In nuclear power plants, a lot of failure cases by high cycle thermal fatigue are reported, which is induced by temperature fluctuation of the coolant. To ensure the safety of nuclear power plants, thermal fatigue should be evaluated adequately. To evaluate thermal fatigue, frequency response functions were developed by Kasahara et al... These functions were derived theoretically to calculate thermal stress caused by thermal striping and thermal stratification oscillation, which are main causes of high...
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Development of thermal stress evaluation method and fatigue damage evaluation method for thermal stratification oscillation

In nuclear power plants, a lot of failure cases by high cycle thermal fatigue have been reported, which is induced by temperature fluctuation of the coolant. To ensure the safety of the nuclear power plants, the thermal fatigue failure should be prevented adequately. Thus The Japan Society of Mechanical Engineers (JSME) published the high cycle thermal fatigue evaluation guideline. In the guideline, it is proposed that the structural integrity can be judged by the location of thermal stratification, which...
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Study on the mechanism of stress generation of straight pipe and elbow pipe which has thermal stratification

Thermal fatigue failure and vibration fatigue failure occur frequently in spite of well known. Because they are complicated multi-physics phenomena. Furthermore, there are many influence factors in both of loadings and strength. For design, conservative evaluation methods were applied to both loadings and strength. However, best estimation with uncertainty evaluation are suitable for trouble shootings and risk analyses. To satisfy above requirements, authors propose a total evaluation of loadings and s...
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Total evaluation of loadings and strength for fatigue damage prediction

Our aim is to develop a technology to suppress the expansion of accident damage by improving the reactor structural resilience as a solution to the problem of restoring the safety function of structures after destruction, which has been an issue since the Fukushima Daiichi Nuclear Power Plant accident. In this research, the visualization method of resilience of nuclear structures was proposed in order to visualize the capacity to mitigate and to recover safety function loss by applying and improving the res...
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Visualization of resilience improvement effect by fracture control technology using resilience index

In recent years, reports have increased about failure cases caused by high cycle thermal fatigue both at light water reactors and fast breeder reactors. One of the reasons of the cases is a turbulent mixing at a Tee -junction, where hot and cold temperature fluids are mixed, in a coolant system. In order to prevent thermal fatigue failures at Tee-junctions, The Japan Society of Mechanical Engineers published the guideline which is an evaluation method of high cycle thermal fatigue damage at nuclear pipes. ...
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Comparison of Evaluation Results of Piping Thermal Fatigue EvaluationMethod based on Equivalent Stress Amplitude

The conventional purpose in the field of structural strength has been to prevent damage to design basis events (DBE). For beyond design basis events (BDBE), it is necessary to mitigate the impact on safety on the premise that damage will occur. The authors propose a mitigation method that suppresses the consequence into a fracture mode with a large impact by reducing the load due to a fracture with a small impact on safety. We will introduce the research results for individual component, extend the applicab...
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New approach to beyond design basis events in structural strength field

Experimental and analytical study was carried out with notched specimens which simulated multiaxial stress state in structural discontinuity, in order to reveal the mechanism and dominant parameters of “local failure”. Both the tensile test and finite element analyses (FEA) exhibited, notch strengthening. Furthermore, in the tensile test, failures of notched specimens were progressed from inside, where hydrostatic stress showed the maximum value in the FEM, whereas Mises stress did not show the maximum valu...
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Experimental and Analytical Study on Dominant Parameters of Local Failure of Structures

Nuclear piping has various kinds of thermal fatigue failure modes. Main causes of thermal loads are structural responses to fluid temperature changes during plant operation. These phenomena have complex mechanisms and so many patterns, that their problems still occur even though well-known issues. To prevent thermal fatigue due to above thermal loads, the JSME guideline is adopted. Both thermal load and fatigue failure mechanism have been investigated and summarized into the knowledgebase. Based on abo...
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Development of thermal fatigue evaluation methods of piping systems

Abstract Effect of loading history on the high cycle fatigue crack propagation behavior was experimentally studied in SUS 316 stainless steel, paying a special attention to an interaction between low-cycle thermo-mechanical fatigue loading and high cycle fatigue one in the fatigue crack propagation rates. The experimental results clearly demonstrat ed that the interaction was significant. It was shown that the stress ratio which was built-up under an influence of previous loading history made a major contr...
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Fatigue Crack Threshold Depending on Loading History.