Abstract: Preparation for DEC (design extension condition) is one of the lesson learned from Fukushima nuclear accident. From the structural point of view, it is needed to know the failure modes of the pipe structure to make adequate preparation against excessive seismic loading. But the failure modes under seismic loading are still not clear. Low cycle fatigue is one of the major failure modes observed at seismic experiments. Ratcheting is also observed at some other experiments. And collapse is assum...
英字タイトル:
Failure modes investigation of pipe structure under excessive seismic loading

Preparation for DEC (design extension condition) is one of the lessons learned from Fukushima Daiichi nuclear accident. Best estimation is required for DEC. For best estimation of structural strength against seismic load, it is needed to know the failure modes of the piping to make adequate preparation against excessive seismic loading. Ratcheting, collapse and fatigue are the probable failure modes of piping due to seismic loading. But the occurrence conditions of these failure modes under seismic loadi...
英字タイトル:
Numerical study on piping failure modes under seismic loading - ratcheting and collapse

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...
英字タイトル:
Progressive deformation by dynamic loadings and effects of frequency

According to the design standards of nuclear equipment, ductile fracture is assumed as the failure mode due to monotonic loading in the elastic-plastic region, but it is known that failure mode called local failure occurs at the part with high stress triaxiality. In the past, the authors have proposed a fracture surface that can uniformly evaluate transition of failure modes from ductile fracture to local failure. This research proposes the extension method of the fracture surface to creep region. ...
英字タイトル:
Investigation on extension of local failure evaluation method in plastic region to creep region

The failure mode so called a local failure could occur at a specific structural discontinuities of pressure vessels. Local failure, which is a type of ductile fracture, generally occurs under multiaxial stress conditions. In this paper, tensile tests and elastic plastic finite element analyses for smooth and notched specimens were performed to study a mechanism of local failure. From these investigation, it was concluded that the local failure occurs under high triaxial stress conditions and this condit...
英字タイトル:
Study on Mechanism of Local Failure and Proposal of Fracture Surface Based on the Mechanism

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...
英字タイトル:
Study on the mechanism of stress generation of straight pipe and elbow pipe which has thermal stratification

Laser peening is a surface enhancement process that introduces compressive residual stress on materials by irradiating laser pulses under aqueous environment. The process utilizes the impulsive effect of high-pressure plasma generated by ablative interaction of each laser pulse. It is very beneficial to shorten ou tage period if laser peening is available during refueling work. It is confirmed that laser peening can be available in the situation by experiment and analys is. This report describes detail of ...
英字タイトル:
Study on availability of laser peening during refueling work- Preventive maintenance to shorten outage period