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

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

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

Fuel cladding is one of the key components in a fission reactor to keep confining radioactive materials inside a fuel tube. During reactor operation, the cladding is however sometimes breached and radioactive materials leak from the fuel ceramic pellet into the coolant water through the breach. The primary coolant water is therefore monitored so that any leak is quickly detected, where the coolant water is periodically sampled and the concentration of, for example the radioactive iodine 131 (I-131), is...
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Monte Carlo Modeling for Realizing Optimized Management of Failed Fuel Replacement