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Advanced Nuclear Energy Research 先進原子力エネルギー研究グループ

(1)Research on New-Type Nuclear reactors and Accelerator Driven Subcritical Reactors

1)Development of New-Type Nuclear Reactors

(Graduate School of Engineering) Tomoaki Kunugi, Zensaku Kawara

Plan and Achievement in 2008

In order to realize high efficiency and safety for new-type nuclear reactors as promising advanced nuclear energy source, precise knowledge is essential on the coolant flow, which is gas-liquid two-phase flow in complex system. Measurement and analytical technology for multi-phase flow are needed as the fundamental technology. In this study, measurements are taken for the temporal-spatial behavior of gas-liquid interface at various two-phase flow regime by using two-phase flow experiment loop, and its experimental database are used for development of high-accurate and high-speed analytical technology on multiphase flow. In this year, experimental loop of large cross-sectional rectangular flow channel were set up for three-dimensional behavior of bubbles, and measurement system for multiphase flow were sophisticated by introducing optical probe system, flow visualization system with high resolution, etc. Numerical technology combining multiphase flow and structure were being developed, and speeding up of numerical analysis for multiphase flow were also investigated.

2)Research on Reactor Physics of Accelerator Driven Subcritical Reactors

(Research Reactor Institute)Tsuyoshi Misawa, Hironobu Unesaki, Ken Nakajima

An Accelerator Driven Subcritical system (ADS) is expected to be a safety and innovative energy resource for the future. In order to evaluate the feasibility and establish the technology bases on ADS, a series of experiments have been conducted using a proton accelerator, FFAG, combined with a subcritical core of Kyoto University Critical Assembly (KUCA). In the ADS reactor physics experiments,high-energy neutrons generated from FFAG proton beam injected to tungsten target have been introduced to subcritical core constructed at KUCA. High-energy neutron spectrum measurement by foil activation method, reaction rate measurement and spectrum measurement by foil activation method, reactor response measurement at beam trip / beam injection and sudden insertion of negative reactivity, subcriticality measurement by pulse neutron method and source multiplication method and reactor kinetics parameter measurement using noise method have been performed.

3)Development of FFAG Proton Accelerator

(Research Reactor Institute) Yoshiharu Mori, Yoshihiro Ishi

The FFAG proton accelerator at KURRI is a chain of three FFAG rings; injector, booster and main ring. The injector is eight-sector spiral focusing type of FFAG accelerator and the field gradient of each sector magnet can be changed precisely for varying the maximum attainable beam energy of this system. The booster and the main ring are eight-sector and twelve-sector radial focusing FFAG accelerators, respectively. In the first ADS experiment with the FFAG accelerator, the proton beam energy was 100 MeV and the beam was transported to KUCA cores through the MCBT line which consists of many dipole and quadrupole magnets. The beam intensity and quality at the KUCA core, which affect the ADS experimental results, depend largely on the tuning of the MCBT line. In this study, a power supply system for the MCBT magnets has been improved to increase the magnetic field stability. In order to increase the beam intensity of the FFAG accelerator in future, development of charge-exchange beam injection with negative hydrogen ions has been also started in this study, where beam optics for this scheme was designed, and some of the vacuum chambers and beam ducts were fabricated.

4)Development of materials for Accelerator Driven Subcritical Reactors

(Research Reactor Institute) Toshimasa Yoshiie, Qiu Xu

In order to ensure the safety of accelerator driven subcritical reactor, it is necessary to develop the materials which withstand the irradiation of protons with high energy. In addition to the displacement damage, material degradation is also induced by helium and hydrogen produced by high energy protons. The purpose of this study is to investigate the materials degradation mechanism experimentally. In this year, materials irradiation system using the proton accelerator of FFAG in the Research Reactor Institute was developed.

(2)Research on Nuclear Fusion Reactors

1)Research on Plasma Confinement with Heliotron J

(Institute of Advanced Energy)Tohru Mizuuchi

New diagnostic systems in the magnetically confined high-temperature plasma have been developed for (a) electron density profile by introducing a microwave reflectometer and (b) impurity ion temperature and the rotation velocity profiles by introducing charge exchange recombination spectroscopy (CXRS) system. A newly installed power amplifier for the reflectometer increases the injected microwaves power from 10dBm to 20dBm, resulting that the detection sensitivity can be improved for 200MHz amplitude-modulated microwaves of 33-56GHz frequencies. This makes the phase detection accurate, expecting that the electron density measurement is more reliable. By using a high sensitive and time-resolved CCD camera the CXRS system has a capability to improve the resolution of the rotation velocity more than several times higher than the conventional one, aiming at precise estimation of the radial electric field being a key factor in fusion reactor design.
On the other hand, to develop modules of an integrated code which is capable of performing hierarchical simulation for plasmas in a non-axisymmetric fusion reactor, a workstation with eight cores has been introduced. At present, we are developing several simulation modules for analyzing the neoclassical transport and detailed MHD equilibrium of helical plasmas.

1)Development of Integrated Tokamak Simulation code

(Graduate School of Engineering) Atsushi Fukuyama

In order to predict plasma performance and optimize operation scenario of magnetic fusion core plasmas, self-consistent simulation of ion cyclotron heating and electron cyclotron current drive was carried out by developing a numerical code which describes the time evolution of multi-species momentum distribution functions precisely including the effects of Coulomb collisions between the particles species, and the install of more main memory of the integrated simulation server has enabled simulations with higher resolution.

2)Development of Compact Tokamak Fusion Reactor

(Graduate School of Energy Science)Takashi Maekawa

As a proof of principle study for realization of compact tokamak fusion reactor with no central solenoid, an experiment to produce a spherical plasma torus by using microwave power has been conducted in the Low Aspect ratio Torus Experiment (LATE) device. In addition, characteristics of the plasma have been studied by un-isotropic pressure model parallel and perpendicular to the magnetic field.

3)Fusion Reactor System Design

(Institute of Advanced Energy)Satoshi Konishi

The research plan in the fiscal year 2008 in the fusion reactor system design area intended the establishment of design concept of energy system, and the preparation for the research activity to concretely design the system based on this concept.
In order to implement the above plan, guidelines were made by the discussion with the scenario group as follows:

  • ―Fusion cannot expect large market share in Japan and significant contribution for global CO2 reduction.
  • ―If fusion requires decades to be introduced, market chance in the developing countries will be significantly smaller because market will be expanded and matured during that period. In order to make considerable contribution, early energy production is needed.
  • ―In the electricity markets in the world, competition with hydro, renewable such as solar and nuclear is anticipated, and it does not result in the significant reduction of CO2 emission.
  • ―Global fuel market has several times larger scale, and dependence on the fossil such as oil is higher, therefore supplying substitute of fuel is expected to make significant CO2 reduction in the global scale.

 Concept development based on the above guideline resulted in the proposal of “Fusion-Biomass Hybrid System” that converts fusion energy to high temperature heat with liquid metal blanket, and synthesizes hydrogen and fuels from biomass. This system is possible with current level of plasma performance, and provides liquid fuel instead of electricity, that is quite unique in the world fusion community. By this concept, we suggested that fusion can make significant contribution in near future as a substitute of fossil energy toward CO2 zero emission. Also as a preparation for the practical design study from the next year, simulation codes system for neutronics and thermal hydraulics were established.

 These results satisfied the original research plan for the fiscal year 2008, and the outcome is so significant that the contribution of the energy system concept proposed here would be an important part of the entire zero emission energy scenario to be established by this GCOE project.

(3)Development of Advanced Nuclear Materials

1)Research on Thermal Diffusivity Estimation of Irradiated Ceramics

(Graduate School of Engineering)Masafumi Akiyoshi

 Material that survives under severe irradiation environment is the key factor to develop the future fusion reactor and other nuclear applications, such as high-temperature gas cooling fission reactor. Especially, these reactors are designed to operate at high-temperature to achieve higher generation efficiency or to actualize direct hydrogen production, and ceramics are one of the candidate materials. Thermal diffusivity is one of the most important factors for materials used at high temperature, but it has been reported that the thermal diffusivity of neutron-irradiated ceramics showed significant degradation. Changes after the irradiation that depend on the irradiation conditions were clarified step by step with the past study, still changes during the irradiation is not estimated, and that inhibit to obtain the guide to develop materials.
 The thermal diffusivity at the irradiation temperature is evaluated from the dependence of thermal diffusivity on measurement temperature, and it can be considered to represent the thermal diffusivity during irradiation with several assumptions. In this work, 30MeV electron accelerator is used to induce defects to ceramic materials at several temperatures, and then the thermal diffusivity of post-irradiation specimens is measured to obtain relation between thermal diffusivity at the irradiation temperature and the irradiation temperature. Specimens are radio activated with the irradiation, so all measurements are operated in radiation controlled area at Radiation Laboratory, Uji campus.
 In this project, sample preparation system was equipped by introducing automatic polishing machine, that can form ceramic materials in high precision efficiently, and we have prepared specimens for electron-irradiation experiments. Also we improved measurement system of thermal diffusivity to present better measurement efficiency.

2)Improvement of In-situ Observation System of Irradiation Defects

(Graduate School of Engineering)Hidetsugu Tsuchida

 Nowadays, positron annihilation method is widely used to investigate the irradiation defects, and expected to clarify the behavior of irradiation defects under the irradiation environment. In previous works, the behavior of irradiation defects has been analyzed by measurements of post irradiation specimen, but behavior during the irradiation is little studied. So, we have been trying in-situ observation of defects during ion-beam irradiation using tandem accelerator in Radiation Laboratory, Uji campus. But still time resolution of positron annihilation lifetime measurement is not enough good, and each measurement required very long time, so improvement of the system is required.
 In this project, the existing system that measure positron annihilation lifetime was improved. BaF2 crystals of scintillation detectors were changed to larger one to achieve higher detection efficiency. The irradiation chamber was modified, and measurement layout using avalanche-photo-diode was arranged to achieve better time resolution. This improved measurement system may present more detailed behavior of defects during irradiation, so now we fix the setting of the system to obtain the guide to develop materials that was used irradiation environment.

3)Development of Advanced Oxide Dispersion Strength Ferritic Steels

3)Development of Advanced Oxide Dispersion Strength Ferritic Steels

 Nuclear energy is one of the promising energy to reduce the emission of carbon dioxide near future. In this research, innovative structural materials R&D is performed for applications to next generation nuclear systems which require high-performance to structural materials. It is essential to elevate operation temperature of the plants, which is controlled by upper limit temperature of the materials, to increase thermal efficiency of the plants. In this research, advanced oxide dispersion strengthened (ODS) ferritic steels were selected as a candidate of the structural materials of the next generation nuclear plants, because nano-sized oxide particle dispersion has been considered to be effective to improve materials performance.
 In 2008, Ph.D course students lead the discussion for developing ODS steels from a point of view of requirements for advanced nuclear systems. Finally, it was concluded that one of the most important key technologies for high performance of ODS steels are the size and number density of the oxide particles. Based on the discussion, it is concluded that the R&D of ODS steels can be focused on the processing technology to form nano-sized oxide particles in high density.
 A research group of Japanese and Korean student worked together to collect scientific information by attending at annual meeting of Japan Institute of Metals and Atomic Energy Society of Japan. Collaborative research was carried out among Kyoto University, Korea Advanced Institute of Science and Technology and China Academy of Institute of Modern Physics. The following symposiums and workshop were held:

  • Research group meeting on fuel cladding (Kyoto University)
  • Research group meeting on fusion materials (NIFS)
  • US/Japan Workshop on blanket structural materials (Kyoto University)
  • Summer school on nuclear materials(Hakone)

Finally, a model ODS material was produced as a surveillance test materials on the bases of the above research activities. The research group was well organized by students, and the objective of this working group was clearly defined. Japan/Korea/China collaborative research by Ph.D students also started with the effective support by professors of each country.