Spray atomization is widely used in nuclear power equipment to ensure its safe and stable operation.In the spraying,some droplets will impinge on the equipment wall and expand and evolve in the form of liquid film.This study investigated droplet jet impingement based on Fluent's Discrete Particle Model-to-Volume of Fluid(DPM-to-VOF,DTV)transition method,and the accuracy of the simulation method was validated using experimental images of two droplet falling processes.The research investigated the influence of droplet injection velocity and incident angle on the wall liquid film morphology and obtained the variation of droplet splash rate with incident conditions.Furthermore,the effects of gravity,surface tension,velocity components,and other factors on the expansion process of liquid film morphology and droplet splash rate during droplet impingement on the wall were analyzed.It is found that increasing the injection velocity could enhance the disturbance to the liquid film,significantly increasing the contact area between the liquid film and the wall and the width and height of the liquid film area.Increasing the incident angle had a significant impact on the change of liquid film morphology,which was reflected in the increase in the width and decrease in the height of the liquid film area,leading to decreased stability of the liquid film surface.The splash rate increased with the increase of injection velocity and incident angle,with the incident angle having a more significant impact on the splash rate.
After an emergency shutdown of a lead-bismuth fast reactor, thermal stratification occurs in the upper Plenum, which negatively impacts the integrity of the reactor structure and the residual heat removal capacity of natural circulation flow. The research on thermal stratification of reactors has mainly been conducted using an experimental method, a system program, and computational fluid dynamics (CFD). However, the equipment required for the experimental method is expensive, accuracy of the system program is unpredictable, and resources and time required for the CFD approach are extensive. To overcome the defects of thermal stratification analysis, a high-precision full-order thermal stratification model based on CFD technology is prepared in this study. Furthermore, a reduced-order model has been developed by combining proper orthogonal decomposition (POD) with Galerkin projection. A comparative analysis of thermal stratification with the proposed full-order model reveals that the reduced-order thermal stratification model can well simulate the temperature distribution in the upper plenum and rapidly elucidate the thermal stratification interface characteristics during the lead-bismuth fast reactor accident. Overall, this study provides an analytical tool for determining the thermal stratification mechanism and reducing thermal stratification.
Monte Carlo (MC) method is widely adopted in radiation transport calculation due to its high accuracy, but suffers from high variance in deep-penetration problems. To obtain reasonable results, variance reduction techniques are necessary and thus be widely studied worldwide. The Consistent Adjoint Driven Importance Sampling (CADIS) method is proved to be an effective variance reduction technique, which generally employs finite-difference discrete ordinate (SN) code to obtain the adjoint flux, and generates parameters of source biasing and weight window for MC code. However, the finite-difference method, which models through structural meshes, will introduce considerable geometric approximations in complex geometry. The finite element method (FEM) performs calculations with lower truncation error and can employ unstructured meshes, which are capable of modeling complex geometry with relatively lower geometric approximations. Therefore, the adjoint flux calculated by unstructured-mesh FEM is able to generate more appropriate parameters of source biasing and weight window which will further reduce the variance of forward MC calculation. A fully automatic unstructured-mesh CADIS method is studied and implemented in this paper, parallel three-dimensional unstructured-mesh neutron-photon coupled transport calculation code NECP-SUN based on the SN method and discontinuous FEM is developed and embedded into the MC code NECP-MCX to calculate the adjoint flux with unstructured meshes. The updated code is applied to the HBR-2 benchmark, the numerical results show that the relative statistic error is reduced by up to 22
针对核级闸阀卡滞故障,提出一种基于运行过程变量特征分析的闸阀故障诊断方法.闸阀开关运行过程往往包含故障特点及变化规律,因此该方法首先利用Shannon熵对闸阀开关过程振动信号功率谱进行信息化度量,计算出功率谱熵均值作为目标过程变量,分析闸阀健康情况下和故障情况下的目标过程变量的特征变化,进而划分故障区域和非故障区域,对闸阀进行故障诊断.最后基于核级闸阀实验,对该方法进行实验验证,结果表明该方法能够有效地诊断出核级闸阀故障,并且该方法具有一定的故障预测能力.因此该方法的使用能够降低因为闸阀卡滞故障造成的核设施事故发生概率,同时该方法能够用于其他领域闸阀故障诊断.
开式自然循环系统作为新型非能动余排系统最终热阱排放回路,其安全稳定运行对于事故工况下堆芯余热安全导出至关重要,本研究通过可视化实验方法观察了开式自然循环系统出口排热管内流型演化特性,发现随着加热功率增加,开式自然循环逐步建立,该系统出口排热管内依次出现单相流、间歇性汽泡流、弥散泡状流、弹状流和间歇喷射流5种典型流型,分析了出口排热管内流型与系统稳定运行之间的关系,发现了开式自然循环系统剧烈振荡的根源,为提高开式自然循环系统流动稳定性提供了参考.
