The purpose of this study is to investigate environmental effects on SUS316 in different strain rate condition. The fatigue tests were conducted under different strain rate (0.4%/s and 0.004%/s) in simulated PWR environment with interrupting tests and the effect of strain rate on crack growth rate was evaluated by the observation of test specimen surface. From the results of investigation, the followings were confirmed; ・The effect of strain rate on crack growth rate is larger in 0.004%/s than 0.4%/s. ・The ...
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Environmental effect of stainless steel in PWR environment. (Investigation of Crack initiation and growth behavior by Replica Observation)

The relaxation behavior of the compressive stress in nickel-based alloy 600 introduced by WJP and buffing stress improving treatments has been investigated. Hardness reduction behavior in WJP and buffing processed samples during thermal aging has been found to follow the Johnson-Mehl-Avrami equation and the rate constant for hardness reduction to be expressed by the Arrhenius equation. EBSD crystal orientation analysis has confirmed that the strain is introduced mainly in the surface region. Positron lifeti...
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Mechanism for stress relaxation behavior of WJP and buffing stress improving treatments

Nuclear power plants (NPPs) are required to ensure safety in long term operation under aging degradation. The fatigue degradation is one of the major ageing phenomena and is evaluated to ensure safety by design fatigue curve obtained by the results of axial fatigue test. On the other hand, the stress that occurs in piping element such as elbow is not uniaxial but biaxial. For accurate evaluation of fatigue crack growth, it is required to confirm the effect of biaxial stress. In this study, membranous pressu...
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Study on the Behavior of Fatigue Crack Growth of Austenitic Stainless Steel Piping under biaxial Stress

In order to investigate that the hardening with δ hydrides generation in Zr was influenced by the relationship between the slip plane of dislocation and the habit plane of δ hydride, the EBSD analysis, the nano-indentation hardness test and the in-situ TEM observation during tensile test were performed. In the case when the δ hydrides of crystal orientation relationship (habit plane) of (0001)α plane//{111}δ plane and <2-1-10>α direction//<110>δ direction were precipitated in the Zr sample, the hardening of...
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The hardening amount evaluation with δ hydrides generation in Zr by using the nano-indentation hardness test and microstructure observation

Many lawsuits against civil nuclear power facilities have been brought after the severe core damage accident occurred at Fukushima Daiichi NPS. Especially, requests for provisional disposition order to prohibit operation of one nuclear power reactor has been filed to more than one district court by different plaintiffs including those who live far away from the reactor site. Measures are studied in order to avoid losing lawsuits against nuclear power plant licensed through rigorous NRA review with upgraded ...
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Study of Measures to Reduce Risk of Lawsuits for Nuclear Power Plants

Hamaoka nuclear power plant unit-5 had the sea water intrusion incident in 2011 during the shut-down process. We, Chubu electric power company, have conducted some researches for unit-5 re-start, since we had some concerns about the aftercare of pitting corrosions occurred in the inner surface of RPV. The aftercare includes the determination of whether corrosion pitting might propagate until RPV, determination of whether or not to clean Chloride ions in corrosion pits and the determination of need for weld ...
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Weld repair of sea water induced corrosion pits in inner RPV surface

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

福島第一事故をめぐる裁判の中で、国の（損害賠償）責任を追及する事例がある。そこでの主要 な論点は次の三つである。①国に規制権限があったのか（バックフィット制度の有無、およびそ の対象）、②規制権限を行使する前提として H14 年長期評価は十分に信頼性のあるものであったのか、③規制権限を行使しなかったことに過失等はなかったのか。多くの裁判所は、前記の三論 点について国の責任を認めている。...
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State Responsibility concerning 1F Accident

The fatigue tests were conducted under different temperature (325℃ and 200℃) in simulated PWR reactor coolant condition with interrupting tests and replica-observation. By observing fatigue crack on the specimen surface, the effect of temperature on crack initiation and growth were studied. From the results of the fatigue tests, the followings were confirmed; ・The number of cycles that fatigue cracks initiate is almost the same in different temperature. On the other hand, the number of cracks that initiate ...
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Influence of Temperature on the Fatigue Crack Initiation and Growth in Reactor Coolant Environment

This paper covers the recent decisions made by Osaka and Saga district courts, respectively, for Nos. 3 and 4 reactors at the Ohi NPP and Nos. 3 and 4 reactors at the Genkai NPP, and discusses the disputed points in determination of design basis ground motions to be used for seismic safety checking, which are regulated in Nuclear Regulatory Authority (NRA) review guide. In the paper, the points in these decisions are clarified and the authors’ view regarding those points are presented, and finally the sugge...
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Scientific Rationality and Engineering Decision Towards Risk-informed Decision Making