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Vol.6 No.3previousSP12 (78-79-80-81)- NT 66

Academic Articles
Vol.6, No.3(2014) p.48 - p.106

Special Issue 12

Hybrid-type Agent System to Diagnose Small Disturbances of Plant

 
Relevant Field
Diagnosis, Operation
 
Keywords
Diagnosis of Plant Condition, Small Disturbance, Monju, Information Integration, Hybrid-type Agent System
 
Preface
For the safe and stable operation of nuclear power plants, the development of techniques to detect a small disturbance and diagnose the disturbance is one of important issues. Up to now, many studies are devoted to develop diagnostic techniques for a small disturbance. Each diagnostic technique has its advantageous features and limitations of application depending on its diagnostic principle. The introduction of new techniques of advanced signal processing and/or artificial intelligence is one approach to develop an improved diagnostic technique. Another promising approach is to develop a hybrid-type diagnostic system that gives a final diagnostic result by integrating the results of diagnostic sub-systems as human operators often make a final decision by examining the information from various information sources. An integrated system composition also has several advantageous features in adding and improving diagnostic functions of the system.
This special issue invites four papers on a hybrid-type diagnostic agent system studied for a fast breeder reactor “Monju” as a four-year research project, where some advanced techniques such as Wavelet transformation, support vector machine, case-based reasoning are applied for the development of sub-diagnostic systems. Thermal-hydraulic simulations are also applied to generate necessary data for developing and evaluating diagnostic techniques.




Guest Editor,
Akio GOFUKU
EJAMAA_SI12_editor_A.Gofuku
 

Akio GOFUKU, Kazuma TAKATA, Kenji TAKATORI, Makoto TAKAHASHI

A hybrid-type diagnostic system to give a final diagnostic result by integrating the results of sub-systems is one of promising ways to develop a flexible diagnostic system. This paper describes a hybrid-type diagnostic agent system for a fast breeder reactor “Monju”. This paper also proposes an integration technique of diagnostic results by sub-systems using what are called confidence values and trust values. Two simulations under the condition that a diagnostic sub-system diagnoses plant condition by a random process are conducted to examine the applicability of the proposed integration technique. The results suggest the applicability of the proposed technique and some applicable conditions for the diagnostic performances of sub-systems.

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Hiroyasu MOCHIZUKI

The objectives of the present study are to analyze plant transients caused by small abnormalities and to find plant parameters by which operators can recognize these small abnormalities. In order to evaluate the plant transient during an abnormal situation in the water system using the plant system code NETFLOW++, the turbine and feedwater (FW) systems should be analyzed with good precision. The code is validated using the measured data at “Monju”. Several abnormalities in the water system are candidates of the present study, e.g., FW control valve degradation, FW pump degradation, heat transfer degradation due to fouling on heat transfer tubes of the evaporator, loss-of-feedwater-heating, etc. All major components in the tertiary system are included in the calculation model such as the steam generators, the high-pressure turbine, the deaerator, the FW pump, the FW heaters, the FW control valves, the steam control valve, extraction lines and drainpipes. In case of a malfunction of a FW control valve resulting in low flow rate, a large temperature increase at the outlet of the evaporator is observed. On the other hand, a temperature decrease at the outlet of the evaporator occurs if heat transfer tubes in the evaporator have fouling. As a result of the calculations, it was determined that temperature at the outlet of the evaporator is a good indicator to detect abnormal situations.

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Takashi NAGAMATSU, Yuki JOU, Akio GOFUKU, Takayuki FUJINO, Zhong ZHANG

In order to detect anomalies in rotating machines such as pumps at an early stage, we developed a system using wavelet transform. The pump diagnostic experiment equipment was designed taking into consideration the structure of the pump used for the water-steam system of the fast breeder reactor “Monju”. For improving detection capability, it is desirable to use a mother wavelet (MW) whose shape is similar to the anomaly signal that is required to be detected. We call the constructed MW on the basis of the real signal the real mother wavelet (RMW). The parasitic discrete wavelet transform (P-DWT) that has a large flexibility in design of the MW and a high processing speed was applied for detecting process signals. The vibration and sound signals were measured using the pump diagnostic experiment equipment when three types of anomalies (injection of an object, change of a balance of the impeller, and damage to the axis of the impeller) occur. Complex RMWs were constructed on the basis of the measured signals, and subsequently, parasitic filters were constructed. Signal detection was performed by calculating the fast wavelet instantaneous correlation using the parasitic filter. We evaluated three types of anomalies, and found that P-DWT is useful for detecting these anomalies. Furthermore, we developed a diagnostic agent using P-DWT as one of the diagnostic agents of our hybrid diagnostic agent system, which is intended to work together with the “Monju” distributed diagnostic agent system.

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Hirotsugu MINOWA, Akio GOFUKU

Accidents of industrial plants cause large loss on human, economic, social credibility. In recent, studies of diagnostic methods using techniques of machine learning are expected to detect early and correctly abnormality occurred in a plant. However, the general diagnostic machines are generated generally to require all process signals (hereafter, signals) for plant diagnosis. Thus if trouble occurs such as process sensor is broken, the diagnostic machine cannot diagnose or may decrease diagnostic performance.
Therefore, we propose an important process signal selection method to improve impact mitigation without reducing the diagnostic performance by reducing the adverse effect of noises on multi-agent diagnostic system. The advantage of our method is the general-purpose property that allows to be applied to various supervised machine learning and to set the various parameters to decide termination of search.
The experiment evaluation revealed that diagnostic machines generated by our method using SVM improved the impact mitigation and did not reduce performance about the diagnostic accuracy, the velocity of diagnosis, predictions of plant state near accident occurrence, in comparison with the basic diagnostic machine which diagnoses by using all signals.
This paper reports our proposed method and the results evaluated which our method was applied to the simulated abnormal of the fast-breeder reactor Monju.

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EJAM Vol.6 p.47-105 Academic Articles Special Issue on ""