal design. The reason is that larger systems have larger flow passages and heat transfer surfaces, and do not strangle the flow of the currents that must flow. Three fundamental examples show how to predict this trend: a power plant with fluid friction and finite heat transfer area, a vascular body with building blocks optimized at every level of assembly, and a vascular body designed based on a duct-pairing algorithm. The examples show that the performance improves as the size increases, and that the architecture changes with the size. These constructal-design features constitute the basis for scaling up and scaling down the configurations of flow systems, from desktop models to life size installations.