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[en] As a part of the project 'development of hydrogen production technologies by high temperature electrolysis using very high temperature reactor', we have developed an electrolyzer model for high temperature steam electrolysis (HTSE) system and carried out some preliminary estimations on the effects of heat recovery on the HTSE hydrogen production system. To produce massive hydrogen by using nuclear energy, the HTSE process is one of the promising technologies with sulfur-iodine and hybrid sulfur process. The HTSE produces hydrogen through electrochemical reaction within the solid oxide electrolysis cell (SOEC), which is a reverse reaction of solid oxide fuel cell (SOFC). The HTSE system generally operates in the temperature range of 700∼900 .deg. C. Advantages of HTSE hydrogen production are (a) clean hydrogen production from water without carbon oxide emission, (b) synergy effect due to using the current SOFC technology and (c) higher thermal efficiency of system when it is coupled nuclear reactor. Since the HTSE system operates over 700 .deg. C, the use of heat recovery is an important consideration for higher efficiency. In this paper, four different heat recovery configurations for the HTSE system have been investigated and estimated
[en] The steam generator water level evaluation was established by modeling and simulating steam generator water level response and by comparing with the steam generator water level operation data for 4.5% power uprated nuclear plants. The evaluation has been performed to assess thermodynamic and flow balance of feedwater system designs after power uprating. The operation date of the steam generator level behavior and control system for Kori 4 after power uprating were taken from Kori site. The results of operation data such as pump speed, feedwater control valve open position and steam generator water level were compared with the calculation of the previous simulation study for the unit.
[en] The analysis was performed to provide useful insights for operator guidelines to maintain critical safety functions during SBO for shutdown modes. For Shutdown State A, if the SG PORV is manually opened at 4,000 sec by operator and secondary external injection by operator was provided at 5hours, the core boiling is not expected and core is cooled well. For Shutdown State C, if RWST gravity feed by operator is provided at 4,000 sec, the core is not uncovered and core is cooled well. This study would be useful for improving a strategy to cope with loss of all AC power while on shutdown cooling. The purpose of this study is to provide strategies for maintaining core cooling and protecting the reactor core in the event of complete loss of all AC power while on Residual Heat Removal (RHR) cooling. In this study, in order to comprehend the Fukushima accident, the transient analysis was performed to provide insights into mitigating strategies for SBO while on a shutdown state using the RELAP5/MOD3.3 code
[en] An electrolyzer model for the analysis of a hydrogen production system using a solid oxide electrolysis cell has been developed, and the effects of principal parameters have been estimated via sensitivity studies based on the developed model. The main parameters considered were current density, area-specific resistance, temperature, pressure, molar fraction, and flow rates in the inlet and outlet. A simple model is also estimated for a high-temperature hydrogen production system that integrates the solid oxide electrolysis cell with a very high temperature reactor. (author)
[en] After the Fukushima accident, there has been a growing interest in countermeasures against station black out (SBO) in nuclear power plants. In particular, there have been needs to prepare a strategy for responding to power plants considering the loss of all the AC power, so called the Extended Loss of All AC Power (ELAP). It would be seemed that the current Emergency Operating Procedures (EOP) of domestic nuclear industry is not enough to deal with the ELAP accident. So the additional procedures or strategies for coping with ELAP situation have been required. The purpose of this study is to identify the behavior and response capacity of the CANDU 6 plant (Wolsong Unit 1,2,3,4) during shutdown operation for ELAP. In case of analysis for the full power condition, the fuel cladding and pressure tubes are damaged within 2 hours without the operator actions during ELAP. The analysis was performed to estimate the behavior and the response of CANDU 6 plant at shutdown operation mode 4 with ECCS blocked during ELAP accident. If there is no operator action in the accident, the damage of the pressure tube occurs within about 7 hours.
[en] The purpose of this study is to identify the behavior and response capacity of the CANDU 6 plant during ELAP such as the one occurred in the Fukushima accident. The analysis was performed with CATHENA, which is an Industry Standard Toolset (IST) to simulate thermal-hydraulic phenomena in pressurized heavy water reactor. The disasters brought the long-term Station Black-out (SBO). For these lessons of the Fukushima nuclear accident, the US and, European governments, IAEA and other regulatory agencies around the world have recommended followup measures to build and develop a strategy to cope with the Extended Loss of All AC Power (ELAP). The analysis was performed to estimate behavior and response of CANDU 6 plant during ELAP condition such as the one occurred during the Fukushima accident. Without the operator action during ELAP, the fuel cladding and pressure tubes are damaged within 2 hours. However, if the operator acts appropriately with several available measures, the plant cooling could be maintained without core damage
[en] The reactor core melt-down and release of massive radioactive materials occurred due to the accident. After the accident, the equipment and strategies against the Extended Loss of All AC Power (ELAP) were recommended strongly in the nuclear industry. The purpose of this study is to provide strategies for maintaining core cooling and protecting the reactor core in the event of complete loss of all AC power while on mid-loop operation. The transient analysis was performed to comprehend the Fukushima accident, and to provide insights into mitigating strategies for SBO while on mid-loop operation using the RELAP5/MOD3.3 code. The transient analysis was performed to provide useful insights for operator guidelines to maintain critical safety functions during SBO for shutdown modes. For the shutdown state C, the PTR gravity feed flow decreases as the water level in PTR is lowered. So, PTR should be refilled or primary external injection is required at 14,400 sec. If PTR gravity feed is provided at 4,000 sec and primary external injection is provided at 14,400 sec, the core is covered with coolant and cooled well. In the conclusion, the long-term cooling strategy should be established by primary external injection or PTR refill. This study would be useful for improving a strategy to cope with loss of all AC power while on mid-loop operation in the Framatome NPP.