低温精馏氢同位素分离全回流模式研究

为探求全回流模式下低温精馏氢同位素分离过程中有关操作参数的内在联系,研究了再沸器加热功率对脱氘率、床层压降、液氢液位等的影响。当再沸器加热功率从5W增加到12.4W时,脱氘率从88%增加到99.6%,脱氘率与再沸器加热功率基本呈线性关系。随再沸器加热功率的增加,液氢液位下降,床层压降增加,但在该功率范围内未出现液泛现象。随加热功率增加,精馏柱操作压力从100kPa升高到190kPa,冷凝器和冷头为提供更多冷量而温度降低。     

蒙脱石含量对膨润土膨胀行为影响的试验研究

高放废物深地质处置中,作为缓冲回填材料的膨润土应具有良好的膨胀性能。为了解蒙脱石含量对膨润土膨胀行为的影响,采用自行设计的试验装置对不同蒙脱石含量膨润土的膨胀行为进行了试验研究。结果表明,在试验条件下,成型膨润土膨胀行为的各项指标(轴向最大膨胀力和径向最大膨胀力)均随着蒙脱石含量的增加而增加,且呈线性关系。蒙脱石含量为70%时,径向、轴向最大膨胀力分别达到2.03 MPa和2.25 MPa,其比值为0.902。结果可为膨润土设计提供参考。     

膨润土与水相互作用初步研究

为研究膨润土与水作用后对高放废物地质处置安全性产生的影响,将不同蒙脱石含量的临安钠基膨润土和兴和钙基膨润土置于水中长期浸泡3 000 h。结果表明:二种膨润土的膨胀指数皆随着蒙脱石含量的增加而增加,且最大膨胀指数与蒙脱石含量间的对数值呈线性关系;膨胀平衡后上清液中一价阳离子浓度大于二价阳离子的浓度,且随着蒙脱石含量的增加而增加,数据表明Na⁺浓度与膨润土中蒙脱石含量的对数值呈线性关系;上清液烘干后残留物质量随蒙脱石含量增加而增加,XRD图谱表明其中已存在蒙脱石。这些结果可作为进一步开展地质处置中缓冲材料与地下水相互作用的研究基础。     

无损检测技术在缓冲材料砌块压制质量检测中的应用

缓冲材料是高放废物地质处置库的最后一道人工屏障,通常是以高压实预制砌块的形式堆砌在废物罐周围,砌块压制质量将极大地影响其工程性质。以缓冲材料压实砌块为研究对象,使用超声波测试、热传导测试和激光三维扫描3种无损检测方法,对不同尺寸和干密度的小型试样、大型砌块的不同位置进行了质量检测和分析。结果表明：小型试样的纵波波速随干密度和含水率的增大而增大,纵波波速与干密度呈近似线性关系,大型砌块的纵波波速随压制面距离的增加而减小;大型砌块顶面各个位置的导热系数变化不明显,砌块高度方向导热系数随压制面距离的增加而减小,且与纵波波速测试结果具有一致性。激光三维扫描技术可以快速、全面获取砌块的线、面和体等各种数据参数。因此,超声波测试、热传导测试和激光三维扫描可为缓冲材料大型砌块制备工艺的优化和砌块压制均匀性的评价提供重要的参数依据和技术支撑。     

零功率摇摆条件下自然循环试验回路中流动规律实验研究

以清华大学研发的多用途小型堆NHR为基础,建立全尺寸、全参数1∶1自然循环试验回路研究零功率摇摆条件下自然循环的流动规律。通过分析几组不同摇摆运动下的实验结果,探讨了单自由度摇摆运动摆角幅值ψ_m和摇摆周期T对自然循环速度的影响,并给出自然循环流速波幅V_o和摇摆运动参数ψ_m与T之间的线性关系。研究结果表明：ψ_m对加热段两侧流速影响最为显著,V_o随ψ_m的变大而增大且两侧流速波动相位相差90°;V_o随T的增大而减小,流速波动相位差与T无关;在零功率摇摆条件下,流速波幅的平方V²_o与ψ_m、频率平方w²_d及当量摇摆半径R_eq的乘积呈线性关系。     

自然循环条件下窄通道ONB点影响因素灰色关联度研究

采用反映系统序列间正、负相关性的灰色关联度模型,对自然循环条件下影响窄通道过冷沸腾起始点(ONB点)发生的相关因素进行分析.结果表明:在所选参数范围内,加热功率与ONB点位置呈负相关性,质量流量和工质压力与ONB点位置呈正相关性,即加热功率增加ONB点提前出现,质量流量增加、工质压力提高ONB点推后出现;窄缝间隙与ON...     

非对称工况下并联通道流动不稳定性研究

针对并联矩形通道,基于集总参数法建立了并联通道流动不稳定性分析模型,并基于此模型分析了非对称工况对系统稳定性的影响。分析结果表明,非对称工况对并联通道流动不稳定性有显著影响,在保持平均节流系数恒定的情况下,非对称节流的影响随压力增大而降低,随质量流速增大而增大;界限功率随加热不对称度增加呈先上升后下降趋势,且非对称加热的影响随压力增大而增大,随入口过冷度和质量流速增大而减小。     

热管反应堆堆芯缩比模块瞬态特性分析

热管堆具有长寿期、高可靠性等优势,是当下空间核反应堆的研究焦点之一。为研究热管堆瞬态过程中的核热耦合现象,本文基于半物理仿真技术,搭建了针对热管反应堆堆芯缩比模块的核热耦合实验平台,通过实验模块测量了堆芯缩比模块的温度分布,在仿真模块中基于点堆模型计算了输出功率随时间的变化情况。通过耦合实验模块和仿真模块,探索了瞬态条件下堆芯缩比模块核热耦合特性,分析了引入不同初始反应性时堆芯温度、加热功率和剩余反应性的瞬态演变过程,揭示了系统热容量造成的温度迟滞变化效应,即热惯性现象。结果表明,堆芯缩比模块的热惯性随引入的初始反应性的增大及初始功率水平的增加而减小,且与基体材料的热扩散率呈反比。     

FLiNaK熔盐高温试验回路电磁感应加热的数值模拟

FLiNaK熔盐高温试验回路中的球床实验区旨在研究FLiNaK熔盐与燃料球的换热、腐蚀特性。石墨球床实验区采用独特的中频感应加热技术加热石墨球导体,模拟球床先进高温堆(Pebble Bed Advanced HighTemperature Reactor,PB-AHTR)堆芯燃料球的释热。为了研究石墨球堆积方案对感应加热的影响,利用有限元方法对电磁感应加热进行数值模拟,获得石墨球导体的涡流损耗功率,并从涡流功率和功率分布两方面对三种石墨球堆积方案进行对比分析。结果表明:三种堆积方案的相对轴向功率分布几乎一样,每层石墨球不相切堆积方案的径向功率分布比另外两种堆积方案的径向功率分布更均匀;为了均匀加热石墨球,更好地模拟PB-AHTR堆芯燃料球释热,建议采用每层石墨球间不相切的堆积方案。     

核电厂堆芯出口温度测量表征性分析

堆芯出口温度测量对于掌握反应堆运行状态有着重要的意义，本文通过计算流体动力学（CFD）方法对堆芯出口温度测量的表征性进行分析。通过对燃料组件及仪表管结构进行模拟计算，获得了仪表管内冷却剂流场和温度分布；通过对9种典型功率分布下堆芯出口温度测量结果的定量分析，获得了堆芯出口温度表征性与燃料组件功率的关系。结果显示，测点平均温度与燃料棒功率基本呈线性关系，其测点温度随燃料棒功率的增加而增加，测温表征性随燃料棒功率的升高而变差。研究结果为堆芯出口温度测量的校正提供了一定的依据。     

Dependency of Doppler Factors on Resonance Self-Shielding Factors for Gold and Silver

A simple model was developed to evaluate the effect of the radial power profile on the thermo-hydraulics in the core during reflood phase of loss-of-coolant accident in PWRs. It was incorporated into REFLA code, a reflood analysis code.

The model assumes that the fluid mixes completely among subchannels and additionally that the fuel temperature is not affected each other among fuels. This model is featuring no three-dimensional treatment for the evaluation on effect of the radial power profile.

The model improved the predictability of clad temperature and gave a better prediction than a method which is generally used in the safety analysis. The model predicted a poorer core cooling in high radial power region than data. The error of the prediction increased with the increase in radial power ratio. These indicates the conservativeness of the model on the maximum clad temperature prediction. The reason of the conservativeness is due to the neglection of the heat transfer enhancement by two-dimensional effect in high power region.     

Quantitative Evaluation of Heat Transfer Enhancement due to Radial Power Distribution during Reflood Phase of PWR-LOCA

Experimental studies using Slab Core Test Facility (SCTF) and Cylindrical Core Test Facility (CCTF) indicated that the degree of heat transfer enhancement due to the radial power distribution during the reflood phase of a PWR-LOCA was governed mainly by the radial power ratio itself and less dependent on the shape of radial power distribution within the maximum power ratio of 1.36. The experimental condition covering the wide ranges of the reflood phase and the scale of core radius from 1/4.6 to 1/1 had little effect on the two- dimensional heat transfer behavior. The heat transfer coefficient under nonuniform radial power distribution was expressed as a sum of the heat transfer coefficient obtained under a complete mixing condition and an additional value given by an empirical correlation based on the SCTF results. The temperature rise at the peak power rod calculated with this expression tended to be lower than that calculated with the complete mixing model used in a reflood analysis code REFLA. That is, the complete mixing model was proved to give a conservative result under a nonuniform radial power distribution condition in a full size core.     

兆瓦级热管反应堆堆芯核热特性研究

基于美国MegaPower兆瓦级热管反应堆设计方案,本文利用蒙特卡罗软件OpenMC与有限元分析软件COMSOL开展堆芯核热特性研究。研究表明：堆芯轴向功率分布呈先升高后降低趋势,且下半段功率水平比上半段高。径向功率随径向距离的增大而降低,在靠近径向反射层处出现反弹升高,且这些区域的功率分布明显受转鼓组件的影响。“大小转鼓”的设计方案不利于兆瓦级热管反应堆的反应性控制。边界区域位置热管失效会造成更高程度的基体/燃料温度上升。3根热管失效工况下的燃料棒温升是2根热管失效的32倍。即使3根热管失效的极端事故工况下,堆芯基体及燃料棒峰值温度仍在安全限值内,表明兆瓦级热管反应堆这种固态导热堆芯的优越安全性。     

Numerical Investigation of Heat Transfer Enhancement Phenomenon during the Reflood Phase of PWR-LOCA

The heat transfer in higher power bundles was enhanced in large-scale reflood tests at Japan Atomic Energy Research Institute. The heat transfer enhancement in the core under a radial power distribution is very important to quantify the safety margin in PWR-LOCA. In this study, we analyzed the physical mechanism by numerical simulations with a multi-dimensional two-fluid model code, REFLA/TRAC, using data from the large scale reflood test. The heat transfer enhancement is caused by the increase of local upward liquid velocity resulting from the formation of flow circulation in the core. The flow circulation is generated by a radial difference of waterhead below quench front under a radial power distribution. The upward liquid velocity depends on the bundle power and the cross flow resistance. The higher power and the smaller cross flow resistance give the higher upward liquid velocity, which increases the magnitude of the heat transfer enhancement. Through the present study, some guidelines were obtained for the multi-dimensional analyses to predict the heat transfer enhancement phenomenon with high accuracy.     

Experimental Study of Two-Dimensional Thermal-Hydraulic Behavior in Core during Reflood Phase of PWR LOCA

Two-dimensional effects on the core cooling behavior during the reflood phase of a PWR-LOCA were experimentally studied by performing four tests with various radial core power profiles under the same total power and initial core stored energy conditions using the Slab Core Test Facility (SCTF). The heat transfer was enhanced and the cladding temperature was reduced for the higher and average power bundles in the steep radial power profile test especially at the upper elevation. The effect of radial power profile on the cladding temperature was quantitatively evaluated. For all tests with different radial power profiles, the collapsed water level in the upper plenum became higher in the hot leg side and the quench in the upper half of the core was delayed in the bundles corresponding to the outer bundles of a PWR core. The delay of the quench is considered to be caused by a flow stagnation trend in those bundles because the pressure in the outer bundles became higher than the pressure in the inner bundles due to the nonuniform water accumulation in the upper plenum.     

Investigation of radial heat conduction with 1D self-consistent model in helicon plasmas

A 1D radially self-consistent model in helicon plasmas has been established to investigate the influence of radial heat conduction on plasma transport and wave propagation.Two kinds of 1D radial fluid models,with and without considering heat conduction,have been developed to couple the 1D plasma-wave interaction model,and self-consistent solutions have been obtained.It is concluded that in the low magnetic field range the radial heat conduction plays a moderate role in the transport of helicon p...     

热管冷却反应堆核热力耦合研究

热管冷却反应堆（简称“热管堆”）高温运行下的结构热膨胀效应会显著影响反应堆的传热和中子物理输运过程。本文提出了一种考虑固体堆芯显著膨胀的几何更新和反应性反馈方法,并构建了基于动态几何的中子物理/热工/力学3场核热力耦合分析程序。在核热力耦合中主要考虑温度引起微观截面的变化、材料密度的变化以及热膨胀引起堆芯尺寸的变化。基于提出的核热力耦合方法,对MegaPower热管堆进行了核热力耦合分析,分析了不同松弛因子下,堆芯功率分布和径向功率因子的收敛性。核热力计算表明,热膨胀造成堆芯边通道的中子泄漏增加,从而产生负反应性反馈;同时,边通道中子泄漏增加加剧了功率分布的不均匀性,传热恶化,考虑核热力耦合后,径向功率因子从非耦合情形的1.20提升到1.23,燃料峰值温度增加11 K。      

Thermo-hydraulic analysis for SCWR during power-raising phase of startup

The study of thermal characteristics during startup is one of the most important aspects for safety analysis of supercritical water-cooled reactor(SCWR).According to the given sliding pressure mode of SCWR,thermal analysis on temperature-raising phase and power-raising phase of startup are carried out.Considering the radial heterogeneity of power distribution,thermal characteristics for different assemblies during startup are also put forward.The results show that,during temperature-raising phase with core power increased only,the temperature of moderator,coolant and fuel cladding in inner assemblies are increased with little amplitude.During power-raising phase with core power and feed-water flow rate increased,the coolant temperature keeps unchanged,but the moderator temperature is decreased.With a greater variation of power,fuel cladding temperature shows a greater increase.Furthermore,considering the uneven distribution of radial power,thermo-hydraulic characteristics with uneven cladding temperature distribution shows a certain horizontal heterogeneity for different fuel assemblies,which becomes serious as flow rate and power increase.By adjusting flow rate distribution in different fuel assemblies or changing power setting during startup,the cladding temperature difference could be effectively reduced,which provides a certain reference for startup optimization of SCWR.     

熔融池相变传热特性的大涡模拟数值研究

研究反应堆熔融池内部的流动与传热特性对保证熔融物堆内滞留具有重要意义。本文基于开源软件OpenFOAM平台,结合大涡模拟湍流方法和熔融池相变过程建立熔融池传热模型,针对典型熔融池传热实验LIVE工况开展数值计算,得到了熔融池内速度场和温度场以及下封头内壁面硬壳厚度和热流密度分布情况。结果表明,熔融池内速度、温度和热流密度随高度或径向角度的增大而增大;硬壳厚度随径向角度的增大而减小;下封头壁面上的热负荷在顶部聚集。传热参数计算结果与实验数据整体符合较好,可以有效反映出熔融池内自然对流与相变过程,验证了计算模型的可靠性,可为进一步研究熔融池相变传热特性提供参考。      

不凝性气体对高温锂热管传热特性的影响研究

热管作为一种具有高热导率的传热装置,工作核心在于其内部工作流体的蒸发和冷凝。若热管工作过程中气腔内存在不凝性气体,主流区中蒸气和不凝性气体在对流运动的作用下将一起移动到气-液分界面,不凝性气体的存在阻碍了工作流体在气-液交界面处的正常冷凝。本文基于热阻网络法添加了不凝性气体区域传热模型,研究了不凝性气体对高温锂热管稳态传热特性的影响。结果表明,热管达到稳态时不凝性气体的存在缩短了热管的有效传热长度,破坏了热管的等温性和良好的传热效率。此外随着不凝性气体体积份额的增大,不凝性气体区域温度降低幅度越大;随着热管蒸发段输入功率的增大,热管正常工作区域整体温度越高,相同质量的不凝性气体占据的体积份额越小,热管壁面温度出现明显温度梯度降低的位置随着功率升高而向下游移动。