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Ohgama, Kazuya; Nakano, Yoshihiro; Oki, Shigeo
Journal of Nuclear Science and Technology, 53(8), p.1155 - 1163, 2016/08
Times Cited Count：1 Percentile：10.71(Nuclear Science & Technology)The power distribution and core characteristics in various configurations of fuel subassemblies with an innerduct structure in the Japan Sodium-cooled Fast Reactor were evaluated using a Monte Carlo code for neutron transport and burnup calculation. The correlation between the fraction of fuel subassemblies facing outward and the degree of power increase at the core center was observed regardless of the compositions. This indicated that the spatial fissile distribution caused by innerduct configurations was the major factor of the difference in the power distribution. A power increase was also found in an off-center region, and it tended to be greater than that at the core center because of the steep gradient of neutron flux intensity. The differences in the worth of control rods caused by innerduct configurations were confirmed.
Hidaka, Akihide; Nakano, Yoshihiro; Watanabe, Yoko; Arai, Nobuyoshi; Sawada, Makoto; Kanaizuka, Seiichi*; Katogi, Aki; Shimada, Mayuka*; Ishikawa, Tomomi*; Ebine, Masako*; et al.
JAEA-Review 2016-011, 208 Pages, 2016/07
JAEA-Review-2016-011-01.pdf:33.85MBJAEA-Review-2016-011-02.pdf:27.68MB
JAEA has been conducting the Instructor Training Program (ITP) since 1996 under the auspices of MEXT to contribute to human resource development in currently 11 Asian countries in the field of radiation utilization for seeking peaceful use of nuclear energy. ITP consists of Instructor Training Course (ITC), Follow-up Training Course (FTC) and Nuclear Technology Seminars. In the ITP, trainings or seminars relating to technology for nuclear utilization are held in Japan by inviting nuclear related people from Asian countries to Japan and after that, the past trainees are supported during FTC by dispatching Japanese specialists to Asian countries. News Letter is also prepared to provide the broad range of information obtained through the trainings for local people near NPPs in Japan. The present report describes the activities of FY2014 ITP and future challenges for improving ITP more effectively.
Nishihara, Kenji; Iwamura, Takamichi*; Akie, Hiroshi; Nakano, Yoshihiro; Van Rooijen, W.*; Shimazu, Yoichiro*
Proceedings of 21st International Conference & Exhibition; Nuclear Fuel Cycle for a Low-Carbon Future (GLOBAL 2015) (USB Flash Drive), p.388 - 395, 2015/09
The present study focuses on transmutation of Pu and minor actinide in Japanese case without utilizing Pu as resource. Pu can be transmuted by two groups of technology: conventional ones without reprocessing of spent fuel from transmuter and advanced ones with reprocessing. Necessary number of transmuters, inventory reduction of actinide and impact on repository are revealed by nuclear material balance analysis. As a whole advanced technology performs better in transmutation efficiency, although required number of transmuters is larger.
Yamaji, Akifumi; Nakano, Yoshihiro; Uchikawa, Sadao; Okubo, Tsutomu
Nuclear Technology, 179(3), p.309 - 322, 2012/09
Times Cited Count：5 Percentile：38.04(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 
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.
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.
Nakano, Yoshihiro; Okubo, Tsutomu
Annals of Nuclear Energy, 38(12), p.2689 - 2697, 2011/12
Times Cited Count：10 Percentile：60.88(Nuclear Science & Technology)The isotopic composition and amount of Pu in spent fuel from high burnup BWR and PWR (HB-BWR, HB-PWR), each with 70 GWd/t discharge burnup and 6% U enrichment were estimated to evaluate FBR fuel composition in the transition period from LWRs to FBRs. The HB-BWR employs spectral shift rods. The fraction of fissile Pu (Puf) in HB-BWR spent fuel after 5 years cooling is 62%, which is larger than that of conventional BWRs with burnup of 45 GWd/t, because of the spectral shift operation. The amount of Pu produced in the HB-BWR is also larger than that produced in a conventional BWR. The HB-PWR uses a wider pitch 17
17 assembly to optimize neutron slowing down. The Puf fraction of HB-PWR spent fuel after 5 years cooling is 56%, which is smaller than that of conventional PWRs with burnup of 49 GWd/t, mainly because of the wider pitch. The amount of Pu produced in the HB-PWR is also smaller than that in conventional PWRs.
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
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.
Akie, Hiroshi; Nakano, Yoshihiro; Okubo, Tsutomu
Proceedings of 19th International Conference on Nuclear Engineering (ICONE-19) (CD-ROM), 10 Pages, 2011/10
Uchikawa, Sadao; Okubo, Tsutomu; Nakano, Yoshihiro
Nuclear Technology, 172(2), p.132 - 142, 2010/11
Times Cited Count：1 Percentile：9.99(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 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 and MOX fuel technologies and related infrastructures which have been established for the current LWR-MOX utilization.
Okubo, Tsutomu; Nakano, Yoshihiro; Uchikawa, Sadao; Fukaya, Yuji
Revue G
nrale Nuclaire, (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.
fuel rods in fuel assembly designs for plutonium conservation in FLWRUchikawa, 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 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 and MOX fuel technologies and related infrastructures which have been established for the current LWR-MOX utilization.
Nakatsuka, Toru; Nakano, Yoshihiro; Okubo, Tsutomu
Nihon Genshiryoku Gakkai Wabun Rombunshi, 9(2), p.139 - 149, 2010/06
The viability of fuel assembly designs of Reduced-Moderation Water Reactor (RMWR) with fewer kinds of plutonium enrichment of MOX fuel which may result in high local peaking factor in peripheral rods were assessed in the present report. Critical powers of 217-rod bundles with peripheral peaks for upper and lower MOX regions of double-flat core of the RMWR were calculated by a subchannel analysis code NASCA. Peripheral peaking with the corresponding local peaking factor for the uniform plutonium enrichment design yields almost the same critical power as for the flat power distribution. Reduction in fuel fabrication burden may be possible by decreasing the number of the kind of plutonium fuel enrichment while maintaining the same thermal-hydraulic margin as the fuel assembly design with five enrichment types of MOX fuels.
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.
Fukaya, Yuji; Nakano, Yoshihiro; Okubo, Tsutomu
JAEA-Research 2009-041, 86 Pages, 2009/12
JAEA-Research-2009-041.pdf:9.52MB
The purpose of this research is to investigate spent fuel characteristics of High Conversion type core of FLWR (HC-FLWR). HC-FLWR is a new reactor concept and the spent fuel characteristics have been investigated comparing with other types of reactor. For the evaluation, the ORIGEN code was also used. The ORIGEN libraries for HC-FLWR were generated using the SWAT code. 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 FP nuclides from the HC-FLWR spent fuel are almost the same as those of LWRs and full-MOX-LWRs with the discharge burn-up of 45GWd/t, and the decay heat and the radioactivity of actinides are higher than others, because of its large amount of loaded Pu inventory and the Pu composition from the LWR spent fuel including large amount of 
Pu. However, the Pu vector of the spent fuel is better than that of full-MOX-LWRs, because of the harder spectrum.
Fukaya, Yuji; Nakano, Yoshihiro; Okubo, Tsutomu
Annals of Nuclear Energy, 36(9), p.1374 - 1381, 2009/09
Times Cited Count：6 Percentile：41.05(Nuclear Science & Technology)In order to ensure sustainable energy supplies based on the well-established light water reactor (LWR) technologies, conceptual design studies have been performed on the innovative water reactor for flexible fuel cycle (FLWR) with the high conversion ratio core. For early introduction of FLWR, the conceptual design of the high conversion type one (HC-FLWR) was constructed. Furthermore, the investigation of minor actinide (MA) recycling based on the HC-FLWR core concept has been performed in this study. It would be a good option as early introduction if HC-FLWR can recycle MAs. To recycle MAs in HC-FLWR, the core design should be changed. Then, the investigation on the core characteristics were performed using the results from parameter surveys with core burn-up calculations. The major core specifications are as follows. The Puf content is 13wt%. The discharge burn-up is about 55 GWd/t. Around 2wt% of Np or Am can be recycled. The MA conversion ratios are around unity.
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.
Fukaya, Yuji; Nakano, Yoshihiro; Okubo, Tsutomu
Journal of Nuclear Science and Technology, 46(8), p.819 - 830, 2009/08
Times Cited Count：6 Percentile：41.05(Nuclear Science & Technology)The investigation on the characteristics of void reactivity coefficients for the high-conversion-type core of the FLWR (HC-FLWR) concept for MA recycling has been performed. They are the major restrictions for the core design of HC-FLWR for MA recycling, because the loaded MA makes them worse. Thus, the investigation of void reactivity coefficients has been performed using the exact perturbation calculations. In the exact perturbation theory, the reactivity is divided into scattering, leakage, absorption, and fission terms. Then, the worsening of the void reactivity coefficient caused by the MA loading mainly via the scattering term is found. Moreover, the void reactivity coefficient becomes better via the scattering term for the smaller fuel rod diameter, and via the leakage term for the lower core height. In addition, it is found that the 100% void reactivity coefficient cannot be negative only with the scattering effect, but can be negative with the leakage effect.
Nakano, Yoshihiro; Okubo, Tsutomu; Koma, Yoshikazu
Journal of Nuclear Science and Technology, 46(5), p.436 - 442, 2009/05
Times Cited Count：0 Percentile：0.01(Nuclear Science & Technology)In the case where uranium recovered by an advanced aqueous reprocessing is utilized in light water reactors (LWRs), the effects of the decontamination factor (DF) of the reprocessing on core neutronic characteristics were examined. The amounts of transuranium (TRU) elements and fission products (FP) contained in the recovered uranium depend on the DF of the reprocessing process, and also 
U is generated by neutron capture of U. These all act as poisons in the fuel. Therefore, in this paper, the additional U enrichment necessary to compensate for the produced TRU, FP and U was evaluated for three cases of representative DF values: 10
, 10
and infinity. The low value, 10, corresponds to the advanced aqueous reprocessing process investigated here. An APWR core with a discharge burnup of 49 GWd/t when the initial U enrichment is 4.6% was considered as the reference core. It was calculated that the recovered uranium has to be re-enriched up to 5.24% even when DF is infinity in order to achieve the same burnup of 49 GWd/t as the reference core. On the other hand, it was also found that the necessary U enrichment after the advanced aqueous reprocessing studied here with the low DF value 10 is only slightly different. The effect of the DF value on moderator reactivity coefficient was also studied, and no effect was found.
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 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 and MOX fuel technologies and related infrastructures, which have been established for the current LWR-MOX utilization.
Akie, Hiroshi; Nakano, Yoshihiro; Okubo, Tsutomu
Proceedings of 2009 International Congress on Advances in Nuclear Power Plants (ICAPP '09) (CD-ROM), p.9304_1 - 9304_9, 2009/05
Innovative Water Reactor for Flexible Fuel Cycle (FLWR) is a low moderation water reactor which can realize Pu breeding and multiple recycling. And for the introduction stage, a high conversion (HC) type FLWR is also proposed to keep technical continuity from current LWRs. When the HC type core is shifted to the breeder (BR) core, there exist both types of fuel assemblies in the same core configuration. The power distribution in the HC + BR assemblies mixed core configuration is studied, because there might appear a power peaking in the adjacent region between HC and BR assemblies due to the difference in neutron spectrum. As a result, though a power peaking can be very large in the adjacent regions between the assemblies, the power distribution can be effectively flattened by considering a rod-wise fuel enrichment distribution and by optimizing the fuel assembly loading pattern. It is expected that FLWR can be shifted from HC type to BR type without major neutronic difficulties.
