Spacer Effect Model for Subchannel Analysis

Mean velocity and velocity fluctuation in a test channel that consisted of five subchannels with and without ferrule-type spacer were measured using air as a working fluid, to clear turbulence intensity enhancement due to spacer. Measurements were performed at Reynolds number of 0.5–1.2×10⁵, which simulated vapor flow velocity of annular-dispersed flow in BWR condition. It was confirmed that magnitudes of velocity fluctuations in radial direction were proportional to Reynolds number and square root of friction factor downstream from a spacer. New spacer effect model to describe turbulence intensity enhancement due to the spacers was developed. In the model, dependence of the velocity fluctuation on ferrule thickness was correlated by blockage ratio. It was found that the present spacer model is applicable to prediction of turbulence intensity enhancement due to spacer.     

Prediction of Transient Boiling Transition in BWR Fuel Rod Bundles by Subchannel Analysis Program MENUETT

Transient CHF (critical heat flux) tests of a 4 X 4 rod bundle were analyzed by the subchannel analysis program MENUETT. MENUETT is based on a non-equilibrium, five equation, two-phase flow model and is available both for steady state and transient analyses. Turbulent mixing and void drift effects are taken into account to calculate cross flows in fuel rod bundles. The tendency of calculated subchannel mass fluxes and qualities agreed with experimental data. By using a critical quality correlation obtained from steady state CHF data, the position of the earliest boiling transition could be predicted regardless of non-uniform axial heat flux distributions. This transition occurrence time was predicted within a difference of 0.1～0.3 s from the experimental time. MENUETT applicability was confirmed for transient calculations predicting thermalhydraulic behavior in bundles.     

Transient Analysis of Boiling Transition Phenomena Using Liquid Film Flow Model

An evaluation has been made for the covariances of neutron cross sections of ⁵²Cr, ⁵⁶Fe, ⁵⁸Ni and ⁶⁰Ni contained in JENDL-3.2. Reactions considered were the threshold reactions such as (n, 2n), (n, nα), (n, np), (n, p), (n, d), (n, t) and (n, α), the radiative capture reaction above the resonance region, and the inelastic scattering to discrete and continuum levels. Evaluation guidelines and procedures were established during the work.

A generalized least-squares fitting code GMA was used in estimating covariances for reactions of which JENDL-3.2 cross sections had been evaluated by taking account of many measured data. For cross sections that had been evaluated by nuclear reaction model calculations, the KALMAN code, which yields covariances of cross sections and of associated model parameters on the basis of the Bayesian statistics, was used in conjunction with reaction model codes EGNASH and CASTHY.

The evaluated uncertainties of a few percent to 30% in the cross sections look reasonable, and the correlation matrices show understandable trends. Even though there is no strict way to confirm the validity of the evaluated covariances, tools and procedures adopted in the present work are appropriate for producing covariance files based on JENDL-3.2. The covariances obtained will be compiled into JENDL in the near future. Meanwhile, new sets of optical model and level density parameters were proposed as one of byproducts obtained from the KALMAN calculations.     

Prediction of Liquid Film Dryout in Two-Phase Annular-Mist Flow in a Uniformly Heated Narrow Tube Development of Analytical Method under BWR Conditions

A method was developed based on the conservation lows to predict critical heat flux (CHF) causing liquid film dryout in two-phase annular-mist flow in a uniformly heated narrow tube under BWR conditions. The applicable range of the method is within the pressure of 3–9 MPa, mass flux of 500–2,000 kg/m²·s, heat flux of 0.33–2.0 MW/m² and boiling length-to-tube diameter ratio of 200–800.

The two-phase annular-mist flow was modeled with the three-fluid streams with liquid film, entrained droplets and gas flow. Governing equations of the method are mass continuity and energy conservation on the three-fluid streams. Constitutive equations on the mass transfer which consist of the entrainment fraction at equilibrium and the mass transfer coefficient were newly proposed in this study.

Confirmation of the present method were performed in comparison with the available film flow measurements and various CHF data from experiments in uniformly heated narrow tubes under high pressure steam- water conditions. In the heat flux range (q“<2MW/m²) practical for a BWR, agreement of the present method with CHF data was obtained as, (Averaged ratio)±(Standard deviation)=0.984±0.077, which was shown to be the same or better agreement than the widely-used CHF correlations.     

基于液膜蒸干模型的低压低流量环状流CHF理论研究

为对低压低流量下的环状流临界热流密度（CHF）进行预测,建立了考虑液膜蒸发、液滴沉积和夹带的液膜蒸干模型,并用已有的实验数据对其进行验证。计算结果表明：在实验参数范围内,CHF计算值与实验值相对偏差在25%以内,两者符合较好。以建立的环状流CHF模型为基础,研究了进口焓差、质量流速、管径和加热长度对CHF的影响。该模型能够有效地计算低压低流量环状流CHF和分析CHF随不同参数的变化趋势。     

液膜蒸干模型在液态金属CHF预测中的应用

为对圆管中环状流烧干型沸腾临界进行预测,建立了考虑液滴沉积夹带作用的液膜蒸干模型。沉积率、夹带率等相关关系式采用水等常规流体的已有关系式。在一定参数范围内,将模型预测结果与实验数据和经验关系式进行了比较。结果表明：基于常规流体的液膜蒸干模型大体可应用于液态金属,但在临界热流密度（CHF）较大时可能造成较大偏差;钠、钾两种液态金属在CHF较低时预测准确度区别不大,但在CHF较高时区别较为明显。为更加准确预测液态金属CHF,应开发专门的沉积率、夹带率等相关关系式。     

Development of a Transient Boiling Transition Analysis Method Based on a Film Flow Model

A new single-channel, transient boiling transition (BT) prediction method based on a film flow model has been developed for a core thermal-hydraulic code. This method could predict onset and location of dryout and rewetting under transient conditions mechanically based on the dryout criterion and with consideration of the spacer effect. The developed method was applied to analysis of steady-state and transient BT experiments using BWR fuel bundle mockups for verification. Comparisons between calculated results and experimental data showed that the developed method tended to predict occurrence of rewetting earlier, however, onset time of BT and maximum rod surface temperature were well predicted within 0.6 s and 20°C, respectively. Moreover, it was confirmed that consideration of the spacer effect on liquid film flow rate on the rod surface was required to predict dryout phenomena accurately under transient conditions.     

Critical Heat Flux for Rod Bundle under High-Pressure,Low-Flow and Mixed Inlet Conditions

The authors have developed a new on-line corrosion product monitor (OCPM) to automatically measure the concentrations of corrosion products in PWR secondary water. The corrosion products of interest for this application are mainly iron and copper. The OCPM offers a number of outstanding features: (1) it measures trace metals on-line; (2) it allows simultaneous quantitative multi-element analysis; (3) its operation is fully automatic with an excellent lower detection limit; and (4) it is transportable and easy to operate. During its development stage, the OCPM was applied at an actual PWR plant and was able to successfully automatically analyze the concentrations of iron and other trace metals contained in the PWR secondary water, while maintaining operational stability without operator intervention for long periods of time. It was also shown that the use of this new system would greatly reduce the workload of plant water chemistry personnel, providing a better alternative to conventional chemical analysis methods. The OCPM is now being introduced into several PWR plants in Japan, with the objectives of conducting detailed studies of the corrosion product behavior in the plant systems and reducing the workload of plant personnel.     

基于双区域模型的钠冷快堆组件子通道分析程序的开发与验证

子通道分析程序是钠冷快堆堆芯热工水力设计和安全分析的重要工具。本文为计算和分析钠冷快堆组件在径向均匀与倾斜功率分布工况下的热工水力特性,利用双区域绕丝交混模型开发了一款适用于钠冷快堆组件分析的子通道程序SPLICA,并与FFM2A 19棒束实验数据与WARD 61棒束实验数据进行了对比验证。由于本文开发的子通道分析程序SPLICA使用了详细的绕丝交混模型,与经过二次开发后的COBRA程序的计算结果相比,对于FFM2A实验SPLICA程序计算得到的结果与实验结果符合得更好。这两个实验数据的验证结果证明了本文开发的子通道分析程序的准确性以及对高流量工况和低流量工况均具有良好的适用性。本程序能为钠冷快堆组件热工水力分析提供有效的设计和研究手段。     

基于流固共轭传热的两相流动数值模拟及燃料子通道CHF预测研究

为对过冷沸腾两相流动进行准确模拟,并探索临界热流密度（CHF）预测方法,本文基于共轭传热和两相CFD分析的方法,通过流固界面耦合,建立流固共轭传热两相流动耦合求解的数值模型。首先通过典型燃料棒栅元过冷沸腾两相流动的模拟,验证数值模型的正确性。随后对燃料子通道内两相流动进行模拟,并在两相流动模拟的基础上,通过准瞬态的方法,建立与CHF试验过程非常近似的CHF预测方法,将加热壁面的温度飞升作为CHF判定的标准,实现对燃料组件子通道CHF的数值预测。研究表明,本文建立的数值模拟方法,可为燃料组件或其他换热系统的CHF预测奠定基础,为燃料组件的设计提供新的辅助手段。     

汽液两相均相流动模型的小波分析热工计算方法

利用小波分析法的多分辨分析特性,对汽液两相均相流动模型进行了数值求解。结果证明：这种数值方法可用于汽液两相流动的耦合微分方程组的计算。     

基于核电站网络安全的信息流模型

为了准确描述从1E子网流入非1E级子网的核电站网络的信息流动,本文给出了一个基于核电站网络安全的新的信息流模型。该模型引入了将子网密级和客体密级相结合的二维密级函数的概念,利用该函数值来划分安全类,用两个客体的函数值定义信息流策略。经过严格的数学证明,新的信息流模型合理且安全,能较好反映核电站网络的安全要求。     

The Corrected Simulation Method of Critical Heat Flux Prediction for Water-Cooled Divertor Based on Euler Homogeneous Model

An accurate critical heat flux(CHF) prediction method is the key factor for realizing the steady-state operation of a water-cooled divertor that works under one-sided high heating flux conditions.An improved CHF prediction method based on Euler's homogeneous model for flow boiling combined with realizable k-ε model for single-phase flow is adopted in this paper in which time relaxation coefficients are corrected by the Hertz-Knudsen formula in order to improve the calculation accuracy of vapor-liquid conversion efficiency under high heating flux conditions.Moreover,local large differences of liquid physical properties due to the extreme nonuniform heating flux on cooling wall along the circumference direction are revised by formula IAPWSIF97.Therefore,this method can improve the calculation accuracy of heat and mass transfer between liquid phase and vapor phase in a CHF prediction simulation of water-cooled divertors under the one-sided high heating condition.An experimental example is simulated based on the improved and the uncorrected methods.The simulation results,such as temperature,void fraction and heat transfer coefficient,are analyzed to achieve the CHF prediction.The results show that the maximum error of CHF based on the improved method is 23.7%,while that of CHF based on uncorrected method is up to 188%,as compared with the experiment results of Ref.[12].Finally,this method is verified by comparison with the experimental data obtained by International Thermonuclear Experimental Reactor(ITER),with a maximum error of 6% only.This method provides an efficient tool for the CHF prediction of water-cooled divertors.     

核动力装置混合智能故障诊断系统研究

针对核动力装置的状态监测与故障诊断问题,为克服单一故障诊断方法的局限性,本文提出了基于多层流模型(MFM)和信息融合理论的混合智能故障诊断方法。利用信息融合的方法来提高故障诊断的快速性和准确性,同时利用MFM方法解释故障发生时报警的传播路径,提高对诊断结果的可理解性。仿真实验表明,混合智能诊断方法能迅速判明故障并提交报警分析。