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Journal Articles

Design study to increase plutonium conversion ratio of HC-FLWR core

Yamaji, Akifumi; Nakano, Yoshihiro; Uchikawa, Sadao; Okubo, Tsutomu

Nuclear Technology, 179(3), p.309 - 322, 2012/09

 Times Cited Count:5 Percentile:48.35(Nuclear Science & Technology)

HC-FLWR effectively utilizes the uranium (U) and the plutonium (Pu) resources by achieving a fissile Pu conversion ratio of 0.84 without a significant technical gap from the current BWR technology. In this study, a new core design concept for HC-FLWR has been developed to achieve the conversion ratio of 0.95. The concept of the FLWR/MIX fuel assembly, which had been originally proposed for tight fuel bundle, was used to raise the conversion ratio without deteriorating the core void reactivity characteristics. For a semi-tight fuel rod lattice with rod clearance of 0.20 to 0.25 cm, the design ranges of the conversion ratio and the average discharge burnup are 0.91 to 0.94 and 53 to 49 GWd/t, respectively. The conversion ratio can be raised to 0.97 by increasing the $$^{235}$$U enrichment from 4.9 to 6.0 wt%. Two representative core designs and one alternative design option have been obtained. Hence, the flexibility of HC-FLWR concept to achieve the conversion ratio of 0.84 to 0.95 has been revealed.

Journal Articles

Advanced light water reactor with hard neutron spectrum for realizing flexible plutonium utilization (FLWR)

Uchikawa, Sadao; Okubo, Tsutomu; Nakano, Yoshihiro

Proceedings of International Conference on Fast Reactors and Related Fuel Cycles (FR 2009) (CD-ROM), 8 Pages, 2012/00

An advanced LWR with hard neutron spectrum named FLWR is a BWR-type reactor with a core consisting of hexagonal-shaped fuel assemblies with a triangular tight-lattice fuel rod configuration. It has been proposed in order to ensure sustainable energy supply in the future based on the well-experienced LWR technologies. The reactor concept of the FLWR is designed to utilize the most of the existing Advanced Boiling Water Reactor (ABWR) plant system. Therefore, only the core concept is new. The FLWR aims at effective and flexible utilization of uranium and plutonium resources by adopting a two-stage concept of core designs. The core in the first stage of FLWR is for intensive utilization and conservation of plutonium with no degradation of the isotopic quality of plutonium based on the experience of the current LWR-MOX utilizations. The one in the second stage realizes sustainable multiple plutonium recycling with a high conversion ratio over 1.0. When the technologies and infrastructures for multiple recycling with MOX spent fuel reprocessing are established, the core of the first stage proceeds to the second stage by only changing the fuel assembly design in the same reactor system. The present paper summarizes the recent core design studies of FLWR.

Journal Articles

Stepwise evolution of fuel assembly design toward a sustainable fuel cycle with hard neutron spectrum light water reactors

Uchikawa, Sadao; Okubo, Tsutomu; Nakano, Yoshihiro

Proceedings of International Conference on Toward and Over the Fukushima Daiichi Accident (GLOBAL 2011) (CD-ROM), 8 Pages, 2011/12

An advanced LWR with hard neutron spectrum, named FLWR, aims at efficient and flexible utilization of nuclear resources by evolving its fuel assembly design under the same core configuration, mainly corresponding to available fuel cycle technologies and related infrastructures. The paper summarizes an evolution process of the FLWR fuel assembly design toward a sustainable fuel cycle by dividing the reactor operation into three stages, that is, the one based on the current LWR MOX fuel cycle infrastructure such as reprocessing of UO$$_{2}$$ spent fuel and fabrication of MOX fuel, the one for transitioning from the LWR fuel cycle to the FR fuel cycle, and the one based on the FR fuel cycle infrastructures such as MOX spent fuel reprocessing.

JAEA Reports

Stepwise evolution of core and fuel design toward a sustainable fuel cycle with FLWR

Uchikawa, Sadao

JAEA-Research 2011-011, 50 Pages, 2011/06

JAEA-Research-2011-011.pdf:7.75MB

An advanced LWR with hard neutron spectrum, named FLWR, aims at efficient and flexible utilization of nuclear resources by evolving its fuel assembly design under the same core configuration, mainly corresponding to available fuel cycle technologies and related infrastructures. The paper summarizes an evolution process of the FLWR fuel assembly design toward a sustainable fuel cycle by dividing the reactor operation into three stages, that is, the one based on the current LWR MOX fuel cycle infrastructure such as reprocessing of UO$$_{2}$$ spent fuel and fabrication of MOX fuel, the one for transitioning from the LWR fuel cycle to the FR fuel cycle, and the one based on the FR fuel cycle infrastructures such as MOX spent fuel reprocessing.

Journal Articles

Fuel assembly design for plutonium conservation in a light water reactor with hard neutron spectrum

Uchikawa, Sadao; Okubo, Tsutomu; Nakano, Yoshihiro

Nuclear Technology, 172(2), p.132 - 142, 2010/11

 Percentile:100(Nuclear Science & Technology)

The FLWR is a BWR-type reactor with hard neutron spectrum based on the well-experienced LWR technologies. The present paper has proposed a new concept of the fuel assembly design for the first stage of FLWR to conserve plutonium effectively with a fissile-plutonium conversion ratio of around 1.0, keeping negative void reactivity characteristics. The enriched UO$$_{2}$$ fuel rods are arranged in the peripheral region of the assembly, surrounding the MOX fuel rods in the central region. Performance evaluation shows that the FLWR/MIX concept is effective for controlling the void reactivity characteristics in the tight-lattice fuel rod configuration and promising under the framework of the UO$$_{2}$$ and MOX fuel technologies and related infrastructures which have been established for the current LWR-MOX utilization.

Journal Articles

Early introduction core design for advanced LWR concept of FLWR to recycle Pu or TRU

Okubo, Tsutomu; Nakano, Yoshihiro; Uchikawa, Sadao; Fukaya, Yuji

Revue G$'e$n$'e$rale Nucl$'e$aire, (6), p.83 - 89, 2010/11

An advanced LWR concept of FLWR has been investigated in order to contribute to establish sustainable energy supply in the future by recycling Pu or TRU based on the well-developed LWR technology. The concept utilizes the tight-lattice core with the MOX fuel, and consists of two steps in the chronological sequence. The first is to realize early introduction of FLWR and is represented by a high conversion type one (HC-FLWR), which is basically intended to keep the smooth technical continuity from the LWR/MOX-LWR technologies. The second is represented by RMWR, which realizes a very high conversion ratio over 1.0 and is preferable for the long-term sustainable energy supply through Pu or TRU multiple recycling. The key point is that the two core concepts utilize the compatible and the same size fuel assemblies, and hence, the former concept can proceed to the latter in the same reactor system based flexibly on the future fuel cycle circumstances.

JAEA Reports

Combined use of MOX and UO$$_2$$ fuel rods in fuel assembly designs for plutonium conservation in FLWR

Uchikawa, Sadao; Nakano, Yoshihiro; Okubo, Tsutomu

JAEA-Research 2010-008, 30 Pages, 2010/06

JAEA-Research-2010-008.pdf:1.54MB

The FLWR is an innovative BWR-type reactor with hard neutron spectrum based on the well-experienced LWR technologies. It aims at effective and flexible utilization of uranium and plutonium resources by adopting a two-stage concept of core designs corresponding to the advancement of the fuel cycle technologies and related infrastructures. A new concept of the fuel assembly design named FLWR/MIX has been proposed for the first stage of FLWR to conserve plutonium effectively with a fissile-plutonium conversion ratio of around 1.0, keeping negative void reactivity characteristics. The enriched UO$$_2$$ fuel rods are arranged in the peripheral region of the assembly, surrounding the MOX fuel rods in the central region. Performance evaluation shows that the FLWR/MIX concept is feasible and promising under the framework of the UO$$_2$$ and MOX fuel technologies and related infrastructures which have been established for the current LWR-MOX utilization.

JAEA Reports

Research on high conversion type FLWR (HC-FLWR) core

Nakano, Yoshihiro; Fukaya, Yuji; Akie, Hiroshi; Ishikawa, Nobuyuki; Okubo, Tsutomu; Uchikawa, Sadao

JAEA-Research 2009-061, 92 Pages, 2010/03

JAEA-Research-2009-061.pdf:9.5MB

A series of research on a high conversion type innovative water reactor for flexible fuel cycle (FLWR) has been conducted. This FLWR is a boiling water reactor (BWR) with a tight triangular fuel rod lattice and the uranium plutonium mixed oxide (MOX) fuel. FLWR is designed for two types of cores to be developed in succession. The preceding core is a high conversion type FLWR (HC-FLWR) and the other core is Reduced Moderation Water Reactor (RMWR) of which the conversion ratio is more than 1.0. Three design studies and a senario study on HC-FLWR are presented in this report. The first design study is for a representative core. The second one is for a transition core from HC-FLWR to RMWR. In the transition core, both assemblies for HC-FLWR and RMWR exist. The third one is for a core to recycle minor actinides (MAs). Regarding to the scenario study, based on design results of the representative core, effective plutonium utilization in future LWR was considered within general framework.

Journal Articles

Early introduction core design for advanced LWR concept of FLWR to recycle Pu or TRU

Okubo, Tsutomu; Nakano, Yoshihiro; Uchikawa, Sadao; Fukaya, Yuji

Proceedings of International Conference on Advanced Nuclear Fuel Cycle; Sustainable Options & Industrial Perspectives (Global 2009) (CD-ROM), p.1703 - 1710, 2009/09

An advanced LWR concept of FLWR is proposed to contribute to sustainable energy supply in the future by recycling Pu or TRU based on well-developed LWR technology. The concept utilizes the tight-lattice core with MOX fuel, and consists of two steps in the chronological sequence. The first is to realize early introduction of FLWR by a high conversion type one (HC-FLWR), which is to keep the smooth technical continuity from LWR/MOX-LWR technologies. The second is represented by RMWR, which realizes a very high conversion ratio over 1.0 and is for the long-term sustainable energy supply through Pu or TRU multiple recycling. The key point is that the two core concepts utilize the compatible and the same size fuel assemblies, and hence, the former concept can proceed to the latter in the same reactor system based flexibly on the future fuel cycle circumstances. In the present paper, the design of the early introduction core for FLWR is presented as well as the core design strategy.

Journal Articles

Breeder-type operation based on the LWR-MOX fuel technologies in light water reactors with hard neutron spectrum (FLWR)

Uchikawa, Sadao; Okubo, Tsutomu; Nakano, Yoshihiro

Proceedings of 2009 International Congress on Advances in Nuclear Power Plants (ICAPP '09) (CD-ROM), p.9022_1 - 9022_9, 2009/05

An advanced LWR concept, FLWR, is a BWR type reactor, in which the moderation of neutron in the core is reduced by use of tight-lattice fuel rod configuration. It aims at realizing effective and flexible utilization of uranium and plutonium resources by two stages, corresponding to the advancement of the fuel cycle technologies and related infrastructure. The present paper has proposed advanced fuel and core designs for realization of breeder-type operation in the first stage of FLWR. To achieve a high fissile-plutonium conversion ratio over 1.0, a new design concept of the MOX fuel assembly has been developed, in which MOX rods are arranged in the central region of the assembly, while enriched UO$$_{2}$$ rods in the peripheral region of the assembly. Performance evaluation shows that the proposed concept is feasible and promising under the framework of the UO$$_{2}$$ and MOX fuel technologies and related infrastructures, which have been established for the current LWR-MOX utilization.

Journal Articles

Advanced LWR concept with hard neutron spectrum (FLWR) for realizing flexible plutonium management

Uchikawa, Sadao; Okubo, Tsutomu; Nakano, Yoshihiro; Kobayashi, Noboru

Proceedings of 16th Pacific Basin Nuclear Conference (PBNC-16) (CD-ROM), 6 Pages, 2008/10

An advanced LWR concept with hard neutron spectrum (FLWR) has been proposed in order to ensure sustainable energy supply in the future based on the well-experienced LWR technologies. The FLWR is essentially a BWR-type reactor, in which the moderation of neutron in the core is reduced by use of the hexagonal-shaped fuel assemblies with the triangular-tight-lattice fuel rod configuration. The core design concept of FLWR is to realize effective and flexible utilization of uranium and plutonium resources by two stages, corresponding to the advancement of the fuel cycle technologies and related infrastructures. The core in the first stage of FLWR aims at intensive utilization and preservation of plutonium based on the experiences of the current LWR and MOX utilization, and the one in the second stage realizes sustainable multiple plutonium recycling with a high conversion ratio over 1.0. The present paper summarizes the recent core design studies of FLWR.

Journal Articles

TRU recycling in BWR type reactor of FLWR with hard spectrum

Okubo, Tsutomu; Nakano, Yoshihiro; Fukaya, Yuji; Kobayashi, Noboru; Uchikawa, Sadao

Proceedings of International Conference on the Physics of Reactors, Nuclear Power; A Sustainable Resource (PHYSOR 2008) (CD-ROM), 3 Pages, 2008/09

In order to ensure sustainable energy supply in the future based on the well-established LWR technologies, conceptual design studies on the innovative water reactor for flexible fuel cycle (FLWR) have been performed at JAEA. FLWR is a BWR type advanced LWR concept with the triangular tight-lattice core of uranium (U) and plutonium (Pu) mixed oxide (MOX) fuel rods. Accordingly, FLWR can achieve a high conversion ratio from U to Pu in the hard neutron spectrum core. This core characteristic is also suitable for recycling of Pu and/or the minor actinides (MA) based on the fuel recycling strategy. FLWR core consists of two concepts of HC-FLWR and RMWR with different conversion ratios. It has been confirmed that even in HC-FLWR with a lower conversion ratio around 0.85 TRU recycling with about 2% MA would be possible.

Journal Articles

Investigation on spent fuel characteristics of Reduced-Moderation Water Reactor (RMWR)

Fukaya, Yuji; Okubo, Tsutomu; Uchikawa, Sadao

Nuclear Engineering and Design, 238(7), p.1601 - 1611, 2008/07

 Times Cited Count:3 Percentile:70.64(Nuclear Science & Technology)

The spent fuel characteristics of the reduced-moderation water reactor (RMWR) have been investigated using the SWAT and ORIGEN codes. In the code calculation, the ORIGEN libraries for RMWR were necessary. Since there were no open libraries for RMWR, they were produced in this study by using the SWAT code. In order to investigate the characteristics of the RMWR spent fuel, the decay heat, the radioactivity and the content of each nuclide were evaluated with ORIGEN using these libraries. In this study, the spent fuel characteristics of other types of reactors were also evaluated with ORIGEN. It has been found that the decay heat and the radioactivity of the RMWR spent fuel are lower than those of full-MOX-LWRs and FBR, and are the same level as those of the high burn-up PWR. In addition, from the waste disposal point of view, the characteristics of the heat generation FP elements, the platinum group metals, Mo and the long-lived FPs (LLFPs) were also investigated.

JAEA Reports

Thermal-hydraulic design of high conversion type core of FLWR

Kobayashi, Noboru; Onuki, Akira; Uchikawa, Sadao; Okubo, Tsutomu

JAEA-Research 2008-054, 145 Pages, 2008/05

JAEA-Research-2008-054.pdf:2.39MB

A thermal-hydraulic design of the high-conversion (HC) type core of the innovative water reactor for flexible fuel cycle (FLWR) was constructed under the natural circulation core cooling, in order to achieve that HC-FLWR core can be converted to a breeder type one. The criteria on the thermal-hydraulic design of HC-FLWR were that the average void fractions in the core was smaller than 50%, and that the critical power ratio was larger than 1.3. The criterion on void fractions was determined from the nuclear design of HC-FLWR. The length of the chimney and the settings of the inlet orifice are common in both types of cores. The coefficient of the lower tie-plate of the HC-FLWR core and the temperature of the feed water were parametrically changed. Consequently, the design criteria were satisfied by adopting the setting of the form loss coefficients of the lower tie-plate comparable to those of the current BWRs and by lowering the feed water temperature to 505 K.

JAEA Reports

Investigation on spent fuel characteristics of Reduced-Moderation Water Reactor (RMWR)

Fukaya, Yuji; Okubo, Tsutomu; Uchikawa, Sadao

JAEA-Research 2008-041, 98 Pages, 2008/03

JAEA-Research-2008-041.pdf:14.15MB

The purpose of this research is to investigate spent fuel characteristics of Reduced-Moderation Water Reactor (RMWR). The characteristics should be investigated comparing with other types of reactor. It is important for the safety of spent fuel management to investigate the characteristics. The ORIGEN code was used in this research. Moreover, the ORIGEN libraries for RMWR were generated using SWAT code, because there are no open ORIGEN libraries for this purpose. To investigate the spent fuel characteristics, the decay heat and the radioactivity after a cooling time of 2 years and 4 years were evaluated. As a result, the decay heat and the radioactivity of the RMWR spent fuel are lower than those of full-MOX-LWRs and FBR, and the same levels as those of the high burn-up PWR. In addition, from the waste disposal point of view, the characteristics of spent fuel were also investigated.

JAEA Reports

Conceptual core design of the breeder type FLWR using recovered uranium as blanket fuel

Uchikawa, Sadao; Nakano, Yoshihiro; Okubo, Tsutomu; Kobayashi, Noboru

JAEA-Research 2008-040, 24 Pages, 2008/03

JAEA-Research-2008-040.pdf:8.5MB

The present study deals with the potential effects of utilization of uranium recovered from LWR spent fuels as the axial blanket fuels in the core of the breeder type FLWR, which is characterized by the five-layer double-flat-core structure. Design studies shows that the adoption of recovered UO$$_{2}$$ blanket can reduce the required plutonium inventory to attain the same core performances as the previous core design of depleted uranium blankets. Furthermore, the utilization of re-enriched recovered uranium with $$^{235}$$U enrichment of about 5wt% as the internal blanket fuel is evaluated to have a potential of a conversion ratio of 1.1. The core design with reduced plutonium inventory and high conversion ratio can contribute to realize a smooth and speedy transition from the LWR fuel cycle to the sustainable fuel cycle, as a core design for the transitioning period, during which a sufficient amount of uranium recovered from LWR spent fuels is available as resources.

JAEA Reports

Core design of high conversion type FLWR

Nakano, Yoshihiro; Akie, Hiroshi; Okumura, Keisuke; Okubo, Tsutomu; Uchikawa, Sadao

JAEA-Research 2008-006, 37 Pages, 2008/03

JAEA-Research-2008-006.pdf:35.13MB

A core design of a high conversion type innovative water reactor for flexible fuel cycle (HC-FLWR) with thermal output of 3926 MW has been constructed. The design study of HC-FLWR consists of two steps of analyses. The first step was preliminary parametric survey calculations and the second step was more detailed calculations with a nuclear and thermal-hydraulic coupled calculation code MOSRA. Through the 1-D core burnup calculations, the following design values were obtained. The Puf enrichment of MOX fuel is 11%. The heights of upper blanket, MOX and lower blanket regions are 5 cm, 85 cm and 5 cm, respectively. With these values, 3-D core burnup calculations were performed. In this analysis, effects of the fuel loading pattern were also investigated. Finally, a neutronics design of HC-FLWR core with a negative void reactivity coefficient, a conversion ratio of 0.84 and a discharged burnup of 56 GWd/t was obtained.

Journal Articles

Advanced LWR concept of FLWR for TRU recycling

Iwamura, Takamichi; Okubo, Tsutomu; Uchikawa, Sadao

Proceedings of International Conference on Advanced Nuclear Fuel Cycles and Systems (Global 2007) (CD-ROM), p.1718 - 1724, 2007/09

An advanced LWR concept of FLWR for TRU recycling has been investigated. The design study has shown the promising results for the feasibility of the concept, in conjunction with the investigated results obtained from the related R&D's for some key issues of FLWR development. In order to establish a robust nuclear energy supply system for the future, an appropriate combination of both the LWR and the FBR technologies, i.e. FLWR and Na-FBR, is considered to be preferable and realistic. This type of preferable combination is proposed in this paper.

Journal Articles

Conceptual design study on high conversion type core of FLWR

Nakano, Yoshihiro; Akie, Hiroshi; Okubo, Tsutomu; Uchikawa, Sadao

Proceedings of 2007 International Congress on Advances in Nuclear Power Plants (ICAPP 2007) (CD-ROM), 9 Pages, 2007/05

no abstracts in English

Journal Articles

Thermal-hydraulic design of high conversion type core of FLWR

Kobayashi, Noboru; Onuki, Akira; Okubo, Tsutomu; Uchikawa, Sadao

Proceedings of 15th International Conference on Nuclear Engineering (ICONE-15) (CD-ROM), 6 Pages, 2007/04

A thermal-hydraulic design of the high-conversion (HC) type core of the innovative water reactor for flexible fuel cycle (FLWR) was constructed. HC-FLWR is required to proceed to the breeder type of FLWR with no change of any reactor systems. Although tightness of the fuel pin arrangement is significantly different between the two types of cores, the natural circulation cooling is adopted in both cores. TRAC analyses were performed under the condition that chimney length for natural circulation and the setting of the inlet orifice were common to the both types of cores. Form loss coefficients of lower tie-plate were differently set to control the natural circulation flow rate and feed water temperature were adjusted to realize preferable value of average void fraction of HC-FLWR core. The analyses showed that both types of the FLWR could be cooled by the same reactor system.

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