Parameter estimation during a transient – application to BWR stability

The estimation of system parameters is of obvious practical interest. During transient operation, these parameters are expected to change, whereby the system is rendered time-varying and classical signal processing techniques are not applicable. A novel methodology is proposed here, which combines wavelet multi-resolution analysis and selective wavelet coefficient removal with classical signal processing techniques in order to provide short-term estimates of the system parameters of interest. The use of highly overlapping time-windows further monitors the gradual changes in system parameter values. The potential of the proposed methodology is demonstrated with numerical experiments for the problem of stability evaluation of boiling water reactors during a transient.     

Fault diagnosis and classification based on wavelet transform and neural network

In this paper we present a novel method in fault recognition and classification in Nuclear Power Plant (NPP) using wavelet transform based Artificial Neural Network (ANN). We first simulate 10 design basis accidents (DBA) of a VVER-1000 using 15 input parameters with employing a Multilayer Perceptron (MLP) Neural Network with Resilient Backpropagation (RBP) algorithm. Afterwards we present the application of wavelet transform for its temporal shift property and multiresolution analysis characteristics to reduce disturbing perturbations in input training set data. Simulation of Artificial Neural Network and wavelet transform was performed using MATLAB software. The results show an enhanced accuracy and speed in fault recognition and high degree of robustness.     

Evaluation of the dependencies related to passive system failure

A major issue to be addressed in safety and risk studies related to advanced reactors is the reliability of the implemented passive safety features. The passive safety system operation is a quite complex process. This complexity gives rise to unpredictable failure patterns. While there are a number of well-established failure analysis (physics-of-failure) models for individual components, these models do not hold good for complex systems as their failure behaviours may be totally different. Failure analysis of individual components does consider the environmental interactions but is unable to capture the system interaction effects on failure behaviour. These models are based on the assumption of independent failure mechanisms. Dependency relationships and interactions of components in a complex system might give rise to some new types of failures that are not considered during the individual failure analysis of that component.The approach to the passive system reliability assessment based on independent modes of failure begins by identifying critical parameters, as input to basic events, corresponding to the failure modes, arranged in a series system configuration. Within this methodology, the selected system critical parameters are properly modelled through the construction of probability functions. The application of the methodology to a realistic thermal-hydraulic passive system design is illustrated. The analysis reveals that the critical parameters are not suitable to be chosen independently of each other, mainly because of the expected synergism between the different phenomena under investigation, with the potential to jeopardize the system performance. This conclusion allows the implementation of the proposed methodology, by properly capturing the interaction between various failure modes.     

基于两流体模型的流动沸腾瞬态数值模拟程序

基于两流体模型与固壁非稳态导热模型,结合相关关联式组合,建立了流道内流动沸腾传热的瞬态数值模拟程序。通过不同入口瞬态下流道两相流动沸腾过程的算例计算分析,确认了程序进行流动沸腾瞬态模拟的能力。通过对不同固壁加热条件下流动沸腾行为的算例计算,检验了该程序进行流壁耦合行为模拟的功能。程序可进一步向系统分析程序和子通道程序发展。     

华龙一号海外首堆反应堆控制系统优化设计

反应堆控制系统是核电厂重要仪控系统之一,对保障核电厂的正常运行起着重要作用。为确保控制系统在核电厂运行过程中的良好控制品质和减少现场调试时间,有必要在设计阶段通过仿真研究对控制系统参数进行优化设计。分析了三代核电华龙一号（HPR 1000）海外首堆的反应堆控制系统功能,对各控制系统被控变量进行了说明;在此基础上,对控制系统参数优化流程进行说明;利用核电厂数字化仿真工具,通过系统建模仿真对控制系统参数进行敏感性分析,根据不同参数取值下的系统静态和动态响应特性得到较优的控制系统参数,经性能验证满足设计要求。所获得的反应堆控制系统参数已用于海外华龙一号首堆反应堆控制系统设计,并用于指导核电厂现场调试和核电厂运行。      

Consistent output estimate with wavelets: An alternative solution of least squares minimization problem for identification of the LZC system of a large PHWR

A novel technique for estimating system parameters based on consistent output estimate in wavelet domain is proposed as an alternative solution to the classical least squares minimization problem, in this paper. The algorithm is computationally efficient and exhibits excellent performance in cross validation. An iterative algorithm, alternately projecting the solution in time and wavelet domain for penalized minimization of local error in wavelet coefficients, is presented in the paper. As a case study, the paper addresses the problem of modeling a complex process in a large Pressurized Heavy Water Reactor (PHWR) based on the evolution of input and output. Xenon-induced spatial oscillations are kept from growing in large PHWRs, by means of the Liquid Zone Control System (LZCS). In this work, an identification scheme of a single input single output linear time invariant model of the LZCS is studied. Shift invariant orthogonal wavelets are used for consistent output estimate of the LZCS process. The technique is verified on the real experimental data obtained from the LZCS test set-up. It is observed that even a low order wavelet based model gives excellent approximation from fewer numbers of input–output data points.     

反应堆功率控制半实物仿真系统

对于新型研究堆,其功率自动调节系统的设计缺乏基本的设计参数和依据,需要通过半实物仿真试验对功率自动控制系统的控制参数和性能进行研究.半实物仿真系统是一个半实物的反应堆闭环控制系统.它根据当前功率与给定功率的偏差执行功率调节算法,输出步进电机控制信号,使步进电机正、反向转动,以此达到功率调节作用.通过在半实物仿真系统上进行的各种控制方式的闭环运行试验得到结论:需根据不同的棒位区域取不同的控制器参数,才能够较好地满足预定的控制指标和性能要求,为新型研究堆功率自动调节系统的设计及闭环运行提供理论依据和技术基础.     

Uncertainty and sensitivity analysis of MCPs’ trip events at Ignalina NPP

Eight main circulation pumps (MCPs) are employed for the cooling water forced circulation through the RBMK-1500 reactor at the Ignalina nuclear power plant (NPP). There have been a few events when one or more MCPs were inadvertently tripped.This paper presents investigation of a one MCP trip event and all MCPs’ trip events at Ignalina NPP. Thermal-hydraulic analysis was conducted using the best estimate system code RELAP5/MOD3.3. Uncertainty and sensitivity analysis of flow energy loss in different parts of the main circulation circuit (MCC), initial conditions and code-selected models was performed. Such analysis allows to estimate the influence of separate parameters on the calculation results and find those modelling parameters that have the largest impact on the investigated events. Uncertainty analysis indicates that natural circulation provides adequate cooling in the case of all MCPs tripped, and that the reactor is reliably cooled by forced circulation in the case of a single tripped MCP. On the basis of this analysis, recommendations for the further improvement of model are developed.     

Dynamic analysis of VVER type nuclear power plants using different procedures for consideration of soil-structure interaction effects

The dynamic response of structures due to seismic loadings is conventionally analyzed in the time domain using substructure methods (decoupled system models). This procedure uses frequency-independent impedances to represent capabilities of the soil underneath the structure. The soil parameters are tuned to the fundamental frequencies of the soil-structure system. This is a common procedure widely used in the preliminary design of power plant structures which provides conservative results. However, parallel to the rapid progress being made in upgrading the capability of data processing systems, methods and software tools have become available which work also in the frequency domain using complex models (for the soil and the structure) or models in which the soil is represented by frequency-dependent impedances. This procedure (coupled system models) also allows realistic treatment of kinematic interaction effects and especially consideration of the embedment parameters of the building structure. The main goal of the study presented here was to demonstrate the effects of different procedures for consideration of soil-structure interaction on the dynamic response of the structures mentioned above. The analyses were based on appropriate mathematical models of the coupled vibrating structures (reactor building, turbine hall, intermediate building structures of a VVER 440/213 as well as the main building of the VVER 1000) and the layered soil. On the basis of this study, it can be concluded that substructure methods using frequency-independent impedances (equivalent dashpots) and cut-off of modal damping usually provide conservative results. Coupled system models which allow the soil-structure interaction effects to be realistically represented (by coupled models of the soil and the structure or by frequency-dependent impedances) provide more accurate results. The advantage of the analysis using coupled system models will be demonstrated and discussed, based on results obtained for the VVER 440/213 PAKS and VVER 1000 Kozloduy.     

The effect of a changing fuel solution composition on a transient in a fissile solution

This paper presents an extension to a point kinetics model of fissile solution undergoing a transient through the development and addition of correlations which describe neutronics and thermal parameters and physical models. These correlations allow relevant parameters to be modelled as a function of time as the composition of the solution changes over time due to the addition of material and the evaporation of water from the surface of the solution. This allows the simulation of two scenarios. In the first scenario a critical system eventually becomes subcritical through under-moderation as its water content evaporates. In the second scenario an under-moderated system becomes critical as water is added before becoming subcritical as it becomes over-moderated. The models and correlations used in this paper are relatively idealised and are limited to a particular geometry and fissile solution composition. However, the results produced appear physically plausible and demonstrate that simulation of these processes are important to the long term development of transients in fissile solutions and provide a qualitative indication of the types of behaviour that may result in such situations.     

Flow Simulation and Optimization of Plasma Reactors for Coal Gasification

This paper reports a 3-d numerical simulation system to analyze the complicated flow in plasma reactors for coal gasification, which involve complex chemical reaction, two-phase flow and plasma effect. On the basis of analytic results, the distribution of the density, tempera-ture and components‘ concentration are obtained and a different plasma reactor configuration is proposed to optimize the flow parameters. The numerical simulation results show an improved conversion ratio of the coal gasification. Different kinds of chemical reaction models are used to simulate the complex flow inside the reactor. It can be concluded that the numerical simulation system can be very useful for the design and optimization of the plasma reactor.     

超临界水自然循环流量信号降噪分析

当自然循环流量的时间序列信号存在噪声时,在计算分析时可能产生错误结论。为了避免错误的产生,在超临界水自然循环流动实验数据信号的基础上,通过选择各种不同的小波基函数,对实验流量信号进行信号去噪分析。通过指标计算对比分析,结果表明,经Dmey小波基函数变换后的自然循环流量去噪信号值,其标准偏差和均方根误差（RMSE）最小、相关系数最大、信噪比较高。因此,Dmey小波基函数适用于超临界水自然循环流量实验数据的信号降噪分析处理。      

^14C造成的环境辐射剂量计算模式及参数

＾１４Ｃ是全球剂量起主要贡献的放射性核素之一，由于＾１４Ｃ行为的特殊性，通常采用特定的模式和参数来计算其对公众造成的辐射剂量，为在环境影响评价中使用方便，本文在对有关文献调研的基础上，综合分析，归纳推导了为两种计算模式，并介绍了在实用中采用的参数。     

Cyclic plastic deformation tests to verify FEM-based shakedown analyses

Fatigue analyses are conducted with the aim of verifying that thermal ratcheting is limited. To this end it is important to make a clear distintion between the shakedown range and the ratcheting range (continuing deformation). As part of an EU-supported research project, experiments were carried out using a 4-bar model. The experiment comprised a water-cooled internal tube, and three insulated heatable outer test bars. The system was subjected to alternating axial forces, superimposed with alternating temperatures at the outer bars. The test parameters were partly selected on the basis of previous shakedown analyses. During the test, temperatures and strains were measured as a function of time. The loads and the resulting stresses were confirmed on an ongoing basis during performance of the test, and after it. Different material models were applied for this incremental elasto-plastic analysis using the ANSYS program. The results of the simulation are used to verify the FEM-based shakedown analysis.     

Output data from simplified electromagnetic models for structure analysis of main ITER components

The distribution of forces, acting on components of the electromagnetic (EM) system considered herein has been analyzed with the use of simplified models and equivalent dynamic simulators for a variety of plasma event scenarios. The work was aimed at the formulation of the problem of the global force balance and the approach to its resolution, identification of the main factors of the force interaction between components, development of the numerical models for qualitative and quantitative assessment of the problem and relevant parameters and the computations and assessment of the results. The use of equivalent simulators with elimination of redundant details and degrees of freedom (DOFs) principally reduces computational complexity of the problem. The selection (identification) of the equivalent system on the basis of the evaluation of the significance of impacts on the parameter of interest provides the effective and natural filtering of secondary or irrelevant information. The finding of equivalent minimum dynamic systems (EMDS) opens, at a certain rate of computations, a way to develop real-time simulators. The paper describes simplified models, the principles of definition (synthesis) and use of EMDS, the structure of the database (magnitude and time evolution of distributed and integral basic parameters) required for the evaluation of the EM loads and examples of the data.     

Iterative PET Image Reconstruction Using Translation Invariant Wavelet Transform

The present work describes a Bayesian maximum a posteriori (MAP) method using a statistical multiscale wavelet prior model. Rather than using the orthogonal discrete wavelet transform (DWT), this prior is built on the translation invariant wavelet transform (TIWT). The statistical modeling of wavelet coefficients relies on the generalized Gaussian distribution. Image reconstruction is performed in spatial domain with a fast block sequential iteration algorithm. We study theoretically the TIWT MAP method by analyzing the Hessian of the prior function to provide some insights on noise and resolution properties of image reconstruction. We adapt the key concept of local shift invariance and explore how the TIWT MAP algorithm behaves with different scales. It is also shown that larger support wavelet filters do not offer better performance in contrast recovery studies. These theoretical developments are confirmed through simulation studies. The results show that the proposed method is more attractive than other MAP methods using either the conventional Gibbs prior or the DWT-based wavelet prior.     

Engineering Improvements and Physics Studies of the Accelerated Compact Toroid in the CTIX Injector

The main goals of the experimental studies on the CTIX compact toroid accelerator are to improve CT parameters through engineering modification, and to quantify CT dynamics by the comparison of experimental measurements to MHD theories. Over this research period, the final CT kinetic energy has been increased by about 30%, with increased efficiency of first-cycle capacitor energy utilization. The efficiency increase is obtained through a combination of engineering modification to passive magnetic switching (saturable Metglas cores), and a fast gas system in the acceleration section of CTIX. Using the new switching system and gas puffing, the final CT density has been increased up to a factor of 5, compared to operation without puffing. The second task of the CTIX project is to compare the experimental data with the existing theoretical models. The most relevant models are that of force-free equilibrium, and a Hall-MHD model. From analysis of magnetic field data, it is determined that the Hall-MHD model gives better agreement, if effects of fluid vorticity are also included. This analysis has been reported in a recent paper (S. J. Howard et al., Submitted). Finally, a new plasma density measurement technique, deflectometry, has been compared with conventional interferometry method. A significant data base has been produced to show that the deflection measurements correlate well with the HeNe laser interferometry.     

级联水力学动态仿真模型研究及应用

级联的流体状态是影响级联分离效果和运行安全的重要因素。为开展级联动态水力学研究,针对层架型级联系统,利用各模块仿真模型搭建了级联动态仿真系统并对部分动态过程进行了模拟,通过与实际运行数据对比分析,确定了主机轻馏分流量方程及压强调节器动态调节方程的具体形式。计算结果表明,利用研究得到的系统仿真模型进行仿真模拟,所得到的系统参数变化与实际运行数据符合较好,模拟结果合理可信,所得仿真模型可用于其他级联系统的仿真研究,由此得到的级联各设计参数可作为实际级联调整和设计的参考依据。同时,利用研究所得的系统仿真模型,针对级联系统中可能存在的故障情况进行了模拟验证,仿真结果与实际运行数据符合良好,从而以仿真模拟的手段验证了系统中存在的问题。     

Study on the performance of an open-loop passive containment cooling system

The containment is an ultimate and important barrier to keep the radioactivity from release. The integrity of the containment is crucial to control the consequences of either loss of coolant accident or main steam line break accident. A passive containment cooling system concept designed to remove the heat by natural circulation means is proposed, which is composed of a series of heat exchangers, long connecting pipes with relative large diameter, valves, and a water tank. The performance of the system is numerically simulated and the self-developed codes are validated by the experimental data. The influences of several key parameters are investigated on the performance of the system from different aspects. The results confirm that four distinct operating stages could be experienced as follows: startup stage, single-phase quasi-steady stage, flashing speed up transient stage, and flashing dominated quasi-steady operating stage. Furthermore, the mechanisms of the ways through which the parameters influence the behaviors of the proposed system are thus analyzed. Moreover, the feasibility of the system is also commented on the basis of the numerical results.