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

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

The prediction of the initiation and propagetion of irradiation-assisted stress corrosion cracking is one of the issues for aging countermeasures in nuclear power plants, and it is desirable to improve the accuracy of the prediction. In recent years, theoretical calculations have shown that irradiation defects introduced by neutron irradiation generate internal stress. Therefore, in this research, we calculate the increase of internal stress using the molecular dynamics method when irradiation defects are f...
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Influence of internal stress by irradiation defect formation on irradiation assisted stress corrosion cracking

Ten years have already passed since the accident at the Fukushima Daiichi Nuclear Power Plant caused by the Tohoku Earthquake. Thanks to the efforts of all concerned, the extraordinary work toward the decommissioning and reconstruction of Fukushima is progressing steadily. However, it is difficult to imagine what Fukushima will look like after reconstruction, and the public's trust in nuclear power has not yet been restored. Even in this atmosphere, nuclear power must be revived, because the abnormal weathe...
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Can nuclear power really play a role in “Energy 2050”?

The phase decomposition behaviour of an experimental High-chromium Ferritic steel containing 40 wt.% chromium (Fe-40Cr) irradiated with 8 MeV electrons was studied by positron annihilation lifetime (PAL) measurements and coincidence Doppler broadening (CDB) of positron annihilation radiation measurements. Electron irradiation at 100 and at 475 ?C were performed on the specimens to nominally 0.03 to 0.3X10-3 dpa. The rapid increase of W-parameter obtained from the specimen irradiated at 100 ?C is most like...
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Effect of Thermal Aging and Electron Irradiation on Microstructure Changes of High Chromium Steels