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Journal Articles

Preheat effect on titanium plate fabricated by sputter-free selective laser melting in vacuum

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:1 Percentile:59.26(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$$^{circ}$$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.

Journal Articles

Role of multichance fission in the description of fission-fragment mass distributions at high energies

Hirose, Kentaro; Nishio, Katsuhisa; Tanaka, Shoya*; L$'e$guillon, R.*; Makii, Hiroyuki; Nishinaka, Ichiro*; Orlandi, R.; Tsukada, Kazuaki; Smallcombe, J.*; Vermeulen, M. J.; et al.

Physical Review Letters, 119(22), p.222501_1 - 222501_6, 2017/12

 Times Cited Count:12 Percentile:11.2(Physics, Multidisciplinary)

Fission-fragment mass distributions were measured for $$^{237-240}$$U, $$^{239-242}$$Np and $$^{241-244}$$Pu populated in the excitation-energy range from 10 to 60 MeV by multi-nucleon transfer channels in the reaction $$^{18}$$O + $$^{238}$$U at the JAEA tandem facility. Among them, the data for $$^{240}$$U and $$^{240,241,242}$$Np were observed for the first time. It was found that the mass distributions for all the studied nuclides maintain a double-humped shape up to the highest measured energy in contrast to expectations of predominantly symmetric fission due to the washing out of nuclear shell effects. From a comparison with the dynamical calculation based on the fluctuation-dissipation model, this behavior of the mass distributions was unambiguously attributed to the effect of multi-chance fission.

Journal Articles

Photonuclear reactions triggered by lightning discharge

Enoto, Teruaki*; Wada, Yuki*; Furuta, Yoshihiro*; Nakazawa, Kazuhiro*; Yuasa, Takayuki*; Okuda, Kazufumi*; Makishima, Kazuo*; Sato, Mitsuteru*; Sato, Yosuke*; Nakano, Toshio*; et al.

Nature, 551(7681), p.481 - 484, 2017/11

 Times Cited Count:26 Percentile:3.91(Multidisciplinary Sciences)

Journal Articles

Analysis of fuel subassembly innerduct configurational effects on the core characteristics and power distribution of a sodium-cooled fast breeder reactor

Ohgama, Kazuya; Nakano, Yoshihiro; Oki, Shigeo

Journal of Nuclear Science and Technology, 53(8), p.1155 - 1163, 2016/08

 Times Cited Count:1 Percentile:76.09(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.

JAEA Reports

Summary of instructor training program in FY2014 aiming at Asian countries introducing nuclear technologies for peaceful use (Contract program)

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:33.85MB
JAEA-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.

Journal Articles

Comparative study of plutonium and minor actinide transmutation scenario

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.

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

Plutonium isotopic composition of high burnup spent fuel discharged from light water reactors

Nakano, Yoshihiro; Okubo, Tsutomu

Annals of Nuclear Energy, 38(12), p.2689 - 2697, 2011/12

 Times Cited Count:5 Percentile:50.9(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$$times$$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.

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.

Journal Articles

Power distribution investigation in the transition phase of the low moderation type MOX fueled LWR from the high conversion core to the breeding core

Akie, Hiroshi; Nakano, Yoshihiro; Okubo, Tsutomu

Proceedings of 19th International Conference on Nuclear Engineering (ICONE-19) (CD-ROM), 10 Pages, 2011/05

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.

Journal Articles

Effect of the introduction of amide oxygen into 1,10-phenanthroline on the extraction and complexation of trivalent lanthanide in acidic condition

Kobayashi, Toru; Yaita, Tsuyoshi; Suzuki, Shinichi; Shiwaku, Hideaki; Okamoto, Yoshihiro; Akutsu, Kazuhiro*; Nakano, Yoshiharu*; Fujii, Yuki*

Separation Science and Technology, 45(16), p.2431 - 2436, 2010/11

 Times Cited Count:24 Percentile:27.92(Chemistry, Multidisciplinary)

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.

Journal Articles

Study on effect of local power distribution of fuel assembly on critical power of Reduced-Moderation Water Reactor (RMWR)

Nakatsuka, Toru; Nakano, Yoshihiro; Okubo, Tsutomu

Nippon 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.

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.

JAEA Reports

Investigation on spent fuel characteristics of High Conversion type core of FLWR (HC-FLWR)

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 $$^{242}$$Pu. However, the Pu vector of the spent fuel is better than that of full-MOX-LWRs, because of the harder spectrum.

Journal Articles

Study on high conversion type core of innovative water reactor for flexible fuel cycle (FLWR) for minor actinide (MA) recycling

Fukaya, Yuji; Nakano, Yoshihiro; Okubo, Tsutomu

Annals of Nuclear Energy, 36(9), p.1374 - 1381, 2009/09

 Times Cited Count:6 Percentile:50.95(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.

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.

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