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[en] This work presents a new experimental approach to determine the reactivity levels of subcritical systems. The method employs the subcritical kinetic model developed by Gandini and Salvatores and it is based only on measured quantities such as counting rates of the detectors employed in the experiments and the parameters arising from the least squares fitting of the APSD (Auto Power Spectral Density) and CPSD (Cross Power Spectral Density). Detector efficiencies, quantity required in other procedures such as Neutron Source Multiplication (NSM) method, are not needed in the proposed method. The only hypothesis made in the method was the independence of the effective delayed neutron fraction and the prompt neutron generation time to the subcriticality level of the system. The proposed method was applied to measure the reactivity of several subcritical configurations of the IPEN/MB-01 reactor. Measurements of APSD and CPSD were performed in several degrees of subcriticality (up to around -7000 pcm). The spectral densities data were least squares fitted to get the prompt decay mode (α) and other quantities. Beside the startup source of the facility, an external neutron source of Am-Be was installed near the core in order to improve neutron counting statistics. The final experimental results are of good quality. The proposed experimental method shows clearly that the classical point kinetic theory cannot describe the measured reactivity. Instead, the reactivity inferred from this model follows closely the subcriticality index (ζ) for the source arrangements in the experiment. The agreement of the MCNP5 and GPT-TORT results, both with ENDF/B-VII.0 as the basic nuclear data library, when compared to the corresponding experimental ones was also good. (author)
[en] It has been discovered that communication errors are reasons for many incidents and accidents in various industries including the nuclear industry. As a communication error has been given a considerable attention in analyzing accidents in NPP, there have been numerous studies attempted to explore on communication errors. These works illuminate the communication process, and many cases are simply focused on the statistical analysis of the failure on the information transfer process and the patterns of the communication rather than influential human factors which need to avoid the communication errors. In order to prevent communication errors, an analysis method to find the causes for the communication errors is necessary. Therefore, the analysis method for speaking which is considered important in the conventional works. The qualitative analysis method performs a retrospective and predictive analysis. Through the retrospective analysis, it is possible to fine the root causes when the event is known. And through the predictive analysis, it is possible to find the expected event when the cause is given. In order to complete this methodology, context conditions (CCs), error modes, antecedent-consequent links, and relation between error modes and antecedents are defined. The quantitative method evaluates the probability of the predicted errors in the cognitive speaking process (CSP). In order to complete this method, the CSP and other essential specifications of the methodology are defined. These methods are useful for analyzing communication errors systematically so that we may avoid the communication errors and related events. This work is also useful for the basis for research such as developing the communication support procedure and the communication support tools for cooperation in NPPs
[en] This work presents a theoretical study of reactor kinetics focusing on the methodology of calculation and the experimental measurements of the so-called kinetic parameters. A comparison between the methodology based on the Dulla's formalism and the classical method is made. The objective is to exhibit the dependence of the parameters on subcriticality level and perturbation. Two different slab type systems were considered: thermal one and fast one, both with homogeneous media. One group diffusion model was used for the fast reactor, and for the thermal system, two groups diffusion model, considering, in both case, only one precursor's family. The solutions were obtained using the expansion method. Also, descriptions of the main experimental methods of measurements of the kinetic parameters are presented in order to put a question about the compatibility of these methods in subcritical region. (author)
[en] In chamber experiments, we investigated the effectiveness of a task ventilation system with an air supply nozzle located underneath the front edge of a desk and directing air toward a heated mannequin seated at the desk. The task ventilation system provided outside air, while another ventilation system provided additional space cooling but no outside air. Test variables included the vertical angle of air supply (-15(sup o) to 45(sup o) from horizontal), and the supply flow rate of (3.5 to 6.5 L s(sup -1)). Using the tracer gas step-up and step-down procedures, the measured air change effectiveness (i.e., exhaust air age divided by age of air at the mannequin's face) ranged from 1.4 to 2.7, which is higher than typically reported for commercially available task ventilation or displacement ventilation systems
[en] The on-line monitoring (OLM) defined as an automated method of monitoring instrument output signal and assessing instrument calibration have been developed in various research institutes and the systems are divided into two types which are event identification and signal validation. The event identification system helps operators make their decision more accurate in abnormal situations. The signal validation system has a function to calculate instruments signal to suggest the calculated values that describe its situation as real as possible. The OLM systems can help operators to do their work more safe and also make industries save the costs. Because of the benefit of the use of OLM systems, manufacturing industries have applied OLM systems and these are also expected to apply the field of Nuclear Power Plants (NPPs) in Korea. In order to apply the OLM systems, feasibility test to evaluate the effect should be conducted in advance. Two event identification systems and two signal validation systems are selected to do the feasibility test. The results show the accuracy how much the systems carry out their function correctly
[en] RFID (Radio Frequency Identification) system, one of the most anticipated ubiquitous technologies is an automatic identification method using devices called RFID tags. RFID antenna detects each approach of RFID tags and recognizes the tags' ID and transfer to reader to do information processing. Since first introduced in the logistics industry, production management and maintenance organization in various fields of domestic and foreign enterprises introduce the RFID. Nuclear power plants are also using RFID to manage materials lately. However, the current status on the use of RFID is just a little more advanced on the use of bar code. Therefore, it seems that the important characteristic of RFID is not enough actualized to keep seeing. In point of Maintenance Information Field based on ubiquitous technology, the most important concept is real-time information processing. And RFID is quite proper to develop this information field system because it satisfies for the matter of that concept. The leading content in ubiquitous maintenance system is that maintenance personnel can get information what he needs and he can also transfer information what he gets whenever and wherever he is. In this paper, some examples of applying RFID in development of ubiquitous maintenance system are suggested
[en] A new topology optimization scheme based on a Harmony search (HS) as a metaheuristic method was proposed and applied to static stiffness topology optimization problems. To apply the HS to topology optimization, the variables in HS were transformed to those in topology optimization. Compliance was used as an objective function, and harmony memory was defined as the set of the optimized topology. Also, a parametric study for Harmony memory considering rate (HMCR), Pitch adjusting rate (PAR), and Bandwidth (BW) was performed to find the appropriate range for topology optimization. Various techniques were employed such as a filtering scheme, simple average scheme and harmony rate. To provide a robust optimized topology, the concept of the harmony rate update rule was also implemented. Numerical examples are provided to verify the effectiveness of the HS by comparing the optimal layouts of the HS with those of Bidirectional evolutionary structural optimization (BESO) and Artificial bee colony algorithm (ABCA). The following conclu- sions could be made: (1) The proposed topology scheme is very effective for static stiffness topology optimization problems in terms of stability, robustness and convergence rate. (2) The suggested method provides a symmetric optimized topology despite the fact that the HS is a stochastic method like the ABCA. (3) The proposed scheme is applicable and practical in manufacturing since it produces a solid-void design of the optimized topology. (4) The suggested method appears to be very effective for large scale problems like topology optimization.
[en] IAEA defined safety culture as follows: 'Safety Culture is that assembly of characteristics and attitudes in organizations and individuals which establishes that, as an overriding priority, nuclear plant safety issues receive the attention warranted by their significance'. Also, celebrated behavioral scientist, Cooper, defined safety culture as,'safety culture is that observable degree of effort by which all organizational members direct their attention and actions toward improving safety on a daily basis' with his internal psychological, situational, and behavioral context model. With these various definitions and criteria of safety culture, several safety culture assessment methods have been developed to improve and manage safety culture. To develop a new quantitative safety culture evaluation method for an operating team, we unified and redefined safety culture assessment items. Then we modeled a new safety culture evaluation by adopting level 1 PSA concept. Finally, we suggested the criteria to obtain nominal success probabilities of assessment items by using 'operational definition'. To validate the suggested evaluation method, we analyzed the collected audio-visual recording data collected from a full scope main control room simulator of a NPP in Korea
[en] In advanced MCR, various automation systems are applied to enhance the human performance and reduce the human errors in industrial fields. It is expected that automation provides greater efficiency, lower workload, and fewer human errors. However, these promises are not always fulfilled. As the new types of events related to application of the imperfect and complex automation are occurred, it is required to analyze the effects of automation system for the performance of human operators. Therefore, we suggest the quantitative estimation method to analyze the effectiveness of the automation systems according to Level of Automation (LOA) classification, which has been developed over 30 years. The estimation of the effectiveness of automation will be achieved by calculating the failure probability of human performance related to the cognitive activities
[en] Small quantity nuclear material are not subject to use permit under the Nuclear Safety Act, but are subject to national accounting management and reporting under the Korea-IAEA safeguards agreement. Therefore, small quantity of nuclear material need to be managed at the national level. However, due to lack of relevant regulations and the smallness of the use agencies, practical management is difficult. In particular, there are no clear procedures or standards for the disposal of small quantity nuclear material, which may cause various problems in the future.