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.     

Dynamic testing of full-scale nuclear power plant structures and equipment

Three steps are required in the design of reliable nuclear power plants to be located in seismic areas. In addition to development of realistic analytical models, it is necessary to perform dynamic tests to verify the models and acquire the information needed to establish the dynamic parameters for modeling. The third and final step is to perform high level proof tests to validate analysis and test results. This report is an overview of dynamic testing methods.Testing can be performed in the laboratory or in the field. Laboratory tests are useful because a wide range of effects can be studied and test parameters are more easily controlled. Care must be exercised to insure that the laboratory situation faithfully reproduces the actual structure in such details as supports, appurtenances, appendages, and mounting methods. In general, laboratory methods permit high level excitation of structures weighing up to a few metric tons (a few facilities in the world have capabilities up to 100 t). Since actual structures of interest to nuclear power plant designers often weigh up to 10 000 t, field testing is also important. Test procedures have been developed, using portable structural vibrators, for testing structures as large as nuclear power plant containment buildings. High level tests can be performed using explosives buried in the soil to excite structures. Recent work performed by the author demonstrates that explosive tests which produce a predetermined, specified response spectrum can be conducted.     

Efficient approach to simulate EM loads on massive structures in ITER machine

Operation of the ITER machine is associated with high electromagnetic (EM) loads. An essential contributor to EM loads is eddy currents induced in passive conductive structures. Reasoning from the ITER construction, a modelling technique has been developed and applied in computations to efficiently predict anticipated loads. The technique allows us to avoid building a global 3D finite-element (FE) model that requires meshing of the conducting structures and their vacuum environment into 3D solid elements that leads to high computational cost. The key features of the proposed technique are: (i) the use of an existing shell model for the system “vacuum vessel (VV), cryostat, and thermal shields (TS)” implementing the magnetic shell approach. A solution is obtained in terms of a single-component, in this case, vector electric potential taken within the conducting shells of the “VV + cryostat + TS” system. (ii) EM loads on in-vessel conducting structures are simulated with the use of local FE models. The local models use either the 3D solid body or shell approximations. Reasoning from the simulation efficiency, the local boundary conditions are put with respect to the total field or an external field. The use of an integral-differential formulation and special procedures ensures smooth and accurate simulated distributions of fields from current sources of any geometry. The local FE models have been developed and applied for EM analyses of a variety of the ITER components including the diagnostic systems, divertor, test blanket modules, cryopumps, blanket modules. (iii) Two integration algorithms can be applied to an ordinary differential equation system (ODES) describing a discrete problem. First, a direct integration of ODES can be performed in accordance with operating scenarios (variations of field sources). Second, complex variations of field sources can be decomposed for each source into individual components via a set of basic (influence) functions. A generalized solution is obtained as a superposition of individual solutions. (iv) The use of a combination of different computer codes implementing the shell models and 3D solid-body models. The codes and developed models were validated and approved, particularly, in the course of an ITER-initiated extensive benchmark to support of the blanket modules design.     

Present and future of equipment qualification for dynamic loads

This paper reviews the existing methods being used to justify equipment under transient dynamic loads of extreme magnitudes. Based on the experience gained during the past ten years in qualifying equipment for such loads, the author discusses future developments needed to obtain a consistent and reliable technology. The potential and the direction for future developments combined analysis test to obtain a unified approach are presented. This study includes qualification by test and combined analysis test.     

Soil-structure interaction for transient loads due to safety relief valve discharges

Dynamic responses of BWR Mark II containment structures subjected to axisymmetric transient pressure loadings due to simultaneous safety relief valve discharges were investigated using finite element analysis, including the soil-structure interaction effect. To properly consider the soil-structure interaction effect, a simplified lumped parameter foundation model and an axisymmetric finite element foundation model with viscous boundary impedance are used. Analytical results are presented to demonstrate the effectiveness of the simplified foundation model and to exhibit the dynamic response behavior of the structure as the transient loading frequency and the foundation rigidity vary. The impact of the dynamic structural response due to this type of loading on the equipment design is also discussed.     

Dynamic characteristics of charging effects on the dielectric constant due to E-beam irradiation: a numerical simulation

A series of synthetic variations of material intrinsic properties always come with charging phenomena due to electron beam irradiation.The effects of charging on the dielectric constant will influence the charging dynamic in return.In this paper,we propose a numerical simulation for investigating the dynamic characteristics of charging effects on the dielectric constant due to electron beam irradiation.The scattering process between electrons and atoms is calculated considering elastic and inelastic collisions via the Rutherford model and the fast secondary electron model,respectively.Internal charge drift due to E-field,density gradient caused diffusion,charges trap by material defect,free electron and hole neutralization,and variation in the internal dielectric constant are considered when simulating the transport process.The dynamics of electron and hole distributions and charging states are demonstrated during E-beam irradiation.As a function of material nonlinear susceptibility and primary energy,the dynamics of charging states and dielectric constants are then presented in the charging process.It is found that the variation in the internal dielectric constant is more with respect to the depth and irradiation time.Material with a larger nonlinear susceptibility corresponds a faster charging enhancement.In addition,the effective dielectric constant and the surface potential have a linear relationship in the charging balance.Nevertheless,with shrinking charging affect range,the situation with a higher energy primary electron comes with less dielectric constant variation.The proposed numerical simulation mode of the charging process and the results presented in this study offer a comprehensive insight into the complicated charging phenomena in electron irradiation related fields.     

系统背压对稳压器安全阀性能的影响

分析了稳压器先导式安全阀系统背压波动情况是否会对安全阀启闭精度、排量以及密封性等性能产生影响。通过分析计算结果显示,系统背压在规定范围内波动时,对安全阀的性能影响较小。但是应注意合理控制先导阀瓣有效密封面积和波纹管有效密封面积的比值,有利于进一步减小系统背压对安全阀性能的影响。     

Determination of earthquake loads on structures — Research and development required

This paper discusses the research and development work required in three aspects of seismic analysis, i.e. modal combination criteria in the response spectrum analysis, the techniques in modeling and simulating structures, systems and components, and the determination of dynamic lateral earth pressure during an earthquake.In the seismic analysis of structures, the lumped mass method is commonly used. For this method, the thin wall beam theory approach and the rigidity approach used in determining the effective shear areas and the distributions of translational shears are discussed. In the analysis of structures, either the time history or response spectrum method is used. When the response spectrum modal analysis method is used, the exact phase angle relation among maximum modal responses is not defined; therefore, a logical combination criterion must be established. The criterion for closely spaced modal responses to obtain system response is also mentioned. Finally, the significantly different lateral earth pressures on basement walls of embedded structures obtained using the Mononobe-Okabe method and the finite element method are also discussed. Hopefully, through further research and development work in these areas, safe and economic design can be achieved.     

安全阀水动力特性的CFD模拟和研究

运用计算流体动力学方法(CFD)对安全阀从开启到排放过程进行数值模拟,研究了安全阀的动态特性.通过动网格的生成与消亡,较好地解决了因阀瓣运动所导致计算区域瞬时变化问题.并以弹簧直接载荷式安全阀为对象,研究了不同阀前静压力下的弹簧开度、泄流量及阀芯所受轴向力变化等特性,获得了安全阀内部流场分布.模拟结果表明,应用CFD技术对安全阀动态过程的模拟,将为研究安全阀水动力特性提供一种有力工具.     

改善弹簧直接作用式安全阀密封特性的实验研究

利用力的平衡关系设计的平衡机构，可使弹簧直接作用式安全阀的密封比压力变成系统工作压力的阶跃函数，为克服弹簧直接作用式安全阀的超前泄漏提供了有利条件，本文所介绍的实验验证了平衡关系对改善弹簧直接作用式安全阀密封特性的作用。     

核级阀门模拟件制作及鉴定要求

核安全级阀门作为核电厂的一类典型重要设备,一直受到国家核安全监管部门的重点关注。申请核安全级阀门民用核安全设备设计/制造许可证的单位,按照相关核安全法规的要求,需要制作对应的模拟件,并须完成全部相应的鉴定试验。但相关规定中对于模拟件的尺寸选择、需要完成的鉴定试验项目没有给出具体的要求。本文结合许可证技术审查的经验反馈,对于申请核安全级阀门设计/制造许可证的申请单位选择模拟件的尺寸参数、准备模拟件制作的前期工作及实施模拟件制作的工艺过程控制等方面提出了一些基本要求,指出鉴定试验过程中可能产生的一些问题,为核安全级阀门民用核安全设备设计/制造许可证的申请提供技术参考。     

Simplified approach for the seismic analysis of equipment attached to elastoplastic structures

A simple approximate procedure is presented to estimate the maximum response of equipment, piping, or any other light secondary system mounted on nonlinear structures subjected to earthquake ground motions. The procedure is based on the consideration of structure and equipment as an integrated combined system, and on a response spectrum method for the analysis of nonlinear multistory structures. It is formulated in terms of the initial dynamic properties of the independent structure and equipment components, and the nonlinear response spectrum of a specified earthquake ground motion. It may be applied to any linear multiple-degree-of-freedom secondary system connected at one or two arbitrary points of a multistory structure. It fully takes into account the interaction between primary and secondary systems and the nonclassical damping character of structure-equipment systems. It is restricted, however, to structures with elastoplastic load-deformation behavior and to those cases in which the mass of the secondary system is small in comparison with the mass of the structure. Its accuracy is evaluated by means of a comparative study with the numerical integration solutions of a number of idealized systems. In this comparative study, the proposed procedure estimates the numerical integration solutions with an average error of about 2%.     

Seismic resistant design of safety class structures and equipment

Some commonly encountered problems in the seismic resistant design of nuclear power plant facilities are discussed. The topics included here are ground input motions, local geology versus source mechanism and travel path, three components inputs, torsional responses, floor response spectra, seismic resistant design of heavy equipment, the application of component mode synthesis technique, seismic resistant design of piping systems, equipment qualification by testing, the effects of close modes, underground pipe design, and soil structure interaction.     

Dynamic fragility concepts for equipment design and qualification

Fragility concepts are explored for use in the design and qualification of nuclear plant equipment and for relating the ultimate capability of equipment to that of the overall plant. In the most general sense, the fragility level of a device may depend on several different types of environmental stress or challenge factors (i.e., heat, nuclear radiation, vibration, etc.) that influence its operation. However, emphasis is concentrated on the dynamic and particularly the seismic fragility levels of equipment. A general definition of dynamic fragility and various methods for its measurement are described. The state of published data on nuclear equipment fragility is discussed, and limitations on its use are noted. From there, the concept of a standardized seismic fragility data base and its potential uses are considered. Various gaps in the methodology are identified, and recommendations for further research are suggested.     

核安全1级阀门典型违规事件分析

某制造厂在核级阀门返厂维修过程中出现核1级阀门锻件违规补焊事件,之后又在核级阀门制造过程中出现无损检验违规事件,两起事件造成核级阀门出现了质量隐患。该违规事件反映出制造厂质量保证体系运转存在严重问题,工程公司和业主监造不力。事件相关方应加强质量管理和过程控制,消除质量隐患,做好经验反馈,确保核设备质量。     

TRANTH软件基于稳压器安全阀组流量试验的确认与评估

热工水力瞬态分析软件TRANTH用于分析核电厂安全性,其中,考虑了两区质量守恒和能量守恒的关键模型之一稳压器模型可对稳压器安全阀、释放阀、电加热器、喷淋和相关系统进行模拟。在软件开发完成后需进行相关软件验证,故结合方家山核电厂1号机组稳压器安全阀流量试验数据和软件模拟结果,验证稳压器模型。结果表明,模拟计算结果与现场试验数据符合度高,模型精度满足工程设计要求。