Aihara, Jun; Yasuda, Atsushi*; Ueta, Shohei; Ogawa, Hiroaki; Honda, Masaki*; Ohira, Koichi*; Tachibana, Yukio
Nippon Genshiryoku Gakkai Wabun Rombunshi, 18(4), p.237 - 245, 2019/12
Development of fabrication and inspection technologies of oxidation resistant fuel element for improvement of safety of high temperature gas-cooled reactors (HTGRs) in severe oxidation accident was carried out. Simulated coated fuel particles (CFPs), alumina particles, were over-coated with mixed powder of Si, C and small amount of resin to form over-coated particles, and over-coated particles were molded and hot-pressed to sinter simulated oxidation resistant fuel elements with SiC/C mixed matrix. Simulated oxidation resistant fuel elements with matrix whose Si/C mole ratio is 1.00 were fabricated. Failure fraction of CFPs in fuel elements is one of very important inspection subjects of HTGR fuel. It is essential that CFPs are extracted from fuel elements without additional failure. Development of method for extraction of CFPs was carried out. Desolation of SiC by KOH method or pressurized acidolysis method should be applied to extraction of CFPs.
Aihara, Jun; Honda, Masaki*; Ueta, Shohei; Ogawa, Hiroaki; Ohira, Koichi*; Tachibana, Yukio
Nippon Genshiryoku Gakkai Wabun Rombunshi, 18(1), p.29 - 36, 2019/03
Japan Atomic Energy Agency carried out development of fabrication technology of oxidation resistant fuel element for improvement of safety of high temperature gas-cooled reactors in serious oxidation accident, based on precursor research in former JAEA. Dummy coated fuel particles (alumina particles) were over-coated with mixed powder of Si, C and small amount of resin to form over-coated particles, and over-coated particles were molded and hot-pressed to sinter dummy oxidation resistant fuel elements with SiC/C mixed matrix. We fabricated dummy oxidation resistant fuel elements with matrix whose Si/C mole ratio (about 0.551) is three times as large as that in precursor research. Si peak was not detected by X-ray diffraction of matrix. Better oxidation resistant was confirmed with oxidation test in 20% O at 1673 K than that of ordinal fuel compact with ordinal graphite/carbon matrix. All dummy coated fuel particles were held in specimen after 10 h oxidation.
Yasuda, Satoshi; Uchibori, Yosuke*; Wakeshima, Makoto*; Hinatsu, Yukio*; Ogawa, Hiroaki; Yano, Masahiro; Asaoka, Hidehito
RSC Advances (Internet), 8(66), p.37600 - 37605, 2018/11
We present a quantitative study on the effect of a newly obtained thermal history on the formation of Fe-N-C catalytic sites. A short and repeated heating process is employed as the new thermal history, where short heating (1 min) followed by quenching is applied to a sample with arbitrary repetition. Through electrochemical quantitative analysis, it is found that the new process effectively increases the Fe-N-C mass-based site density (MSD) to almost twice that achieved using a conventional continuous heating process, while the turn-over frequency (TOF) is independent of the process. Elemental analysis shows that the new process effectively suppresses the thermal desorption of Fe and N atoms during the initial formation stage and consequently contributes to an increase in the Fe-N-C site density. The resultant catalytic activity (gravimetric kinetic current density (0.8 V vs. RHE)) is 1.8 times higher than that achieved with the continuous heating process.
Ishizaki, Shuhei; Hayakawa, Tsuyoshi; Tsuzuki, Katsunori; Terada, Hiroaki; Togawa, Orihiko
JAEA-Technology 2018-007, 43 Pages, 2018/10
When North Korea has carried out a nuclear test, by a request from Nuclear Regulation Authority (NRA), Nuclear Emergency Assistance and Training Center (NEAT) predicts atmospheric dispersion of radionuclides by WSPEEDI-II system in cooperation with Nuclear Science and Engineering Center (NSEC), and submits the predicted results to NRA as the activity to assist responses by the Japanese Government. This report explains frameworks of the Japanese Government and Japan Atomic Energy Agency (JAEA) to cope with nuclear tests by North Korea, and describes a series of activities by NEAT regarding predictions of atmospheric dispersion of radionuclides in response to the 5th and 6th nuclear tests carried out by North Korea in September 2016 and September 2017. Future plans and issues to be solved for responses to nuclear tests are also described in this report, together with an outline of a computer program system used in the predictions.
Hino, Ryutaro; Takegami, Hiroaki; Yamazaki, Yukie; Ogawa, Toru
JAEA-Review 2016-038, 294 Pages, 2017/03
In the aftermath of the Fukushima nuclear accident, safety measures against hydrogen in severe accident have been recognized as a serious technical problem in Japan. Therefore, efforts have begun to form a common knowledge base between nuclear engineers and experts on combustion and explosion, and to secure and improve future nuclear energy safety. As one of such activities, we have prepared the "Handbook of Advanced Nuclear Hydrogen Safety" under the Advanced Nuclear Hydrogen Safety Research Program funded by the Agency for Natural Resources and Energy of the Ministry of Economy, Trade and Industry. The concepts of the handbook are as follows: to show advanced nuclear hydrogen safety technologies that nuclear engineers should understand, to show hydrogen safety points to make combustion-explosion experts cooperate with nuclear engineers, to expand information on water radiolysis considering the situation from just after the Fukushima accidents and to the waste management necessary for decommissioning after the accident, etc.
Yamamoto, Tsuyoshi; Hashimoto, Yasunori*; Kitazawa, Sin-iti; Yatsuka, Eiichi; Hatae, Takaki; Sugie, Tatsuo; Ogawa, Hiroaki; Takeuchi, Masaki; Kawano, Yasunori; Itami, Kiyoshi
Fusion Engineering and Design, 96-97, p.1012 - 1016, 2015/10
Japan Domestic Agency (JADA) is responsible for six diagnostic systems in the ITER project. We have successfully developed an instrumentation and control (I&C) system for the diagnostic systems. The I&C system manages internal operations for measurement such as health checks of sensors, configuration of measurement parameters, and consistency checks between measurement parameters. We developed a conversion tool to convert operational flowcharts to EPICS records. The sequencing management function coordinates the execution of operation steps by monitoring changes in the record values. It was designed so that the relationship between the records and steps is determined automatically according to the flowcharts as much as possible. We validated the performance of the I&C system for the thermocouple measurement system, and are continuing the development of even more complex I&C systems for other JADA diagnostic systems.
Kitazawa, Sin-iti; Maruyama, Toshiyuki; Ogawa, Hiroaki; Itami, Kiyoshi; Casal, N.*
Plasma and Fusion Research (Internet), 10(Sp.2), p.3402044_1 - 3402044_4, 2015/04
Takeuchi, Masaki; Sugie, Tatsuo; Ogawa, Hiroaki; Ishikawa, Masao; Shimada, Takahiko; Kusama, Yoshinori
Plasma and Fusion Research (Internet), 8(Sp.1), p.2402147_1 - 2402147_5, 2013/11
Divertor IR Thermography is one of the diagnostics which Japan is in charge of development in ITER project. The conceptual design has been performed so far, and the progress is reported here. By reducing the size of mirrors, and making the optical path a labyrinthine structure, the design of a new optics that fills requirements of both spatial resolution and neutron shielding has been advanced. To achieve the required measurement accuracy, the detected signal and the noises such as bremsstrahlung light, detector noise and thermal noise of optical components were evaluated. Higher photons than the bremsstrahlung light are obtained, excluding the low temperature range. The simulation calculation of reflection from wall was started. Detailed method of data processing of deriving the profiles of surface temperature in the divertor plates from the observed signals and in-situ calibration strategies of the optical system are important issues and will be discussed.
Okayasu, Yuichi*; Tomizawa, Hiromitsu*; Matsubara, Shinichi*; Sato, Takahiro*; Ogawa, Kanade*; Togashi, Tadashi*; Takahashi, Eiji*; Minamide, Hiroaki*; Matsukawa, Ken*; Aoyama, Makoto; et al.
Proceedings of 1st International Beam Instrumentation Conference (IBIC 2012) (Internet), 5 Pages, 2012/10
no abstracts in English
Iwamae, Atsushi*; Ogawa, Hiroaki; Sugie, Tatsuo; Kusama, Yoshinori
JAEA-Research 2011-045, 11 Pages, 2012/02
In order to investigate reflection properties on plasma-facing material in ITER, the bi-directional reflectance distribution function (BRDF) of a tungsten block sample has been measured. On the machining surface of the block, one-directional machining lines are engraved. Two laser diodes 652 nm and 473 nm were used to simulate H and H emissions, respectively. The reflected light is affected by the machining surface. The reflected light traces a line when the incident light is injected in the perpendicular direction to the engraved line. On the other hand the reflected light traces an arc shape when the incident light is injected in the parallel direction to the engraved lines. Ray tracing simulation qualitatively explains the experimental results.
Iwamae, Atsushi; Sugie, Tatsuo; Ogawa, Hiroaki; Kusama, Yoshinori
Plasma Physics and Controlled Fusion, 53(4), p.045005_1 - 045005_17, 2011/04
Iwamae, Atsushi; Ogawa, Hiroaki; Sugie, Tatsuo; Kusama, Yoshinori
Review of Scientific Instruments, 82(3), p.033502_1 - 033502_4, 2011/03
Journal of Physical Chemistry C, 114(36), p.15544 - 15545, 2010/08
no abstracts in English
Journal of Physical Chemistry C, 114(5), p.2134 - 2143, 2010/01
I propose a site-occupying model for hydrogen solution in metal because there is a logical discrepancy between the concept of conventional site-blocking models and an experimental fact. This model is based on the experimental fact that hydrogen atoms in metal cannot mutually come closer to less than about 0.21nm each other under hydrogen pressure of 1MPa or less. The solubility has been analyzed, developing a statistical-mechanical method. The validity of this method has been judged by agreement with experimental data on the solubility. Comparisons also have been made between the conventional site-blocking models and this model. This model can make its theoretical curve agree well with the experimental data compared to those of the conventional site-blocking models at high hydrogen solubility over 0.5H/M. In the statistical-mechanical description, the solution behavior of tritium is similar to that of hydrogen, rather than that of deuterium from the difference in the spin weights.
Iwamae, Atsushi; Sugie, Tatsuo; Ogawa, Hiroaki; Kusama, Yoshinori
Plasma and Fusion Research (Internet), 4, p.042_1 - 042_11, 2009/10
Ogawa, Hiroaki; Sugie, Tatsuo; Kasai, Satoshi*; Katsunuma, Atsushi*; Hara, Hirotsugu*; Takeyama, Norihide*; Kusama, Yoshinori
Fusion Engineering and Design, 83(10-12), p.1405 - 1409, 2008/12
no abstracts in English
Iwamae, Atsushi; Ogawa, Hiroaki; Sugie, Tatsuo; Kasai, Satoshi*; Kusama, Yoshinori
Proceedings of 18th International Toki Conference on Development of Physics and Technology of Stellarator/Heliotrons en route to Demo (ITC-18) (CD-ROM), p.450 - 453, 2008/12
Sugie, Tatsuo; Ogawa, Hiroaki; Kasai, Satoshi*; Kusama, Yoshinori
AIP Conference Proceedings 988, p.218 - 221, 2008/04
The detailed design of the Impurity Influx Monitor (divertor) has been carried out to provide the measurement capability in the harsh environment. The potential damaging effects for the first mirrors mounted close to the plasma are the formations of coatings of impurities and the deposition of the dust. Mitigating measures to minimize the degradation of their performance by these effects, such as changes in the reflectivity, are adopted: for example, the plasma is viewed through a small aperture, and baffle plates are inserted in front of the first mirrors. However, it will not be possible to prevent the degradation completely. It is important to know the change of the sensitivity of the optical systems. It is not feasible to install a light source in the vacuum chamber of ITER during operations and so an alternative method is needed. The in-situ calibration system using a micro retro-reflector array has been developed as a possible method.
Ogawa, Hiroaki; Sugie, Tatsuo; Kasai, Satoshi; Katsunuma, Atsushi*; Hara, Hirotsugu*; Kusama, Yoshinori
Plasma and Fusion Research (Internet), 2, p.S1054_1 - S1054_4, 2007/11
no abstracts in English
Ogawa, Hiroaki; Kiuchi, Kiyoshi
Hyomen Gijutsu, 58(9), p.543 - 549, 2007/09
The oxidation mechanism of nuclear system components accelerated under irradiation was basically examined using a micro-balance device installed an rf low energy plasma source. Six alloys with different Cr contents of Fe-Ni alloy, stainless steels, Ni base alloys and metallic Cr were used in the experiment. The difference in the oxidation behavior between the low energy plasma and thermal equilibrium in oxygen atmosphere of 20 Pa was evaluated at 873 K for 20 hours. The oxidation behavior was analyzed with the in-situ weight change and the surface analysis by X-ray photoelectron spectroscopy (XPS). On the thermal equilibrium, the weight gain is depressed with increasing Cr contents. On the other hand, the weigh loss was observed in the materials with high Cr contents in the low energy oxygen plasma with the high excitation condition. The oxidation behavior was analyzed with the mechanistic model, by considering the evaporation rate of volatile CrO on the surface and the migration rate of O into the substrate.