The 2011 off the Pacific coast of Tohoku Pacific Earthquake and the Tsunami gave the serious damage to the Fukushima-Daiichi Nuclear Power Plants (NPPs). The lessons from the accidents, IAEA’s Integrated Regulatory Review Service (IRRS) team conducted review for NRA. The mission provided recommendations and suggestions for improvements in most of the areas covered by the review. include: 1) The NRA should work to attract competent and experienced staff, and enhance staff skills relevant to nuclear and r...
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Improvement of NRA’s Inspection by IRRS recommendation and Innovative Integrated New Maintenance System for NPPs

Four monolithic refractory ceramics (Al2O3, SiC, TiC and TiN) were exposed to severe thermal shock caused by thermite reaction. Such experiments were intended to simulate the exposure of a core catcher to hot debris of melted core in nuclear reactor. Moreover, the chemical interactions between tested materials and products of thermite reaction were investigated by holding samples in laboratory furnace for 5 hours at 1000oC in air. None of the materials entirely withstand such sudden temperature rise, o...
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Molten Core Concrete Interaction and Development of Core Catcher (2) Thermal shock effects for advanced high temperature ceramics

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The 2011 off the Pacific coast of Tohoku Pacific Earthquake and the Tsunami gave the serious damage to the Fukushima-Daiichi Nuclear Power Plants (NPPs). The accidents occurred in Unit 1, 2, 3 and 4. It is said that the height of tsunami attacked Fukushima NPP was more than 14m. After 50 minutes from the automatic shut-down, tsunami a ttacked the NPPs in Fukushima Daiichi NPPs. For example, the Unit 1 lost A/C power caused the loss of water injection function; it made the core meltdown and unusual increase...
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Lessons Learned from the TMI-2 Accident and Chernobyl Nuclear Disaster for Nuclear SafetyInnovation

During the Fukushima Daiichi Nuclear Power Plant accident, fuels in the each core in units 1, 3 and 2 melted, and the melted core might dropped down into the lower plenum of the RPV. The core debris heated the bottom structure of reactor vessels and dropped down onto the pedestal through the melted pass of the vessel bottom structure. High temperature core debris might attack concrete or PCV bottom. In order to protect core concrete reaction, several types of core catchers were developed, but they are...
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Study on Compact-Type Core Catcher for Current Nuclear Power Plants

When a heat transfer tube wall in a steam generator of a sodium-cooled fast reactor fails, high-pressure steam leaks into low-pressure liquid sodium side. Then the high-temperature and highly corrosive reaction jet causes secondary failures of neighboring heat transfer tubes. The objective of the present study is to develop an experimental method to obtain data that is necessary to validate and improve a safety evaluation code on the sodium?water reaction. In the present paper, the methods of sodium?...
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Development of Erosion Test Methods on Underexpanded Inert-Gas Impinging Jets Injected in Liquid Sodium

This paper describes how to write a manuscript of the 18th PES Proceedings. In the Fukushima Daiichi Nuclear Power Plant accident, a great deal of radioactive material was released to surrounding environment. After the accident, the Filtered Containment Venting System (FCVS) that can remove radioactive material from steam in containment vessel has attracted a great deal of attentions. However, there is few knowledge of filtered vent in Japan because almost filtered vent were developed in Europe after ...
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Research related to Filtered Venting System

Many studies about the vibration of rotating vane of turbine had been performed. As in this paper, it was observed on a centrifugal pump operation that stationary part, ring-hat disk vane was vibrating, then it was studied that a mechanism of the phenomena was presumed from the vibration mechanism of turbine vanes.he experimental studies by using actual pump and analytical studies were performed. It was made clear that the interference between pump vanes and pump volute water cuts generate turbulence...
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Cause and Countermeasure of Stationary Disk Vibration Damage in Centrifugal Pump

There are various leak phenomena in nuclear power plants, such as thermal or vibration fatigue crack, grand of valve, valve sheet, mechanical seal and SG tubes, and so on. In the current power plant, engineers should find such probl ems by annual inspection. But, in case of severe accident, operators should conduct a prompt action without mistake. It is very difficult to do such action with limited information and AM tools. Therefore, authors have conducted to develop online leak rate evaluation method for...
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Development of Online Leak Rate Evaluation Method for Various Leak Phenomena in NPPs

Various leak events have happened in nuclear power plants so far. And plants have bad conditions because of these leakages. Several leak events must be investigated, and we have to prepare these leakages. Like this, systematizing evaluation s of several leak events brings upgrades in regulations or new system of inspections, plans for aging deterioration. By using this method, we know deeper about Fukushima-Daiichi NPP. For example, here, from changes of CV pressure, we can conclude that SB-LOCA was NO...
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Studies about Development of Leak Event Evaluation Method in Nuclear Power Plant