Kaburagi, Masaaki; Torii, Tatsuo; Ogawa, Toru
JAEA-Review 2019-031, 251 Pages, 2020/01
There is high expectation for advanced remote technology and robotics to reduce the radiation exposure for workers in harsh nuclear environments such as the decommissioning of the Fukushima Daiichi Nuclear Power Station (FDNPS). However, the radiation tolerance of state-of-the-art key components, sensors and electronic devices, for remote operation is still limited. In order to extend the application of robotics in nuclear energy, it is pertinent to develop "Radiation hardness" of components and "Radiation smartness" in operation procedures. Furthermore, developments of "Radiation measurement" and "Technology to recognize the location and to grasp the surrounding environment", including the radiation imaging of the high dose-rate fields inside the FDNPS and the detection of nuclear fuel debris, are necessary for the future nuclear fuel debris retrieval. This Fukushima Research Conference aims to share the future vision for advancing the remote technology among experts from diverse fields.
Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Arai, Takehiko*; Nakauchi, Yusuke*; Nakamura, Tomoki*; Matsuoka, Moe*; et al.
Science, 364(6437), p.272 - 275, 2019/04
The near-Earth asteroid 162173 Ryugu, the target of Hayabusa2 sample return mission, is believed to be a primitive carbonaceous object. The Near Infrared Spectrometer (NIRS3) on Hayabusa2 acquired reflectance spectra of Ryugu's surface to provide direct measurements of the surface composition and geological context for the returned samples. A weak, narrow absorption feature centered at 2.72 micron was detected across the entire observed surface, indicating that hydroxyl (OH)-bearing minerals are ubiquitous there. The intensity of the OH feature and low albedo are similar to thermally- and/or shock-metamorphosed carbonaceous chondrite meteorites. There are few variations in the OH-band position, consistent with Ryugu being a compositionally homogeneous rubble-pile object generated from impact fragments of an undifferentiated aqueously altered parent body.
Yano, Kimihiko; Kitagaki, Toru; Washiya, Tadahiro; Miyamoto, Yasuaki; Ogawa, Toru
Progress in Nuclear Science and Technology (Internet), 5, p.225 - 228, 2018/11
According to the roadmap for decommissioning of Fukushima Daiichi NPS, fuel debris retrieval will start from 2021, after a decade from fuel debris generation. Fuel debris will stay in the reactors until the end of defueling. In addition, it is not hard to anticipate that storage is necessary for fuel debris removed from reactors. In order to consider such a post-accident operation for fuel debris, it is indispensable to discuss the states and characteristics of fuel debris during several decades. Therefore, JAEA directed R&D strategy on mid- and long-term behavior of fuel debris tentatively and is making a start of fundamental studies on this issue in corporation with the domestic universities and other research institutes.
Denki Gakkai-Shi, 138(8), p.518 - 521, 2018/08
Technical issues for the accomplishment of the decommissioning of Fukushima Dai-ichi Nuclear Power Station are reviewed. Harsh radiation environment of 1F is summarized in comparison with the past decommissioning projects of Three Mile Island Unit-2 as well as JPDR. Needs for advancement in radiation management and remote technology are discussed.
Wada, Yuki*; Bowers, G. S.*; Enoto, Teruaki*; Kamogawa, Masashi*; Nakamura, Yoshitaka*; Morimoto, Takeshi*; Smith, D.*; Furuta, Yoshihiro*; Nakazawa, Kazuhiro*; Yuasa, Takayuki*; et al.
Geophysical Research Letters, 45(11), p.5700 - 5707, 2018/06
Do, Thi Mai Dung*; Sujatanond, S.*; Ogawa, Toru
Journal of Nuclear Science and Technology, 55(3), p.348 - 355, 2018/03
In order to better understand the behavior of cesium in the severe accident of the LWR, the high-temperature chemistry of CsMoO in HO+H gas was studied. The pseudo-binary system, CsMoO-MoO, was thermochemically modeled with Redlich-Kister formulation to form a basis to analyze the high-temperature behavior of CsMoO. The model prediction was compared with the thermogravimetric measurements of CsMoO in dry and humid argon, which revealed that the mass-loss rate was enhanced in the humid atmosphere. Thermochemical model was further applied to predict the partitioning of cesium and molybdenum among gaseous species in the BWR core degradation condition typical of Short-Term Station Blackout.
Lam, Do Van*; Suematsu, Hisayuki*; Ogawa, Toru
Journal of the American Ceramic Society, 100(10), p.4884 - 4892, 2017/10
Nanoparticles of ZrN, ZrO and ZrN, '-ZrON were synthesized by pulsed wire discharge. Morphology and phase analyses were carried out by X-ray diffraction and field-emission transmission electron microscopy (FE-TEM). By bright field image observation, electron energy loss spectroscopy (EELS) and selected area electron diffraction (SAD) analyses, those nanoparticles were separately characterized.
Lam, Do Van*; Do, Thi Mai Dung*; Ogawa, Toru
Journal of Nuclear Science and Technology, 54(7), p.784 - 794, 2017/07
In order to clarify the Zr-rich corner of the Zr-N-O ternary system, a series of nitridation and controlled low-pressure oxidation heatings were made on zirconium metal. Low-partial pressures of oxygen were obtained by using a redox couple of either Mo/MoO or CuO/CuO. The heated samples were characterized by X-ray diffraction (XRD), optical microscopy and electron probe micro analysis (EPMA). Experimental results were coupled with a preliminary thermodynamic analysis with a sublattice formalism to draw a provisional ternary isotherm at 1373 K.
Nemoto, Yoshiyuki; Kaji, Yoshiyuki; Ogawa, Chihiro; Kondo, Keietsu; Nakashima, Kazuo*; Kanazawa, Toru*; Tojo, Masayuki*
Journal of Nuclear Materials, 488, p.22 - 32, 2017/05
The authors previously conducted thermogravimetric analyses on zircaloy-2 in air. By using the thermogravimetric data, an oxidation model was constructed in this study so that it can be applied for the modeling of cladding degradation in spent fuel pool (SFP) severe accident condition. For its validation, oxidation tests of long cladding tube were conducted, and computational fluid dynamics analyses using the constructed oxidation model were proceeded to simulate the experiments. In the oxidation tests, high temperature thermal gradient along the cladding axis was applied and air flow rates in testing chamber were controlled to simulate hypothetical SFP accidents. The analytical outputs successfully reproduced the growth of oxide film and porous oxide layer on the claddings in oxidation tests, and validity of the oxidation model was proved. Influence of air flow rate for the oxidation behavior was thought negligible in the conditions investigated in this study.
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.
Okamoto, Koji; Ogawa, Toru
Proceedings of 2016 EFCOG Nuclear & Facility Safety Workshop (Internet), 3 Pages, 2016/09
The decommissioning of the Fukushima-Daiichi Nuclear Power Plant has required and will continue to demand conducting many challenging activities, many of which do not have prior experience in the nuclear industry. International decommissioning knowledge and technology advances will be required to support the challenging work. The Collaborative Laboratories for Advanced Decommissioning Science (CLADS) was established by the Japan Atomic Energy Agency (JAEA) in April 2015. The main objectives of CLADS are the management, research and development for decommissioning at the Fukushima-Daiichi site. Not only is the coordination of research and development important to effective decommissioning, but also the management of research activities around the world. A status of the CLADS program will be provided. The CLADS central research office will be located at Tomioka Town, near the Fukushima site, in April 2017.
Matsumoto, Yoshinobu*; Do, Thi-Mai-Dung*; Inoue, Masao; Nagaishi, Ryuji; Ogawa, Toru
Journal of Nuclear Science and Technology, 52(10), p.1303 - 1307, 2015/10
Effects of zirconium oxides and oxidation products of zircaloy-4 on water radiolysis were investigated to predict the hydrogen generation from the water-immersed debris after a severe accident of a nuclear power plant. Observed yields of hydrogen in water containing the oxides were measured as a function of their weight fractions. Assuming that energies of Co-60 -ray deposited to water and the oxides brought about the water radiolysis to generate hydrogen independently, the radiolysis showed an additional term of hydrogen generation due to the energy deposition to the oxides. This term seemed to be dependent on the specific surface area or particle size of oxides, but not on the crystal structure of oxides in our experimental results. The oxides in distilled water gave the strong enhancement of term. The enhancement tended to saturate with increasing the weight fraction of oxides and was not apparent in the seawater.
Kim, Y.*; Kim, J.*; Yamanaka, Satoru*; Nakajima, Akira*; Ogawa, Takashi*; Serizawa, Takeshi*; Tanaka, Hirohisa*; Baba, Masaaki*; Fukuda, Tatsuo; Yoshii, Kenji; et al.
Advanced Energy Materials, 5(13), p.1401942_1 - 1401942_6, 2015/07
An innovative electro-thermodynamic cycle based on temporal temperature variations using pyroelectric effect has been presented. Practical energy is successfully generated in both synchrotron X-ray diffraction measurements under controlled conditions and real engine dynamometer experiments. The main generating origin is revealed as a combination of a crystal structure change and dipole change phenomenon corresponds to the temperature variation. In particular, the electric field induced 180 domain switching extremely improves generating power, and the true energy breakeven with temperature variation is firstly achieved.
Tomizawa, Hiromitsu*; Sato, Takahiro*; Ogawa, Kanade*; Togawa, Kazuaki*; Tanaka, Takatsugu*; Hara, Toru*; Yabashi, Makina*; Tanaka, Hitoshi*; Ishikawa, Tetsuya*; Togashi, Tadashi*; et al.
High Power Laser Science and Engineering, 3, p.e14_1 - e14_10, 2015/04
no abstracts in English
Motokawa, Ryuhei; Endo, Hitoshi*; Yokoyama, Shingo*; Ogawa, Hiroki*; Kobayashi, Toru; Suzuki, Shinichi; Yaita, Tsuyoshi
Langmuir, 30(50), p.15127 - 15134, 2014/12
Nagaishi, Ryuji; Morita, Keisuke; Yamagishi, Isao; Hino, Ryutaro; Ogawa, Toru
Proceedings of 2014 Nuclear Plant Chemistry Conference (NPC 2014) (USB Flash Drive), 9 Pages, 2014/10
Two years after Three Mile Island Unit 2 (TMI-2) loss-of-coolant accident, radioactive contaminated water has been processed by Submerged Demineralizer System (SDS) with two types of zeolite adsorbents to remove radioactive nuclides. During and after the process, adsorption amount and distribution of nuclides on the zeolites, residual water content and thermal conductivity in the SDS vessels have been measured or estimated for verification of safety in the process, subsequent transportation and disposal. Hydrogen generation has been also evaluated mainly by direct monitoring in the large-scale of vessel after the process. In this work, the revaluation of hydrogen generation was demonstrated on the basis of the open information of vessel, and the latest experimental data obtained in adsorption and radiolysis occurring in small-scale of zeolite-water mixtures. As a result, the evaluated data was found to be comparable with the reported data obtained in the large-scale of real vessel.
Nagaishi, Ryuji; Inoue, Masao; Hino, Ryutaro; Ogawa, Toru
Proceedings of 2014 Nuclear Plant Chemistry Conference (NPC 2014) (USB Flash Drive), 9 Pages, 2014/10
Since seawater has been used as a coolant for reactors and spent fuel pools in broken reactor buildings at Fukushima Daiichi NPS accident, radioactive contaminated water emitted following the accident has contained salt content of seawater at high concentrations, different from that at TMI-2 accident. Radiolysis of seawater leading to hydrogen generation and corrosion has been simulated and reported by several groups. However, the proposed radiolysis models cannot be always applied to water radiolysis at the wide range of salt concentrations present in the NPS, mainly because primary yields of radiolysis products of water and radiation-induced reactions are dependent on the salt concentration. In this study, the radiolytic behavior in diluted and concentrated systems of seawater was considered on the basis of results in steady state and pulse radiolysis experiments, in which the above salt effects were demonstrated from the obtained results.
Shirasu, Noriko; Kurata, Masaki; Ogawa, Toru*
Proceedings of 2014 Water Reactor Fuel Performance Meeting/ Top Fuel / LWR Fuel Performance Meeting (WRFPM 2014) (USB Flash Drive), 6 Pages, 2014/09
In the accident of Fukushima-Daiichi Nuclear Power Plant, degraded fuels containing Zircaloy probably reacted with BC control blades containing stainless steel cladding or blade sheath. Since light elements like B and C are able to react easily with various elements and form various chemical species, several concerns are pointed out, such as variation in volatility and heat generation by oxidation of B and C. The chemical states of degraded fuel were evaluated on the assumption of thermodynamic equilibrium under various conditions of oxygen potential and temperature. The chemical behavior of B affects significantly the variation in oxygen potential with progressing severe accident, and many kinds of volatile compounds are formed by oxidation. The behavior of B causes the changes of volatility of FPs, such as Sr, Cs and Mo.
Kurata, Masaki; Shirasu, Noriko; Ogawa, Toru*
Nippon Genshiryoku Gakkai Wabun Rombunshi, 12(4), p.286 - 294, 2013/12
In the severe accident of Fukushima-Daiichi Nuclear Power Plant, large amount of sea water was introduced into reactor pressure vessels. Not only sodium chloride but also several minor elements contained in sea water possibly reacted with degraded fuel debris or molten corium. Varous concerns are pointed out, such as volatilization of FP, characterization of fuel debris, formation of corrosive gases, and etc. Thermodynamic evaluation can give useful information on the general tendency of these sea-water effects. Volatility of Cs, Sr, and Te is potentially increased due to the change in the chemical species. Corrosive gases, such as HCl, HS, and etc. are possibly generated from sea-water heated at high temperature. These phenomena are predicted to be varied with change in oxygen potential.
Iguchi, Masahide; Saito, Toru; Kawano, Katsumi; Chida, Yutaka; Nakajima, Hideo; Ogawa, Tsuyoshi*; Katayama, Yoshinori*; Ogata, Hiroshige*; Minemura, Toshiyuki*; Tokai, Daisuke*; et al.
Fusion Engineering and Design, 88(9-10), p.2520 - 2524, 2013/10
ITER TFC structures are large welding structures made of heavy thick stainless steels. JAEA plans to apply narrow gap TIG welding with FMYJJ1 which is full austenitic stainless filler material to manufacture TFC structure. FMYJJ1 is specified in "Codes for Fusion Facilities -Rules on Superconducting Magnet Structure (2008)". In order to evaluate effect of base material combinations and thickness of welded joint on tensile properties at 4 K, tensile tests were conducted at 4 K by using tensile specimens taken from 40 mm thickness weld joints of four combinations and 200 mm thickness ones of two combinations of base materials. These weld joints were manufactured by one side narrow gap TIG welding with FMYJJ1. As the results, it was confirmed that yield and tensile strengths of welded joint at 4K were decreased with decreasing of nitrogen of base material, and there were no large distribution of strengths at 4 K along the thickness of welded joints of 200 mm thickness.