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[en] A fuzzy learning algorithm is developed in order to construct the useful control rules and tune the membership functions in the fuzzy logic controller used for water level control of nuclear steam generator. The fuzzy logic controllers have shown to perform better than conventional controllers for ill-defined or complex processes such as nuclear steam generator. Whereas the fuzzy logic controller does not need a detailed mathematical model of a plant to be controlled, its structure is to be made on the basis of the operator's linguistic information experienced from the plant operations. It is not an easy work and also there is no systematic way to translate the operator's linguistic information into quantitative information. When the linguistic information of operators is incomplete, tuning the parameters of fuzzy controller is to be performed for better control performance. It is the time and effort consuming procedure that controller designer has to tune the structure of fuzzy logic controller for optimal performance. And if the number of control inputs is many and the rule base is constructed in multidimensional space, it is very difficult for a controller designer to tune the fuzzy controller structure. Hence, the difficulty in putting the experimental knowledge into quantitative (or numerical) data and the difficulty in tuning the rules are the major problems in designing fuzzy logic controller. In order to overcome the problems described above, a learning algorithm by gradient descent method is included in the fuzzy control system such that the membership functions are tuned and the necessary rules are created automatically for good control performance. For stable learning in gradient descent method, the optimal range of learning coefficient not to be trapped and not to provide too slow learning speed is investigated. With the optimal range of learning coefficient, the optimal value of learning coefficient is suggested and with this value, the gradient descent learning algorithm can provide the stable learning and fast learning speed. For more fast learning speed, the modified momentum is applied to the learning scheme. Fuzzy logic controller with learning algorithm described above is applied to water level control of nuclear steam generator through two learning patterns; one is the off-line learning and the other the on-line learning. Fuzzy logic controller trained off-line is useful in the situation that the controller designer is over-burdened with the tuning works for the fuzzy controller structure and the recorded data from plant operation is rich. In the off-line learning, the desired data is required from the control actions of the plant operator or other controllers such as PI controller. The gradient descent learning algorithm extracts the useful rules among total 343 rules which are generated from the relational product of three controller inputs (7x7x7) and tunes membership functions for controller input domain. In practice, it is almost impossible to tune 343 rules constructed in three input dimensions by trial-and-error method of a human designer. The fuzzy logic controller trained off-line shows the good general mapping capability of controller's input-output relationships and also shows excellent robustness to sudden, large load disturbances. Fuzzy logic controller with on-line learning algorithm, which is called Self-Organizing Fuzzy Logic Controller, constructs the controller structure with no control rules at initial in such a way that it creates control rules and tunes controller input membership functions based on the performance criterion as control action goes on and modifies its control structure when uncertain disturbance is suspected during plant operation. Selected tuning parameters of fuzzy logic controller are updated on-line in the learning algorithm. This control algorithm is divided into two types based on the two performance criteria, i.e., performance index table and performance cost function. After single control run is completed by use of this control algorithm, the fuzzy logic controller which is designed optimally by on-line learning algorithm may be used for the same plant control in the next time, which is the original objective of the self-organizing controllers in the past researches, or it's learning function may continue to organize the structure of fuzzy logic controller in the next control run so that the tuning parameters are updated slightly in order to give the better performance for the unexpected situation than the so called 'trained' fuzzy logic controller. Both types show good tracking and regulation performances when they are applied to linear and nonlinear steam generator models in computer simulations. Also, the fuzzy logic controller trained by on-line learning algorithm shows the acceptable tracking performance and good regulation performance
[en] The FAQs(Frequently Asked Questions) in the Fire Probabilistic Safety Assessment(FPSA) are the issues occurred during performing the engineering evaluation based on NFPA-805. In this report, the background and resolutions are reviewed and described for 17 FAQs related to FPSA among 57 FAQs. The current FAQs related to FPSA are the issues concerning to NUREG/CR-6850, and are almost resolved but for the some FAQ, the current resolutions would be changed depending on the results of the future or on-going research. Among FAQs related to FPSA, best estimate approaches are suggested concerning to the conservative method of NUREG/CR-6850. If these best estimate solutions are used in the FPSA of nuclear power plants, realistic evaluation results of fire risk would be obtained
[en] In an advanced HANARO reactor (AHR), the instrumentation and control (I and C) systems are designed based on the digital system rather than the analog system installed in an existing HANARO instrumentation and control systems. While the safety and functionality of analog-based instrumentation and control system are experienced over a long period of operating time and also well-validated, the obsolescence and the lack of flexibility of this system have to move from the analog technology to the digital technology in the instrumentation and control systems to be used in nuclear power plants as well as nuclear research reactors. For establishing the adequate structure of instrumentation and control systems for an AHR, various instrumentation and control architectures are analyzed for their merits and demerits for use in I and C systems of an AHR and the most promising instrumentation and control architecture for an AHR are drawn from this analysis. The conceptual configuration of a digital-based safety shutdown system is proposed in this report
[en] Highlights: • We develop a modified FMEA analysis suited for applying to software architecture. • A template for failure modes on a specific software language is established. • A detailed-level software FMEA analysis on nuclear safety software is presented. - Abstract: A method of a software safety analysis is described in this paper for safety-related application software. The target software system is a software code installed at an Automatic Test and Interface Processor (ATIP) in a digital reactor protection system (DRPS). For the ATIP software safety analysis, at first, an overall safety or hazard analysis is performed over the software architecture and modules, and then a detailed safety analysis based on the software FMEA (Failure Modes and Effect Analysis) method is applied to the ATIP program. For an efficient analysis, the software FMEA analysis is carried out based on the so-called failure-mode template extracted from the function blocks used in the function block diagram (FBD) for the ATIP software. The software safety analysis by the software FMEA analysis, being applied to the ATIP software code, which has been integrated and passed through a very rigorous system test procedure, is proven to be able to provide very valuable results (i.e., software defects) that could not be identified during various system tests
[en] This report is to describe the issues on regulation and technical elements for the multiple spurious operation of equipment due to fire-induced cable failures and to analyze the spurious operations of the pilot systems selected among multiple spurious operation scenarios for Ulchin Unit 3 and 4. Also, this report is to describe the suggestions on the management strategy for mitigating the multiple spurious operations of the domestic nuclear power plants
[en] In the MMIS (Man-Machine Interface System) conceptual design requirements as a part of the instrumentation and control (I and C) for the advanced research reactor, the basic conceptual framework is decided that all the alarm system and information for the reactor operation are displayed on the display device on the work space of an operator, discarding the conventional operation mechanisms by moving through alarms and records spread over various boards of a control room. For the conceptual framework, the MMIS should be configured based on the digital system rather than the analog system whose dependability has been accumulated from the past operating experiences, because the existing analog system lacks of the capability of proving a human-centered information display environment that requires highly flexible and multi-functional capabilities. From a thorough review of the human-machine requirements for nuclear power plants and of the existing materials for research reactors, the conceptual design requirements for the MMIS of an advanced research reactor are established and they are as follows: Compact operator workstation, Large scale information display, Functionally organized alarm system, Information navigation in station, Staff organization in the control room, Intelligent operator aids, Level of automation, and Information redundancy
[en] The economic benefits of introducing nuclear systems on these vessels and platforms are significant. The advantage of a nuclear power system is that it is a high-density, large-capacity energy source. So, there is no need for frequent refueling like fossil fuels. In the case of floating nuclear power systems, it is possible to fundamentally solve the problem of securing the site as one of the biggest problems of the construction of a nuclear power plant, and has an advantage of supplying electric power to a remote island region from the mainland. In this paper, additional considerations have been considered when designing I&C systems for maritime applied nuclear systems based on the existing I&C system design considerations. According to the purpose of these nuclear system, the I&C system can have a variety of structures to provide various functions. For application environments that require multiple nuclear systems, high-level automation systems and I&C architectures such as integrated control and management systems may need to be considered.
[en] In this paper, a method of measuring the size of defects on the wall and restructuring the defect image is proposed based on the estimation algorithm of a camera orientation which uses the declination angle of the line slit beam. To reconstruct the image, an algorithm of estimating the horizontally inclined angle of CCD camera is presented. This algorithm adopts a 3-dimensional coordinate transformation of the image plane where both the LASER beam and the original image of the defects exist. The estimation equation is obtained by using the information of the beam projected on the wall and the parameters of this equation are experimentally obtained. With this algorithm, the original image of the defect can be reconstructed into the image which is obtained by a camera normal to the wall. From the result of a series of experiment shows that the measuring accuracy of the defect is within 0.5% error bound of real defect size under 30 degree of the horizontally inclined angle. Also, the accuracy is deteriorates with the error rate of 1% for every 10 degree increase of the horizontally inclined angle. The estimation error increases in the range of 30∼50 degree due to the existence of dead zone of defect depth, and defect length can not be measured due to the disappearance of image data above 70 degree. In case of under water condition, the measuring accuracy is also influenced due to the changed field of view of both the camera and the laser slit beam caused by the refraction rate in the water. The proposed algorithm provides the method of reconstructing the image taken at any arbitrary camera orientation into the image which is obtained by a camera normal to the wall and thus it enables the accurate measurement of the defect lengths only by using a single camera and a laser slit beam
[en] The system evolves over time as the system parameters vary as the power level changes, the fuel burns up, etc. This makes it difficult to use a single linear controller for the nuclear reactor power control over the entire operating ranges. These circumstances necessitate robust and optimal power tracking controllers for nuclear reactor operation. This study presents the application of integral sliding mode control-based optimal tracking controller to secure both robustness and optimality in nuclear reactor power control. The validity and effectiveness of the proposed control scheme are demonstrated by simulations. The effectiveness of ISMC over SMC can be visualized by comparison of sliding variable phase portraits. Figure 4 and 5 are the phase portraits of ISMC and SMC, respectively.
[en] A fuzzy algorithm with learning function is applied to the steam generator level control of nuclear power plant. This algorithm can make its rule base and membership functions suited for steam generator level control by use of the data obtained from the control actions of a skilled operator or of other controllers (i.e., PID controller). The rule base of fuzzy controller with learning function is divided into two parts. One part of the rule base is provided to level control of steam generator at low power level (0 % - 30 % of full power) and the other to level control at high power level (30 % - 100 % of full power). Response time of steam generator level control at low power range with this rule base is shown to be shorter than that of fuzzy controller with direct inference. (Author)