振动条件下平行孔板间流体的作用力实验

乏燃料贮存格架自由放置在乏燃料水池内,格架 格架、格架 池壁之间有一定间隙。在地震载荷下,这些间隙中流体的流固耦合作用耗散了结构的能量,保证了格架的结构完整性。根据AP1000和CAP1400系列反应堆型的格架储存腔设计,格架的侧壁有平板或孔板两种方案。对格架进行结构动力学分析时,为了简化流体间隙附加质量的计算,工程上一般将孔板直接简化为平板。这样的方法并不能精确反映出实际的流固耦合效应。为获得格架与格架、格架与池壁间流体的流固耦合特性,搭建实验台架,通过振动实验,测量孔板的间隙流体在不同激振频率、不同间隙条件下的流体作用力。实验最终给出孔板的间隙流体的流体力,并给出了不同间隙条件下附加质量,本文可为AP1000和CAP1400系列乏燃料储存格架的流固耦合参数选取提供依据。     

乏燃料贮存格架时程分析方法

乏燃料贮存格架是用于贮存换料后的乏燃料组件的重要设备,其自由放置在核电厂乏燃料水池中,在地震载荷下的响应属于非线性响应,包含了各种复杂的运动:滑移、碰撞、扭转、倾覆等。为了准确描述上述非线性响应,本文建立了乏燃料贮存格架整池有限元模型并进行非线性时程分析,考虑了滑移、碰撞、摩擦等影响因素,同时还考虑了乏燃料贮存格架在水池中的流固耦合效应。通过时程分析得到了乏燃料贮存格架在地震载荷下的位移、载荷等计算结果。该方法可用于乏燃料贮存格架的抗震分析。     

乏燃料贮存格架流固耦合参数的数值模拟

乏燃料贮存格架是储存乏燃料组件的重要设备。在地震载荷下,其响应是非线性的,可能产生滑移、颠覆等。发生地震时,存在于格架间隙内的流体耗散了结构的能量,保证了格架的完整性。本文使用3/10缩比模型,利用CFD软件Fluent进行了乏燃料贮存格架2D瞬态分析。计算过程中利用动网格方法模拟格架强迫振动,并进行了参数不确定性分析。利用CFD瞬态流体力分别获得了双Ⅱ区、双Ⅰ区格架附加质量矩阵。利用同轴圆柱体附加质量的计算解与解析解进行对比验证,证明了本文计算方法的准确性。本文计算所得的附加质量矩阵可为乏燃料贮存格架结构动态软件提供流固耦合参数。     

乏燃料水池贮存格架水下安装工艺研究

通过拆除乏燃料水池内原有的乏燃料贮存格架,安装更密集的乏燃料贮存格架,可提升乏燃料水池的贮存能力。以国内某商用核电站乏燃料水池扩容改造为研究对象,分析了乏燃料贮存格架在水下安装的难点,提出了根据测量池底的不平整度调平乏燃料贮存格架的垂直度,然后在水下进行定位安装施工,并制定了乏燃料贮存格架水下安装精度检验方法。在水下安装的乏燃料贮存格架达到了使用规定的位置、高度和垂直度,保证了燃料组件的安全装载。该工艺可为国内各大核电站进行乏燃料水池扩容改造提供经验参考。     

乏燃料贮存格架热工水力分析

通过计算流体力学的方法对新型国产乏燃料贮存格架进行热工水力分析,评估新型CPR乏燃料贮存格架在乏燃料池中的局部热工性能,计算在最大水力阻力下,包含放热量最大的乏燃料组件的格架贮存单元的局部最高温度。同时,经过理论计算分析了乏燃料池失去冷却水的极端工况下,乏燃料池的沸腾时间和贮存格架裸露时间。数值计算应用CFX流体分析软件,基于多孔介质模型完成计算分析。分析结果表明乏燃料池局部最高温度低于当地压力下水的饱和温度,满足格架的应用要求;在功率运行工况下失去冷却水,乏燃料水池沸腾时间足以用于采取有效措施应对极端工况。     

窄间隙流固耦合结构抗震分析流程规范化研究

对于窄间隙流固耦合效应,采用简化方法得到附加质量和地震激励修正系数。在乏燃料贮存格架的抗震分析中,对其分析流程进行规范化,即在考虑流体附加质量的同时,也对地震激励进行修正,从而得到乏燃料贮存格架在地震载荷下的力学响应。在此研究基础上可以进一步建立窄间隙流固耦合结构抗震分析标准。     

海洋核动力平台乏燃料贮存格架设计及安全分析研究

针对海洋核动力平台乏燃料组件海上长期贮存所面临的安全保证问题,通过改进燃料组件与贮存小室之间固定形式、优化贮存小室与贮存格架本体之间连接形式以及增加贮存格架与乏燃料水池池壁之间的缓冲结构,设计了一种满足设计基准以及适应海洋环境的乏燃料贮存格架,并采用蒙特卡罗程序MCNP-5、计算流体力学软件Fluent 14.0、有限元分析软件ANSYS 17.0对该贮存格架进行临界、热工、结构仿真计算。结果表明,该贮存格架设计合理、安全性高,可为海上浮动式核电站乏燃料贮存提供解决方案。      

秦山核电二期工程乏燃料贮存格架的设计

在秦山核电二期工程的设计中，乏燃料的贮存采用了中子毒物镉的密集型贮存格架，与疏松型贮存格架相比，大大提高了乏燃料贮存水池单位面积的贮存能力。镉密集贮存格架的设计在国内尚属首次．本文介绍了该型贮存格架的方案选择以及设计中考虑的主要原则和要求。     

基于机器视觉技术的乏燃料贮存格架自动定位试验方法研究与应用

乏燃料贮存格架定位试验是核燃料装卸与贮存系统调试的一项关键性试验,直接影响着核燃料组件接收与贮存操作的安全性与高效性。通过对传统的人工手动定位试验方法进行研究,提出了一种基于机器视觉技术的乏燃料贮存格架自动定位试验方法。工程应用实践表明,该方法可以大幅提升定位试验效率并减少人力需求,同时在乏燃料水池异物防护与设备保护方面也卓有成效,具有可观的经济与安全质量效益。      

基于超单元技术的乏燃料贮存格架多自由度非线性抗震分析

基于有限元软件ANSYS超单元分析技术,建立乏燃料贮存格架整池超单元模型,对格架地震响应进行更精确的多自由度模拟。考虑了格架间流-固耦合影响,对整池格架进行非线性时程抗震分析,获得了格架的跳起位移、碰撞加速度、滑移位移等计算结果,并将超单元模型抗震分析结果扩展到格架详细模型,得到格架地震下的变形和应力。分析结果表明:基于超单元分析建模的技术方法显著提高了分析效率,格架响应计算也更为精确,可用于乏燃料贮存格架的抗震设计。      

Nonlinear 3-D dynamic time history analysis in the reracking modifications for a nuclear power plant

An independent seismic response evaluation of spent fuel storage racks was performed on the reracking modifications for a typical operating pressurized water reactor type nuclear power plant using nonlinear dynamic time history analysis methods per the U. S. Nuclear Regulatory Commission (USNRC) criteria. The submerged free standing rack system and surrounding water are coupled due to fluid-structure-interaction effects using potential theory. Three dimensional (3-D) single rack and whole pool multiple rack finite element models were developed with features that allow the consideration of geometrically and materially nonlinearities including 1) the impact of a fuel bundle to a rack cell, a rack to adjacent racks or pool walls, and rack support legs to a pool floor; 2) the hydrodynamic coupling of a fuel assembly with a rack and of a rack with adhacent racks or pool walls; and 3) the tilting and frictional sliding of the rack supports. The methodologies and typical results using a 3-D single rack model as well as a 3-D whole pool multiple rack model developed herein are presented.     

Improved method to demonstrate the structural integrity of high density fuel storage racks

Reracking of existing fuel pools to the maximum extent is desirable from an economical point of view. This goal can be achieved by minimizing the gaps between the spent fuel storage racks. Since the rack design is aimed at enabling consolidated fuel rod storage, additional requirements arise with respect to the design and the structural analysis. The loads resulting from seismic events are decisive for the structural analysis and require a specially detailed and in-depth analysis for high seismic loads. The verification of structural integrity and functionality is performed in two phases. In the first phase the motional behavior of single racks, rows of racks and, where required, of all racks in the pool is simulated by excitation with displacement time histories under consideration of the fluid–structure interaction (FSI). The displacements from these simulations are evaluated, while the loads are utilized as input data for the structural analysis of the racks and the pool floor. The structural analyses for the racks comprise substantially stress analyses for base material and welds as well as stability analyses for the support channels and the rack outside walls. The analyses are performed in accordance with the specified codes and standards.     

核电厂乏燃料贮存格架水下吊装工具研制

针对某二代核电厂乏燃料贮存格架水下吊装的需求,根据乏燃料贮存格架的水下布置特点,对水下吊装接口安全性及操作便利性进行分析,研制了一种通过抓放格架底板流水孔来实现格架水下自锁的兜底式格架吊装工具,并详细介绍了此水下吊装工具的结构组成、使用操作及工作原理;最后将此格架用于某二代核电厂20台格架的吊装作业。现场应用表明,此吊装工具操作简便、结构可靠,满足格架水下吊装需求。      

Passive cooling of the PBMR spent and used fuel tanks

The pebble bed modular reactor (PBMR) is a new generation high temperature gas-cooled reactor, making use of spherical fuel elements. The spent fuel and partially burnt fuel (called used fuel) is stored in large storage tanks. This paper presents the cooling design of the storage tanks, with special emphasis on its passive cooling ability.For corrosion protection, the tanks are cooled with a closed loop active system, however, passive cooling is seen as the ultimate cooling mode for the storage tanks. If the active cooling fails, the flow automatically bypasses the active system and passive cooling takes over. The active cooling is thus not safety-related; rather its purpose is for investment protection.The storage tank design with its longitudinal internal cooling pipes has a good passive cooling ability. The layout of the tank concrete cubicle ensures that cooling air can flow only in the desired direction. Computational fluid dynamics (CFD) analyses have been done for various heat load scenarios inside the tank. Passive cooling exists for tanks with a low spent fuel fill level with heat load below 25 kW up to a tank containing a full PBMR core (used fuel) with heat load of 640 kW. For all scenarios, the maximum fuel temperature is below 400 °C.A method was developed to calculate the passive cooling characteristics of the tank at a fraction of the time it takes CFD by using the pipe network simulation software Flownex. The method was also used to analyze transient passive cooling events and showed flow phenomenon similar to what CFD analyses have predicted.A small-scale two-dimensional representation of the storage tank and cubicle layout has been built. This experiment demonstrates the passive cooling ability of the tank. It also proved the flow characteristics that were predicted by the CFD and Flownex analyses.It has been shown through diverse techniques that the fuel inside the tanks can be cooled passively. There are still a few aspects which need to be explored in more detail, but overall it can be said that passive cooling of the PBMR spent and used fuel in bulk storage tanks is viable.     

Beyond design basis accidents in spent-fuel pools — Generic Issue 82

Nuclear reactor plants include storage facilities for the wet storage of spent-fuel assemblies. The safety function of the spent-fuel pool (SFP) and storage racks is to cool the spent-fuel assemblies and maintain them in a subcritical array during all credible storage conditions and to provide safe means of loading the assemblies into shipping casks.Generic Issue 82 (GI-82) relates to the concern that for a postulated accident sequence that results in the loss of water from a light-water reactor (LWR) spent-fuel storage pool, a Zircaloy cladding fire could occur and propagate to older stored fuel. This issue was identified during hearings concerning SFP reracking amendments in the late 1970s when licensees were starting to use high-density storage racks. High-density racks are used to accommodate the storage of spent fuel in SFPs at reactor sites until such time as the Department of Energy (DOE) repository is available and spent fuel can be removed from the reactor sites. Maintaining a low-density storage configuration for recently discharged spent fuel would reduce the Zircaloy cladding fire probability by an order of magnitude, but at a greater cost for additional onsite storage space.The accident sequences that could result in water loss from the SFP, including beyond design basis earthquakes, various types of seal failures and dropped shipping casks, and the Zircaloy cladding fire issues have been studied by the NRC staff. The results of these studies are provided in NUREG-1353, “Regulatory Analysis for the Resolution of Generic Issue 82, Beyond Design Basis Accidents in Spent-Fuel Pools”. Although these studies conclude that most of the spent-fuel pool risk is derived from beyond design basis earthquakes, this risk is not greater than the risk from core damage accidents due to these beyond design basis earthquakes. Therefore, reducing the risk from spent-fuel pools due to events beyond the safe shutdown earthquake would still leave a comparable risk due to core damage accidents. The risk due to beyond design basis accidents in spent-fuel pools, while not negligible, is sufficiently low that the added cost involved with further risk reduction is not warranted.     

压水堆燃料组件附加质量仿真研究

为了准确探究反应堆冷却剂与燃料组件间存在流固耦合行为对燃料组件振动特性的影响,本文采用计算流体动力学（CFD）软件Fluent平台,运用其中的动态网格技术,以压水堆燃料组件为研究对象,通过建立燃料组件模拟棒束、堆芯围板以及冷却剂模型,实现燃料组件与堆芯围板分别单独运动工况的燃料组件附加质量计算。结果显示：燃料组件运动工况下,燃料组件附加质量系数均值为2.4712;围板运动工况下,燃料组件附加质量系数均值为–3.4713,均与文献值偏差小于5%。叠加附加质量后,燃料组件振动频率计算值与水中振动试验测试结果偏差小于5%,验证了分析方法的合理性。本研究建立的仿真计算方法能够用于压水堆燃料组件附加质量计算。     

Heat transfer in spent fuel storage

Heat transfer and fluid flow analyses are described for the underwater storage of spent fuel from nuclear power reactors. The analytical methods and supporting test measurements have been employed by General Electric Company in the design and licensing of two spent fuel storage systems: (a) High-density racks for storage of BWR spent fuels in at-reactor water basins [1]. (b) Multi-element baskets for storage of BWR and PWR spent fuel in GE's facility near Morris, IL [2]. The results show that natural convection flow through individual spent fuel bundles provides safe and effective temperature control. Under accident conditions the relatively slow dynamics of the basin system permits timely repair to a loss of basin cooling capability without significant risk to the spent fuel in storage.     

核电厂中流固耦合现象数值模拟研究综述

流固耦合现象在核电厂中广泛存在，该现象引起的结构动力学问题对核电厂结构完整性和安全性有重要影响。目前，国内外对核电厂中流固耦合现象的研究给予越来越多的关注。本文介绍华北电力大学在该方面的一些研究进展，例如，快堆燃料组件抗震分析新的流体附加质量计算方法研究；蒸汽发生器换热管双管漩涡脱落的数值模拟；一个先进堆燃料组件平行板上流动引起的漩涡脱落数值模拟；由地震引起的自由表面对快堆主容器冲击现象的研究；移动粒子法求解液面晃动及晃动引起离散现象的研究等。