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

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 risk assessment method of failure of reactor pressure vessel at PTS event was developed for the risk- based maintenance. The failure risk was caused by fluctua...
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Reduce the risks associated with irradiation embrittlement of RPV steels: Approach from simulation of microstructural change in steels during irradiation

Continuous efforts should be made to keep the safety of light-water reactors, not only at the design and construction phases but also at the operation phase. Fuel cladding is a key barrier in containing fission product. However, fuel failures yet occur in operating nuclear power plants, often leading to reactor shutdown based on the conservative, sometimes too conservative, judgment. Therefore, an appropriate judgment of how to treat the fuel failure is required to achieve reasonable management of reac...
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Risk assessment of reactor shut-down due to fuel failure for sufficient management of nuclear reactors

Newspaper articles were analyzed to investigate the public understanding on nuclear energy utilization in Japan, which was structurized based on the graph theory and visualized with the digraph. The digraph is composed of 19 factors such as politics, economics, the environment, etc., and these are linked with each other by various causal relationships. The digraph may show what kind of issues such stakeholders face with each other as the people, the power company, and the government. Also, it may indicate t...
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Structurizing public understanding on nuclear energy

A multiscale viewpoint is introduced into the modeling methodology of radiation damage processes in fission and fusion materials, where the p rocesses occur at a wide variety of time and length scales. Attempt is also made to apply this viewpoint to the reactor integrity technology....
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Multiscale viewpoint of material's degradation due to irradiation and its possible application to the lifetime assessment of nuclear power plants

Since structural materials used in a fission reactor are subjected to irradiation by high energy neutrons, materials degradation due to irradiation should be taken into account when reactor design and maintenance are made. One of significant issues to be solved for a realization of long term operations beyond 40 years is to clarify the validity of a predictio n of material’s degradation due to long term irradiation that is not experienced yet. Material’s behavior due to 60 years irradiation in a reactor sh...
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Numerical evaluation of radiation damage in metals under various neutron irradiation conditions