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JAEA Reports

Flow separation at inlet causing transition and intermittency in circular pipe flow

Ogawa, Masuro*

JAEA-Technology 2019-010, 22 Pages, 2019/07

JAEA-Technology-2019-010.pdf:1.5MB

Transition phenomena from laminar to turbulent flow are roughly classified into three categories. Circular pipe flow of the third category is linearly stable against any small disturbance, despite that flow actually transitions and transitional flow exhibits intermittency. These are among major challenges that are yet to be resolved in fluid dynamics. Thus, author proposes hypothesis as follows; "Flow in a circular pipe transitions from laminar flow because of vortices released from separation bubble forming in vicinity of inlet of pipe, and transitional flow becomes intermittent because vortex-shedding is intermittent." Present hypothesis can easily explain why linear stability theory has not been able to predict transition in circular pipe flow, why circular pipe flow actually transitions, why transitional flow actually exhibits intermittency even due to small disturbance, and why numerical analysis has not been able to predict intermittency of transitional flow in circular pipe.

Journal Articles

Proposals of new basic concepts on safety and radioactive waste and of new high temperature gas-cooled reactor based on these basic concepts

Ogawa, Masuro

Nuclear Engineering and Design, 308, p.133 - 141, 2016/11

 Times Cited Count:1 Percentile:14.27(Nuclear Science & Technology)

A new basic concept on safety; Not causing any serious catastrophe by any means and a new basic concept on radioactive waste; Not returning any waste that possibly affects the environment are proposed in the present study, aiming at nuclear power plants which everybody can accept, in consideration of the serious catastrophe that happened at Fukushima in 2011. In the present study, physical phenomena are used to continue confining, rather than confine. To continue confining is meant to apply natural correction to fulfill inherent safety function. Fission products must be detoxified to realize the new basic concept on radioactive waste, aiming at the final processing and disposal of radioactive wastes as same as that in the other wastes such as PCB. The New HTGR is proposed based on the new basic concepts. It is indicated that the New HTGR can response to social requirements for safety and environmental conservability against radioactive wastes, industrial requirements for economy, uranium resource sustainability and so on, and national requirements for non-proliferation and environmental protection against carbon dioxide.

Journal Articles

Study on reduction of potential radiotoxicity for spent fuel by using HTGR

Fukaya, Yuji; Kunitomi, Kazuhiko; Ogawa, Masuro

Nihon Genshiryoku Gakkai Wabun Rombunshi, 14(3), p.189 - 201, 2015/09

A study on reduction of potential radiotoxicity for spent fuel by using High Temperature Gas-cooled Reactors (HTGRs) have been performed. Unlike Partitioning and Transmutation (P&T), the reactor concept is investigated from the viewpoint of reduction of the radiotoxicity generation itself. To reduce the radiotoxicity, $$^{238}$$U, which generates Pu, Am and Cm, should be excluded. Therefore, we proposed HTGR fueled by new concept fuels with alternative fuel matrix instead of $$^{238}$$U. Those are Yttria Stabilized Zirconia (YSZ) and thorium, and the fissile material is Highly Enriched Uranium (HEU) with the enrichment of 93%. With the HEU, the radiotoxicity can be significantly reduced, and the cooling time to decay to a natural uranium level can be shorted down to approximately 800 years. Fuel integrity and proliferation resistance can be remained by the dilution using YSZ, and neutronic characteristics of self-regulation is remained by the loading of erbium. The fuel can generate heat as same amount as ordinary uranium fuel. The electricity generation cost is as cheap as ordinary GTHTR300. It is concluded that the proposed reactor concept can reduce the cooling time less than 1% from 100 thousand years to a 800 years without additional technology development.

Journal Articles

Process evaluation of use of High Temperature Gas-cooled Reactors to an ironmaking system based on Active Carbon Recycling Energy System

Hayashi, Kentaro*; Kasahara, Seiji; Kurihara, Kohei*; Nakagaki, Takao*; Yan, X.; Inagaki, Yoshiyuki; Ogawa, Masuro

ISIJ International, 55(2), p.348 - 358, 2015/02

 Times Cited Count:5 Percentile:34.67(Metallurgy & Metallurgical Engineering)

Reducing coking coal consumption and CO$$_{2}$$ emissions by application of iACRES (ironmaking system based on active carbon recycling energy system) was investigated using process flow modeling to show effectiveness of HTGRs (high temperature gas-cooled reactors) adoption to iACRES. Two systems were evaluated: a SOEC (solid oxide electrolysis cell) system using CO$$_{2}$$ electrolysis and a RWGS (reverse water-gas shift reaction) system using RWGS reaction with H$$_{2}$$ produced by IS (iodine-sulfur) process. Both the effects on saving of the coking coal and reduction of CO$$_{2}$$ emissions were greater in the RWGS system. It was the reason of the result that excess H$$_{2}$$ which was not consumed in the RWGS reaction was used as reducing agent in the BF as well as CO. Heat balance in the HTGR, SOEC and RWGS modules were evaluated to clarify process components to be improved. Optimization of the SOEC temperature was desired to reduce Joule heat input for high efficiency operation of the SOEC system. Higher H$$_{2}$$ production thermal efficiency in the IS process for the RWGS system is effective for more efficient HTGR heat utilization. The SOEC system was able to utilize HTGR heat to reduce CO$$_{2}$$ emissions more efficiently by comparing CO$$_{2}$$ emissions reduction per unit heat of HTGR.

Journal Articles

Process evaluation of use of HTGRs to an ironmaking system based on active carbon recycling energy system (iACRES)

Hayashi, Kentaro*; Kasahara, Seiji; Kurihara, Kohei*; Nakagaki, Takao*; Yan, X.; Inagaki, Yoshiyuki; Ogawa, Masuro

Tanso Junkan Seitetsu Kenkyukai Saika Hokokusho; Tanso Junkan Seitetsu No Tenkai, p.42 - 62, 2015/02

Reducing coking coal consumption and CO$$_{2}$$ emissions by application of HTGRs (high temperature gas-cooled reactors) to iACRES (ironmaking system based on active carbon recycling energy system) was investigated using process flow modeling. Two systems were evaluated: a SOEC (solid oxide electrolysis cell) system using CO$$_{2}$$ electrolysis and a RWGS (reverse water-gas shift reaction) system using RWGS reaction with H$$_{2}$$ produced by IS (iodine-sulfur) process. Coking coal consumption was reduced from a conventional BF (blast furnace) steelmaking system by 4.3% in the SOEC system and 10.3% in the RWGS system. CO$$_{2}$$ emissions were decreased by 3.4% in the SOEC system and 8.2% in the RWGS system. Remaining H$$_{2}$$ from the RWGS reactor was used as reducing agent in the BF in the RWGS system. This was the reason of the larger reduction of coking coal consumption and CO$$_{2}$$ emissions. Electricity generation for SOEC occupied most of HTGR heat usage in the SOEC system. H$$_{2}$$ production in the IS process used most of the HTGR heat in the RWGS system. Optimization of the SOEC temperature for the SOEC system and higher H$$_{2}$$ production thermal efficiency in the IS process for the RWGS system will be useful for more efficient heat utilization. One typical-sized BF required 0.5 HTGRs and 2 HTGRs for in the SOEC system and RWGS system, respectively. CO$$_{2}$$ emissions reduction per unit heat input was larger in the SOEC system. Recycling H$$_{2}$$ to the RWGS will be useful for smaller emissions per unit heat in the RWGS system.

Journal Articles

Thermal analysis of heated cylinder simulating nuclear reactor during loss of coolant accident

Sato, Hiroyuki; Ohashi, Hirofumi; Tachibana, Yukio; Kunitomi, Kazuhiko; Ogawa, Masuro

Journal of Nuclear Science and Technology, 51(11-12), p.1317 - 1323, 2014/11

 Times Cited Count:7 Percentile:55.77(Nuclear Science & Technology)

Transient analyses are presented of temperature behavior of reactor during loss-of-coolant accident with scram. The influence of reactor thermal properties, operating power density, geometry of active core and selection of fuel type on the capability of decay heat removal against the accident are studied. It is shown that the reactor design envelope is fully determined by the key parameters. The range of the envelope is shown to enlarge considerably by selecting high refractory fuel. High temperature gas-cooled reactor (HTGR), a graphite-moderated reactor with TRISO coated fuel particle, is the primary candidate which can fulfill the requirement to the design concept of nuclear reactor independent of coolant for decay heat removal.

JAEA Reports

Economic evaluation of HTGR IS process hydrogen production system

Iwatsuki, Jin; Kasahara, Seiji; Kubo, Shinji; Inagaki, Yoshiyuki; Kunitomi, Kazuhiko; Ogawa, Masuro

JAEA-Review 2014-037, 14 Pages, 2014/09

JAEA-Review-2014-037.pdf:8.84MB

Thermochemical iodine-sulfur (IS) process is one of the promising technologies, which harnesses heat energy of high temperature gas-cooled reactors (HTGRs). An economic estimation of hydrogen production by a future commercial HTGR-IS process hydrogen production system was performed on the basis of economic evaluation data of an existing commercial hydrogen production plant using fossil fuel as a raw material. Hydrogen production cost was estimated at 25.4 JPY/Nm$$^{3}$$ under this estimation conditions. Capital cost and energy cost account for 13% and 78% of the total hydrogen production cost, respectively. To decrease HTGR construction cost, to increase HTGR availability, to improve hydrogen production thermal efficiency are important for cost reduction of hydrogen. The cost will be competitive with estimated costs by fossil fuel hydrogen production methods. It is appropriate that the hydrogen production cost is set for a goal of present R&Ds.

Journal Articles

Feasibility study on Naturally Safe HTGR (NSHTR) for air ingress accident

Ohashi, Hirofumi; Sato, Hiroyuki; Tachibana, Yukio; Kunitomi, Kazuhiko; Ogawa, Masuro

Nuclear Engineering and Design, 271, p.537 - 544, 2014/05

 Times Cited Count:3 Percentile:28.59(Nuclear Science & Technology)

The concept of the Naturally-safe HTGR is that the release of radioactive materials is kept at very low level and no harmful effect on people and the environment is ensured by only physical phenomena without any engineered safety features. In this study, the CO concentration and the heat generated by graphite oxidation inside the circular tube were evaluated parametrically using a steady-state one-dimensional model to confirm the feasibility of the Naturally-safe HTGR at a severe condition of the air ingress accident (i.e., a massive air ingress by simultaneous rupture of two primary pipes). It was confirmed that the CO concentration at the outlet of coolant channel can be maintained below the explosion limit due to the reaction with oxygen in the air, and the reaction heat can be removed with the decay heat by physical phenomena under certain conditions of the coolant channel geometry without any engineered safety features.

Journal Articles

Process flow sheet evaluation of a nuclear hydrogen steelmaking plant applying very high temperature reactors for efficient steel production with less CO$$_{2}$$ emissions

Kasahara, Seiji; Inagaki, Yoshiyuki; Ogawa, Masuro

Nuclear Engineering and Design, 271, p.11 - 19, 2014/05

 Times Cited Count:3 Percentile:28.59(Nuclear Science & Technology)

Nuclear hydrogen steelmaking (NHS) system was evaluated by flow sheet analysis using very high temperature reactors (VHTRs) and thermochemical hydrogen production IS process. Heat input and CO$$_{2}$$ emissions including material production, material transportation, and power generation were evaluation criteria. Though total heat input to the NHS system was 130-142% of a conventional blast furnace steelmaking system, CO$$_{2}$$ emissions were 13-21%. Pre-heating of hydrogen by coal combustion before blowing to a shaft furnace was effective to decrease heat input although CO$$_{2}$$ emissions increased. Direct nuclear pre-heating was also effective without increase of CO$$_{2}$$ emissions if close location of the nuclear reactor to the steelmaking plant was publicly accepted. Hydrogen production thermal efficiency had a significant influence on the heat input. Conceptual design of a plant unit of the NHS system producing steel of 1.47 $$times$$ 10$$^{6}$$ t/y with 2 VHTRs of 600MW heat and one shaft furnace and electric arc furnace was proposed. This article is revised from a proceeding presented in HTR2012.

Journal Articles

Analysis of core heat removal capability under DLOFC accidents for HTGRs

Sato, Hiroyuki; Ohashi, Hirofumi; Tachibana, Yukio; Kunitomi, Kazuhiko; Ogawa, Masuro

Nuclear Engineering and Design, 271, p.530 - 536, 2014/05

 Times Cited Count:2 Percentile:19.81(Nuclear Science & Technology)

Design envelope of prismatic High Temperature Gas-cooled Reactors in terms of core heat removal capability under depressurized loss-of-forced-circulation accidents without operating active or passive decay heat removal systems are investigated. Lumped element models consist of core, reactor pressure vessel and cavity wall are presented in order to evaluate transient response of core temperature. Parametric calculations changing the core height, initial core temperature, thickness of side reflector, cavity size and peaking factor are performed. A series of calculation provides relationships of core radius to average power density and reactor thermal power which can remove the heat in core without reliance on specific design features. The results clarified the design envelope for the Naturally Safe HTGR in terms of core decay heat removal.

Journal Articles

Inherently-safe high temperature gas-cooled reactor for hydrogen production

Ogawa, Masuro; Kunitomi, Kazuhiko; Sato, Hiroyuki

Keynote Lecture for International Conference of PM2.5 & Energy Security 2014 (PMES 2014), p.72 - 74, 2014/03

The present paper reviewed the overview of HTGR technologies as well as excellent characteristics, such as environmental friendliness, safety, minimum waste, economic competitiveness, sustainability, usability and proliferation resistance, suitable for an energy supply system to be deployed in the field of heat utilization.

Journal Articles

Concept on inherent safety in high-temperature gas-cooled reactor

Ohashi, Hirofumi; Sato, Hiroyuki; Kunitomi, Kazuhiko; Ogawa, Masuro

Nihon Genshiryoku Gakkai Wabun Rombunshi, 13(1), p.17 - 26, 2014/03

A new concept on inherent safety in High Temperature Gas-cooled Reactor (HTGR) was proposed to accomplish no harmful consequences for people and the environment even in the failures in safety and safety related systems. The safety concept is that the progression of the events that lead the loss or degradation of the confinement function of the coated fuel particle is suppressed and the release of radioactive materials is kept at very low level by only physical phenomena. The feasibility studies and related information revealed that the reactor design on this safety concept is technically feasible. The physical phenomena can be appeared with the cause of event (i.e., temperature increase, oxidation of fuel cladding and explosion of carbon monoxide) and can prevent or mitigate the events.

Journal Articles

Thermochemical water-splitting hydrogen production iodine-sulfur process

Kubo, Shinji; Ogawa, Masuro

Nihon Enerugi Gakkai-Shi, 92(11), p.1041 - 1045, 2013/11

no abstracts in English

Journal Articles

Steelmaking process employing hydrogen produced by a very high temperature reactor and the scale of the plant

Kasahara, Seiji; Kubo, Shinji; Inagaki, Yoshiyuki; Ogawa, Masuro

Zairyo To Purosesu (CD-ROM), 26(2), p.498 - 501, 2013/09

Outline was discussed for very high temperature reactors (VHTRs), IS process for hydrogen production and hydrogen steelmaking process integrated with them. Hydrogen of 7.07$$times$$10$$^{6}$$ Nm$$^{3}$$/d was produced and electricity of 497 MW was generated using 5 VHTRs of 600 MW thermal output to produce steel of 1$$times$$10$$^{4}$$ t/d, similar scale to a conventional blast furnace (BF) plant. A significant reduction of CO$$_{2}$$ emission to 13% of that from a BF plant was expected by the hydrogen steelmaking plant. Sensitivity analysis of steelmaking cost on hydrogen production cost showed that the hydrogen production cost of 3.0 US${$}$/kg-H$$_{2}$$ was required for the lower steelmaking cost than conventional steelmaking processes.

Journal Articles

Inherently-safe high temperature gas-cooled reactor

Ogawa, Masuro

Zero-Carbon Energy Kyoto 2012, p.183 - 194, 2013/00

High temperature gas-cooled reactor (HTGR), also known as VHTR, is one of the six Generation-IV nuclear energy systems. It can generate electricity at 50% thermal efficiency, and also produce hydrogen and supply high-quality process heat. Its production remains highly economical and safe even at as small as 600 MWt plant size. In this report, a new concept of inherently-safe HTGR is proposed never to compromises the safety of the public, society and environment for any accidents. It is designed so that any accident will be self-controllable to safe state only with physical phenomena but without reliance on active and/or passive devices and systems. Some inherent-safety characteristics of the inherently-safe HTGR have already been confirmed by test of the HTTR. The balance of the inherent safety characteristics required to establish the inherently-safe HTGR concept is analyzed. These results of the inherently-safe HTGR are presented, here.

Journal Articles

Analysis of core heat removal capability under DLOFC accidents for HTGRs

Sato, Hiroyuki; Ohashi, Hirofumi; Tachibana, Yukio; Kunitomi, Kazuhiko; Ogawa, Masuro

Proceedings of 6th International Topical Meeting on High Temperature Reactor Technology (HTR 2012) (USB Flash Drive), 9 Pages, 2012/10

Design criteria of prismatic High Temperature Gas-cooled Reactors (HTGRs) in terms of core heat removal capability under depressurized loss-of-forced-circulation accidents without operating active or passive decay heat removal systems are investigated. Lumped element models consist of core, RPV and surroundings and soil are presented in order to evaluate transient response of core and RPV temperatures. The results clarified the design criteria for the Inherently-safe HTGR in terms of core heat removal under DLOFC accidents.

Journal Articles

Process flow sheet evaluation of a nuclear hydrogen steelmaking plant applying high temperature gas-cooled reactors for efficient steel production with less CO$$_{2}$$ emissions

Kasahara, Seiji; Inagaki, Yoshiyuki; Ogawa, Masuro

Proceedings of 6th International Topical Meeting on High Temperature Reactor Technology (HTR 2012) (USB Flash Drive), 8 Pages, 2012/10

Nuclear hydrogen steelmaking (NHS) system was evaluated by flow sheet analysis using High Temperature Gas-cooled Reactors (HTGRs) and thermochemical hydrogen production IS process. Heat input and CO$$_{2}$$ emissions of the system including material production, material transportation, and power generation were evaluation criteria. The result was compared with that of a conventional blast furnace steelmaking (BFS) system. Though total heat input to the NHS system was 141-159% of the BFS system, CO$$_{2}$$ emissions were 9-17%. Pre-heating of hydrogen by coal combustion before blowing to the shaft furnace was effective to decrease heat input although CO$$_{2}$$ emissions increased a little. Direct nuclear pre-heating was expected to be less heat input without increase of CO$$_{2}$$ emissions if the problems with nearby location of the nuclear reactor to the steelmaking plant would be solved. Influence of hydrogen production thermal efficiency on heat input of the NHS was great. A conceptual design of a plant unit of the NHS system producing steel of 7.43$$times$$10$$^{5}$$ t/y with a HTGR of 600 MW heat and a shaft furnace and an electric arc furnace was proposed.

Journal Articles

Feasibility study on naturally-safe HTGR for air ingress accident

Ohashi, Hirofumi; Sato, Hiroyuki; Tachibana, Yukio; Kunitomi, Kazuhiko; Ogawa, Masuro

Proceedings of 6th International Topical Meeting on High Temperature Reactor Technology (HTR 2012) (USB Flash Drive), 10 Pages, 2012/10

The concept of the Naturally-safe HTGR is that the release of radioactive materials is kept at very low level and no harmful effect on people and the environment is ensured by only physical phenomena without any engineered safety features. At an air ingress accident, possible physical events to loss of the confinement function of the fuel coating layers are the crack of the coatings caused by the explosion of CO produced by the graphite oxidation and failure of the coatings by melting or sublimation caused by core heat up due to the reaction heat. The CO concentration and the heat generated by graphite oxidation inside the circular tube were numerically evaluated. It was confirmed that the CO concentration at the outlet of coolant channel can be maintained below the explosion limit due to the reaction with oxygen in the air, and the reaction heat can be removed by physical phenomena under certain conditions of the coolant channel geometry without any engineered safety features.

Journal Articles

Technical examination on high temperature gas-cooled reactor as energy source of active carbon recycling energy system for steelmaking

Kasahara, Seiji; Sato, Hiroyuki; Inagaki, Yoshiyuki; Ogawa, Masuro

Zairyo To Purosesu (CD-ROM), 25(2), p.647 - 650, 2012/09

Application of ACRES (Active Carbon Recycling Energy System) to steelmaking process is proposed for reduction of CO$$_{2}$$ emission and security of fossil fuel supply. ACRES is the concept of reuse of carbon element in CO$$_{2}$$ from fossil fuel usage by reducting to CO using non-fosssil primary energy. Selection of the primary energy and CO$$_{2}$$ reduction technology is important for the usability evaluation. High temperature gas-cooled reactor is a candidate of the energy, which can supply electricity, hydrogen and high temperature heat usable for CO$$_{2}$$ reduction. Technical examination on high temperature gas-cooled reactor as energy source of ACRES for steelmaking was carried out. Renewable solar energy is an also promising energy source. Here, ability of HTGR to follow load change was investigated and validated for parallel use of HTGR and solar energy.

Journal Articles

Flow sheet model evaluation of nuclear hydrogen steelmaking processes with VHTR-IS (Very High Temperature Reactor and Iodine-Sulfur process)

Kasahara, Seiji; Inagaki, Yoshiyuki; Ogawa, Masuro

ISIJ International, 52(8), p.1409 - 1419, 2012/08

 Times Cited Count:4 Percentile:33.38(Metallurgy & Metallurgical Engineering)

Flow sheet model evaluation of nuclear hydrogen steelmaking (NHS) and nuclear hydrogen partial reduction steelmaking (NHPRS) systems applying VHTR-IS (Very high temperature reactor and iodine-sulfur process) was carried out. Heat input and CO$$_{2}$$ emissions of these systems were analyzed. Total net heat input to the NHS system was 28.4 GJ/t-high quality steel (HQS), including material production, material transportation, and power generation. This value was much larger than that of blast furnace steelmaking (BFS) system of 17.6 GJ/t-HQS. Reduction of hydrogen consumption in the shaft furnace and electricity consumption in the electric arc furnace were desired for lowering the heat input. Total net heat input of the NHPRS system was 31.9 GJ/t-HQS. Optimization of operation parameters such as reduction ratio of partial reduced ore (PRO) and PRO input ratio to the blast furnace is desired to decrease the heat input. CO$$_{2}$$ emissions from the NHS and the NHPRS systems were 9% and 50% of that from BFS system. Substitution of hydrogen for coal and reduction of transportation weight contributed to the reduction. Steelmaking cost was also evaluated. When steelmaking scale of each system was unified to one million t-HQS/y, NHS was economically competitive to the BFS and Midrex steelmaking. And NHS was advantageous at higher cost of resources.

149 (Records 1-20 displayed on this page)