The purpose of this study is to investigate environmental effects on low cycle fatigue crack growth of SUS316. Low cycle fatigue test and periodical observation on inner surface of a hollow specimen was conducted by developing new type of replica observation. The crack growth in PWR environment was measured and the investigation of environmental effects on crack initiation and propagation was conducted. Crack initiation rate of fatigue test in PWR environment is faster than in air condition. Crack pr...
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Environmental Effect on Low Cycle Fatigue Crack Growth of SUS316

The purpose of this study is to investigate environmental effects on low cycle fatigue crack growth of SUS316. Low cycle fatigue test and periodical observation on inner surface of a hollow specimen was conducted by developing new type of replica observation. The crack growth in PWR environment was measured and the investigation of environmental effects on crack growth was conducted. Crack initiation rate of fatigue test in PWR environment is faster than in air condition. Crack initiation is estimated ...
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Environmental Effect on Low Cycle Fatigue Crack Growth of SUS316

The purpose of this study is to generalize P-curve for strain range condition focusing on crack initiation life and crack growth life. The fatigue tests under different constant strain range conditions were conducted in air and the observation of fatigue cracks on specimen surface was also conducted. Using data derived from experiment, dispersion of cry using two-parameter Weibull distribution. Furthermore, the relationship between strain range and shape parameter or scale parameter of crack initiation mo...
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Study on fatigue crack initiation model in air for type 316 stainless steel

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)

A fatigue damage assessment procedure based on crack growth prediction was shown, in order to quantify the risk for failure of nuclear power plant components. First, crack initiation and growth behavior during low-cycle fatigue tests was reviewed and it was shown that the fatigue life could be estimated by predicting the crack growth without considering incubation period before the crack initiation. The change in crack size with the number of cycles was obtained by using the equivalent stress intensity...
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Fatigue Damage Assessment Procedure based on Crack Growth Prediction

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

To prevent degradation at Nuclear Power Plants (NPPs) by maintenance activity, fatigue evaluation should be improved to be more accurate. Studies of crack growth under equi-biaxial fatigue which is caused by thermal stress have been conducted for these purposes. Previous study shows that crack growth rate under equi-biaxial stress is faster than under uniaxial one. But the comparison is not quantitative. In this study, the difference of crack growth rate between equi-biaxial and uniaxial is confirmed q...
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Study on the Behavior of Fatigue Crack Growth of Austenitic Stainless Steel under Equi-biaxial Stress

We have developed a new index called Resilience index, which evaluate the reliability of system safety of nuclear power plant under severe accident by considering the capability to recover from the situation the system safety function was lost. In this paper, a detailed evaluation procedure for the Resilience index was described. System safety of a PWR plant under severe accident was then assessed according to the Resilience index concept to discuss applicability of the index. We found that the Resilie...
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Fundamental Study on Applicability of Resilience Index for System Safety Assessment

In order to show validity of the strain intensify factor for predicting crack growth in the low-cycle fatigue regime, fatigue crack growth tests using Type 316 stainless steel in room temperature were reviewed. It was shown that the crack growth rates correlated well with the equivalent stress intensify factor, which was derived using strain range instead of stress range. Furthermore, the effective equivalent stress intensify factor derived using the effective strain range exhibited excellent correlati...
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Crack Growth Prediction of Stainless Steel for Low-Cycle Fatigue Regime

１．はじめに 事故時における原子力発電所の安全確保上重要なのは、一時的に喪失した安全機能をアクシデントマネジメント(AM)によりいかに早く必要なレベルまで回復できるかにある。そこで、原子力発電所の事故時における安全機能の信頼度を経年変化と保全の効果を取り入れて簡易かつ定量的に評価するため「レジリエンス指標」が提案され、その策定手法の開発が進められている。[1] 本研究では、レジリエンス指標を活用するため、低サイクル疲労による構造物損傷確率モデルを作成し、静的劣化要因に対する機器信頼性評価への適用性について......
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Study on Reliability Analysis for Degradation of Static Components in the Application of Resilience Index