不同运行工况下蒸汽发生器热工水力稳态特性数值研究

基于相似模化理论建立了蒸汽发生器一、二回路流体及传热管流 固耦合传热的单元管三维物理模型,对大亚湾核电厂蒸汽发生器不同工况下的热工水力稳态特性进行了数值模拟研究。采用热相变模型描述二回路汽液两相流动与换热、流-固耦合模型描述一回路冷却剂借助U型管与二回路流体换热。数值计算结果表明：满负荷运行时,传热管内壁温度变化趋势与一次侧流体基本一致,外壁温度与二次侧流体温度变化趋势相同;截面平均含汽率沿传热管高度的升高呈上升趋势,出口质量含汽率与大亚湾核电厂实际运行参数相符;随负荷降低一回路出口温度基本不变,二回路出口温度升高,质量含汽率及传热系数下降,平均传热系数与Rohsenow经验关联式的计算结果基本吻合。     

蒸汽发生器一维均相流模型及其换热性能

以大亚湾核电站蒸汽发生器为原型,在合理假设基础上,分别以一回路流体、二回路流体及U形管内、外壁为研究对象,建立了蒸汽发生器一维均相流模型。采用Jacobi迭代法编制了基于MATLAB的仿真程序,对蒸汽发生器不同工况下的稳态换热性能进行计算,得出各流程关键参数的变化规律,计算结果与大亚湾核电站实际运行数据相吻合。计算结果揭示了蒸汽发生器的内在传热规律,可为蒸汽发生器优化设计提供一定的理论依据。     

基于MOOSE平台的高阶全隐式核反应堆一回路系统分析

基于多物理场耦合平台MOOSE开发了模块化系统安全分析程序ZEBRA,并采用高阶全隐式离散格式建立了核反应堆一回路系统模型,对核反应堆系统中子扩散、二维固体导热和一维流体进行耦合计算。针对单管流动传热问题,对ZEBRA程序进行了耦合验证,对比了稳态工况下一阶、二阶空间离散格式和瞬态工况下Implicit-Euler、Crank-Nicolson、BDF2 这3种时间离散格式的求解精度,并对压水堆回路系统稳态和降功率瞬态工况进行了模拟分析。结果表明,高阶空间离散格式具有较高的求解精度,BDF2时间离散格式与理论解符合最好;压水堆回路系统温度、速度、压力分布合理,稳态、瞬态计算结果与RELAP5程序计算结果符合良好。      

HTR-10一回路放射性石墨粉尘实验系统设计及研究

在10MW高温气冷堆(HTR-10)氦净化系统中,设计并建造了用于取样收集一回路放射性石墨粉尘的实验系统。结合国外已有的研究结果,根据HTR-10氦净化系统的运行参数进行了模拟计算。计算结果表明,该实验系统能有效过滤收集到的放射性石墨粉尘。所设计的取样过滤器便于拆卸和后期测量,可实现对放射性石墨粉尘进行长期系统的研究,给出反应堆不同运行工况下一回路氦净化系统中石墨粉尘及固体裂变核素活度的信息,将为HTR-10高温气冷堆裂变产物行为研究提供大量重要的实验研究数据。     

两相条件下主泵特性试验研究

针对自主研发百万千瓦级核电主泵项目,本研究在专设台架上对经过模化缩比后的模型试验泵开展特性研究,首先开展泵单相液体条件下正常工况、水轮机工况、耗能工况、卡轴工况、飞逸工况的流动特性试验,之后逐一针对两相空泡份额为0.1、0.2、0.3、0.4、0.5、0.6、0.7、0.8、0.9、1.0条件下的泵在上述具体运行工况开展研究,最终利用比例定律,对多个转速下的实验数据进行整理,进而掌握了其扬程在不同空泡、不同流量下的变化规律,在单相液体基础上的泵扬程比例定律曲线随着空泡份额的增大会存在不断“漂移”和再回归的过程,当空泡份额达到0.7左右时,“漂移”程度最大,当流体变为单相气体时,实现再回归,上述实验结果为后续核主泵设计的深入研究及一回路安全分析提供了数据支撑。      

中国实验快堆一回路热工水力稳态计算程序开发

针对中国实验快堆(CEFR)的具体结构和稳态运行特点,利用Fortran语言开发了CEFR一回路热工水力稳态计算程序。重点开发了有关钠的多种物性的子程序、适应不同工况的钠的流动与换热计算子程序,并对关系式进行了对比分析,最后建立了稳态计算模型并开发了程序。在此基础上,对CEFR的一回路系统在满功率下的稳态热工水力特性进行了计算分析,所获得的结果同设计参数吻合,证明了所开发的子程序及稳态程序的正确性。     

横摇运动下铅铋回路热工水力特性数值研究

为研究横摇运动下铅铋回路系统热工水力特性，利用商用CFD软件开发了铅铋回路系统的计算模型以及横摇运动的计算方法，并采用实验数据对数值计算结果进行了验证，其中，横摇运动流量的最大偏差在3%以内。计算结果表明，横摇运动会使回路系统的自然循环流量发生周期性波动，流量波动的周期与运动周期一致，波动的幅度会随着横摇运动最大幅度的增大、运动周期的减小而增大，在最大摇摆角20°摇摆周期7.5 s工况下流量的瞬时波动最大达到了140%,并在一些时刻产生倒流现象。横摇运动也会让系统的流动和传热特性参数发生周期性的瞬时波动，这种波动的规律与自然循环流量的波动规律相似，其中Nu的最大瞬时波动达到了515%,最大时均波动可达66%。本研究获得的结果对横摇运动下的铅铋回路系统设计优化具有重要的工程应用价值和科学意义。     

气空间可压缩性对两相流动系统稳定性的影响

实验研究了反应堆一回路上方气体空间可压缩性对反应堆一回路自然循环两相流流动稳定性的影响。通过发迹液位的办法改变一回路中气空间占整个回路的体积比，得到了不同体积比条件下，流量振幅与加热段入口过冷度的关系。     

CEFR在ULOF工况下的自然循环能力分析

自然循环能力是衡量钠冷快堆固有安全性的重要指标,堆芯布置、回路设计及工况参数等都会影响堆芯自然循环能力,因此不同堆型的自然循环能力有很大差异。为了保证堆芯事故得到有效缓解,中国实验快堆(CEFR)的设计中通过优化系统布置,重点考虑了堆芯自然循环。本文采用SAS4A程序对CEFR进行系统建模,分析了CEFR在无保护失流(ULOF)工况下的堆芯热工水力参数瞬态特性,验证了CEFR利用自身自然循环和负反馈设计进行事故缓解的能力,本文还对一回路流动阻力和二回路钠装量对堆芯自然循环的影响进行分析。计算结果表明,CEFR具有良好的自然循环特性,在ULOF工况下可以依靠其负反馈停堆,并能够建立起稳定的自然循环从而导出堆芯余热。     

一体化小型堆主回路自然循环稳态特性实验研究

在模拟一体化小型堆主回路的自然循环试验台架上,进行了小型堆主回路自然循环稳态流动特性的实验研究。结果表明:在输入的外部条件保持一致的情况下,实验本体内的自然循环流动保持了很好的对称性;影响自然循环流量的主要因素是加热功率,入口温度、系统压力等参数的影响较小;提出了一个表征系统自然循环能力的综合特征参数k,可当作指标参数来衡量不同的自然循环回路或不同的运行工况下的自然循环能力,对进一步优化一体化自然循环反应堆的参数设计具有重要指导意义。     

Steady-state performances and scaling analyses for an open flashing-driven natural circulation system

Simulating investigations are carried out to study the steady-state performances, the pressure resistance distributions and the scaling methods of the single-phase and flashing-induced two-phase flow in the open natural circulation system, which is designed for the passive containment cooling system. The results show that the steady-state mass flow rate changes with the heat transfer regularly both in the single-phase and flashing-induced two-phase flow under a certain inlet subcooling. From the sensitivity analysis, it can be found that the riser height only has impact on the single-phase flow but has little influence on the flashing-driven two-phase flow. Both increasing the diameters of the riser and downcomer can enhance the flow and heat transfer in sing-phase and two-phase flow when keeping the structure of the heat exchanger unchanged, but the influence degree for each flow type is different. The flow resistance distributions of the loops under different flow modes have been studied to provide the foundation for improving the heat transfer capacity by choosing the structural parameters reasonably. The pressure resistance distribution of the steady single-phase flow only relates to the geometrical, but the pressure resistance distribution of the two-phase flow relates both to the pipe diameters and to the external conditions. The acceleration pressure resistance in the riser section is the main resistance under the higher-quality two-phase conditions. Therefore, the influence of the riser diameter on the flashing-induced two-phase flow is far greater than that of downcomer diameter and the most effective method to improve the two-phase flow and heat transfer is to increase the diameter of the riser. Finally, the scaling analysis is performed for the penetration and economy considerations after selecting the optimal dimensions. The scaling of the cold and hot sections is considered separately to insure the driven force of the system unchanged, and different scaling criterions are given for the single-phase and flashing-induced two-phase flow according to the analyses of the pressure resistance distributions. The results show that the scaling criterion of the two-phase flow can deal with the scaling problem accurately both in the single-phase and two-phase flow. However, the scaling criterion of the single-phase flow only can solve the single-phase scaling problem, but it will overestimate the operating results in the scaling model.     

垂直管内超临界水传热实验研究

在宽广的实验范围内对直径10 mm垂直管内超临界水在不同工况下的传热特性进行了实验研究,分析了热流密度、质量流速及压力变化对内壁面温度及传热系数的影响规律。实验参数为：压力23、25、26 MPa,质量流速450~1 200 kg/（m²•s）,热流密度200~1 200 kW/m²。实验结果表明：随主流温度的升高,壁面温度逐渐上升,在拟临界点附近由于物性剧变存在传热强化现象;热流密度的增加以及质量流速的减小均会削弱传热强化现象,并导致传热恶化;压力的影响主要体现在传热恶化、强化的起始热流密度和起始主流温度的不同。     

Fluid-to-fluid scaling of heat transfer in circular tubes cooled with supercritical fluids

Experimental investigations of heat transfer at prototypical conditions of supercritical water cooled reactors (SCWRs) are strongly limited due to their huge technical and financial efforts required. One of the possible solutions is the application of model fluids, which have much lower critical pressure and critical temperature. Model fluid technique has been widely applied in the thermal-hydraulic studies of nuclear engineering. In spite of growing activities of heat transfer at supercritical conditions using model fluids, there does still not exist any reliable fluid-to-fluid scaling methods, to transfer the test data in model fluids directly to the conditions of prototype fluid. This paper presents a fluid-to-fluid scaling method for heat transfer in circular tubes cooled with supercritical fluids. Based on conservation equations and boundary conditions, one set of dimensionless numbers and the requirements of a complete scaling are determined. Scaling of pressure and temperature ensures the similarity of thermo-physical properties of various fluids. A new dimensionless number, presenting the product of the so-called pseudo Boiling number, Reynolds number and Prandtl number, is applied to scale heat flux. The distortion approach is used to scale mass flux. The scaling of heat transfer coefficient is based on Nusselt number. In addition, a new approach is introduced to validate the scaling law. The validation results show good feasibility and reasonable accuracy of the proposed scaling law. Assessment of scaling factors of various parameters indicates the high feasibility of Freon-134a as model fluid for SC water. Some guidelines can be derived for the future experimental investigations on heat transfer at supercritical pressures using model fluid techniques.     

简化反应堆一回路系统自然循环的动态比例特性研究

在反应堆安全领域,合适的比例分析对非能动系统实验台架的设计起到了关键作用。为深入了解比例缩放时自然循环瞬态过程的变化机理,基于简化反应堆一回路系统,分别采用H2TS（双向分层比例分析）和DSS（动态比例分析）方法进行了自然循环的比例分析,计算了升降功率工况下的自然循环,对比分析了不同尺度下关键参数的动态变化。结果表明,基于RELAP5的计算结果与实验结果基本一致,5%初始功率以下的阶跃变化不会造成大的流量波动;基于两种比例分析方法所得缩比模型下的计算结果均可基本反映原型参数变化;所有工况下,自然循环流量和冷热段温差在初始阶段05个循环周期内存在较大的波动,之后则相对平稳。     

破口事故比例模拟中安全壳破口源项参数评估研究

采用基于破口总焓相似、强迫射流及浮力羽流流场相似及传热传质过程相似的多约束分析体系,归纳与质能源项相关的传热传质过程、耗散过程以及自然循环过程的时间尺度,确定模拟实验源项满足的各种模拟工况所必须遵循的设计约束条件。分析表明,自然循环过程时间常数是约束不同物理过程最重要的基础参数,也是模拟装置设计的基本约束参数。给出适用于确定安全壳破口源项试验参数的计算关系式,用于计算获得试验装置的几何参数和试验边界条件。     

燃料组件稳态回路辐照考验多热工参数耦合特性研究

燃料组件稳态回路辐照考验是研究组件抗辐照性能的关键环节,鉴于回路辐照考验热工参数对试验运行的重要性,本文针对稳态辐照考验回路,结合燃料组件对回路辐照考验热工参数的需求,分析了一次水流量及入口温度发生变化、装置内部存在换热以及不同换热器运行方式下回路系统的关键热工参数耦合特性。研究表明,随着换热器一次水入口温度和流量的下降,主换热器的最大换热功率有明显下降,在严重偏离设计工况下,主换热器换热能力存在不能满足燃料组件辐照运行的风险。同时,辐照装置内部换热对主换热器换热极为不利。在回路运行温度需求较高,而装置内部换热较强情况下,主换热器二次水流量的设计裕量不能低于装置内的热交换比例,且该裕量取值需趋大。两台主换热器并联运行的优势主要体现在较大一次水流量情况,且存在一个较小的一次水流量,使得单台换热器独立运行与两台换热器并联运行时的换热能力一致,低于该流量比例时,两台换热器并联运行时的换热能力反而弱于单台换热器运行。      

Systematic and exact scaling analysis of the single-phase natural circulation flow: The hydraulic similarity

For the study of the hydraulic similarity in a single-phase natural circulation loop, the integral momentum equation is non-dimensionalized with respect to the initial flow kinematic energy of reference section, without intuitively specifying any reference parameters. By this mean, a unique hydraulic time scale, characterizing the system hydraulic response, is identified along with two dimensionless physical numbers: the dimensionless flow resistance number and the dimensionless gravitational force number. From the integral momentum equation, the mass flow rate at steady state is also obtained. The identified dimensionless parameters are then applied to derive a set of scaling criteria for the design of a full-pressure reduced-size similar model for a PWR (Pressurized Water Reactor). For exact hydraulic similarity, it was found for the first time that the cross sectional area scaling ratio should be related to the axial length scaling ratio. In addition, it is also found out that the relative cross-sectional area ratio should be preserved in order to preserve the flow resistances. Moreover, the scaling ratio for the number of the U-tubes was found to be unity if exact hydraulic similarity is pursued for the whole system. Three sets of scaling criteria for the design of a full-pressure model for a PWR are summarized in a table for different application. The accuracy and applicability of this proposed scaling method is demonstrated by proposing a simple loop and a PWR-like system, by scaling down the systems to get two corresponding models with this proposed scaling methodology, and by comparing the model results with their corresponding prototype results. Furthermore, the method for the evaluation of both system-level and local hydraulic scaling distortions are addressed.     

Scaling methodology for a reduced-height reduced-pressure integral test facility to investigate direct vessel injection line break SBLOCA

A scaling methodology for a small-scale integral test facility was investigated in order to analyze thermal-hydraulic phenomena during a DVI (direct vessel injection) line SBLOCA (small break loss-of-coolant accident) in an APR1400 (advanced power reactor 1400 MWe) pressurized water reactor. The test facility SNUF (Seoul National University Facility) was utilized as a reduced-height and reduced-pressure integral test loop. To determine suitable test conditions for simulating the prototype in the SNUF experiment, the energy scaling methodology was propose to scale the coolant mass inventory and the thermal power for a reduced-pressure condition. The energy scaling methodology was validated with a system code (MARS) analysis for an ideally scaled-down SNUF model and that predicted a reasonable transient of pressure and coolant inventory when compared to the prototype model. For the actually constructed SNUF, the effect of scaling distortions in the test facility's thermal power and the loop geometry was analytically investigated. To overcome the limitation of the thermal power supply in the facility, the convective heat transfer between primary and secondary systems at the steam generator U-tubes was excluded and a modified power curve was applied for simulating the core decay heat. From the code analysis results for the actual SNUF model, the application of the modified power curve did not affect the major events occurring during the transient condition. The results revealed that the scaling distortion in the actual SNUF geometry also did not strongly disturb significant thermal-hydraulic phenomena such as the downcomer seal clearing. Thus, with an adoption of the energy scaling methodology, the thermal-hydraulic phenomena observed in the SNUF experiment can be properly utilized in a safety analysis for a DVI line break SBLOCA in the APR1400.     

CFD-assisted scaling methodology and thermal-hydraulic experiment for a single spent fuel assembly

A computational fluid dynamics (CFDs)-assisted scaling methodology is proposed for a TN24P cask (Creer et al., 1987). In the proposed methodology, the height and the number of assemblies were scaled down based, respectively, on the integral scaling criteria by Ishii and Kataoka (1984) for a natural-circulation loop under single phase flow and on the concept of an insulator on the surface of the basket. The controlling scaling parameters for the TN24P cask (the scaling ratio of the heat flux, 1.6; the thickness and conductivity of the insulator, 9 mm and 0.05 W/m K, respectively) were estimated by comparing the results of a TN24P cask experiment (Creer et al., 1987) with those of a CFD simulation of a TN24P cask scaled down, using Fluent code. Based on the proposed scaling methodology and its scaling parameters, a thermal-hydraulic experiment with a half-height single assembly was carried out. The experiment was analyzed in comparison with a CFD simulation to validate the proposed CFD models in Fluent code. The results showed good agreement for the peak cladding temperature (215 °C from the experiment, 212 °C from the CFD). It is regarded that the proposed scaling methodology was reasonably validated as maintaining the similarity of the temperature gradient and the peak cladding temperature.     

杆式支撑换热器换热的数值模拟

采用数值模拟方法研究杆式支撑换热器．可以克服实验研究方式的不足。利用相似理论确定数值模拟模型,分析了各结构参数变化对换热器传热和流动性能的影响．利用最小二乘法．进一步回归出杆式支撑换热器层流下的传热和流动阻力的准数关联式．设计,建造了一套可变结构参数的杆式支撑换热器热模实验装置．在壳程单排管间布杆或双排管间布杆、不同流速和不同折流栅结构参数情况下测得了100个实验值．将实验测量值和计算值进行了比较。结果表明：数值模拟计算的Nu值和△p值与实验测量值吻合很好,由实验数据回归得到的传热和流动阻力无因次准数关系式与数值模拟程序计算得到的准数关系式也吻合较好．显示出数值模拟方式进行换热器研究的显著优点.