棒束子通道CHF机理模型开发及初步验证

目前棒束通道中临界热流密度的预测多基于实验关系式,受限于特定的适用范围,无法有效外推或外推后预测精度下降。为满足不同轻水堆中临界热流密度的预测要求,有必要开发适用于不同几何尺寸及热工边界的宽范围临界热流密度预测方式。本文以子通道分析方法为基础,考虑偏离泡核沸腾和干涸两类临界现象,通过耦合子通道分析程序与临界热流密度机理模型,实现对棒束通道中临界热流密度的计算。通过与临界热流密度实验数据的对比,初步证明了耦合程序对棒束通道中临界热流密度具有较好的预测精度。     

测量和预测棒束CHF数据对比方法研究

通过采用子通道程序FLICA建模分析5×5棒束临界热流密度试验,并分别采用直接代入法(DSM)和能量平衡法(HBM)两种方法利用已有临界热流密度关系式获得计算的临界热流密度,并将计算的临界热流密度与试验获得的临界热流密度对比分析,探讨了棒束临界热流密度试验数据的处理方法。结果表明,在棒束临界热流密度试验数据与已有关系式计算数据的对比中,HBM是一种更合理的方法。     

双面均匀加热矩形窄缝通道内DNB型临界热流密度理论预测

基于微液层蒸干的临界触发机理,构建了偏离泡核沸腾(DNB)型的临界预测模型。通过对临界点处的汽块进行受力平衡分析,基于优化后的侧面提升力系数CL,确定了汽块滑移速度、微液层液膜厚度等参数,实现对均匀加热下DNB型临界热流密度的理论预测。采用2种加热长度下矩形窄缝通道内的临界热流密度实验数据对该模型进行了验证。结果表明:模型所预测矩形窄缝通道内的临界热流密度值与实验结果的偏差均在±15%之内,该模型的预测精度高于Bowring公式和Bettis公式的预测精度。     

压水堆堆芯临界热流密度的预测方法综述

针对压水堆堆芯临界热流密度(CHF)预测这一重要科学问题,分析了棒束中存在的格架效应、冷壁效应和非均匀加热效应对CHF的影响,对比了基于不同假设的6类CHF机理模型,给出了棒束CHF关系式的开发途径,并得出了CHF机理模型和经验关系式在棒束CHF预测上的优缺点。建议进一步充实已有的CHF实验数据库,优化CHF关系式的开发方法,并积极开发棒束CHF机理模型。     

紧密排列棒束燃料组件临界热流密度实验研究

基于高转换比紧密布置堆芯研究背景,针对堆芯紧密排列螺旋绕肋棒束组件开展了临界热流密度(CHF)实验研究,获得了棒束在不同热工条件下临界热流密度。研究结果表明:紧密排列棒束燃料组件CHF主要发生在热棒元件,临界发生时加热元件壁面温度迅速升高,同时压力升高,流量降低;系统压力、质量流速、含汽率、入口过冷度等热工参数对组件临界热流密度影响较大;获得了CHF计算关系式,计算值与实验值偏差在±10%以内。     

极限干度现象区CHF评估

在圆形管内,对极限干度区的临界热流密度(CHF)进行了理论研究.通过对Whalley模型进行数值求解,并分析其在极限干度流动条件下的适应性,得到了适用于圆形管内环状流临界热流密度的本构方程.数值预测结果通过与几个主要的CHF预测模型相比较表明该本构方程对极限干度区CHF的预测精度较高.     

长棒束临界热流密度实验研究

提供了用组装式长棒束取得的95个临界热流密度实验数据,介绍了实验本体的结构特点及适应长棒束临界热流密度研究的实验方法和数据处理结果。实验是在高压热工回路上完成的。棒束为3×3正方形排列,水由下而上垂直流过棒束。组装成棒束的电加热实验元件的直径为9.5mm,棒中心距为12.6mm,轴向热流密度均匀分布,有效加热长度2200mm。实验参数范围是:压力p=14.4～15.7MPa,质量流速W_g=1204～3545kg/(m~2.s),临界点含汽量X_c=(-17.3～15.7)％。全部实验数据按截面平均法在VAX机上进行了综合处理,得到了适用于上述参数范围的临界热流密度经验关系式。公式计算值与实验数据比较的标准偏差为6.5％。     

基于逐步回归无量纲棒束CHF关系式开发与DNBR限值确定

针对目前国内外先进压水堆棒束临界热流密度（CHF）经验关系式普遍存在数学形式复杂、自变量系数众多且缺乏物理意义的共性问题,以美国电力研究院（EPRI）棒束CHF数据库中遴选的485个5×5压水堆棒束CHF数据点为基础,基于逐步回归分析开发了一套新型无量纲棒束CHF关系式。考虑了导向管冷壁效应与轴向非均匀加热效应后,实测CHF与预测CHF之比M/P的平均值为0.998,均方根偏差为0.0546,标准差为0.0546,基于分组法确定了关系式的95/95偏离泡核沸腾比（DNBR）限值为1.16。     

基于CFD方法的棒束通道内临界热流密度预测

为研究棒束通道内临界热流密度现象,采用基于对气、液两相分别建立基本守恒方程的欧拉两流体六方程模型和改进的壁面热流密度分配模型,利用CFD商用软件FLUENT 14.5对捷克大型水介质实验回路上开展的临界热流密度（CHF）实验进行数值模拟。通过计算获得CHF发生前、后计算域内重要热工水力参数的分布及CHF发生值,将CFD计算获得的CHF与实验测得值进行对比,结果表明,大多数工况的偏差在±30%以内,证明了欧拉两流体模型结合改进的壁面热流密度分配模型对CHF预测的准确性。本研究可为复杂结构的CHF预测提供依据。     

定位格架对4×4棒束临界热流密度流体模化的影响

基于棒束临界热流密度(CHF)流体模化研究现状,进行了 4×4 棒束 CHF流体模化的实验研究。实验结果表明:适用于圆管的CHF流体模化模型不再适用于 4×4 棒束,最后一道定位格架对 4×4 棒束在氟利昂 12中的 CHF有明显的影响,表明定位格架对棒束 CHF流体模化有复杂的影响,需进一步研究。     

Measurements of critical heat flux in CANDU 37-element bundle with a steep variation in radial power profile

An experiment has been performed to obtain dryout power measurements with a 37-element bundle string simulating radial power profiles of high-enriched fuel (which contains slightly higher enrichment than the CANDU fuel and is not the same as the traditional highly enriched uranium) and natural-uranium fuel. The electrically heated bundle string was cooled with Refrigerant-134a and installed vertically inside the test station. Occurrences of CHF were detected using sliding thermocouples installed inside each element. Measurements showed that the dryout power for the high-enriched fuel bundle is lower than that for the natural-uranium fuel bundle by 26%, on average. Similarly, the corresponding critical heat flux (CHF) values for the high-enriched fuel power profile are lower than those for the natural-uranium fuel power profile by about 48%. A correlation previously proposed for the effect of radial power profile on CHF underpredicts considerably the CHF for the high-enriched fuel power profile. The correlation has been revised to improve the prediction accuracy. The revised correlation represents closely the available database. It exhibits a correct asymptotic trend and hence can be extended to bundles with more severe variation in radial power profile than those covered in the current experiment.     

Assessment of a DNB-type theoretical critical heat flux model for rod bundles with non-uniform axial power shapes

A general critical heat flux (CHF) prediction method with a wide applicable range and reasonable accuracy is essential to the thermal-hydraulic design and safety analysis at the conceptual design stage for a new pressurized water reactor (PWR). In this study, the Korea Advanced Institute of Science and Technology (KAIST) liquid sub-layer dryout CHF prediction model for Departure from Nucleate Boiling (DNB) region has been implemented in a sub-channel analysis code, and investigated for the method's possible use in a rod bundle environment with various non-uniform axial power shapes. The KAIST model showed comparable prediction capability to Lin's method for bottom-, center-, and top-peaked heat flux shapes. The KAIST model, without any correction factors or empirical constants, turned out to be suitable to fulfill the needs for a basis of a general CHF prediction method as compared to Lin's method and Westinghouse-3 (W-3) correlation.     

燃料组件精细化定位格架模型开发及评价

为提高燃料组件子通道内两相局部参数预测的准确性,本文基于分布式阻力方法建立精细化定位格架模型,选用合适的摩擦阻力表达式,对格架上的交混翼进行精细化建模,采用Carlucci湍流交混模型计算湍流交混速率,引入阻塞因子计算由定位格架引起的湍流交混效应,并将建立的精细化定位格架模型植入子通道分析程序（ATHAS）,对压水堆子通道和棒束实验（PSBT）基准题进行计算分析。结果表明,本文开发的精细化定位格架模型能够提高燃料组件子通道内空泡份额和温度分布的预测准确性,为棒束通道流场、焓场计算和临界热流密度（CHF）预测奠定了基础。      

Development of a bundle correction method and its application to predicting CHF in rod bundles

A bundle correction method, based on the conservation laws of mass, energy, and momentum in an open subchannel, is proposed for the prediction of the critical heat flux (CHF) in rod bundles from round tube CHF correlations without detailed subchannel analysis. It takes into account the effects of the enthalpy and mass velocity distributions at subchannel level using the first derivatives of CHF with respect to the independent parameters. Three different CHF correlations for tubes (Groeneveld's CHF table, Katto correlation, and Biasi correlation) have been examined with uniformly heated bundle CHF data collected from various sources. A limited number of CHF data from a non-uniformly heated rod bundle are also evaluated with the aid of Tong's F-factor. The proposed method shows satisfactory CHF predictions for rod bundles both uniform and non-uniform power distributions.     

基于高斯过程回归的临界热流密度预测

准确地预测临界热流密度（CHF）对于反应堆的安全和运行十分重要。针对现有人工神经网络（ANNs）预测方法所存在的缺点,提出一种基于高斯过程回归（GPR）的CHF预测方法。首先对获取的当地条件下CHF数据进行预处理,将数据划分为训练集和测试集;然后,利用训练数据对GPR模型进行训练,并得到最优超参数;再利用训练好的GPR模型对CHF进行预测,并将结果与径向基神经网络（RBFNN）进行比较,同时分析了重要参数对CHF的影响趋势。结果表明,与RBFNN相比,GPR模型的预测结果具有更高的预测精度和更小的误差,且与对应的实验值吻合较好,其参数趋势符合通用的趋势变化规律。      

适用于新型PWR燃料组件的CHF关系式的开发及应用

以中国核动力研究设计院（NPIC）的棒束临界热流密度（CHF）实验数据为依据，基于具有自主知识产权的子通道分析程序CORTH，采用最小偏离泡核沸腾比（DNBR）点法开发了适用于新型压水堆（PWR）燃料组件的CHF关系式（CF-DRW关系式）并对其进行了应用分析。典型事故分析结果表明，采用CF-DRW关系式的计算结果相比FC-2000关系式具有相当或者更大的热工裕量。      

用灰色系统理论预测环形通道内液钠的临界热流密度

用灰色系统理论对在两台液钠沸腾实验回路上测得的实验数据进行了钠沸腾临界热流密度（CHF）值影响因素的灰色相关分析,并用GM（1,1）模型对CHF进行预测,选用GM（1,h)模型对CHF进行了建模,计算及预测结果与实验值符合较好。     

基于两相CFD的非均匀加热圆管CHF预测方法研究

为建立非均匀加热工况临界热流密度（CHF）预测方法，以对换热系统的安全分析提供新的辅助手段，本研究采用欧拉两流体模型和壁面沸腾模型，对非均匀加热圆管的CHF进行预测。通过数值计算得到不同热流密度下近壁面空泡份额和壁面温度的分布，将壁面温度出现二次峰值和此时近壁面空泡份额的峰值位置分别作为CHF发生的依据和CHF发生的点，并用此方法对2种不同功率分布圆管的CHF进行研究。研究结果表明，预测得到临界时的平均热流密度及临界发生的位置都与实验结果符合较好。因此，本研究建立的数值预测方法能够用于非均匀加热圆管CHF的预测。      

The 2006 CHF look-up table

CHF look-up tables are used widely for the prediction of the critical heat flux (CHF). The CHF look-up table is basically a normalized data bank for a vertical 8 mm water-cooled tube. The 2006 CHF look-up table is based on a database containing more than 30,000 data points and provides CHF values at 24 pressures, 20 mass fluxes, and 23 qualities, covering the full range of conditions of practical interest. In addition, the 2006 CHF look-up table addresses several concerns with respect to previous CHF look-up tables raised in the literature. The major improvements of the 2006 CHF look-up table are:

• An enhanced quality of the database (improved screening procedures, removal of clearly identified outliers and duplicate data).

• An increased number of data in the database (an addition of 33 recent data sets).

• A significantly improved prediction of CHF in the subcooled region and the limiting quality region.

• An increased number of pressure and mass flux intervals (thus increasing the CHF entries by 20% compared to the 1995 CHF look-up table).

• An improved smoothness of the look-up table (the smoothness was quantified by a smoothness index).

A discussion of the impact of these changes on the prediction accuracy and table smoothness is presented. The 2006 CHF look-up table is characterized by a significant improvement in accuracy and smoothness.     

人工神经网络在圆管临界热流密度数据分析中的应用研究

将人工神经网络 (ANN)应用到圆管CHF实验数据的分析中 ,得到了一套基本成熟的基于人工神经网络的圆管CHF预测系统 ,并基本建成了训练这一系统的可随时进行更新和对网络进行再培训的圆管CHF实验数据库。与常规CHF预测关系式和CHF查询表方法相比 ,ANN方法主要优势在于其具备较强的容错能力和较好的鲁棒性 ,可在宽范围内提高CHF的预测精度 ,更新和使用更为方便 ,易于推广应用到同类和相似物理问题中去