It is important for maintenance of nuclear power station facilities in the future to promote mathematical techniques which support judgement to modify maintenance practices, such as maintenance tasks, maintenance implementation timing, and so on. Mathematical Maintenance Working Group, which has been established by Maintenance Standardization Committee since July 6, 2018, is investigating application examples of such mathematical techniques in maintenance planning as influence evaluation of changing maint...
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Investigation on application examples of mathematical techniques to support judgement to modify maintenance practices

For decommissioning of the Fukushima Daiichi Nuclear Power Station, installation of an optical fiber seismic vibrometer using a specially designed robotic system was demonstrated. A water tank with 4.5m diameter and 5m depth was used as a demo-plant of tank type critical assembly. Micro-earthquake response of a water tank was detected by the optical fiber seismic vibrometer. Vibration characteristic of the window of the water tank was monitored by laser Doppler interferometer....
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Development of micro-earthquake response detection by optical fiber seismic vibrometer with a water tank and a specially designed robotic system

Radioactive liquid waste from the Tokai Reprocessing Facility Analytical Laboratory is temporarily stored in intermediate waste storage tanks by using receiving valves. Then, the liquid waste is transferred to liquid treatment facility by using liquid feed valves. The deterioration of the gasket part of these valves (leakage of waste liquid) was confirmed in 2004. Since then, the material of gaskets was changed from polyethylene to polytetrafluoroethylene(PTFE). In 2016, the gaskets were replaced by periodi...
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Physical property evaluation of valve seal material at analytical radioactive liquid waste storage tanks in reprocessing facility

The Japan Atomic Energy Agency (JAEA) has been developing High Temperature Gas-cooled Reactor technology since 1960s. In December 2020, Japanese Government clearly stated “Green Growth Strategy Through Achieving Carbon Neutrality in 2050” that noted a commitment to the milestone and developing and implementing significant efforts in various sectors for achieving carbon neutrality around 2050. High Temperature Gas-cooled Reactor (HTGR) is expected to play one of a dominant roles to reduce carbon generated fr...
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Current Status of HTGR Research and Development in JAEA

Reactor pressure vessel (RPV) of the light water reactor is the most important safety related component. To prevent non-ductile fracture of RPVs during operation, the degree of irradiation embrittlement of RPV steels is monitored by surveillance tests, and structural integrity assessment of RPVs is conducted based on the test results. The assessment method based on probabilistic fracture mechanics (PFM) is known as a rational one in assessing the integrity of RPVs, and efforts for practical applications of ...
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Study on Practical Application of Probabilistic Structural Integrity Assessment Method for Reactor Pressure Vessels

In order to quantitatively evaluate the ability of a nuclear plant to recover its safety functions, we are developing a method to simulate accident management in chronological order according to an accident scenario, rather than simply evaluating the probability, and to evaluate whether or not a major accident will eventually occur, i.e., whether or not the minimum necessary safety functions can be recovered within a time limit. In this presentation, we will discuss the development of a method to evaluate w...
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Visualizing method for resilience of nuclear power plant

In order to decommission TEPCO Fukushima Daiichi nuclear power plant, the removal of fuel nuclear debris is planned from 2021. It is demanded to grasp nuclear material element contents of the debris remaining inside the accident reactors for the effective and safe removal. Our research team aims to do the on-site analysis of the extracted debris by the Spectral X-ray CT method with the portable X-band (9.3 GHz) 950 keV/3.95 MeV electron linac X-ray sources and GAGG X-ray detector. It is expected to realize ...
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Fukushima Nuclear Fuel Debris Component Analysis by Spectral CT with Portable High Energy X-ray Source

The trial case against operation of OOI nuclear power plant is studied from the view point of nuclear science and engineering. This case the negative judgements was decided, whose judgement is found to base on the bench’s logical at very superficial constitution, which lacked a consideration for statistical data analysis....
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A study on the trial case about OOI NPP

Severe accidents of sodium-cooled fast reactors (SFRs), which is called core disruptive accidents (CDA), are categorized into typical accident phases, i.e., initiating phase, transitions phase, and material relocation and cooling phase. In recent years, experimental data are accumulated and safety analysis codes are developed focusing on the later phases of accidents. This is because achievement of in-vessel retention (IVR) utilizing superior characteristics of sodium coolant is one of the important objecti...
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Outcome and Direction of Safety Research for Sodium-cooled Fast Reactors in Japan

照射材料試験施設は、核燃料物質使用施設であり、放射性物質を取扱うホットセル内を常時負圧に維持するため換気設備を設置している。竣工から約 40 年経過し、換気設備の経年劣化によるホットセル負圧機能低下を防止するため計画的に短期間での部分更新を行った。 ...