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JAEA Reports

Investigation on future nuclear power reactors and fuel cycle systems

Otaki, Kiyoshi*; Tanaka, Yoji*; Katsurai, Kiyomichi*; Aoki, Kazuo*

JAERI-Review 2005-035, 79 Pages, 2005/09


In order to collect technical information for the assessment on future nuclear power reactors and fuel cycle systems in Japan, investigation has been made on the characteristics and performance of future reactor options including reduced moderation water reactors (RMWRs) and their fuel cycle systems since the fiscal year 1998. The subjects of investigation are divided into three categories; breeder reactors and their fuel cycle, alternative to sodium-cooled FBR systems,plutonium recycling, spent fuel reprocessing and waste disposal. This report is a summary of the investigation carried out so far.

Journal Articles

Research for thermal-hydraulic performance in tight-lattice fuel assembly, 1; Outline of research program

Akimoto, Hajime; Tamai, Hidesada; Onuki, Akira; Takase, Kazuyuki

Nihon Konsoryu Gakkai Nenkai Koenkai 2005 Koen Rombunshu, p.229 - 230, 2005/08

A thermal-hydraulic research program for Reduced-Moderation Water Reactor (RMWR) has been performed since 2002. The RMWR has a tight-lattice core to attain the breeding of nuclear fuel for the effective use of Plutonium in a light-water reactor system. In this R&D program, large-scale thermal-hydraulic tests, several model experiments and development of advanced numerical analysis codes are being carried out to confirm the cooling performance in tight-lattice fuel assembly of the RMWR. In this paper, outline of the research program is described as well as the latest results of critical power measurement in the large-scale thermal-hydraulic tests and model experiments, which simulates the tight-lattice core of the RMWR.

JAEA Reports

Rod displacement measurements by X-ray CT and its impact on thermal-hydraulics in tight-lattice rod bundle (Joint research)

Mitsutake, Toru*; Katsuyama, Kozo*; Misawa, Takeharu; Nagamine, Tsuyoshi*; Kureta, Masatoshi*; Matsumoto, Shinichiro*; Akimoto, Hajime

JAERI-Tech 2005-034, 55 Pages, 2005/06


In tight-lattice bundles with about 1mm gap between rods, a rod displacement might affect thermal-hydraulic characteristics. The inside-structure observation of the simulated seven-rod bundle of RMWR was made with the high-energy X-ray CT of JNC. The CT view assured that the rod position was almost the same as expected by design. In the heat transfer experiments, all thermocouples on the center rod showed almost simultaneous BT-induced temperature increase and on the same axial heights showed quite similar time-variation behaviors in the vapor cooling heat transfer regime. It showed that the effect of the geometrical asymmetry was small on the BT characteristics. The calculated critical power by subchannel analysis with the input of the CT measured rod position was smaller by about 5% than that with the designed rod position. It concluded that the error in the calculated critical power was attributable not to the asymmetry in the rod position, but to the models in the subchannel analysis code.

Journal Articles

Proving test and analyze for critical power performance in the RMWR tight lattice rod bundles under transient condition

Liu, W.; Tamai, Hidesada; Onuki, Akira; Kureta, Masatoshi*; Sato, Takashi; Akimoto, Hajime

Proceedings of 2005 International Congress on Advances in Nuclear Power Plants (ICAPP '05) (CD-ROM), 10 Pages, 2005/05

A major concern in the design of RMWR is that sufficient cooling capability be provided to keep fuel cladding temperature below specified values, even for a postulated abnormal transient process. In this research, centered the postulated transient cases that may be possibly met in the RMWR running, transient BT tests are performed in 7-rod and 37-rod double-humped tight lattice bundles, under the RMWR nominal operating condition (P = 7.2 MPa, Tin =556 K) for mass velocity G = 300 - 800 kg / (m$$^{2}$$s). Experiments are analyzed with TRAC code, in which JAERI critical power correlation is implemented for BT judgment. The traditional quasi-steady-state prediction of BT in transient process is confirmed being applicable for the postulated nominal transients in the RMWR cores.

JAEA Reports

Measurement and analysis of breeding index in the first mock-up core (XXII-1(65V)) for water-cooled breeder reactor at FCA (Contract research)

Fukushima, Masahiro; Okajima, Shigeaki; Ando, Masaki; Yamane, Tsuyoshi; Kataoka, Masaharu*

JAERI-Research 2005-008, 57 Pages, 2005/03


no abstracts in English

JAEA Reports

The Possible role of reduced-moderation water reactors and its sensitivity to fuel recycling conditions

Tatematsu, Kenji; Sato, Osamu

JAERI-Research 2004-024, 35 Pages, 2005/01


Many scenarios were defined for future development of nuclear power generation and fuel cycle systems in Japan. These scenarios were quantitatively analyzed from the viewpoint of plutonium recycling, natural uranium consumption, stock of spent fuel, etc. Following findings were obtained from the analysis. RMWRs will contribute to control the uranium consumption at certain finite levels if net conversion ratio (CR) is kept higher than 1.0. However, since RMWRs do not have an excellent breeding performance in comparison with FBRs, their effect is very sensitive to the conditions on fuel recycling processes. Judging from the results of analysis using a RMWR design with gross CR 1.06, it would be necessary for RMWRs to have net CR 1.04 in order to replace enriched uranium fuelled LWRs by around the year 2200, and thereby to keep ultimate natural uranium consumption at rather low levels. This can be achieved by controlling fuel duration time outside reactors to shorter than 4 years or 6 years, when total loss of plutonium during the processes of recycling is 1.0% or 0.2%, respectively.

Journal Articles

Master plan and current status for feasibility study on thermal-hydraulic performance of reduced-moderation water reactors

Onuki, Akira; Takase, Kazuyuki; Kureta, Masatoshi*; Yoshida, Hiroyuki; Tamai, Hidesada; Liu, W.; Akimoto, Hajime

Proceedings of Japan-US Seminar on Two-Phase Flow Dynamics, p.317 - 325, 2004/12

We start R&D project to develop the predictable technology for thermal-hydraulic performance of Reduced-Moderation Water Reactor (RMWR) in collaboration with Power Company/reactor vendor/university since 2002. The RMWR can attain the favorable characteristics such as effective utilization of uranium resources, multiple recycling of plutonium, high burn-up and long operation cycle, based on matured BWR technologies. MOX fuel assemblies with tight lattice arrangement are used to increase the conversion ratio by reducing the moderation of neutron energy. Increasing the in-core void fraction also contributes to the reduction of neutron moderation. The confirmation of thermal-hydraulic feasibility is one of the most important R&D items for the RMWR because of the tight lattice configuration. In this paper, we will show the R&D plan and describe the current status on experimental and analytical studies. We will confirm the thermal-hydraulic performance in the tight-lattice bundles by this project and develop a predictable technology for the RMWR in future.

Journal Articles

Characteristics of severe accidents of Reduced-Moderation Water Reactor (RMWR)

Yonomoto, Taisuke; Akie, Hiroshi; Kobayashi, Noboru; Okubo, Tsutomu; Uchikawa, Sadao; Iwamura, Takamichi

Proceedings of 6th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, Operations and Safety (NUTHOS-6) (CD-ROM), 11 Pages, 2004/10

Reduced-Moderation Water Reactor (RMWR) is a light-water cooled high-conversion reactor that is being developed by JAERI with collaboration from the Japanese industries. Since RMWR utilizes the highly enriched plutonium, the safety concern for RMWR includes the possibility of recriticality during severe accidents as is the case with the liquid metal cooled fast breeder reactor. In order to clarify this concern, characteristics of severe accidents of RMWR are analyzed in this study. The results obtained so far indicate that (1) the mechanical impact of recriticality in the core, if occurs, is supposed to be insignificant due to the absence of water, (2) the mixture of the fuel and cladding debris in the lower plenum does not cause recriticality when they are well mixed and distributed flatly, and (3) if requires, the installation of neutron-absorption material with realistic geometry can effectively prevent recriticality in the lower plenum even for the conservatively-assumed spherical accumulation of core debris.

JAEA Reports

Research and development on reduced-moderation light water reactor with passive safety features (Contract research)

Iwamura, Takamichi; Okubo, Tsutomu; Akie, Hiroshi; Kugo, Teruhiko; Yonomoto, Taisuke; Kureta, Masatoshi; Ishikawa, Nobuyuki; Nagaya, Yasunobu; Araya, Fumimasa; Okajima, Shigeaki; et al.

JAERI-Research 2004-008, 383 Pages, 2004/06


The present report contains the achievement of "Research and Development on Reduced-Moderation Light Water Reactor with Passive Safety Features", which was performed by Japan Atomic Energy Research Institute (JAERI), Hitachi Ltd., Japan Atomic Power Company and Tokyo Institute of Technology in FY2000-2002 as the innovative and viable nuclear energy technology (IVNET) development project operated by the Institute of Applied Energy (IAE). In the present project, the reduced-moderation water reactor (RMWR) has been developed to ensure sustainable energy supply and to solve the recent problems of nuclear power and nuclear fuel cycle, such as economical competitiveness, effective use of plutonium and reduction of spent fuel storage. The RMWR can attain the favorable characteristics such as high burnup, long operation cycle, multiple recycling of plutonium (Pu) and effective utilization of uranium resources based on accumulated LWR technologies.

Journal Articles

("3D"+"2D+Time") visualization of vapor/water in the reactor observed by neutron beam

Kureta, Masatoshi

VizJournal, (11), 5 Pages, 2004/06

This paper explains the neutron radiography thermal-hydraulic measurement technique, especialy visualization technique, which was developed at Japan Atomic Energry Research Institute. Observation of large and fine-mesh data obtained by the new measurement technology is important from a research point of view. We developed the advanced visualization software which puts into practice effective observation by using new visualization methods, and we made the vizualization of phenomena possible by using VR and/or animation displays etc. by this system. Especially in this paper, the visualization techniques which were used in a prize-winning work of the "Visual Sience Festa 2003" by NIKKEI SCIENCE as easy to read for a general reader as possible by using many figures and movies.

JAEA Reports

Measurement of infinite multiplication factor in the mock-up core for reduced-moderation water reactor at FCA

Kojima, Kensuke; Okajima, Shigeaki; Yamane, Tsuyoshi; Ando, Masaki; Kataoka, Masaharu*; Iwanaga, Kohei

JAERI-Tech 2004-016, 38 Pages, 2004/03


To investigate the void coefficient in the Reduced-Moderation Water Reactor (RMWR), an infinite multiplication factor was measured in the FCA-XXII-1 (65V) core. Axial and radial fission rate distributions were measured by micro fission chambers with four different kinds of nuclides. The infinite multiplication factor was derived from the material buckling, which was obtained from both the axial and radial fission rate distributions, and the migration area calculated. The value of it in the test region of the FCA-XXII-1 (65V) core was 1.344$$pm$$0.034. It was compared with the calculation, the ratio of the calculation to the measurement was 1.008$$pm$$0.026. The improvement in measurement accuracy was also considered.

Journal Articles

Analysis of MOX fuel behavior in reduced-moderation water reactor by fuel performance code FEMAXI-RM

Suzuki, Motoe; Saito, Hiroaki*; Iwamura, Takamichi

Nuclear Engineering and Design, 227(1), p.19 - 27, 2004/01

 Times Cited Count:7 Percentile:45.16(Nuclear Science & Technology)

To assess the feasibility of the 31percentPu-MOX fuel rod design of reduced-moderation boiling water reactor in terms of thermal and mechanical behaviors, a single rod which is assumed to be irradiated in the core of RMWR up to 106 GWd/tHM has been analyzed by a fuel performance code FEMAXI-RM which is an extended version of FEMAXI-6 code. In the analysis, design specifications of fuel rod and irradiation conditions have been input, and available models of both MOX fuel and UO$$_{2}$$ fuel have been used complementally. The results are: FGR is several tens of percent, rod internal pressure does not exceed the coolant pressure, and the highest fuel center temperature is 2400K, while cladding diameter increase caused by pellet swelling is within 1percent strain. These predictions suggest that the MOX fuel rod integrity will be held during irradiation in RMWR, though actual behavior of MOX pellet swelling requires to be investigated in detail.

JAEA Reports

Summary of the 6th Workshop on the Reduced-Moderation Water Reactor; March 6, 2003, JAERI, Tokai

Nabeshima, Kunihiko; Nakatsuka, Toru; Ishikawa, Nobuyuki; Uchikawa, Sadao

JAERI-Conf 2003-020, 240 Pages, 2003/11


The research on Reduced-Moderation Water Reactors (RMWRs) has been performed in JAERI for the development of future innovative reactors. The workshop on the RMWRs has been held every year since 1998 aimed at information exchange between JAERI and other organizations such as universities, laboratories, utilities and vendors. The workshop began with five lectures on status of research and development on RMWRs in JAERI entitled "Status and Future Program of Research and Development on Reduced-Moderation Water Reactors", "Design of Small Reduced-Moderation Water Reactors", "Critical Experiments for Reduced-Moderation Water Reactors", "Critical Heat Flux Experiments in Tight Lattice Core" and "Development of High Performance Cladding". Then two lectures followed: "Status of Phase II of Feasibility Studies on Commercialized Fast Breeder Reactor System" by JNC and "Present Status of Study on Super-critical water Cooled Power Reactor" by Toshiba Corporation.

JAEA Reports

Nuclear Energy System Department annual report; April 1, 2002 - March 31, 2003

Department of Nuclear Energy System

JAERI-Review 2003-023, 232 Pages, 2003/09


The Department has carried out researches and developments (R&Ds) of innovative nuclear energy system and their related fundamental technologies to ensure the long-term energy supply in Japan. The report deals with the R&Ds of an innovative water reactor, called Reduced-Moderation Water Reactor (RMWR), which has the capability of multiple recycling and breeding of plutonium using light water reactor technologies. In addition, as basic studies and fundamental researches of nuclear energy system in general, described are intensive researches in the fields of reactor physics, thermal-hydraulics, nuclear data, nuclear fuels, and materials. These activities are essential not only for the R&Ds of innovative nuclear energy systems but also for the improvement of safety and reliability of current nuclear energy systems. The maintenance and operation of reactor engineering facilities belonging to the Department support experimental activities.

Journal Articles

Research and development of Reduced-Moderation Water Reactor (RMWR)

Iwamura, Takamichi; Okubo, Tsutomu

Proceedings of 2nd Asian Specialist Meeting on Future Small-Sized LWR Development, p.7_1 - 7_5, 2003/00

An innovative water-cooled reactor concept named Reduced-Moderation Water Reactor (RMWR) is under development at JAERI, aiming at effective fuel utilization through plutonium (Pu) multiple recycling based on the well-experienced water-cooled reactor technology. The reactor is able to achieve a high conversion ratio more than 1.0 with MOX fuel, to establish the sustainable Pu recycling. Such a high conversion ratio can be attained by reducing the moderation of neutrons, i.e. reducing the water fraction in the core. Detailed research and development activities have been performed on the core design, in conjunction with the other related studies such as on the thermal hydraulics in the tight-lattice core, the reactor physics and the fuel irradiation behavior, including the experimental activities. Also, for the total feasibility demonstration of the RMWR technologies, a design investigation for Reduced-Moderation Demonstration Reactor (RMDR) of 180MWt is being performed.

Journal Articles

Development of Reduced-Moderation Water Reactor (RMWR) for sustainable energy supply

Iwamura, Takamichi; Okubo, Tsutomu; Kureta, Masatoshi; Nakatsuka, Toru; Takeda, Renzo*; Yamamoto, Kazuhiko*

Proceedings of 13th Pacific Basin Nuclear Conference (PBNC 2002) (CD-ROM), 7 Pages, 2002/10

In order to ensure sustainable energy supply in Japan, the reduced-moderation water reactor (RMWR) has been developed by JAERI since 1998. MOX fuel assemblies with tight lattice arrangement are used to increase the conversion ratio. In order to establish negative void reactivity coefficient, the core should be short and flat to increase neutron leakage from the core. The core designs were accomplished to a large core with 1,356MWe and a small core with 330MWe. For both cores, negative void coefficient and natural circulation cooling of the core were realized. To confirm thermal-hydraulic feasibility, critical heat flux experiments were performed using 7-rod bundles with the gap width of 1mm and 1.3mm. The results indicated that enough cooling was assured for the tight lattice core. Further R&D studies, including large scale thermal-hydraulic experiments, reactor physics experiments, development of high burn-up fuel cladding material and simplified reprocessing technology, are necessary to realize commercial introduction of RMWR by 2020's for the replacement of current generation LWRs.

Journal Articles

Feasibility study of BWR-type reduced-moderation water reactor core design in thermal-hydraulic view point

Araya, Fumimasa; Kureta, Masatoshi; Akimoto, Hajime

Proceedings of 2nd Japan-Korea Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS-2), p.309 - 314, 2000/00

no abstracts in English

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