A fuzzy modeling approach to the identification of transients in nuclear components

In this paper, a fuzzy-logic modeling approach is adopted for the identification of the causes of transients in a component of a nuclear power plant. The if–then rules, representing the underlying processes are inferred from the available input–output signal data. The method is applied to the early classification of the causes of transients in a steam generator of a pressurized water reactor (PWR). Based on the measured signals, the forcing function responsible for the transient is readily classified and its amplitude is estimated. The case of two concurrent causes of transients is also considered.     

A fuzzy data envelopment analysis approach for FMEA

We present a data envelopment analysis approach for determining ranking indices among failure modes in which the typical FMEA parameters are modeled as fuzzy sets. By this approach, inference rules of the IF THEN kind can be bypassed. The proposed approach is applied to a typical PWR auxiliary feedwater system. The results are compared to those obtained by means of: the risk priority numbers, pure fuzzy logic concepts, and finally the DEA-APGF (profiling of severity efficiency) approach. The results demonstrate the potential of the combination of fuzzy logic concepts and data envelopment analysis for this class of problems.     

A new series-expansion approach in Monte Carlo: Application to neutron shielding

A new method for series expansion by means of the Monte Carlo technique is presented. It is applied to neutron shielding problems with very good results.     

Use of a fuzzy decision-making method in evaluating severe accident management strategies

In developing severe accident management strategies, an engineering decision would be made based on the available data and information that are vague, imprecise and uncertain by nature. These sorts of vagueness and uncertainty are due to lack of knowledge for the severe accident sequences of interest. The fuzzy set theory offers a possibility of handling these sorts of data and information. In this paper, the possibility to apply the decision-making method based on fuzzy set theory to the evaluation of the accident management strategies at a nuclear power plant is scrutinized. The fuzzy decision-making method uses linguistic variables and fuzzy numbers to represent the decision-maker's subjective assessments for the decision alternatives according to the decision criteria. The fuzzy mean operator is used to aggregate the decision-maker's subjective assessments, while the total integral value method is used to rank the decision alternatives. As a case study, the proposed method is applied to evaluating the accident management strategies at a nuclear power plant.     

A simple probabilistic approach to evaluate radioiodine behavior at severe accidents: Application to PHEBUS test FPT1

A simple probabilistic approach is proposed to quantify the relative importance of selected processes and mechanisms which govern the behavior of radioiodine under conditions pertaining to a postulated severe accident. In principle, these are sensitivity studies of a dedicated, small event tree which describes the iodine behavior at an accident. The emphasis is put on the processes taking place in containment at a late phase of the accident. Here, volatile species of iodine (volatile iodine: I₂ and various organic iodides) could form from the species which were transported from RCS to containment originally as non-volatile. The relative importance of the processes leading to volatile iodine formation in containment is, for a long time, a subject of some dispute among the international research communities. The proposed probabilistic insight could be one of the many ways to address these complicated questions. In this work, the probabilistic approach was tested against the results of the well-documented PHEBUS FPT1 experiment. The small containment iodine event tree was processed by the EVNTRE code with a direct call from within the tree to the detailed iodine chemistry program calculating the speciation of iodine in containment. The French program IODE, as a part of the ASTEC suite of codes, has been used for this purpose. The results of this sensitivity study of PHEBUS FPT1 are promising as for the possibility to use such (or similar) probabilistic method for thorough analyses of uncertainties linked with the iodine behavior in containment at an accident. Similar approach could be used even for the iodine behavior modeling in whole-plant PRA analyses.     

Application of a self-organizing fuzzy logic controller to nuclear steam generator level control

In this paper, the self-organizing fuzzy logic controller is investigated for the water level control of a steam generator. In comparison with conventional fuzzy logic controllers, this controller performs the control task with no initial control rules; instead, it creates control rules and tunes input membership functions based on the performance criteria as the control behavior develops, and also modifies its control structure when uncertain disturbance is suspected. Selected tuning parameters of the self-organizing fuzzy logic controller are updated on-line in the learning algorithm, by a gradient descent method. This control algorithm is applied to the water level control of a steam generator model developed by Irving et al. The computer simulation results confirm the good performance of this control algorithm for all power ranges. This control algorithm can be expected to be used for the automatic control of a feedwater control system in a nuclear power plant with digital instrumentation and control systems.     

Application of fuzzy decision making method to the evaluation of spent fuel storage options

In this paper, a fuzzy decision making method is proposed which is based on the fuzzy set theory and the hierarchical structure analysis. The method employs two key concepts: linguistic variables and fuzzy numbers. The linguistic variables and fuzzy numbers are used to represent the decision-maker's subjective assessments for the decision criteria and the decision alternatives versus the decision criteria. The fuzzy mean operator is used to aggregate the decision-maker's subjective assessments and the total integral value method is used to rank the decision alternatives. As a case study, the method is applied to evaluating the spent fuel storage options in Korea.     

A novel approach to correlation reflectometry

The use of microwave synthesized sources improved significantly the performance of correlation reflectometry diagnostics for fusion plasmas providing broadband operation with high quality signals and fast frequency switching times. Recent new developments of those sources made at IPFN opened an all-new way to build correlation reflectometry diagnostics with improved performance and measuring capability. Some of the key features now attainable are independent probing and local oscillator signals generated by separated frequency synthesizers; very good frequency control and synchronization of both the local and the radio-frequency oscillators providing very high stability. The technological advances make it possible to further reduce the switching time between adjacent probing frequencies while keeping the ability to operate in a broad frequency range.Here we present a multichannel correlation system based on those novel technologies using several independent and self-contained fully synthesized broadband channels. With this type of system various type of measurements are possible: (i) fast stepwise radial scans to extract the radial profile of turbulence parameters (spectra, RMS, rotation from Doppler shift, etc.); (ii) radial scans of the plasma using two identical systems in parallel where one system operates in frequency steps and the other makes multiple small steps around each selected frequency of the first system. The proposed diagnostic is very powerful and versatile. With a system having n identical channels, all transmitting and receiving simultaneously, the number of simultaneous correlations measurements that can be performed is given by n × (n ? 1)/2. The minimal configuration uses two channels thus providing one (time domain) correlation signal channels can be easily added at any time increasing the measuring capability of the diagnostic. Several examples are given that illustrate the wide range of measurements that can be made using the novel approach for correlation reflectometry diagnostics.     

环境辐射防护--关于科学和决策的未来挑战

随着ICRP 91号出版物关于电离辐射对非人类物种影响的出版,国际放射防护委员会(ICRP)已经在把环境问题纳入辐射防护一体化方面采取了重大步骤。回应公众对环境问题的需求和关心,已经制定了概念大纲,它是以国家和国际级的一些组织的技术开发为基础的。欧共体资助的FASSET项目(环境影响评价大纲)于2004．年完成,开发出的评价大纲包括：源的特性和初始危害分析;生态系统描述和参考生物的选择;照射分析包括的剂量率的转化;效应分析;和解释导则。基于FASSET和其它最新进展的经验,可以得出如下结论：(1)目前正在使用或建议的不同大纲间的概念方法实质上是一致的。(2)技术方法的不同主要归因于所关心的生态系统的不同或国家监管要求的不同。未来主要挑战是开发一个一体化方法使得决策能够由可靠的科学判断指导。这就要求,尤其是,通过有目的的实验、理论(包括专家意见)和实例分析填补评价和防护相关的基础知识的不足;开发风险表征方法;条件允许情况下,开发筛选标准;开发用户友好的评价工具;和利益相关者的参与,包括建立支持通讯的战略。这些问题发表在2004年春季第6次欧共体大纲计划启动的ERICA项目中(电离污染物的环境危险——评价和管理)。     

Adaptive fuzzy inference causal graph approach to fault detection and isolation of field devices in nuclear power plants

An adaptive fuzzy inference causal graph is presented as an integrated approach for fault detection and isolation of field devices including sensors, actuators, and controllers in nuclear power plants. In this approach, nuclear plant systems are represented as a causal graph consisting of individual process variables connected with adaptive fuzzy inference system models. The adaptive fuzzy inference system models generated from historical data are used to characterize the relationships among process variables during normal operation. Fault detection and isolation is achieved by monitoring and cause-effect reasoning on the residuals. This unique cause-effect reasoning strategy for fault isolation can avoid seeking signatures patterns from fault data, which are usually very difficult to obtain for a large system. The most parsimonious model structure, which is a decisive factor in building robust data driven models, is achieved through the system decomposition that inherent in a causal graph. The developed approach has been demonstrated for a simulated pressurized water reactor steam generator system. Both simple faults and complex faults with fault propagation can be successfully isolated during their incipient fault stages, regardless of fault magnitudes and initial power level.     

A modular approach to lead-cooled reactors modelling

After an overview of the lego plant simulation tools (LegoPST), the paper gives some details about the ongoing LegoPST extension for modelling lead fast reactor plants. It refers to a simple mathematical model of the liquid lead channel dynamic process and shows the preliminary results of its application in dynamic simulation of the BREST 300 liquid lead steam generator. Steady state results agree with reference data [IAEA-TECDOC 1531, Fast Reactor Database, 2006 Update] both for water and lead.     

A reliability program approach to operational safety

A Reliability Program (RP) model based on proven reliability techniques is being formulated for potential application in the nuclear power industry. Methods employed under NASA and military direction, commercial airline and related FAA programs were surveyed and a review of current nuclear risk-dominant issues conducted. The need for a reliability approach to address dependent system failures, operating and emergency procedures and human performance, and develop a plant-specific performance data base for safety decision making is demonstrated.Current research has concentrated on developing a Reliability Program approach for the operating phase of a nuclear plant's lifecycle. The approach incorporates performance monitoring and evaluation activities with dedicated tasks that integrate these activities with operation, surveillance, and maintenance of the plant. The detection, root-cause evaluation and before-the-fact correction of incipient or actual systems failures as a mechanism for maintaining plant safety is a major objective of the Reliability Program.Embodied within the approach are (1) determination of acceptable safety system performance criteria and associated alert levels: (2) tracing and/or trending of in-plant and industry systems performance and management of the associated surveillance, maintenance, and reportable event data base; (3) determination of risk-importance prioritized systems, components, and root-causes and ad hoc response to inplant safety problems or potentially applicable industry problems identified by NRC or INPO; and (4) a closed-loop failure reporting and corrective action program for correcting performance criteria violations or identified problems either through changes in operation or maintenance or through changes in utility management practices.     

A consistent approach to severe accident management

The approach adopted for severe accident management (SAM) at the Loviisa nuclear power plant (in Finland) is presented and discussed. The approach includes a number of significant hardware changes and procedures that allow lowering of the lower head thermal insulation and neutron shield assembly, opening of the ice condenser doors, and spraying (externally) of the steel shell of the containment. It is expected that with these changes we can assure in-vessel debris coolability and retention, gradual burning of the hydrogen with good access to the ice condenser, and long term stabilization of the containment pressure, even in the absence of the residual heat removal system. Methodological aspects of demonstrating these SAM objectives, and the status of work in support of related quantifications (of key phenomena), are included in sufficient detail to provide an integrated perspective of the approach taken. The detailed quantifications, separately on each task, will follow, as respective research and quantification programs come to completion.     

A thin film approach to protein crystallography

A novel approach for the investigation of proteins or macromolecules is outlined in this conceptual study. The preparation of grapho-epitaxial layers on nanotemplated substrates is proposed as an alternative to the preparation of single crystals by vapour diffusion techniques. Crystal structure investigations of such layers may then be performed via grazing-incidence diffraction (GIXRD) in the Laue mode. Quantitative expressions for the position and intensities of XRD peaks in this geometry are presented that fully consider the effects of refraction and absorption. A simulation of the Laue-GIXRD pattern of single-crystalline layers of Concanavalin A is given. The main challenges of the approach are concluded to relate to the preparation of single-crystalline protein layers. However, if those obstacles could be overcome, a 10–100-fold faster sample throughput would become possible.     

Irradiation-induced precipitation: A thermodynamical approach

A binary alloy (A,B) under steady-state irradiation is treated as a ternary alloy (A, B, defects) in constrained equilibrium (the constraint represented by the irradiation consists of maintaining a given supersaturation of point defects). The free energy surfaces of the ternary system have been calculated with Kikuchi's Cluster Variation Method with a tetrahedron as basic figure. All possible two-body interactions have been checked between the solvent A, the solute B and the defects C. Radiation-induced precipitation of a new phase that is richer in solute than the initial solid solution is expected to occur under the following necessary conditions: (i) for a binary alloy (A, B) showing ordering or being ideal, the binary (solute, defects) must show ordering; (ii) for a binary alloy (A, B) showing clustering, the temperature must be close to the critical mixing temperature T^D_AB it is shown that the actual alloys in which radiation-induced precipitation has been observed do not meet these requirements.     

集合扩散模拟技术在应急决策中的应用研究

应用集合扩散模拟的概念,结合不同的气象场与扩散场模式,以某厂址的现场实验为研究对象进行中小尺度集合大气扩散模拟研究。将多模式模拟结果与现场实验结果进行集合分析,从空间分析、时间分析与离散度检验三方面对各类集合分析指标进行研究。结果表明:集合扩散模拟与分析可综合考虑多模式计算结果,给出烟云可能覆盖区域范围与概率、不同置信度水平的烟云浓度分布、关心点(区域)的烟云浓度变化、烟云到达与离去时间概率等,同时可结合监测结果进一步判断与修订模拟结果从而更加接近真实值。将集合扩散模拟方法应用于应急决策领域具有现实指导意义。     

Application of model predictive control strategy based on fuzzy identification to an SP-100 space reactor

In this work, a model predictive control method combined with fuzzy identification, is applied to the design of the thermoelectric (TE) power control in the SP-100 space reactor. The future TE power is predicted by using the fuzzy model identified by a subtractive clustering method of a fast and robust algorithm. The objectives of the proposed fuzzy model predictive controller are to minimize both the difference between the predicted TE power and the desired power, and the variation of control drum angle that adjusts the control reactivity. Also, the objectives are subject to maximum and minimum control drum angle and maximum drum angle variation speed. The genetic algorithm that is effective in accomplishing multiple objectives is used to optimize the fuzzy model predictive controller. A lumped parameter simulation model of the SP-100 nuclear space reactor is used to verify the proposed controller. The results of numerical simulations to check the performance of the proposed controller show that the TE generator power level controlled by the proposed controller could track the target power level effectively, satisfying all control constraints.