In this research, a new index “The Resilience Index” was proposed to evaluate the capability of nuclear power plant to recover from the situation of safety function lost. Three elements assumed to evaluate the resilience index are the achievement rate, necessary time, and probability of success of each accident management activity. The resilience index is expected to visualize the improvement of safety of each nuclear power plant against severe accidents. ...
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Development of Resilience Evaluation Method for Nuclear Power Plant (Part.1: Proposal of Resilience Index for Assessment of Safety of Nuclear Power Plant under Severe Accident)

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. ...
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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...
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Study on Mechanism of Local Failure and Proposal of Fracture Surface Based on the Mechanism

After Fukushima accident in 2011, demand in a design and management to predict severe accidents like Fukushima accident have been realized. To realize them, we must clarify fracture event of reactor pressure v essels or containment vessels. However, the mechanism of failure of structure under severe condition like overpressure or hyperthermia is not clear completely. If we can to predict damage or failure causing se vere accidents in advance by some method, we can take some measures retaining soundness of ...
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Image analysis for the deformation of a specimen with tensile loading

Abstract After Fukushima accident, the threats of terrorism are increasing. However, countermeasures for insider terrorists are insufficient because the main target of Physical Protection System (PPS) is outsider. Thus development of automatic detection of insider terrorists is required. In this paper, focusing on the hand motion, final goal is image recognition by Convolutional Neural Network (CNN) and analysis of each finger’s position and angle and detection of signs of malicious behavior. And For ...
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Automatic Detection of Malicious Insider Behavior for Nuclear Security

１．緒言 福島事故以降、原子力施設における核セキュリティの重要性は増大している。原子力発電所における核セキュリティの最大の目的は悪意のある行為者による原子力施設の安全機能の喪失のリスクを可能な限り下げることである。その中でも特に重要視すべきものが妨害破壊行為である。妨害破壊行為は一般的にアウトサイダーによるものとインサイダーによるものの2 つに分類される。現状の核セキュリティはアウトサイダーへの対応に比べインサイダーへの対応は十分とは言えない可能性がある。そのため原子力施設内でインサイダーが行う妨害破壊行......
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Development of Dangerous Behavior Detection Method using Machine Learning

Abstract Fast breeder reactors which are operated at elevated temperature must be designed considering creep deformation in addition to elastic-plastic deformation. Especially at structural discontinuities, strain concentration induced by stress-strain redistribution reduces creep- fatigue strength. For this reason, a design method is needed for appropriately evaluating inelastic behavior at structural discontinuities. As one of the simplified methods with elastic analysis, a rational method with Stress Re...
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Study on the Stress-Strain Redistribution Caused by Inelastic Deformation inPerforated Plates with Triangular Pattern of Holes

Fluid temperature fluctuates at an incomplete mixing area of high and low temperature fluids in nuclear components. It induces random variations of local temperature gradients in structural walls, which lead to high cyclic thermal fatig ue damage. Since this phenomenon is a complex fluid-structural interaction problem, evaluation methods were developed in each field. In order to integrate above methods into maintenance engineering, their synthesis approach is proposed....
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Synthesis of High Cycle Thermal Fatigue Evaluations against Fluid Temperature Fluctuation

The temperature oscillation produced by thermal stratification phenomenon induces thermal fatigue damages on structures of nuclear components, which should be prevented. To evaluate thermal fatigue, the frequency response function was developed. However, this theoretical method does not take particular effects of thermal stratification oscillation into account. To clarify these effects, finite element simulations were conducted with two fluid temperature models. Based on mechanisms of the effects, the ...
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Study on the frequency response mechanisms of thermal stress induced by thermal stratification oscillation phenomenon

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...
英字タイトル:
Development of thermal stress evaluation method and fatigue damage evaluation method for thermal stratification oscillation