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...
英字タイトル:
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...
英字タイトル:
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...
英字タイトル:
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....
英字タイトル:
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...
英字タイトル:
Numerical evaluation of radiation damage in metals under various neutron irradiation conditions

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...
英字タイトル:
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...
英字タイトル:
Can nuclear power really play a role in “Energy 2050”?

Possible explanation on a difference of microstructural evolution in fcc and bcc metals during temperature change after irradiation, is given based on atomistic evaluation of the binding states of helium to a matrix void, a dislocation and a grainboundary. It is here emphasized that the difference of helium bubble formation in those metals is pro duced by the fact: helium atoms are most strongly trapped by a matrix void in bcc metals, while a grainboundary is a strongest trapping site in fcc metals. These ...
英字タイトル:
Theoretical Insight into a Difference of Helium Bubble Formation in Austenitic and Ferritic Steels during Post-Irradiation Welding

Challenging efforts are discussed to establish an advanced methodology for prediction of material's property and performance changes by irradiation, which will be necessary by all means for the advanced reactor maintenance technology in the future. The changes of material's properties and perfor mance caused by irradiation, such as irradiation-induced hardening, ductility loss, and material's degradation leading to reduction in reactor lifetime, are primarily determined by microstructural changes in materi...
英字タイトル:
How can we predict microstructural changes caused by the multiscale irradiation process occurred in materials havingcomplicated and hierarchical structures?

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...
英字タイトル:
Monte Carlo Modeling for Realizing Optimized Management of Failed Fuel Replacement