平成 25年 7月に福島第一原子力発電所の事故の教訓や世界の最新知見を踏まえて原子力規制委員会が策定した「新規制基準」が施行された。原子力発電所の再稼働にあたっては、「新規制基準」に従って、テロ対策、過酷事故対策、耐震・耐津波性能の強化、自然現象に対する考慮の新設、電源の信頼性の強化等、幾重にも安全性を確保、維持するためのハードとソフトの対策が要求されている。その対策のひとつが近隣火山の噴火が発生した場合においても炉心の著しい損傷を防止する準備である。泊発電所においては、火山現象時においても炉心損傷防止に必要となる電力供給を安定的にできるよう外気の取入れが必須である大容量の電源設備に対して火山灰除去が可能か検討してきた。本解説では、これまで筆者らが検討してきた省人化に向けた連続運転可能な火山灰除去装置の概念設計および原型試験装置の開発と成果について紹介する。...

Continuous monitoring of stress corrosion cracking (SCC) in chloride solution containing thiosulfate was performed using type 304 stainless steel pipe specimen with weldments. Induced Current Potentia l Drop (ICPD) method was used to the continuous monitoring of the SCC growth. The ICPD method permit s continuous monitoring of the SCC growth which initiates from the inner wall of the pipe specimen....
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Continuous Monitoring of Stress Corrosion Cracking Growth in Type 304 Stainless Steel Pipe Weldments using Potential Drop Method.

The predictive and preventive maintenance technologies are of increasingly importance for the long term operation (LTO) of Light Water Reactor (LWR) plants. In order for the realization of LTO, it is essential to prevent the degradation phenomena from emergence using proper maintenance programs on foreseeing the phenomena and evaluating their rates of development. In this paper, the research subjects which should be required for the aging degradation phenomenon in LWR structural materials which were ...
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Proactive Material Degradation Research Subjects for LWR

Plastic strain as a function of the distance from a growing stress corrosion crack tip is quantitatively evaluated by three-dimensional ela stic-plastic finite element analysis. The strain distribution obtained by node-release simulation of crack growth follows the logarithmic l aw. The criteria for the transition from a stationary crack to a growing crack were investigated. Results suggested that the prediction of crack growth by the FRI model, in which oxidation kinetics and continuum mechanics has been...
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Finite Element Analysis of Plastic Strain Distribution at a Distance from Growing Stress Corrosion Crack in Light Water Reactor Environment

１．はじめに軽水炉発電プラントの高経年化(aging)と長期安定運用(Long Term Operation : LTO)が世界的な課題となっている。一般に多くの機器構造物は供用開始とともに高経年化が始まるが、初期の想定寿命（設計のために想定される供用期間）範囲を超えた供用を行う場合には運転実績やその間の実働の負荷を評価し、設計上の想定経年劣化や実働において顕在化した劣化の受容性を評価し、その後の妥当な供用期間を想定する事になる。この間には、当然の事として供用前検査(Pre-service Inspe......

At nuclear power plants, measures are required for emergency power supply equipment under the condition that high-concentration volcanic ash will continue to fall on the order of several g / m3 for 24 hours. A pre-filter is installed as the main countermeasure, but a lot of manpower is required in anticipation of clogging. Therefore, it is desired to develop a device with a capability to stably remove a large amount of high-concentration volcanic ash from intake air for a long period. In this work, a volcan...
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Development of large flow rate micro differential pressure intake type volcanic ash removal device capable of continuous operation

The test methodology using specimens in the shape of tubes was developed to create axial SCCs on the inner w all of the specimen, and its effectiveness was verified by performing SCC tests under LWR environment. It w as shown that the axial stress corrosion cracking was generated from the deepest point of pre-crack by modif ying the loading mode, though the crack was not created around the loading point due to compressive stress....
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Stress Corrosion Cracking Test Methodology for inner axial cracks and its cracking behavior

Surface oxide behavior on alloys in high temperature plays an important role in the stress corrosion clacking (SCC) mechanism according to plausibl e existing SCC models. In this investigation, roughness analysis of oxide/alloy interface on stainless steels after exposure in oxygenated high pur ity water under high stress conditions. A special emphasis was placed on how the oxidation penetration localized and went through the surface harde ned layer. It was pronounced that SCC initiation on hardened layer ...
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Oxidation Behavior of Austenitic Alloys under High Stress Condition in High Temperature Water-Effect of Surface Hardened Layer

In this study, nickel-chromium binary alloys are used on the oxidation test in high temperature water to reveal the effect of chromium conten t on the oxidation behavior under high stress condition. It was shown that the oxidation behavior was affected by chromium content, stress co ndition and surface hardened layer. The feature which induced the localization of oxidation behavior was found on the oxide film of low chro mium alloys. It was thought that the presence of threshold conditions about chromium c...
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The Oxidation Behavior of Austenitic Alloys under High Stress Condition in High Temperature Water-Effect of Chromium Content

Long term operation of NPP has been receiving a great concern based upon the plant operation experiences and progressive improvement in countermeasu res and mitigations. At the same time of this LTO movement, proactive materials aging management is also receiving a great concern to realize the LT O in NPP. Recent PMDM activities in Japan as well as some international one are reviewed and a necessity of an international cooperation is emphasiz ed in relation to reliable maintenance performance connected fro...
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Proactive Materials Aging Management and Multi-Layered Maintenance