Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Kubo, Kotaro; Zheng, X.; Tanaka, Yoichi; Tamaki, Hitoshi; Sugiyama, Tomoyuki; Jang, S.*; Takata, Takashi*; Yamaguchi, Akira*
Proceedings of the Institution of Mechanical Engineers, Part O; Journal of Risk and Reliability, 11 Pages, 2022/04
Times Cited Count：2 Percentile：53.91(Engineering, Multidisciplinary)Probabilistic risk assessment (PRA) is a method used to assess the risks associated with large and complex systems. However, the timing at which nuclear power plant structures, systems, and components are damaged is difficult to estimate if the risk of an external event is evaluated using conventional PRA based on event trees and fault trees. A methodology coupling thermal-hydraulic analysis with external event simulations using Risk Assessment with Plant Interactive Dynamics (RAPID) is therefore proposed to overcome this limitation. A flood propagation model based on Bernoulli's theorem was applied to represent internal flooding in the turbine building of the pressurized water reactor. Uncertainties were also taken into account, including the flow rate of the floodwater source and the failure criteria for the mitigation systems. The simulated recovery actions included the operator isolating the floodwater source and using a drainage pump; these actions were modeled using several simplifications. Overall, the results indicate that combining isolation and drainage can reduce the conditional core damage probability upon the occurrence of flooding by approximately 90%.
Ishii, Mamoru*; Shiota, Daiko*; Tao, Chihiro*; Ebihara, Yusuke*; Fujiwara, Hitoshi*; Ishii, Takako*; Ichimoto, Kiyoshi*; Kataoka, Ryuho*; Koga, Kiyokazu*; Kubo, Yuki*; et al.
Earth, Planets and Space (Internet), 73(1), p.108_1 - 108_20, 2021/12
Times Cited Count：4 Percentile：53.52(Geosciences, Multidisciplinary)We surveyed the relationship between the scale of space weather events and their occurrence rate in Japan and we discussed the social impact of these phenomena during the Project for Solar-Terrestrial Environment Prediction (PSTEP). The information was compiled for domestic users of space weather forecasts for appropriate preparedness against space weather disasters. This paper gives a comprehensive summary of the survey, focusing on the fields of electricity, satellite operations, communication and broadcasting, satellite positioning usage, aviation, human space activity, and daily life on the Earth's surface, using the cutting-edge knowledge of space weather. Quantitative estimations of the economic impact of space weather events on electricity and aviation are also given.
Kubo, Kotaro; Zheng, X.; Tanaka, Yoichi; Tamaki, Hitoshi; Sugiyama, Tomoyuki; Jang, S.*; Takata, Takashi*; Yamaguchi, Akira*
Proceedings of 30th European Safety and Reliability Conference and 15th Probabilistic Safety Assessment and Management Conference (ESREL 2020 and PSAM-15) (Internet), p.2279 - 2286, 2020/11
Probabilistic risk assessment (PRA) is one of the methods used to assess the risks associated with large and complex systems. When the risk of an external event is evaluated using conventional PRA, a particular limitation is the difficulty in considering the timing at which nuclear power plant structures, systems, and components fail. To overcome this limitation, we coupled thermal-hydraulic and external-event simulations using Risk Assessment with Plant Interactive Dynamics (RAPID). Internal flooding was chosen as the representative external event, and a pressurized water reactor plant model was used. Equations based on Bernoulli's theorem were applied to flooding propagation in the turbine building. In the analysis, uncertainties were taken into account, including the flow rate of the flood water source and the failure criteria for the mitigation systems. In terms of recovery action, isolation of the flood water source by the operator and drainage using a pump were modeled based on several assumptions. The results indicate that the isolation action became more effective when combined with drainage.
Kubo, Kotaro; Zheng, X.; Tanaka, Yoichi; Tamaki, Hitoshi; Sugiyama, Tomoyuki; Jang, S.*; Takata, Takashi*; Yamaguchi, Akira*
Proceedings of Joint International Conference on Supercomputing in Nuclear Applications + Monte Carlo 2020 (SNA + MC 2020), p.308 - 315, 2020/10
Dynamic probabilistic risk assessment (PRA) is a method for improving the realism and completeness of conventional PRA. However, enormous calculation costs are incurred by these improvements. One solution is to select an appropriate sampling method. In this paper, we applied the Monte Carlo, Latin hypercube, grid-point, and quasi-Monte Carlo sampling methods to the dynamic PRA of a simplified accident sequence and compared the results for each method. Quasi-Monte Carlo sampling was found to be the most effective method in this case.
Sato, Yuji*; Tsukamoto, Masahiro*; Shobu, Takahisa; Yamashita, Yoshihiro*; Yamagata, Shuto*; Nishi, Takaya*; Higashino, Ritsuko*; Okubo, Tomomasa*; Nakano, Hitoshi*; Abe, Nobuyuki*
Applied Physics A, 124(4), p.288_1 - 288_6, 2018/04
Times Cited Count：16 Percentile：66.12(Materials Science, Multidisciplinary)The dynamics of titanium (Ti) melted by laser irradiation was investigated in a synchrotron radiation experiment. As an indicator of wettability, the contact angle between a selective laser melting (SLM) baseplate and the molten Ti was measured by synchrotron X-rays at 30 keV during laser irradiation. As the baseplate temperature increased, the contact angle decreased, down to 28 degrees at a baseplate temperature of 500
C. Based on this result, the influence of wettability of a Ti plate fabricated by SLM in a vacuum was investigated. It was revealed that the improvement of wettability by preheating suppressed sputtering generation, and a surface having a small surface roughness was fabricated by SLM in a vacuum.
Iwai, Yasunori; Kubo, Hitoshi*; Oshima, Yusuke*; Noguchi, Hiroshi*; Edao, Yuki; Taniuchi, Junichi*
Fusion Science and Technology, 68(3), p.596 - 600, 2015/10
Times Cited Count：2 Percentile：18.84(Nuclear Science & Technology)We have newly developed the hydrophobic platinum honeycomb catalysts applicable to tritium oxidation reactor since the honeycomb-shape catalyst can decrease the pressure drop. Two types of hydrophobic honeycomb catalyst have been test-manufactured. One is the hydrophobic platinum catalyst on a metal honeycomb. The other is the hydrophobic platinum catalyst on a ceramic honeycomb made of silicon carbide. The fine platinum particles around a few nanometers significantly improve the catalytic activity for the oxidation tritium at a tracer concentration. The hydrogen concentration in the gaseous feed slightly affects the overall reaction rate constant for hydrogen oxidation. Due to the competitive adsorption of hydrogen and water molecules on platinum surface, the overall reaction rate constant has the bottom value. The hydrogen concentration for the bottom value is 100 ppm under the dry feed gas. We have experimentally confirmed the activity of these honeycomb catalysts is as good as that of pellet-shape hydrophobic catalyst. The results support the hydrophobic honeycomb catalysts are applicable to tritium oxidation reactor.
Sakai, Toru; Hijii, Keigo*; Okubo, Susumu*; Ota, Hitoshi*; Nakano, Hiroki*; Miyashita, Seiji*
Applied Magnetic Resonance, 46(9), p.997 - 1002, 2015/09
Times Cited Count：1 Percentile：6.93(Physics, Atomic, Molecular & Chemical)The S=1/2 kagome-lattice antiferromagnet is investigated by the numerical diagonalization of 18-spin finite-size cluster. The matrix elements proportional to the intensity of the singlet-triplet ESR transition are calculated in the presence of the Dzyaloshinsky-Moriya interaction. Some angle-dependent selection rules is also proposed.
Kubo, Hitoshi*; Oshima, Yusuke*; Iwai, Yasunori
JETI, 63(10), p.33 - 36, 2015/09
Tanaka Kikinzoku Kogyo provides a broad range of precious metals products and technologies. Tanaka Kikinzoku Kogyo and Japan Atomic Energy Agency have jointly developed a new method of manufacturing catalysts involving hydrophobic processing with an inorganic substance base. As a result, previous technological issues were able to be solved with the development of a catalyst that exhibited no performance degradation in response to radiation application of 530 kGy, a standard for radiation resistance, and maintenance of thermal stability at over 600C, which is much higher than the 70C temperature that is normally used. The application of this catalyst to the liquid phase catalytic exchange process is expected to overcome significant technological hurdles with regards to improving the reliability and efficiency of systems for collecting tritium from tritiated water. It is also anticipated that the hydrophobic platinum catalyst manufacturing technology used for this catalyst could be applied to a wide range of fields other than nuclear fusion research. It was verified that if applied to a hydro oxidation catalyst, hydrogen could be efficiently oxidized, even at room temperature. This catalyst can also contribute to improving safety at non-nuclear plants that use hydrogen in general by solving the aforementioned vulnerability issue.
Iwai, Yasunori; Kubo, Hitoshi*; Oshima, Yusuke*
Isotope News, (736), p.12 - 17, 2015/08
We have successfully developed a new hydrophobic platinum catalyst for collecting tritium at nuclear fusion reactors. Catalysts used to collect tritium are called hydrophobic precious metal catalysts. In Japan, hydrophobic precious metal catalysts manufactured from polymers have been used for heavy water refinement.However, this catalyst has issues related to embrittlement to radiation and thermal stability. These technological issues needed to be solved to allow for its application to nuclear fusion reactors requiring further enrichment from highly-concentrated tritiated water. We developed a new method of manufacturing catalysts involving hydrophobic processing with an inorganic substance base. As a result, previous technological issues were able to be solved with the development of a catalyst that exhibited no performance degradation in response to radiation application of 530kGy, a standard for radiation resistance, and maintenance of thermal stability at over 600C, which is much higher than the 70C temperature that is normally used. The catalyst created with this method was also confirmed to have achieved the world's highest exchange efficiency, equivalent to 1.3 times the previously most powerful efficiency. The application of this catalyst to the liquid phase catalytic exchange process is expected to overcome significant technological hurdles with regards to improving the reliability and efficiency of systems for collecting tritium from tritiated water.
Iwai, Yasunori; Kubo, Hitoshi*; Oshima, Yusuke*
Kagaku, 70(5), p.35 - 40, 2015/05
We have successfully developed a new hydrophobic platinum catalyst for collecting tritium at nuclear fusion reactors. Catalysts used to collect tritium are called hydrophobic precious metal catalysts. In Japan, hydrophobic precious metal catalysts manufactured from polymers have been used for heavy water refinement. However, this catalyst has issues related to embrittlement to radiation and thermal stability. These technological issues needed to be solved to allow for its application to nuclear fusion reactors requiring further enrichment from highly-concentrated tritiated water. We developed a new method of manufacturing catalysts involving hydrophobic processing with an inorganic substance base. As a result, previous technological issues were able to be solved with the development of a catalyst that exhibited no performance degradation in response to radiation application of 530 kGy, a standard for radiation resistance, and maintenance of thermal stability at over 600C, which is much higher than the 70C temperature that is normally used. The catalyst created with this method was also confirmed to have achieved the world's highest exchange efficiency, equivalent to 1.3 times the previously most powerful efficiency. The application of this catalyst to the liquid phase catalytic exchange process is expected to overcome significant technological hurdles with regards to improving the reliability and efficiency of systems for collecting tritium from tritiated water.
Iwai, Yasunori; Kubo, Hitoshi*; Sato, Katsumi; Oshima, Yusuke*; Noguchi, Hiroshi*; Taniuchi, Junichi*
Proceedings of 7th Tokyo Conference on Advanced Catalytic Science and Technology (TOCAT-7) (USB Flash Drive), 2 Pages, 2014/06
Hydrophobic platinum catalysts have been developed especially for combustion of hydrogen isotopes released in a nuclear facility. A new type of hydrophobic hydrogen combustion catalyst commercially named TKK-KNOITS catalyst is hardly susceptible to water mist and water vapor in the atmosphere and water produced by hydrogen combustion. It is capable of maintaining the activity even at relatively low temperatures. The TKK-KNOITS catalyst is superior to other previous hydrophobic catalysts in applicability to wide range of hydrogen concentration from very thin to dense. The catalyst which carrier is composed of inorganic oxide has thermal stability up to 873 K.
Aizawa, Kosuke; Chikazawa, Yoshitaka; Ishikawa, Nobuyuki; Kubo, Shigenobu; Okazaki, Hitoshi*; Mito, Makoto*; Tozawa, Katsuhiro*; Hayashi, Masateru*
Proceedings of 2012 International Congress on Advances in Nuclear Power Plants (ICAPP '12) (CD-ROM), p.465 - 474, 2012/06
A conceptual design study of an advanced sodium-cooled fast reactor JSFR has progressed in the "Fast Reactor Cycle Technology Development (FaCT)" project in Japan. JSFR has two failed fuel detection systems in the core. One is a failed fuel detection (FFD) system which continuously monitors a fission product from failed fuel subassembly. The other is a failed fuel detection and location (FFDL) system which locates when it receives signals from FFD. In this study, requirements to the FFD-DN and the FFD-DN design to meet the requirements were investigated for the commercial and demonstration JSFR. For the FFDL systems, experiences in the previous fast reactors and the research and development of FFDL system for JSFR were investigated. Operation experiences of the Selector-valve FFDL system were accumulated in PFR and Phenix. Tagging-gas system experiences were accumulated in EBR-II and FFTF.
Iwai, Yasunori; Sato, Katsumi; Taniuchi, Junichi*; Noguchi, Hiroshi*; Kubo, Hitoshi*; Harada, Nobuo*; Oshima, Yusuke*; Yamanishi, Toshihiko
Journal of Nuclear Science and Technology, 48(8), p.1184 - 1192, 2011/08
Times Cited Count：31 Percentile：90.66(Nuclear Science & Technology)The inorganic-based hydrophobic Pt-catalyst named H1P has been developed especially for efficient oxidation of a tracer level of tritium in the ambient temperature range even in the presence of saturated water vapor. The overall reaction rate constant for H1P catalyst in the ambient temperature range was considerably larger than that for traditionally applied Pt/Al
O
catalyst. Moreover, the decrease in reaction rate for H1P in the presence of saturated water vapor compared with in the absence of water vapor was slight due to its excellence in hydrophobic performance. Oxidation reaction on the catalyst surface is the rate-controlling step in the ambient temperature range and diffusion in a catalyst substratum above 313 K due to its fine porosity. The overall reaction rate constant in the ambient temperature range was dependent on the space velocity and hydrogen concentration in carrier.
Osawa, Hideaki; Umeki, Hiroyuki; Makino, Hitoshi; Takase, Hiroyasu*; McKinley, I. G.*; Okubo, Hiroo*
Karyoku Genshiryoku Hatsuden, 59(6), p.512 - 519, 2008/06
The information explosion resulting from modern technology is identified as a critical problem for deep geological disposal of high-level radioactive waste (HLW). A paradigm shift is needed in the basic concept for information management. This recognition had led to the development of a next generation Knowledge Management System (the JAEA KMS) that makes maximum use of recent developments in Information Technology (IT) and the methodology of Knowledge Engineering (KE) as applied in other technical fields. This paper provides a brief outline of the design concept of the JAEA KMS and then overviews recent progress towards development of an operational system.
Makino, Hitoshi; Kawamura, Makoto; Wakasugi, Keiichiro; Okubo, Hiroo*; Takase, Hiroyasu*
JAEA-Data/Code 2007-005, 67 Pages, 2007/02
JAEA-Data-Code-2007-005.pdf:6.66MB
In this study, based on an improvement method for treatment of FEP interaction a computer tool to support scenario analysis by specialists of performance assessment has been developed. Anticipated effects of this tool are to improve efficiency of complex and time consuming scenario analysis work and to reduce possibility of human errors in this work. This tool also enables to describe interactions among a vast number of FEP's and the related information as interaction matrix, and analysis those interactions from a variety of perspectives.
Maeda, Atsushi; Kowata, Koichi; Yamazaki, Yasuo; Takahashi, Kozo; Okubo, Toshiyuki; Miyazaki, Hitoshi
Dekomisshoningu Giho, (33), p.58 - 66, 2006/03
By the Japan Atomic Energy Agency (JAEA), designed decommissioning of nuclear facility and the treatment and disposal of radioactive waste will be carried out systematically and efficiently as responsibility as the installer of the nuclear power facility and generator of radioactive waste. This paper shows the present status of radioactive waste management in O-arai Research and Development Center, one of the research and development bases of JAEA. The management of low-level radioactive waste, including those accepted from outside operator of O-arai district, is carried out by the major premise of ensuring safety at O-arai Waste Management Facility. Treatment related to volume reduction and stabilization by means such as incineration and compression of solid waste, and solidification of liquid, as well as waste storage management is steadfastly promoted, so that these substances may be adequately stored and managed until they are disposed of.
Kondo, Hitoshi; Miyazaki, Hitoshi*; Okubo, Toshiyuki
JNC TN9410 2005-009, 32 Pages, 2005/03
JNC-TN9410-2005-009.pdf:4.62MB
When the plan of Decommissioning such as nuclear fuel cycle facilities and small-scale research reactor is settled on, it is necessary to optimize the index concerning the decommissioning (such as the cost, the waste and the term of works. etc) by selecting the technology and the process appropriately. In Waste Management section, the development of the Decommissioning Management System (DECMAN) which can calculate these decommissioning indexes from the facilities data and the dismantlement technique automatically is advanced. This report describes the problem found in 2003 and the solution concerning the operation and the evaluation technique.
Wada, Yusaku; Okubo, Toshiyuki; Miyazaki, Hitoshi; none; Donomae, Yasushi
JNC TN9410 2005-007, 94 Pages, 2005/03
JNC-TN9410-2005-007.pdf:6.07MB
None
Fukuda, Seiji; Kondo, Hitoshi; Okubo, Toshiyuki
JNC TN9410 2004-010, 56 Pages, 2004/03
JNC-TN9410-2004-010.pdf:1.53MB
The Old Waste Treatment Facility of JOYO(0ld JWTF), operation of which stopped in 1995, is scheduled to be dismantled starting in 2010. In order to reduce worker's radiation exposure, it is necessary to reduce radiation dose rate of the main equipments by system chemical decontamination before dismantling. In thjs research, the decontamination solutions were selected in view of reduction of consequential waste amount and expense of treatment of decontamination waste. We evaluated decontamination factor (DF) in test with contaminated samples (Hot test). Moreover we performed a conceptual design of the decontamination system using the decontamination solution that obtained the highest DF in hot test. The solution selected in hot test did not achieve the target DF to all equipments. For some equipment more aggressive solutions, which dissolve contaminants and base metal, would be needed, however using these solutions would tend to increase consequential waste amount and expense of treatment of decontamination waste. Therefore, we evaluated the dissolution rate of these solutions for stainless steels in test with non-contaminated samples (Cold test). The main result of obtaining through the hot test and the cold test is shown below.(1)By alternating immersions in sodium hydroxide solution and nitric acid, the highest DF was obtained. (Maximum of DF=10.7, 80 deg-C). (2)The decontamination system is composed of two decontamination solution tanks, a washing water tank, a pump that supplies decontamination solutions and washing water, and filters for removing contaminants. (3)The test samples were immersed in various solutions (HN03 + HF, HCl, H2S04) for 24 hours at room temperature. As a result, it was confirmed that the dissolution rate of HN03 + HF is remarkably large compared with other solutions (7.43 micro-m/day).
Kondo, Hitoshi; Fukuda, Seiji; Okubo, Toshiyuki
JNC TN9410 2004-007, 48 Pages, 2004/03
JNC-TN9410-2004-007.pdf:7.35MB
When the plan of decommissioning such as nuclear fuel cycle facilities and small-scale research reactors is examined, It is necessary to select the technology and the process of the work procedure, and to optimize the index (such as the radiation dose, the cost, amount of the waste, the number of workers, and the term of works, etc.) concerning dismantling the facility. In our waste management section, Development of the decommissioning management system, which is called "DECMAN", for the support of making the decommissioning plan ls advanced. DECMAN automatically calculates the index by using the facility data and dismantling method. This paper describes the remodeling of program to the personal computer and the system verification by evaluation of real work (Dismantling of the liquor dissolver in the old Joyo Waste Treatment Facility (the old JWTF), the glove boxes in Deuterium Critical Assembly (DCA), and the incinerator in Waste Dismantling Facility (WDF)). The outline of remodeling and verification is as follows. (1)Additional function. 1)Equipment arrangement mapping, 2)Evaluation of the radiation dose by using the air dose rate, 3)I/O of data that uses EXCEL (software) (2)Comparison of work amount between calculation value and results value: The calculation value is 222.67 man-hour against the result value 249.40 man- hour in the old JWTF evaluation. (3)Forecast of accompanying work is predictable to multiply a certain coeffient by the calculation value. (4)A new idea that expected the amount of the work was constructed by using the calculation value of DECMAN.
