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

By using the FCVS technology, we had started to develop a high decontamination air cleaning system to remove multi-nuclides for radiation protection to conduct decommissioning the Fukushima NPP. High efficiency multi-nuclide aerosol filters for radiation protection during a process of cutting core debris has been developing at Hokkaido University. A plasma cutter, laser cutter, wire cutter, drilling machine, etc., will be used and will generate aerosols. Therefore, the air cleaning system should be neede...
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Development of a high efficiency multi-nuclide aerosol filters for radiation protection during a process of cutting core debris (2) Measurement of DF for Metal Fiber Filter

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

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...
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Numerical evaluation of radiation damage in metals under various neutron irradiation conditions

In the Fukushima Daiichi Nuclear Power Plant unit 1, isolation condenser (IC) should play an important role in core cooling during the station blackout. To evaluate cooling capacity of the IC, two phase flow analyses with the TRAC-BF1 code and experiments simulating the IC were conducted. The analyses for the actual BWR indicated that the decay heat could be removed if the IC worked properly at 18:18. However, our results showed that core uncovery occurred at 17:30, which leaded to hydrogen production f...
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Study on Evaluation of Cooling Capacity of Isolation Condenser in Fukushima Daiichi Unit 1

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

In order to establish the nuclear power system with sufficient safety, a lot of continuous efforts towards pursuing further plant safety should be made, not only at the plant design and construction stages, but also at the plant maintenance after start using as aging management. In many cases, plant aging are associated with material's degradation due to irradiation, cycle fatigue loading, high temperature, high pressure, etc. It is therefore very important that the degradation of materials under those se...
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Theoretical evaluation of oxidation behavior of fuel cladding in light-waterreactor for prediction of fuel reliability

The water level in the fuel zone is an important parameter to conduct properly accident management. In the Fukushima Daiichi Nuclear Power Plant accident, measurement error of the water level occurred, which was caused by evaporation of water in a reference leg. To measure the water level properly, the reference leg connected to the condensing chamber must be filled with water. We focused on the method called backfill to keep the performance of water level gauge during severe accident. Backfill is applied ...
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Study on keeping performance of water level gauge under the severe accident.