Temper bead welding (TBW) is one effective repair welding method for the large-scale nuclear power plants instead of post weld heat treatment (PWHT). Consistent Layer (CSL) technique is the theoretically most authoritative method among the five temper bead welding techniques. For TBW, toughness is the key criteria to evaluate the tempering effect. A neural network-based method for toughness prediction in heat affected zone (HAZ) of low-alloy steel has been investigated to evaluate the tempering effect...
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Prediction of Toughness in HAZ produced by Temper Bead Welding of Consistent Layer Technique

Abstract : In this research, the performance and efficiency of a centrifugal pump under operation are diagnosed with high precision by measurement of electric current, voltage, flow rate, and pressure. Moreover, mechanical faults (misalignment etc.) and the faults in fluid (cavitation etc.) were diagnosed precisely with the vibration signals, and the reason of efficiency fall was clarified theoretically and experimentally. In this report, we proposed the condition diagnosis method for pump equipment by...
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Condition Diagnosis Method and of Efficiency Trend in Fault State for a Centrifugal Pump

Rapid response processes are essential for enabling resilience, which provides a potential target for assessment. The response cycle is considered in three phases: (1) information transmission from system to Decision-Maker, (2) information processing, and (3) feedback action on the system. This research focuses on the first of the three phases, information transmission, and proposes a novel resilience assessment using an Information-Theoretic approach. From this point of view, resilience is considered t...
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An Information-Theoretic Approach to Resilience Assessment

1. はじめに米国では、リスク概念を導入した確率論的安全評 価 (PSA) を原子力発電所の安全管理に利用し合理化を 進めている。ASME Section XI(維持規格) については、 すでに確率論を導入し合理的な保守管理に入っており、 Section II (設計・建設規格)についても、今後確率 論を導入した合理的な規格に改定していくことを計画 している。日本では、原子力配管設計においては、これまでASME Section IIを参考にして設計技術基準を定めてきた。 現行の ASME の手法は主に決定......
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Study on Prediction of Thickness in Nuclear Reactor Piping and Estimation of Inspection Intervals by Applying Reliability-base Method

In this research, the new method to predict the near-future of the movie images captured by video camera based on the combination of t he Principle Component Analysis (PCA) and the Singular Spectral Analysis (SSA). In the normal condition of machines, the real-time ca ptured movie is supposed to correspond to the predicted one. If the error between the both becomes significantly large, it may suggest some anomalous motion of the machines. So the movie prediction method has a possibility of the sensitive an...
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Development of Anomalous Detection using Movie Prediction

Progressive deformation (ratcheting) is one of the failure modes by excessive seismic loadings. These occurrence conditions seem to be similar to the conditions for thermal ratcheting which is called Bree’s diagram. After experiments for ratcheting have done, there were similar results with Bree diagram in some frequency of input waves and not in other frequency. This paper shows detail results by numerical analysis and gives three frequency regions to clarify different characteristics in dynamic load...
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Progressive deformation by dynamic loadings and effects of frequency

Abstract For the last couple of years, issue of defects in Alloy 600 weld lowered the capacity factor of nuclear power plants. To apply newly developed repair technique, like temper-bead welding that has not been prescribed in technical standards, it is necessary to evaluate its technical applicability to the requirement. In the previous cases, this process has been completed by issuance of no action letter for specific area and condition, utilizing implementation process, such as confirm testing by J...
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Study on implementing newly developed repair welding technique within a limited time frame for nuclear power plant

Assuring the structural integrity of a reactor pressure vessel (RPV) is known as one of the critical issues to maintain the safe long-term operation of a nuclear power plant. Authors have been conducting extensive research on the improvement of structural integrity assessment methods of RPVs. In this paper, we describe some research results obtained from the recent activity including the review on the technical background of the methods and study on probabilistic methods for the applicability to the cu...
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Study on Structural Integrity Assessment of Reactor Pressure Vessels

Stress corrosion cracking (SCC) is one of serious aging degradation problems for the Alloy 600 components of pressurized water reactors (PWRs). In order to prevent SCC, various methods such as water jet peening (WJP), laser peening (LP), surface polishing have been used to introduce compressive stresses at the surfaces of the PWR components. However, it has been reported that such compressive residual stress introduced by these methods might be relaxed during the practical operation, because of high te...
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Kinetic analysis on the long term stability of the effect obtained by various residual stress improvement methods ― Evaluation for long term stability of residual stress improving treatment on Ni base alloy (report 2) ―

Many anchor bolts have been used for fixing many components in nuclear power plant (NPP), securing safety against seismic ev ents. Some methods have been developed to detect crack-like defects in bolts which may occur after seismic events. On the ot her hand, assuming long term use of NPP, a method to detect bolt thinning was thought to be needed. In this study, by using bolt specimens with an artificially grinded portion, a new method to detect thinning and to measure its depth was developed....
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Development of inspection method for thinned bolts by PA-UT