[en] The objective of this study is to enhance the safety and the economics of SFR(Sodium Fast Reactor). In order to achieve the objectives, several activities were implemented such as the development of design concept of Supercritical C0₂ Bratyon Cycle system, the development and analysis of major components, the evaluation of system transients for the strategy of system operation and control logics. Through the studies, Supercritical CO₂ Bratyon Cycle system coupled to KALIMER-600 was developed with the design and evaluation of major components such as compressor, turbine and heat exchanger necessary to the system. The application of C0₂ Bratyon Cycle system to a SFR makes it possible to eliminate sodium water reaction which enhance the safety of SFR system. At the same time, the plant economics were also achieved via elimination of turbine building by reduction of the size of turbine and other components. In the course of system development 6 computer codes were developed for the system and component design. The technology and computer code produced through the system development is to be applicable to a all the power plants such as fossil plant, SFR, VHTR(Very High Temperature gas cooled Reactor) and fusion reactor and the expected economic outcomes must be incredibly high

[en] The calculation algorithm for variable setpoint in order to follows various plant conditions in digital plant protection system. Since the analog system has the continuous properties, the variable setpoint can be easily changed on the analog circuits as following the measures to represent the plant conditions. The digital system must, however, require the algorithm for change of variable setpoint according to the plant conditions, because the digital systems have the characteristics of discontinuous sampling and execution period and. We have developed the variable setpoint calculation algorithms which can follow the allowable measures and decide the trip status in the case of abnormal plant conditions. In this paper, we have developed the algorithms for manual reset variable setpoint to be changed step by step from the plant conditions and operator's request and the algorithm for rate-limited variable setpoint to be changed according to the various plant conditions. In the rate-limited variable setpoint, if the measures from plant conditions are changed under the allowable range, then the rate-limited variable setpoint follows the measures. If not, then the rate-limited setpoint should vary as the predefined rate

[en] The new analytic model to analyze the load follow operation was developed. It was based on the neural network theory with the capability of modeling the input/output relationships of a nonlinear system. In order to evaluate the accuracy and the capability, the measurement data of load follow operation of a PWR were compared to the simulated data using the developed model. The model had a comparable accuracy. Required computing time for simulating the load follow operation was, also, comparable to that of fast predictor module without the additional engineering factors. The maximum errors of the axial offset and the critical boron concentration throughout the simulation are within 2.5% and 15ppm, respectively. The new model using the neural networks was proved for a fast-running capability and an adaptability without engineering factor

[en] Many epidemiological studies showed increases of cancer risk in humans following radiation exposure. But, these results mainly came from high dose and high rate radiation exposure and the risk related low dose exposure still remains in question. To overcome the problem about statistical power due to limitation of study population, IARC is processing international collaborative study for pooling data analysis. In Korea, reconstructed cohort of NPP workers based on dosimetry records has followed since 1994. Based on this cohort, we introduce epidemiological study about NPP workers in Korea and investigate the exposure level and death cases in NPP workers exposed to protracted low-dose radiation

[en] The design elements of CEDM power supply system were analyzed based on reviews of electro-mechanical phenomena of CEDM. Several improved items were discovered as the results of reviewing conventional CEDM power supply systems. The major items is to supply over-power to CEDM due to applying over-estimated design margin of holding current, because of unstable power quality of the conventional system. While the suggested method based on pulse width modulating methodology can be reduced the amount of supplied power and dissipated heat of coils when holding power is supplied. In addition, as a method to reduce the drop out delay, the negative voltage applied method was suggested. But there are still remain some shortcomings such as increase of component complexity, etc. regarding the suggested power supply method

[en] The CEDMCS of the Korea Next Generation Reactor has been developeded as a major equipment of CEDM Performance Test Facility. The developed CEDMCS has enhanced operator interfaces by appling the soft-control and digital signal analysis features. The CEDMCS also has active functional features and enhanced power performance characteristics by using PWM control methodology. The result of performance test through a test load which simulates the CEDM coil characteristics, showed that the outputs of voltage and current against the input controls met the design requirements

[en] Flow blockage of subassembly in the Korea Advanced Liquid Metal Reactor (KALIMER) can be occurred by fragments from failed fuel or foreign materials left in primary coolant system. Flow blockage of subassembly may cause failure of fuel and eventually core damage accident. Therefore, the development of Flow Blockage Detection System is required for the protection of core damage accidents by early detection of flow blockage. In this paper, gas and materials from failed fuel, local and gross boiling phenomena and temperature change due to flow blockage are established as the detection sources for the detection system by the analysis of physical phenomena, and gas tag, delayed neutron detector, acoustic detector, thermocouple are selected for the detection means of each source. After analysis of detection methodology based on temperature and acoustic, the preliminary architecture is established through the extraction of functional and detection requirements and the classification of function with protection and monitoring

[en] Although the use of COTS(commercial off-the-shelf) software in the safety-related systems of nuclear power plants has been considered, a methodology of COTS software dedication is not well established. A three-phase COTS software selection procedure for the design of digitalized SMART MMIS was developed. The critical characteristics and technology criteria of the COTS software are identified through investigating the COTS software in step one. The selection criteria is documented in step two. A COTS software is selected in step three after the safety of the COTS software is assured through testing and analyzing the COTS software. The developed selection procedure is being applied for the design of the SMART MMIS

[en] The failures of check valves are one of the most important problems to safety in nuclear power plants because the reverse flows through the failed check valve impact on the healthy hydraulic loop. We have suggested the monitoring and diagnostic algorithm for the condition of a check valve by using acoustic emission sensors for detecting the failures of check valves through measuring and analyzing the backward leakage flow without disassembling the check valve. Since the acoustic emission sensor could detect the sound originated from any flow, we have chosen the acoustic emission sensors as the detecting devices for sound originated from backward leakage flow of a failed check valve. For validating the suggested algorithm, we designed a hydraulic test loop installing a typical four inches swing typed check valve. We have assumed that the major failure modes of check valves are disk wear in operation period and insertion of foreign object. The test loop was designed to identify the mechanical failures of the check valve in the case that the reverse backward leakage flows are induced through a failed section in the check valve with disk wear or an inserted foreign object. After experimenting the hydraulic test with various sized disk wear or inserted foreign objects at the various pressures with room temperature, we have developed the monitoring and diagnosis algorithms by using a neural network model in order to identify the type and size of failure in the check valve without any help of expert's knowledge

[en] Neural network model is used for prediction of reactor power, Xenon worth and axial offset with different burnups in load following operations. Scaled Conjugate Gradient algorithm is employed to speed up the training of neural networks that consist of neural network ensemble. Training and testing data are generated by ONED94 code. The test results presented exhibit the neural network ensemble model is more effective than single neural network model for the prediction and can be prone to the problem of incremental learning