The structural integrity of reactor pressure vessels (RPVs) is an important issue in the field of nuclear power plants. The RPV contains a reactor core, which is impossible to substitute. The pressurized thermal shock (PTS) loading is a critical issue in assessing the safety of RPV. The most severe situation takes places during cold water injection in the cold legs when the emergency core cooling system (ECCS) is operated due to LOCA. Under these circumstances, the PTS loading may lead the RPV to brittle fr...
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3D-CFD and FEM Based Deterministic PTS Analysis for Optimizing RPV Maintenance Strategy

In order to keep nuclear safety, management of irradiation embrittlement of LWR pressure vessel steels is the one of important issues. In this study, we focus on the prediction of irradiation embrittlement. Conventionally, irradiation embrittlement prediction is performed by a numerical model based on the mechanism. In recent years, research in fields such as AI and Bayesian statistics has rapidly progressed. Therefore, in this study, in order to advance the irradiation embrittlement prediction, the irradia...
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Modeling for Prediction of Irradiation Embrittlement of RPV steels using AI

The structural integrity of a reactor pressure vessel (RPV) is significant for nuclear plant safety. In assessing the integrity of the RPV, one of the most severe situations to be considered is pressurized thermal shock (PTS) during emergency water cooling. Many efforts have been made to understand this PTS, and these efforts assumed symmetric reactor cooling injection. However, once extreme circumstances occur, such as a major earthquake, some of the cooling injections will fail. This failure makes symmetr...
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Pressurized Thermal Shock Analysis of a Reactor Pressure Vessel for Optimizing the Maintenance Strategy: Effect of Asymmetric Reactor Cooling

An embrittlement correlation method is one of the most important techniques to ensure the integrity of pressure vessel steels in nuclear power plants. In Japan, this is being addressed in accordance with the Japan Electric Association Code (JEAC4201) that was constructed using actual measured data of irradiation embrittlement of pressure vessel steels. In the present study, as a key step towards developing more reliable methodologies, statistical arguments were made on the embrittlement data. Based on this,...
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Application of Bayesian Estimation Method to Irradiation Embrittlement Correlation of RPV Steels

Reactor pressure vessel (RPV) steels are subjected to neutron irradiation that can lead to loss of fracture toughness. One of the critical issues for RPV structural integrity is related to the pressurized thermal shock (PTS) event. Risk assessment is important for safety evaluation and maintenance planning of a nuclear power plant. In this study, a new method was developed to assess a failure risk of RPV at PTS event for the risk-based maintenance. The failure risk was caused by fluctuations of stress...
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Risk-based Optimization of Reactor Pressure Vessel Maintenance

The structural integrity of a reactor pressure vessel (RPV) is important part of nuclear power plant safety. Pressurized thermal shock (PTS) takes place when the emergency core cooling system (ECCS) is operated and the coolant water is injected into the RPV due to a loss-of-coolant accident (LOCA). With the neutron irradiation, PTS loading may lead a RPV to fracture. In the present study, optimization of RPV maintenance is considered, where two different attempts are made to investigate the RPV integri...
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From the Viewpoint of Maintenance, the Probabilistic Integrity Evaluation of Reactor Pressure Vessel

The integrity of the Reactor Pressure Vessel (RPV) subjected to Pressurized Thermal Shocks (PTS) by cold water injection through the cold leg owing to a Loss-Of-Coolant Accident (LOCA). Fracture Mechanics (FM) analysis evaluation for cracks of the inner surface in the RPV during PTS events, which is important in assessing the safety of nuclear power plants. Conventional, one-dimensional thermal hydraulic analysis and simple model fracture mechanics analysis has been performed. In the present study, the...
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3D-CFD & FEM analysis of RPV stress intensity factor for cracks subjected to PTS phenomena 京都大学 阮 小勇 Xiaoyong RUAN Member

A multiscale viewpoint is introduced into the modeling of radiation damage processes in nucle ar fission and fusion materials, where the processes occur at a wide variety of time and leng th scales. This viewpoint enables us to understand the dose-rate dependence of microstructural changes in materials, which is important for establishment of irradiation correlation rules....
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Prediction of radiation-induced damage in nuclear materials

In Japan, the government decided that nuclear power was used as one of the energy sources for base load energy. Nuclear power plants are required more safety. The plant safety have kept since the start of operation due to the maintenance. Since the maintenance plan should be continued improving, there is still issues for improvement in the plan. In this study, we systematize the methods of the plant maintenance. We review the maintenance plan of reactor pressure vessel and fuel cladding tube and indic...
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Advanced maintenance methodology was developed for the keeping integrity of reactor pressure vessel

The reactor pressure vessel (RPV) has the function as the reactor coolant pressure boundary (RCPB) which is damaged by neutron irradiation embrittlement. In order to keep the function, maintenance activities should be done to manage irradiation embrittlement. In this study, we investigated the precision of the prediction model of irradiation embrittlement applied by Japan’s nuclear regulation. Finally, we discussed the precision required for adequate management. ...
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Integrity Assessment of Reactor Pressure Vessel Steel: Ambiguity of Predicting Irradiation Embrittlement